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Any natural event or hazard is called a disaster when it threatens lives or property. Natural disasters include avalanches, cyclones, droughts, earthquakes, floods, hailstorms, landslides, snowstorms, tornadoes, tsunamis, volcanic eruptions and wildfires. Some happen suddenly, like earthquakes, others happen slowly, like droughts. Not every country is at risk from a natural disaster but some countries are vulnerable to more than one type.
Droughts happen when there is a shortage of rainfall usually over two or more years so there is not enough water for plants, animals and people. When crops fail, food becomes scarce. People use up any stored food they have and begin to suffer from hunger and then malnutrition.
When pressure below the earth’s surface builds, an active volcano erupts, ejecting molten rock through a vent. Eruptions can happen suddenly or take weeks or months. Hazards include mudflows, clouds of ash, poisonous gases, lava flows and showers of rocks.
Tropical cyclones are violent storms with heavy rain and high winds of over 120 kilometres per hour. The winds move in a huge spiral around a calm centre. Cyclones build up over warm tropical sea but lose force as they travel over land. The winds whip up huge waves that can raise tides up to 5 metres above normal. Winds do the most damage to buildings but flooding and mudslides cause most of the deaths. (Cyclones are also called hurricanes or typhoons)
When pressure increases along fault lines on the earth’s surface, rock structures collapse causing the earth to move suddenly. Earthquakes start with a deep rumbling followed by violent tremors where the ground moves in waves. Buildings often collapse as their foundations are shaken. Deep cracks can appear where the ground has split apart under the pressure.
Heavy monsoon rains and tropical storms are often the cause of flooding. Rivers overflow their banks and the fast-moving water covers low-lying land, stripping vegetation and sweeping away bridges, buildings and people. When the flooding subsides, a layer of mud covers everything.
Tsunamis are large sea waves caused by an earthquake suddenly moving the ocean floor. The waves move at high speed and can travel thousands of kilometres before they run up on shore. At sea the waves appear low but as they approach land their speed decreases and their height increases. Without warning, the tsunami can strike areas far away from the earthquake that first started it.
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