Landslides
A landslide is a geological event, in which the top layer of earth on the side of a hill or mountain becomes loose and moves downwards. Although gravity is the main force behind a landslide the side of a hill or mountain can become unstable due to many factors:
- sinking groundwater
- loss of vegetation
- movement of glaciers
- heavy rain
- earthquakes
- volcanic eruptions
- erosion by rivers and waves
All of these events can cause parts of a slope to break off and move.
Landslides can also be caused by humans through
- deforestation
- more and more traffic
- construction work
- changing of the landscape due to mining
- overgrazing
- building new settlements
Landslides can occur slowly, hardly noticeable over a period of years. Creep is the slowest movement of land. It is so slow that special instruments must be used to measure the speed of land movement, which is often only a few cm a year. However, sometimes rock and mud move down slopes at tremendous speeds
Mud flows are common forms of landslides. They occur after heavy rains, when the soil is saturated with water so that it cannot seep into the ground. Such a landslide can destroy everything that is in its way, including houses, cars and bridges located at the foot of a slope. Many happen in alpine areas, where mud flows block rivers and lead to the flooding of whole valleys.
In other cases, where rain does not play an important part, rocks can loosen themselves and trigger a landslide. If slopes start moving in oceans they can cause tsunamis that may hit regions thousands of kilometres away.
About 8,000 people are killed by landslides around the world every year. They often occur without warning and can travel for many miles before they come to a standstill.
Although landslides cannot be avoided there are measures that can be taken to limit their damage or slow them down. An exact mapping of an endangered area and the right land management can reduce the dangers. Reforestation after cutting down large areas of a forest can also help prevent landslides.
