Geography notes for F.6Geography notes for F.6

•Natural LandscapeNatural Landscape

What is geomorphology?What is geomorphology?

• It is the study of the origin and evolution It is the study of the origin and evolution of landforms on the earth’s surface .of landforms on the earth’s surface .

• Most of the earth’s landforms are creatMost of the earth’s landforms are created mainly by tectonic or endogenic forced mainly by tectonic or endogenic forces (es ( 內在內在 ) operating in the earth’s crust.) operating in the earth’s crust.

1.1. Continental DriftContinental Drift

• Alfred Wegener,publisheAlfred Wegener,published a book on continental d a book on continental drift in 1915.drift in 1915.

• His idea is widely acceptHis idea is widely accepted into the theory of plated into the theory of plate tectonicse tectonics

Evidence of continental driftEvidence of continental drift

a)a) Geometric matching of continental Geometric matching of continental borders borders

(like jigsaw puzzle)(like jigsaw puzzle)

b)b) Geological evidenceGeological evidence

- the form and pattern of the ancient fo- the form and pattern of the ancient fold ld mountainsmountains

- evidence yielded by rocks- evidence yielded by rocks

- belt of Mesozoic basalt (it can be find - belt of Mesozoic basalt (it can be find everywhere)everywhere)

c) Biological evidencec) Biological evidence- diverse and specialised groups on various conti- diverse and specialised groups on various continental fragments nental fragments

d) Palaeoclimatic evidenced) Palaeoclimatic evidence ( ( 史前氣候因素史前氣候因素 ))- fossils found in conditions seem impossifossils found in conditions seem impossi

bleble - coal was found in Antarctica - coal was found in Antarctica

e)Palageomagnetic evidencee)Palageomagnetic evidence ( ( 古地磁學古地磁學 ))

- Palaeomagnetism is the study of earth magn- Palaeomagnetism is the study of earth magn

etism during the geological past etism during the geological past

• - minerals sens- minerals sensitive to the maitive to the magnetic field alignetic field align themselves gn themselves to the earth’s to the earth’s magnetic pole magnetic pole when it cooled when it cooled and solidifiedand solidified

2. Seafloor spreading2. Seafloor spreading • It provide an explanation for continental drift It provide an explanation for continental drift • mid-oceanic ridge is formedmid-oceanic ridge is formed• Evidence : Heat flow with minerals, young oceaEvidence : Heat flow with minerals, young ocea

n floor and palaeomagnetic evidence n floor and palaeomagnetic evidence

Examples of moving plateExamples of moving plate

The first ship used for The first ship used for geological studygeological study

Modern ship used for Modern ship used for geological survey geological survey

3. Plate tectonic3. Plate tectonic

• It is a theory combining the concepts of continIt is a theory combining the concepts of continental drift and seafloor spreadingental drift and seafloor spreading

• It is divided into a number of plates “floatingIt is divided into a number of plates “floating” on the asthenosphere ” on the asthenosphere

• Volcanic and earthquake zones are confined tVolcanic and earthquake zones are confined to the plate boundary o the plate boundary

• The growth of new lithosphere below the oceaThe growth of new lithosphere below the ocean is balanced by the destruction of the lithospn is balanced by the destruction of the lithosphere along the convergent boundarieshere along the convergent boundaries

Causes of plate movementCauses of plate movement

• Convection CurrentsConvection Currents- it is fuelled by radioactive process in the it is fuelled by radioactive process in the

mantle mantle - Difference heating in rock cause rising-siDifference heating in rock cause rising-si

nking motionsnking motions- It cause a dragging force on the lithosphIt cause a dragging force on the lithosph

eric plate eric plate

The mechanismThe mechanism

- all continents once formed one supercoall continents once formed one supercontinent called ntinent called PANGAEA PANGAEA

(( 聯合古陸聯合古陸 ) )

- It split intoIt split into Laurasian Laurasian and and GondwanalanGondwanalandd

B Internal structure of the B Internal structure of the earthearth

• Earth has a diameter of 6370 km and Earth has a diameter of 6370 km and about 40000km in circumferenceabout 40000km in circumference

• It consist of a solid crust (about 6km It consist of a solid crust (about 6km beneath the oceans and 35-40 km beneath the oceans and 35-40 km under mountains )under mountains )

• A solid mantle(about 3000km thick)A solid mantle(about 3000km thick)• A core (solid inner core and liquid A core (solid inner core and liquid

outer core)outer core)

Materials in the earth crust Materials in the earth crust

ContinentContinents s

30%30% Sial Sial 2.7g/cm2.7g/cm

Under the Under the ocean ocean

70%70% Sima Sima 3g/cm3g/cm

Moho (Mohorovicic Discontinuity)Moho (Mohorovicic Discontinuity)(( 莫霍界面莫霍界面 ))• The thickness of the earth is found by a YugoslThe thickness of the earth is found by a Yugosl

avian scientists ,Andrija Mohorovicicavian scientists ,Andrija Mohorovicic

• It is the abrupt change (It is the abrupt change ( 突然轉變突然轉變 )in density b)in density between the crust and the mantle etween the crust and the mantle

• This boundary zones averages about 10 km beThis boundary zones averages about 10 km below sea level in oceans basin and and about 30 low sea level in oceans basin and and about 30 km beneath high mountains km beneath high mountains

Some important terms Some important terms

• The mantle is much hotter than the crust .It coThe mantle is much hotter than the crust .It compose of mineral olivine.mpose of mineral olivine.

• The density is 5g/cmThe density is 5g/cm• The inner core is solid while the outer core is liThe inner core is solid while the outer core is li

quid quid • Lithosphere is the crust and rigid uppermost pLithosphere is the crust and rigid uppermost p

arts of upper mantle,at a depth of about 100karts of upper mantle,at a depth of about 100km m

• Asthenosphere (Asthenosphere ( 軟流圈軟流圈 )is a zone of weaker an)is a zone of weaker and more plastic rocks and extend to 240km d more plastic rocks and extend to 240km

WavesWaves

• When an earth tremor(When an earth tremor( 震動震動 ),primary an),primary and secondary waves are transmitted throd secondary waves are transmitted through the epicentre (ugh the epicentre ( 震央震央 ),the point at wh),the point at which the earthquakes occurich the earthquakes occur

• Primary waves travel through solids and Primary waves travel through solids and liquid while secondary waves travel throliquid while secondary waves travel through only solids ugh only solids

A. Constructive plate marginA. Constructive plate margin

• It is a boundary where two plates It is a boundary where two plates move apart. A fissure move apart. A fissure develops,allowing hot ,molten rock to develops,allowing hot ,molten rock to well up from the mantle and to from well up from the mantle and to from new materials as it solidifies,the new materials as it solidifies,the fissure is called a spreading,or “pull fissure is called a spreading,or “pull apart” centre.apart” centre.

Mid-oceanic ridge map by Mid-oceanic ridge map by computer computer

Mauna Loa in Hawwii Mauna Loa in Hawwii

Erta Ale in East Africa – an active zErta Ale in East Africa – an active zone of rift valleyone of rift valley

• Mid- Atlantic ridge Mid- Atlantic ridge is a good exampleis a good example

• It will cause It will cause

volcanic activity, volcanic activity, Iceland and the Iceland and the AzoresAzores

• High magnitude High magnitude volcanic eruptions volcanic eruptions on and around the on and around the ridges,volcanic ridges,volcanic island producedisland produced

B. Destructive plate marginB. Destructive plate margin

• It is a boundary where two plates collide.It is a boundary where two plates collide. The more dense plate will normally be d The more dense plate will normally be deflected beneath the less dense plate,aneflected beneath the less dense plate,and will be destroyed and absorbed at depd will be destroyed and absorbed at depth.th.

• Such action take place at the zone of suSuch action take place at the zone of subduction. Crumped (bduction. Crumped ( 摺曲、扭曲摺曲、扭曲 ) mount) mountain ranges,volcanoes earthquakes and oain ranges,volcanoes earthquakes and ocean trenches (cean trenches ( 海溝海溝 )are found )are found

Andes Mountain – a type of Andes Mountain – a type of destructive plate boundary destructive plate boundary

Three types of collisionThree types of collision• Collision between oceanic plate and continential plateCollision between oceanic plate and continential plate

Collision between oceanic Collision between oceanic platesplates

Collision between continental Collision between continental platesplates

The moving path of Indian The moving path of Indian plate plate

Conservative plate margin Conservative plate margin

• It is also called It is also called transform fault transform fault

The formation of transform The formation of transform faultfault

San Andrea’s fault San Andrea’s fault

Plate tectonics and ManPlate tectonics and Man

• The existing features of the continents The existing features of the continents and ocean basins are explained by the and ocean basins are explained by the theory of plate tectonictheory of plate tectonic

• Produce environmental hazards: Produce environmental hazards:

volcanic eruptions and earthquakes volcanic eruptions and earthquakes

• Produce mineral resources Produce mineral resources

Ring of Fire Ring of Fire

Earthquakes Earthquakes

• Magnitude of earthquakes refer to the eMagnitude of earthquakes refer to the energy released at the sourcenergy released at the source

• It is measured by either by Richter ScaleIt is measured by either by Richter Scales (0-8logarithmic scale) (s (0-8logarithmic scale) ( 里氏震級表里氏震級表 ) or ) or Mercalli Scales (12 gradations)Mercalli Scales (12 gradations)

• There is no direct relationship between tThere is no direct relationship between the magnitude and the damage caused ihe magnitude and the damage caused in the earthquake n the earthquake

Human Response to Human Response to EarthquakesEarthquakes• Made seismic hazard zone maps for landMade seismic hazard zone maps for land

use planninguse planning

• Man-made measure to trigger small earthMan-made measure to trigger small earthquakes quakes

• Drills and shock-proof buildings are desigDrills and shock-proof buildings are designed ned

• Extensive monitoring of the earthquakesExtensive monitoring of the earthquakes

• Seismometers (Seismometers ( 地震儀地震儀 )are used to dete)are used to detect small earthquake ct small earthquake

• Tiltmeters (Tiltmeters ( 傾斜儀傾斜儀 ) and electronic dista) and electronic distance measurers (nce measurers ( 電子距離儀電子距離儀 ) are used to ) are used to measure the shape of the volcanoes measure the shape of the volcanoes

• Fertile soil is produced Fertile soil is produced

• Iron,copper,zinc,lead,uranium ,etcIron,copper,zinc,lead,uranium ,etc

Hotspot (Hotspot ( 熱點熱點 ))