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Disasters: earthquakes, volcanic eruptions, hurricanes, and floods 

Disasters: earthquakes, volcanic eruptions, hurricanes, and floods

Disasters: earthquakes, volcanic eruptions, hurricanes, and floods

Peter J. Baxter

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Natural disasters (earthquakes, volcanic eruptions, hurricanes, floods) affect the lives of hundreds of millions of people every year, and their impact is increasing year on year because of continuing expansion of human populations into increasingly exposed areas, with environmental degradation making these settlements more vulnerable, especially in heavily urbanized areas. Future climate change may exacerbate matters, with many forecasts predicting an increase in hurricanes, severe wind storms, flooding and droughts.

Disasters are chaotic, but communities can plan and prepare to reduce their impacts. Most deaths in sudden disasters happen before outside aid arrives, hence building local response capacity is crucial. However, international disaster relief can be rapidly and effectively dispatched to needy countries that are politically willing to accept it, and relief teams have an important role in restoring roads and bridges, bringing in potable water, ensuring solid waste management, food protection, vector control, and sanitation. Attendances at medical facilities may return to normal within a few days of a disaster, and restoration of primary care then becomes the priority, rather than emergency treatment.


Between 500 and 700 natural catastrophes occur throughout the world each year and the total numbers whose lives are affected is now running into hundreds of millions annually. The numbers of reported natural disasters is increasing almost exponentially (Fig., as are the numbers of people affected globally (Fig. In the past 25 years, floods have killed over 70 000 people and adversely affected more than 300 million throughout the world, while earthquakes, windstorms, volcanic eruptions, and landslides have killed almost 200 000 people and adversely affected more than 60 million. The tsunami that devastated the Indian Ocean region on 26 December 2004 was the greatest recent natural disaster, killing more than 250 000 people and leaving 1.7 million displaced in poor conditions in 10 countries.

Fig. Reported natural disasters, 1900–2006.

Reported natural disasters, 1900–2006.

Reproduced from EM−DAT: The OFDA/CRED International Disaster Database − − Université Catholique de Louvain, Brussels, Belgium.

Fig. Total numbers of people affected globally by all types of disasters, 1900–2006.

Total numbers of people affected globally by all types of disasters, 1900–2006.

Reoproduced from EM−DAT: The OFDA/CRED International Disaster Database − − Université Catholique de Louvain, Brussels, Belgium.

Global changes responsible for the worsening impact of disasters include continuing, usually unplanned, expansion of human populations into increasingly exposed areas, and environmental degradation making these settlements more vulnerable, especially in heavily urbanized areas. This reckless development is going on throughout the world, even in areas of well-known risk.

On current trends, climate forecasts of an increase in the world’s average temperature of 2 to 3 °C and warming of the oceans could increase the potential for more intense hurricanes over wider areas and, in temperate regions, more severe wind storms and fluctuations in rainfall (floods and drought). Rising sea levels will increase the severity and the frequency of coastal floods.

Predisaster measures

Natural disaster results from massive ecological breakdown in the relation between humans and their environment, a serious and sudden (or insidious, as in drought) event on such a scale that the stricken community needs extraordinary efforts to cope with it, often with outside help or international aid. Accurately forecasting the timing and size of natural disasters is rarely possible. This constrains efforts to prevent loss of life by timely evacuation of people from the areas at risk. Disasters are quite different from major incidents in that normal lifelines and infrastructure usually break down. But despite their chaotic elements, disasters are amenable to scientific study and communities can plan and prepare to reduce their impacts. Health workers have a key role in hazard management, risk assessment, predisaster planning, and preparedness, as well as in the emergency response.

Following the agreement leading to the Hyogo Framework of Action 2005–2015, a multihazard, comprehensive approach to disaster risk reduction is slowly becoming accepted and is being enacted in civil protection legislation in many countries. However, poverty and marginalization in developing countries remain potent sources of global vulnerability to natural disasters. Less well publicized are insidious humanitarian crises (complex emergencies) that last for years and can result in the loss of millions of lives, for example, in the eastern Democratic Republic of Congo, Darfur (Sudan), and Eritrea (Ethiopia) They involve conflict and displacement of large populations and are becoming more common, and yet world responses are still poorly prepared for dealing with natural disasters that might occur on top of such pre-existing crises. Thus, in the Asian tsunami, access to some regions of Indonesia and Thailand was prevented by security issues. In 2008, Burmese people living in the Irrawaddy delta had no warning from their government of the approach of cyclone Nargis and hurricane preparedness measures were nonexistent. Over 80 000 people died, most from drowning. The storm of wind, water, and sand was so intense that it blasted away the skin, leaving raw wounds like burns. The disaster was made even worse when, in the immediate aftermath, 1.5 million homeless survivors were left without food, water, or shelter, whilst the Burmese government vacillated for weeks over accepting international aid. In contrast, international disaster relief is nowadays rapidly dispatched to needy countries and is on such a global scale that epidemics and famine are no longer the feared horsemen of the apocalypse they once were.


Many parts of the world are known to be vulnerable to devastating earthquakes, but it remains impossible to predict where and when a quake will strike. Most deaths and injuries are caused by collapsing buildings and secondary causes such as fires. When timber, masonry, reinforced concrete, and other types of buildings collapse, they inflict injuries in different ways and of different degrees of severity. In masonry buildings, an important cause of death is often suffocation from the weight and dust from the wall or roof material which buries the victims. Falling masonry causes crush injuries to the head and chest, external or internal haemorrhage, and chest compression (traumatic asphyxia). Little is known about the survival times of people trapped in collapsed buildings, but most victims die immediately or within 24 h, depending upon such factors as the severity of aftershocks, fire outbreaks, and rainfall. Rapid extrication of survivors and application of first aid by the uninjured immediately after the event could save up to 25 to 50% of injured victims. The greatest demand for emergency medical services is within the first 24 h and the need for emergency treatment fades after 3 to 5 days. Causes of delayed death include dehydration, hypothermia, crush syndrome, and postoperative sepsis. Most of those requiring medical assistance suffer minor injuries such as lacerations and contusions.

An earthquake of magnitude 9 on the Richer scale off the coast of the island of Sumatra on 26 December 2004 suddenly forced the sea floor upwards by some 10 m, creating a wave that surged through the Indian Ocean. The surface perturbation was initially small but when the water grew shallow, near the coast, the tsunami wave formed. Without warning, the wave hit Indonesia and Thailand within an hour, and then Sri Lanka and India, ultimately reaching as far as East Africa. The province at the north-western end of Sumatra, Aceh, suffered overwhelming devastation. More than 20 000 homes were destroyed, over 100 000 people were killed, and some 700 000 people were displaced. Many victims were health service staff, which hampered the emergency response.

In all countries affected, the main public health infrastructure remained intact as the devastation was limited to coastlines, so the feared epidemics of vector-borne diseases, such as malaria and dengue, as well cholera and dysentery, were able to be prevented. Vast numbers of dead and small numbers of major injuries in survivors are typical of flood disasters, in general, as the severely injured succumb in the water; the injured were mainly treated by local health teams. Many of the patients requiring surgery had infected wounds following contamination by sand and mud. Respiratory tract infections and pneumonias were common among patients who had come close to drowning. Psychosocial needs were identified on a massive scale, but the appropriateness and effectiveness of specific interventions in such disasters remains a controversial area.

An example of the importance of disaster preparedness was the earthquake in Bam, Iran, on 26 December 2003, which resulted in 26 271 deaths and the nearly complete destruction of the city of 80 000 inhabitants. The loss of about one-third of the inhabitants (including 200 out of 500 doctors) was attributable to the weak mud-brick construction. The health infrastructure was destroyed, but within 48 h 11 972 out of 15 000 injured survivors had been air-evacuated by the military to hospitals in the rest of the country and others were transported to facilities by relatives. By the time foreign medical teams arrived, their main task was to provide routine health care to a residual population living in shelters. In contrast, the Pakistan earthquake on 8 October 2005 hit the impoverished mountainous north of the country where access to hundreds of remote villages was hindered by damaged and blocked roads. Over 73 000 people died and 69 400 people had serious injuries; over 3 million people were left homeless. Houses were mostly constructed of weak rubble masonry walls supporting concrete slabs for roofs; the shaking easily razed buildings to the ground or triggered land slides. Roof slabs fell on top of the occupants (Fig. and caused multiple trauma, such as spinal and pelvic fractures. Significant numbers of amputations were performed and postdisaster reconstructive plastic surgery was frequently needed to treat the often severe and localized soft-tissue damage caused by entrapment (Figs. In 2008, the recent rapid economic development and accompanying building boom in China lay behind the destruction by the largest earthquake (7.9 on the Richter scale) to strike the country in recent times, when entire towns collapsed in the mountainous Sichuan province, leaving 80 000 people dead and at least 5 million homeless. Poor building quality has been blamed for the catastrophic failure of homes and schools. Despite the rapid mobilization of thousands of troops to the area, only a few survivors were retrieved from the rubble, sadly emphasizing the country’s failure to incorporate seismic resistance in new community developments.

Fig. Pakistan earthquake: collapsed concrete roof slab.

Pakistan earthquake: collapsed concrete roof slab.

(Source: Emily So)

Fig. Pakistan earthquake: severe soft tissue crush injuries.

Pakistan earthquake: severe soft tissue crush injuries.

(Source: Emily So)

Volcanic eruptions

About 500 to 600 quiescent volcanoes around the world are known to be capable of eruptive activity and several major eruptions occur every year. The vast majority of volcanoes are explosive and unpredictable in their behaviour, providing little opportunity for people to escape unless full evacuation measures are taken as soon as premonitory signs develop. In contrast, the less common lava flow eruptions normally allow people to escape by the time the lava heads towards them. Most deaths and injuries in explosive eruptions (such as the one that engulfed ancient Pompeii) are caused by pyroclastic flows and surges, which are clouds of hot ash and gas that can travel at hurricane speeds. Survival is uncommon but victims will have severe, extensive skin burns and inhalation injuries. The worst volcanic disaster in the 20th century was at St Pierre, Martinique, in 1902, when 28 000 people were killed in a laterally directed pyroclastic surge. Mount Vesuvius in Italy remains one of the world’s most dangerous volcanoes, but uncontrolled building has resulted in over 1 million people living in an area which could be devastated by pyroclastic flows in a new eruption. Another major cause of death is lahars or wet flows of debris, either ash that has built up on the slopes of the volcano or unstable masses that are mobilized during the eruption, by rain, or rarely by release of water from a crater lake. The eruption of Nevado del Ruiz volcano in Colombia in 1984 triggered a lahar by rapid melting of the glacier at the summit, the melt waters rushing down valleys and mixing with debris as they went. Although adequate warning could have been given to the people below, lack of preparedness meant that the mud flow engulfed towns including Armero, killing around 24 000 people. In one of the largest eruptions of the century, at Mount Pinatubo in the Philippines in 1991, 50 000 people were successfully evacuated from the threat of pyroclastic flows, but over 300 died, from collapse of roofs burdened with accumulated rain and ash, while sheltering in their homes.

The eruption of the Soufrière Hills volcano on the tiny Caribbean island of Montserrat began in July 1995 and gradually escalated, forcing the evacuation of thousands of people from their homes because of the threat of pyroclastic flows. By 1997, these flows had devastated the southern part of the island, evicting three-quarters of the population of 12 000 people. Air pollution from volcanic gases and ash has been a major consideration because of the close proximity of the population to the volcano and the frequent eruption of fine, respirable ash containing hazardous amounts of the crystalline silica mineral cristobalite, which can cause silicosis.


Hurricanes are one of a broad class of extreme weather phenomena that include winter storms (snow, sleet, freezing rain), thunderstorms (e.g. tornadoes, heavy rains, lightning, wind, and hail), extreme precipitation (e.g. flood and flash floods), and windstorms. Hurricanes (or typhoons as they are called in the western Pacific) are tropical cyclones that form over warm oceans with ocean surface temperatures over 26 °C. Once over land they soon run out of energy and rapidly abate, but can still cause flooding from heavy rain. Very high wind speeds, up to 250 km/h, are restricted to a relatively narrow track, usually no more than 150 km wide, within which localized gusts may even achieve tornado speeds and be extremely destructive. However, most deaths and injuries are not from the effect of wind on people (who normally remain inside for protection) or from building damage (building collapse or being struck by flying debris). Instead, deaths and injuries are commonly the result of flooding from the sea surge as the hurricane strikes land, concurrent heavy rainfall (typically up to 60 cm, over a larger area and extending further inland than wind speed) and resulting landslides. Hurricanes lift the sea, forming a sea surge that typically rises 3 to 4 m above existing tides, and the wind generates waves on top of these. Some storm surges can hit coastal areas well ahead of the landfall of the actual storm and can travel with nearly the same rapidity, and destructiveness, as tsunami waves.

Over 90% of fatalities in hurricanes are drownings associated with storm surges or floods. Other causes of death include burial beneath houses collapsed by wind, penetrating trauma from broken glass or wood, blunt trauma from floating objects or debris, or entrapment in mudslides. The greatest need in the postimpact phase is the provision of adequate shelter, water, food, and clothing, and sanitation. Most victims suffer from lacerations caused by flying glass or other debris, or minor trauma such as closed fractures and puncture wounds.

Katrina was the third most powerful storm ever to make landfall in the United States of America, attaining hurricane category 5 status before it struck the Louisiana coast on the morning of 29 August 2005. It left breaches in the levée system of New Orleans that created catastrophic flooding of an area of more than 400 km2, submerging half a million homes and trapping tens of thousands of people. Critically, the city’s mayor did not issue a mandatory evacuation order until the day before the hurricane hit, which was too late for many, including the poor, who had no means of transport. In Louisana and Mississippi 1700 people died, most by drowning. The emergency response was woeful. Up to 20 000 evacuees were abandoned in the city’s Superdome sports stadium for 5 days before being evacuated to other shelters. Two public hospitals were left cut off for days without electrical power, clean water, and medical supplies. The victims were predominantly black and poor. In the aftermath, nearby states were able to absorb several hundred thousand evacuees from the city in a few days. Despite forebodings, epidemics of diarrhoeal diseases, respiratory tract infections and mosquito-borne disease, in particular West Nile virus, did not occur.


In addition to the major losses of life that can be caused by hurricanes and their associated sea surges, floods mostly result from moderate to large events (rainfall, snow melt, high tides) occurring within the expected range of stream flow or tidal conditions. In the United Kingdom, as in many countries with low-lying coastal land, the hazard of coastal flooding from sea surges and high tides dominates over river flooding, although the latter is more frequent. Flood warning and forecasting, combined with effective land management, community preparedness, and evacuation planning, are as essential as engineered river and coastal defences.

The primary cause of death from floods is drowning, but trauma from impact with floating debris and hypothermia due to cold exposure are also important. The proportion of survivors requiring emergency medical care is small as most injuries are minor, such as lacerations. This absence of victims with severe or multiple trauma is likely to reflect the long delay in reaching survivors, so they die from their injuries or from exposure before search and rescue teams can arrive. Increased morbidity and mortality in survivors who experience flooding was reported in the year after the East Coast Flood in 1953 and a river flood in Bristol in 1968; there was an increase in suicides and mental health problems after the severe flooding caused by heavy rains in central Europe in July 1997.

Postdisaster relief

Myths surrounding postdisaster relief include:

  • Any kind of international assistance is needed.

  • The affected population is too shocked and helpless to take responsibility for their own survival.

  • Natural disasters trigger secondary disasters through outbreaks of communicable diseases.

  • Life gets back to normal after a few weeks.

Most deaths in sudden disasters happen before outside aid arrives, and so building local response capacity is most important. However, relief teams have an important role in restoring roads and bridges, bringing in potable water, ensuring solid waste management, food protection, vector control, and sanitation. Attendances at medical facilities may return to normal within a few days of a disaster, and restoration of primary care then becomes the priority rather than emergency treatment. Epidemiology has an important role in postdisaster assessment and health surveillance, particularly when large populations have been relocated, as well as investigating the causes of mortality and morbidity in disasters, including mental ill health and long-term health sequelae.

Further reading

Disasters and humanitarian emergencies. Epidemiol Rev, 27, 2005. [This special issue contains excellent review articles on hurricanes, floods and earthquakes.]Find this resource:

    Noji EK (ed.) (1997). The public health consequences of disasters. Oxford University Press, New York.Find this resource: