When a lot of soil, rocks and other stuff slides down a hill it is called a landslide. Landslides are caused by rain and melting snow that goes into cracks in the earth on top of a mountain or hill. Then the earth is weakened because the water makes the soil loose. Landslides can also be caused by erosion. Erosion is when things like a river or mining slowly eats away the bottom of a hill or slope. The top of the hill is no longer supported by the bottom. The loose soil can be set off by things like mine explosions, thunder, traffic noise, earthquakes, machinery, ice etc. If the soil or rocks are weak enough any of these things could start a landslide.
Types of Landslides
There are three different kinds of landslides: falls, slides and flows.
A rockfall is rocks that break off steep cliffs and fall because they have been loosened by frost or ice. When they hit the ground, if there is a slope, the rocks start rolling down the hill and become a rockslide.
A rockslide is large rocks that break off the top of a hill and slide down. This can happen after heavy rains or in an area where lots of trees were uprooted. The roots of the trees are important because they hold the rocks and soil in place.
A mudflow is a watery kind of landslide made of a mixture of soil and water. It usually happens after heavy rains and can go as fast as 90 km/hr.
Where Most Common
Landslides are most common in the United States and the Rocky mountains. Between 25 and 50 people die each year from landslides in the United States.
Vaiont, Italy, 1963
One of the world's highest arch dams was built in Vaiont, Italy in 1960. Three years later, at 10:41 pm on the night of 9th October, millions of tons of rock slid down from Mount Toc into the Vaiont reservoir. It went across the reservoir and came back and made a 100-metre high wave. The wave went over the 262-metre high dam and into the valley below.
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