Coasts KQ2- How are coastal landforms developed? Flashcards
Define weathering
The in-situ decomposition of rock by chemical, biological, and physical processes
What is the effect of an increase of surface area of rock due to physical weathering?
-allows other weathering processes to take place
What climatic conditions mean physical weathering has more of an effect?
Large temperature fluctuations
Name 4 types of physical weathering
- freeze-thaw
- pressure release
- thermal expansion
- salt crystallisation
What causes freeze-thaw weathering?
- water enters cracks in the rock and when it freezes it expands
- the expansion puts pressure on the rock and can enlarge existing joints
What is the effect of freeze-thaw weathering?
- even resistant rocks are split
- pieces of rock break off
What causes pressure release?
- Overlying rocks are removed by weathering and erosion
- the release of pressure means underlying rock expands and fractures
What is the effect of pressure release?
-Parallel fractures are formed
What causes thermal expansion?
- rocks experience repeated cycles of temperature change
- when heated rock expands
- when cooled rock contracts
What is the effect of thermal exapansion?
Outer layers of rock may crack and flake off
What causes salt crystallisation?
- solutions of salts get into rock pores
- salts precipitate and form crystals in pore spaces in rocks
- this causes pressure within the rock
What is the effect of salt crystallisation?
Rock disintegrates
Which 2 salts are particularly effective at salt crystallisation?
Sodium sulfate and sodium carbonate
Name 5 types of chemical weathering
Oxidation Carbonation Solution Hydrolysis Hydration
What causes oxidation?
minerals in rock react with oxygen in air or water
What effect does oxidation have?
The original structure of rock is destroyed and disintegrates
Which element and type of rock is particularly susceptible to oxidation?
Iron and sandstone
What causes carbonation?
- rainwater reacts with dissolved carbon dioxide, forming weak carbonic acid
- The weak acid reacts with calcium carbonate to form calcium bicarbonate
- calcium carbonate is soluble in water
What is the effect of carbonation?
Rocks containing CaCO3 are dissolved
What causes solution?
-some salts are soluble in water or under specific conditions (e.g iron is only soluble in very acidic water)
What is the effect of solution?
Rock minerals dissolve, reducing the size of the rocks. This can sometimes undermine structural integrity
Name a type of solution
Carbonation
What causes hydrolysis?
Silicates combine with water, reacting chemically to produce clays
What is the effect of hydrolysis?
- the secondary minerals formed are softer than the original minerals
- these means the rock is more easily eroded
What causes hydration?
- When water molecules react with rocks new minerals
- these have a larger volume
- this exerts pressure
What is the effect of hydration?
surface flaking of rock occurs
Name two causes of biological weathering
Tree roots and organic acids
How does tree root weathering occur?
- tree roots grow into cracks and exert pressure
- if these trees topple they act as a lever
What is the effect of tree roots on rocks?
- pressure exerted on cracks can expand fissures in the rock
- trees toppling bring soils and rock to the surface allowing them to be weathered further
How does organic acid weathering (chelation) occur?
- Molluscs secrete acids
- The decomposition of plant an animal litter can cause soil water to become acidic
- Blue-green algae can also have a weathering effect
What is the effect of organic acid weathering?
- Molluscs create small surface hollows in the rock
- this increases surface area for other weathering processes
- acidic soil reacts with some minerals
How does high permeability of rock affect weathering?
- can increase weathering
- as it allows weathering fluids to flow through the rock
Does salt crystallisation result from the evaporation of sea water?
Yes
Define mass movement
The downslope transportation of material under gravity
What is soil creep?
- results from the repeated contraction and expansion of individual soil particles
- causes them to very slowly move downwards under gravity
What is Mudflow?
- Movement of material downslope in the form of a fluid
- Material on a slope becomes saturated with water, making it much heavier
Under what conditions do mudflows usually occur?
- after a period of intense rainfall
- areas that have thin soils overlying impermeable bedrock
Under what conditions do rock slides usually occur?
-rocks that have jointing or bedding planes roughly parallel to the angle of the slope
Under what conditions do rock falls usually occur?
-on slopes in excess of 40 degrees
What can prompt rock falls to occur?
- extreme physical or chemical weathering
- storm action
- Earthquakes
What signs can point to rock falls having occurred on a cliff?
A tallus/scree slope at the foot of the cliff
Under what conditions does rotational slumping usually occur?
-When weaker rocks/clays overlie more resistant impermeable rocks
What signs can point to slumping having occurred on a cliff?
The presence of a recurved slip plane
Name the 5 wave action processes
Abrasion Attrition Hydraulic action Pounding Solution
Which are the two most significant processes?
Pounding and hydraulic action
What is abrasion?
Water containing rock particles scour the coastline (rock rubbing against rock)
What is attrition?
Rock particles transported by wave action, collide with each other and become worn away, smaller, and rounder
What is hydraulic action?
- When waves break against the cliff face air and water trapped in cracks and crevices becomes compressed
- as the water recedes pressure is released and the air and water expands
- this widens the crack
What is pounding?
The mass of a breaking wave exerts pressure on the rock, weakening it
What is solution?
Minerals are dissolved by water, this is limited by the quantity of minerals in the rock
Give an example of a mineral dissolved in sea water
Magnesium carbonate
