Social Sciences Term 3 Geography

Seite 1

UNIT 1 :

1. Concept of weathering

Weathering is a group of processes that breaks down rocks so oils and minerals into smaller pieces through contact with the earths atmosphere and waters.

Weathering is slow process

Create unique features

Erosion is the process by which rock particles already broken down by weathering are carried away.

1.1 PHYSICAL WEATHERING

P weathering is the physical breakdown of rocks into smaller components without changing their chemical composition.

P weathering is a result if extreme temp changes.

When rock minerals are heated they expand at different rates, breaking down rocks.

temp. changes

freezing and thawing of water

wetting and drying rocks

All of the above can contribute to weathering

GRANULAR DISINTEGRATION - rocks break up into smaller grains or pieces to form sand or gravel

EXFOLIATION - the rocks weather by peeling off into sheets ( layers )

BLOCK SEPARATION - rocks break up into large fragments related to rock joints. ( main cause = frost shattering. Ice is formed in the joints of the rocks. The ice expands and breaks up rocks )

1.2 CHEMICAL WEATHERING

C weathering is the breakdown of the rocks into particles with a dfferent mineral composition or make up from the original rock.

Agents :

water

o2

co2

Occurs thro : (...) example

solution - Minerals dissolve directly in water (such as salt in water)

oxidation - Rock minerals react with dissolved o2 to produce red or yellow oxides, AKA hydroxides. (Red a yellow soils found in tropical areas )

carbonation - When co2 dissloves in water to form weak carbonic acid. This solution can weather carbonate rock ( chalk , limestone )

hydration - Minerals in the rock absorb water and expand. The expansion causes the rock to break up. (physical weathering process )

hydrolysis - occurs when there is a chemical reaction between the rock minerals and the hydrogen in the rain water.

Feldspar - rock forming mineral

1.3 BIOLOGICAL WEATHERING

B weathering involves living things

P actions that break down rock : Plant root growth Animal burrows Chemical actions ( secretion of acids )

Decomposition of organic matter ( animals, plants, leaves ). They release corrosive substances into the enviro. One of these substances is co2 which can for carbonic acid gas, this weathers some rocks.

Co2 causes acid rain

Human activities can increase rate of weathering.

burning of fossil fuels / release chemicals. Acid rain can eat into limestone and break it down ( buildings )

Rock blasting ( rocks are blasted into smaller pieces )

Mining activities

Quarrying

Seite 2

UNIT 2 :

1. Erosion and Deposition

WEATHERING

The breaking down of rocks, minerals as well as artificial materials thro. contact with the earth atmosphere and waters. ( movement of eroded mat. does not occur )

EROSION

Process by which oil and rock, broken down by weathering, are moved from one area on the earth to another by natural means. For example : wind / water flow / and deposited in a different location

DEPOSITION

Occurs eroded material is deposited in a new location. It is the end of the process that started weathering.

E and D create nat. features we see. For example : create features along the banks of a stream such as bank erosion.

Agents of E and D :

gravity

water

glaciers

sea waves

wind

Gravity ( main agent ) causes erosion by mass-wasting ( downward movements of rocks and sediments ). Gravity moves material from high elevations to low elevation, transporting agents like streams and glaciers can them pick them up and move it to an even lower elevation.

Seite 3

2 . Features of Erosion and Deposition along a river course :

River flows from a river source to the ocean. Passes thro. 3 stages :

1. Youth Stage ( UPPER COURSE )

beginning of a river

fast and a lot of energy

smaller and has waterfalls

cuts thro mountains, slopes, V-shaped valley

rapids

2. Mature River

valley with a wide floor

side erosion ~ U shaped vally

gently slopes

narrow flood plain

meanders

3. Old age stage

relief ~ flat

river flow is slow and still meanders

oxbow river develops ( U shaped lake that is formed when the river channel is cut off from the main stream )

3. Features of erosion and deposition associated with wave action

Wave action has power to cause E and D.

A cliff is a steep rock face formed by wave erosion. Coastal cliffs are formed by erosion of the rock at the foot of a slope. (cause : waves). This process is followed by abrasion - the scraping or wearing away of rocks by other smaller rocks when they rub against eachother.

Headland is a narrow piece of land that juts out from the coast line into the sea

Bay is a area of ocean enclosed by land with a wide mouth that allows access to the sea

Sea Cave - opening at the base of the sea cliff formed by waves hitting the weak rocks

Arch - nat. bridge formed when a cliff is subj. to erosion

Stack - Isolated piece of rock that has been separated form a headland. ( Formed by the collapse of an arch. )

Stump : small out throw of a rock formed by the erosion of a coastal stack

Wave cut platform - flat surface formed by wave erosion

pg.170 Fig. 19

Erosion by wave action :

HYDRAULIC ACTION

force of water on the cliffs / coastal rocks. force of water strong enough to break rocks / pebbles

ABRASION ( CORRASION )

rocks / peb. flung by waves wear coastal rocks.

ATTRITION

eroded rock particles are worn and become small and round

CORROSION

certain rocks and minerals are dissolved in water

Deposition associated to wave action forms :

spits ( waves break and form sand bars )

barrier islands ( shoreline is flat / gentle slopes, first line of defense for storms )

beaches , pg.171

4. FEATURES OF EROSION AND DEPOSITION ASSOCIATED WITH GLACIATED LANDSCAPES :

Moving ice = glacier, causes erosion by abrasion and plucking

Abrasion - scraping by the impact of rocks carried in the ice

Plucking - bedrocks under the glacier are pulled from the surface as the glacier moves

Features of glacier erosion :

horns

cirques*

pg.171 Fig.20

Glacial deposition :

called till or moraine

till - clay or otr. sediments deposited by glacier

moraine - the till deposited along edges of a glacier

( lateral or terminal moraine )

5. Wind Erosion :