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SHIVAJI UNIVERSITY, KOLHAPUR
CENTRE FOR DISTANCE EDUCATION
Geography
(From Academic Year 2013-14)
Paper-I & II
For
B. A. Part-I
K
Semester - I & II
J
Copyright ©
Registrar,
Shivaji University,
Kolhapur. (Maharashtra)
First Edition 2014
Prescribed for B. A. Part-I
All rights reserved, No part of this work may be reproduced in any form by mimeography or
any other means without permission in writing from the Shivaji University, Kolhapur (MS)
Copies : 300
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Registrar,
Shivaji University,
Kolhapur-416 004
Printed by :
Shri. B. P. Patil
Superintendent,
Shivaji University Press,
Kolhapur-416 004
ISBN- 978-81-8486-551-6
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Further information about the Centre for Distance Education & Shivaji University may be
obtained from the University Office at Vidyanagar, Kolhapur-416 004, India.
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This material has been produced out of the Developmental Grant from UGC, Distance
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(ii)
Centre for Distance Education
Shivaji University, Kolhapur
n ADVISORY COMMITTEE n
Prof. (Dr.) N. J. Pawar
Vice-Chancellor,
Shivaji University, Kolhapur
Prof. (Dr.) M. M. Salunkhe
Vice-Chancellor,
Yashwantrao Chavan Maharashtra Open
University, Nashi.
Prof. (Dr.) K. S. Rangappa
Hon. Vice-Chancellor,
University of Mysore
Prof. P. Prakash
Pro. Vice-Chancellor,
Indira Gandhi National Open University,
New Delhi
Prin. (Dr.) A. S. Bhoite
Pro-Vice-Chancellor,
Shivaji University, Kolhapur
Prof. (Dr.) Cima Yeole
Git Govind, Flat No. 2,
1139 Sykes Extension,
Kolhapur-416001
Dr. A. P. Gavali
Dean, Faculty of Arts and Fine Arts,
Shivaji University, Kolhapur
Dr. J. S. Patil
Dean, Faculty of Social Sciences,
Shivaji University, Kolhapur
Dr. C. J. Khilare
Dean, Faculty of Science,
Shivaji University, Kolhapur
Dr. R. G. Phadatare
Dean, Faculty of Commerce,
Shivaji University, Kolhapur
Prof. (Dr.) A. B. Rajage
Director, B.C.U.D.,
Shivaji University, Kolhapur
Prof. (Dr.) D. V. Muley
Registrar,
Shivaji University, Kolhapur
Shri. M. A. Kakade
Controller of Examinations,
Shivaji University, Kolhapur
Shri. V. T. Patil,
Finance and Accounts Officer,
Shivaji University, Kolhapur
Prof. (Dr.) A. R. Bhosale
(Member Secretary)
Director, Centre for Distance Education,
Shivaji University, Kolhapur.
n B. O. S. IN GEOGRAPHY AND METEOROLOGY n
Chairman- Dr. B. N. Gophane
Venutai Chavan College, Karad, Dist. Satara
l
Dr. P. D. Raut
Head of Department, Geography Dept.
Shivaji University, Kolhapur
l
Dr. A. B. Patil
Arts, Commerce Mahavidyalaya, Ashta,
Tal. Walwa, Dist. Sangli
l
Dr. S. B. Gaikwad
Miraj Mahavidyalaya, Miraj, Dist. Sangli
l
l
Dr. H. Y. Karande
Mahila Mahavidyalaya, Mangalwar Peth,
Karad, Dist. Satara
Dr. B. L. Ajgekar
Karmvir Hire College of Arts, Science,
Commerce and Education, Gargoti
l
Prof. Dr. A. S. Raymane
Benglor University, Bengalore
l
Prof. A. S. Jadhav
Geography Department,
l
l
Dr. S. S. Kothawale
Padmbhushan Dr. Vasantraodada Patil
Mahavidyalaya, Kavathemahankal,
Mumbai University, Mumbai.
Dr. K. A. Mali
Rajaram College, Kolhapur
(iii)
Centre for Distance Education
Shivaji University,
Kolhapur.
B. A. I : Geography
Writing Team
Sem. III
Units
Sem. IV
Units
Dr. H. Y. Karande
Mahila Mahavidyalaya, Karad
1
-
Dr. B. S. Jadhav
Vijaysinh Yadav Arts & Science College,
Peth - Vadgaon
2
-
Dr. A. B. Patil
Arts, Commerce Mahavidyalaya, Ashta.
3
-
Dr. S. D. Shinde
Dept. of Geography, Shivaji University, Kolhapur
4
-
Dr. C. U. Mane
Balasaheb Desai College, Patan
-
1
Dr. K. R. Jadhav
Krantisinha Nana Patil Mahavidyalaya, Walwa
-
2
Dr. P. V. Patil
Sambhajirao Kadam Mahavidyalaya, Deur
-
3
Shri. R. G. Varekar
Smt. Gangabai Khivraj Ghodawat
Mahavidyalaya, Jaysingpur
-
4
Writers Name
n
Editors n
Dr. B. N. Gophane
Venutai Chavan College, Karad, Dist. Satara
Dr. B. S. Jadhav
Vijaysinh Yadav Arts & Science
College, Peth - Vadgaon
Dr. S. D. Shinde
Dept. of Geography,
Shivaji University, Kolhapur
(iv)
Preface
Shivaji University has introduced the Distance Education mode for
external students since 2007-08. I on behalf of Board of Studies in
Geography and Meteorology feel extremely happy to present this book on
'Introduction to Physical Geography' at B. A. Part-I (both semesters). We
hope that we have completed the task quite satisfactorily alloted to us by
the university authoriety.
Syllabus of both the semester is included in this book. We have
introduction of Geomorphology for first semester in which all the fundamental
concepts have been covered. The students may get introduced the basic
knowledge about the earthsurface, where as in the second semester
climatological study is included. Concept of atmosphere, its composition
and components of climates are delt in detail. The last unit is kept for some
practical things; in which only theory of particular practicals is taken into
account.
While preparing this SIM Material for external students as per new
syllabus which is being introduced 2013-14, all the possible care has been
taken.
I on behalf of Board of Studies in Geography and Meteorology grateful
to Prof. N. J. Pawar Hon'ble Vice Chancellor and his officers as well as
Hon'ble Director and his staff of Distance Education of University.
Dr. B. N. Gophane
Chairman, BOS and
Editor SIM
(v)
B. A Part-I
GEOGRAPHY
INDEX
Unit No.
Topic
Page No.
Semester-I : Paper I
Geomorphology
1.
Introduction to Geomorphology
1
2.
The Earth Crust
12
3.
Diostroaphic Movements
34
4.
Weathering and Erosion
62
Semester-II : Paper-II
Climatology
1.
Atmosphere
79
2.
Insolation, Temperature and Atmospheric Pressure
97
3.
Winds, Humidity and Precipitation
127
4.
Practical (only theory)
152
(vii)
Each Unit begins with the section objectives Objectives are directive and indicative of :
1. what has been presented in the unit and
2. what is expected from you
3. what you are expected to know pertaining to the specific unit,
once you have completed working on the unit.
The self check exercises with possible answers will help you
understand the unit in the right perspective. Go through the possible
answers only after you write your answers. These exercises are not to
be submitted to us for evaluation. They have been provided to you as
study tools to keep you in the right track as you study the unit.
Dear Students
The SIM is simply a supporting material for the study of this paper.
It is also advised to see the new syllabus 2013-14 and study the
reference books & other related material for the detailed study of the
paper.
(viii)
Unit 1
INTRODUCTION TO GEOMORPHOLOGY
1.0
Objectives
1.1
Introduction
1.2
Presentation of Subject Matter
1.2.1
Introduction to Geomorphology
1.2.2
Definitions of Geomorphology
1.2.3
Nature of Geomorphology
1.2.4
Scope of Geomorphology
1.2.5
Significance of Geomorphology
1.2.6
Recent Trends in Geomorphology
1.3
Summary
1.4
Terminology and Meaning
1.5
Check Your Progress
1.6
Answers to Check Your Progress
1.7
Exercise
1.8
Field Work
1.0
Objectives
1.
To understand the Geomorphology.
2.
To know the nature, scope and importance of Geomorphology.
3.
It helps to state the recent trends in Geomorphology.
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1.1
Introduction
Aim of geography is to study the earth. In this science study the correlation
between natural phenomenon and human being. All the natural phenominon are
called as natural factors. Which includes solid, liquid and gases phenomina. The
solid phenomina called as lithosophere, liquid phenominan called as hydrosphere
and gases phenomenon called as atmosphere. When scope of geography was limited,
all these phenomenon were studied in unique branch but as expanded the scope of
geography all these phenomenon are studied in different branches. The nature of
branches of physical geograph is as given below.
Physical Geography :
♦
Astrology
♦
Geomorphology
♦
Climatology
♦
Meterology
♦
Oceanography
♦
Soil Geography
♦
Geology
♦
Plant Geography
♦
Animal Geography
Geomorphology is an important branch of physical geography which studies
the lithosphere .
The term geomorphology stems from greek words that is geo meaning earth,
morphe meaning form and logos meaning a discourse (description). Therefore,
Geomorphology is science of description of carious forms of the earth surface. The
word Geomorphology firstly used by Kinth in 1894. Before that physical features. This
term was usually used for Geomorphology. But physical features is a broad term whis
includes landforms as well as oceanography, climatology, meteriology also. In brief
geomorphology is a science of earth forms.
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1.2
Presentation of Subject Matter
1.2.1
History of Geomorphology
Geomorphology has developed through ancient period. Scholars like
Herodotus, Strabbo contributed for the development of geomorphology and express
that the land forms are results of physical processes. But modern Geomorphology
developed in let eighteenth century. James Hutton, John Play- Fair, and Charles Lyell
state that land froms are creation of exogenetic forces. In twententh century Willum
Moris, Davis, Walter Penck, Lester King developed various theoryes and create
foundation of conceptual view. In let 20th century R.E. Horton, A.N. Straler apply
quantitative method in Geomorphology. The development of Geomorphology was
initiated in Germany and after word that spread all over the world.
1.2.2
Definitions of Geomorphology :
The conceptual thinking and research in Geomorphology was done by various
scholers, several geographers define the discipline Geomorphology. The important
definition are as below :
1.
P.G.Worcester (1940) : defined Geomorphology as "the interpretative
description of the relief features of the earth."
2.
Von Engeln(1950): Engeln does not consider Geomorphology to be merely
the science of landforms, but also includes in it's fold, the shape of the entire
earth, its configuration and the disposition of its largest units.
3.
A.N. Strahlar ( 1958) Geomorphology is an analysis of the origin and evolution
of earth features, Geomorphology does not study merely the physical, chemical
and biological processes affecting the evolution of landforms but also the
structure of the earth crust, the geological processes as well as the climatic
influences, because it is the combined influence of all these factors that
determines landforms.
4.
Arthur Bloom- (1979) defines Geomorphology as "the systematic anylasis of
landscapes and processes that change them."
5.
B.W. Sparks (1972) : He stated that "essentially it is the study of evolution of
landforms, especially landforms produced by the processes of erosion"
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6.
D. Stamp - He stated that "Geomorphology is science of landforms in which
study the shape of earth, evolution and Origin of earth surface.
7.
W.G. Moor- He stated that "Geomorphology is a study of physiography of
earth, nature of earth crust and structure of the earth.
1.2.3 Nature of Geomorphology :
Geomorphology is the study of evolution of earth. This study is also done in
several earth sciences, but micro level study of landforms is done in only
Geomorphology. In this study land and oceans are studied broadly descriptive manor,
because these are first order landforms of the earth. The relief features like mountain,
plaetue, plains, ocean floor, continental shelf, continental slepe, oceanic plains, deeps,
trenches etc are second order landform are also studied in this discipline. The relief
features at the third order are the results of exogenetic forces like, vally, canyons,
waterfalls, beaches, sand dunes, cirques etc. are creation of river, wind and glaciears,
these feathers are studied in Geomorphology.
Such study is not possible in laboratory. The whole earth is laboratory for this
study. Therefore, geomorphologist studies the distribution of land and water, explain
their characteristics as well as it’s formation and changes also. The processes of
evolution of land forms, rock structure, composition, and various types are studied in
this discipline.
Geomorphological studies are not only earth movements. Characteristics of
land forms but also anylyse the see shores. Denudation is also another important
aspect of this science. Study of denudation is helpful for analysis of development of
drainage patterns. We can understand the stages of natural cycle of erosion. With the
help of historical account of landforms we can aware about the climate, erosional and
depositional processes in that period.
The above discussion express that the Geomorphology is a major branch of
physical geography and earth sciences. The natural processes are studied in this
discipline. Therefore, the science is concern with soil science, gismography, science
of volcanos, climatology etc. Now a days modern techniques like arial photography,
satilite imeges, remote sencing also used for this study.
Geomorphology is a applied science, because we obsever direct or indirect
impact of landform on human being. Importance of land forms is also marked in
conservation of culture, human activities, human physical characteristics, housing,
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4
clothing and food habits. The impact of human environment on physical environment
is also important aspect. All there issues studied in Geomorphology conclusively. We
can say Geomorphology is an important discipline for management of natural and
human cultural environment.
1.2.4
Scope of Geomorphology
Geomorphology is a important branch of physical geography, there fore factors
and processes concerning lithosphere studied scientifically in this branch. Factors of
Geomorphology are concern with earth crust. In this discipline includes three major
aspects.
i) dimension and scale of relief features. ii) processes that shape the landforms
and iii) the approaches to the geomorphic studies. The systematic study of landforms
requires some fundamental knowledge of geology. In formation of landforms. There is
major role of geological processes . Geology helps in understanding the nature of
landforms the origin of different types of reliefs like mountains, plateaus continent and
ocean basins, plains.
Thus on the basis of dimension and scale, the relief features of the earth
surface, the core subject matter of geomorphic study. In this contest R.D. Salisbury in
1919 grouped all landforms in three groups. This classification useful for micro level
study of landforms. This classification shows the unity of formation as well as describe
the periodical description.
A.
First order landforms : Include the continental platforms and the ocean basins.
The arrangement of continent and oceans appear to be fairly stable, but in
the long geological history of the earth, we come across evidences of many
changes in their form, extension and geographical location.
B.
Second order landforms : There are super imposed on the continents and
oceans basins and includes plains, plateaus and mountains on the continental
surface can mid-oceanic ridges, oceanic plains, deeps, trenches , etc on the
ocean floor, besides several features of the continental margins like continental
shelf, continental slope all relief features owe their origin mainly to endogenetic
forces. Especially diastrophism and volcanicity. Although some plains, plateaus
and mountains may be formed by erosional processes. Basically they formed
by endogenetic forces.
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5
C.
Third order landforms : These landforms develop on the relief features of
the second order. Valleys, canyons, waterfalls, beaches, sand dunes, cirques
etc. are examples of relief features of the third order which are the result of
exogenetic forces through process of erosion. These relief features includes
both erosional as well as depositional landforms. A study of these features
occupies a lot of space in Geomorphology.
Except above mentioned features rock formation structure, distribution and
minerals also studies in this discipline. This study is useful for understanding the internal
processes.
First and important stape at studding physical factors of earth is observation.
The information about structure, texture, layers is impossible obtained by observation.
Where inductive method will be applicable. Therefore landform should be introduced
by principle, theory's and hypotheses.
Geomorphology is studied by different views, In ancient period only describe
the landforms, after that distribution of land form was stated. When quantitative
revolution takes place in Geomorphology , accurate measurement was done. This
approach first used in united states in 1940, after that diffused allover world.
Afterward Geomorphology was studied in regional approach. These dynamic
approaches made Geomorphology maximum scientific and conceit results of research.
1.2.5
Significance of Geomorphology
Any discipline is become meaningful, when it is useful for human life. In this
contest Geomorphology is very important science. Which is useful for solve the
problems. There are several crises created in man and environment relation sheep.
These crises could be minimize peacefully with the help of geomorphology.
Geomorphology affects the human activities like agriculture, forest, irrigation, production
of power, mining , Industries, urbanization and urban planning , water supply, transport
and communication, trade etc.
In the contest of environmental resources, Geomorphology is important
discipline. In this sense resource management and impact of them on earth also studied.
The importance of this study is concern to mining of various minerals lines as Oil
mining irrigation and hydal power physvital role.
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H. Verstappen -(1983) has outlined the following areas at interest where
geomorphic knowledge and techniques may be applied for understanding and solving
problems arising out of interaction of man with environment.
1.
Topographical and thematic mapping of natural resources.
2.
Survey of natural hazards, landslides, avalanches, earthquakes, Vulcanism,
flooding and droughts and natural hazard reduction.
3.
Rural development and planning emphasizing land utilization, control of man
induced soil erosion. Channel manipulation and river basin management .
4.
Urbanization, mining and construction.
5.
Engineering design of transport network, dams, cannals etc.
According to R.J. Chorley (1985) application of Geomorphology can be divided
into two categories.
i)
Man as a geomorphicagent.
ii)
Geomorphology as an aid to resource evaluation. The unintentional effects of
human economy changes natural landscape for engineering work, mining,
construction of dom and oil drilling etc.
The resource evaluation and planning aspects of applied geomorphology are
concerned with such matter. Geomorphology is useful for invention of resources,
environmental management, evaluation of soil and land, planning for water, prevention
of erosion and mapping of natural disasters and hazards.
1.2.6
Recent trends in Geomorphology
The present status of Geomorphology is the result of gradual but successive
development of geomorphic thoughts postulated in different periods by innumerable
philosophers, experts and geoscientists.
The foundation of modern Geomorphology was postulated by Greek and Roman
philosophers. Herodotus (B.C.485 to BC. 425), Aristotal (BC 384 to BC 322), Strabbo
(54 BC to 25 AD). These scholers contribute valuable contribution in field of
Geomorphology. But the first century to 14th century these 1400 years are known as
dark age. Global unstability and Religious pressure stoped the research activities.
Whole world goes back in educational sector. At the beginning of 18th century education
and research process started againg slowly but silently. James Hutton, Leonardo de
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7
Vinci , Buffon, Targioni Tozetti and many others geographers and scholars restarted
the research in geomorphy. In this period scientific analysis of landforms was done by
there scholars.
Recent Trends :
Up to beginning of 19th century Geomorphology was a part of physical
geography . After that it begains separate branch of physical geography. From this
period geomorphic thoughts done at local level. In this century the development of
this branch was established in Europe and America.
The european Geographers James Hutton and Sir Charles Lyell postulate
concept of uniformitarism. A. Penck and Bruckner after their observations of Pleistocene
glaciations over the Alps identified four glacial periods during Pleistocene ice age. Sir
Andrew Ramsay presented detailed description of marine platforms made by marine
erosion. After Ramsay B.F. Richtofen made significant contribution in the field of marine
erosion.
In this period American school has credited for making maximum contribution
in the field of Geomorphology. Last two decades of 19th century and first two decades
at 20th century are considered a golden age of American Geomorphology. In this
period W. M. Davis, Major J. W. Powell, Gilbert, Dutton contributed in this discipline.
Powell study of Colorado plateau and uinta mountain suggested geological structure
as a basis for the classification of landforms. He attempted a genetic classification at
landforms. He attempted a genetic classification of river valleys and consequently
classified them. C.F. Dutton was the first geo scientist to use the term isostasy to
denote equilibrium condition of upstanding landmasses of the earth's surface. W.M.
Davin in 1899 postulated theory of cycle of erosion.
The beginning of the 20th century was heralded by methodological revolution
in geomorphological studies. Davis and Perck postulated various theories and explain
every land for is result of processes and time.
Post 1950 geomorphology has undergone more changes in the methods and
approaches to the study of landform. In this period cycle model replace by dynamic
equilibrium model. Qualitative treatment of landforms replaced by quantitative
geomorphology. Inductive method of landforms analysis replaced by deductive method.
Introduction of models and system approach. Emergence of process geomorphology,
climatic geomorphology, applied geomorphology and environmental geomorphology.
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8
The decade 195- 60 was devoted more for the quantitative study of landforms.
In this period the concept of landscape cycle and hill slope cycle was developed.
At the end of 20th century geomorphology established as applied science.
Every discipline have two major factors. 1) Conceptual and distributional factors 2)
Applied factors. In this contest several scholars develop the conceptual and
distributional factors in this field up to mid 20th century. But let 20th century develop
the applied nature of the geomorphology. Various problems concerning earth studied
in the discipline and sujest remidies for that. This was the begning of applied
Geomorphology.
According to D.K.C. Jones (1980) applied Geomorphology may be defined as
the application of geomorphic understanding to the analysis and solution of problems
concerning land occupancy, resource exploitation, environmental management and
planning. The application of geomorphological techniques and the results of
Geomorphological investigations for resources evaluation, socio-economic
development and mitigation of natural hazards and disasters like flood, earth quake,
volcanos, droughts , land sliding etc. are significant aspect of applied geomorphology
which should be taken into consideration by the geomorphologists. In the field of town
planning, minning, irrigation, and water management this discipling contributers
important role. In 21th century the study of the science not remain traditional, it becomes
modern. Modern techniques are used for anylyase the geomorphic factors. Therefore,
in future this study will be use for solving the various problems of society.
1.3
Summary
Geomorphology is the significant applied branch of physical Geography. It
deals with different land forms of the earth surface, its origin and development. Beside
this the distribution with appropriate description is also studied in this branch of physical
geography. The nature of Geomorphology has been changing time to time from the
era of Eratostheries to today. The recent days quantitative and statistical data as well
as modern technology are applied to reach on particular conclusion. Therefore,
Applicability of geomorphology is increasing and this science become a applied science.
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9
1.4
Terminology and Meaning
Land forms
:
Different relief shape and sized parts of the earth
surface.
Evaluation
:
Transformation in land forms.
Internal / Indogenic forces
:
The forces which are originate benith the crust.
External / Exogenetic forces :
The forces which are originate on the earth crust.
Oceanic Deposits
Various material deposited on sea floor as per
relief, corresponding with their size.
1.5
:
Check Your Progress
Que. 1 Choose the correct word and rewrite the sentences.
1)
2)
3)
4)
5)
Solid material of the earth crust is known as..................
(a) Stratosphere
(b) Soil layer
(c) lithosphere
(d) hydrosphere
The term Geomorphology stems from .......... language
(a) Lattin
(b) Greek
(c) Urdu
(d) French.
W.M. Davis is famous geographer of ............. nation
(a) U.S.A.
(b) England
(c) Germany
(d) France
Mountains are ................ order landforms.
(a) First
(b) Second
(c) Third
(d) Fourth
Every landform on the earth is result of endogenetic process and ..............
(a) Period
(b) River
(c) Exogenitic forces
(d) Endogenetic forces.
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10
1.6
Answers to Check Progress
1) c
1.7
2) b
3) a
4) b
5) c
Exercise
A) Write short notes.
1)
Definitions of Geomorphology
2)
Importance of Geomorphology
3)
Development of Geomorphology
B) Write the answers in detailed of the following questions.
1)
Define the Geomorphology and explain its nature and scope
2)
Give detail account of development of Geomorphology and modern trends in
the Geomorphology.
1.8
Field Work
1.
Observe the different land forms in your surrounding and describe its formation
process with suitable diagram.
❖❖❖
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11
Unit 2
THE EARTH CRUST
2.0
Objectives
2.1
Introduction
2.2
Presentation of Subject Matter
2.2.1
Distributional Characteristics of Continents and Oceans
2.2.2
Alfred Wegener’s Continental Drift Theory
2.2.3
Plate Tectonic Theory
2.3
Summary
2.4
Terminology and Meaning
2.5
Check Your Progress
2.6
Answers to Check Your Progress
2.7
Exercise
2.8
Field Work
2.0
Objectives
1)
It helps to know the distributional characteristics of continents and oceans.
2)
Wegener’s continental drift theory makes essay to understand the movements
of continents.
3)
Through the palate tectonic theory we can know the movements of Plates and
its effects on earth surface.
12
2.1
Introduction
Different scholars have been propounded different theories about the origin of
the earth. These scholar’s have their individual perceptions about the earth formation
but one thing is common among them and that is all planets of the solar system are
the byproduct of the sun. As per the scientists’ in historical era in space there was one
primeval rotating cloud of gas which is today called nebula. The nebula was revolving
around its axis with high velocity. Due to its velocity and internal collision of particles
generated heat and therefore, the temperature and size of nebula is increased. The
nebula started spinning so rapidly that the outer part of nebula thrown in to space.
Remaining inner matter of nebula is a sun and outer matter accumulated separately
which become the planets. In initial stage the planets release the heat and changed in
to liquid form there after it become solid. In this way our solar system has been formed.
The earth is one the planet of our solar system with containing biosphere. The
earth surface has distinguishing structures and its one significant character is the
origin of the continents and water bodies. After the earth formation the continents and
water bodies were shaped. According to Chemberlin ‘in the process of cooling of earth
simultaneously some cracks and fissures are developed on the earth surface. Primary
stage cracks (silt) and fissure were filled by water and formed the seas. In time being
temperature of the earth is come down and condition took place and its result is rainfall.
The rain water deposited in fissures, volcano crater and low land area of earth surface
etc. due to those lakes and seas were formed in lot of numbers. These leaks and seas
were expanded and meet each other and slowly converted into oceans.
An elevated portion of the earth surface is come under the influence of
denudation. The eroded material is lying at sea or ocean floor. Therefore, the weights
of continents are decreasing as well weight of sea floors are increasing. Sea floors are
come under the tremendous pressure of sediments and its results sea floors are
down thrown. But the intense hit is in inner part of earth crust maintain the magama
which is useful to maintain the equilibrium between land and water bodies.
The distribution of continents and water bodies, its distributional characteristics,
continental drift and plate tectonic etc. aspects are the core study matter of this unit.
13
2.2
Presentation of Subject Matter
2.2.1 Distributional Characteristics of Continents and Oceans
A)
Distribution of Continents and Oceans
The continent and ocean are the first order landforms of the earth and it has
their own importance but these are unevenly distributed. The land and water has covered
some portion of the earth surface. The portion of the earth surface which is under land
is called as continent and the part of earth is under water is called water bodies or
ocean.
Fig. 2.1 : Distribution of Continents and Oceans
♦
Generally water bodies are covers 2.5 times more area of the earth than the
land.
♦
According to Sir John Moore – total area of the earth is about 510 million sq km
and out of this nearly 361 million sq km area is under the water and about 149
sq km area under land.
♦
As per estimation of Alfred Wegener – out of the total area of the earth surface
nearly 71.70 per cent is under water and remaining 28.30 per cent area is
covered by land.
14
♦
As per the opinion of Kramel 70.80 per cent area occupied by the water bodies
and less area nearly 29.20 per cent covers by the land.
♦
Considering the above all matter it is generally stated that 71 per cent and 29
per cent area of the earth surface is under water bodies and land mass
respectively.
Fig. 2.2 : Distribution of Land and Water
B)
Distributional Characteristics of Continents and Oceans
Through simple observation of World map shows some distributional
characteristics of continents and oceans. These are as follows:
1.
The distribution of land and water are uneven on the earth surface as well less
area is under land and vast area is covered by water.
2.
Not only uneven distribution of land and water on earth but also uneven
distribution in north and southern hemisphere.
3.
By simple observation, particularly in the northern hemisphere there is higher
proportion of land than the water. Therefore, the northern hemisphere is known
as ‘Land Hemisphere’.
4.
As compare to southern hemisphere to northern hemisphere in the respect of
water proportion. It is observed that the southern hemisphere has occupied
maximum portion of the earth surface by water. So, southern hemisphere is
known as ‘Water Hemisphere’.
15
5.
On the earth surface continents are discontinuous e.g. Europe, Africa, Asia
and Antarctica but ocean bodies ate continuous e.g. Pacific ocean, Atlantic
ocean, Indian ocean and Arctic ocean.
6.
In all continents, Asia is the biggest continent and in ocean Pacific Ocean is
the largest ocean among all oceans.
7.
On the earth surface the land is nucleus at Caspian Sea and in Pacific ocean
at Tahiti island the waters nucleus.
8.
The centre of land is water and the water is land.
9.
The general shape of continents and oceans are triangular.
10.
Concern to continents the base of triangle at north and tapering towards the
south but its opposite condition in the respect of triangular shape of oceans
the base at south and tapering towards the north.
11.
From World map it is indicated that the inclination of continents e. g. North and
South America towards east, Africa towards west and Asia, Africa and Europe
inclined towards north.
12.
The area around the North Pole (centre) is covered by water and the area
around the South Pole (centre) is covered by the land.
13.
In northern hemisphere Arctic Ocean has ring of North America, Europe and
Russian continents.
14.
In south hemisphere Antarctica continent has ring of South Pacific Ocean,
South Atlantic Ocean and Indian Ocean.
15.
Structural arrangement of continents and oceans are opposite on another e.g.
on the opposite of Indian ocean is south America, opposite side of south Atlantic
ocean is Australia and opposite of Africa and Europe there is Pacific ocean.
16.
The continents of the earth are having one island towards the south-east e. g.
India has Srilanka, Australia has Tasmania, Africa has Madagascar and Tierra
del Fuego is located at southern margin of South America.
17.
The continents of the earth have undulating nature of surface. The World’s
highest mountain peak Mount Everest (8848 m) in Himalaya and in ocean
deepest deep Marianna trench (11033 m) is located in Pacific Ocean.
16
C)
HYPSOGRAPHIC or HYPSOMETIC CURVE
Sir Jon Moore had been studied the relief features of the earth and its distribution.
He was explained that the distribution of continents and water bodies are uneven, the
height of land and depth of seas as well as its structures are different. Firstly he was
used hypsograph to show the distribution of landforms and undulating nature of the
earth surface. The graph which is used for demarcating elevation of land and depth of
seas as well its distribution is called hypsography or hypsometric curve.
Fig. 2.3 : Elevation, Depth and Distribution of Surface Land Forms
17
Table No. 2.1: Earth’s Landforms – Height, Depth and Distribution
Contents
Covered area
Water Bodies
Covered area
in %
(Depth in m)
in %
More than 4000
1
0 – 200
5
2000 – 4000
2
200 – 1000
3
1000 – 2000
5
100 – 2000
2
200 – 1000
13
200 – 4000
15
0 – 200
8
4000 – 6000
41
More than 6000
5
Total
71
(Height in m)
Total
29
Source: Khatib K. A., Prakrutic Bhugol, 2008.
According to Sir Jon Moore – very less part of earth surface (only 01 %) is
under more elevated land. But less elevated land covered maximum portion (50 %) of
the continents. Very less area of sea floors is under deepest deeps (only 05 %) as well
vast area of sea floors are covered by plain and its undulating nature and that was 49
per cent. With the help of hypsograph it can be easy to represent the sea floor structure
like as continental shelf, continental slope, deep sea plains, ocean deeps and islands
which is shown in fig. 2.5.
Fig. 2.4 : Relief of Ocean Floor
18
Relief of Ocean Floor (Landforms on Sea Floor)
1)
Continental Shelf
Continental shelf is that zone of sea floor which lies close to the continental
margin. Such zone made of the same material as the adjacent land. They vary in width
from few meters to the 1300 km. The coast of Ireland it stretches westward for a
distance of 80 km and it is more observed at the coast of Siberia it reaches maximum
width of 1300 km and its depth is varying between 5 m to 200 m. The angles of slopes
are different and are usually less where the shelf is widest. The slope is always found
up to 2°.
Continental shelf is shallow part of ocean floor. On it sediments ate continuously
deposited and sun’s rays are reaching up to its floor. Due to this condition, the vegetation
likes plankton grows naturally. Therefore, such areas are well known for fishing zones
of the World. Beside this continental shelf’s are very rich in power resources e.g.
natural oil, natural gas and coal.
2)
Continental Slope
Towards sea side after continental shelf second landform on sea floor is
continental slope. The end point of shelf the slope of ocean floor is increasing and
relatively rapid increase in depth. The angle of the continental slope varies far more
than that of the shelf. The continental slope is varies from coast to coast. Along the
Ireland coast it is 5° but near the Spain it is much steeper as much as 36°. An average
slope of this feature is 5.5° and the width of continental slope is differing from place to
place.
3)
Sea Plains
The third sea floor landform from continental slope which is occupied extensive
plane area is called as sea plane. The sea planes are confined generally on depth of
4000 – 6000 m. Such landform is having some hills and also observed at central parts
of oceans.
19
4)
Sea Deeps
The narrow, deep and steep sloppy area of sea floor is known as sea deep. It is
also known as submarine trench. The area of such trenches is generally small. The
deeps are not usually lie in the middle of the oceans but along the margins of islands
and near the coasts. The Mariana deep in Pacific ocean which is as much as 11033 m
deep close to Guam island. Beside this in the same ocean, trenches are Tonga, Kurile,
Aleutian and Sunda trench (7454 m) in Indian Ocean etc. are the some important
ocean deeps.
5)
Sea Islands
The land mass which is covered by water from all sides is called as island. On
the basis of size islands are divided into two categories first is small and second is big
islands. The islands which are close to continents these are known as continental
islands e.g. Srilanka and Madagascar. The islands which are situated far away from
continents in seas such islands are known as Sea Islands e.g. Mauritius and Hawaii.
2.2.2 Alfred Wegener’s Continental Drift Theory
Alfred Wegener was Garman meteorologist but he had been perfounded
continental drift theory in 1912. Due to First World War and its Garman version this
theory almost unnoticed. The second edition of the theory came in English version and
it attracted Worldwide attention. The Wegener had supported his theory by providing
various evidences through scientific manner.
Basically Wegener was meteorologist and he had studied the climatic condition
of the World and he came cross number of evidences which indicate that there have
been changes in climate in the past. Today Antarctic continent has polar climate which
is under cover of thick ice cover but in past it was in hot climate. Similarly, there are
signs of glaciations in Indian peninsula but today India have tropical climate. Signs of
carboniferous ice age are also present in South America, Africa and Australia. All these
land masses have hot climate today. These climatic changes he was explained on the
basis of two possibilities:
20
1.
The sun might be lost its control over the climatic regions due to lead to change
in climate.
2.
The climatic regions are remained in their original locations but continents are
drifted.
Wegener can’t prove that climatic regions were changed but he had various
evidences to prove second possibility. Thus Wegener’s theory was based on idea of
continental drift.
Outline of Continental Drift Theory
According to Wegener – the continents are formed from Sial which has less
density. Below this there is Sima and it has more density. Due to such physio-chemical
condition Sial is floating on Sima. Paleozoic period (40 crore years ago) there was
only one continent and that was named as Pangaea by Wegener. The Pangaea was
surrounded by vast water body called as Panthalasa. 30 crore years ago or in
carboniferous era Pangaea had developed east-west crack and broken into two
landmasses. The northern part of Pangaea named as Laurasia and southern part was
called as Gondwana. The sea was originated between the Laurasia and Gondwana
was called as Tethys sea. After that Mesozoic period (11 crore years ago) the both
Laurasia and Gondwana landmasses were braking and formed the today’s continents.
North America, Europe and Eurasia are the parts of Laurasia and the continents like
South America, Africa and Antarctica made from Gondwana landmass. Further in tertiary
period (6.5 crore years ago) the Antarctica was braked and present Madagascar, India
and Australia have been formed. The Wegener assumed the forces which are
gravitational force, force of buoyancy and tidal force breaking the continents and there
drift.
21
Fig. 2.5 : Wegener’s Continental Drift
Evidences of Continental Drift Theory
1.
Jigsaw Fit
Jigsaw fit is the most significant evidence of this theory. The east coast of
South America and west coast of Africa are the best example of jigsaw fit. The bulk of
Brazil is well fit with Gulf of Guinea (African west coast). Today Australia, Africa and
India are the isolated continents but in their coast have similarities which are built-in
one another. Like this east coast of South America can be fitted with west coast of
Africa. On the ground of jigsaw fit it is conclude that today’s individual continents are
the part of Pangaea. After breaking these continents are drifted and get present position
on the earth.
Fig. 2.6 : Jigsaw Fit
22
2.
Geological Evidences
There are common geological facts are observed along the east and west
sides of Atlantic Ocean. The availability of rocks on continent at particular places have
indentified on other continent which is well fitted to first e. g. north-western part of
Africa and eastern part of Brazil have a same rock and that’s are basalts. There are
another striking geological correlation on both side of Atlantic Ocean is mountain ranges.
The mountain ranges of Appalachian presently found in North America and it also
appears in Greenland and Europe with same age and type. The same thing is observed
on South American east coast and African west coastal area.
3.
Paleontological Evidences
In Upper Carboniferous age there were only one continent and as per the
climatic regions of this continent particularly types of animals and plants were origin.
Due to the braking of continents and its drift they are placed away from each other with
having vast water bodies between them. It is commonly observed that the same fauna
and flora and their fossils e.g. in Antarctica as well as in all continents of southern
hemisphere have contain fossils of lystrosaurus, mesosaurus, glossopteris and
sinonouthus. Wegener has been considered that all these areas were contiguous and
separated due to continental drift.
4.
Biological Evidences
There are similarities among the animals in the eastern part of North America
and western part Europe. In the present day after some interval certain living birds of
Europe and Scandinavia have migrating towards the North America. These birds are
plunge into Atlantic Ocean. It is a sign of fact that Europe and North America were
conversant with land in past but now they are take apart and have vast water body of
Atlantic ocean.
5.
Paleoclimatological Evidences
North-east of USA, England and Antarctica have coal deposits and itself it proves
that there were tropical climate in past but now the percent climate in these lands does
not indicate such luxuriant growth of vegetation because today these continents have
polar climate. The continents like South America, Africa, India and Australia have been
23
showing the signs of glaciations landforms, it reveals that the past climate of these
lands were polar but now a day’s these continents have enjoying with hot desert climate.
It can be prove the drifting of continents.
6.
Proof of Actual Drift
The actual measurements of distance between North America and Greenland
in 1823, 1870 and 1917 have indicated that Greenland is actually drifting towards North
America at the rate of 32 meters per year. Similarly measurements between England
and Greenland in 1873 and 1907 have shown that the distance between these areas
has increased by 35 years.
7.
Young Fold Mountains
As per accordance of Wegener the formation and distribution of young fold
mountains have been going on. The North and South America drifts towards the west
and its outcome are the formation of Rocky and Andes. Similar to this Himalaya, and
Alps mountains were formed due to folding in sediments of Tethys sea. It shows the
convergent of Laurasia and Gondwana.
Critical Evaluation of Wegener’s Theory
1.
Most of the scientists have criticized that Wegener did not properly explained
the forces which was utilized for the breaking the Pangaea and drifting of the
continents. These scientists are believed that for the breaking of Pangaea there
is need of 1000 times more power than the present power, but such power
does not generate from the origin of the earth to present time. If it had such
force, it would be stopped the earth’s rotation. The rotation of the earth is not
stopped till date it reveals such type of powerful force is not origin then how it is
as present to product the required effects.
2.
According to Prof. Hess, sima layer is formed from the harden material then
the sial material. If it is considered that sima is made from soft material and
then the sima. Sial is floating on sima then it is happen to continuous process
of changing the shape of continents and their locations. But neither changes in
the shape of the continents nor their locations.
24
3.
The Wegener had been suggested the period of continental drift that period
was questioned by the number of scholars. The period, in which the braking of
Pangaea was taking place, why Pangaea was broken in that particular period
and why Pangaea was not broken before or after that particular period?
4.
Wegener had been supporting his theory with jigsaw fit but many scientists
have found faults with it. Only few exceptional locations have this jigsaw fit.
The recent studies in such area presents jigsaw fit is available more than 500
m depth in the sea water.
Up to some limit Wegener’s theory was criticized but resent studies can be
provide some concrete supports.
1.
The magnetic survey of Prof. Laccyti can provide best base for this theory.
2.
The recent measurements between the continents are shows the continental
drifts.
3.
The World wide universities and their researches are proving the horizontal
movement in continents.
2.2.3 Plate Tectonic Theory
Introduction
Wegener’s continental drift theory attracted worldwide attention. World’s number
of scholars was involved in the study of continental movements and presented their
views concern to Wegener’s theory. After 1960, the study of plate tectonic was going
on. Kipping in this mind the plate tectonic theory is recognized as a modified version of
Wegener’s theory. Similarly plate tectonic theory is also recognized as a modern
multiform theory or global movement theory.
The concept of plate tectonic was firstly used by Candian Tuzo Wilson in 1965.
Who was promoter of the sea floor spreading concept and with this concept he indicates
the continental drift through faults model, the fault type necessary to make the mobility
of the plates on global work out. According to him structural changes in plates and
inter-relations of the outer boundaries of the two or more than two continents or ocean
basins are called plate tectonic and harden part of lithosphere is called plate.
The Royal Society of Londan had organized a symposium which was the official
beginning of the acceptance of plate tectonics studies. In this symposium, Edward
25
Bullard showed with computer calculation how the structure of continents along both
east and west sides of Atlantic Ocean’s. In 1967, W. J. Morgan had been proposed the
plate tectonic theory.
The meaning of tectonic is to construct or structure and plate tectonic means
due to internal forces results in distinguishing characterized land forms are created on
lithosphere. In the process of plate tectonic, there are some common incidences like
as eruption of lava, earthquake, continental movements, folding, faulting, inclination
and deep down of the crust.
Plate Tectonic Theory
The earth crust is discontinuous and simplistically, the earth consists of the
plates and plate boundaries, those zones where the plates contact and interact. The
crust has form from major seven and sub or small twenty plates. Each plate is separate
from its neighboring plate and independently hovering on asthenosphere. It is
characterize as a flaccid and the floating continents are made from sial and sea floors
composed from sima. A plate may be an ocean basin alone or a continent alone or a
combination of ocean basin and continent. The plate that outer rigid layer of the earth
is divided into couple of dozen ‘plates’.
Major Plates
1) America
2) European
3) Africa
4) Indo-Australian
5) Pacific
6) Atlantic
1) Nazca
2) Cocas
3) Philipiens
4) Caribbean
5) Arabian
6) Bismark
7) Carolina
8) Scotia
9) Juan de fuca
7) Antarctica
Sub-Plates or Small plates
10) Somalian etc.
The current motion of the plates are calculated through remote sensing satellite
data sets and calibrated with ground station measurements.
26
Plate Movements
The earth crust is balancing on the asthenosphere and it is unstable. So, it is
floating in various directions continuously. According to Arther Homes, tremendous
forces are in asthenosphere which generates conventional currents in magma which
causes plate movements. On the earth surface there are presences of sea floor
mountain ranges, big faults and active folding zones are the best evidences of plate
tectonics in present era. In the process of plate movements, the plates are contact
with each other by three ways:
a)
Convergent Movement
When two plates attracts each other and hit one another is called as convergent
movement. In this process the sides of plates which come in the contact have goes
under the vertical movements. Due to this one plate is thrown upward direction and
other plate thrown down ward. Convergent movement plate regions are always prone
for earthquakes and volcanoes e.g. the scientists are in the view of the earthquake of
26th December, 2004 at Sumatra, Java, Indonesia and Thailand caused tsunami in
Bengal Sea.
b)
Divergent Movement
Close two or more than two plates are drifting opposite sides are called as
divergent movements. Particularly such movement generally occurs on see floors at
the mountain ranges due this the basaltic magma appears on sea floor and formed
the crust and it can also forming the rift valleys e.g. in middle Atlantic portion there is
Surtsey island results of divergent movements. The incidents of earthquake and volcano
are the common and frequently at the plate divergent regions.
c)
Parallel Movement
If close two plate boundaries of the crusts are moving back or frontward direction
parallel to each other is known as parallel movements. There are damages have been
taking places on parallel boundaries of the plates. The earthquakes and faulting is
common phenomenon on these region are generally observed.
27
Merits and Demerits of the Plate Tectonic Theory
Merits of the Theory
1)
The plate tectonic theory can provide the necessary information to better
understanding of regional relief features of the earth surface.
2)
This theory also gives the useful information about the functions, process and
its effects which are responsible for the different changes happening on the
earth surface.
3)
It is a one kind of source of information to understand the changes on sea
floors and its movements.
4)
The plate tectonic theory has flash light on the forces those are responsible for
the drifting of the continents.
5)
The grate revolution has been taking place in the study of physical geography
after the formation of plate tectonic theory.
Demerits of the Theory
1)
In his theory Morgan didn’t given the actual thickness of the crust. Therefore,
how the movements of plates are occurred it becomes a question in mind.
2)
The plate tectonic theory does not provide proper information regarding the
movements of plats. Is movements of plats occurred in past? If the movements
of plats had taken places in past then its actual period and its nature of
movements are not explained in this theory.
3)
Due to plate tectonic generally mountains are formed but sometimes mountains
are subsided its explanation is not given in this theory.
4)
The divergent movement of plate results mountain building on middle portion
of sea floor due to vertical movement. But both right and left sides land of
mountain are down thrown then how it is happen?
28
2.3
Summary
The origin of the sun to the formation of earth is a matter of curiosity among the
scholars. Different scholars have been perfounded their views about the origin of solar
system. The scholars have the controversy in their views but they are common on one
point that is the origin of the earth from sun. Today’s state of earth is take place due to
the radiation of hit from earth.
On the earth surface the distribution of continents and water bodies are uneven.
Out of the total area of earth surface occupied by the water nearly 71 percent and
continents are having nearly 29 percent. If we study the distribution of continents and
oceans and its distributional characteristics it reveals the various salient features. The
northern hemisphere has occupy maximum area under land due to that it is known as
land hemisphere and on other side southern hemisphere has occupied more area
under water than the land therefore it is called as water hemisphere. The appearance
of continents is discontinuous and water bodies are in continuous form. In all ocean
bodies Pacific ocean is the biggest ocean and among continents Asia is the largest
continent. The oceans and continents are in general triangular shape. There are opposite
structural arrangement at North Pole and South Pole, the availability of water on North
Pole and land on South Pole.
The German metrologiest Alfred Wegener was studied the World climate. He
was observed that the climate of some continents is changed. Kipping this view in
mind he putforth the theory of continental drift in 1912. The Pangaea was only one
continent present in Paleozoic period. The Pangaea was surrounded by vast water
bodies called as Panthalasa. In carboniferous era Pangaea had developed east-west
crack and broken into two landmasses. The northern part of Pangaea named as
Laurasia and southern part was called as Gondwana. The sea between the Laurasia
and Gondwana was called as Tethys sea. After that Mesozoic period the both Laurasia
and Gondwana landmasses were braking and formed the today’s continents. North
America, Europe and Eurasia are the parts of Laurasia and the continents like South
America, Africa and Antarctica made from Gondwana landmass. In tertiary period the
Antarctica was braked and present Madagascar, India and Australia have been formed.
The Wegener assumed the forces which are gravitational force, force of buoyancy
and tidal force breaking the continents and there drift. The Wegener had given the
number evidences to prove the continental drift. Beside that some scientists were
criticized on his theory.
29
Wegener’s continental drift theory attracted worldwide attention. World’s number
of scholars was involved in the study of continental movements and presented their
views concern to Wegener’s theory. After 1960, the study of plate tectonic was going
on. Kipping in this mind the plate tectonic theory is recognized as a modified version of
Wegener’s theory. Similarly plate tectonic theory is also recognized as a modern
multiform theory or global movement theory.
The plate tectonic theory is recognized as a modified version of Wegener’s
theory and it is also recognized as a modern multiform theory or global movement
theory. The concept of plate tectonic was firstly used by Candian Tuzo Wilson in 1965.
In 1967, W. J. Morgan had been proposed the plate tectonic theory. The meaning of
tectonic is to construct or structure and plate tectonic means due to internal forces
results in distinguishing characterized land forms are created on lithosphere. There
are seven major plates and twenty small plates are formed the crust. The movements
of these plates are in three ways and these are convergent, divergent and parallel
movements.
2.4
Terminology and Meaning
Solar system
:
Sun and its all planets and sub-planets of planets its
combine system.
Northern Hemisphere :
0° to 90° N. latitude covered part of earth surface.
Southern Hemisphere:
0° to 90° S. latitude covered part of earth surface.
Plates
:
Part of lithosphere.
Tectonic
:
Structure, construction or building.
Divergent
:
Opposite movements
Landforms
:
Structural arrangement of the earth surface.
Relief
:
Difference between height and sea level of undulating
surface of the earth.
30
2.5
Check Your Progress
Choose the correct alternative for the following questions:
1.
Generally how much area of the earth surface is covered by the water?
(a) 29 Percent
2.
5.
(d) None of these
(d) West
(d) Arabian sea
What is the name of island which is located on southern margin of South
America ?
(b) Malagasi
(c) Srilanka
(d) Tasmania
(c) Srilanka
(d) Tasmania
Which island is situated on south of Africa ?
(b) Malagasi
In which ocean World’s deepest deep Mariana trench is located ?
(b) Atlantic
(c) Indian
(d) Arctic
Name the ocean which was surrounded super continent Pangaea ?
(b) Atlantic
(c) Tethys
(d) Panthalasa
Which continent is not formed from the Gonadwana land ?
(a) Europe
10.
(c) Tahiti
(c) Triangular
(a) Pacific
9.
(b) Caspian sea
(b) Rectangular
(a) Pacific
8.
(c) East
(a) Spherical
(a) Tierra del Fuego
7.
(b) South
In general what type of shape has the continents and oceans ?
(a) Tierra del Fuego
6.
(d) 71 Percent
Around which land there is concentration of water body?
(a) Red sea
4.
(c) 61 Percent
On the basis of continent and oceans distributional character which hemisphere
is known as water hemisphere?
(a) North
3.
(b) 51 Percent
(b) South America c (c) Africa
After braking of Gondwana which continent is formed ?
(a) Eurasia
(b) Asia
(c) North America
(d) South America
31
(d) Antarctica
11.
12.
13.
14.
15.
2.6
By which name the plate tectonic theory is knowned as ?
(a) Continental Drift
(b) Global Movement Theory
(c) Cycle of Erosion
(d) Gravitational
Which is the major plate of the crust ?
(a) Pacific
(b) Nazca
(c) Carolina
(d) Juan de Fuca
What is the name of tectonic movement, if two plates are attracted each other ?
(a) Convergent
(b) Divergent
(c) Parallel
(d) Convergent and divergent
Which is the plate movement results the best example of California’s San Andris
fault ?
(a) Convergent
(b) Divergent
(c) Parallel
(d) Convergent and divergent
Which type of plate movement suggested by the scientist, it is occurred at
Sumatra, Indonesia and Java on 26th December, 2004 ?
(a) Convergent
(b) Divergent
(c) Parallel
(d) Convergent and divergent
Answers to Check Your Progress
1) 71 Percent
2) South
3) Tahiti
4) Triangular
5) Teradelfugo
6) Malagasi
7) Pacific
8) Panthalasa
9) Europe
10) South America
11) Global Movement Theory
12) Pacific
13) Convergent
14) Parallel
15) Convergent
32
2.7
Exercise
A)
Write in detail answers for the following questions.
1.
Write on distribution and distributional characteristics of land and oceans.
2.
Describe the structural arrangement of sea floor.
3.
Critically evaluate the Wegener’s continental drift theory.
4.
Describe the Plate Tectonic theory.
B)
Write Short Notes.
1.
Distributional characteristics of the land and oceans.
2.
The Hypsometric graph.
3.
Sea floor structure.
4.
The central them of Wegener’s continental drift theory.
5.
The merits and demerits of Wegener’s continental drift theory.
6.
Jigsaw Fit
7.
Plate movements.
2.8
Field Work
1.
Study the relief features of your surrounding area.
2.
Collect the information through media and internet regarding the earthquake,
volcanoes, folding and faults which are recently occurred in World and study
its impact on land of concern region.
3.
Collect the temporal imagery of the earth and study the distribution and
distributional characteristics of the continents and oceans.
❖❖❖
33
Unit 3
DIOSTROAPHIC MOVEMENTS
3.0
Objective
3.1
Introduction
3.2
Presentation of Subject Matter
3.2.1 Endogenetic and Exogenetic forces and their effects.
3.2.2 Earthquakes : causes, effects, and distribution.
3.3.3 Volcanoes: causes, effects, and distribution.
3.3
Summary
3.4
Terminology and Meaning
3.5
Check You Progress
3.6
Answers to Check Your progress
3.7
Exercise
3.8
Field Work
3.0
Objectives
1.
It helps to understand the information of landforms of the earth.
2.
It is useful to know the endogenetic forces and through that we can understand
an effects of folding and faulting.
3.
It is useful to know the sudden forces and through that we can understand an
effects of earthquakes and volcanoes.
3.1
Introduction
The study of forces affecting the crust of the earth or of geological processes
is of paramount significance because these forces and resultant movements are
involved in the creation, destruction, recreation and maintenance of geomaterials and
numerous types of relief features of varying magnitudes. The surface of the land is
34
not uniform in height or in appearance. The different major land forms like mountains,
plateaus and plains not only vary in size and shape but they also change with the
passage of time. The surface of the earth is continually changing. The forces affect
and change the earth surface. Change is the law of nature. Various structural or relief
features come in to existence due to two types of natural processes. These forces
may be divided into two types.
3.2.1 Internal Forces or Diastrophism :
The forces originate in the interior of earth. They are also known as 'Endogenetic
Forces', due to intense heat and pressure, different forces develop in the interior of
the earth. Some of these forces are very slow and their effects are visible only after a
long period of time. While other forces act suddenly, like earthquakes or volcanism
and their effects on the earth's crust are visible within a short period. These forces are
responsible for the formation of mountain and continent (plateaus).
External Forces :
They are also known as 'Exogenetic forces'. These forces develop at the surface
of the earth and act on the surface only.
Endogenetic or Diastrophic Movements
Endogenetic or Internal Forces
Distrophism includes all the process or forces which disturb and dislocate the
earth's crust. The forces coming from within the earth are called as endogenetic forces
and these forces caused by two types of movements in the earth these are horizontal
35
movements and vertical movements. Diastropheric forces include both vertical and
horizontal movements which are caused due to forces deep within the earth. All
diastrophic forces operate very slowly and their effects become discernible after
thousands and millions of years.
Slow Movements
On the basis of their results on the relief features, the diastrophic slow
movements are divided into two groups.
Epeirogenetic or Vertical Movements
This name was derived from Greek word 'Epeiros' meaning a continent. These
force act vertically i.e. along the radius either upward or downward from the centre of
the earth to the surface. They result either in subsidence or uplift of large landmasses
in relation to surrounding areas. As a result large continents and plateaus come into
existence and hence these forces are also known as continent building movements.
Upward Movements
These forces act upwards from centre of the earth. They result in rising of the
landforms. When upward movements act near the coast, the coastal region is uplifted.
In this type of uplift, the horizontal layers of rocks are usually not disturbed. There are
numerous examples of emergence of coastal areas in Saurashtra in Gujarat.
Fig. 3.1 : Upward Movement
Downward Force
These forces act downward towards the centre of the earth due to which
submergence of landmass take place. These movements are clearly visible near coastal
areas. The examples of these forces are at Mumbai and Pondecherry coasts.
Fig. 3.2 : Downward Movement
36
Orogenic or Horizontal Movements
The word orogenic has been drived from the Greek word 'Oros' meaning
mountain. These movements are responsible for the formation of mountain ranges
and hence, the name. These movements work horizontally i.e. at a tangent to the
surface of the earth it resulting in compression and tension in the earth crust. So,
these movements are also known as mountain building movements.
Due to horizontal compression takes place in the earth's crust. Horizontal
movements acting towards a comman point produce compression, which forms bends
in the rock strata. If the rocks are comparatively soft while fracture or bends takes
place and if the rocks are hard then faulting is happened.
Thus orogenic movements are of two types these are as following:
a)
Folding
b)
Faulting
FOLDING
Folding occurs as a result of compressional forces. Horizontal movements
acting towards a comman point produce compression, which forms bends in the rock
strata. These bends are known as folds. Fold mountain come into existence due to
such folding.
Nature of Fold
A simple fold consists of two distinct parts. The layers of rock that bend upwards
form anticlines while the layers of rocks that bend downwards form synclines. The
sides of a fold are known as limbs. The central line of either fold is known as the axis.
Whith the anticlines and synclines, the whole crust appears like a wave.
Fig. 3.3 : Fold
37
Types of Folds
The nature of the folds depends on the intensity of the compressional forces
and accordingly the folds attain various shapes.
i)
Symmetrical Folds
Fig. 3.4
Symmetrical folds are very simple folds, the limbs (both) of which incline
uniformly. These folds are an example of open fold. When the compressional force is
even from both sides symmetrical folds are formed the slope of both sides are equal.
But in real world symmetrical folds are very rarely found.
ii)
Asymmetrical Folds
When the compressional forces acting on the same point are of uneven intensity,
the limbs of the folds are asymmetrical. The limb is steep along the direction where
this force is greater while the other limb is gentle slope. Thus, the limbs are asymmetrical
in terms of inclinations and length.
Fig. 3.5 : Asymmetrical Fold
iii)
Over Fold
When the compressional forces are very intense, the asymmetrical anticline is
pushed right over. This is known as an over fold.
Fig. 3.6 : Over Fold
38
iv)
Recumbent Fold or Overturned Folds
This type of intense folding shows one limb practically resting on another and
the two limbs are more or less in a horizontal position.
Fig. 3.7 : Recumbent or Overturned Fold
v)
Overthrust Fold or Nappes
When the pressure exerted on a recumbent fold is great, the rocks may fracture
and are bodily carried forward over great distance along the plane of the fracture.
Such fold is known as Overthrust fold or Nappe. There are many Nappes in Himalaya
and Alps.
Fig. 3.8 : Overthrust Fold and Nappe
vi)
Fan Fold or Anticlinorium and Synclinorium
It is large folds in which there are several small folds, anticline has several
anticlines in it and it is known as anticlinorium. Similarly there are several small synclines
in the bigger synclines and is known as synclinorium. Such fold resembles a fan.
Fig. 3.9 : Fan Fold
39
Relief Features Produced by Folding
Fold Mountain :
Fold mountains are formed due to folding of rock strata as a result of
compressional forces. In the past geological ages vast geosynclines came into
existence. Geosynclines are sea beds or low-lying areas with great thicknesses of
sediments brought down by rivers. When compressional forces acted on geosynclines,
the sedimentary rocks strata were compressed and folding resulting into the formation
of syncline and anticlines. The anticlines formed the Fold Mountains while synclines
formed valleys. The Himalayas, the Alps, the Rockies and the Andes mountains came
into existence and these are the best examples of fold mountains.
On the basis of the period of their origin, the Fold Mountains are divided into
following groups.
♦
Caledonian Fold Mountain: e.g. Aravallies (India).
♦
Hercynian Fold Mountain: pre carboniferous age e.g. Ural.
♦
Alpine Fold Mountain: e.g. Himalayas, Alps and Rockies etc.
FAULTING
Compressional at one place involves tension at another place and this tension
usually results in the fracture of the earth's crust. Sometimes such fractures also
develop due to intense compression. When a fracture takes place, the rocks are
displaced on either side of it. This displacement is known as a fault. The plane along
which the displacement takes place after breaking is known as the fault plane. A fault
plane may be vertical, or inclined, or horizontal, or curved or of any type and form. The
movement responsible for the formation of a fault may operate in vertical or horizontal
or in any direction. In fact, fault movement or the displacement of rocks occurs only
upto a few meters only at a time. Fault, in fact, reprents weaker zones of the earth
where crustal movements become operative for longer duration. There are few terms
regarding an ideal fault like fault plane, fault dip, upthrown side, downthrown side,
hanging wall and foot wall.
Fault plane is that plane along which the rock bloks are displaced by tensional
and compressional forces acting vertically and horizontally to form a fault. Fault dip is
the angle between the fault plane and horizontal plane. Upthrown side represents
the uppermost block of a fault. Downthrown side represents the lowermost block of
40
fault. Hanging wall is the upper wall of fault and foot wall represents the lower wall of
a fault.
Types of Fault :
(i)
Normal Fault :
When the inclination of the fault plane and the direction of the down-throw are
both to the left or both to the right the fault is known as Normal fault. Such fault occurs
due to the tension.
Fig. 3.10 : Normal Fault
The fault plane is usually between 45º and the vertical. The steep scarp resulting
from normal faults is called fault-scarp or fault-line scarps the height of which ranges
between a few meters to hundreds of meters.
(ii)
Reverse Faults :
Reverse faults develop due to compression. in this type of faulting displacement
takes place in the upward direction.
Fig. 3.11 : Reverse Fault
Tensional or comprassional forces usually don't produce a single, but produce
a number of faults that may lie parallel to one another or may make an angle of
various degrees with each other. The fault plane , in a reverse fault, is usually inclined
at an angle between 40 degree and horizontal (0 degree). The vertical tress is minimum
and horizontal stress is maximum.
(iii)
Lateral or strike-slip faults :
These faults are occurred when the rock blocks are displaced horizontally
along the fault plane due to horizontal movement. These are called left-lateral or sinistral
faults when displacement of the rock blocks occurs to the left on the far side of the
fault and right-lateral when the displacement of rock blocks takes place to the right on
the far side of the fault.
41
(iv)
Step Faults :
Step faults forming on the slope area and all faults are in same direction, these
faults are called step faults. It is prerequisite condition for the formation of step faults
that the downward displacement of all the downthrown blocks must occur in the same
direction.
Relief Features Produced by Faulting
1.
Horst or Block Mountain
Due to tension or compression, two parallel faults come into existence and
displacement of rock strata takes place along both the fault planes and a block of the
earth's crust is raised between two parallel faults. The upthrown block stands like a
mountain and it is known as Horst. It is also known as a block mountain. Sometimes,
the land on the other sides of the faults slides down along a fault plane leaving the
area in between at a higher level. This portion is also known as a horst. The slope of
horst is very steep and they usually don't have peaks.
The Vosges Mountain that lie to the west of the Rhine River and the Black
forest plateau to the east of this rive are horsts or block mountains.
Fig. 3.12 : Horst or Block
2.
Rift Valley or Graben
A rift valley is also known as graben. When a block of land between two parallel
faults subsides along a fault plane leaving the adjoining areas at a higher level, the
subside part is known as a Graben. In German it means 'Trough'. They are called rift
valley. These valleys have steep wall like slopes and the valley floors are comparatively
wider. The Dead sea basin, the Great Rift Valley of East Africa, the Narmada and Tapi
valleys are also rift valleys of India.
Fig. 3.13 : Rift Valley or Graben
42
SUDDEN MOVEMENTS
Sudden movements originated because of sudden endogenetic forces coming
from the deep interior of the earth. These sudden movements affect massive destruction
on and below the earth surface. These events are like earthquakes and volcanoes
abruptly bring about changes in the features of the earth's surface. Such movements
are disastrous hazards when they occur in densely populated regions or places. But
sudden movements like earthquakes and volcanoes create certain relief features on
earth surface.
3.2.2 EARTHQUAKE
An earthquake is a sudden, temporary motion or series of motion which originate
in a limited region and then spread out from the place of origin in all directions.
Earthquakes are tremors which are produced by the passage of vibratory waves through
the rocks of the earth. If you throw a stone in the well or pond of still water, a series of
concentric waves are produced on the surface of water. These waves extend out in all
directions from the point where the stone strikes the water. Similarly, any sudden
disturbance in the earth's crust may produce vibrations in the crust which travel in all
directions from the point of disturbance.
Definitions :
1)
"Vibration or tremors produced in the rocks of the earth crust are known as
earthquakes".
2)
According to J. C. Macelwane "an earthquake is a vibration or oscillation of the
surface of the earth caused by transient disturbance of the elastic or gravitational
equilibrium of rocks at or beneath the surface".
An earthquake usually originates some kilometers beneath the surface. The
point in the crust at which an earthquake occurs is known as the Focus of the
earthquake. The point on the earth surface situated above the point of origin is known
as the Epicentre. Vibrations spread in all directions from the focus of an earthquake
they first reach the epicenter.
Seismic Focus
Fig. 3.14
43
Earthquake Waves
The earthquake waves are of three types:
i)
Primary Waves or Push Waves ('P' Waves)
These waves are like sound caves in which the movement is to and fro in the
lines of propagation. The velocity of these waves increases while travelling through
rocks of higher density. They can pass through liquid and solid medium also and
velocity is 10 to 12 km per second.
ii)
Secondary or Transverse Waves ('S" Waves)
These waves are similar to light waves where each particle is displaced at
right angles to its direction of movement. These waves cannot travel through a liquid
medium and velocity is 8 to 10 km per second.
iii)
Longitudinal or Ground Waves ('L' Waves)
These waves travel along the surface of the ground. These waves pass through
the liquid and solid mass of the earth crust and its speed is about 6 to 8 km per
second.
Fig. 3.15
Causes of the Earthquakes
In ancient times, there was no scientific treatment of the causes of earthquakes
and the earthquakes were considered to be the result of supernatural powers and
God's anger against man's sins. But these ideas have no place in the scientific treatment
of the subject in the modern days. Following are considered to be the main causes the
earthquakes.
i)
Volcanic Activity
When the air compressed within the interior of the earth, escapes out, it shakes
some part of the land. In other words, there is a deep relationship of cause and effect
to between the two phenomenons. Earthquakes occur at the time of volcanic eruptions
and sometimes earthquakes cause volcanic eruptions. When hot lava, gases, steam
etc. try to come to the surface due to great pressure in the interior of the earth, it
causes vibrations in the crust and an earthquake is occurred.
44
ii)
Isostatic Adjustment
The isostatic balance between the raised and depressed blocks of land on the
surface of the earth is not always maintained. When erosion takes place on the
mountains, it results in deposition on the sea bed and the isostatic balance is disturbed.
In order to maintain the balance magma from the neighbouring areas flows under the
raised surface and earthquakes occur at zones of weakness. An earthquake takes
place only is the isostatic adjustment is sudden and quick. Such earthquakes normally
occur in the zone of Young Folded Mountains where the land surface is yet to attain
isostatic equilibrium. The example of such earthquake was Uttar Kashi in 1991.
iii)
Faults
The tectonic forces including tension and compression cause folding and
faulting in the earth's crust. Tension results in the formation of rift valleys and Block
Mountains. When these forces act suddenly, an earthquake is the natural result.
iv)
Elastic Rebound
Majority of the earthquakes occur along the fracture line where slipping and
settling down of rock masses takes place. Stresses on the two sides of the fault
accumulate and cause bending of the rocks. When rocks can bear no more stress,
breaking with sudden displacement of the rocks on two sides of the fault takes place.
It produces a blow to the rocks on one side of the fault-plane and to the lower rocks on
the other side. This is called the elastic rebound hypothesis.
v)
Accumulation of Water
Whenever there is large scale accumulation of water, it causes strain in the
underlying rocks. When the strain becomes too much, it breaks the rocks and sudden
vibrations take place in the form of an earthquake. Such earthquakes are associated
with dams, lakes and tanks e.g. earthquake of Koyana (Maharashtra) in 1968.
Vi)
Local Causes
Minor earthquakes take place due to local causes such as landslides, emission
of water vapor under high pressure and sudden collapse of roof of the caves in Karst
region etc.
45
Vii)
Other cause
According to the some geologist, earthquakes originate mainly in the mentle.
In this zone, continuous changes are taking place in the crystalline structure of the
silicate minerals due to which localized energy increases. It is of an explosive nature
and causes earthquakes.
The earthquakes are measured in terms of their magnitude and intensity. The
earthquake magnitude is related to the energy released during the quake and is
recorded by an instrument called Seismograph. It is measured on the Richter scale.
This scale was developed by Charles Francis Richter in 1935. The magnitude is
expressed in absolute numbers, 0-10. The intensity or destructive power of an
earthquake is an evolution of the severity of ground motion at a given location. It is
measured in relation to the effects of the earthquake on human life and is described in
terms of damage caused to buildings, dams and other structures. The intensity of an
earthquake is measured on Mercalli scale developed by an Italian seismologist Mercalli
in 1902. The range of intensity scale is I to XII.
Effects of the Earthquakes
Apart from the immediate destruction of life and property, earthquakes brings
several changes in and on the earth's crust.
i)
Earthquakes cause heveay loss to life and property. The maximum damage is
caused near the epicentre of the earthquake. The most earthquake is the one
which rocked Bhuj in Gujrat on 26th Jan.2001. Its tremors were felt all over the
Indian subcontinent including India, Pakistan and Nepal. It measured 7.9 on
the richter scale. About one lakh people lost their lives.
ii)
If the cracks develop in the hilly area, they result in landslides which may block
the rivers. Sometimes these cracks damage the dams' constructions. The river
water submerges the surrounding low-laying areas causing severe floods. The
flood in the Brahmaputra valley in 1950 was caused by an earthquake.
iii)
Some wells may become dry while other gets more water.
iv)
Rivers may change their courses, if fissures develop in their beds.
v)
Earthquake occurring in sea, result in high waves in the sea water and cause
heavey damages to ships. Such seismic sea waves are called Tsunamis in
Japanese. Tsunamis which hit 11 countries surrounding the Indian ocean on
26th December,2004 are still fresh in our minds. It was caused a severe
46
earthquakes measuring 8.9 on the richter scale and occurring off the coast of
Sumatra (Indonesia). Tsunami which struck Japan on March 11 th, 2011 was
also caused a powerfull earthquake measuring 8.9 on the richter scale on the
N.E. coast of Honshu.
vi)
Contraction of rock strata takes place, which is evident from the bending of
railway lines and pipelines.
vii)
Earthquakes may form depressions forming lakes.
viii)
Fires break out due to earthquakes which inflict great losses.
ix)
Glaciers are breached and their avanches scatter too far off places. The
numbers of ice-bergs increase suddenly.
x)
Underground water is also affected by earthquakes.
xi)
Due to earthquakes new springs may be appear on the surface.
xii)
Earthquake waves are helpful in knowing about the interior of the earth.
xiii)
New mineral areas are uncovered or raised up. It provides much needed mineral
wealth.
xiv)
Rivers adopt new courses which provide new agricultural land.
xv)
Faults, thrusts and folds are often associated with earthquakes. An earthquake
disrupted several country roads on the floor of a broad valley in Japan during
the earthquake of 1891. A tremendous fault occurred during the California
earthquake of 1906.
Distribution of the Earthquakes
The distribution of earthquake is more or less similar to that of volcanoes. No
place on the earth surface is totally free from earthquakes but the earthquakes are
occur more frequently in certain area. These areas are the weak and unstable parts of
the earth's crust. These belts are as below:
i)
The Circum-Pacific Belt
This belt encircle the Pacific ocean and follows the western coast of the South
and North America, Aleution Islands and islands of the eastern coast of Asia like
Japan and Philippines. Nearly 68 per cent of the earthquakes of the world originate in
this belt. This area is known as the 'ring of fire'. This is the area of intense volcanic
47
activity also. This area is closely linked with the region of crustal dislocations and
volcanic phenomenon. Mountains here run along the border of continents and nearly
parallel to the depressions in oceans. It causes shar-pest break in relief which becomes
a cause for the earthquakes.
ii)
Mid-World Mountain Belt
This belt is associated with the young fold mountain ranges of the Alps,
Himalayas, and their continuation in the south-east Asian islands. Nearly 22 per cent
of the earthquakes of the world originate in this belt. It extends parallel to the equator
from Mexico across Atlantic Ocean, the Mediterranean Sea, from Alpine-Caucasus
ranges to the Caspian, Himalayan Mountains and the adjoining lands. This zone has
folded mountains, large depressions and active volcanoes.
iii)
Minor Belts
The remaining 11 per cent of the shocks are recorded outside these two belts.
Only a few occur along the fracture in African lakes, Red and the Dead Sea zone.
Fig. 3.16 : World Distribution of Earthquakes
3.2.3 Volcanoes
A volcano is a sudden and abrupt explosion in the crust of the earth through
which magma, gas, dust, smoke and solid material is ejected. The hot molten magma
below the earth's surface is brought to the surface as lava. Lava is at very high
48
temperature, varying from 800º to 1300º Celsius and contains steam and several
other gases. All these materials are ejected at great pressure through a pipe which is
known as its 'vent' or 'Neck'. The lava forms a cone like feature on the surface of the
earth which is known as 'Volcanic Cone'. The top of the cone has funnel-shaped or
saucer-shaped depression which is known as 'crater'. The diameter of the crater may
vary from a few meters to a few kilometers. Sometimes lava comes to the surface
through joints on the sides of the main cone and forms secondary cones. The term
vulcanicity includes all the processes through which solid, liquid and gaseous material
from the interior of the earth is forced into the earth's crust or is ejected on to surface.
The term volcanoes are generally applied to the extrusive type of vulcanicity in which
the magma reaches the surface of the earth.
Materials Ejected by Volcanoes :
i)
Gases :
The gaseous substances are mainly composed of steam, products being
hydrochloric acid, ammonium chloride, sullphur dioxide, hydrogen sulphide, hydrogen
and carbon dioxide. Water vapor is the most important of all the gases as it accounts
for 60 to 90 per cent of all the gases thrown out by a volcano. The water vapor causes
heavy rainfall after condensation in the atmosphere.
ii)
Liquids :
The liquid matters are the lava or magma and water. The temperature of freshly
ejected lava may be ranges between 600º C to 1200º C. Water also comes out along
with lava. The speed of lava flow depends upon its composition, mobility and the slope
of the ground. Usually, the movement is very slow and even a speed of 15 km per
hour is rarely achieved. But sometimes the speed may be as high as 80 km per hour.
iii)
Solids :
The solid material consists of ash, dust particals and angular fragments mostly
of lava rock blown up from within the vent. If the diameter of the solid block thrown out
by a volcano is more than 33 mm it is known as volcanic bomb or blocks. The pipes of
4 to 25 mm diameter are known as volcanic lapilli while smaller pieces under 4 mm
are called volcanic dust or ash.
49
Causes of Volcanoes
Our knowledge regarding the causes of volcanic eruptions is extremely limited
because the source of their origin lies deep into the earth. Most of our knowledge
about the volcanoes is derived from the indirect sources. The major causes are
described as under:
i)
Percolation of Cold Water
The water percolating through the cracks and fissures in the earth's crust and
comes into contact with the molten or potentially molten rock. Due to high temperature
the water convert into steam and it required more space. It results into eruption.
ii)
Earth Movements
The lava in the interior of the earth is subjected to great pressure which does
not allow the lava to melt. When the orogenetic forces causing earth movements
affect the earth's surface, the sedimentary rocks rise in folds. The pressure on lava is
reduced and if such zones are weakness. At these places, the lava is melted due to
reduced pressure over it and from weak section of earth crust cause the eruption.
iii)
High Temperature in the Interior
The temperature found in the interior of the earth is very high. This is due to
the presence of high pressure, chemical reactions and radio-active substances there.
It is estimated that the temperature rises in the interior of the earth at the rate of 1°c
per 32 meters. Thus the molten material at high pressure comes out at the surface of
the earth and a volano eruption takes place.
Types of Volcanoes
A)
On the basis of the mode of eruption of lava, volcanoes are classified into two
types.
i)
Central Type
When the volcanoes eruption occurs through the single vent or a group of
closely related vents. It is known as central type of volcanoes e.g. Fuji Yama, Vesuvius
are the examples of this type.
50
ii)
Fissure Type
Volcanic eruption takes place through fissure. Along a line of considerable
length or at numerous points along it. e.g. Deccan Trap.
B)
Volcanoes are also classified on the basis of their degree of activity. On this
basis volcanoes are divided into three types.
i.
Active Volcanoes
Those volcanoes that erupt fairly frequently are called active volcanoes.
Stromboli and Vesuvius are the examples of this type. The Etna volcano of Italy has
been active for the last 2500 years. Stromboli volcano of Sicily Island explodes after
every 15 minutes and is known as the Light House of the Mediterranean.
ii.
Dormant or Sleeping Volcanoes
The dormant volcanoes are that which eruption has not occurred regularly for
a long time. But they cause great damage to life and property when they suddenly
become active after remaining dormant for a sufficiently long time. Visuvius volcano
of Italy has exploded only 10 times in about 1500 years. The volcano of Barren Island
to the east of Andamans in India exploded in 1991 after remaining dormant for several
years. Such volcanoes are known as sleeping volcanoes. Katmai in Alaska is the
examples of this type.
iii.
Extinct or Dead Volcanoes
The volcanoes that have not erupted during historical times and not show any
sign of activity are known as extinct volcanoes. The vent of an extinct volcano is
blocked and its crater is filled with rain water to form a crater lake. Vegetation starts
growing on it. The possibilities of future explosion become remote. Popa of Myanmar
is its outstanding example and Mount Egmont in New Zealand is the examples of this
type.
Many a time, an extinct volcano suddenly becomes active. This has happened
in case of Krakato volcano. Its eruption in the year 1883 blew off the top of the mountain
by an explosion which caused tidal waves about 16 meters high, killing 36000 people
in west Java. The volcanic dust, ashes and smoke spread in about 27 km, the rock
fragments and lava rose to a height of about 800 meters. The volcanic dust and gases
encircling the globe in the atmosphere caused strange sunrise and sunset conditions
for about three years.
51
Effects of Volcano :
Volcanic eruptions cause heavey damage to human lives and property through
advancing hot lavas and fallout of volcanic materials; destruction to human structures
such as building, factories, roads, rails, airports, dams and reservoirs through hot
lavas and fires caused by hot lavas: floods in the rivers and climatic changes. A few of
the serve damages wrought by volcanic eruptions may be summarized as given below.
1.
Huge volumes of hot and liquid lavas moving at considerably fast speed bury
human structures, kill people and animals, destroy agricultural farms and
pastures, plug rivers and lakes, burn and destroy forest. The great eruption of
Mt. Loa on Haawaii poured out such a huge volume of lavas that these covered
a distance of 53 km down the slope. The thick covers of green and dense
forests on the flanks of Mt. St. Helens were completely destroyed due to severe
forest fires kindled by hot lavas.
2.
Fallout of immense quantity of volcanic materials including fragmental materials,
dusts an ashes, smokes etc. covers large ground surface and thus destroys
crops, vegetation and buildings, disrupts and diverts natural drainage systems,
creates health hazards due to poisonous gases emitted during the eruption
and causes killer acid rains.
3.
All types of volcanic eruption, if not predicted well in advance, cause tremendous
losses to precious human lives. Sudden eruption of violent and explosive type
through central pipe does not give any time to human beings to evacuate
themselves and thus to save themselves from the clutches of death looming
large over them.
4.
Earthquake caused before and after the volcanic eruptions generates
destructive tsunamis seismic waves which create most destructive and
disastrous sea waves causing innumerable deaths of human beings in the
affected coastal areas.
5.
Volcanic eruptions also change the radiation balance of the earth and the
atmosphere and thus help in causing climatic changes. Greater concentration
of volcanic dusts and ashes in the sky reduces the amount of insolation reaching
the earth's surface as they scatter and reflect some amount of incoming
shortwave solar radiation.
52
6.
A group of scientists believes that volcanic eruptions and fallout of dusts and
ashes cause mass extinction of a few species of animals. Acid rains
accompanied by volcanic eruptions cause large-scale destruction of plants
and animals.
Landforms Associated with Volcanoes
i.
Volcanic Plateau
Extensive plateaus are formed due to fissure eruption. The piling up of lava
flows on after another result in enormous thickness extending over wide areas. The
Deccan Trap region of peninsular India is a classic example of volcanic plateau.
ii.
Volcanic Cones
The volcanic cones are hill-like masses formed around a pipe by the
accumulation of molten rock material and fragments of rock.
Fig. 3.17
On the basis of their shapes volcanic cones are divided among following types.
a)
Ash and Cinder Cones
During explosive eruption, fragmental material like dust, ash, cinders and bombs
are thrown out from the volcanic vent, again fall back to earth around the vent.
Fig. 3.18
53
b)
Composite Cones
These are the most common volcanoes that come into existence as a result of
a number of eruptions and hence they take a long time for their build up. These cones
are made up of layers of ash and lava e.g. Mount Etna and Vesuvius in Italy and
Chimborazo in S. America are this type.
Fig. 3.19
c)
Shield Volcanoes
At the processes of eruption lava is very mobile and flow over a considerable
distance before it becomes solid. Hence, these volcanoes are not very high and have
small angles of slope e.g. Hawaii Islands.
Fig. 3.20
d)
Dome Volcanoes
They come into existence when acid lava is ejected during eruption. The mud
like lava doesn't flow over a long distance and rapidly become cold. Domes of this
type are found in the central Massif of France.
Fig. 3.21
54
e)
Caldera
A caldera is a remnant of the former crater which was destroyed and a second
cone is built by eruptions of lesser intensity,. Most of the composite cones are
surrounded by the calderas. In Alaska have numerous calderas.
Fig. 3.22
f)
Crater Lake
Sometimes the volcanic eruption are violent. The tops of the cones are blown
off forming's a large depression on the top of the volcanic cone. Water may collect in
the crater. It is funnel shaped. Such lade are known as 'Crater lake' e.g. lake Toba in
Sumatra.
Fig. 3.23
g)
Volcanic Plug or Greeva
Sometimes solidification of lava takes place in the vent of a volcano. When the
surrounding rock material is removed by different agents of erosion, the vent stands
prominently. It is known as a volcanic plug or greeva. The Devil Tower in Wyoming
State of the USA is the best example of this type.
Fig. 3.24
55
1.
Distribution of Volcanoes
Most of volcanoes are near the sea coast or on the islands because there are
great possibilities of percolation of water in these areas. The second important area of
volcano activity is that of new fold mountains. The mountain building forces have left
a very thin and weak crust in areas of folding and faulting. 486 active volcanoes have
been found all over the world since 1500 A.D. The total numbers of active and dormant
volcanoes is nearly 800, they mainly occur in the belts or zones. Following are the
main volcanic belts of the World.
a)
Circum-Pacific Belt
This is the most outstanding volcanic belt of the World in which 403 active
volcanoes are found. This belt more or less surrounds the Pacific Ocean and is known
as 'girdle of fire'. Nearly 66 per cent of the active volcanoes lie in this belt. On the east
coast of the Pacific Ocean, this belt extends from Cape Horn of South America to
Alaska in North America. Along the western coast of the Pacific, this belt extends to
Kurile islands, Japan and Philippines Islands. It runs through the young fold mountains
of the Rockies and Andies in North and South America and along eastern coastal
areas and islands of east Asia e.g. Fuji Yama, Mayon etc.
b)
The Alpine-Himalayan or Mid-World Mountain Belt
The belt start from the Canary Islands and stretches through the Mediterranean
and Middle East to south-eastern Asia. Vesuvius, Etna and Stromboli are the famous
volcanoes in this belt.
c)
The African Rift Valley Belt
This belt starts from Lake Region to Red Sea in the eastern part of Africa and
further goes up to Palestine in the north. Belt passes through the Red sea and extends
up to Israel in the north Kilimanjaro in Tanzania in this belt is an extinct volcano. Mt.
Kilimanjaro of Tanzania is an extinct volcano and lies out of this rift valley.
d)
Other Areas
Some volcanoes are situated in the mid-Atalntic where Cape Verde is very
famous. Azores,St. Helena, and Ascencion are volcanic islands but they are most
inactive. Islands have about 20 very active volcanoes. Comoro, Mauritius and Reunion
are important volcanoes near Madagascar in the Indian Ocean. Some active volcanoes
such as Arelus and Terror are found close to Antarctica. Hawaiian Islands have many
volcanoes.
56
3.3
Summary
The surface of the land is not uniform in height or in appearance. The different
major land forms like mountains, plateaus and plains not only vary in size and shape
but they also change with the passage of time. The forces originate in the interior of
earth. They are also known as 'Endogenetic Forces', due to intense heat and pressure,
different forces develop in the interior of the earth. Some of these forces are very slow
and their effects are visible only after a long period of time.
They are also known as 'Exogenetic forces'. These forces develop at the surface
of the earth and act on the surface only. Distrophism includes all the process or forces
which disturb and dislocate the earth's crust. The forces coming from within the earth
are called as endogenetic forces and these forces caused by two types of movements
in the earth these are horizontal movements and vertical movements. Diastropheric
forces include both vertical and horizontal movements which are caused due to forces
deep within the earth. All diastrophic forces operate very slowly and their effects become
discernible after thousands and millions of years.
Folding occurs as a result of compressional forces. Horizontal movements
acting towards a comman point produce compression, which forms bends in the rock
strata. Compressional at one place involves tension at another place and this tension
usually results in the fracture of the earth's crust. Sometimes such fractures also
develop due to intense compression. Sudden movements originated because of sudden
endogenetic forces coming from the deep interior of the earth.
These sudden movements affect massive destruction on and below the earth
surface. These events are like earthquakes and volcanoes abruptly bring about changes
in the features of the earth's surface. Such movements are disastrous hazards when
they occur in densely populated regions or places. But sudden movements like
earthquakes and volcanoes create certain relief features on earth surface. Earthquakes
are tremors which are produced by the passage of vibratory waves through the rocks
of the earth. If you throw a stone in the well or pond of still water, a series of concentric
waves are produced on the surface of water. These waves extend out in all directions
from the point where the stone strikes the water. A volcano is a sudden and abrupt
explosion in the crust of the earth through which magma, gas, dust, smoke and solid
material is ejected. The hot molten magma below the earth's surface is brought to the
surface as lava.
57
3.4
Terminology and Meaning
Anticline
:
A fold in sedimentary strata resembling an arch.
Endogenetic forces
:
The forces originate in the interior of earth.
Exogenetic forces
:
These forces develop at the surface of the earth and
act on the surface only.
Epeiros
:
This name was derived from Greek word 'Epeiro'
meaning a continent.
Fault plane
:
Is that plane along which the rock bloks are displaced
by tensional and compressional forces acting vertically
and horizontally to form a fault.
Fault dip
:
Is the angle between the fault plane and horizontal
plane.
Upthrown side
:
Represents the uppermost block of a fault.
Downthrown side
:
Represents the lowermost block of fault.
Hanging wall
:
Is the upper wall of fault and foot wall represents the
lower wall of a fault.
Earthquakes
:
"Vibration or tremors produced in the rocks of the earth
crust are known as earthquakes".
Focus of the earthquake :
The point in the crust at which an earthquake occurs
is known as the Focus of the earthquake.
Epicentre
:
The point on the earth surface situated above the point
of earthquake origin is known as the Epicentre.
Vent or Neck
:
All these materials are ejected at great pressure
through a pipe which is known as its 'vent' or 'neck'.
Volcanic Cone
:
The lava forms a cone like feature on the surface of
the earth which is known as 'Volcanic Cone'.
Crater
:
The top of the cone has funnel-shaped or saucershaped depression which is known as 'crater'.
58
3.5
Check Your Progress
Choose correct alternatives for the following questions.
1.
2.
3.
4.
5.
6.
7.
Block mountains are formed by which process?
(a) Epeirogeny
(b) Faulting
(c) Volcanic action
(d) Denudation
Which landform is formed due to subsidence of land between parallel faults ?
(a) Rift Vally
(b) Block Mountain
(c) Conical Hill
(d) V Shaped Valley
Which is the fundamental cause of folding?
(a) Horizontal tension
(b) Intrusion of lava
(c) Horizontal compression
(d) Vertical Tension
What is the meaning of graben?
(a) A down-faulted area
(b) A down-folded area
(c) An up-folded area
(d) A up-faulted area
Which one of the following is an example of endogenic forces?
(a) Erosion
(b) Deposition
(c) Volcanism
(d) Gradation
Which one of the following is not associated with diastropism?
(a) Orogenic process
(b) Plate tectoies
(c) Epeirogenic process
(d) Gradation
Which of the following statements is true about the focus of an earthquake?
(a) It is a point on the surface of the earth.
(b) It is a point inside the earth at a certain depth.
(c) Maximum damage occurs at this point.
(d) It is point of no damage
8.
Which of the following statements is true about tectonic earthquakes?
(a) They are caused by sliding of rocks along the fault plane.
(b) They owe their origin to volcanic eruptions.
(c) They occur in mining areas due to collapse of underground mines.
(d) Nuclear explosion causes such earthquakes.
59
9.
Which type of volcanic eruptions have caused Deccan Trap formations?
(a) Shield
10.
(b) Flood
12.
13.
14.
15.
16.
(b) Visuvious
(c) Barren Island
(d) Popa
Which of the following is a part of ring of fire?
(a) Coastalline of Pacific Ocean
(b) Alpine-Himalayan belt
(c) The African Rift Valley
(d) Mid-Atlantic Ridge
Which earthquake waves are very distructive ?
(a) Primary Waves
(b) Secondary Waves
(c) Surface Waves
(d) Transverse Waves
Which of the following instrument is useful to record earthquake frequency?
(a) Thermograph
(b) Barograph
(c) Seismograph
(d) Pentograph
The point of origin of an earthquake is known as ........
(a) Quakecenter
(b) Epicenter
(c) Sesmic focus
(d) Tectonic point
Primary waves of earthquake can travel through the .............
(a) Only solid material
(b) Only Liquid material
(c) Only gases material
(d) Solid and liquid material.
Which is the measuring unit of earthquake intensity ?
(a) Beaufort
17.
(d) Caldera
Which of the following is an active volcano?
(a) Stromboli
11.
(c) Composite
(b) Richter
(c) Mercalli
(d) Centimeter
At which place, an earthquake of 6.5 magnitude occurred in Maharashtra in
1967 ?
(a) Latur
(b) Bhuj
(c) Koyana
(d) Anjar
3.6
Answers to Check Your Progress
1)
b
2)
a
3)
c
4)
a
5)
c
6)
c
7)
b
8)
a
9)
b
10)
a
11)
a
12)
c
13)
c
14)
c
15)
d
16)
b
17)
c
60
3.7
Exercise
A)
Broad Questions :
1.
Give an account of the endogenetic forces ?
2.
What is an earthquake? Explain the causes and effects of the earthquakes ?
3.
Describe the different types of folding with suitable diagrams ?
4.
Write the causes and effects of volcano ?
5.
Explain the distribution of earthquake ?
B)
Short Notes :
1.
Types of fold
2.
Types of fault
3.
Effects of fault
4.
Effects of earthquakes
5.
Distribution of earthquakes
6.
Distribution of volcanoes
7.
Causes of Volcanoes
3.7
Field Work
1.
Visit an earthquake affected area and collect information of effect of an
earthquake.
2.
Observe surrounding hill landforms or visit Mahableshwar and observe volcanic
depositional features and describe it.
3.
Collect additional information of earthquakes, volcano and tsunami through
paper cutting, magazines and internet.
❖❖❖
61
Unit 4
WEATHERING AND EROSION
4.0
Objectives
4.1
Introduction
4.2
Presentation of Subject Matter
4.2.1
Weathering : Meaning and Types
4.2.2
Concept of Cycle of Erosion
4.2.3
Erosional and Depositional Features of River and Wind
4.3
Summary
4.4
Terminology and Meaning
4.5
Check Your Progress
4.6
Answer to Check Your Progress
4.7
Exercise
4.8
Field Work
4.0
Objectives
1.
To understand the meaning and types of weathering.
2.
To study the concept of cycle of erosion.
3.
To know the erosional and depositional features of river and wind.
4.1
Introduction
In the last chapter we discussed the endogenetic forces make the surface
uneven and exogenetic forces destroy the raised portions and level them down. The
exogenetic forces through weathering and erosion destroy the relief of the earth’s
62
surface. In this unit we will discuss the meaning and types of weathering, concept of
cycle of erosion and erosional and depositional features of river and wind.
4.2
Presentation of Subject Matter
4.2.1
Weathering : Meaning and Types
Rocks, generally formed inside the crust are subjected to different types of
physical and chemical changes when they exposed and come into contact with the
atmospheric moisture and temperature conditions prevalent there. This process is
called weathering. Weathering is a static geomorphological process which is important
for the soil formation.
We can explain meaning and concept of weathering with the help of definitions.
According to Sparks : “Weathering is the mechanical fracturing and chemical
decomposition of rocks, insitu by natural agent at the surface of the earth.”
Weathering is the process of dissinteration and decomposition of rocks insitu.
Types of Weathering :
There are three main types of weathering which are as follows :
1)
Physical / Mechanical Weathering
Physical weathering break rocks into smaller pieces without changing their
chemical composition. Physical weathering attack exposed rock and can penetrate
into rock along cracks, joint and bedding planes. The action of water and changes in
temperature are most important agents of physical weathering.
(a)
Temperature Changes and Expansion
This process effective where temperature is high in day and very low at night.
The minerals in rocks expanse in the day time due to high temperature and contract at
the night due to low temperature. The differential expansion and contraction create
tension between minerals leading to the breaking of rock.
63
(b)
Freezing, Jhawing and Frost Wedging
This process is most effective at high elevation in mid latitude where freezing
and melting is often repeated. Frost weathering occurs due to growth of ice within
pores and cracks of rocks during freezing and melting. When water enters in rock and
freeze it expands by about 9%, creating pressure on rock. Repeated cycle of freezethat cause fragmentation of rock in the form of block, scree and talus.
(c)
Exfoliation
Exfoliation is a type of weathering where scaling of rocks takes place. This
process results in curved sections of exposed rock peeling off from the core. This is
known as spheroidal weathering when caused by chemical factors.
2)
Chemical Weathering
Chemical weathering decomposes the rock mass to form new minerals and
substances. Solution, Hydration, Oxidation and Carbonation are leading chemical
processes affecting on rocks.
(a)
Solution
The water or acid with dissolved content is called solution. This process involves
removal of solid in solution which depend upon solubility of mineral in water. Soluble
rock forming mineral like potassium, sulphate, nitrate etc. are affected by this process.
Minerals like calcium carbonate and calcium magnesium bicrabonate present in
limestone are soluble in water. Common salt is also a rock forming mineral is susceptible
to process of solution.
(b)
Hydration
In this process water is added into minerals, due to addition of water into
minerals it expands, it causes an increase in the volume of rock.
e.g. Calcium sulphate takes in water it turns to gypsum.
64
(c)
Carbonation
In this process minerals that contains calcium, sodium are changed to
carbonates by the action of carbonic acid is known as carbonation, calcium carbonate
and magnesium carbonates are dissolved in carbonic acid and carried away in solution.
(d)
Oxidation
Oxidation means a combination of a mineral with oxygen to form oxides. When
the rock affected contain iron, the ferrous state in which iron commonly occurs changes
or oxidizes to ferric state and the crust crumbles. It takes place very rapidly in the
presence of water.
3)
Biological Weathring
The weathering which is caused by action of organism is called as bilogical
weathering. This can physically break down rock or lead to chemical attack.
(a)
Faunal Weathering
The burrowing animals like worms, gophers, rabbit, rats, jackle etc. help in
gradual breakdown or fragmentation of rock. Small organisms play more important
role in rock and soil weathring.
(b)
Floral Weathering
Weathering of rock by vegetations takes place in two ways i.e. (i) physical
weathering and (ii) chemical weathering which is called as biochemical weathering.
Root of plants make cracks in rock which lead to disintigration of rock. The
decomposition of organic matter produces humic acid, and respiration by soil organisms
produces CO2 which combines with water and form carbonic acid. These acids can
become concentrate in soil and accelerate chemical weathering.
65
Fig. 4.1 : Weathering Types
66
Importance of Weathering
The soil is formed by weathering, without which vegetation could not grow and
all animal life depends upon vegetation. Weathering helps to the erosional process.
Continuous removal and transfer of weathered material lead to gradual lowering of the
surface.
4.2.2
Concept of Cycle of Erosion
W. M. Davis an American geomorphologist emphasized that the landform evolve
and degrade in a cyclic manner. Davis postulated his concept of cycle of erosion in
1899 to present genetic classification and systematic description of landforms.
Geographical cycle is a period of time during which an uplifted landmass
undergoes its transformation by the process of landsculpture ending into low featureless
plain or peneplain. Davis explained these stages in the context of the landforms made
through the action of river, therefore cycle of erosion also called the fluvialo cycle of
erosion.
Fluvial Cycle of Erosion
In the ideal condition the cycle of erosion denotes sequential changes in
landform from youth to old stage.
Youth Stage
This stage is characterized by a few consequent trunk streams, a few large
tributaries and rapid rate of vertical erosion because of steep slope. V shaped valleys,
rapids, waterfall are formed in this stage.
Stream divides will be broad and stream meandering exist in this stage.
Mature Stage
In this stage vertical erosion or valley deepering is remarkably reduced. This
stage is heralded by lateral erosion and well integrated drainage network. The lateral
erosion leads to valley widening which transform ‘V’ shaped valley into wide valley.
Flood plain, natural levees, meanders are formed in this stage.
67
Old Stage
In this stage a landmass has been reduced by erosion almost to base level,
such a erosional plain is called ‘Peneplain’, sometimes the peneplain may be interrupted
by an isolated hill, such a erosional remnants of this type are called monadnocks.
Criticism :
1.
Davis’s view was purely descriptive.
2.
His cycle was not based on precise measurements or observations.
3.
The approach was qualitative.
4.2.3 Erosional and Depositional Features of River
Running water is a major gradational agent that are constantly work in shaping
the land. As an agent of gradation running water perform both the function of erosion
and deposition. The rainwater reaching the earth’s surface becomes runoff. The runoff
becomes a stream when water flow from certain height. The geological work of fluvial
processes taken place into 3 ways erosion, transportation and deposition. The fluvial
landforms are divided into two major groups i.e. (1) erosional landforms and (2)
depositional landforms.
Erosional Landform
The significant landform resulting from fluvial erosion by streams are river valley,
waterfall, pot holes, rapids etc.
(a)
River Valley (‘V’ Shaped Valley)
The valley formed in Youth Stage of river. The valley is deep and narrow, both
valley sides meet together at valley floor. The valley formed due to accelerated rate of
vertical erosion.
Valleys are divided into two types i.e. Gorges and Canyon.
68
A Gorge is a deep valley with very steep to straight sides and canyon is
characterized by steep step-like side slopes. It is extended form of canyon e.g. different
‘V’ shaped vallies formed by Himalayan Rivers.
(b)
Waterfall
Waterfall defined as a vertical drop of water of enormous volume from a great
height in the long profile of river. Waterfall formed due to sudden descent break in the
longitudinal course of river, like variation in the relative resistance of rock (soft - hard
rock chain).
e.g. Gersoppa fall, India, Angel fallin Venezuela etc.
(c)
Pot Holes
The Kettle like depression in the rocky bed of river valley is known as pot holes.
Pot holes are generally cylindrical in shape. The pot hole drilling is the mechanism
through which the grinding tools (boulder, pebbles etc.) when caught in the water
whirling, the diameter of pot holes ranges between from few centimeters to several
meters. Pot holes of bigger size is called as plunge pool. Various plot holes are formed
over Chhota Nagpur plateau.
(d)
River Meanders
“The bends of longitudinal course of the river is known as meanders.” In the
mature stage of river meander loops develop with deposition inside each loop. Overtime,
the size of meanders is increased leading to the widening flood plain.
(e)
Structural Benches
The step like flat surface formed at either side of lowest valley floor. The benches
are formed due to differential erosion of alternate band of soft and hard rock.
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Depositional Landforms
River deposit eroded material when the velocity of water decrease. Deposition
caused due to sudden decrease in slope.
The heavy material is deposited first and smaller and coarest sediment
suspended load deposited after.
(a)
Bars
Bars are ridge like features, which forms inside the bank of ends.
(b)
Alluvial Plan
Itis expanse of flat land on either side of river. When a river floods its banks and
spills on to its flood plain, it leaves behind a layer of alluviam / sediment. This sediment
enriches the soil, forming an alluvial plain.
(c)
Ox-bow Lake
The lake is formed due to impounding of water in the abondoned meander loop
is called as Ox-bow lake. It is formed during flood time, when portion of channel cut off,
as the stream tends to seek a straighter path.
(d)
Natural Levees
“The belt of ridges built by the deposition of sediment by river on its either bank
is called natural levee”. Levees are formed due to deposition of sediment during flood
period. Average height of natural levees is within 10 meters.
(e)
Delta
The traingulart shape alluvial tract at the mouth of river is called delta. Delta
formed when the sediment supply is high and there should be absence of tidal, current
and waves action. There are various types of delta like Arcute delta, Bird foot delta,
Estuarine delta, Cuspate delta etc.
e.g. Bird foot delta of Mississippi.
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Fig. 4.2 : Depositional Features of River
4.2.4 Erosional and Depositional Features of Wind
Wind is less effective gradational agent than river, sea waves, ground water
and glacier. Wind is an effective in desert areas. Wind erosion is limited to few meters
from ground surface. Wind is a significant gradational agent and contributes to the
shaping of the landforms. The landform created by wind are called Aeolian Landforms.
Erosional Landform of Wind (Aeolian Landforms)
Wind is an major erosional agent in desert or arid area. Wind erosion is taken
place by abrasion, deflation and attrition processes. These processes or action
produces ventifact, mushroom-rock, zeugens, yardang etc.
(a)
Ventifacts
Faceted rock cobbles and pebbles abraded by long periods of wind erosion are
called Ventifacts.
The rock pieces having three abraded facets are called Dreikanter.
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(b)
Yarding
Yarding are steep sided deeply undercut overhanging rock ridges separated
from one another by long corridors. Yarding are formed when alternate bands of hard
and soft rocks are vertical. They are parallel to each other.
(c)
Zeugen
These are rock masses of tabular form look like a capped ink pot standing on
softer rock. These are formed where alternate bands of hard and soft rock are in
horizontal manner.
Fig. 4.3 : Features Produced By Wind Erosion (Abrasion)
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(d)
Mushroom Rock
The rock of broad upper part and narrow base look like a umbrella or mushroom
is called mushroom rock. The base of rock eroded vigorously from all side because of
direction of wind not a constant. The upper part of rock least affected by erosion. The
mushroom rocks called ‘Gara’ in Sahara.
(e)
Deflation Basin
Depression is formed in desert due to removal of sand due to process of deflation
is called deflation basin / blow outs. The size of these basins varies from few meters
to kilometer.
Depositional Landforms of Wind
Wind transport the load by suspension, saltation and traction processes. When
obstructions occurs in the direction / way of wind then wind deposite the material on
either side of obstacles. Due to deposition of sand various landforms are formed like a
Ripple mark, Dunes, Sand drift etc.
(a)
Ripple Mark
These are small scaled depositional feature of sand. They are wave like feature
and formed due to saltation process.
(b)
Sand Dunes
Heaps or Masses of sands are called sand dunes. These are formed because
of accumulation of sand due to obstruction in wind speed. The dunes are mobile they
are not stable.
(c)
Seif
This is one of the type of dunes. These are longitudinal sand dunes. Windward
side of these dunes is gentle while leeward slope is steep.
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(d)
Barchan
These are crescent shaped dunes having two horns. The winward side of this
dunes is convex and leeward side is concave. In areas of abundant supply of sand,
barchans are large and well developed.
(e)
Loess
Loess is wind blown silt. It is fine grained sediment with small clay fraction and
higher content of carbonate mineral. Loess deposits very distant place from the source
areas. Loess deposits are seen in China, Alaska, Europe etc.
Prevailing wind
Fig. 4.4 : Features Produced by Wind Deposition
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4.3
Summary
Weathering is a static geomorphological process involves dissintegration and
decomposition of rocks in situ. For the convenience of study weathering is physical /
mechanical chemical and biological weathering. The type and rate of rock weathering
is influenced by a rocks mineral makeup.
The work of a river includes erosion, transportation and deposition creates
number of erosional and depositional features.
The work of wind is dominant in the arid and semi-arid regions of the world and
it also creates different erosional and depositional features on the surface of the earth.
4.4
Terminology and Meaning
1)
Base Level
:
The surface of a lake or a river or a sea into which
it flows.
2)
Deflation
:
The process by which wind remove particles of dust from
the land surface in an arid region.
3)
Erosion
:
The incorporation and transportation of material by a
mobile agent usually water wind or ice.
4)
Peneplain
:
An area of low relief developed at the end of ageomorphic
cycle under humid fluvial conditions.
5)
Hydraulic Action :
The denudation by the force of moving water against
solid rock.
4.5
Check Your Progress
A)
Choose the correct alternatives for the following questions.
1.
Decomposition and Disentigration of rock insity is known as ........
(a) Erosion
2.
(b) Weathering
(c) Mass Movement (d) None of these
Solution is the effective in a .............. terrain.
(a) basaltic
(b) granite
(c) shaly
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(d) limestone
3.
Clacium sulphate changed into gypsum by ..............
(a) Hydration
4.
(d) Solution
(b) Penck
(c) Strahler
(d) Hutton
(c) Youth
(d) None of these
Waterfall formed in ................ stage.
(a) Old
6.
(c) Oxidation
The concept of cycle of rosion propounded by ...........
(a) Davis
5.
(b) Carbonation
(b) Mature
Natural Embankment found along river banks, build up during flood period is
called .............
(a) Levee
7.
(c) Ox-bow lake
(d) None of these
................. is erosional features produced by rivers.
(a) Alluvial plain
8.
(b) Peneplain
(b) Ox-bow lake
(c) Potholes
(d) Delta
Meanders are ..............
(a) products of weathering of Rock
(b) waves produced along a sea shore
(c) bend along the longitudinal course of river
(d) deposition feature of wind.
9.
Loess is commonly formed by the deposition of ................
(a) Wind
10.
(d) Volcano
(b) Arid
(c) Coastal
(d) Glaciated
Longitudinal sand dunes are called ..............
(a) barchan
12.
(c) River
Barchan are found in .................. areas.
(a) Limestone
11.
(b) Wave
(b) seif
(c) spit
(d) yarding
The process of which blow outs formed in arid region is called .........
(a) degradation
(b) abrasion
(c) attrition
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(d) deflation
4.6
Check Your Progress
1. (b)
2. (d)
3. (a)
4. (a)
5. (c)
6. (a)
7. (c)
8. (c)
9. (a)
10. (b)
11. (b)
12. (d)
4.7
Exercises
A)
Broad Questions
(i) What is Weathering ? Discuss the different types of weathering.
(ii) Describe the erosional features produced by wind.
(iii) Critically examine the cycle of rosion as given by W. M. Davis.
(iv) Explain with examples depositional features produced by river.
B)
Short Notes.
(i) Biological Weathering
(ii) Delta
(iii) Depositional Landforms of Wind
4.8
Field Work
1.
Collect information about the types of weathering in your surrounding area.
2.
Observe the erosional and depositional features of river.
❖❖❖
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