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Destabilization of Cliffs depends on the Material that Makes Up the Cliff
Sea action includes waves, wind, and tide action that can cause erosion at the base of cliffs. This is the starting point for the destabilization of the cliff. This undercuts the cliff and starts other sliding collapses, which are determined by the nature of the cliff materials and their geotechnical properties. Weathering action is further helped by the wind transport of sand which is quite common in seaside areas.
If the cliff is of material that is non-cohesive and of rock, this collapse of the upper layers could cause the formation of talus or a collection of materials at the foot of the cliff. This in itself may act as a protection for the eroded base and reduce the effect of wave action or storm surge and the cliff may get stabilized without any further action being needed.
Cliff material that is a mixture of sand, clay, silt, and rock will maintain quite steep slopes before becoming destabilized, and can deteriorate with the increase in water pressure due to ground water from the land area above the cliff. This is further aggravated in wintry conditions when the water can freeze and cause greater pressures.
Cliffs which consist of clay and silt, which is more plastic, can get destabilized when conditions are created that can cause slides of entire swathes of the material.
Image Source: Wikimedia: Cliffs
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Rocky cliffs get stabilized to some extent by the formation of talus but the stabilization can be further helped by drilling of long anchors into the rock face and grouting the same with cement. If the rock is fissured to a large extent, a steel mesh can be use to cover the face of the rock, with the mesh being held again by anchors into the rock. Such mesh may however require constant maintenance in areas exposed to sea air. Prevention of erosion can be done with the use of groynes or additional material like tetra pods at the base of the cliff, which can reduce the effect of waves.
Artificial smoothing of slopes is the best method of stabilizing cliffs made of other material than rock. These slopes have to have a gradient lesser than the angle of repose of the soil for the best effect. This angle of repose further reduces where water content in the soil is high and may have to be accompanied by cliff dewatering. This can be done by creating horizontal or vertical drains that reduce the effect of water runoff. Cliff stabilization on such slopes can be helped by the growth of vegetation cover in the form of shrubbery that can hold the soil together. Addition of granular material at the base of the cliff can help stabilization by preventing further erosion that had started the destabilization process in the first place.
Cliff stabilization is possible only when there is sufficient place at both the base and land above the cliff. This may not be possible in areas where there is development close to the cliff. Here the remedies available for cliff stabilization may have to include more costly solutions like retaining walls.
Image Source: Wikimedia: Cliffs