In managing vulnerability to natural disasters, with case studies of volcanic disasters on non-industrialized islands

PART II Case Studies: Volcanic Disasters on Non-Industrialized Islands


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Case Studies: Volcanic Disasters on Non-Industrialized Islands
9. Volcanic Disasters

9.1 Introduction

This chapter describes the risk from volcanoes and the volcanic disasters which have ensued. Section 9.2 categorizes and provides a brief overview of volcanic hazards, and is thus representative of the natural hazard component of risk depicted in Figure 2-1. An indication of how volcanic hazards can lead to volcanic disasters is also given, although section 9.3 details the vulnerability component of risk and discusses previous and potential disasters in more depth.

9.2 Volcanic Hazards

The information is this section is summarized and adapted predominantly from Chester (1993), van Rose & Mercer (1991), and Blong (1996). For further reading, Chester (1993) provides the most detail while Blong (1996) provides the most straightforward discussion. Other significant sources are referenced within the text. Figure 9-1 displays a schematic diagram for this section. Table 9-1 lists major volcanic disasters in history and the most significant hazards during those events.

9.2.1 Gas Hazards

Land volcanoes are estimated to emit 7.131011 kg/year of water (H2O), 6.51010 kg/year of carbon dioxide (CO2), 1.91010 kg/year of sulphur dioxide (SO2), 3109 kg/year of hydrogen chloride (HCl), and 1108 kg/year of hydrogen fluoride (HF) (Decker and Decker, 1998). Minor emissions include hydrogen (H2), carbon monoxide (CO), carbonyl sulphide (COS), hydrogen sulphide (H2S), sulphur (commonly denoted S), oxygen (O2), nitrogen (N2), hydrogen bromide (HBr), hydrogen iodide (HI), metal halogens (MpXq, with elements such as sodium and aluminum (M) bonded with chlorine, fluorine, iodine, or bromine (X)), and noble gases (helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn)).

If large amounts of these gases are emitted without oxygen, there is the danger of suffocation as occurred beside Lake Monoun, Cameroon in 1984 with 37 deaths and beside Lake Nyos, Cameroon in 1986 with 1,746 deaths. Even with the presence of oxygen, volcanic gases are poisonous, which is one of the reasons that there is relatively little growth adjacent to volcanic vents, termed fumaroles. The temperature of vented gases, usually at least several hundred degrees Celsius, is another discouraging factor to life near fumaroles. Blasts of steam and other hot gases can occur unexpectedly and can be lethal.

igure 9-1: Schematic of Volcanic Hazards

Table 9-1: Selected Volcanic Eruptions

(Because the number of fatalities varied amongst sources, the most popular value or range is listed for each eruption without providing a specific reference)



Fatalities and Main Causes

c. 3500 years before present

Santorini, Greece

unknown (likely tsunamis, solid ejecta, and the blast force)

August 24, 79

Mount Vesuvius, Italy

2,000 (ash falls and pyroclastic flows)

February 4, 1169

Mount Etna, Italy

15,000 (ash falls and pyroclastic flows)


Kelud, Indonesia

10,000 (lahars)

December 16, 1631

Mount Vesuvius, Italy

6,000 (ash falls and pyroclastic flows)


Raung, Indonesia

several thousand (lahars and pyroclastic flows)

March 11, 1669

Mount Etna, Sicily, Italy

20,000 (ash falls and pyroclastic flows)

August 4, 1672

Merapi, Indonesia

3,000 (pyroclastic flows)

December 10, 1711

Awu, Indonesia

3,177 (lahars)

September 22, 1760

Makian, Indonesia

2,000 (lahars)

August 11, 1772

Papandajan, Indonesia

2,957 (avalanche and lahars)

July 26, 1783

Asama, Japan

1,200 (lahars and pyroclastic flows)

June 8, 1783

Laki, Iceland

10,521 (famine)

May 21, 1792

Mount Unzen, Japan

14,524 (avalanche and tsunamis)

February 1, 1814

Mayon, the Philippines

more than 2,200 (falling rocks and fires)

April 10, 1815

Tambora, Indonesia

92,000 (10,000 from pyroclastic flows, and 82,000 from famine and disease)

March 2, 1856

Awu, Indonesia

2,806 (lahars)

October 8, 1882

Galunggung, Indonesia

4,011 (pyroclastic flows)

August 27, 1883

Krakatoa, Indonesia

36,000 (tsunamis)

June 7, 1892

Awu, Indonesia

1,532 (lahars)

May 7, 1902

La Soufrière, St. Vincent

1,600 (pyroclastic flows)

May 8, 1902

Mount Pelée, Martinique

28,000 (pyroclastic flows).

October 24, 1902

Santa Maria, Guatemala

several thousand (pyroclastic flows)

May 19, 1919

Kelud, Indonesia

5,110 (lahars)


Merapi, Indonesia

1,369 (pyroclastic flows)

January 21, 1951

Mount Lamington, Papua New Guinea

2,942 (pyroclastic flows)

March 17, 1963

Mount Agung, Indonesia

1,184 (lahars and pyroclastic flows)

March 29, 1982

El Chichón, Chiapas, Mexico

5,000 (ash falls and pyroclastic flows)

November 13, 1985

Nevado del Ruiz, Colombia

approximately 25,000 (lahars; see section 5.3.3 for details).

August 21, 1986

Lake Nyos, Cameroon

1,746 (toxic gases).

June 10-15, 1991

Mount Pinatubo, the Philippines

500-1000 (see Chapter 14 for details).

July 18, 1995 to the present

Soufrière Hills, Monserrat

19-30 (see Chapter 15 for details).

The build-up of gases which cannot vent properly is one of the main causes, along with magma motion, of volcanic explosions. The gases released by volcanoes also play important roles in atmospheric chemistry thereby contributing to atmospheric variability and change such as global warming (e.g., CO2), acid rain (e.g., SO2), and stratospheric ozone depletion (e.g., HCl), which have their own subsequent environmental hazards (section 9.3 provides more discussion of volcanic climate variability and change).

9.2.2 Gas-Solid and Gas-Liquid Hazards

Pyroclastics are fragments of magma, ash, and rock often emitted by volcanoes in a gas-solid dispersion. Although the terminology and categorization of pyroclastic hazards is inexact, the three main categories are pyroclastic falls, pyroclastic flows, and pyroclastic surges. Pyroclastic falls are essentially solid hazards and thus are discussed in section 9.2.3. Pyroclastic flows are a concentrated (dense) gas-solid dispersion travelling at hundreds of kilometers per hour with temperatures in excess of 100C. The peak velocities and temperatures rarely occur for longer than several minutes. Steam is the most common gas in pyroclastic flows. Pyroclastic surges are a low-concentrated (dilute) gas-solid dispersion with wide-ranging temperatures and velocities. Because of the low concentration of solids, pyroclastic surges can move rapidly across complex terrain and can mount obstacles up to 1 km high.

Aerosols are gaseous suspensions of fine solid or liquid particles11. When gases dissolve in water aerosols, acid aerosols--such as sulphuric acid (H2SO4), hydrochloric acid (HCl(aq)), and hydrofluoric acid (HF(aq))--are formed, which are corrosive to vegetation, lungs, and property. Solid aerosols close to the Earth’s surface can also damage lungs or settle to the surface, impacting vegetation and property. Solid and liquid aerosols in the troposphere and stratosphere cause significant backscattering of solar radiation, cooling the Earth (section 9.3 provides more discussion of volcanic climate variability and change).

9.2.3 Solid Hazards

A large amount of material falling or sliding down a mountainside is termed a rock avalanche (rockslide) or a debris avalanche (landslide). Volcanic eruptions or tremors can trigger such avalanches by shaking loose material. The reverse can also occur, as was observed at Mount Saint Helen’s in Washington, U.S.A. A volcanic earthquake triggered a landslide on the north side which removed material. The slope was weakened sufficiently to permit the trapped gases and magma to blast through on May 18, 1980 killing 57 people including a volcanologist who was camped on the north slope.

Ejected material from volcanoes ranges in size from dust (see also the discussion about pyroclastics and solid aerosols in section 9.2.2) to boulders. Finely pulverized rock and lava particles are termed ash. Larger ejecta are termed tephra or pyroclastics (both words are of Greek origin) and are pieces of lava, crystals, or frothed glass (pumice). Lapilli are approximately pea-sized to walnut-sized, while blocks or bombs refer to larger chunks. Pyroclastic or tephra falls involve material injected into the atmosphere or hydrosphere with a high velocity which then falls back to the Earth’s surface or the body of water’s floor. Volcanoes can eject material up to 55 km into the atmosphere, although columns between 3 km and 10 km high are more regularly observed. Fallout can cover thousands of square kilometers with layers several meters thick.

9.2.4 Solid-Liquid Hazards

Lava (an Italian word from the Neapolitan dialect) is molten rock which has egressed from the volcano (compared to magma, which is molten rock underground) and is a hazard both as a liquid and in its cooled solid form, due to its high temperature. Upon ejection, lava is usually between 750C and 1100C, although temperatures of up to 1400C may occur. Due to its low thermal conductivity and high heat capacity, lava can remain hot enough to start fires and cause serious burns for years after an eruption. Lava viscosity, and hence velocity and final cooled thickness, varies with its composition, but velocities rarely exceed 65 km/hr and are usually much slower, permitting most mobile creatures to evade flows much of the time. Vegetation and property are not so fortunate and fires started by lava can range much farther than the lava itself.

A lahar (a Javanese word) is any collection of volcanic fragments transported by water regardless of origin or sedimentological properties, but particularly referring to quick flows of mud of volcanic origin. There are more than a dozen methods of lahar formation, but all result in a mixture of solid volcanic material and water. The water could be from the volcano, a river, melted ice or snow, or rain which often mobilizes ash or tephra deposits. Lahars can be of various temperatures, can travel in excess of 100 km at speeds reaching 100 km/hr (especially down slopes), and can inundate thousands of square kilometers, often breaking dams and topping riverbanks. Even after coming to rest, the solid material can be remobilized by subsequent floods or precipitation, generating a lahar hazard for years following an eruption.

9.2.5 Liquid Hazards

A jökulhlaup (an Icelandic word) is an explosive flood of glacial origin, also described as a glacial outburst, which is often caused by subglacial volcanic activity melting ice. Non-volcanic jökulhlaups occur, but are not characteristically different from those of volcanic origin. The challenge of the jökulhlaup hazard is their sudden appearance and large volumes of water moving swiftly, sometimes with a discharge rate more than 100,000 m3/s.

A tsunami (a Japanese word) consists of a series of waves separated by several minutes or more than an hour which are usually turbulent, onrushing surges with the largest one generally being the second or third wave. The misnomer “tidal wave” is often applied, but a tsunami is never of tidal origin and is not a single wave that breaks onto the shore. Volcanic tsunamis are caused by the force of an eruption or by an eruption-generated or tremor-generated landslide. The volcano can be underneath, adjacent to, or partially in the ocean. Tsunamis can devastate coastlines and islands thousands of kilometers from the originating event, taking several hours to cross the ocean.

9.2.6 Massless Hazards12

The force of a volcanic explosion causes air shocks which can upset nearby aircraft and sound waves which shatter windows and ear drums. Some eruptions have been heard thousands of kilometers away and have felled nearby forests. The force of the volcanic explosion also exacerbates other hazards: solids, liquids, and gases ejected at faster velocities do more damage than those ejected at slower velocities. Furthermore, the angle of the blast impacts the hazard experienced. Larger objects fall farther from a volcano during a lateral blast than during a vertical blast, and thus larger regions are exposed to these hazards during lateral blasts. Lighter objects, such as dust, which are ejected vertically often reach the high troposphere or stratosphere and are then transported by winds around the globe.

Volcanoes can create their own microclimate during eruptions, which often includes lightning. Ash and tephra clouds move turbulently while erupting and friction amongst particles builds up enough static electricity to result in spectacular lightning flashes from one part of the cloud to another part (Kemp, 1988). The lightning may continue in clouds more than 200 km from the volcano. Cloud-to-ground lightning also can occur in the vicinity of the volcano.

Ground deformation is a dominant hazard, particularly preceding an eruption. Rising magma can fissure, change the elevation of, and tilt ground. Elevation changes involve the growth of dome structures above the magma or ground collapses, usually immediately preceding or during an eruption. Calderas are large, basin-like depressions formed when the centre of a volcano collapses inwards due to an eruption. Subsidence following an eruption can impact hundreds of square kilometers surrounding the volcano if a large amount of material is released, thereby undermining support for the land. Volcanic earthquakes are also precursors and consequences of ground deformation and eruptions, and can have magnitudes equivalent to the most powerful fault earthquakes.

9.2.7 Indirect Volcanic Disasters

Many consequences of volcanic events tend to be referred to as indirect hazards in the literature, pushing the limits of the description of “natural hazard” presented in section 2.5, since the resulting situations tend to be better classified as natural disasters (section 2.9). These events, though, are suitable for section 9.2 which discusses the dangers from volcanoes, and so they are presented here, but are classified as disasters.

Volcanic material--such as gases, ash, tephra, and lahars--severely impact agriculture by killing livestock and crops. Deposits and flows also contaminate water supplies and inhibit treatment and disposal of wastewater. Transportation13, energy, and/or communication networks are often damaged too, along with other infrastructure such as houses and hospitals, making day-to-day survival challenging. Famine and disease are thus regular aftermaths of volcanic events. Even with the sophisticated relief responses and operations witnessed currently, evacuation camps often facilitate the spread of disease due to the large number of people living in close proximity and the difficulty of maintaining supplies of food, water, and medicine.

In addition to disease and malnutrition, medical emergencies resulting from volcanic events include emotional and physical shock, asphyxiation from volcanic gas emissions, lung damage from inhalation of particulates and corrosive substances, and the usual plethora of injuries present during emergency situations such as burns, blood loss, broken bones, cardiac arrest, and concussions. A breakdown in civil authority leading to riot, looting, insurrection, and crime can also occur.

As mentioned in sections 9.2.1 and 9.2.2 and expanded upon in section 9.3, volcanoes contribute to local and global atmospheric variability and change with far-reaching consequences. Section 5.2.5 discussed volcanoes’ impact on global biogeochemical cycles which can lead to further hazards and disasters. As well, there are event combinations which yield bizarre situations; for example, tephra can absorb much water, becoming a superb electricity conductor, so if it rains or floods onto a tephra deposit which rests amongst downed but live power lines, the possibility of electrocution exists for the unwary who venture into the area.

9.2.8 Relative Dangers from Volcanic Hazards

Blong (1996) points out that the relative dangers from the different volcanic hazards are specific to each volcano and to each eruption. Forming general conclusions or ranking the hazards by an overall danger or risk index is misguided and detrimental to educating society about volcanic hazards. Developing a relative danger index for a specific volcano and for a specific eruption or anticipated eruption, however, assists in identifying and communicating the main hazards of concern to the surrounding population.

9.3 Society’s Vulnerability to Volcanic Disasters

Worldwide, more than 1,300 volcanoes have had at least one eruption in the last 10,000 years, and approximately 50 volcanoes erupt in an average year, with only a few of these causing fatalities (Smith, 1996; Tilling, 1990). Nearly 400,000 people are reported to have been killed throughout history by volcanic eruptions, though some authors (e.g., Decker and Decker, 1991) claim more than 1 million deaths. As seen in Table 9-1, the five most fatal eruptions in history caused slightly more than 200,000 of these deaths and the four most fatal eruptions in history occurred recently--two in the 19th century and two in the 20th century.

Casualties from volcanic disasters appear to be dramatically increasing over time, yet one or two devastating disasters skew the data spectacularly (after Tilling, 1991). Any real increase in deaths is likely attributable to population increases rather than to changes in the frequency of volcanic hazards. Around the world, close to half a billion people are at risk from volcanoes--a population equivalent to the global population 400 years ago (Tilling and Lipman, 1993). Furthermore, Boggs (1991) argues that population increases have far outpaced the increase in deaths from volcanoes, so the probability of dying during a volcanic disaster has actually decreased in the 20th century compared to previous centuries.

Compared to other severe natural disasters, major volcanic disasters occur infrequently and do not cause many human casualties (Chester, 1993; Tilling, 1990). Table 9-2 lists some natural disaster events with death tolls in excess of the total fatalities caused by volcanic eruptions throughout history. Single-event droughts, floods, and storms causing more deaths than the worst single volcanic event (92,000 deaths from Tambora, Indonesia in 1815) have occurred several times throughout history (Nash, 1976), hence the historical total of fatalities for these disasters far exceeds the volcanic toll. Earthquakes have killed more than 3 million people in the past five hundred years (Bolt, 1993)--an order of magnitude greater than volcanoes.

Table 9-2: Selected Natural Disasters With Death Tolls in Excess of the Total Fatalities Caused by Volcanic Eruptions

(Volcanic eruptions have killed nearly 400,000 people throughout history)







Bubonic Plague (Black Death)

Europe, Russia, and North Africa

approximately 50 million

Maloney (1976)

1851 to 1866


Beijing-Shanghai-Hankow triangle, China

40 to 50 million

Nash (1976)




25 million

Maloney (1976)

Nash (1976)



western China

5 million

Nash (1976)

August 1931


Huang He River, China

approximately 3.7 million

Lawford et al. (1995)

January 23, 1556


Shensi, China

over 830,000

Bolt (1993)

Smith (1996)

July 28, 1976


Tangshan, China

up to 750,000

Smith (1996)

November 12, 1970

Cyclone and Tsunami


300,000 to 500,000

Nash (1976)

November 1, 1530




Nash (1976)

Volcanic events, however, cause widespread damage to property and to the environment as demonstrated by the following two examples (National Geographic, 1997):

•On January 23, 1973, a new volcano started erupting near Vestmannaeyjar on the island of Heimaey, Iceland. At the end of the eruption four months later, 300 houses had been destroyed by fire, 1.18109 kg of ash covered the town burying 65 houses in a layer up to 6 m thick, and the town’s harbour was nearly closed in by lava; and

•On May 18, 1980, Mount Saint Helen’s in Washington, U.S.A. erupted devastating 368 km2 of forest, filling a valley to a maximum depth of 183 m, and raising the bottom of Spirit Lake by 60 m.

The eruption of Mount Pinatubo in the Philippines and the destruction of two American military bases (Chapter 11) also illustrates the amount of property devastation, and the influence on international politics, which volcanoes can have.

Volcanic eruptions often affect global climate as well, at least in the short-term. Volcanic gases and particulates ejected high into the stratosphere disperse around the world and backscatter incoming solar radiation in the visible and ultraviolet regions of the spectrum, while permitting re-radiation from the Earth in the infrared region of the spectrum, to escape. The 1815 eruption of Tambora in Indonesia likely resulted in “The Year Without a Summer” in 1816 with New England experiencing a snowstorm in June and frost in every month. Handler and Andsager (1994) associate injection of aerosols into the atmosphere by volcanic eruptions with subsequent ENSO (El Niño-Southern Oscillation) events, and the affiliated extreme weather and storms. Their case studies focus on Mount Pinatubo, the Philippines in June 1991; Nevado del Ruiz, Colombia in November 1985; and the combination of Nyamuragira in the Democratic Republic of Congo (formerly Zaïre) in November 1981 and El Chichón in Mexico in March 1982. Another global impact on the atmosphere of volcanic ejecta is the potential of chlorine gases to destroy stratospheric ozone, in a manner similar to chlorofluorocarbons (CFC’s).

Climate variability and change caused by volcanic eruptions has caused many more fatalities than have been recorded. Some famine deaths are reported in Table 9-1, but they occurred in the immediate vicinity of the volcano because pyroclastic flows, lahars, or ash falls ruined communities and crops. Determining the toll from famine induced by climate variability and change, along with deaths due to cold temperatures and storms, would be extremely challenging and is rarely completed, but such deaths would likely account for the vast majority of volcano fatalities. For example, the most probable explanation for a famine in northern China which killed millions of people from 207 B.C.E. to about 204 B.C.E.14 was a volcanic eruption in Iceland in about 210 B.C.E. which severely reduced solar energy input to the Earth for three years (Anderson, 1987). Another Icelandic eruption in 1773-1774 produced fluorine-rich gas, ash, and rain which decimated crops and starved 24% of Iceland’s population (Simkin, 1994).

These examples typify the diversity of ways in which volcanoes can kill, and the wide range of hazards described in section 9.2 along with the main causes of volcanic deaths listed in Table 9-1, add support. Lahars, pyroclastic flows, and ash flows dominate the fatalities in Table 9-1, but avalanches, tsunamis, fire, and poison gas are represented. Steam blasts, lateral blasts, rock falls, lightning, and lava burns are implicated in eruptions with smaller death tolls, not listed in Table 9-1. Displacement of populations due to volcanic eruptions can exact a heavy toll too. For example, between February 5, 1943 and February 17, 1952 Parícutin in Mexico killed three people from lightning and approximately 100 due to resettlement (Krafft, 1993; Luhr and Simkin, 1993). As well, the immediate toll from the 1991 Mount Pinatubo eruption in the Philippines was dominated by later deaths due to resettlement (Chapter 11).

The toll on human life from volcanic eruptions is therefore much larger than reported, and data on the numbers of people injured, affected, or displaced suffer similarly. As well, the potential for a terrible disaster exists. Recalling the discussion in section 6.3, society has not existed long enough to have experienced an extreme volcanic event on Earth’s temporal scale--an event which would be cataclysmic to society. The 20th century has twice witnessed the annihilation of a city of more than 20,000 inhabitants by a volcanic event (St. Pierre, Martinique by Mount Pelée in 1902 and Armero, Colombia by Nevado del Ruiz in 1985), both of which were considered major, international tragedies yet resulted from relatively minor volcanic eruptions. The 1815 eruption of Tambora, the largest recorded eruption in human history, produced 150 km3 of tephra as a maximum estimate (Decker and Decker, 1991) compared to the 2500 km3 produced by an eruption in Yellowstone National Park, U.S.A. two million years ago (Simkin, 1994). Another Yellowstone eruption 630,000 years ago yielded 1,000 km3 of magma compared to about 40 km3 from Tambora (Decker and Decker, 1991). Society has not yet experienced volcanism at its full potential.

Society’s lack of experience with volcanism is further illustrated by the relatively high death toll of volcanologists on the job (Table 9-3). At least thirteen volcanologists were killed by volcanoes during the first third of the IDNDR, with three of the most renowned volcanologists in history--Geoffrey Brown, Maurice Krafft, and Katia Krafft--amongst the casualties. One of the top American volcanologists, Stanley Williams, was with Brown at Galeras, Colombia and required several months to recover from his injuries. The Kraffts had just completed a video on the dangers of pyroclastic flows when they were engulfed by a pyroclastic flow at Mount Unzen, Japan on June 3, 1991. At the time of their death, their video was being widely shown around Mount Pinatubo in the Philippines, which turned out to be a significant factor in the ease of communicating the dangers of pyroclastic flows, saving many lives during the eruption (section 11.3.5). Each incidence of volcanologist casualties indicates to the scientific community how dangerous volcanic events are and how little are understood about them, even by those who study them.

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