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Geography notes for F.6
•Natural Landscape
What is geomorphology?
• It is the study of the origin and evolution
of landforms on the earth’s surface .
• Most of the earth’s landforms are created
mainly by tectonic or endogenic forces (內
在) operating in the earth’s crust.
1. Continental Drift
• Alfred Wegener,published
a book on continental
drift in 1915.
• His idea is widely
accepted into the theory
of plate tectonics
Evidence of continental drift
a) Geometric matching of continental borders
(like jigsaw puzzle)
b) Geological evidence
- the form and pattern of the ancient fold
mountains
- evidence yielded by rocks
- belt of Mesozoic basalt (it can be find
everywhere)
c) Biological evidence
- diverse and specialised groups on various
continental fragments
d) Palaeoclimatic evidence
(史前氣候因素)
- fossils found in conditions seem impossible
- coal was found in Antarctica
e)Palageomagnetic evidence
(古地磁學)
- Palaeomagnetism is the study of earth
magnetism during the geological past
• - minerals
sensitive to the
magnetic field
align
themselves to
the earth’s
magnetic pole
when it cooled
and solidified
2. Seafloor spreading
• It provide an explanation for continental drift
• mid-oceanic ridge is formed
• Evidence : Heat flow with minerals, young ocean
floor and palaeomagnetic evidence
Examples of moving plate
The first ship used for geological
study
Modern ship used for geological
survey
3. Plate tectonic
• It is a theory combining the concepts of
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•
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continental drift and seafloor spreading
It is divided into a number of plates “floating” on
the asthenosphere
Volcanic and earthquake zones are confined to
the plate boundary
The growth of new lithosphere below the ocean
is balanced by the destruction of the lithosphere
along the convergent boundaries
Causes of plate movement
• Convection Currents
- it is fuelled by radioactive process in the
mantle
- Difference heating in rock cause risingsinking motions
- It cause a dragging force on the
lithospheric plate
The mechanism
- all continents once formed one
supercontinent called PANGAEA
(聯合古陸)
- It split into Laurasian and Gondwanaland
B Internal structure of the earth
• Earth has a diameter of 6370 km and
about 40000km in circumference
• It consist of a solid crust (about 6km
beneath the oceans and 35-40 km under
mountains )
• A solid mantle(about 3000km thick)
• A core (solid inner core and liquid outer
core)
Materials in the earth crust
Continents
30%
Sial
Under the
ocean
70%
Sima
2.7g/cm
3g/cm
Moho (Mohorovicic Discontinuity)
(莫霍界面)
• The thickness of the earth is found by a
Yugoslavian scientists ,Andrija Mohorovicic
• It is the abrupt change (突然轉變)in density
between the crust and the mantle
• This boundary zones averages about 10 km
below sea level in oceans basin and and about
30 km beneath high mountains
Some important terms
• The mantle is much hotter than the crust .It
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•
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compose of mineral olivine.
The density is 5g/cm
The inner core is solid while the outer core is
liquid
Lithosphere is the crust and rigid uppermost
parts of upper mantle,at a depth of about
100km
Asthenosphere (軟流圈)is a zone of weaker and
more plastic rocks and extend to 240km
Waves
• When an earth tremor(震動),primary and
secondary waves are transmitted through
the epicentre (震央),the point at which the
earthquakes occur
• Primary waves travel through solids and
liquid while secondary waves travel
through only solids
A. Constructive plate margin
• It is a boundary where two plates move
apart. A fissure develops,allowing
hot ,molten rock to well up from the
mantle and to from new materials as it
solidifies,the fissure is called a
spreading,or “pull apart” centre.
Mid-oceanic ridge map by computer
Mauna Loa in Hawwii
Erta Ale in East Africa – an active
zone of rift valley
• Mid- Atlantic ridge is a
good example
• It will cause volcanic
activity, Iceland and
the Azores
• High magnitude
volcanic eruptions on
and around the
ridges,volcanic island
produced
B. Destructive plate margin
• It is a boundary where two plates collide.
The more dense plate will normally be
deflected beneath the less dense
plate,and will be destroyed and absorbed
at depth.
• Such action take place at the zone of
subduction. Crumped (摺曲、扭曲)
mountain ranges,volcanoes earthquakes
and ocean trenches (海溝)are found
Andes Mountain – a type of
destructive plate boundary
Three types of collision
• Collision between oceanic plate and
continential plate
Collision between oceanic plates
Collision between continental plates
The moving path of Indian plate
Conservative plate margin
• It is also called
transform fault
The formation of transform fault
San Andrea’s fault
Plate tectonics and Man
• The existing features of the continents
and ocean basins are explained by the
theory of plate tectonic
• Produce environmental hazards: volcanic
eruptions and earthquakes
• Produce mineral resources
Ring of Fire
Earthquakes
• Magnitude of earthquakes refer to the
energy released at the source
• It is measured by either by Richter Scales
(0-8logarithmic scale) (里氏震級表) or
Mercalli Scales (12 gradations)
• There is no direct relationship between
the magnitude and the damage caused in
the earthquake
Human Response to Earthquakes
• Made seismic hazard zone maps for
landuse planning
• Man-made measure to trigger small
earthquakes
• Drills and shock-proof buildings are
designed
• Extensive monitoring of the earthquakes
• Seismometers (地震儀)are used to detect
small earthquake
• Tiltmeters (傾斜儀) and electronic distance
measurers (電子距離儀) are used to
measure the shape of the volcanoes
• Fertile soil is produced
• Iron,copper,zinc,lead,uranium ,etc
Hotspot (熱點)