weathering

Question 1

define denudation

Answer 1

wearing away of the earth’s surface done via weathering, erosion, mass movement

Question 2

define weathering

Answer 2

breakdown/disintegration of rock in-situ due to long term exposure to elements in weather such as action of rainwater, extreme changes in temperature and biological activity

Question 3

define erosion

Answer 3

removal of surface of earth by agents of erosion such as wind, water and ice

Question 4

list three types of weathering

Answer 4

physical/mechanical
chemical
biological

Question 5

define physical/mechanical weathering

Answer 5

involves rock breaking apart disintegrating without any chemical change taking place

Question 6

define chemical weathering

Answer 6

chemical change causes rocks to dissolve/decay and disintegrate
due to alteration in chemical composition of rock caused by chemical reaction

Question 7

define biotic/mechanical weathering

Answer 7

disintegration of rock involving living organisms like plants and animals or acids from rotting vegetables

Question 8

where does freeze thaw/frost shattering/frost action occur

Answer 8

occurs in areas where temperature fluctuates above and below 0 degrees celsius for instance on some mountainous areas and some temperature regions
most likely to occur on steeper bare rock slopes

Question 9

when does freeze thaw occur

Answer 9

when rocks are porous (contains holes) or permeable (allow water to pass through)
rock must be exposed at surface with little vegetation cover to protect rock from weather conditions

Question 10

explain the process of frost action weathering

Answer 10

during the day, when temperature is above zero degrees and water, either from moisture from dew, melting snow or ice or from rainwater, can trickle into cracks/crevices or pores in the rock
at night when temperature is below zere degrees c the water in the cracks freezes and turns into ice which takes up 9-10 percent more volume/space than equivalent amount of water
exerts pressure on crack in the rock
repeated freezing and thawing slowly widens cracks until pieces of rocks may break off
broken pieces of rocks will slide downhill easily under force of gravity on slopes
angular rock fragments collect at base of slope in a fan shaped pile called scree or tallus

Question 11

when does pressure release occur

Answer 11

when overlying material/rock removed by erosion exposes underlying rock
release of pressure causes exposed rock to expand upwards which causes fractures to form parallel to rock surface
weathering and erosion results in these layers peeling away called exfoliation

Question 12

name a feature caused by pressure release

Answer 12

sugar loaf mountain in brazil, rio de janeiro

Question 13

where does onion skin weathering occurs

Answer 13

places of extreme changes in temperature such as deserts can also lead to exfoiliation in rocks
or the large diurnal range of temperature ie large difference between max and min daily temp

Question 14

explain onion skin weathering/ alternate expansion and contraction/ isolation weathering

Answer 14

due to a lack of cloud coverage and vegetation during the day the temperature exceeds 40 C causing outer layer of rocks to expand
at night temperature may drop to below freezing causing outer layer of rocks to contract
continuous expansion and contraction of outer layer of rocks weaken it until eventually peels off
after one layer has broken the next layer is then attacked by temperature changes

Question 15

explain process of salt crystallization weathering

Answer 15

sea water gets into cracks in rocks
when water evaporates leaves behind salt crystals which occupies more volume
over period of time salt accumulates and exerts pressure in cracks in rock which eventually causes it to fracture and disintegrate or sometimes can create small holes which become larger in rocks
results in sandstone

Question 15

where is salt crystallization most common

Answer 15

in coastal areas or semi arid areas

Question 16

where is chemical weathering most common

Answer 16

in warm and wet climates

Question 17

explain the rate of chemical weathering

Answer 17

rate of chemical weathering doubles for every 10 C increase in temperature

Question 18

where does oxidation occur

Answer 18

occurs when rocks are exposed to oxygen in air and water

Question 19

explain oxidation

Answer 19

iron in its ferrous state changed by addition of oxygen into iron in its ferric state
rock or soil which may have been blue or grey in colour changes into reddish brown
process is more commonly known as rusting and causes rock to crumble more easily

Question 20

explain carbonation

Answer 20

rainwater contains carbon dioxide absorbed from atmosphere forming weak acid called carbonic acid
able to dissolve calcium based rock or calcareous rocks
carboniferous limestone and chalk most affected because composed of almost pure calcium carbonate