Tsunamis
Tsunamis are generated both by underwater volcanic eruptions and earthquakes and by massive landslides that fall into the sea. If there is a big shift in the earth under the ocean it creates a column of water that gathers speed and height as it travels closer to the shore.

In deep water, the tsunami can be up to 200km (90 miles) wide but only 0.5m high. As it travels towards the coastline and shallow water it can move at over 700kmph (320mph), as fast as a jet aeroplane. By the time it reaches the shore, a tsunami could be 50m high. As it rushes inland it can wash away buildings and vegetation with an incredible force.

The largest recorded tsunami hit Lituya Bay, Alaska, in 1958. An earthquake measuring 8 on the Richter scale caused a huge landslide into the sea that triggered a wave 524m (1,720ft) high. That’s taller than the Empire State Building! Amazingly there were only two deaths and the damage was restricted to three boats and coastal vegetation because it wasn’t a highly populated area.

Flooding
The United Nations estimate that one billion people (1/6th of the world’s population) live in an area under threat from a flooding disaster. The number of serious floods is rising every year, killing an average of 25,000 people worldwide annually. Homes, crops, roads, bridges and power lines are washed away leaving flood survivors to cope with starvation and disease.

Some floods are caused by heavy rainfall, when rivers burst their banks and the ground becomes too saturated to soak up excess water. Flat areas surrounded by mountains can flood in the spring when snow and ice melts. Coastal areas suffer from flooding when they are hit by cyclones, hurricanes and tidal waves.

Many people are killed by flash floods because they don’t realise how strong currents can become. Just six inches of water can knock you off your feet and it only takes two feet of water to carry away a car!

Drought
Don’t think that droughts only occur in hot countries – in fact they can happen almost anywhere in the world. Severe droughts are caused over a long period of time (a year or more) when rainfall drops below the average for an area, leaving it suffering from major water shortage. Other factors that can contribute to drought are high winds, high temperatures and low humidity.

Without water, crops will fail and vegetation and livestock will die. If the problem isn’t solved by spending time and money digging wells and building proper irrigation, it can lead to famine and starvation. When the drought is over, crops can still fail because the soil has have been starved of essential nutrients and contaminated by mineral salts.

In 1984, a series of droughts contributed to a famine which killed almost one million people in Ethiopia. In June 2004, the same number faced hunger in Kenya for exactly the same reason.

Hail
Hailstones are solid balls of ice that can range from 5mm (0.2in) to the size of a grapefruit. In many parts of the world storms are common where hailstones the size of tennis balls fall from the sky.

Hailstones are formed when pellets of ice fall through a cloud, picking up moisture on the way. This moisture freezes as the pellets are then forced back up through the cloud by air currents, making the pellet bigger. This happens a number of times until the pellet becomes a hailstone that is heavy enough to fall to the ground. Large hailstones can cause extensive damage, flattening crops, smashing through roofs, denting cars and breaking windscreens.

The record for the largest hailstones was set in Bangladesh during a storm that killed 92 people. Hailstones weighed in at almost 1kg (2.2lbs) and fell at around 50 metres per second.

Rain
Rain is formed when evaporation occurs from bodies of water, like lakes and oceans, and rises as vapour to form clouds. As it rises, the vapour cools down and forms raindrops. Small raindrops join together in the cloud until they are heavy enough to fall as rain. 80% of the world lives in areas which experiences regular rainfall.

Because of the climate in different countries, some places get huge amounts of rain and others hardly get any at all. The Atacama Desert in Chile and Peru only gets 0.1mm of rain every year, which makes it the driest place on earth. One of the wettest is Cherapungee in north-east India, which gets a massive 11.5m of rain a year.

You may have heard “it’s raining cats and dogs”, but how about fish and frogs?! This has been known to occur when tornados and waterspouts scoop them up and carry them miles away, where they fall as some very strange rain!