Hurricanes
Hundreds of thousands of people on France's Indian Ocean island of Reunion hunkered down in their homes under a strict lockdown on Monday as a devastating storm that has already left one dead started to rip through the territory. VIDEOGRAPHIC
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00:00 Hurricane
00:06 Hurricanes form in areas of intense low pressure
00:11 and throughout their cycle can build up energy levels equivalent to 10,000 nuclear bombs.
00:17 Usually occurring in each hemisphere's summer months,
00:20 hurricanes are also known as cyclones or typhoons.
00:24 They form over warm ocean waters,
00:26 when sea temperature is 26.6 degrees Celsius or higher at a depth of some 50 metres,
00:32 when there's enough humidity,
00:34 and when surface winds meet.
00:37 When warm air comes into contact with the ocean's surface,
00:40 it heats up and starts to rise, creating an area of low pressure underneath.
00:44 New, cooler air swirls in to take its place.
00:47 As the heated, moist air rises and then cools off,
00:50 the resulting water vapour forms clouds.
00:52 Fed by the ocean's heat and surface evaporation, the swirls of air gather pace, whipping up a storm.
00:58 Moving at about 30 kilometres an hour, generally from east to west,
01:01 the storm's diameter ranges from 300 metres to 1,000 kilometres.
01:05 In just over a week, it can travel thousands of kilometres.
01:09 The Suffer-Simpson scale rates hurricanes from 1 to 5, depending on wind speed.
01:14 A Category 1 hurricane could bring down trees and cause temporary power cuts,
01:18 while a Category 5 would destroy homes and cause catastrophic damage.
01:23 Meanwhile, in the eye of the storm, conditions can be calm enough for birds to fly.
01:30 Once they move inland or over cool waters, hurricanes finally die out.
01:35 Some scientists believe a recent increase in number and intensity could be due to global warming.
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