What kind of natural hazard is a landslide?

Answer 1

Landslides are, in general, the failures of slopes to hold their shape. (The slopes can be on land or under water.) Naturally unstable material in the slope can fail spontaneously, and the landslide can occur. The landslide can be triggered by earthquakes or even a tremor, which is probably the most common cause. A blast (mining or construction) can also trigger a slide. The stability of the slope will determine how much of a "jolt" will be needed to create a landslide.

Just the weight of additional material on the slope can cause a slide, and anything that "upsets" the surface, such as the actions of plants or just "moving things around" in a landscaping or grading project can cause a slide.

If we do things to the slope to change it internally and modify the structure, we can cause a slide. Water can seep into the ground during heavy rains and saturate the sublayers of the slope and cause it to fail to stay together. This happens frequently. Scientists currently believe that future climates in North Western Europe will see increases in summer temperatures and also increases in the intensity of rain fall events. These two factors could both act to reduce the stability of slopes in the future and contribute to the increased occurrence of landslides and is a major research topic in civil engineering at the present time. The mechanisms that cause this instability are described in a little more detail below:

The phenomena of slope instability and land slides is in part caused by the shrink and swell cycles that occur in clay soils as you add and remove water. So in the summer if you have prolonged dry warm periods, you get high evaporation from the soil surface leading to the loss of moisture causing it to shrink and crack. This in turn increases the vertical permeability of the soil, so when you get a wet spell, the water can infiltrate very quickly to a deeper level in the soil slope than would otherwise occur. This causes the soil to swell again and at a greater depth. These seasonal volume changes cause the soil to soften (it's stiffness or the amount it deforms under a given load decreases) over time.

The presence of soil water also increases something called the pore water pressure - this is related to the fact that water is relatively incompressible so acts to push the soil grains apart. This decreases the soils strength. This reduction in strength due to the pore water and the reduction in stiffness due to volume changes can contribute very significantly to slope failures and land slides.

It is possible to destabilize a slope by heating it or introducing other materials from below, all of which volcanism can do.

There are some other factors that can cause or contribute to a landslide, and Wikipedia has a great post on this phenomenon where you can gather additional information. There is also a very dramatic video showing a rainfall induced landslide that occurred in San Fratello in Sicily in February 2010.

Please see the related links below.

Answer 2

Natural factors

1. Intensity of rainfall
2. Steep slopes
3. Stiffness of slopes
4. Highly weathered rock layers
5. Soil layers formed under gravity
6. Seismic activity
7. Poor drainage

Answer 3

There are 3 things that trigger a landslide,a earthquake,heavy rains,erosion.

Answer 4

earthquakes

excessive rain (technically a mudslide)

Answer 5

There are many triggers.... gravity, rain, snow and wind being the commonest causes.