Geological Disasters

Geological disasters are sudden, often destructive events that originate in natural Earth processes. They include earthquakes and the tsunamis they can trigger, river and coastal floods, snow avalanches, and unusually large ocean waves. Although these hazards differ in their mechanisms, they share a common feature: energy that accumulates gradually is released quickly, frequently with little warning and serious consequences for people living nearby.

Earthquakes occur when stress built up along faults in the crust is released as the rock slips, sending seismic waves through the ground. When such a movement happens beneath the sea, it can displace a vast volume of water and generate a tsunami — a train of long waves that crosses the open ocean at high speed and grows steep and dangerous in shallow coastal water. Floods arise when rivers overflow after heavy rain or rapid snowmelt, or when storm surges push seawater inland. Avalanches send masses of snow, sometimes mixed with rock and debris, sliding rapidly down steep slopes.

The open sea can also produce freak or rogue waves, exceptionally tall waves that rise unexpectedly from the surrounding sea state and can endanger ships. Once regarded as sailors' legend, they are now recognised and measured by instruments. Understanding all of these hazards relies on monitoring networks, historical records and an appreciation of local geology and weather, which together support warning systems, building standards and land-use planning aimed at reducing loss of life.

Frequently asked questions

How is a tsunami different from a normal wave?

Ordinary waves are driven by wind at the surface, while a tsunami is set off by a sudden displacement of water, often by an undersea earthquake. Tsunami waves carry energy through the whole water column and have very long wavelengths.

What is a rogue or freak wave?

It is an unusually large and steep wave that appears suddenly amid otherwise smaller seas. Such waves can be hazardous to ships and are now confirmed by direct measurement.

What causes most river floods?

River floods usually result from prolonged or intense rainfall, rapid snowmelt, or both, which deliver more water than a channel can carry. Storm surges and dam failures can also cause flooding.