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Saturday, 21 October, 2000, 11:57 GMT 12:57 UK
Clues to landslides
Aerial view of Neubrueck-Stalden, Switzerland
Swiss mudslide swept away houses and blocked roads
By Helen Sewell of BBC Science

A team of geologists in the United States has discovered that tiny variations in the way soil is packed in the ground can mean the difference between life and death in a landslide.

Fast landslides are much more dangerous, but until now little has been known about what determines the speed.

Hundreds of people die in landslides each year. This year the worst hit areas have been countries in South and Central America, Asia and Central Europe.

In October alone, mudslides caused by torrential rain in the European Alps have killed more than 20 people. Another 20 died in a landslide at a mine in China.

Landslide experiment

In a report in the journal Science, the geologists say one of the reasons why landslides like these are particularly dangerous could well be because of the way the soil is packed in the ground.

The scientists carried out an experiment in which they used a tilted concrete platform covered in soil to mimic a mountainside.

They watered it from below and above, and used sensors to track changes in the spaces between the grains of soil.

They discovered that when soil was loosely packed, adding water reduced the friction between grains. This allowed the soil to become more liquid and to move more quickly.

They say this means that loosely packed soil leads to faster, more dangerous landslides.

It is hoped that this new research could help the authorities in areas prone to landslides make more informed decisions about where to construct new buildings.

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See also:

15 Oct 00 | Europe
In pictures: Europe's floods
03 Aug 00 | Americas
Dozens buried in Brazil mudslides
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