Mass Movement.
“Transfer of mass of rock debris ,down the slopes under the direct influence of gravity"
- Active in weathered slopes rather than over unweathered materials
- Weathering aids mass movements
- But its not a prerequisite for mass movement
- NO ,geomorphic agent participates in mass movements
What favours Mass movement ?
- Faults
- Steeply dipping beds
- Vertical cliffs
- Steep slopes
- Abundant precipitation
- torrential rains
- Scarcity of vegetation ..,etc
Causes precede mass movements.
- removal of support from below to materials above through natural or artificial means;
- increase in gradient and, height of slopes;
- overloading through addition of materials naturally or by artificial filling;
- overloading due to heavy rainfall, saturation and lubrication of slope materials;
- removal of material or load from over the original slope surfaces;
- occurrence of earthquakes, explosions or machinery;
- excessive natural seepage;
- heavy drawdown of water from lakes, reservoirs and rivers leading to slow outflow of water from under the slopes or river banks;
- Indiscriminate removal of natural vegetation.
Mass Movements - 3 Forms
- Heave
- Flow
- Slide
Slow mass movements:
1.Creep
- Cannot be seen .For Instance, poles on roads will bend overtime due to creep
Based on Materials involved,
- Soil creep
- Talus Creep
- Rock creep
- Rock glacier creep
2.Solifluction
"Flowing Soil mass/fine grained rock debris"
- lubricated with water
- Location : Moist temperate Areas
Rapid Movements:
1.Earth Flow
"Movement of water, saturated clayey earth materials down low angle terraces”
- Rocks also may slide
2.Mud Flow
“Looks like Stream of mud ,within a valley Occurs in the absence of vegetation with huge rainfall”
- Very destructive
- Location: Frequently near volcanoes
3.Debris Avalanche
“Similar to snow avalanche"
- Much faster than mudflow
- with / without vegetation cover
4.Land Slide
- Dry material involves
Size and shape of detached mass depends on nature of
- Discontinues in rock
- Degree of weathering
- Steepness of slope
5.Slump
“slipping of one/several units of rock debris with a backward rotation with respect to slope “
6.Debris Slide
“Rapid rolling /sliding of earth debris without backward rotation of mass”
7.Rock Slide
“Slide of individual rock masses down bedding surfaces”
LandSlides/Debris avalanche occurs frequently in himalayas,But western ghats doesn’t frequently?
Because,
Himalayas :
- Tectonically active
- Mostly made of sedimentary rocks .unconsolidated & semi consolidated deposits
- Slopes - very steep
western ghats:
- tectonically stable
- Made of very hard rocks
but,still, debris avalanches and land slides occur though not as frequently as in the Himalayas, in these hills
- Almost vertical cliff escarpments
- Heavy rainfall but overshoot periods
- Mechanical weathering ,due to temperature changes
So there is almost direct rockfall quite frequently along with land slides and debris avalanches