Published by Australian Academy of Science
Glossary | Calculating the threat of tsunami

asteroid. A small body that orbits the sun. Most asteroids are thought to be the result of debris left over from the formation of the solar system. Most asteroids occur in the region between Mars and Jupiter. Collisions among the bodies in the asteroid belt and adjacent planets displace fragments and place them on a collision course with Earth. The asteroid belt is thought to be the source of most meteorites.

More information can be found at Asteroids data sheet (SPACE.com, USA).

meteorite. A fragment of an asteroid or a planet that has been broken off by a collision and eventually falls on the Earth. It consists of solid matter which survives the descent and lands on the Earth's surface.

Richter scale. A scale for measuring the magnitude or size of an earthquake. The scale relates to the energy released by an earthquake and is determined from the logarithm of the amplitudes (heights) of the seismic waves recorded at seismograph stations on the Earth's surface. For more information see The Richter magnitude scale, The severity of an earthquake, Measuring the size of an earthquake and Magnitude/intensity comparison (United States Geological Survey).

salinisation. The accumulation of soluble salts in soil or water so that they become unfit for their normal uses, such as growing plants or providing drinking water. The main salt is sodium chloride (common table salt) but potassium chloride and magnesium sulfate can also accumulate.

tectonic plates. The Earth's surface is made up of huge tectonic plates that have moved very slowly during geological history, and continue to move, thus changing the position of continent and oceans. The plates are about 100 kilometres thick and move at a rate of about 1-12 centimetres per year. For more information see Plate tectonics (Nova: Science in the news, Australian Academy of Science).

topography. Surface features of a region (eg, mountains, valleys).