Natural hazards

The Earth is a calm place most of the time. But sometimes the ground shakes, a volcano spews ash, a river bursts its banks or a mass of snow thunders down a slope. Such natural events have always happened, long before humans existed. If you understand where and why they occur, you can prepare, and that is exactly what saves lives.

When the Earth shakes

The outer shell of the Earth is made of huge plates that move slowly. At their boundaries they get stuck, tension builds up, and when it releases with a jolt, the Earth quakes. That is why most earthquakes and volcanoes lie along plate boundaries, for example around the Pacific. The strength of a quake is given as its magnitude: one step up means roughly 32 times the released energy. A magnitude 7 quake therefore releases about a thousand times as much energy as a magnitude 5 one and is far more destructive.

Water and snow on the move

It is not only the ground that can turn dangerous. After heavy rain or snowmelt, rivers swell and flood valleys and towns. In steep mountains a blanket of snow can break loose and race downhill as an avalanche. And when a strong quake lifts the seafloor, a tsunami is born: in the open ocean the wave is flat but as fast as an aeroplane, and at the coast it piles up into a destructive wall. That is why coasts, river valleys and steep slopes are especially exposed places.

From event to disaster

A volcanic eruption on an uninhabited island is just a natural event. It only becomes a disaster when people are affected. That is why early warning systems operate all over the world: measuring stations detect quakes, buoys report tsunamis, weather services warn of floods. On top of that come smart precautions and solid construction: earthquake proof houses, dikes along rivers, protective forests against avalanches and emergency plans that everyone knows. The better a region is prepared, the less harm the same event does.