Booklet 6- What weathering and erosion and how do they affect the coast? Flashcards
Type of Weathering-Freeze thaw
During the day, water enters cracks in the rock and at night when the temperature drops the water expands as it freezes. The increase of volume by 9% exerts pressure on the fissures of the rock and weakens it internally.
-During the day, when the temperature rises again, the ice melts. The process reoccurs repeatedly until the rock breaks apart. The material is then loose and then falls onto the shore
Type of Weathering-Insolation
Thermal fracturing; repeated changes in temperature weaken the rock
Type of Weathering-Salt
Like freeze thaw, but caused by expansion of salt crystals; creates piles of weathered debris called regolith
Type of Weathering-Hydrolysis
In certain rocks with minerals that are reactive to water or chemicals in the water.
-This is where particular minerals break down due to their contact with water leading to loss of rock coherence and structure
Type of Weathering-Oxidation
Occurs on cliff faces and shoreline rocks where iron elements are present within rocks. The ‘rusting’ of the iron content may cause rocks to disintegrate
Type of weathering-Exfoliation
This occurs when the daytime and night-time temperatures are distinctively different on dry rock. During the day, the sun heats up the surface of the rock and at the night the outer layers cool down.
Type of weathering-Biological
On cliff faces, both animal and plant action can loosen large amounts of rock material. Trees and plant roots can prise apart rocks by growing in between the bedding planes and joints enlarging them as they increase in size.
-Equally damaging is when small animals burrow underground and loosen rocks such as sand martians. Microorganisms in the soil are also able to break down the rocks; particularly carbonate rocks
-However, plants soak up water which can prevent saturated soils which are more likely to slump, mass move
Positive feedback in weathering
1) Weathering weakens the cliff
2) Material is picked up and removed by the sea faster than it is deposited
3) This provides material for erosion to use
4) This speeds up erosion and weakens the cliff more
5) Weathering can happen more easy in the future
Negative feedback in weathering
1) Weathering weakens the cliff
2) Material is not picked up by the sea
3) Debris is deposited at the bottom of the cliff
4) This provides a barrier between the sea and the cliff
5) This slows down erosion
6) The cliff is not weakened
How is weathering affecting the Holderness Coast?
Weathering is speeding up the formation of coastal landforms
Weathering causes mass movement> as sediment slumps or slides downhill under gravity
-slumps the coastal landscape as Boulder Clay is prone to weathering
Sub-ariel definition
Weathering above the sea
Run-off definition
Water thats not soaked into the surface
Percolation definition
Downward movement of water within the surface
Sheer strength definition
The rock strength, how likely it is to collapse
How will climate change affect weathering?
Increased chemical weathering due to more acidic rainfall
-Physical weathering is also likely to increase due to more extreme temperatures and variations in temperature and rainfall
-The chalk cliffs at Flamborough head are likely to be attatched quicker by increased chemical weathering from acidic rain but also more acidic oceans due to ocean acidifications
-Chalk cliffs are calcium carbonate
What causes mass movement
Weight of rain water+weak geology
Height reliefs, steep cliffs
Wave action at the base of a cliff undercuts the cliff face
How fast does mass movement happen
Mass movement can range between speeds of being really slow like 1cm per year to horrifyingly fast.
-If debris removal from the base of cliffs is slow this will lead to a build up of debris (scree) that reduces the exposure of the cliff face.
-Weathering and mass movement rates will decrease-negative feedback
Why is mass movement?
Mass movement forms an important group of processes and flows within the coastal system, transferring both energy (in response to gravity) and sediment.
-The sediment forms an important input to shoreline processes, forming the ‘tools’ for erosion and providing materiel to be transported and deposited elsewhere along the coastline
-Mass movement, along with cliff erosion, provides an important input to sediment cells
Type of mass movement-Rockfall
The rapid free-fall of rock from a steep cliff face
-rock fragments fall from face of cliff due to gravity
-weathering freeze thaw action can loosen rocks that become unstable and collapse the slope
-earthquakes can dislodge rocks, hot weather can dry out soil causing it to shrink allowing rocks to fall-forming scree slopes
-EXAMPLE- Pennington Point
Type of mass movement-Rockslide
Occur when rocks or debris become detached and slide downhill ‘en masses’ (together)
-Piles of rock (scree) are common at the base of a rockslide or debris slide.
EXAMPLE- Lake District and Stob Coire, Scotland
Type of mass movement-Mudflow
Occurs on steep slopes over 10 degrees. A rapid sudden movement which occurs that periods of heavy rainfall.
-Where soil becomes completely saturated and turns into a liquid and flows
-occurs when theres a lack of vegetation to hold soil
-saturated soil flows over impermeable sub-soil and endangering lives
-EXAMPLE-Stonebarrow Hill, Dorset (Englands largest landslide)
Types of mass movement-Rotational slip
This is where there are two types of rock.
-a layer that is permeable on top of a layer that is impermeable rock
-when it rains, water soaks through the layer of permeable rock but a layer of water collects between the two layers until the top layer slips
-EXAMPLE-Holbeck hall landslide, Scarbrough
- a hotel collapsed due to 140mm of rainfall and drainage issues
Types of mass movement-Soil creep
Soil creep is a slow but continuous process
-typically exceeds speeds of 1cm per year
-occurs as the result of repeated expansion and contraction of material
-soil creep is a seasonal mass movement therefore changes over time.
-EXAMPLE-Malborough Dons,Wiltshire
Types of mass movement-Runoff
Moves fine material down-hill particularly where overland flow occurs as a thin continuous layer (sheet flow) and washes silt and clay sized particles.
-Occurs during periods of heavy rainfall when there is rapid movement of water over the ground
-water moves and picks up sediment transporting it before depositing it else where
Well jointed rocks definition
Rocks that have many cracks
Scree slope definition
Debris from a cliff at the bottom
Subsoil definition
Soil lower down (often impermeable)
Topsoil deinition
-Soil near the surface (often permeable)
