How does Mass Movement affect a slope's shape & characteristics?

  • Created by: Max Oscar
  • Created on: 09-04-22 10:08

What you need to know!

Different parts of a slope have specific names:

- Crest

- Cliff/freeface/scarp slope

- Talus scree slope/debris slope

- Knickpoint

- Pediment

When describing the 4 types of mass movement:     Creep/heave, Slide/slump, Flow, Fall

You need to know how each affects the shape of slope

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How do Heaves affect slope shape & characteristic

Heave is thought to be responsible for the small ridges across hillsides known as terracettes.

This makes the slope more ridged/stepped & less steep

If the heave meets an obstacle such as a fence it tilts it as the ground moves slowly downhill from underneath it.

e.g. Creep on Milk Hill, Wiltshire in the UK has resulted in terracettes down the valley

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How do Flows affect slope shape & characteristics

Flows can have a significant impact on slope characteristics and shape

For example:

It can carve out a large hollow, which both increases and decreases the angle

It can form a track (an eroded path along which the flow has moved)

It forms an elongated area to the slope (the toe) where the flow has made the slope longer

e.g. Maokong, Taiwan, 2008

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How do Slides effect slope shape & characteristics

Influence on slope shape:

Planar slope failure (rare but occurs in well-bedded rocks like sandstone):

- Mass movement along a slip plane where bedding planes are parallel to the angle of the slope.

A large section of slope (i.e. the block) moves downward in a block leaving behind a slip plane which is a large area of under soil exposed by the moving block called a scar. The block forms a mound lower down the slope. The slope is more gentle sloping.

A scar = a slip plane left behind by the downward movement of a block in which a large area of under soil is exposed by the moving block

A large section of the slope slides & moves backwards at the same time causing a backward tilting block which forms a feature called a terrace. With several rotational slumps in a row there will be a sequence of terraces called steps. The area exposed by the slump is called a scar. The slope is more gentle sloping.

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How do Falls affect slope shape & characteristics

The top of the slope forms a steep free face (a straight element of bare rock)

Rockfalls produce scree (talus) which accumulates as cones or fans at the base. This results in busal concavity (the base of the slope has a concave shape).

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