Sediment flows and earthquakes

Granular flows

In the granular flows, the sediment flows that contain between 0 to 20% water. The fluid-like behavior is given by these flows by mixing with the air. The granular flows are not saturated with water. Granular flow is subdivided into the following types:

• Creep

The very slow usually the continuous movement of the regolith down the slope is the creep. Creep occurs in almost all the slopes but the rates may vary and the evidence for creep is often seen in the bent trees, offsets in roads and fences, and the inclined utility poles.

• Earth flows

The earth flows are usually associated with the heavy rains and move at the varying velocities. They usually remain active for the long period of the time and tend to be narrow tongue-like features that begin at a scrap or the small cliff.

• Grain flows

The grain flows usually flow in the relatively dry material, such as a sand dune, on a steep slope. In this the small disturbance sends the dry unconsolidated grains moving rapidly down the slope.

• Debris Avalanches

The debris avalanche moves with the very high velocity with the large volume mixture of the rock and the regolith from the complete collapse of the mountains slope. They move down the slope and can travel for the considerable distances along the relatively gentle slopes. They are often triggered by the earthquakes and the volcanic eruptions.

• Subsidence

Subsidence is the downward movement of the rock mass without any horizontal motion. Mostly it takes place due to the slow removal of the materials beneath the surface due to the chemical action of the ground water or when the plastic materials overlain by the heavy rock mass. The collapsed area of the surface due to the underground enlargement of the caverns in limestone regions and also sometimes in the mining areas where there is a surface down warping shows the subsidence.

Triggers of the mass wasting

The soil and the regolith that remained on the hill slope only while the gravitational forces are unable to overcome the frictional forces keeping the material in the place. The factors that reduce the frictional resistance relative to the downslope forces and initiate the slope movement include the following factors:

• Seismic shaking
• Increased overburden from the structures
• Increased soil moisture
• Reduction of the roots holding the soil to the bedrock
• Undercutting of the slope by excavation or erosion
• Weathering by frost heap.

Earthquakes

The abrupt and the temporary vibration or the shaking of the surface of the earth due to the release of the energy stored beneath the earth surface in the rocks is called as the earthquake. The shaking of the surface is caused by the passage of the seismic waves originated from the point in the earth’s interior where the sudden and rapid motion has taken place. The earthquake generally lasts from the few seconds to the minute. The larger vibrations of the earthquake cause the loss of the lives and the properties. The branch of the science that deals with the study of the earthquake is known as seismology.

The main point within the earth at which the earthquake originates is called focus and from the focus, the waves of the vibration spread in all the directions. The earthquake wave that first reaches the ground immediately above the focus is called epicenter, where the earthquake is felt first.

During earthquakes, the sudden release of the energy takes place in the form of the waves and the amount of energy that is radiated decreases with the increase of the distance. Since the time of origin, the earth is continually undergoing deformation due to the stress that is set up within it. If the stress continues to build up over the long period of the time, a fracture may take place resulting in an earthquake which tells us that the earthquakes are generally associated with the fault line.

Seismic waves

The outcomes of the elastic deformation of the rock are known as seismic waves. The seismic waves are related to the compression and the shear deformations. It is classified into the following type: