Natural disasters fall into three broad groups:

1. Those caused by movements of the Earth. These occur with the minimum amount of warning and include earthquakes, volcanic eruptions and tsunamis. They are difficult to predict and impossible to stop. All that can be done is to take appropriate action to limit damage and loss of life after they occur.

2. Weather related disasters. These will include hurricanes, tornadoes, extreme heat and extreme cold weather. There will usually be some degree of advanced warning, but since weather is unpredictable, nothing can be done to stop these disasters from developing once the weather system develops. Again, in areas prone to this sort of disaster, some provision can be made to limit damage and loss of life.

3. Floods, mudslides, landslides and famine. These are usually the consequence of extreme weather events, or are supplementary to other natural disasters. Often they are the result of extreme and unforeseen conditions.

Someone living in an area that is prone to one or other of these natural disasters will be well aware of the fact, so the most important factor is to be prepared. If you live in an area that is prone to earthquakes, you might not experience one for a number of years, but they can occur with very little warning.

The first indication of an earthquake might be a roaring or rumbling sound that gradually grows louder. There might be a rolling sensation that starts out gently but within a second or two becomes very violent. Alternatively there might be a violent jerk followed by severe shaking that makes it very difficult to stand up or move from room to room.

The strength of an earthquake is usually measured using the moment magnitude scale. An earthquake measuring between 6.1 and 6.9 on this scale could cause a lot of damage in a very populated area. Around 100 of these occur each year. One measuring 7.0 to 7.9 would be considered a major earthquake and would cause significant damage. About 20 of these occur each year. The earthquake that occurred in Japan on 11 March 2011 was measured at magnitude 9.0 by the US Geological Survey and was one of the most powerful ever recorded.

If an earthquake occurs under the sea it can cause a tsunami. The most destructive of these are generated from large shallow earthquakes with an epicentre or fault line near or on the ocean floor. The sudden vertical displacement generates waves that can travel great distances at high speed. While out in the ocean these waves can be no more than a few centimetres high, but as they approach the shore the waves are compressed and become very much higher.

The tsunami that hit northeastern Japan following the 11 March earthquake was 15 metres high some areas and it travelled 10 km inland. Moving at high speed it washed away everything in its path including people and property. It also devastated the nuclear power plant at Fukushima. As a result of this natural disaster the number of people dead or missing is put at around 30,000 and the Japanese economy has suffered a major blow.

Tsunamis are not uncommon in Japan and usually there is a limited amount of warning before they hit. There are well-rehearsed procedures that are followed when they occur, but the one on 11 March exceeded all previous expectations.

Volcanoes are mountains that are characterised by having a crater that opens downwards to a reservoir of molten rock. When pressure from gases within the molten rock becomes too great, an eruption occurs. These can be quite modest and result in little more than a trickle, or they can explode with considerable force and be accompanied by lava flows, flattened landscapes, poisonous gases, flying rock and ash.

Due to their great heat the lava flows are a great fire hazard and in forested areas wildfires often result. Lava flows destroy everything in their path, interrupting watercourses and causing flooding and mudslides, but since they generally move fairly slowly, people can usually get out of their way.

The volcanic ash is mainly pulverised rock. This can be abrasive, acidic, gritty and smelly, but apart from infants, elderly people and those suffering from respiratory problems, to most adults it is relatively harmless, although it can prove lethal to machinery. Following an Icelandic volcanic eruption in 2010, when large clouds of volcanic dust were released into the atmosphere, concern about possible damage to aero engines severely disrupted air traffic in Europe and North America.

Volcanoes also give out gases such as carbon dioxide and sulphur dioxide. These are normally quickly dispersed by the wind, but can collect in hollows. High concentrations can cause suffocation. This is the most common cause of death following a volcanic eruption.

Tropical cyclones have been the cause of a number of natural disasters. They are storms with large low-pressure centres and numerous thunderstorms that produce high winds and heavy rain. Generally they are known as hurricanes, but in the northwest pacific region they are known as typhoons. A hurricane is defined as having a wind speed in excess of 73 mph (117 kph), but maximum sustained winds in the strongest tropical cyclones have been estimated to reach 195 mph.

Cyclones form out in the ocean and there are distinct hurricane seasons in different parts of the world, lasting for between five and eight months. Special weather watches are kept during these times and in populated areas there are generally well-rehearsed plans that are put in place when a tropical cyclone approaches.

They often hit the coast with tremendous force causing significant damage, but having hit land, friction slows them down. While the winds will abate somewhat, heavy rains will continue and can cause serious flooding. Coastal storm surges can produce extensive flooding up to 25 miles (40 km) inland.

Hurricane Katrina struck the states of Louisiana and Mississippi in August 2008. 1,836 people died as a result and overall damage was estimated as exceeding $100 billion. Although this was America's costliest natural disaster, the deadliest natural disaster in US history was the Galveston Hurricane of 1900 that killed between 6,000 and 12,000 people in Galveston.

Tornadoes can also be a lethal weather event. A tornado is a violent, dangerous rotating column of air that is in contact with the surface of the Earth and a cumulonimbus cloud. Because of their appearance they are often call twisters.

Most tornadoes are about 250 feet across, have wind speeds of up to 110 mph and blow themselves out after a few miles, but in extreme cases they can be 2 miles across, attain speeds of more than 300 mph and stay on the ground for considerable distances.

Although they can occur almost anywhere, the vast majority occur in the US, where the average is about 1,200 a year. They are most common in the spring, but they can occur at any time of the year. Worldwide the peak time for them is 5 pm, but one of deadliest in history, the Gainesville Tornado, occurred at 8.30 am local time.

In areas prone to tornadoes many people will have an underground shelter. Without this kind of protection the only hope is to get out of the way or get underneath something strong, like a heavy table.

It is not easy to escape extreme cold and this can also cause fatalities, especially among the old and chronically sick. These groups are not so mobile and it is particularly important for them to keep warm.

In extremely cold weather and in the event of heavy snowfall it is fairly usual for transport to grind to a halt. Roads and railways become blocked, aircraft are grounded and schools close. Diesel fuel often gels in extremely cold weather, causing further disruption. Farm animals can suffer and vegetable crops are difficult to harvest. Fuel consumption rises and water mains often burst.

All in all it is a pretty bleak picture. Then when the snow and ice thaws we often have floods. Rivers burst their banks, roads and bridges are washed away and normal communication can become impossible. There will be widespread destruction to homes and property. In serious cases those who are not drowned will have to find somewhere relatively safe and wait to be rescued.

Floods can also come from the sea. Early in 1953 there was a major natural disaster when serious floods hit countries bordering the North Sea. The Netherlands was particularly badly hit with a tidal surge that reached 5.6 metres in places, completely overwhelming the sea defences. 1,835 people and an estimated 30,000 animals drowned.

Coincidentally the number of people drowned in the Dutch flood was almost identical to the number of people who died when Hurricane Katrina hit New Orleans in August 2005. In this case the estimated number of deaths was 1,836.

Periods of prolonged extreme heat seem to be getting more frequent. In addition to causing illness and significant loss of life, they can have a serious economic effect on transportation, agriculture production, energy and infrastructure. Extreme heat can disrupt railways by twisting rails and roads can buckle or tarmac can melt. Aircraft lose lift in extreme temperatures and stress is placed on the cooling systems of the engines of raid and rail vehicles that can lead to an increase in mechanical failure.

Agricultural crop production can be ruined, milk production is reduced and animals are distressed. Excessive heat causes power lines to sag and short out. As more people use fans or air conditioning, demand for electricity is pushed to the point where supply companies can no longer cope.

Extreme heat can kill people, even though most of the deaths are preventable. It is reported that in the 24 years between 1979 and 2003 more people died in the United States of extreme heat than from hurricanes, lightning, tornadoes, floods and earthquakes combined.

The golden rules are to drink plenty of fluids, dress in cool clothes and stay in the shade if possible. A cool shower can help, as can air conditioning. Since most shopping malls, public libraries and big stores are air conditioned, if all else fails a trip there might be worth the journey, especially if the bus is also air-conditioned.

Extreme heat can also bring wild fires. A UN study reported that in almost every case drought is a major factor that prolonged or exacerbated a blaze. Often after many months without rain a single spark is all that is necessary to create an inferno. Wildfires can move at tremendous speed and will devour everything in their path. They can quickly change direction, which makes it very difficult for someone on the ground to escape.

These mega-fires as they are sometimes called are mainly caused by humans and are characterised by their massive destruction. The February 2009 Black Saturday blazes in Australia killed 173 people and completely obliterated several towns. In 2010 similar fires in Russia killed 62 people and destroyed about 23,000 square kilometres, an area more than half the size of The Netherlands.

A recent UN report (May 2011) suggests that the growing number of mega-fires around the world may be contributing to global warming. In its report the Food an Agriculture Organisation (FAO) says that policy makers should improve their monitoring of carbon gas emissions from wildfires to better determine their potential impact on climate change.

It is a vicious circle; climate change causes drought; drought causes wildfires; and wildfires cause further climate change.

Almost everywhere you look you find references to climate change associate with natural disasters. A UN report on climate change observed that the increase in tropical cyclone intensity was larger than climate models had predicted and the conclusion was drawn that it was more likely than not that there had been some human contribution to increase this intensity.

It is clear that the world is getting warmer, probably due to a natural process, but it is reasonable to assume that this process is being speeded up by mankind's release into the atmosphere of large amounts of greenhouse gas. It is also reasonable to assume that these greenhouse gas emissions are having a profound effect on the world's weather.

It is easy to blame every natural disaster on global warming, but meteorology is not an exact science and while in some cases this blame might be quite justified, in many cases these natural disaster occur for purely natural reasons.