mass movement and slope development Flashcards
what is mass movement
all downhill movement of regolith in response to gravity
regolith?
looses uncemented mixture of soil and rock particles that cover the earths surface
what is soil creep? and explain 2 ways in which it occurs
soil creep is the slowest downhill movement with less than 1cm per year on slopes +- 5degrees
- wet dry periods - heavy rainfall increases weight of soil causing expansion downhill. following dry period , soil dry out and contracts
- Freeze Thaw - regolith freezes, ice crystals in soil increases volume , ground later thaws and lifted particles fall vertically down slope
solifluction
slightly faster movement at 5cm - 1m per year, occurs in periglacial conditions, in winter bedrock and regolith are frozen, summer causes surface layer to thaw but bedrock remains frozen, surface becomes saturated and moves downslope as an active layer
Earthflows
moves 1 - 15km per year on slopes 5 - 15 degrees, regolith saturated by water so moves downhill, may produce flow tracks which are tounge like shaped
mudflows
rapid movement at +- 1km/hr on steep slopes, following periods of intense rainfall , where both volume and weight are added to soil giving it higher water content than earthflow
difference between slides and flows
slides do not suffer internal derangement and move en masse
name 3 types of slides
planar landslide, rotational landslide, rockfall
slope decline
in humid climates, steepest slopes at the beginning of process, angle continues to decrease in time to give a convex upper slope and concave lower slope
slope replacement
in tectonic areas, maximum angle decreases as the gentler lower slopes erode back to replace steeper ones giving a concave central portion to the slope
parallel retreat
in semi arid landscapes, sea cliffs and wave cut platforms, maximum angle of slope remains constant as do all slope facets apart from the lowest one that increases in concavity
how does rock structure effect slope development
areas of bare rock are vulnerable to mechanical weathering and some chemical weathering processes
areas of alternating harder more resistant rock and softer less resistant rock is likely to experience movement