Coasts- Weathering and Mass Movement

Question 1

What is weathering?

Answer 1

• the breakdown/disintegration of rock in situ at or close to the ground surface
• weathering leads to the transferring of material
• important links with water cycle (freeze-thaw) and the carbon cycle (carbonation)

Question 2

Weathering positive feedback

Answer 2

• if the rate of debris removal exceeds the rate of weathering then a positive feedback may operate
• as the rate of weathering/mass movement could increase

Question 3

Weathering negative feedback

Answer 3

• if debris removal is slow/ineffective this will lead to a build up of debris that reduces exposure of the cliff face
• weathering rates will therefore further decrease

Question 4

Mechanical weathering- freeze thaw

Answer 4

• freeze thaw (frost shattering) occurs when water enters a crack/joint in the rock when it rains and then freezes in cold weather
• when water freezes it expands in volume by 10%
• this expansion exerts pressure on the rock- forces cracks to widen
• repeated freezing and thawing cause fragments of rock to break away and collect at the base of the cliff
• these are then used as tools in marine erosion

Question 5

Mechanical weathering- salt crystallisation

Answer 5

• when salt water evaporates it leaves salt crystals behind
• these can grow over time and exert stresses in the rock causing it to break up
• salt can also corrode rock- particularly if it contains traces of iron

Question 6

Mechanical weathering- wetting and drying

Answer 6

• frequent cycles of wetting and drying are common on the coasts
• rocks rich in clay expand when they get wet and contract as they dry
• causes them to crack and break up

Question 7

Define biological weathering and give examples

Answer 7

The breakdown of rocks by organic activity eg.

• thin plant roots grow into small cracks in a cliff face- cracks widen as roots grow which breaks up the rock
• water running through decaying vegetation becomes acidic which leads to increased chemical weathering
• birds and other animals dig burrows into cliffs
• marine organisms capable of burrowing into rocks or secreting acids

Question 8

Define chemical weathering

Answer 8

Chemical weathering involves a chemical reaction where salts may be dissolved or a clay-like deposit may result which is easily eroded.

Question 9

Chemical weathering- carbonation

Answer 9

• rainwater absorbs CO2 from the air to form weak carbonic acid
• reacts with calcium carbonate in rocks such as limestone to form calcium bicarbonate (easily dissolved)
• cooler the temperature the more CO2 is absorbed

Question 10

Chemical weathering- oxidation

Answer 10

• the reaction of rock minerals with oxygen eg. iron to form a rusty red powder
• leaves rocks more vulnerable to weathering

Question 11

Chemical weathering- solution

Answer 11

The dissolving of rock minerals eg. halite (rock salt)

Question 12

Soil creep

Answer 12

• slow movement of individual soil particles downhill
• particles rise to ground surface due to wetting/freezing
• then return vertically to surface in respond to gravity as the soil dries out and thaws

Question 13

Mudflows

Answer 13

• involves earth and mud flowing downhill
• usually over unconsolidated/weak bedrock eg. clay after heavy rainfall
• water gets trapped within rock- increasing pore water pressure
• forces rock particles apart leading to slope failure
• mudflows are often sudden and fast-flowing so are a significant hazard

Question 14

Landslides

Answer 14

• involves a block of rock moving very rapidly downhill along a planar surface
• frequently triggered by earthquakes or heavy rainfall (Reduces friction)
• landslides are very rapid
• in 1993, 60m of cliff slid onto the beach near Scarborough- taking with it part of the Holbein Hall Hotel

Question 15

Rockfall

Answer 15

• involves the sudden collapse or breakaway of individual rock fragments at a cliff face
• most commonly associated with steep/vertical cliffs in hard rock
• often triggered by mechanical weathering or an earthquake
• once broken away, rocks fall down the slope to form scree at the foot of the slope

Question 16

Scree

Answer 16

Scree forms a temporary store in the coastal system, with material gradually being removed and transported somewhere else by the sea
-when this occurs, scree forms an input in the sediment cell

Question 17

Runoff

Answer 17

• when overland flow occurs down a slope or cliff face, small particles are moved downslope to enter the littoral zone (potentially forming an input)
• runoff can be considered a type of flow that transfers both water and sediment from one store (rock face) to another (beach/the sea)

Question 18

Solifluction

Answer 18

• in the summer the surface layer of soil that’s out and becomes saturated (because it lays on top of permafrost)
• this soil with its blanket of vegetation slowly moves downhill by heave and flow

Question 19

Landslip/slump

Answer 19

• differs from a landslide in that its slide surface is curved not flat
• commonly occur in weak and unconsolidated clays and sands-often when permeable rock overlies impermeable rock
• causes a build up of pore water pressure
• characterised by a sharp break of slope and the formation of a scar
• multiple landslips can result in a terraced appearance on the cliff face