Rockslides are a common phenomenon in most of the high mountains. This type of slide occurs when solid rock is detached from its surroundings. The topographical features produced by rockslides are talus cones, and slopes located near the base of bare mountain slopes.
These slides cover very large area of the valley floor, and involve several million cubic meters of rock.
Rockslide consists of boulders of varying size which are scattered in an irregular manner over the region. Sometimes such slides dam a river valley and create a temporary lake.
Earth-flow results when the moisture content of moving material is high. This is also the case in mudflow. Due to heavy rains the barren mountain slopes are often saturated, and debris lying on the saturated slopes starts moving downhill.
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Earth flows are usually accompanied by slumping. Slumping refers to a mass of rock or superficial material that becomes detached from a hillside along a slip plane and moves down-slope often as a rotational slip.
Earth flow results from slope instability, perhaps due to human interference (removal of vegetation and undercutting of slope). It can also occur on any steep slope after there has been a period of heavy rainfall, especially when the underlying rocks are impermeable.
As regards mudflow, the greater the liquid content and the finer the soil particles, the further the flow will extend. The materials of the flow form such topographic features as irregular hummocks, ridges etc. which appear as ground moraines.
Soil creep is much more pronounced in temperate and cold humid regions. Open, porous soils, especially those that contain rounded grains and those that take up water easily are more susceptible to creep.
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A persistent mass movement of surface soil is called soil creep. In soil creep, individual soil particles are lifted and disturbed by the expansion of soil moisture as it freezes, by cycles of moistness and dryness, by daily temperature changes, or even by grazing livestock or digging animals.
In the freeze-thaw Moved cycle, particles are lifted at right angles to the slope by freezing soil moisture. However, when the ice melts, particles are pulled straight downward by the force of gravitational pull.
As the process is repeated, the soil cover gradually creeps its way down-slope. Despite various measures to check the mass movement of slope material such as grading the terrain, building terraces and retaining walls, planting ground cover; the soil creep persists.
Thus, the principal causes of soil creep are gravity, soil moisture, drying and cracking of the ground, wedging by roots, and particularly frost. Water in the soil lubricates it and aids gravity in moving it downhill.