Coasts- Weathering and Mass Movement Flashcards Preview

A Level Physical Geography > Coasts- Weathering and Mass Movement > Flashcards

Flashcards in Coasts- Weathering and Mass Movement Deck (19)
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1
Q

What is weathering?

A
  • 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)
2
Q

Weathering positive feedback

A
  • 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
3
Q

Weathering negative feedback

A
  • 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
4
Q

Mechanical weathering- freeze thaw

A
  • 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
5
Q

Mechanical weathering- salt crystallisation

A
  • 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
6
Q

Mechanical weathering- wetting and drying

A
  • 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
7
Q

Define biological weathering and give examples

A

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
8
Q

Define chemical weathering

A

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

9
Q

Chemical weathering- carbonation

A
  • 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
10
Q

Chemical weathering- oxidation

A
  • the reaction of rock minerals with oxygen eg. iron to form a rusty red powder
  • leaves rocks more vulnerable to weathering
11
Q

Chemical weathering- solution

A

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

12
Q

Soil creep

A
  • 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
13
Q

Mudflows

A
  • 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
14
Q

Landslides

A
  • 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
15
Q

Rockfall

A
  • 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
16
Q

Scree

A

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

17
Q

Runoff

A
  • 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)
18
Q

Solifluction

A
  • 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
19
Q

Landslip/slump

A
  • 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