Explaination on natrual hazards and case studies.


natural hazards.

Earthquakes and Volcanoes: Natural hazards such as earthquakes andvolcanoes have Earthquakes and Volcanoes: Natural hazards such as earthquakes and volcanoes have a devastating effect on developing countries, as they tend not to have the resources available to cope with such disasters. Buildings are easily knocked down, medical services are poor and rescue efforts often come too late, especially to remote areas. A weak earthquake in a developing country can cause far more damage and destruction than a more powerful one in a developed country.
Floods: Early in 2000, the world saw how torrential rains and tropical storms could cause wide-spread and devastating flooding in a developing country: Mozambique. The flood waters rose so quickly that many people were stranded, forced to clamber into trees and wait to be rescued. But, as in many developing countries facing such a disaster, the country itself did not have the resources to cope. International aid from countries such as South Africa (helicopters)and Britain (food, medicines and clothes) was required to try to help them get through the disaster.
Drought: Droughts reduce or destroy harvests and mean that water supply is severely limited. Countries in Africa, such as Ethiopia, have been badly affected by droughts, with hundreds of thousands of people dying from starvation or thirst.

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Case study. (Drought)

In 1972 part of Africa was in one of the worst droughts ever to hit earth. To the South of the Sahara Desert lies the marginal zone, better none as the Sahel. This area has been the home to nomads and settling agriculturalists for many hundreds of years. From 1968 the rain slowly decreased until in 1972 there was hardly any rain fall at all............

Major rivers in the area like the Niger and Senegal fell to their lowest levels known in this century. Even the great Lake Chad evaporated into one-third of its normal size. These major water suppliers provided water for millions of animals, humans and their crops of coffee, cocoa and peanuts were totally ruined.

The drought most badly hit the states of Mali, Chad, Mauritania, Senegal, Upper Volta and Niger. In these area the death toll reached a totoal of 200 000. It was only until the middle of the 1973, that the world came to learn about the devastation that was hitting the countries in Africa.

This particular drought affected the government of these countries as well. The Emperor of Ethiopia was not informed about the extent of the drought in the country, and becasue he was unable to help he lost his 40 year reign of power. The drought in Niger also indirectly caused political crisis. This resulted in the overthrow of the Government by a millitary coup.

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case study. (earthquakes)

On the 17th October 1989, at 17.04, an earthquake hit San Francisco and Oakland. It was centred on the Santa Cruz range, some 60 miles south of the city. It was measured between 6.5 and 7.5 on the Richter scale. Aftershocks continued to hit over the next 36 hours. The major factor was the fact that it was rush hour in San Francisco.
The fault ruptured bilaterally, that is in two directions, from the centre of the fault line, causing a relatively short shock. If the fault had ruptured unilaterally, along the entire fault line, the shock would have lasted for almost double the time.

The underlying geology of California causes most of the problems. Much of San Francisco is based on clay at depth. Some areas are built on reclaimed soft soil, e.g. the Marina district was built on reclaimed marshland for an exhibition in 1915. During the past years, the Santa Cruz mountains have moved 6 ft northwards along a 25 mile section of the fault.
The problem comes when the quake occurs. The hard rock of the area provides resistance to the shock waves, and they are impeded and reduced in intensity.

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case study. (floods)

Fact file.

  • is one of the world's most densely populated countries!

  • has a population of 125m inhabitants

  • is one of the poorest countries in the world with a GNP of $200 per head

  • has three of the world's most powerful rivers passing through its country - The Ganges, the Meghna & the Brahmaputra

  • contains virtually no raw materials or rock

  • experiences floods and tropical storms every year

The Physical Causes of the Floods.

  • Most of the country consists of a huge flood plain and delta

  • 70% of the total area is less than 1 metre above sea level

  • 10% of the land area is made up of Lakes and Rivers

  • Snowmelt from the Himalayas takes place in late spring & summer

  • Bangladesh experiences heavy monsoon rains, especially over the highlands

  • Tropical storms bring heavy rains and coastal flooding

The Human Causes of the Floods.

  • Deforestation in Nepal and the Himalayas increases run off and adds to deposition and flooding downstream

  • Urbanisation of the flood plain has increased magnitude & frequency of floods

  • the building of dams in India has increased the problem of sedimentation in Bangladesh

  • Global warming is blamed for sea level rise, increased snow melt & increased rainfall in the region

  • Poorly maintained embankments (levees) leak & collapse in times of high discharge

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