Earthquake

Seismic shaking can transform water-saturated sand into a liquid mass that will not support heavy loads such as buildings. This phenomenon, called liquefaction, causes much of the destruction associated with some earthquakes. Mexico City, for example, rests on the ancient lakebed of Lake Texcoco, which is a large basin filled with liquefiable sand and ground water. In the Mexico City earthquake of 1985, the wet sand beneath tall buildings liquefied and most of the 10,000 people who died were in buildings that collapsed as their foundations sank into liquefied sand.

Jets of sand sometimes erupt from the ground during an earthquake. These sand geysers or mud volcanoes occur when formations of soft, wet sand is liquefied and forcefully squeezed up through cracks in the ground. Despite these names, they have no relation to real geysers or volcanoes. Although they generally cause little damage, they are indications that more widespread liquefaction may have occurred or may be possible in the next earthquake.