The Swiss can never forget the destructive power of water. They have received several reminders in the past few years, when heavy downpours have been the direct or indirect cause of serious loss of life and property.

Thus in October 2000, the village of Gondo in canton Valais on the Italian border was partially destroyed by a mudslide, which left 13 people dead. Such mudslides are triggered by heavy rain. The centre of the town of Brig in the same canton was overwhelmed by mud and debris in September 1993, when the Saltina burst its banks. Two people were killed, as the square in front of the station came under nearly two meters (about six feet) of water and mud.

Such disasters are nothing new. They became more frequent in the 19th century, as the industrialisation of the country - and its neighbours - pushed up the demand for wood, and the forests which had protected the mountain slopes were recklessly felled. Indeed, it was repeated mudslide disasters which eventually led to the Switzerland's first environmental protection law, providing for reafforestation.

But it is not only mudslides which are a threat. Any kind of landslide - perhaps triggered by an earthquake, or by the natural movement of the rocks, or indeed by torrential rain - is made even more disastrous if, as is likely, the debris falls into one of Switzerland's many lakes. In 1806, following weeks of heavy rain, the village of Goldau in central Switzerland was completely buried under a rockslide, but some of the 953 people who died were not crushed under the rocks, but drowned by the tidal wave on Lake Lauerz caused by the wind driven before the falling debris.

A rockslide in 1512 near Biasca in canton Ticino caused a different kind of disaster: it dammed the Blenio valley, but two years later the lake thus formed burst through the barrier, and drowned 600 people.

The town of Zug in central Switzerland suffered a disaster in 1435, when one of its streets built directly on the lake shore slipped into the water. Sixty people died, and 26 houses were destroyed.

A less well documented disaster occurred nearly 900 years earlier, in 563. It appears that part of mount Grammont, near the eastern end of Lake Geneva, fell away, damming the Rhone. When the dam burst a few months later, the lake overflowed, sweeping away villages along both shores, and even destroying the bridge at Geneva and drowning many of its inhabitants.