9.2: mass movement

Question 1

mass movement

Answer 1

mass movements are large scale movement of Earth’s surface not accompanied by a moving agent such as a river, glacier or ocean wave

Question 2

weathering

Answer 2

the decomposition and disintegration of rocks in situ

Question 3

aggradation

Answer 3

to build up a surface or soil through the addition of material such as mass wasting deposits

Question 4

geology

Answer 4

the study of rocks

Question 5

degradation

Answer 5

the wearing down of the land by the erosive action of water wind or ice

Question 6

geological structure

Answer 6

the arrangements of rocks in the Earth’s crust: strata, bedding planes, joints etc

Question 7

regolith

Answer 7

the layer of unconsolidated material covering the bedrock of a planet (soil)

Question 8

aspect

Answer 8

the direction in which a slope faces

Question 9

name three factors which can reduce shear strength

Answer 9

1. water –> loss of grain to grain contact, reducing the cohesion of soil
2. earthquakes and the movement of trees cause vibrational shock
3. burrowing of animals and other biological weathering of roots

Question 10

name three factors which can increase shear stress

Answer 10

1. weathering processes such as freeze thaw, dilatation and hydration can increase stress through lateral pressure
2. water –> increase in pore water pressure as well as adding to the weight of the slope
3. increasing weight by adding vegetation or accumulation of debris eg slag heaps when mining

Question 11

what are slumps

Answer 11

weaker rocks such as clays ‘slump’ with a rotational movement along a curved slip plane

Question 12

explain the key characteristics of a slump

Answer 12

clay saturated with water and minerals expand. the lubrication of slip plane causes a series of material slumps, along curved slip plane. Commonly occurs if the base has been undercut. This can be gradual or sudden separate, jerky events. This can leave a crescent shape scar on the slope.

Question 13

what is a flow

Answer 13

more continuous, smoother form of slump. Occurs in deeply weathered clay, and if particle size is the same or smaller than a grain of sand

Question 14

define a mudflow

Answer 14

fine grains mixed with water, slowing down a channel. Accumulates material down the slope. Faster than earthflows (which are deeper and thicker)

Question 15

define debris flow

Answer 15

loose mud, sand and soil saturated with water. Larger than mudflows, accumulating material as it travels. Its higher water content allows flows to occur on shallow slopes and can occur on saturated toes of a landslide or as a separate event. This can create a scar, flowtrack and toe lobe

Question 16

explain the key characteristics of falls

Answer 16

occurs on steep slopes greater over 40 degrees with bare rock faces and exposed joints. rocks detach and fall freely under gravity. Short fall = straight scree; otherwise a concave scree is produced. Significantly contribute to the retreat of steep rock faces and providing debris for scree/talus slopes. This can create a steep back wall and a lower scree slope

Question 17

define a slide

Answer 17

when an entire mass of material moves along a slip plane - internal structure is maintained