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Classification of mass movement: Topple

Classification of mass movement:Translational slides

1) Geological Structure Influences topples

2) A topple is the forward rotation, out of the slope, it falls through the air.

3) Rock strata have steep seaward dip undercutting by erosion which will led to instability and blocks or material topping seaward

1) At low angles seaward dip will prevent falls

2) Materials tend to slide down the dipslope towards the sea

3)Translational landslides have occurred at Nefyn, Lleyn Peninsula, Wales, along with variety of other landslide types including rotational slides/ slumming flows, falls and debris slides

4) The landslide mass moves along a roughly planar surface with little rotation or backward tilting.

Debris side

Rock Side

Classification of mass movement: Fall

Earth Side

1) Rockfalls, or block falls are rapid form of mass movement common on steep slopes

2) Rock falls may be a single rock, or a mass of rocks, and the falling rocks can dislodge other rocks as they collide with the cliff. Occur on a steep slope

3) On coasts blocks the rock can be dislodged by mechanical weathering or by hydraulic action erosion.

4)Debris falls are similar, except they involve a mixture of soil, regolith, and rocks.

5) Wave cut notches can lead to large falls

6) For example, this is the primary way in which talus slopes are built from frost wedging.

Classification of mass movement:Rotational slides/Slumping

1) Mass movement can occur along a curved failure surface

2) huge masses of material can slowly rotate downslop over periods from days to years

3) Water is crucial in rotational slides

4) This is a slide in which the surface of rupture is curved Concavely upward

Mass Movement

1) Weathering and Erosion is important on many coastlines

2) Mass movement is the main reason why cliff collapse

3) Mass Movement can be classified in a number of ways: Flow, Rotational Slide, Slumping, Translational Slide, Topple, Fall.

4) Rockfalls on coastal cliff can be dramatic and involve large volumes of material.

5) For example, in St Oswald's Bay, Dorset in the cretaceous chalk cliffs mass movement occurred overnight without warning (80-100m long section collapsed taking a section of the South Coast Coastal Path with it.

6) The landslide scar is an area of unvegetated fresh chalk with older vegetated cliff face to the left and right.

7) The debris from rockfall caused the effective coastline to protrude further out to sea than normal

8) A fan shaped talus slope extends down the cliff and into the sea of a broken chalk blocks

Classification of mass movement:Flow

1) They are common in weak rocks such as clay, or unconsolidated sands

2) Flows are landslides that involve the movement of material down a slope in the form of a fluid like heavy rainfall. Materials become saturated and lose their cohesion so they flow downslope

3) When material on a slope becomes saturated with water it makes it much heavier so a debris flow or mud flow may develop.

4) When material is flowing like a slurry of rock and mud, may pick up trees on its route, cars and even houses.

5) The debris flow often blocks streams causing flooding because the path is diverted.

6) As a result flows often leave behind a distinctive upside-down funnel-shaped deposit where the landslide material has stopped moving.

7)An example, of flow landslide is at the A85 road, Glen Ogle, Stirlingshire or the Rest and Be Thankful Pass (A83), Argyll.

Different types of weathering:

Chemical Weathering

Solifluction flow:

Earth Flow:

Debris Flow:

1) This involves a chemical reaction and a generation of new chemical compounds

2)Solution- some minerals like calcium are soluble in acidic water and will dissolve and removed in rainwater

3) Hydrolysis is a breakdown of minerals by the hydrogen and hydroxyl irons in the water. For example, igneous and metamorphic rocks contain feldspar and other silicate minerals.

4)Carbonation- Carbonic acid is formed when dioxide dissolves in rainwater and limestone will be chemically removed. For example, limestone and other carbonate rocks are vulnerable

5) Hydration- Incorporation of water into a crystal structure of a marine can make it easier to degrade by erosive processes

6) Oxidation-the chemical composition of oxygen and with a mineral making it easier to separate to have a mechanical breakdown for example, sandstone, siltstone and shale all contain iron compounds that can be oxidized.

Key Terms

Biological Weathering

1) Speeds up mechanical or chemical weathering through action of plants, bacteria and animals

2) Rock penetration roots may penetrate crevices and physically shatter rocks

3) Plant roots grows in cracks and fissures forcing rocks to split apart. This is important process on vegetated cliff tops it makes it vulnerable which contributes to rock fall

4)Rock boring this is when many species like clams or molluscs bore into rocks and may also discharge chemicals which dissolve rocks

5) Humic acids and Carbon dioxide are produced by soil organisms and chemically attack rock material

6) Sedimentary rocks and carbonate rocks like limestone are vulnerable to rock boring located in the inter-tidal zone

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1) Weathering this is a breakdown of rocks by chemical, mechanical and biological elements.

2) Weathering is influenced by the weather, climate conditions like global warming, extreme temperature, rainwater and biological activity

3) No rock material is removed

4) Weathering process can affect landscapes and can also influence human interaction to the landscapes

5) Weathering contributes to rates of coastal recession in a number of ways by making the rock more vulnerable by weakening it to Erosion or mass movement.

6) Some strata may be more vulnerable then others creating the formation of wave cut notches and affecting cliff stability

7)Rates very slow, even when its hot and wet climates igneous rock weathers at rate of 1-2 mm every 1000 years

5) Rocks are worn away and not eroded

6)Erosion is the breakdown of rock due to the action of some external forces such as wind, waves, flowing water and ice flow

7) Eroded material transported to a new location

8)If water is muddy could be a sign erosion is taking place or if its a brown color indicates bits of rock and soil (sediment) are suspended in the water

Mechanical weathering

9.3 Sub-aerial Processes

1) This breaks down rocks due to exertion of a physical force and does not involve any chemical change

2) Freeze- Thaw this is when water in pores and cracks freeze which exerts a force within cracks and fissures which causes the underlying rock to expand and fracture.

3)This cycle repeats and the pressure forces cracks open and loosens the rock.

4) Any rocks with cracks and fissures can be affected

5) freezing is uncommon in UK coasts especially in south and salt spray can reduce its impact

6)Temperature change can cause the minerals inside rocks to contract at different rates causing lines of weakness and fracturing.

7)Salt Crystallisation is the growth of salt crystals in cracks and pore spaces can exert a breaking force which is less than freeze thaw

8) Porous and fractured rocks like sandstone are vulnerable

9) The effect is greater in hotter, drier climates where evaporation and the precipitation of salt crystals in more pronounced

10) pressure release is when overlying rocks is removed and the release of pressure causes the underlying rocks to expand and fracture

By Zara P.

Rotational slides

Features of Rotational Slides

1) This type of mass movement is difficult to manage because it has multiple causes

2) It can lead to failures deep within the cliff and move large volumes of material

3) They are usually very slow and not sudden and are experienced at St Oswald's Bay

4) Permeable strata like clay and sandstone sit on impermeable strata like clay and mudstone. This rock arrangment is common along south coast of England and can be found in Folkestone, Lyme Bay and Christchurch Bay

5) Can also occur in the glacial boulder clay of the holderness Coast in the East Riding in Yorkshire and on the Norfolk Coast

1) The bedding plane between impermeable clay and permeable sand dips seaward which promotes mass movement

2) Cracks develop in the cliff top when soil and sediment dry out and rainwater can travel through these. Heavy rainfall saturates the permeable sands loading the cliff material.

3) Water percolates through the permeable sand but is forced to move along the sand and clay boundaries this creates internal pressure within cliff because of the high pore water pressure

4) Toe erosion is caused by marine processes which undercuts the cliff from below which makes it more unstable

5) the curved failure surfaces develop in the sand and the whole cliff rotates about a pivot point

6) Rotational slides produce characteristic cliff profiles on the cliff wall.

7)An example of a rotational landslide is the Holbeck Hall landslide, in Scarborough North Yorkshire, England. The 1 million tonnes of cliff failed as a rotational landslide in June 1993 in a couple of days the cliff top was destroyed including this hotel.

Successive rotational slides

Single rotational slide

Multiple rotational slide

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