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| Monday, 11 November, 2002, 20:14 GMT Tornadoes: Small but terrifying ![]() Spin cycle: a tornado rips through Miami Though much smaller and shorter in duration than their hurricane cousins, tornadoes can be some of the most terrifying meteorological phenomena, wreaking havoc that has no equal in nature. They are spawned within storm clouds, where hot upcurrents meet cold downdraughts. The opposed air currents at this boundary create a fast-moving vortex, or funnel of wind. At the core of these vortexes winds can whirl at up to 480 kilometres per hour (300mph).
Houses can seem to explode when a tornado passes overhead. This is due to what experts call "hydraulic ramming". It occurs when tornado winds catch on a small opening into the house, suddenly jamming the house with air - like blowing up a balloon. The resultant "overpressure" can cause the house to blow outwards, appearing to explode. Hurricanes, typhoons and cyclones are the same phenomena, but differ in name according to which geographic region they occur in. Tornadoes, however, can form all over the world apart from around the polar regions, according to Dr David Reynolds at the UK-based Tornado and Storm Research Organisation.
Tornadoes usually last only a few minutes or an hour at most - though in this time they can rampage over 200km. Hurricanes, in contrast, can last days. "Twisters" can sometimes form at the forward right flank of hurricanes, as long as thundery conditions are also present. Waterspouts are simply tornadoes that form over water - usually warm shallows - rather than land. | See also: 11 Nov 02 | Americas 18 Sep 00 | Science/Nature Internet links: The BBC is not responsible for the content of external internet sites Top Science/Nature stories now: Links to more Science/Nature stories are at the foot of the page. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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