What is an earthquake?
The ground beneath our feet seems rock-solid, but our planet’s surface is in fact a dynamic grid of slowly moving sections, known as tectonic plates. Normally, this motion is imperceptible to humans, showing itself only on geological time scales (North America and Europe, for example, are drifting apart at the rate of just five centimetres per year). The movement causes stress to build in the crust. If the stress rises beyond a critical threshold, a portion of the crust will give way, shifting suddenly and violently. This sudden motion usually occurs along a fault or fracture – a zone of weakness in the earth’s crust. The result is what we call an earthquake.
Calamities of the 20th and 21st centuries
The following is a list of some of the worst natural calamities to strike the world since 1900. The list is by definition arguable. Earthquakes, volcanic eruptions, tsunamis, cyclones, hurricanes and other storms are all clearly natural phenomena.
But the picture is less clear for disasters like floods and famine. What some people may consider a natural disaster, others may consider more of a political act (for instance, some of the world’s deadliest floods and famines were caused, at least in part, by policy decisions taken by hostile, indifferent or negligent regimes).
