2.5 sub-aerial processes

Question 1

what are subaerial processes?

Answer 1

land based processes which alter the shape of the coastline. this is a combination of weathering and mass movement

Question 2

describe the process of weathering

Answer 2

the gradual breakdown of rock at or close to the ground

Question 3

describe the mechanical weathering process of freeze-thaw

Answer 3

water enters cracks when it rains
this water then freezes and expands in volume, this causes the cracks to widen. overtime the rocks chip off the cliff and the sediment accumulates at the foot of the cliff as Scree.
this sediment is then carried by the waves and used in corrasion to further erode the cliff

Question 4

describe the mechanical process of salt crystallisation weathering

Answer 4

when salt water evaporates, it leaves salt crystals behind
these crystals then accumulate and grow in size and puts stress on the rock causing it to break apart
salt can also erode rocks through corrosion

Question 5

describe the process of wetting and drying

Answer 5

this is common for geology rich in clay such as shale as they expand when they get wet and compress when they dry causes cracks and joints to form which can then be exploited by marine processes

Question 6

describe the chemical weathering process of carbonation

Answer 6

the slow dissolving of limestone due to rainfall which produces calcium bicarbonate
this weakens rock strata’s and increases rates of erosion

Question 7

describe the chemical weathering process of hydrolysis

Answer 7

the breakdown of minerals to form new clay minerals, plus materials in solution, due to the effect of water and dissolved CO2

this weakens the structure of the rock, increasing rates of erosion

Question 8

describe the chemical weathering process of oxidation

Answer 8

the addition of oxygen minerals, especially iron compounds, which produces iron oxides and increases the volume contributing to mechanical breakdown

this most often effects sand stones, silt stones and shales as they include iron compounds that can be oxidised

this increases rates of erosion by weakening the rock in the cliff

Question 9

describe how plant roots can increase rates of erosion

Answer 9

the roots grow into cracks and fissures in the rock face which increases the size of the cracks meaning they eventually break away from the cliff

Question 10

describe how rock boring can increase erosion

Answer 10

many species of marine wildlife make habitats in the rocks by boring into the rock which weakens the rock

some marine wildlife also secrete chemicals which will dissolve some rock through corrosion

this mostly effects sedimentary rocks such as limestone

Question 11

what is percolation?

Answer 11

percolation is the steady movement of water through a permeable rock

this increases the likelihood of mass movement because the rock has the added weight of the water

Question 12

name the 5 different forms of mass movement

Answer 12

• rockfall
• soil creep
• land slides
• rotational slumping
• mud flow

Question 13

what are rockfalls?

Answer 13

rockfalls are the fastest form of mass movement where blocks of rock become dislodged due to erosion and weathering and they collapse due to gravity forming a foot at the base of the cliff

Question 14

what is soil creep?

Answer 14

Soil creep is the slow, gradual movement of soil downhill due to gravity, often caused by repeated expansion and contraction from processes like wetting and drying or freeze-thaw.

evidence of it on a coastline can be seen when fences and trees are either uprooted or tilted at an angle

Question 15

what are landslides?

Answer 15

landslides are movements of rock that stay together as mass and move quickly down a cliff face that is often slanted or curved

landslides are typically triggered by heavy rainfall and earthquakes

Question 16

what is rotational slumping?

Answer 16

rotational slumping occurs on a curved surface where huge masses of material can slowly rotate downslope over periods which can last from days to years
water plays an important role in the causality of rotational slumping such as percolation can increase the likelihood of rotational slumping

Question 17

what is mud flow?

Answer 17

flows are common in weaker geology such as clays, silts and unconsolidated sands as when they become saturated, they flow downslope

this is often caused by periods of heavy rainfall combined with high tides

Question 18

what is a cliff scar?

Answer 18

after mass movement has occurred, a cliff scar will form where there are clear signs mass movement has occurred such as a lack of vegetation on that section of cliff

Question 19

name a case study example for mass movement

Answer 19

Lyme Regis

Question 20

what types of mass movement are there at Lyme Regis?

Answer 20

• rotational slumping - due to the soft clay
• soil creep - on the gentler slopes
• landslides - during heavy rainfall