WHAT IS LANDSLIDE ?
The term ‘landslide’ includes all varieties of mass movements of hill slopes and can be defined as the downward and outward movement of slope forming materials composed of rocks, soils, artificial fills or combination of all these materials along surfaces of separation by falling, sliding and flowing, either slowly or quickly from one place to another.
TYPES OF LANDSLIDES
The common types of landslides are described below.
Falls:
Abrupt movements of materials that become detached from steep slopes or cliffs, moving by free-fall, bouncing, and rolling. Flows General term including many types of mass movement, such as debris flow, debris avalanche, lahar, and mudflow.
Creep :
Slow, steady downslope movement of soil or rock, often indicated by curved tree trunks, bent fences or retaining walls, tilted poles or fences.
Debris flow :
Rapid mass movement in which loose soils, rocks, and organic matter combine with entrained air and water to form slurry that then flows down slope, usually associated with steep gullies.
Debris avalanche :
A variety of very rapid to extremely rapid debris flow.
Lahar :
Mudflow or debris flow that originates on the slope of a volcano, usually triggered by heavy rainfall eroding volcanic deposits, sudden melting of snow and ice due to heat from volcanic vents, or the breakout of water from glaciers. crater lakes or lakes dammed by volcanic eruptions
Mudflow :
Rapidly flowing mass of wet material that contains at least 50 per cent sand, silt, and clay-sized particles.
Lateral spreads :
Often occur on very gentle slopes and result in nearly horizontal movement of earth materials. Lateral spreads usually are caused by liquefaction. where saturated sediments (usually sands and silts) are transformed from a solid into a liquefied state, usually triggered by an earthquake.
Slides :
Many types of mass movement are included in the general term “landslide.” The two major types of landslides are rotational slides and translational landslides.
Topple :
A block of rock that tilts or rotates forward and falls, bounces, or rolls down the slope.