Question

What is rock instability, sliding blocks and give the types of land slides.

Answer 1

At first we have to understand what is rock instability

Rock instability:- Rock-intability or mass-movement problems occur where either sediment and/or rock and/or snow move downslope in response to gravity. Potential slope-stability problems exist wherever development has taken place at the base of steep slopes.

Landslide:- the movement downslope of a mass of rock, debris, earth, or soil (soil being a mixture of earth and debris). Landslides occur when gravitational and other types of shear stresses within a slope exceed the shear strength (resistance to shearing) of the materials that form the slope.

Types Of Landslides:-

Landslides are generally classified by type of movement (slides, flows, spreads, topples, or falls) and type of material (rock, debris, or earth). Sometimes more than one type of movement occurs within a single landslide, and, because the temporal and spatial relationships of these movements are often complex, their analysis often requires detailed interpretation of both landforms and geological sections, or cores.

now the classification...

SLIDES:-A slide, in the strictest sense, is characterized by failure of material at depth and then movement by sliding along a rupture or slip surface. If sliding is on a predominantly planar slip surface then the slide is called a block slide. If movement is on a curved slip surface then the slide is called a rotational slide. A lot of rotational slide end up as a mudflow leaving a gaping hole in the ground where the slide began. Debris from the slide is strewn down a torrent track along which the mudflow travelled to the base of the slope or where the flow path widens and dissipates. A rotational slide with one or more curved slip surfaces where the movement of material is incomplete, leaving individual slumped blocks, is referred to as a slump.Slides are probably the most common and overall possibly the most destructive type of landslide to hillside developments. Wherever steep mountains or hillside slopes occur or are altered, the possibility of large landslides and consequent disasters exist.

FLOWS:-Flows involve the deformation of an entire soil mass that then flows downslope as a viscous or sticky fluid. Deformation may be due to a high soil water content or seismic shaking that leads to liquefaction and thus generates such a fluid flow. The slopes need not be very steep. Two types of flow can be recognized; if the downslope movement is very slow then is an earthflow, if it is very rapid it is a debris flow or as it is sometimes known, a mudflow.

FALLS AND TOPPLING-A rock-fall is the abrupt free fall or downslope movement, (rolling or sliding) of loosened blocks or boulders of solid rock. It differs from a slide in that free fall is the main type of movement and no marked slide surface develops. This type of slope failure occur in caverns and along steep gorges, sea cliffs and steep road cuts through unstable bedrock. The bedding, jointing and fracturing of the bedrock are the important factors affecting slope stability. The effects of weathering, such as the freezing of water in joints (in cold countries), the pressure of water in fissures, and root pressures may initiate failure in the weak rocks. A rock fall, as in most landslides, is usually the result of a combination of factors. On a sea cliff it could be due to a combination of jointing patterns, percolation of surface water, wedging of tree roots and the impact of and undercutting by waves. Thus a lot of rock-falls along sea cliffs occur during storms when much rain percolates through cracks in the rock and the pressure pushes the blocks over or when heavy surfs strike the cliff causing vibrations and thus causing undercut cliff faces to topple over. The magnitude and scale of rock-falls varies from the breaking off of isolated small rocks to the fall of enormous masses. Largescale failures have been known to dam rivers, creating lakes and destroying parts of towns. On a small scale, the talus commonly found at the base of cliffs and also at the base of slopes in mountainous area is the accumulation of numerous rock-falls over many years

Spreads:-

"Spread is defined as an extension of a cohesive soil or rock mass combined with a general subsidence of the fractured mass of cohesive material into softer underlying material.n spread, the dominant mode of movement is lateral extension accommodated by shear or tensile fractures.