1. What different weathering processes have occurred here?
Haytor, Dartmoor © Herbythyme 2007 ©

2. Weathering and Mass Movement
2B.6 a Weathering (mechanical, chemical, biological) is important in sediment production and influences rates of recession.
2B.6b Mass movement (blockfall, rotational slumping, and landslides) is important on some coasts with weak and/or complex geology.
2B.6c Mass movement creates distinctive landforms (rotational scars, talus scree slopes, and terraced cliff profiles).

3. Sub-aerial processes
Sub-aerial process are land based processes which alter the shape of the coastline. These are a combination of weathering and mass movement (we learnt this on the field trip).
Weathering - Weathering is the decay and disintegration of rock in situ (close to the ground).  There are three main types of weathering that affect the coast. These are mechanical, biological and chemical weathering.
Mass movement – The movement of weathered material down slope due to gravity.

4. Task
Attempt to complete the worksheet on weathering.

5. Mechanical (physical) Weathering
Mechanical or physical weathering is the fracture and breakdown of rocks into fragments.  Along the coast it may be caused by frost shattering (freeze-thaw), salt crystallisation, wetting and drying, or even biologically.
Mechanical weathering refers to physical processes such as  freeze-thaw  and biological weathering. Freeze-thaw occurs when water gets into cracks in rocks and freezes. This then expands by around 10%. The repeated freeze thaw action  puts pressure on the rocks until they eventually crack and break the rock. Freeze-thaw usually occurs when the temperature oscillates around freezing point. The shattered angular fragments of rock accumulate around the base of the cliff as scree (talus). As coastal climates tend to be milder this process is only really effective during very cold winters.
A common type of mechanical weathering found at coasts is salt crystallisation. This is when salt crystals are deposited in cracks and over time the salt accumulates and applies pressure to the crack (similar to freeze-thaw weathering).
Wetting and drying is common along coastlines. Clay rich rocks are prone to expand when they are wet and contract when they dry. This results in cracks which are vulnerable to both freeze-thaw and salt crystallisation.

6. Biological Weathering
Biological weathering is mechanical when there is a physical effect. An example of this is when growing plant roots widen cracks as does the leverage created by bushes and trees swaying in strong winds. Burrowing animals and nesting birds excavate material in partially weathered and eroded cliffs.

7. Chemical Weathering
Chemical weathering involves decomposition of rocks (literally, changing the minerals). Chemical weathering occurs as a result of a weak chemical reaction between water and rock. eg. with limestone. Rainwater mixed with carbon dioxide in the atmosphere forms Carbonic acid. This then reacts with calcium carbonate in limestone to form calcium bicarbonate. Bicarbonate is soluble in water and the limestone gets weathered when carbonation occurs.

8. Task
Having now seen the previous slides, check your worksheet on weathering.
How did you do?

10. Mass Movement Copy the following table
This will all depend on angle of cliff slope, rock type, vegetation cover and how wet the ground is.
Nature of movement
Rate of movement
Type of mass movement
Flow
Imperceptible (very slight)
Soil creep
Solifluction
Slow to rapid
Mudflow/Earthflow
Slide
Rock fall (debris fall)
Rock slide (Debris slide)
Slump

11. Mass movement
Complete the mass movement worksheet by annotation your diagrams.

12. Flows
Soil Creep – this is the slowest form of mass movement but it’s almost continuous.
Individual particles of soil move downhill.
Solifluction
lobes
Solifluction – Movement is 5cm to 1 m per year.
Occurs in areas of permafrost (tundra area). The top layer of soil thaws in the warmer summer but layer below remains frozen (permafrost). The surface layer becomes saturated as frost melts and flows over the subsoil and rock below.

13. Flows
Mudflow/Earth flow – Heavy rain causes a reduction in friction and thus earth turns into mud and flows slowly over the bedrock.
The material will become all jumbled up and flow down the cliff.
Lobe

14. Slides
Rock fall – Occurs when mechanical weathering like freeze-thaw break large chunks of the cliffs away.
Cliff has to be at an angle of 40 degrees or more.
Material that breaks off is called scree and bounces down the cliff to the bottom.
Rock/debris slide – Rocks that are jointed or have bedding planes parallel to the slope are susceptible to landslides.
Again, increase in water can reduce friction and make this easier.
Slabs of rock with slide over the underlying rock, called a slip or plane.

15. Slumps These occur in saturated conditions.
The difference between sliding and slumping is that there is a rotational movement (Walton-on-the-Naze is an example).
These occur on moderate to steep slopes.
Clays or sand overlying more resistant rock or impermeable rock like limestone or granite.
Slumping causes rotational scars.
In can repeat, forming a terraced cliff.

17. Holbeck Hall
Homework – Research Holbeck Hall, it’s location, what happened to it, and what it was like before and now.