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REPORT
Geology Field
Report
A FIELD VISIT TO MALEKHU
SUBMITTED BY:
SAMEER K.C.
1
071/BCE/26
ACKNOWLEDGEMENT
At every step, an engineer has to encounter earth and earth, as a
material or as construction site. So it proves the importance of geology
to civil engineering professionals. He or she must go through the inner
core of engineering geology for his/her perfection and for
professionalism.
The trip was really fruitful to us and certainly we got a lot of knowledge
about the earth.
Thank you Mr. Basanta Devkota and Mr. Madhab Lamichhane for
sharing a part of their brain. Thank you Mr. Sangam Shrestha sir and
Pal??……. sir to help us in field and giving complete suggestions. At
last, we would like to thank all our friends of other groups who
cooperate kindly in team work ………………………...All of you did a
wonderful job to lay out these pages.
At last, we would like to express our gratitude to our college. We are
proud of being students of Lalitpur Engineering College .
Sabindra Bhakta Shrestha (071/BCE/025)
Sameer K.C. (071/ BCE/026)
Santosh Gain (071/ BCE/027)
Saugat Pandit (071/ BCE/028)
Saurav Pokhrel (071/ BCE/029)
2
Table of Contents
1.
INTRODUCTION ................................................................................................................................... 5
1.1 Definition and Concept .................................................................................................................... 5
1.2. Requirement of geological study in the field of civil engineering .................................................... 5
2.
Location .............................................................................................................................................. 5
3.
Objectives of the Field Visit. ............................................................................................................... 5
4.
Methodology ...................................................................................................................................... 6
5.
Study and Identification of Rocks and Minerals ................................................................................. 6
5.1
Igneous Rock: .............................................................................................................................. 7
5.2
Sedimentary Rock: ...................................................................................................................... 8

Identification of Sedimentary rock. ................................................................................................. 8
5.3
Metamorphic Rock ...................................................................................................................... 9
5.4
Description of Rocks Identified in the field. .............................................................................. 10
Right Bank of Malekhu Khola about 700m upstream ........................................................................... 11
Right Bank of Malekhu Khola about 1 km upstream ............................................................................. 12
6.
Geological structures ......................................................................................................................... 12
6.1
Beds and Beddings:- .................................................................................................................. 12
6.2
Types of geologic structures:..................................................................................................... 13
6.3
Factors affecting how a rock deforms: ...................................................................................... 14
6.4
Measuring geological structures: .............................................................................................. 14
6.4.1
I-
Folds .............................................................................................................................................. 14
II-
Faults ............................................................................................................................................. 16
III-
Joints ......................................................................................................................................... 19
A.
Types of joints ............................................................................................................................... 19
6.4.2
B.
7.
Secondary structures ............................................................................................................ 14
Compound Structures ........................................................................................................... 19
Types of unconformities ............................................................................................................... 20
Geological compass ........................................................................................................................... 21
7.1
Clinometer compass.................................................................................................................. 21
7.2 Brunton Compass ............................................................................................................................ 22
7.3 Clark Compass ................................................................................................................................. 23
7.4 Digital Compass ............................................................................................................................... 23
8.
Attitude measurement of the plane ................................................................................................. 24
8.1 Foliation Plane:- .............................................................................................................................. 24
8.2 Joint plane:- .................................................................................................................................... 24
8.3
Attitude: .................................................................................................................................... 24
3
9.
Geological works of physical agents ................................................................................................. 27
9.1
Erosion ...................................................................................................................................... 27
9.2 Transportation ................................................................................................................................ 28
9.3 Deposition ....................................................................................................................................... 28
9.4 The Hjulstrom Curve ....................................................................................................................... 29
A.
Erosion by river water ................................................................................................................... 30
B.
By wind.......................................................................................................................................... 30
C.
By Glaciers ..................................................................................................................................... 31
9.5
10.
Features developed by the activities of physical agents ........................................................... 31
River Channel Morphology ............................................................................................................ 37
10.1
Meandering River Channel ........................................................................................................ 37
10.1.1
Overview of features associated with meandering streams. ................................................ 37
10.1.2 How meanders grow .................................................................................................................. 38
10.2 STRAIGHT RIVER CHANNELS ......................................................................................................... 38
10.3 Braided River Channel................................................................................................................... 39
11.
Conclusion..................................................................................................................................... 40
4
1. INTRODUCTION
1.1 Definition and Concept
Engineering geology is an interdisciplinary field in which pertinent studies
in geology and other geosciences areas are applied toward the solution of
problems involved in engineering works and resources uses. Geology is the
study of the earth, its history, its exterior as well as interior and the processes
that act up on it. Geology is also referred as the earth science or geoscience.
The word Geology comes from the Greek geo, “earth”, and logia, “The study
of”. Geologists seek to understand how the earth is formed and evolved into
what it is today, as well as what made the earth capable of supporting life.
Geology is the study of the changes that the earth has undergone as its
physical, chemical and biological systems have interacted during its billions
years history.
1.2. Requirement of geological study in the field of civil engineering
Nepal is a mountainous country. Since the Himalayan range is a result of
collision of Tibetan and Indian Plates, the zone is the most active tectonic
zone. The area is widely known for its structural deformation. Due to this
Nepal is suffering from different types of geohazards and instabilities. The
rapid construction of infrastructure such as roads, irrigation canals and dams,
without due relating geology and engineering may cause failure of such
infrastructures. So the study of geology is necessary in civil engineering.
Study of Geology helps in mining, town planning, in irrigation, buildings,
transportation, hydropower, industries etc.
2. Location
To study the geological structures we choose Malekhu of Nepal as the right
place. It lies in the Dhading district of Nepal.
3. Objectives of the Field Visit.
 To Study and Identification of Rocks and minerals.
 To Study the different Geological structures.
5
 To Handling of the Geological Compass.
 To Measurement of the attitude of planar feature like joint, bedding,
foliation etc.
 To study the geological works of physical agents.
 To Study of features developed by activities of physical agents.
4.Methodology
We went to the site and observe the geological structures and recognize the
structure and its composition with along its formation. Although the
methodology used for the projects differs from one to the other, all these
projects have three basic similarities. First, they all require an evaluation of
the site geology, i.e. rock types, extent of each rock unit, extent and type of
weathering, etc. This is usually done by conducting detailed site exploration
and investigation using surface mapping, boreholes, trenches, or geophysical
survey. Site exploration and investigation is usually conducted in several steps
(preliminary, advanced, etc.). Second, all the aforementioned projects require
an assessment of the engineering properties (strength, deformability,
permeability, etc.) of the soils and rocks involved in the projects. This is done
by testing rock or soil samples in the laboratory and by field testing. Finally,
engineers need to take into account possible geologic hazards and their impact
on existing and future structures. In general, geological hazards can be divided
into hazards from geological materials (reactive minerals, asbestos, gas
hazards), and hazards from geological processes (volcanoes, earthquakes,
landslides and avalanches, subsidence, floods, coastal erosion).
5.Study and Identification of Rocks and Minerals
Rock is defined as naturally forming hard and compact solid aggregate,
assemblage of minerals forming earth’s crust. Minerals can be defined as the
naturally occurring inorganic substance with fixed composition. There are
three types of rock, they are:-
6
5.1 Igneous Rock:
Form from hot, molten (liquid) rock material that originated deep within
Earth. Only igneous rocks have this origin. Hot, liquid rock is called magma.
(At Earth’s surface magma is known as lava.) We have learned that Earth’s
tempera
ture increases as we go deeper within the planet. In some places
within Earth, it is hot enough to melt rock. When this molten rock rises to or
near Earth’s surface where it is cooler, the liquid rock material changes to
solid rock. Igneous rocks are especially common around volcanoes and in
places where large bodies of rock that have melted and then solidified
underground have been pushed to the surface. So the rock formed by the
cooling and crystallization of magma is known as igneous rock and the
process is known as magmatism.
Figure: Igneous Rock
7
5.2 Sedimentary Rock:
Within Earth’s crust, igneous rock is the most common rock type. However,
most of the surface of our planet is covered with a relatively thin layer of
sedimentary rocks. Unlike igneous rocks, it is difficult to give a precise
definition of sedimentary rocks. Most sedimentary rocks are made of the
weathered remains of other rocks that have been eroded and later deposited as
sediment in layers. Over time, the sediments are compressed by the weight of
the layers above them. In addition, the layers may be cemented by mineral
material left by water circulating through the sediments. The cementing
material is usually silica (fine-grained quartz), clay, or calcite. All sedimentary
rocks are formed at or near Earth’s surface. Although this description applies
only to the classic, or fragmental, group of sedimentary rocks, these are the
most common rocks of sedimentary origin. Fossils are any remains or
impressions of prehistoric life. If fossils are present in a rock, the rock is almost
certainly a sedimentary rock. The processes that create igneous and
metamorphic rocks usually destroy any fossil remains.
We can recognize sedimentary rocks because they are usually composed of
particles, often rounded particles, compressed and cemented into layers. Shale,
the most common rock on Earth’s surface, is made of particles of sediment too
small to be visible without magnification. Shale breaks easily into thin layers.
 Identification of Sedimentary rock.
 Random orientation of rocks and sediments.
 Sediments are cemented by fine matrix.
 Have thick bedding plane.
Cross Sectional View of Sedimentary Rock
8
5.3 Metamorphic Rock
Metamorphic rocks are formed by subjecting any rock type—sedimentary
rock, igneous rock or another older metamorphic rock—to different
temperature and pressure conditions than those in which the original rock was
formed. This process is called metamorphism; meaning to "change in form".
The result is a profound change in physical properties and chemistry of the
stone. The original rock, known as the protolithic, transforms into other
mineral types or else into other forms of the same minerals, such as
by recrystallization.[ The temperatures and pressures required for this process
are always higher than those found at the Earth's surface: temperatures greater
than 150 to 200 °C and pressures of 1500 bars. Rocks compose 27.4% of the
crust by volume.
The three major classes of metamorphic rock are based upon the formation
mechanism. An intrusion of magma that heats the surrounding rock causes
contact metamorphism—a temperature-dominated transformation. Pressure
metamorphism occurs when sediments are buried deep under the ground;
pressure is dominant and temperature plays a smaller role. This is termed
burial metamorphism, and it can result in rocks such as jade.. Where both heat
and pressure play a role, the mechanism is termed regional metamorphism.
This is typically found in mountain-building regions.
9
5.4 Description of Rocks Identified in the field.
Right Bank of Trishuli river about 500m downstream
S.N.
Sample No.
A
B
C
1.
Color
Grenish Gray
White
Grenish Gray
2.
Texture
Non Crystalline
Crystalline
Non Crystalline
3.
Structure/
Foliation Plane /
Bedding
Cleavage
Slaty Cleavage
Plane
Foliation plane/
Slaty Cleavage
4.
Specific Gravity
Low
High
Low
5.
Mineral
Chlorite, Clay
Calcite
Composition
minerals
Acid test/Hammer
Not done
Chloride, clay
mineral, mica,
sericite
Not done
6.
scratch test
7.
Rock types
Metamorphic rock
Sample is reacted
by acid/Scratched
by hammer
Sedimentary rock
Metamorphic
rock
8.
Rock Name
Slate
Limestone
Phyllite
9.
Engineering
a) Strength
Low
High
Low
b) Drillability
High
Low
High
c) Blastibillity
Low
High
Low
properties
10.
Uses
-roofing
-Cement
-dry wall
-filling
-Aggeregate
11.
Geological
Benighat slate
Formation
Malekhu limestone Robhang
formation
10
Right Bank of Malekhu Khola about 700m upstream
S.N.
Sample No.
D
E
F
1.
Color
Grey
White
Milky white
2.
Texture
Crystalline
Crystalline
Crystalline
3.
Structure/ Clevage
Foliation
Random
Orientation
Foliation /
Gnessosity
4.
Specific Gravity
High
High
High
5.
Quartz
Mineral
Compositio
n
Acid test/
Hammer
Hammer scratch test scratched by
rock
Rock types
Metamorph
ic rock
Rock Name
Quartzite
6.
7.
8.
9.
10.
Engineering
Properties
a) Strength
b) Drillability
c) Blastibillity
Uses
11. Geological
Formation
Hig
h
Lo
w-for aggregate
Hig
-for railing
h
Dunga quartzite
11
Feldspar, Quartz,
Muscovite,
Biotite
Not done
Igneous rock
Fledspar, Quartz,
Muscovite,
Biotite
Not done
Granite
Metamorphic
rock
Gness
HighL
ow
High
High
Low
High
-Construction
-Decorative
-Construction
Agra Granite
Right Bank of Malekhu Khola about 1 km upstream
S.N.
Sample No.
G
H
1.
Color
White
Grenish Grey
2.
Texture
Crystalline
Crystalline
3.
Structure/ Cleavage
4.
Specific Gravity
Foliation /
Foliation /
Not perfect cleavage Schistosity
cleavage
High
Low
5.
Mineral Composition
Calcite
6.
7.
Acid test/
Hammer scratch test
Rock types
Reacted /
scrateched by
hammer
Metamorphic rock
8.
Rock Name
Marble
Schist
9.
Engineering properties
g) Strength
h) Drillability
i) Blastibillity
Uses
High
High
High
-Decorative
-Cement
Bhaise Dhobhan
formation
Low
High
Low
-Filling Material
10.
11.
Geological
Formation
Garnet, Chloride,
Muscovite, Biotite
Not done
Metamorphic rock
Raduwa Formation
6.Geological structures
Structure geology deals with the mechanism and types of deformation of rock
or earth’s crust due to the distribution of stress generated through various
geological processes such as earthquake, volcano etc.
6.1Beds and Beddings:Beds refers to the layers of sedimentary rock that possess almost planar top
and bottom surfaces and beddings are the planar top and bottom surface of
the beds. These are the plane of weakness.
12
If thickness of beds is
>100cm
very thick beeded
30-100 cm thick
10-30 cm medium
1-10cm
thin
<1
lamination
6.2Types of geologic structures:
(1) Primary structures: those which develop at the time of formation of the rocks
(e.g. sedimentary structures, some volcanic structures, etc.).
(2) Secondary structures: which are those that develop in rocks after their
formation as a result of their subjection to external forces.
(3) Compound structures: form by a combination of events some of which are
contemporaneous with the formation of a group of rocks taking part in these
"structures".
Stress: is the force applied over a given area of the rock mass. It is of three
different kinds:
(1) Compressional stress which tends to squeeze the rock
(2) Tensional stress, which tends to pull a rock apart
(3) Shear stress, which results from parallel forces that act on different
parts of the rock body in opposite directions.
Strain: Is the change in the shape or size of a rock in response to stress. A rock
is said to deform elastically if it can return to its original size once the stress is
removed. Plastic deformation on the other hand, results in permanent changes in
the size and shape of the rock, even after the stress is removed. Plastic
deformation of a rock is also known as ductile deformation. After deforming
plastically for some time, a rock which continues to be subjected to stress may
finally break, a behavior known as brittle deformation.
13
6.3Factors affecting how a rock deforms:
6.3.1
Depth: Lithostatic pressure + heat
6.3.2
Time
6.3.3
Composition
6.3.4
Fluids
Therefore, a rock may undergo ductile deformation when subjected to stress at
certain depths within the earth where pressures and temperatures are relatively
high, or if fluids are abundant, but the same rock may undergo brittle deformation
at shallower depths.
6.4Measuring geological structures:
Strike: (direction)
Dip: (direction & angle)
6.4.1Secondary structures
Types of secondary geologic structures:
Folds, which are a form of ductile deformation, and (b) fractures, represented by
faults and joints which generally result from the brittle behavior of rocks in
response to stress.
I- Folds
Folds are bends or flexures in the earth's crust, and can therefore be identified by
a change in the amount and/or direction of dip of rock units. Most folds result
from the ductile deformation of rocks when subjected to compressional or shear
stress. In order to understand and classify folds, we must study their forms and
shapes, and be able to describe them. The following definitions are therefore
essential for the description of a fold:
Hinge line: Is the line of maximum curvature on a folded surface. The hinge line
almost always coincides with the axis of the fold defined as a line lying in the
plane that bisects a fold into two equal parts.
14
The axial plane: is an imaginary plane dividing the fold into two equal parts
known as limbs. It is therefore the plane which includes all hinge lines for
different beds affected by the same fold.
The crest: of a fold can be considered the highest point on a folded surface.
The trough: is the lowest point on a folded surface.
The interlimb angle: Is the angle between two limbs of the same fold. It is
measured in a plane perpendicular to that of the fold axis.
The angle of plunge: of a fold is the angle between the fold axis and the
horizontal plane, measured in a vertical plane. The direction of plunge of a fold
is the direction in which the fold axis dips into the ground from the horizontal
plane.
The median surface: Is the surface that passes through points where the fold
limb changes its curvature from concave to convex.
The amplitude: of a fold: is the vertical distance between the median surface and
the fold hinge, both taken on the same surface of the same folded unit.
The wavelength: of a fold system is the distance between two consecutive crests
or troughs taken on the same folded surface.
A) Classification of folds
Folds may be classified based on the direction of dip of their limbs, the inclination
of their axial planes, the value of their interlimb angle, their plunge, and their
general shape and effects on the thickness of the folded layers. In order to describe
a fold correctly, one may have to use more that one of these classifications; e.g.
recumbent anticline, open syncline, tight plunging anticline.... etc.
a) Classification based on the direction of dip of the limbs:
When both limbs of a fold dip away from the fold axis, the fold is called an
antifoam. If both limbs dip towards the fold axis, the fold is known as a synform.
If the relative ages of the folded units are known, such that the oldest units occur
in the core of the antifoam, the antifoam is called "anticline". Similarly, if the
youngest units occur in the "center" of a synformal structure, it is known as a
15
syncline.
A monocline is a single step-like bend in a rock unit, and is often caused by
vertical displacement. A dome consists of uparched rocks that dip in all directions
away from the central point. A basin is a downward in which the layers dip in all
directions from all sides towards the center. A fold is described as isoclinal if
both limbs dip in the same direction at the same angle.
b) Classification based on the inclination of the axial plane:
A symmetrical (or upright) fold is one in which the axial plane bisects the fold
(and is vertical). If the axial plane is inclined at an angle < 45° (measured from
the vertical plane), the fold is said to be inclined. If the angle of inclination of the
axial plane is > 45° (from the vertical plane), then both limbs of the fold will dip
in the same direction, and the fold is known as inverted or overturned. If the
axial plane is horizontal, the fold is known as recumbent.
c)
Classification based on the value of the interlimb angle:
(1) Open folds: those with an interlimb angle > 70°
(2) Closed folds: with interlimb angles between 30 and 70°
(3) Tight folds: with interlimb angles < 30°
(4) Isoclinal folds: have zero interlimb angles.
II- Faults
A fault is a fracture in the earth's rock units along which there has been an
observable amount of movement and displacement. Unlike folds which form
predominantly by compressional stress, faults result from either tension,
compression or shear. In order to correctly describe a fault, it is essential to
understand its components:
1. The fault plane: Is the plane of dislocation or fracture along which
displacement has occurred. The fault plane therefore separates one or more
rock units into two blocks.
2. The Hanging wall and footwall blocks: If the fault plane is not vertical, then
the block lying on top of the fault plane is known as the hanging wall block,
16
3.
4.
5.
6.
7.
8.
whereas that lying below this plane is known as the footwall block.
The downthrown and upthrown blocks: The downthrown block is the one
that has moved downwards relative to the other block, whereas the upthrown
block is that which registers an upward relative movement.
The Dip of the fault plane is the angle of inclination of the fault plane
measured from the horizontal plane perpendicular to its strike.
Fault Throw: Is the vertical displacement of a fault.
Dip slip: Is the amount of displacement measured on the fault plane in the
direction of its dip.
Strike slip: Is the amount of displacement measured on the fault plane in the
direction of its strike.
Net slip: Is the total amount of displacement measured on the fault plane in
the direction of movement.
N.B. In measuring the slip or throw of a fault, the displacement has to be
measured using the same surface of the same unit affected by that fault.
a) Types of Faults
- Normal fault: Is a fault in which the hanging wall appears to have moved
downwards relative to the footwall (i.e. downthrown block = hanging wall
block).
- Reverse fault: Is a fault in which the hanging wall appears to have moved
upwards relative to the footwall (i.e. upthrown block = hanging wall
block). Because the displacement in both normal and reverse faults occurs
along the dip of the fault plane, they may be considered types of dip slip
faults.
- Thrust fault (or thrust): Is a reverse fault in which the fault plane is dipping
at low angles (< 45°). Thrusts are very common in mountain chains (fold
and thrust belts) where they are characterized by transporting older rocks
on top of younger ones over long distances.
- Strike slip (wrench, tear or transcurrent) fault: Is a fault in which the
movement is horizontal along the strike of the fault plane. Strike slip faults
are either dextral or sinistral. When viewed on end , a dextral fault (also
known as right lateral fault) is one in which the block on the observer's
right hand side appears to have moved towards him, whereas a sinistral
17
strike slip fault (also known as left lateral) is one in which the block on the
observer's left hand side appears to have moved towards him.
- Oblique slip fault: is one in which the displacement was both in the strike
and dip directions (i.e. the displacement has strike and dip components).
Keep in mind that an oblique slip fault can also be either normal or reverse.
From this classification of faults, it can be seen that normal faults result
predominantly from tensional stress, reverse faults and thrusts from
compression (or shear), and strike slip faults from tension, compression or
shear.
b)
Fault Associations and Fault Systems
Faults often occur in groups. If two normal faults have parallel strikes and
share the same downthrown block, a trough-like structure results which is
known as a graben. A horst is an uplifted block bounded by two normal
faults that strike parallel to each other (and which share the same upthrown
block the horst). Grabens and horsts are common in areas of very early
rifting (e.g. the East African Rift Valley). Step faults are several faults with
parallel strikes and a repeated downthrow in the same direction giving the
area an overall step - like appearance. They are common in rifted areas (e.g.
on the flanks of the Red sea).
c)
Geomorphological features associated with faults:
Fault planes often result in the exposure of units that erode easily along the
fault trace resulting in the development of valleys or the control of stream
flow. In other cases, faults cause the offset of streams, causing them to bend
sharply when they intersect the fault plane. The topography may also be
strongly influenced by faulting so that the fault plane can be identified on
the ground by a sudden and sharp change in elevation, known as a fault
scarp.
d) Recognition of movement along fault planes
Movement along a fault plane can often be recognized by the following
criteria:
- Fault drag: where small - scale folding or warping of units takes place
18
as a result of the dragging forces along the fault plane.
- Fault breccia and fault gouge: As a result of movement along the fault
plane, rocks are often broken up into sharp angular pieces known as
breccia. The fragments may be further crushed into powder - like
material, known as fault gouge.
- Slickensides: As a result of movement and friction along the fault
plane, this plane may become highly polished or abraded with striations
that are known as slickensides.
III- Joints
Joints are fractures in the rocks characterized by no movement along their
surfaces. Although most joints are secondary structures, some are primary,
forming at the time of formation of the rocks.
A. Types of joints
- Columnar joints: Are joints that form in basalts. When the basaltic lava
cools, it contracts giving rise to hexagonal shaped columns.
- Mud cracks: Are joints that form in mud. As the mud loses its water,
it contracts and cracks.
- Secondary joints: Are joints that form in rocks as a result of their
subjection to any form of stress (compression, tension or shear). Joints
that are oriented in one direction approximately parallel to one another
make up a joint set. Rocks often have more than one set of joints with
different orientations, which may intersect, and are then known as joint
systems (Fig. 9). Note that tensional stress usually results in one set of
joints, whereas compression may form more than one set.
- Sheet joints: Are joints that form in granitic rocks in deserts causing
them to break into thin parallel sheets. These joints form when the rocks
expand as a result of the rapid removal of the overlying rock cover,
possibly due to faulting or quarrying. This process is called exfoliation.
6.4.2Compound Structures
A.Unconformities
An unconformity is a surface (or contact) along which there was no
fracturing (i.e. not a fault or joint) and which represents a break in the
geologic record. An unconformity therefore indicates a lack of continuity
of sedimentary deposition in an area, resulting in rocks of widely different
ages occurring in contact with each other. Unconformities usually result
19
from changes in the sedimentary history of an area, which may be due to
vertical movements (e.g. uplift followed by erosion and deposition),
deformation (also followed by deposition), changes in sea level (which
may be due to climatic changes, among other things), ...etc.
In many cases, unconformities represent a buried erosional surface. In such
cases, erosion of the older units results in their fragmentation into smaller
pieces. As soon as deposition resumes, these fragments may consolidate to
form a rock known as breccia (if the fragments are angular) or
conglomerate (if the fragments are rounded). Because the breccia or
conglomerate occur at the base of the younger units lying on top of the
unconformity surface, and because their fragments are derived from the
units below this surface, the conglomerates or breccias are known as basal
conglomerates or basal breccias.
B. Types of unconformities
- Angular unconformities: are those in which the angle of dip of the
younger layers is different from that of the older ones.
- Disconformities: are those in which the units above and below the
unconformity surface are parallel to each other, but not continuous in
deposition or age.
- Nonconformities: are those in which plutonic or metamorphic rocks
are covered by sedimentary or volcanic units.
Fig :-Unconformility
20
7.Geological compass
Geological compass is defined as the combination of the compass and the
inclinometer. The compass gives the direction whereas the inclinometer gives
the Inclination of the plane to the horizontal.
There are four types of geological compass, they are:7.1 Clinometer compass
It is an instrument for measuring angles of slope (or tilt), elevation or
depression of an object with respect to gravity. It is also known as a tilt meter,
tilt indicator, slope alert, slope gauge, gradient meter, gradiometer, level
gauge, level meter, declinometer, and pitch & roll indicator. Clinometers
measure both inclines (positive slopes, as seen by an observer looking
upwards) and declines (negative slopes, as seen by an observer looking
downward) using three different units of measure: degrees, percent, and topo.
Astrolabes are inclinometers that were used for navigation and locating
astronomical objects.
Figure: Clinometer Compass
21
7.2 Brunton Compass
A Brunton compass, properly known as the Brunton Pocket Transit, is a type
of precision compass made by Brunton, Inc. of Riverton, Wyoming. The
instrument was patented in 1894 by a Canadian-born Colorado geologist
named David W. Brunton. Unlike most modern compasses, the Brunton
Pocket Transit utilizes magnetic induction damping rather than fluid to damp
needle oscillation. Although Brunton Inc. makes many other types of magnetic
compasses, the Brunton Pocket Transit is a specialized instrument used widely
by those needing to make accurate degree and angle measurements in the field.
These people are primarily geologists, but archaeologists, environmental
engineers, and surveyors also make use of the Brunton's capabilities. The
United States Army has adopted the Pocket Transit as the M2 Compass for use
by crew-served artillery.
The Pocket Transit may be adjusted for declination angle according to one's
location on the Earth. It is used to get directional degree measurements
(azimuth) through use of the Earth's magnetic field. Holding the compass at
waist-height, the user looks down into the mirror and lines up the target,
needle, and guide line that is on the mirror. Once all three are lined up and the
compass is level, the reading for that azimuth can be made. Arguably the most
frequent use for the Brunton in the field is the calculation of the strike and dip
of geological features (faults, contacts, foliation, sedimentary strata, etc.). If
next to the feature, the strike is measured by leveling (with the bull's eye level)
the compass along the plane being measured. Dip is taken by laying the side
of the compass perpendicular to the strike measurement and rotating horizontal
level until the bubble is stable and the reading has been made. If properly used
and if field conditions allow, additional features of the compass allow users to
measure such geological attributes from a distance.
Figure: Brunton Compass
22
7.3 Clark Compass
Advanced than other.
Figure: Clark Compass
7.4 Digital Compass
Compatible with PCs.
Figure: Digital Compass
23
8.
Attitude measurement of the plane
8.1 Foliation Plane:These are very thin layer of planes.
8.2 Joint plane:These planes are formed by the breaking down of the
Planes.
8.3 Attitude:
Orientation of the planar feature of the rock is called attitude. It Includes strike
and dip.
a) Strike: - Horizontal trend of inclined plane is called strike.
b) Dip:I) Dip Direction: It is the inclination direction of the plane.
II) Dip amount: It is the angle between inclined and horizontal plane.
For the measurement of the attitude we should keep the compass
perpendicular to the bedding of which we are measuring and then we
should bring the bubble on the center in the compass. After that
readings should be taken and tabulated as follows:
24
Figure: Strike and Dip
S.N.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Dip
direction
176
179
182
180
184
170
180
275
264
170
174
176
173
175
174
174
175
176
176
168
177
175
175
Dip
amount
86
89
86
84
87
87
89
89
80
86
88
84
87
86
86
80
89
85
86
89
84
80
89
Attitudes (dip dirn / Dip
amt.)
176/86
179/89
182/86
180/84
184/87
170/87
180/89
275/89
264/80
170/86
174/88
176/84
173/87
175/86
174/86
174/80
175/89
176/85
176/86
168/89
177/84
175/80
175/89
25
Remarks
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Joint plane
Joint plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
24
25
26
27
28
29
30
31
32
33
34
35
36
37
176
196
179
182
184
174
180
183
171
191
173
183
175
196
86
85
86
86
88
86
89
87
89
89
90
88
89
85
176/86
196/85
179/89
182/86
184/88
174/86
180/89
183/87
171/89
191/89
173/90
183/88
175/89
196/85
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Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
Bedding plane
9.
Geological works of physical agents
The process of disintegration of rocks by the action of physical agents such as
wind, river water, glaciers etc. is geological works. They are by following
process:
9.1 Erosion
Erosion is the breaking down of material by an agent. In the case of a river,
the agent is water. The water can erode the river’s channel and the river’s
load. A river’s load is bits of eroded material, generally rocks that the river
transports until it deposits its load.
A river’s channel is eroded laterally and vertically making the channel
wider and deeper. The intensity of lateral and vertical erosion is dictated
by the stage in the river’s course, discussed in more detail but essentially,
in the upper stage of the river’s course (close to the source of the river)
there is little horizontal erosion and lots of vertical erosion. In the middle
and lower stages vertical erosion is reduced and more horizontal erosion
takes place.
There are several different ways that a river erodes its bed and banks. The
first is hydraulic action, where the force of the water removes rock
particles from the bed and banks. This type of erosion is strongest at rapids
and waterfalls where the water has a high velocity. The next type of erosion
is corrasion1. This is where the river’s load acts almost like sandpaper,
removing pieces of rock as the load rubs against the bed & banks. This sort
of erosion is strongest when the river is transporting large chunks of rock
or after heavy rainfall when the river’s flow is turbulent.
Corrosion is a special type of erosion that only affects certain types of
rocks. Water, being ever so slightly acidic2, will react with certain rocks
and dissolve them. Corrosion is highly effective if the rock type of the
channel is chalk or limestone (anything containing calcium carbonate)
otherwise, it doesn’t have much of an effect.
Cavitation is an interesting method of erosion. Air bubbles trapped in the
water get compressed into small spaces like cracks in the river’s banks.
These bubbles eventually implode creating a small shockwave that
weakens the rocks. The shockwaves are very weak but over time the rock
27
will be weakened to the point at which it falls apart. The final type of
erosion is attrition. Attrition is a way of eroding the river’s load, not the
bed and banks. Attrition is where pieces of rock in the river’s load knock
together, breaking chunks of rock off of one another and gradually
rounding and shrinking the load.
9.2 Transportation
When a river erodes the eroded material becomes the river’s load and the
river will then transport this load through its course until it deposits the load.
There are a few different ways that a river will transport load depending on
how much energy the river has and how big the load is.
The largest of particles such as boulders are transported by traction. These
particles are rolled along the bed of the river, eroding the bed and the particles
in the process, because the river doesn’t have enough energy to move these
large particles in any other way.
Slightly smaller particles, such as pebbles and gravel, are transported
by saltation. This is where the load bounces along the bed of the river because
the river has enough energy to lift the particles off the bed but the particles
are too heavy to travel by suspension.
Fine particles like clay and silt are transported in suspension, they are
suspended in the water. Most of a river’s load is transported by suspension.
Solution is a special method of transportation. This is where particles are
dissolved into the water so only rocks that are soluble, such as limestone or
chalk, can be transported in solution.
9.3 Deposition
To transport load a river needs to have energy so when a river loses energy it
is forced to deposit its load. There’s several reasons why a river could lose
energy. If the river’s discharge is reduced then the river will lose energy
because it isn’t flowing as quickly anymore. This could happen because of a
lack of precipitation or an increase in evaporation. Increased human use
(abstraction) of a river could also reduce its discharge forcing it deposit its
load.
28
If the gradient of the river’s course flattens out, the river will deposit its load
because it will be travelling a lot slower. When a river meets the sea a river
will deposit its load because the gradient is generally reduced at sea level and
the sea will absorb a lot of energy.
9.4 The Hjulstrom Curve
A Hjulström curve is a special type of graph that shows how a river’s velocity
affects it competence and its ability to erode particles of different sizes.
There’s a lot going on the graph but it’s fairly easy to read once you get the
hang of it:
There’s two curves on the Hjulström Curve, a critical erosion velocity curve
and a mean settling velocity curve. The critical erosion curve shows the
minimum velocity needed to transport and erode a particle. The mean settling
velocity shows the minimum speed that particles of different sizes will be
deposited by the river. The shaded areas between the curves show the
different process that will be taking place for particles that lie in those shaded
areas.
As an example, a river flowing at 10cms-1 will transport clay, silt and sand
particles but will deposit gravel, pebble and boulder particles. Conversely, a
river flowing at 100cms-1 will erode and transport large clay particles, silt
particles, sand particles and most gravel particles. It will transport all but the
largest of pebbles and will deposit boulders.
The easiest way to read the curve is to draw a horizontal line from the velocity
you’re trying to read and seeing which shaded area it crosses the particle size
you’re interested in. This will tell us whether that particle is eroded,
transported or deposited at that velocity.
There’s a few interesting things to note about the Hjusltröm Curve. The first
is that clay sized particles don’t appear to have a mean settling velocity. This
is because these particles are so fine that a river would have to be almost
perfectly stationary in order for them to fall out of solution. In addition, the
small particles seem to have an erosive velocity that’s the same as the velocity
for larger particles. This is because smaller particles are cohesive, they stick
together, making them harder to dislodge and erode without high velocities.
29
Figure: The Hjulström Curve
For this mainly three things happens, they are:
A.Erosion by river water
River erosion can be carried out by five ways, they are:
a) Hydraulic action
- with the help of water current
b) Abrasion
- by collision
c) Attrition
- breaking during collision.
d) Cavitation
- by making holes.
e) Corrosion
- by chemical effect.
B.By wind
Wind erosion occurs in three ways, they are:
a) Deflation
b) Abrasion
c) Attrition
30
C. By Glaciers
It occurs by two ways:
a) Plucking
b) Abrasion
9.5 Features developed by the activities of physical agents
1) Pothole
It is a type of failure in an asphalt pavement, caused by the presence of water
in the underlying soil structure and the presence of traffic passing over the
affected area. Introduction of water to the underlying soil structure first
weakens the supporting soil. Traffic then fatigues and breaks the poorly
supported asphalt surface in the affected area. Continued traffic action ejects
both asphalt and the underlying soil material to create a hole in the pavement.
2) Waterfall
It is a place where water flows over a vertical drop in the course of a stream
or river. Waterfalls also occur where melt water drops over the edge of a
tabular iceberg or ice shelf.
Waterfalls are commonly formed when a river is young. At these times the
channel is often narrow and deep. When the river courses over resistant
bedrock, erosion happens slowly, while downstream the erosion occurs more
rapidly. As the watercourse increases its velocity at the edge of the waterfall,
it plucks material from the riverbed. Whirlpools created in the turbulence as
well as sand and stones carried by the watercourse increase the erosion
capacity. This causes the waterfall to carve deeper into the bed and to recede
upstream. Often over time, the waterfall will recede back to form a canyon or
gorge downstream as it recedes upstream, and it will carve deeper into the
ridge above it.[The rate of retreat for a waterfall can be as high as one and
half meters per year.
31
Fig: Formation of waterfalls
3) River Valley
A valley formed by flowing water, or river valley, is usually V shaped. The
exact shape will depend on the characteristics of the stream flowing
through it. Rivers with steep gradients, as in mountain ranges, produce
steep walls and a bottom. Shallower slopes may produce broader and
gentler valleys, but in the lowest stretch of a river, where it approaches its
base level, it begins to deposit sediment and the valley bottom becomes a
floodplain.
4) Floodplain
Flood plain is an area of land adjacent to a stream or river that stretches
from the banks of its channel to the base of the enclosing valley walls and
experiences flooding during periods of high discharge. It includes the
floodway, which consists of the stream channel and adjacent areas that
actively carry flood flows downstream, and the flood fringe, which are
areas inundated by the flood, but which do not experience a strong current.
In other words, a floodplain is an area near a river or a stream which floods
when the water level reaches flood stage.
32
5)
Terrace
Is a step-like landform. A terrace consists of a flat or gently sloping
geomorphic surface, called a tread that is typically bounded one side by a
steeper ascending slope, which is called a "riser" or "scarp." The tread and
the steeper descending slope (riser or scarp) together constitute the terrace.
Terraces can also consist of a tread bounded on all sides by a descending
riser or scarp. A narrow terrace is often called a bench. The sediments
underlying the tread and riser of a terrace are also commonly, but
incorrectly, called terraces, leading to much confusion. Terraces are
formed in various ways.
6) Oxbow lake
It is a U-shaped body of water formed when a wide meander from the main
stem of a river is cut off, creating a free-standing body of water. This
landform is so named for its distinctive curved shape, resembling the bow
pin of an oxbow. In Australia, an oxbow lake is known as a billabong, from
the indigenous language Wiradjuri.
The word "oxbow" can also refer to a U-shaped bend in a river or stream,
whether or not it is cut off from the main stream.
7) River delta
It is a landform that forms at the mouth of a river, where the river flows
into an ocean, sea, estuary, lake, or reservoir. Deltas form from deposition
of sediment carried by a river as the flow leaves its mouth. Over long
periods, this deposition builds the characteristic geographic pattern of a
river delta.
8) Point bar
It is a depositional feature made of sand and gravel that accumulates on the
inside bend of streams and rivers below the slip-off slope. Point bars are
found in abundance in mature or meandering streams. They are crescentshaped and located on the inside of a stream bend, being very similar to,
though often smaller than, towheads, or river islands.
Point bars are composed of sediment that is well sorted and typically
reflects the overall capacity of the stream. They also have a very gentle
33
slope and an elevation very close to water level. Since they are low-lying,
they are often overtaken by floods and can accumulate driftwood and other
debris during times of high water levels. Due to their near flat topography
and the fact that the water speed is slow in the shallows of the point bar
they are popular rest stops for boaters and rafters. However, camping on a
point bar can be dangerous as a flash flood that raises the stream level by
as little as a few inches (centimetres) can overwhelm a campsite in
moments.
A point bar is an area of deposition whereas a cut bank is an area of erosion.
Point bars are formed as the secondary flow of the stream sweeps and rolls
sand, gravel and small stones laterally across the floor of the stream and up
the shallow sloping floor of the point bar.
9) Braid Bars
They are landforms in a river that begin to form when the discharge is low
and the river is forced to take the route of less resistance by means of
flowing in locations of lowest elevation. Over time, the river begins to
erode the outer edges of the bar, causing it to become a higher elevation
than the surrounding areas. The water level decreases even more as the
river laterally erodes the less cohesive bank material resulting in a widening
of the river and a further exposure of the braid bar. As the discharge
increases, material may deposit about the braid bar since it is an area in the
river of low velocity due to its increased elevation in relation to
surrounding areas. During times of extremely high flow, the bars may
become covered; only to resurface when the flow decreases. Most braid
bars do not remain stable or in one location. However, vegetation
succession on braid bars can increase the stability of the landform. They
are commonly composed of sand or gravel and typically occur in braided
rivers.
10) Moraine
Is any glacially formed accumulation of unconsolidated glacial debris (soil
and rock) which can occur in currently glaciated and formerly glaciated
regions, such as those areas acted upon by a past glacial maximum. This
debris may have been plucked off a valley floor as a glacier advanced or it
34
may have fallen off the valley walls as a result of frost wedging or
landslide. Moraines may be composed of debris ranging in size from siltsized glacial flour to large boulders. The debris is typically sub-angular to
round in shape. Moraines may be on the glacier’s surface or deposited as
piles or sheets of debris where the glacier has melted. Moraines may also
occur when glacier- or iceberg-transported rocks fall into a body of water
as the ice melts.
a) Drumlin
From the Irish word droimnín ("little ridge"), first recorded in 1833, is an
elongated hill in the shape of an inverted spoon or half-buried egg formed
by glacial ice acting on underlying unconsolidated till or ground moraine.
11) Kame
Is a geomorphological feature, an irregularly shaped hill or mound
composed of sand, gravel and till that accumulates in a depression on a
retreating glacier, and is then deposited on the land surface with further
melting of the glacier. Kames are often associated with kettles, and this is
referred to as kame and kettle topography.
12) Esker
Is a long, winding ridge of stratified sand and gravel, examples of which
occur in glaciated and formerly glaciated regions of Europe and North
America. Eskers are frequently several kilometers long and, because of
their peculiar uniform shape, are somewhat like railway embankments.
13) Kettle
In geology, depression in a glacial outwash drift made by the melting of a
detached mass of glacial ice that became wholly or partly buried. The
occurrence of these stranded ice masses is thought to be the result of
gradual accumulation of outwash atop the irregular glacier terminus.
Kettles may range in size from 5 m (15 feet) to 13 km (8 miles) in diameter
and up to 45 m in depth. When filled with water they are called kettle lakes.
Most kettles are circular in shape because melting blocks of ice tend to
become rounded; distorted or branching depressions may result from
extremely irregular ice masses.
35
Two types of kettles are recognized: a depression formed from a partially
buried ice mass by the sliding of unsupported sediment into the space left
by the ice and a depression formed from a completely buried ice mass by
the collapse of overlying sediment. By either process, small kettles may be
formed from ice blocks that were not left as the glacier retreated but rather
were later floated into place by shallow melt water streams. Kettles may
occur singly or in groups; when large numbers are found together, the
terrain appears as mounds and basins and is called kettle and kame
topography.
14) Dune
It is a hill of sand built by either wind or water flow. Dunes occur in
different forms and sizes, formed by interaction with the flow of air or
water. Most kinds of dunes are longer on the windward side where the sand
is pushed up the dune and have a shorter "slip face" in the lee of the wind.
The valley or trough between dunes is called a slack. A "dune field" is an
area covered by extensive sand dunes. Large dune fields are known as ergs.
Some coastal areas have one or more sets of dunes running parallel to the
shoreline directly inland from the beach. In most cases the dunes are
important in protecting the land against potential ravages by storm waves
from the sea. Although the most widely distributed dunes are those
associated with coastal regions, the largest complexes of dunes are found
inland in dry regions and associated with ancient lake or sea beds.
Dunes also form under the action of water flow (fluvial processes), and on
sand or gravel beds of rivers, estuaries and the sea-bed.
15) Loess
It is a clastic, predominantly silt-sized sediment, which is formed by the
accumulation of wind-blown dust.
Loess is an aeolian sediment formed by the accumulation of wind-blown
silt, typically in the 20–50 micrometer size range, twenty percent or less
clay and the balance equal parts sand and silt that are loosely cemented by
calcium carbonate. It is usually homogeneous and highly porous and is
traversed by vertical capillaries that permit the sediment to fracture and
form vertical bluffs.
36
10.River Channel Morphology
10.1 Meandering River Channel
Formation of natural levees by spill-over of sediment during floods. Next
to the channel mostly sand is deposited (highest flow velocities), and sand
compacts less than the mud that is deposited farther away. Thus, over time
these near-channel sand deposits will over time rise above the (more
compacted) floodplain and form natural levees.
10.1.1Overview of features associated with meandering streams.
A meandering stream migrates laterally by sediment erosion on the outside
of the meander (that is part of the friction work), and deposition on the
inside (helicoidal flow, deceleration, channel lag, point bar sequence,
fining upwards). Adjacent to the channel levee deposits build up, and
gradually raise up the river over the floodplain (mainly fine sediments). If
the climate is humid the floodplain area beyond the levees may be covered
with water most of the time, and may form a swamp (backswamp). Rivers
that want to enter the main stream may not make it up the levee, and empty
either into the backswamp (filing it up gradually) or flow parallel to the
stream for a long distance until they finally join (Yazoo streams). Meanders
may cut into each other as they grow (neck cutoffs), and then the river
shortcuts (growing meanders reduce the slope, cutoffs are a means to
increase the slope again, feedback loop) and the old meander is abandoned
and slowly fills with fine sediment during floods (oxbow lakes). Also, as a
river builds up its levees and raises itself over the floodplain, the slope and
the transport power of the stream decrease, the channel fills gradually with
sediment, and finally (often during a flood) the river will breach its levee
(this process is called avulsion) and follow a steeper path down the valley.
Figure: Meandering River Streams
37
10.1.2 How meanders grow
Laterally through erosion (outside bend) and sediment deposition (inside
bend, point bar). When the loops get too large and consume too much
energy (friction), the river will eventually find a less energetically "taxing"
shortcut, and a part of the old channel will be abandoned and becomes
an oxbow lake.
Figure: Process of growing River Meandering
10.2 STRAIGHT RIVER CHANNELS
Straight channels, mainly unstable, develop along the lines of faults and
master joints, on steep slopes where rills closely follow the surface
gradient, and in some delta outlets. Flume experiments show that straight
channels of uniform cross section rapidly develop pool-and-riffle
sequences. Pools are spaced at about five bed widths. Lateral shift of
alternate pools toward alternate sides produces sinuous channels, and
spacing of pools on each side of the channel is thus five to seven bed
widths. This relation holds in natural meandering streams.
Figure: straight Channel River
38
10.3 Braided River Channel
Is one of a number of channel types and has a channel that consists of a
network of small channels separated by small and
often
temporary islands called braid bars or, in British usage, aits or eyots.
Braided streams occur in rivers with high slope and/or
large sediment load.[1]Braided channels are also typical of environments
that dramatically decrease channel depth, and consequently channel
velocity, such as river deltas,alluvial fans and peneplains. Alluvial
fans and peneplains.
Braided rivers, as distinct from meandering rivers, occur when a threshold
level of sediment load or slope is reached. Geologically speaking, an
increase in sediment load will over time increase the slope of the river, so
these two conditions can be considered synonymous; and, consequently, a
variation of slope can model a variation in sediment load. A threshold slope
was experimentally determined to be 0.016 (ft/ft) for a 0.15 cu ft/s
(0.0042 m3/s) stream with poorly sorted coarse sand.[1] Any slope over this
threshold created a braided stream, while any slope under the threshold
created a meandering stream or— for very low slopes—a straight channel.
So the main controlling factor on river development is the amount of
sediment that the river carries; once a given system crosses a threshold
value for sediment load, it will convert from a meandering system to a
braided system. Also important to channel development is the proportion
of suspended load sediment to bed load. An increase in suspended sediment
allowed for the deposition of fineerosion-resistant material on the inside of
a curve, which accentuated the curve and in some instances caused a river
to shift from a braided to ameandering profile The channels and braid bars
are usually highly mobile, with the river layout often changing significantly
during flood events. Channels move sideways via differential velocity: On
the outside of a curve, deeper, swift water picks up sediment
(usually gravel or larger stones), which is re-deposited in slow-moving
water on the inside of a bend.
Figure: Braided River Channel
39
11.Conclusion
The report has been prepared with including the important topics and is prepared
with sketches on site observation and their description also. From the field ,we
are able to study and identify about the rocks ,minerals and the various types of
geological structures like bedding, graded bedding ,joint, fault, thrust ,fold and
unconformity. As we also able to use the geological compass during the
investigation of rock structures. By using this also we had measured the attitude
of planner features like joint, bedding and foliation. We studied the river channel
morphology, how they forms and various types of river channel like straight,
meandering and Braded River. We also understand the features developed by this
types of river.
40