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GeomorphologyGrade 10

The Structure of the Earth

• The internal structure of the Earth• How does the Earth look beneath us?

• What does the crust of the Earth look like?

• Types of rocks• Rock Cycle

• How are rocks formed and classified

• Intrusive igneous activity• Landforms associated

• How are they formed? (Batholiths / Pipes / dykes/ sills / laccolith / lopolith)

Structure of the Earth

Laye

rs o

f th

e Ea

rth

Atmosphere640km

Crust6-70km - solid

Sial & Sima

Mantle 2900km Periodite

Semi-molten

Outer core 2000kmLiquid iron, nickel & oxygen

Inner core 2740kmSolid iron nickel - High pressureTemperature above 4500ºC

Layers in the Crust of the Earth

Seafloor

Continent

Mantle Sediments

Oceans

Earth structure

Layers of the crust of the Earth

• Continental crust• Sial – silica & aluminium

• Granite

• Less dense

• ‘Floats’ on Sima

• Not continuous

• Older rock

• Continents

• Seafloor• Sima – Silica & Magnesium

• Basalt

• Denser & heavy

• Covers mantle

• Continuous layer around the Earth

• New rock

• Seafloor

Moho Plane

ContinentSea floor

Sediments

Rock types

• Igneous rock• Lava or magma that solidifies to form rock

• Sedimentary rock• Weathered material deposited in layers that solidify under the

pressure of accumulative layers

• Metamorphic rock• Rock that changes form under high pressure and or temperature

Rock classification• UPPER CRUST: Sedimentary rock

• Sediments (dust/ rocks/ silt/ weather material / organic material) deposited by wind, water and ice build up in layers, weight from above compresses it into solid rock.

• CRUST: Igneous rock• Magma rises, cools down, solidifies

• Deeper Crust : Metamorphic rock• Igneous and sedimentary rock moves downward due to

plate movement, heat and pressure changes it into metamorphic rock

Igneous rock Lava or magma that solidifies to form rock

• When magma cools down and solidifies under the surface it forms intrusive igneous rocks.

• The rocks are later exposed by erosion.

• Examples: granite, dolerite

Characteristics of Igneous rock

• Igneous rocks do not have layers, but are made up of crystals (crystalline)

• It is extremely hard and weathers slowly

• It contains no fossils

• When weathered, it forms fertile soil

Uses of igneous rock

• Often used for building work e.g. road construction, kitchen tops, tomb stones etc.

• Granite is used for stone walls, facing blocks for buildings, stone chips on roads

• Dolerite weathers down to fertile soil

• Contains minerals and ores

Distribution of Igneous rocks in SA

• Granites are common around Nelspruit (Mbombela), Kruger Park, The Bushveld Igneous complex in the Polokwane- Mokopane area

• Paarl rock in Western Cape

• Namaqualand

Igneous rock

Sedimentary rockWeathered material deposited in layers and that solidify under the pressure of accumulative

layers

• Weathered rock is eroded by wind, rivers and glaciers

• This material is deposited in lakes and near to the coastline

• The layers of material that is deposited becomes more and heavier and the lower layers becomes solidified under the accumulative weight.

• The layers become stratified (strata)

• Can be of mechanical, chemical or biological origin, depending on the main type of weathering that broke down the original rock

Characteristics of sedimentary rocks

• They are deposited in layers/ strata

• They contain many fossils

• The erode easily

• Often forms fertile soil.

• The rocks are able to fold and bend and form fold mountains

• Layers are porous and allow water to penetrate

• Layers differ in respect of grain size, colour and composition.

Uses of sedimentary rocks

• Coal: a valuable source of heat and power.

• Sandstone: used for building purposes

• Shale: used in making paths, roadways of old time roof tiles

• Salt: used for domestic purposes and in the chemical industry.

• Limestone: used in making of cement and fertilisers and in the iron and steel industry

• Crude oil: make fuel

Distribution of sedimentary rocks in SA

• They constitute some 75% of the actual surface rocks of the Earth.

• The greatest part of South Africa consists of sedimentary rock.

• Golden Gate in Eastern Free State

• Cape Fold Mountains

RAINBOW MOUNTAINS-CHINA

RAINBOW MOUNTAINS-CHINA

RAINBOW MOUNTAINS-CHINA

RAINBOW MOUNTAINS-CHINA(photo shopped)

Metamorphic rockRocks that changed under high pressure and or temperature

• CHARACTERISTICS:

• Rock is harder than original rock but can be brittle.

• It weathers slowly.

• Can have attractive colours and a fine texture

• Streaky in appearance

Examples of metamorphic rock

• Granite changes to Gneiss

• Sandstone changes to Quartzite

• Limestone changes to Marble

• Coal changes to diamonds under very specific conditions

• Shale changes to slate

Uses of metamorphic rock

• Stone chips for road works.

• Slate is used on roofs and garden paths

• Marble is used in buildings and for sculpture

• Contains many minerals e.g. gold, silver, diamonds

Distribution on metamorphic rock in SA

• Magaliesberg mountains- quartzite

• Mable Hall- marble

• Phalaborwa area- different minerals

• Barberton area- different minerals

• Bushveld Igneous Basin- different minerals

Quartz

Serpentine

Asbestos a type of serpentine also called crocidolite

Tiger’s Eye

Buddstone

Agate

Jasper

Hardness of Rock types

Rock classification

• UPPER CRUST: Sedimentary rock• Sediments (dust/ rocks/ silt/ weather material / organic material) deposited

by wind, water and ice build up in layers, weight from above compresses it into solid rock.

• CRUST: Igneous rock• Magma rises, cools down, solidifies

• Deeper Crust : Metamorphic rock• Igneous and sedimentary rock moves downward due to plate movement,

heat and pressure changes it into metamorphic rock

THE ROCK CYCLE

Activity 2: Understanding the rock cycle, p97• 1) Rock Cycle: The ongoing process of making, destroying, changing and

remaking one type of rock into another type.

• 2) * Rocks change when they are heated and melted underground.

• * On the Earth’s surface weathering and erosion changes rocks.

• * IGNEOUS ROCKS from when lava or magma is cooled.

• * METAMORPHIC ROCK form when igneous or sedimentary rock change because of heat and pressure.

• * SEDIMENTARY ROCKS form when weathered rocks and organic material are deposited (put down) in layers.

• 3) IGNEOUS ROCKS: when magma rises to the earth’s surface and is cooled.

• METAMORPHIC ROCK form when igneous or sedimentary rock change because of heat and pressure.

• SEDIMENTARY ROCKS form when weathered rocks and organic material are deposited (put down) in layers by wind water and ice

• 4) Rock name Type

Shale Sedimentary

Basalt Igneous

Marble Metamorphic

Granite Igneous

Limestone Sedimentary

Intrusive landforms

• Batholith

• This is the largest type of igneous intrusion.

• They form deep in the crust .

• Large round shape.

Laccolith

• This is a mushroom shaped structure where magma forces the overlying strata upwards.

Laccolith

Lopolith

• This is similar intrusion to a laccolith

• The weight of the overlying strata causes the lopolith to sink into a saucer shaped structure .

Sill

• A sill forms where magma intrudes horizontally between layers of rock .

Dyke

• A dyke forms when magma intrudes vertically between layers of rock .

Dikes exposed to surfaces

Pipe

Batolith

Lopolith

Laccolith

Dyke

Sill

PipeMASSIVE

Batholith: Paarl Rock

Underground Igneous Features

Dikes exposed to surfaces

Laccolith

Activity 3: Mind map: Intrusive Igneous activity, p 99

INTRUSIVE IGNEOUS LANDFORMS

Batholiths* The largest of all the forms*Enormous mass of magma pushes up and solidify under the surface* Granite

SillsWhen magma spreads horizontally between sedimentary layers* Dolerite

DykesA Wall-like intrusion, solidified in a thin sheet• Cuts vertically across

horizontal layers• Dolerite• Forms narrow ridges

on top of surface

Lopoliths*Magma intrudes between sedimentary layers, but the layers below cannot support the weight and sinks in a saucer shape• Smaller than Batholith• * Connected to magma

source with pipe/dyke

Laccoliths*Magma intrudes between sedimentary layers and forces the layers upwards in mushroom shape• Smaller than batholith• Connected to magma source by

a pipe or dyke

PipesChimney-shaped intrusion• Magma can move upwards to

the surface (Volcano)• Solidifies as dolerite

Rock structure and landforms

• Resistance

• Permeability

• Sedimentary rocks LAYERS

• Igneous rocks TORS

Activity 4 Paragraph

•Figure 8.3 shows layering in rocks which is an indication of sedimentary rock. The photo shows that lots of erosion has taken place, therefore these rocks are softer.

•Figure 8.4 shows dikes and pipes which indicates that intrusive igneous activity took place therefore these rocks are harder in nature.