lecture 4 - physical weathering

Question 1

W.M Davis’s geographical cycle

Answer 1

aka cycle of erosion

1. initial uplift
2. incision
3. sloped reduce
4. end of cycle results in peneplain

Question 2

what is a peneplain?

Answer 2

level land surface produced by erosion over a long period of time, undisturbed by crustal movement

Question 3

define incision

Answer 3

river cuts through riverbed - may incise through sediment or bedrock

Question 4

Walther Penck’s variable rock uplift model

Answer 4

uplift increase and decreases
denudation and erosion can be contemporaneous
landscape form is dictated by competition

Question 5

J.T Hack’s dynamic equilibrium model

Answer 5

model shows adjustment of landscape to competition between tectonic and surface processes

Question 6

define physical weathering

Answer 6

processes that mechanically fracture rock into smaller sizes (comminution)

Question 7

define comminution

Answer 7

reduction of rock into smaller particles by crushing, fracturing, grinding
increases surface area

Question 8

define erosion

Answer 8

the removal of weathered material by sediment transport processes

Question 9

define denudation

Answer 9

the loss of mass from a landscape by weathering and erosion

Question 10

define exhumation

Answer 10

exposure of formerly buried rocks at the earth’s surface by the removal of rock above

Question 11

define sediment

Answer 11

weathered material that is a) in transport b) has undergone transport and deposition

Question 12

define regolith

Answer 12

loosened rock, has 20 - 50 times water capacity of fractured rock, presence means erosion is transport limited

Question 13

physical weathering processes:

Answer 13

1. thermal stress / insolation weathering
2. frost and salt shattering
3. physical stress
4. corrasion and abrasion

Question 14

thermal stress

Answer 14

• thermal shocks = uneven expansion
• thermal fatigue = repeated thermal cycles weaken the rock
• cause exfoliation of rock surface, shallow concentric layers fall off

Question 15

frost shattering

Answer 15

water in fractures expands on freezing

Question 16

salt weathering

Answer 16

salts crystallise in voids when water is drawn to the rock surface

Question 17

physical stress

Answer 17

rocks deep in the crust are under enormous pressure

exhumation reflects this pressure leading to exfoliation along fractures aligned parallel to the eroding surface

Question 18

corrasion and abrasian

Answer 18

material in transport can cause corrasion of rock surfacesn
abrasion = the effect on bedrock by the removal of rock layers by corrasion
e.g. rivers and glaciers corrade - their bedrock is abraded

Question 19

physical weathering is best where…?

Answer 19

there are strong temperature cycles

Question 20

chemical weathering is strongest where…?

Answer 20

climate is wet and warm