Landslides & Mudflows
It should come as no surprise that steep mountain ranges like the Alps, the Carpathians, the Himalyas, the Andes and the Rocky Mountains are severely affected with rock falls and landslides, as they have been formed by colliding tectonic plates and bedrock movement is common along fault lines. When the mountains are shook by quakes rocks break loose. So living and building in high mountains always involves a risk of rock fall and landslides.
Another cause of landslides is melt-water. At the annual melting of snow and ice in the Himalayas the rivers transport the debris to the sea where it deposits it as thickening sediments. Landslides and rock falls are most common in spring and during the wet season.
The steep mountains of Rio de Janeiro are a well-known place for landslides. During the rainy season moisture-laden clouds move in from the South Atlantic, rise in the mountains, cool off and deposit their water on the Rio inhabitants, often causing floods and even more often landslides. Our database TRITON contains detailed information on more than a thousand landslides in the city of Rio de Janeiro since 1896. 1971–1984 wasdry years and Rio only experienced one slide. Many slides were experienced in 1947, 1966, 1967, 1986, 1988 (160 slides), 1989, 1995 and 1996 (186 slides!). All of these years January saw heavy rain (sometimes 1000 mm) and the worst slides happened in February when the rain fell on water-laden slopes. 1966 and 1996 were the rainiest years in Rio during this period. With long time series of observations it is possible to calculate exactly the amount of rain that must fall before a slide is triggered. Rio has a perfect warning system for landslides. With pinpoint accuracy GeoRio can warn the city quarter at risk, usually a shantytown on a mountainside.
In the Pacific area typhoons and tropical cyclones can carry great volumes of water that fall when the typhoon reaches a colder landmass like Japan, Korea, eastern China or the Philippines. The cloudbursts saturate the earth and landslides automatically follow. Just like in Rio, Japan has well-developed warning systems. The key, as always, is a long series of observations and careful analysis of how the landslides happened.
A special type of mass movements is the lahars, that can happen during but also after volcanic eruptions. These are very common in Indonesia and Japan, in the Philippines and on all high volcanoes in western South, Central and North America. Our database TRITON covers the entire world.