3.2 weathering

Question 1

sedimentary rocks

Answer 1

• rocks created from sediment deposited by water or air
• eg. sandstone/limestone

Question 2

igneous rocks

Answer 2

• rocks created from solidified lava/magma
  -eg. basalt/rhyolite

Question 3

metamorphic rocks

Answer 3

• rocks that have undergone change through heat, pressure, natural processes such as folding or the intrusion of igneous rock
• eg. marble

Question 4

freeze thaw (P)

Answer 4

• water in joints and cracks freezes at 0 C
• expands 10% increasing pressure
• where high moisture and frequent fluctuations above and below freezing point
• cycles

Question 5

salt crystallisation (P)

Answer 5

• water containing salts seep into rocks
• water evaporates leaving salt: expands up to 300% when T increases: forces rock to crack
• frequent when low rainfall: allows salt to accumulate

Question 6

heating and cooling (P)

Answer 6

• cause disintegration in hot desert areas where there is a large diurnal T change
• rocks are poor conductors of heat: outer layers heat
• stress: exfoliation
• requires moisture
• expansion and contraction

Question 7

pressure release/ dilation (P)

Answer 7

• overlying rocks removed by erosion: underlying expand and fracture parallel to surface

Question 8

vegetation root action

Answer 8

• roots grow through joints in the rock

Question 9

carbonation-solution (C)

Answer 9

• on rocks w CaCO3 (silicate, carbonate materials: chalk, limestone)
• rainfall combines with dissolved CO to form a weak carbonic acid
• carbonic acid triggers reaction, insoluble:soluble:removed in solution
• pH affects solubility: Fe below 4.5, Al2O3 below 4 or above 9

Question 10

hydrolysis (C)

Answer 10

• on rocks with orthoclase feldspar to clay (granite)
• rain: H+, OH- ions: chemically combines with material in rock: soluble removed in solution
• water dissolves minerals in rock, producing new compounds
• clay and salts removed in solution
• clay weakens rock: more likely to break

Question 11

hydration (C)

Answer 11

• certain minerals absorb water, expand or change shape
• increase in volume
• take up water, increase in volume and pressure, break over time
• anhydrate to gypsum

Question 12

rock type

Answer 12

• joints and bedding planes
• chemical composition
• nature of cements in sedimentary
• eg. limestone prone to carbonation, feldspar to hydrolysis, quarts are more resistant

Question 13

rock structure

Answer 13

• large scale folding and faulting
• localised patterns of joints and bedding planes
• joint patterns exert a strong control on water movement
• lines of weaknesses create differential resistance
• coarse-grained rocks: void space, permeable
• fine-grained have larger s.a

Question 14

vegetation

Answer 14

• linked with type of climate and nature of the soil
• moisture content/depth/acidity of humus
• secretion of organic acids chemically weather soil
• roots: mechanical
• depth: soil may protect rocks from weathering or may increase due to vegetation it holds

Question 15

relief

Answer 15

• weathered material needs removal
• too shallow, too steep:flows over
• intermediate angles produce most weathering

Question 16

climate

Answer 16

• hard to isolate exact relationship
• peltier’s diagram: shows weathering related to moisture and avg T
• Van’t Hoff’s law: rate of chemical increases 2-3x per increase in temperature by 10 C
• critical temperature changes, diurnal and seasonal variation in T
• areas with less than 500 mm annual rainfall tend to have very slight weathering
• frost shattering increases as freeze thaw cycles increase

Question 17

Carlsbad Caverns National Park in US (New Mexico)

Answer 17

• more than 119 limestone caves created by weathering
• acid rain rapidly weathers limestone