In this chapter - The violent earth | Living in a hazardous world | The human toll | Definition | The human dimension | Classification | Hazard study

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Darkness fell early in Jakarta (Indonesia) on the 27th August 1883. Puzzled islanders were at the time unaware that the cause of their short day was one of the most violent volcanic explosions ever witnessed. The ancient volcanic island of Krakatoa lay 150 km to the west, in the strait between Java and Sumatra. On 27th August the volcano (long believed to be dormant) literally 'blew its top' in a violent explosions that was heard 2,000 km away in Australia. It threw an estimated 20 km³ of rocks and soil high into the atmosphere. Most fell as ash over an area of about 70,000 km², but some was blown literally round the world. Exotic red sunsets throughout the world were being attributed to the volcanic dust in the atmosphere for many years after the event. The explosion also triggered off a giant sea wave (tsunami) 40 m high, which drowned over 36,000 people in coastal towns on nearby Java and Sumatra, and could be detected on tide gauges as far away as the English Channel.

Krakatoa was the most powerful of the 5,567 recorded eruptions from 1.343 volcanoes active over the last 10,000 years. Other destructive examples include the eruption of Mont Pelée on the West Indian island of Martinique in 1902, which killed 29,000 people, and the 1985 eruption and mudflow at Nevada del Ruiz in Colombia, which left 20,000 dead. Between 1970 and 1986 50 to 70 volcanic eruptions a year occurred around the world.

The violence of the earth is not confined to volcanic eruptions; earthquakes also affect many areas and cause much damage. The great Tangshan earthquake in China in 1976 (magnitude 7.6 on the Richter scale) killed an estimated 242,000 people; 9,500 died in the 1985 Mexico City earthquake (magnitude 9.1). Major earthquakes are relatively infrequent; between 1973 and 1983 there were 105 principal destructive earthquakes world-wide (an average of 10.5 per year). But minor earthquakes are very common; between 1966 and 1985 a total of 130,916 epicentres were identified (an average of 6,545 per year). In 1983 alone 9,842 epicentres were identified, a fifth of which (1,983) were from earthquakes which were felt and damaging; nine of them were major events.

Hazards like volcanic eruptions and earthquakes affect people and the environment. Their impacts are often felt over a wide area, and are often long-term as well as immediate. Such hazards are costly and dangerous. But they are by no means the only, nor indeed the main, threats to people and property. The 80 or so named tropical cyclones each year also pose real threats. Some 7,000 people died because of cyclones in Honduras in 1974, and a cyclone forced over 100,000 people to evacuate from their homes in Florida, USA, during 1985. Other common natural hazards include tornadoes, floods, droughts, landslides and avalanches, and weather-related hazards

Most deaths from natural hazards in the USA are associated with lightning, tornadoes and windstorms (Table 1), while floods and hurricanes also kill many people. Soils which expand when wet and shrink in dry periods (expansive soils) cause such widespread structural damage that they are the most costly hazard in the USA (about 80 % of Dallas is affected by such soils). Usually dramatic hazards such as volcanoes and earthquakes do not occur, and their average annual cost is low. However they may dominate hazard damage costs in the years when they do occur.

Table 1 Impacts of selected natural hazards in the United States

SOURCE: based on data in Keller (1988, page 82)

 Many hazards can be influenced (directly or indirectly, deliberately or accidentally) by human activities, and some have great catastrophe potential.

Natural hazards are everyday occurrences around the world; they are not just dramatic interludes in history! Between October 1987 and September 1988, for example, there were many weather-related disasters (Table 2), including the great storm over southern England (October 1987) and Hurricane Gilbert in the Caribbean (September 1988); although that was by no means an untypical twelve months.

SOURCE: Telegraph Weekend Magazine (5 November 1988)

Some hazards are relatively small-scale and short-term, but others are persistent and widespread. Between October 1984 and April 1987, for example, up to a million people died and an estimated 35 million were at risk from drought and food shortages in north Africa.

But hazards are also created by people, especially in industrial accidents. For example, more than 2,500 people died and over 50,000 were injured when the Union Carbide pesticides factory exploded at Bhopal, India, in 1984; 452 died and many thousands were made homeless when gas tanks exploded in Mexico City, also in 1984; nuclear fallout was spread across Europe after the nuclear reactor exploded at Chernobyl in 1986, killing 31 in the short-term but also putting hundreds of thousands of people at risk in the future from cancer.

Clearly different hazards affect humans and the environment to varying extents and in different ways. But the overall cost of hazards, expressed in either monetary terms or through property loss or damage, is extremely high. Kates (1980) estimates the annual cost of natural hazards throughout the world at about $40 billion (US). Most of this is accounted for by floods (40%), tropical cyclones (20%) and drought (15%). Roughly two-thirds of the total cost stems from loss of life and property, and the rest is spent in attempts to reduce risk.

But the cost is human as well as financial. World-wide something like 250,000 people die, in a typical year, as a result of natural hazards.

Loss and damage from natural hazards are spread very unevenly between countries, and poorer developing countries take much more than their fair share of the burden. An estimated 95% of the lives claimed by hazards each year are concentrated in the Third World. But inequalities are also evident within countries; a disproportionately large number of victims come from the poorer, less mobile and less educated groups within society (such as landless labourers, old people, women and children).

Many different events (natural or caused or modified by human activities) give rise to threats which might kill or injure humans, damage property and structures, change or alter the environment. These include natural disasters (like earthquakes, volcanoes, storms, floods and droughts), but threats are also posed by wars, industrial accidents and structural faults such as dam bursts. So, what exactly is a "hazard"?

Burton and Kates (1964) define hazards as "those elements in the physical environment, harmful to man and caused by forces extraneous to him". It is important to stress that a hazard is something with the potential to cause harm (to people, property and/or the environment); it is the hazard event which actually causes the harm.

Unconscious exposure and scale are key factors. Strictly speaking, hazards affect third parties who have not knowingly put themselves at risk; self-induced harm (such as deliberate exposure to poisonous gases) and occupational danger (for instance amongst workers in nuclear installations) cannot properly be defined as natural hazards. Scale is important, because an event which affects one person, lasts for a few moments or affects a small area will differ in significance from an event which affects many people, lasts for a long time or occurs over a wide area; the former would generally be a problem, the latter would probably be a hazard.

Given the rather vague notion of a hazard, it is often useful to have diagnostic criteria available for defining when a hazard as such has occurred. Hewitt and Burton (1971) suggest four such criteria:

1. property damage; when it affects over twenty families, or leads to losses in excess of $50,000 (1971 prices)
2. disruption of social services; including failure of communications (like roads and railways, telephone links) and closure of essential facilities (like schools, government offices, hospitals, airports)
3. sudden unscheduled events; which place a strain on basic services like the police, fire and hospitals, and which require funds, equipment or personnel to be brought in from other sources
4. death and injury; if it kills more than ten or injures more than fifty people.

As Keller (1988) points out, "natural hazards are nothing more than natural processes. They become hazards only when people live or work in areas where these processes occur naturally". Such processes include river flooding, coastal attack by waves, land movements caused by earthquakes and volcanoes, strong winds and drought.

An event in the environment only becomes a hazard if it affects or threatens to affect people and property (directly or indirectly). River flooding per se is not a hazard, but it becomes one when the flood-prone land is occupied or used by people. Earthquakes in uninhabited areas are not really hazards. For example, the submarine volcano in the Atlantic Ocean off Iceland which created the new island of Surtsey in 1963 posed no threat to people. But the 1980 eruption of Mount St Helens in Washington State, USA killed 70 people and destroyed homes and roadways; it clearly was a hazard event.

The location of a hazard event also influences our awareness that it has happened and determines our assessment of its significance. For example, events which are accessible to the media (such as Mount St Helens) are better reported than those which are not (such as the volcanic eruption of El Chichon, Mexico). Only the biggest Bangladesh floods (like the one that occurred in 1998) are covered by the western press.

There are various ways of classifying hazards. One useful typology reflects the extent to which hazards are natural, and it recognizes three groups;

1. natural hazards; such as earthquakes or floods, which arise from purely natural processes in the environment and would continue to exist in the absence of people
2. quasi-natural hazards - such as smog or desertification, which arise through the interaction of natural processes and human activities
3. technological (or man-made) hazards - such as the use of toxic chemical pesticides which can seriously pollute food chains and aquatic habitats, or the accidental release of radiation from nuclear installations (like power stations). Such hazards arise directly as a result of human activities.

There is growing anxiety over the increasing number, distribution and impact of the quasi-natural and technological hazards - like the hole in the ozone layer and atmospheric warming caused by air pollution by greenhouse gases. Such hazards are avoidable ... at a cost. For instance, acid rain - which is caused partly by the release of sulphur dioxide and nitrogen oxide gases from chimneys of coal-fired power stations - could be controlled by expansion of nuclear energy production; but that creates its own set of hazards and environmental problems.

Many technological hazards (apart from sudden industrial accidents) build up more slowly than natural hazards, but they can create greater cumulative impacts which might affect a much larger area. For example, there is a real risk of global sea-level rise from atmospheric warming caused by air pollution, and many air and water pollutants (like acid rain or heavy metals) cause trans-frontier environmental problems.

An alternative way of classifying hazards is by source agent (on the basis of what processes have given rise to the threat). The most widely used scheme (Table 3) was proposed by Burton and Kates (1964), who distinguished between geophysical and biological hazards. Their scheme applies only to natural hazards, but it is fairly wide-ranging (it allows, for instance,for disease and infestations). Overall the geophysical hazards are more common, more catastrophic and more significant when measured in terms of loss of life and damage to property and services.

SOURCE: after Burton and Kates (1964)

 Hazard study

The study of natural hazards belongs to no single discipline. Geologists, hydrologists, climatologists and environmental scientists study the physical causes and characteristics of environmental hazards. Sociologists, economists, anthropologists and medical specialists concentrate on the human aspects of the problem. The interface point of contact between physical and human lies in people's reactions to natural hazards. These reactions involve both perception of hazard risk and adjustment to hazard threat; they form a fertile and inviting field of study which has traditionally fallen within geography (as the study of people-environment relationships).

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Last modified: 17 August 1999