mass movement

Question 1

what is mass movement

Answer 1

downslope movement of rock and soil
-umbrella term for a wide range of specific movements

Question 2

what are the specific types of mass movements

Answer 2

-landslide
-rockfall
-rotational slide

Question 3

4 main influences on mass movement

Answer 3

-size of the sediment
-water content in the slope (pore water pressure)
-vegetation cover
-height and angle of slope (dip)

Question 4

what is pore water pressure

Answer 4

• pressure exerted by water within the pores of a soil, rock, or sediment

Question 5

what is fall

Answer 5

-rapid form of mass movement
-blocks of rocks dislodged by mechanical weathering or by hydraulic action
-undercutting of cliffs by creation of wave cut notches

Question 6

what is topple

Answer 6

-where rock strata have very steep seaward dip, undercutting by erosion will lead to instability of blocks of material toppling seaward

Question 7

what influences topple

Answer 7

-geological structure

Question 8

what influences translational slide

Answer 8

-very low angle seaward dip in strata prevents falls
-material slides down the dip slope towards the sea

Question 9

what is rotational slide/slumping

Answer 9

-occur along curved failure surface
-huge masses of material slowly rotate downslope over periods
-water plays important role

Question 10

what is flow

Answer 10

-common in weak rocks
-materials become saturated, lose cohesion and flow downslope
-saturation because high tides and heavy rainfall

Question 11

what are the stages of rotational slides

Answer 11

-bedding plane between impermeable clay and permeable sand dips seaward
-cracks develop in the cliff top during hot weather as soil and sediment dries out creating routes for rainwater
-heavy rain saturates permeable sand, loading cliff material
-water percolates through permeable sand and forced to move along sand/clay boundary as clay is impermeable
-high pore water pressure in sand creates internal pressure in cliff
-toe erosion by marine processes undercut cliff
-curved failure surfaces develop in sand and whole cliff rotates about a point

Question 12

types of mass movement

Answer 12

-fall
-topple
-translational slide
-rotational slide
-flow

Question 13

difference between rotational and translational landslides

Answer 13

-rotational = downward and outward movement of a mass on top of concave upward failure surface
-translational= slides downwards and outward on top of an inclined planar surface