Bull Volcanol (1990) 52:532-544
Voli Ology
9 Springer-Verlag 1990
Medical effects of volcanic eruptions
I. M a i n c a u s e s o f d e a t h and injury
Peter J Baxter
Department of Community Medicine, University of Cambridge Clinical School, Addenbrooke's Hospital,
Cambridge CB2 2QQ, England
Received November 20, 1989/Accepted May 9, 1990
Abstract. Excluding famine and tsunamis, most deaths
in volcanic eruptions have been from pyroclastic flows
and surges (nudes ardentes) and wet debris flows (lahars). Information on the causes of death and injury in
eruptions is sparse but the available literature is summarised for the benefit of volcanologists and emergency planners. In nu6es, thermal injury may be at least
as important as asphyxia in causing immediate deaths.
The high temperature of the gases and entrained particles readily causes severe burns to the skin and the air
passages and the presence of both types of injury in an
individual may combine to increase the delayed mortality risk from respiratory complications or from infection of burns. Trauma from missiles or body displacement is also common, but the role of asphyxiant or irritant gases, and steam, remains unclear. The ratio of
dead:injured is much higher than in other natural disasters. At the periphery of a nu6e being protected inside
buildings which remain intact appears to greatly increase the chances of survival. In lahars, infected
wounds and crush injury are the main delayed causes
of death, and the scope for preventive measures, other
than evacuation, is small. The evidence from Mount St.
Helens, 1980, and other major eruptions indicates that,
although mortality is high within the main zone of devastation and in the open, emergency planning should
concentrate on the periphery of a nu6e where preventive measures are feasible and could save many lives in
densely populated areas.
Introduction
Disaster planners advocate the drawing up of volcanic
hazard zonation maps in populated areas around active
volcanoes (Crandell et al. 1984). For volcanologists and
healthcare workers to be able to identify and quantify
risks, and to devise suitable preventive health and safety measures using these maps, a knowledge of the
causes of mortality and morbidity in eruptions is important. Moreover, collaborative studies between medi-
cal investigators and volcanologists following an eruption may lead to new insights into eruptive processes
(Baxter and Kapila 1989). In this paper I shall discuss
the main causes of death in the vicinity of explosive
eruptions and relate these to the volcanic phenomena
responsible, namely pyroclastic flows and surges, and
lahars. An analysis of volcanic eruptions in the last 300
years has shown that famine and tsunamis have also
claimed many lives (UNDRO 1985) but these indirect
effects of volcanic activity will not be considered here.
The medical aspects of ash falls and gas emissions, and
advice on the appropriate personal and public preventive health measures to be adopted in eruptions, will be
described in subsequent papers.
Nudes ardentes
Nudes ardentes have been the most common direct
cause of death in eruptions in the last 400 years and
have accounted for at least 70% of the deaths in eruptions this century (Blong 1984). Only scattered, anecdotal reports of deaths and injuries from pyroclastic flows
existed in the geological and medical literature (Blong
1984; National Library of Medicine 1980) before the
Mount St. Helens eruption in 1980. It is currently not
possible to distinguish between the medical effects of
pyroclastic flows and surges, and thus the older term
"nude ardente" will be used to denote both phenomena.
Nu6es vary from dense avalanches of concentrated particles (pyroclastic flows) to dilute turbulent clouds of
particles suspended in hot air and gas (pyroclastic
surges). The same nu+e can have both concentrated and
dilute parts: for example, many dense pyroclastic flows
have an overriding dilute cloud which can travel considerably further than the underlying dense flows.
Nudes contain a substantial proportion of fine particles
(e.g. Sparks 1976), about a quarter of all the solids being less than 60 pm; the few per cent below 2 p,m are
well within the human respirable range (less than 7 p~m)
and capable of entering the smallest air spaces of the
lungs (Cotes and Steel 1987). The nude at St. Pierre,
533
Martinique, left a deposit of about 10 cm only and similar thin deposit surges have been found to have spread
further than the main flows elsewhere. The temperatures of nu6es can vary widely from hundreds of degrees centigrade to below 100~ in cool base surges.
From a medical viewpoint some of the volcanologists' terminology could be misleading. A shock wave or
air blast is not an essential feature of a nude, though the
term "blast" has been widely used in some eruptions,
e.g. Mount St. Helens, 1980. The main, if not only,
force propelling the nu6e is gravity. Thus the effects of
an explosive blast in humans, such as rupture of the ear
drum, contusion of the lung or other organs, systemic
embolism, etc. (Marshall 1977), are not likely to be
found in victims of a nu6e. Another misleading comparison, made by non-volcanologists, is that of a nuclear explosion; although the destruction wrought by a
nu6e and a nuclear bomb may be very extensive the energy release is quite different, the bomb characteristically emitting a true blast wave and thermal and ionising radiation (Glasstone and Dolan 1977).
The gaseous components of a nu6e will also vary
depending on the type of eruption. Probably all nu6es
will contain at least some steam and large amounts are
likely to be present in eruptions which are phreatomagmatic. The steam will usually be superheated initially
but may condense in the flow. Other volcanic gases, e.g.
CO2, CO, SO2, and H2S, are also likely to be present.
Magmatic particles will degas in the nu6e and theoretically volcanic gases could be present at lethal concentrations, but the dilution of the nu6e as it mixes with air
during its course will reduce this hazard, at least at its
margins.
The medical effects reported in nudes are summarised next.
vail 1983). The temperature peak within the nu6e probably lasted somewhere between one to 10 minutes and
rapidly fell to below 150 ~ C as judged by the survival of
paint, colour film, beer cans, polystyrene insulation and
the lack of charring of newspaper (Banks and Hoblitt
1981). The average velocity of the nu6e was estimated to
have been 64 m/s, leaving the crater at over 160 m/s
and slowing to around 28 m/s by the time it reached
25 km away. At a given location the flow probably
lasted no more than two minutes (Moore and Sisson
1981).
About 130 persons were airlifted to safety during
the first two days after the eruption; only nine of these
had serious injuries (mainly skin burns) from which
two died (Eisele et al. 1981). The ratio of the numbers
of dead:injured was 16:1. The retrieval of corpses did
not start until four days after the eruption by which
time decomposition had begun; photographs of the
corpses were taken at autopsy. The description that follows is based on the findings from the 25 autopsies that
were possible to perform (Eisele et al. 1981), and the
accounts of survivors and eye-witnesses (Bernstein et
al. 1986; Rosenbaum and Waitt 1981).
Mount St. Helens, 18 May 1980
Channelised flow zone
This eruption was the first to be investigated by medical
epidemiologists (Baxter et al. 1981; Bernstein et al.
1986; Falk et al. 1980) and pathologists (Eisele et al.
1981), and provides the most complete information on
the effects of a nu6e on unprotected people. About 160
people were in the vicinity when the eruption began
and 58 were believed to have died in the 19 x 40 km
wedge-shaped devastated area of wilderness north of
the volcano. Virtually all the residents had been evacuated and those people left were in the open, in tents or
in vehicles.
Three main areas in the zone of destruction could
be distinguished: rock slide and avalanche (incorporating the mud flow along the Tootle River); downed timber; and damaged or seared trees (Moore and Sisson
1981) (Fig. 1). Kieffer (1981) identified an inner region
where the flow was direct and beyond this an area
where the flow was deflected by topography. The temperature of the flow was estimated to have been over
350~176
near its start and have fallen to 50 ~
200~ at its outer limit where foliage was killed or
singed (Moore and Sisson 1981; Winner and Casade-
Seventeen bodies were examined from this zone. Thermal injury was apparently less important in this zone
compared with acute asphyxia due to inhaling volcanic
ash, which was the commonest cause of death (14 out
of 17). Some victims were inside vehicles but these did
not provide adequate protection against the ash; and
one victim was killed when a rock flew through the vehicle windscreen. Two men in a party of four loggers
died in hospital from the effects of inhaling ash and
from severe thermal burns (Parshley et al. 1982). Three
of the loggers arrived at the hospital 10-13 hours after
the eruption; the body of the fourth was found several
weeks later. The men described how they had been
thinning trees at a spot 19 km from the volcano (Fig. 1)
when they saw the nude coming towards them; they
were knocked down as they tried to flee. They experienced intense heat, total darkness and extreme difficulty breathing until the nu6e had passed. All three received extensive burns (33%-47% body surface area),
the deepest being underneath clothing which itself was
not burnt. Superficial burns were also present on the
tongue and back of the mouth (uvula). The injuries
Direct flow zone
No bodies were found inside this zone, but out of four
found at its perimeter in three cases the causes of death
were thermal burns and in one (who was inside his vehicle) asphyxia by inhalation of volcanic ash. All four
had been partially buried in the deposit, and had fractures of the ribs or limbs; one was dismembered. Thus
the possibility of surviving burial, thermal injury, severe
trauma or asphyxia inside this zone was remote.
534
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Mudslides
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Downed Timber
Mount St. Helens
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Damaged Timber
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miles
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Fig. 1. M o u n t St. Helens eruption 18 May, 1980. Locations of
dead, missing persons and survivors in relation to zones of devastation (between crater and broken line - direct flow zones; beyond
line - channelised flow zone). The circle indicates the location of
were consistent with a nu6e temperature of 50 ~176
(Parshley et al. 1982). The loggers died in hospital from
acute resplratory distress syndrome ("shock lung"),
their burns being heavily colonised with bacteria.
Eight persons survived in addition to the one logger: four protected themselves by falling into a hole in
the ground and another rolled under a fallen tree (but
broke a leg).
drove to safety in advance of the oncoming nu6e. Various survivors reported experiencing intense heat that
followed soon after the arrival of the nu+e blast and
which passed off within a few minutes or less; some
could hear their hair singe, denoting a temperature
greater than 120~ (Rosenbaum and Waitt 1981). Enveloped by total darkness several experienced difficulty
breathing because their mouths and nostrils became
clogged with ash. Two felt a sensation of lack of oxygen
but none reported any gaseous odours.
four loggers (see text). Modified from Bernstein et al. 1986
Marginal zone
The deaths furthest from the volcano (28.2 km) were two
people who were driving their automobile when they
became enveloped in and asphyxiated by the ash cloud.
Another two were killed in this zone when a tree fell on
their tent. Of the 43 survivors seven were saved by the
flow being deflected at the north fork of the Tootle River; seven others were in three automobiles which they
M o r t a l i t y by z o n e
Investigators from the Centers for Disease Control
(CDC) surveyed the locations of the dead and survivors
and calculated the mortality rates in the different zones
(Bernstein et al. 1986). The rates depend upon how a
survivor is defined; the CDC included only those lo-
535
Table 1. Mount St. Helens eruption 18 May 1980: mortality in the zone of devastation
Zone
Number of
dead or missing
Number of
survivors
Total
(%mortality)
Direct and channelised a
Marginal b
Unknown location
Total
46
4
8
58
9
43
-52
55 (84)
47 (8)
8 (-)
110 (53%)
a Includes downed and damaged (seared) tree zones, and mud flow (see Fig. 1)
b Zone where location of victims in relation to end of nu6e imprecise
Fig. 2 a, b. Enlargements from original plates of photographs of corpses in the Mount Pelbe eruption, 1902 (courtesy of British Museum Natural History). Lacroix (1904) used the normal size photographs in his monograph
cated north o f the summit within about 2 km of the
tree damage line and not the 48 people on the south
side of the volcano who were not really at risk. The
outer zone of damaged or scorched timber contained
too few people to analyse separately. Table 1 shows
that in the zones of downed and scorched timber combined the mortality rate was 84%, with the survivors
confined to the peripheral areas. At the edge of the
nube the rate fell to 8%. Although the numbers of
deaths are small and there are no comparable figures
available from other eruptions, the findings suggest that
the overall survival rate (47%) is better than that normally envisaged in a nu6e and would represent many
lives if extrapolated to an eruption in a densely populated area.
Mount Pel~e, Martinique, 1902
On 8 May 1902, about 28000 people, almost the entire
population of the town of St. Pierre, were killed within
minutes in a cataclysmic nu6e erupted by Mount Pel~e
6 km away.
According to reports (Lacroix 1904; Anderson and
Flett 1903; Will 1903) most of the corpses in the open
lay north-south in the direction of the nu+e and in every
conceivable position, e.g. crouching, extended, or with
the limbs rigidly contorted. Most lay prone, many with
the face resting on the forearms or covered with the
hands, and with their clothes missing. Numerous
corpses lay in the "pugilistic" attitude (limbs flexed and
spine extended) associated with exposure to intense
heat (at least 200 ~
~ C) at or shortly after the time of
death; some were charred and had singed hair, and
large numbers were believed to have been cremated in
the conflagration of the city that ensued from the fires
ignited by the nude. Necropsies were not performed
and the corpses were not studied in any detail, though
three days after the eruption Will (1903) observed that
many corpses did not show signs of actual burning even
tough they were shrunken, dried up and mummified.
(Mummification was noted at Mount St. Helens: it is a
process that is favoured by heat and a dry, acidic environment as provided by freshly erupted volcanic ash.)
Lacroix's account contains several photographs of
corpses and Figs. 2a and 2b are enlargements from two
of these. The apparently naked body in Fig. 2a lies partially buried in erupted debris and covered by a layer of
fine material; the facial features may have been obliterated by the rain of mud that fell about half-an-hour
536
after the nu6e struck and "plastered all objects on
which it fell as with a thick coating of cement - houses,
ships and the heads of human beings" (Hill 1902). Lacroix (1904) refers to a black, sticky coating impregnated with ash which made the identity or skin colour
of the corpses unrecognisable. The corpse lying in the
open (Fig. 2b) shows the flexed limbs typical of exposure to intense heat and the skin is also covered in light
and dark layers of fine material. Similar appearances
may be observed in an enlargement of a photograph of
the nude victims in Taylor's monograph (1958) on the
Mount Lamington eruption (Fig. 3). Lacroix also commented on the state of victims who had died in huts
which had remained intact and shut up in the main area
of destruction: their skin had not been burnt, but a
layer of ash inside indicated that they had died in the
nuee.
There were two known survivors in the city and several on ships in the harbour. Two others were caught at
the edge of the nu6e above the city and received burns
to the back beneath their clothes, the feet inside their
shoes, and the skin of the hands which had at once
peeled off in strips (Kennan 1969). In the city the prisoner Ciparis was saved from the volcanic blast by his
jail building which served as a protective bunker, but
he received bad burns on his back (underneath his undamaged shirt), legs, feet and hands, whilst his face and
hair escaped the effects of the hot air and ash which
entered his cell through the door grating (Kennan
1969). The cobbler Comp6re-Lhandre was burned on
the hands and feet before he got indoors and into a
room where he was joined by four others seeking refuge. As the ash fell on to the roof and poured into the
room he watched one of them, a girl aged about 10, die
within minutes. The three adults he later found dead
nearby (Lacroix 1904; Heilprin 1903).
On the steamship Roraima in the harbour, nine
crewmen survived. They had been sheltered from the
Fig. 3. Enlargement from the original negative of Taylor (1958) of
corpses at Mount Lamington eruption, 1951 (courtesy of Bureau
of Mineral Sources, Geology & Geophysics, Australia). The appearances of the corpses resemble those in Fig. 2 and are difficult
to interpret on the photographic evidence alone
-f
Right
ung
Right
/
Diaphragm
Fig. 4. Anatomy of the human respiratory tract. Laryngeal and
pulmonary oedema are referred to in the text: oedema is the excessive accumulation of serous fluid in the intercellular spaces of
the tissue. Thus laryngeal oedema results in the swelling of the
tissues which can in severe cases occlude the airway (death may
be prevented by emergency laryngotomy, or inserting a breathing
tube or large-bore needle through the skin below the larynx). Pulmonary oedema may result in death from asphyxia (lack of oxygen) due to air in the lungs being replaced by fluid. Acute respiratory distress syndrome is a severe and complex reaction of lung
tissue to injury
nu6e as follows: four were in apartments with closed
doors, two in the engine room, and three had been protected by the bodies of the other men who had died in a
heap above them. The vessel was set on fire by the nu+e
which was hot enough to ignite light, flammable articles (Kennan 1969). Lacroix (1904) attributed the fires
to the hot ash, the temperature of which he estimated to
be at least 450 ~ C. At the edge of the nu6e he put the
temperature nearer 100~ or lower. All the survivors
agreed that the duration of the nu6e was brief. A common experience was first a momentary blast of heat
when it felt too hot to breath, after which it seemed
there was nothing to breath for a time so they were left
gasping as if in a vacuum. The nu6e had a slight sulphurous smell if any was noted at all.
Lacroix described the injured rescued from the
ships and from the edge of the nu6e. Most had received
burns to uncovered skin, and many to the lips, the pharynx, larynx and bronchi, with separation of the mucous membranes and the surface of the tongue (Fig. 4).
They had difficulty breathing, with noisy inspiration
and expiration accompanied by wheezing, and, despite
severe thirst, found it too painful to swallow. These victims had internal burns and soon died, whereas others
with only skin burns recovered. Because only 163 in-
537
jured reached hospital, with as many as 123 of these
surviving, the more badly burnt must have died at the
scene from the effects of their injuries, e.g. from shock.
The ratio of dead :injured was 230:1.
An eruption on 30 August 1902 involved the inhabitants of Morne Rouge who had returned prematurely
after the main eruption. Jaggar (1949) described this
episode as a series of "steam downblasts" following
rapidly on one another. Where cottages had doors and
windows which withstood the blast there were few injuries. In less robust dwellings survivors described a hot
blast followed by an extreme, but temporary, difficulty
in breathing, a choking sensation, and a mild to strong
sulphurous odour. The widow Martin received burns to
the skin of the back, arms, hands, breasts and the burning dust also penetrated inside her ears, nose and
mouth: she did not complain of any great throat trouble but she died later from a "pulmonary complication"
(Jaggar 1949).
cient to protect the skin against burns or at least minimise them. About 90% of the deaths were attributed to
the thermal and asphyxiating effects of the nude, the
remainder being caused by collapse of the roofs of huts
under the weight of ash, or people being struck by
lightning or falling stones. Many houses were ignited
by hot stones or lightning (Anderson and Flett 1903).
Of the 194 victims treated in hospital 191 suffered
extensive, mainly superficial, burns to the skin, including the face, ears, neck, forearms and backs of hands,
legs and feet; 20% had body burns as well, especially
on the shoulders and buttocks. Seventy-nine of the
burns patients died, most from infection of their lesions, but some from respiratory infections and four
from tetanus. Three people had been hospitalised for
other injuries and one of these died (Will 1903). As at
St. Pierre, hospital patients were likely to have been a
"survivor group", many of the more severely injured
having died through inadequate treatment or delayed
rescue at the scene.
La SoufriOre, St. Vincent, 1902
This eruption illustrates the protection afforded by robust housing. Almost all survivors had taken refuge in
cellars or rooms the only openings of which faced away
from the crater and were moreover tightly closed with
wooden doors or shutters (Hovey 1902). In contrast, all
animals caught in the open were killed (Anderson and
Flett 1903). The toll of dead or missing was put at 1565 ;
194 survivors were admitted to hospital (80 of these
died, mainly from severe burns) and a further 30 attended for dressing of their burns (Will 1903). The ratio
of dead:injured was approximately 11:1. As in the Pe16e eruptions, no necropsies were conducted.
The nu6e had less mechanical force than the one at
St. Pierre for by the time it reached the populated areas
on St. Vincent it was no longer capable of overturning
trees or sturdy structures. Survivors in rooms or cellars,
the doors or windows of which remained intact, reported experiencing intense heat and a strong smell of
SO2 which, together with the fine dust which infiltrated
the rooms, caused parching of the throat, a sensation of
suffocation and spasmodic coughing. In one man's
house the feeling of suffocation prevented articulation
within a few seconds: of the seven who died there several threw up their hands and fell down dead, whilst
the remainder collapsed and lingered for an hour or
more. Four or five persons survived by opening the
window and breathing fresh air once the nu6e had
passed. That gases may have played a part in the suffocating sensation was further corroborated at a house
where 50 people were crammed into one large room;
here they experienced suffocation soon after the cloud
had passed over, by which time gases may have built up
inside the room. The fine, hot dust was intensely irritant to the eyes and mouth; people covered their eyes
with their hands and many stuck their caps in their
mouths. As at St. Pierre, the mucous membranes of the
nose and mouth were scorched and in some victims
peeled off. However, thin cotton garments were suffi-
Mount Lamington, Papua, New Guinea, 1951
Taylor's account (1958) of the destruction wrought by
this eruption bears close resemblance to the preceding
descriptions of the effects of nudes. The furthest extent
of the nu6e was 10-13 km from the crater and it was
possible to demarcate an inner zone of devastation
where the destruction of trees and houses was virtually
complete, and a marginal zone of scorched and partially damaged trees. Most of the inhabitants of the villages in the marginal zone were killed and there were
few, if any, survivors in the zone of devastation. The
total number of deaths was 2942. Forty victims located
in two villages on the boundary of the marginal zone
were able to make their way to a nearby mission, but
their body burns were so severe that 22 died before the
next day. A small group of rescue workers brought out
an unknown number of casualties from the zone of devastation, but further details are not recorded except
that deaths occurred on that day and on the days following. However, during the three days after the eruption 70 casualties, whose location was unrecorded, were
airlifted to hospital and only three of these died.
The attitude of the corpses in Taylor's sole photograph of the dead (Fig. 3) shows that they were subjected to intense heat at the time of death, as at St.
Pierre. Their location was in the open at the edge of the
zone of devastation. Environmental evidence indicated
that the temperature of the nude in the vicinity was not
sufficiently hot to ignite or char, but plastic objects
were deformed; Taylor (1958) estimated a nude temperature of 200 ~ C lasting for one-and-a-half minutes. The
photographic appearances of the corpses suggest a
combined temperature and duration of at least these
values. There were no necropsies performed and it is
not possible to deduce much more from Taylor's own
observations. From his sparse data the approximate
dead:injured ratio was 44:1.
538
Eruptions in the Philippines
The year 1911 marked one of the most violent eruptions
in the history of Taal volcano which left 1335 people
killed or missing and 199 injured, many mortally (Pratt
1911; Worcester 1912). The volcano is situated on Volcano Island which is about 5 km in diameter near the
centre of Lake Bombon (Taal), itself nearly 20 km in
diameter. On Volcano Island and in a sharply demarcated area of 230 sq km on the adjacent mainland to the
west of the volcano the destruction of life and property
was virtually complete. A water wave generated by the
eruption also caused damage and loss of life along part
of the shoreline.
An American army private was in a survey party
which had camped on the mainland about 6 km northwest of the crater and 400 m from the shore in an area
which the nure was to subsequently partially destroy,
leaving 98 out of 800 local people dead. The party was
swept by a heavy wind which blew away the tent and
threw the soldier 5 m. Then a further rain of ashes fell
to a depth of 20 cm. The air became oppressive and the
party gasped for breath for about 20 s at one point.
After the men had gone to higher ground the camp was
washed away by the water wave. Only one person was
injured: he received slight burns on the arms from the
hot ash (Worcester 1912).
Some survivors owed their lives to being blown into
the lake or being situated in well-protected places. The
temperature of the nure was considered to b e no higher
than boiling water (not unusual for a water-rich eruption); interestingly, there was no evidence of thermal
damage to vegetation, even on the island. The burns on
the injured were mostly superficial, and there was some
doubt as to their cause. One explanation lay in the
heavy fall of mud that occurred late in the eruption for
this was reportedly charred with acid strong enough to
burn the skin and kill vegetation. Most of the 199 recorded survivors had received traumatic injuries and lacerations from flying stones and debris. Worcester
(1912) believed that many had been killed or injured by
a sandblasting effect of the nure (severe abrasion of the
skin could be confused with burns) and that explosive
gases from the volcano had ignited inside dwellings,
thereby adding to the deaths. A strong smell of SO2 was
observed during the eruption and this gas may also
have contributed to mortality. Using the sparse data
available the estimated dead:injured ratio is 10:1.
The next major eruption of Taal was in 1965
(Moore et al. 1966). About 190 people, mostly residents
of Volcano Island, were killed. Nu+es were formed at
the base of the main eruption column and these base
surges contributed to the deaths, though details are
lacking. Once again there was no evidence of charring
or burning within the zone of devastation. In the inner
area where trees were sandblasted the temperature was
put at slightly above 100 ~ C and below this figure where
trees were plastered with mud. One large calf was
found to have been blinded and the hair sandblasted
off the back of its ears and off its rump.
A series of explosive eruptions occurred at Mayon
volcano in 1968 (Moore and Melson 1969). At least six
people were killed. Surrounding the area of nube deposits was a scorched zone up to 2 km at its widest, but
averaging a few hundred metres only, where vegetation
was charred and splintered yet on which only a thin
layer of airfall ash was deposited. In this zone all animals were killed and a farmer received second and
third degree burns from which he died shortly afterwards. He ran 1 km after being burned and reported
that he had been caught in a blast of hot gas.
Rabaul, Papua, New Guinea, 1937
More than 500 people lost their lives in the major eruption of Vulcan in 1937, some in nure-like events (Johnson and Threlfall 1985; McKee et al. 1983; McKee et
al. 1985). A missionary and his people located at about
4 km north of Vulcan saw a fast moving "black wall" of
ash approaching and sought refuge inside the church.
Here they survived whilst trees in the banana plantations outside were snapped off or uprooted. Another
missionary, stationed about 5 km west southwest, had a
similar experience. He and a group sheltered beneath a
house and covered themselves with sheets of corrugated iron. When the darkness cleared after 10 min they
too saw all the trees lying on the ground, but the house
had not collapsed as two coconut palm trees had fallen
across it and propped it up. As there was no mention of
asphyxiation doubts were raised whether these clouds
were nu+es at all, but it would seem reasonable to regard them as a dilute type.
El Chicon, Mexico, 1982
Three nu+es (base surges) from this volcano devastated an area as far as 8.5 km away, killing all people
and animals within it. No details on casualties appear
to be available except 187 bodies were buried and over
1700 people were missing. Environmental evidence indicated that the temperature throughout the surge zone
had been at least 220 ~ C, high enough to char wooden
furniture. In its distal parts the surge destroyed the
town of Naranjo but the deposit was only 2-3 cm thick.
A marginal zone extending on average 2 0 0 - 3 0 0 m
beyond the surge could be identified where the temperature had been high enough to blister paint and melt
plastics, but glass was unaffected (Sigurdsson et al.
1984; Sigurdsson et al. 1987).
Kilauea, Hawaii, 1790
This eruption was the most explosive to have occurred
in Hawaii's recorded history. A base surge is believed
to have been responsible for the deaths of 5405 native
warriors (Swanson and Christiansen 1973). Some narrators who saw the corpses said that they had been
scorched but otherwise not badly burnt and some of the
539
dead were sitting upright in a lifelike manner, clasping
one another as in the act of taking leave. This phenomenon will be discussed below (see Instantaneous
Deaths).
Vesuvius, Italy, A.D. 79
This famous eruption has been the subject of detailed
study by volcanologists and archaeologists (Sigurdsson
et al. 1982; Sigurdsson et al. 1985). Around 2000-3000
people out of a population of 20000 are believed to
have perished in Pompeii, 10km from the crater. A
unique feature was the discovery of moulds of some of
the victim's bodies within the debris of two surges and
covered by thick pyroclastic flow deposits. The fine ash
of the surges hardened around the bodies and formed
moulds on top of the pumice fall deposit about 2.5 m
above street level and beneath 2 m of further erupted
material. The surges had been preceded by 18 hours of
pumice airfall, during which the majority of the inhabitants are thought to have fled. The author reviewed
photographs of 41 different casts of intact torsoes (with
limbs) stored in the archives at Pompeii; about half (18)
lay in an attitude of limb flexion (with or without extension of the spine) compatible with exposure to extreme heat either as a cause of death or following
shortly afterwards (Fig. 5), as was found at St. Pierre
and Mount Lamington. Some authors have used the
casts of bodies in attitudes of seeming repose as evi-
dence that death had been caused by slow asphyxia
(e.g. Maiuri 1961), but these postures are compatible
with rapid death in a nu6e (see Fig 2a). Thus the appearances of the Pompei casts are not at variance with
the geological evidence which suggests that the people
were killed by, or covered soon after death, in hot pyroclastic surges. Such clues depend upon the casts being
accurate replicas of the corpses at about the time of
death, but little can be inferred on the mode of death
from the lifelike appearances of the skeletons discovered in chambers at Herculaneum.
Lahars
Lahars (torrents of mud and stones) are another type of
debris flow driven by gravity but which originate from
the slopes of a volcano and are mixed with water rather
than air or gases. Blong (1984) has summarised the features of the most important historic lahars. Usually
their range is less than 25 kin, though the largest can
travel for over 50 kin, and their rate of flow often
reaches 50 km per hour or more. Lahars are immensely
mechanically destructive and, depending upon their
origin in the eruptive process, can be hot enough to
cause cutaneous burns. Death is usually by asphyxia or
from traumatic injuries as a result of being engulfed in
the flow.
Nevado del Ruiz, Columbia, 1985
Fig. 5. Photograph of plaster cast from Pompei of victim of the
Vesuvius eruption A.D. 79 showing typical flexed-limb posture
which can be caused by extreme heat (courtesy of Soprintendenza
Archeologica di Pompeii)
The eruption of this volcano led to lahars travelling
60 km or more to engulf settlements without warning
(Lowe et al. 1986; Williams 1987). The official death toll
was estimated at 21015 and 1927 in the towns of Armero and Chinchina respectively (Gueri and Perez
1986). The number of injured was 4470, and 1244 of
these were admitted to hospital (138 subsequently
died). In Chinchina very few trapped or injured people
remained alive, but in Armero the situation was different, probably because of the softer consistency of the
mud. Here, most of the trapped people who could be
saved were rescued within the first three or four days,
though the effort was hampered by the soft mud not
taking the weight of the rescuers or their equiment
(Gueri and Perez 1986). The commonest lesions in the
hospitalised patients were lacerations (69%), penetrating wounds (41%), and fractures (37%); most of the injured had been dragged and roiled by the avalanche
and had more than one lesion. Many of the wounds
were infected on admission. Minor eye lesions were
also frequent (Gueri and Perez 1986). A survey conducted by the CDC (Oxtoby et al., personal communication) on 126 hospital deaths shows that over twothirds were from infectious causes including gas gangrene (17) and tetanus (5). Other victims had severe
crush injuries with open fractures and damage to internal organs: 10 died from traumatic shock, and 24 from
chest injuries and respiratory complications. Many patients had swallowed or aspirated mud. The flow was
540
not hot and minor skin burns were attributed to its high
acidity, though this property was not confirmed.
To this author's knowledge this is the only volcanic
lahar in which the causes of death and injury have been
investigated. It also demonstrate that some m u d flows
can be highly fluid depending u p o n the ratio of water
to sediment (Sigurdsson and Carey 1986), and this ratio
may be a crucial factor in determining the numbers of
potential survivors requiring rescue and treatment.
16e eruption was much greater than the others. The
dead:injured ratio is a reflection of the violence of the
eruption or the vulnerability, for whatever reason, of
the victim population, or both.
Some tentative conclusions can be drawn on the
modes of death and major injury by using the experience from Mount St. Helens (Fig. 1) as a model. Mortality risk will depend u p o n the zone and whether or
not the person is protected by an intact building (Table
3).
Causes of death and injury
Nudes ardentes
Victims in the open
The case histories summarised briefly above show that
much more needs to be learnt about the wide range of
possible medical effects of nu6es in different types of
eruptions. The most striking aspects of nu+es compared
with any other type of natural disaster (Seaman 1984) is
their extraordinarily high dead :injured ratio. It is evident in Table 2 that the lethal impact of the M o u n t Pe-
Directflow zone. Close to the crater there is little chance
of surviving burial or obliteration from the explosive
force of an eruption. The bodies of victims are unlikely
to be found. Just beyond the outer limits of this zone
the evidence from M o u n t St. Helens indicated that
death will be near instantaneous from exposure to the
high temperature of the nu6e if the force is survived -
Table 2. Dead: injured ratios in five eruptions for which information is available
Eruption
VEIa
Number of
deaths
Dead: injured
ratio b
Mount Pel~e, .1902
La Soufri+re, 1902
Taal, 1911c
Mount Lamington, 1958
Mount St. Helens, 1980
4
4
4
4
5
28 000
1565
1335
2 942
58
230:1
11 : 1
10:1
44:1
16:1
Volcanic Explosive Index - see Simkin et al. 1981
b Rounded to nearest whole number
c Mortality rate in hospitalised survivors unknown, but assumed to be approximately 35%
(Mount Pel~e - 25%; La Soufri+re - 46%)
a
Table 3. Summary of known and suggested causes of death in pyroclastic flows and
surges
Area of devastation
Location
Open air
Inside intact building
Central
(direct f l o w )
Burial
Obliteration
Heat
Acute occlusion of large airways
with irrespirable particles (asphyxia)
(buildings destroyed)
Peripheral
(channelised flow)
Acute asphyxia from inhalation of
respirable and large particles
Cutaneous burns
Secondary and tertiary trauma
Pulmonary oedema (thermal injury)
Acute respiratory distress syndrome
Lightning
? Toxic gases
Severe body abrasion
Laryngeal oedema
Marginal a
a
Acute asphyxia from particles
Secondary trauma
See Table 1 for definition
Pulmonary oedema
Acute respiratory
distress syndrome
Cutaneous burns
? Toxic gases
(Low probability of
death, but as above)
541
the airways of three victims situated 15 km from the
summit were free of occlusion by ash indicating that
breathing had stopped immediately after the nu+e
struck. It is therefore an over-simplification to attribute
most deaths in a nu6e to asphyxia. Depending upon the
population distribution around a volcano and the type
of nu6e many deaths could be primarily caused by heat,
as suggested by the findings at Mount Lamington and
Mount Pel6e. At Mount St. Helens, however, the bodies
retrieved from both this and the channelised zone were
not reported to be in pugilistic attitudes, suggesting that
the heat transfer of this nu6e was less than in the nu6es
of the former volcanoes. The extent of heat transfer will
depend upon various characteristics of the nu6e, the
most obvious being its temperature, velocity and duration.
Channelised flow zone. The main possible causes of
death in this zone are acute asphyxia, delayed injury to
the lung, cutaneous thermal burns, trauma, lightning
strikes, and perhaps the effects of toxic gases. Burns to
the skin and respiratory tract seem to be mainly caused
by the solid particles in the nu6e ("ash"). A layer of ash
allowed to accumulate on the body may produce full
thickness cutaneous burns through intact, uncharred
clothing. Acute asphyxia from inhaling air laden with
ash will result from finer particles coating the small airways and larger particles occluding the trachea and filling the mouth making breathing impossible. Victims in
the more dilute parts of the nu6e at the periphery of
this zone who survive asphyxia may die within hours
from lung injury caused by inhaling large amounts of
hot, irritant particles. Irritant volcanic gases adsorbed
on to the particles in volcanic plumes (Rose 1977) may
add to the acute toxicity of ash to the lung. Ash hot
enough to cause injury to the respiratory system will
also produce deep cutaneous burns, the extent depending upon the degree of protection afforded by clothing.
Deep thickness burns exceeding 20% of the body's surface can cause lethal shock in fit young adults within a
few hours whilst less extensive burns may become readily infected and contribute to subsequent mortality
from acute respiratory distress syndrome - "shock
lung" (Lancet 1986).
The upper respiratory tract rapidly conducts away
heat from inspired air and it is uncommon in fires for
the airways and lung tissue to be damaged (Moritz et al.
1945). However, if the skin of the face and inside of the
mouth and pharynx have been badly burned then thermal injury to the airways and lungs should be suspected (Chi-Shing Chu 1981; Munro and Robertson
1975). Many of those injured at the Mount Pel6e eruption in 1902 appeared to have died from the delayed
effects of inhaling gases and ash which caused such
burns, as did the three loggers at Mount St. Helens. The
acute consequences of thermal damage t o the respiratory tract include laryngeal oedema, pulmonary oedema or acute respiratory distress syndrome (Fig. 4); all
are difficult to treat even in modern hospitals with intensive care units and so the prognosis in a disaster will
be poor.
Other important causes of death and injury are impacts from flying rocks and other missiles, falling trees,
etc, and due to physical displacement of the human
body. In these respects the force of a nu6e does cause
the secondary and tertiary trauma seen in explosions
(Glasstone and Dolan 1977; Marshall 1977). The sandblasting effect of the nu6e could also cause severe abrasion of the skin producing lesions resembling burns, a
type of injury suspected at the Taal eruption in 1911
(Worcester 1912).
Lightning strikes may also cause a small proportion
of deaths, a possibility strongly suspected in previous
eruptions but which has yet to be confirmed at autopsy.
The heat of the nu6e, or bombs flung out of the crater,
or lightning strikes, may trigger fires and the injured
may be unable to escape from these.
Most volcanic gases act physiologically as irritants
or asphyxiants (Baxter and Kapila 1989), but their concentrations in nu6es are unknown. The most abundant
gas is water vapour: the presence of steam in the nu6e
would greatly add to its already high capacity to cause
airway and lung damage (Chi-Shing Chu 1981; Munro
and Robertson 1975), but condensation would soon occur as the nu6e mixed with air and so the precise role of
steam remains unclear, despite several authors attributing it a prime role. At the Soufri~re eruption in 1902
SO2 could have contributed to some deaths, though this
was disputed. However, relying on the survivors' sense
of smell as an indication of the presence of irritant volcanic gases such as SO2 and HzS is not appropriate,
particularly when the lining of the nose and respiratory
tract has been assaulted by hot ash particles. Survivors
who have subsequently died hours or days later from
pulmonary complications have probably been victims
of acute respiratory distress syndrome due to the hot
ash particles rather than pulmonary oedema caused by
irritant gases. Because the combined effects of inhaling
large amounts of hot particles mixed with injurious
concentrations of volcanic gases are likely to be devastating to the lungs and capable of causing death from
almost instantaneous pulmonary oedema, persons exposed to irritant gases and hot particles in a nu6e are
most unlikely to survive to tell the tale. Survivors' accounts may therefore be misleading as to the immediate
causes of death. Descriptions of sensations such as
"lack of oxygen" or "breathing in a vacuum", as mentioned above, which rapidly pass off on re-entering
fresh air, point to the presence of an asphyxiant gas
such as CO2; or they could be the after-sensation of inhaling hot air and particles.
Inside buildings
A building which remains intact against a nu6e has
been shown above to offer real chances of survival to
those inside by limiting the infiltration of particles, heat
and gases for the few minutes it will take for the nu6e
to pass. The structure may also protect against missiles
and the destructive force of the nu6e. On the other
hand, a thick ash deposit may lead to roofs collapsing
542
and killing or injuring the occupants. Experience at
Mount St. Helens showed that vehicles offer little refuge by comparison.
What will determine survival inside the intact building? The answer lies in the limits of human tolerance
for exposure to heat, inhalable dusts and possibly toxic
gases. Information on human tolerance limits for extreme heat in emergencies is sparse (Birch 1988). In dry,
motionless air at a temperature of 2000-250 ~
with
equality of air and radiation temperature, a lightly clad
person has an average escape time of 2-5 minutes
(Buttner 1950; Buettner 1950), about the same time as
the duration of a nu6e. Air at this temperature would
still be respirable (Buettner 1950) but skin unprotected
by clothing would burn unless it was covered in sweat
(by comparison, temperatures up to 120~C can be readily tolerated in a sauna). The danger from heat transfer
and thermal injury to the skin and respiratory tract,
however, would be greatly increased by the presence of
ash because particles over 70 ~C would burn almost immediately if placed in direct contact with the skin (Moritz and Henriques 1947). All these consequences of
heat transfer would be much greater in the open with
exposure to a fast-moving nu6e.
A large amount of dust at ordinary temperatures is
required to cause asphyxia through occlusion of the airways. Desaga (1950) estimated that the minimum concentration of dust in air required to suffocate a person
was 100 g / m 3, a level which is presumably attained and
exceeded in a nu6e in the open, as well as in severe dust
storms that have suffocated people and animals (Pewe
1981). Such a level would totally obscure vision and so
could not have been achieved in the inside situations
described above in which survivors have reported
watching others die in front of them. Instead, these
rapid deaths could have been due to laryngeal oedema
caused by the acute effects of the hot ash on the upper
respiratory tract (Fig. 4). If the cough reflexes (Cotes
and Steel 1987) were overwhelmed by quantities of fine
ash the larynx would be exposed to the hot particles;
the transitory choking sensation followed by difficulty
breathing as reported by some survivors is probably indicative of this. Survivors told of instinctively stuffing
cloths in their mouths or putting their hands in front of
their faces to protect themselves, whereas it is speculated that others in their panic or need to breathe may
have taken large or rapid breaths through their mouths
and exposed the larynx to direct thermal damage.
Death from laryngeal oedema occluding the airway
may occur within a few minutes. Pulmonary oedema
and severe constriction of the airways provoked by inhaling fine irritant ash particles deep into the lungs
could also be involved.
of certain volcanic gases, especially CO2, CO or H2S, to
high enough levels to cause asphyxia. Many deaths in
the conflagrations following civilian bombing raids in
the Second World War were attributed to CO, or lack
of 02, amongst those sheltering in cellars or basements
(Irving 1963; Department of the Air Force 1950). A
similar fate could overtake people exposed to gases
erupted in the nu+e or produced by the fires ignited in
its wake. Worcester (1912) even suggested that a buildup of volcanic gases inside dwellings could lead to lethal explosions.
Instantaneous death in n u & s
After the Mount Lamington eruption Taylor (1958) recorded that some of the dead were found in sitting or
kneeling positions. Lacroix (1904) mentioned that some
persons were found in frozen positions - sitting or in
the act of walking - in St. Pierre. In the Taal, 1911,
eruption an American doctor (Heiser 1937) remarked
upon Fillipinos amongst the ruins who were standing
upright and embedded in ashes to their knees, still
holding for umbrellas protection over their heads; their
clothes had been ripped off by a violent blast. At Pompeii, a man is said to have died still standing and wielding a hatchet. As mentioned above, at Kilauea in 1790 a
group of warriors and their families were also found in
lifelike positions.
Extensive muscular contraction (cadaveric spasm)
involving the whole body at the time of death is rare,
and is associated with instant, violent deaths, especially
in wartime. Examples include a dead soldier found in a
kneeling position apparently taking aim with a rifle;
and in a shell hole a group of dead soldiers were in
such lifelike postures that the scene was called "the tea
party", one man holding his water bottle as if drinking
from it (Camps 1976). Cadaveric spasm normally wears
off in 18-36 hours along with ordinary rigor mortis. In
the examples cited above the bodies would have been
subjected to the heat of the nu6e which could have had
the possible additional effect of causing the muscles to
undergo instant thermal coagulation (heat rigor) and
help to fix the corpses in position in some instances.
Lightning has been suggested as causing cadaveric
spasm (Somogyi and Tedeschi 1977). However, until
photographic evidence of corpses in such fixed postures becomes available these unusual reports should
perhaps be regarded as apocryphal, or at least as inexplicable, as the turning of Lot's wife into a pillar of salt
(Klotz 1988).
Lahars
Toxic gases
Airtight buildings will also be protective against gases
so long as survivors open windows or go out into the
open air as soon as a nu6e or gas plume has passed
(Baxter et al. 1989), thereby escaping from a build-ul:f
The evidence from the Ruiz eruption showed that severe crush injury and the contamination of wounds resuiting in infections such as tetanus and gas gangrene
were important causes of death. These problems occur
in other natural disasters in which victims with compression injuries are trapped for long periods (Stewart
543
1987). As in e a r t h q u a k e s t r a p p e d s u r v i v o r s m a y still b e
f o u n d u p to a w e e k o r m o r e a f t e r the d i s a s t e r has
struck, b u t the r e s o u r c e s r e q u i r e d for t h e s u c c e s s f u l
t r e a t m e n t o f the " c r u s h s y n d r o m e " m a y b e b e y o n d
t h o s e a v a i l a b l e l o c a l l y ( R i c h a r d s et al. 1989).
Conclusion
This a n a l y s i s h a s s h o w n the n e e d for t h e a d e q u a t e inv e s t i g a t i o n o f the c a u s e s o f d e a t h a n d i n j u r y in f u t u r e
e r u p t i o n s if v o l c a n i c d i s a s t e r p l a n n i n g a n d m a n a g e m e n t are to b e p l a c e d o n a scientific basis a n d t h e m o r e
s p e c u l a t i v e c o n c l u s i o n s o f t h e p r e s e n t p a p e r are to b e
p u t to t h e test. A t a s k f o r c e o f m e d i c a l scientists s h o u l d
w o r k w i t h v o l c a n o l o g i s t s i m m e d i a t e l y after m a j o r e r u p tions to i n v e s t i g a t e the m e d i c a l effects in the d e a d a n d
survivors.
E m e r g e n c y p l a n n i n g s h o u l d i n c l u d e m e a s u r e s to
p r o t e c t a g a i n s t t h e t h e r m a l a n d r e s p i r a t o r y effects at
the e d g e o f a nu6e w h e r e survival h a s b e e n s h o w n to b e
f e a s i b l e u n d e r s h e l t e r o r i n s i d e s t u r d y b u i l d i n g s . Survival m e a s u r e s a g a i n s t m u d flows are difficult to e n v i s a g e
a n d the a d v a n c e d r e s c u e m e t h o d s a n d m e d i c a l m a n a g e ment needed may be beyond local resources.
The personal and public preventive health measures
w h i c h s t e m f r o m this s t u d y a n d t h a t n e e d to b e a d o p t e d
to c o u n t e r t h e i m p a c t o f a nude, t o g e t h e r with t h e i m p l i c a t i o n s f o r d i s a s t e r p l a n n i n g , will b e d i s c u s s e d in a subsequent paper.
Acknowledgements. I thank Prof R. S. J. Sparks, Prof A. Gresham
and Dr J. Guest for their encouragement and advice, and the following for their assistance in the preparation of this paper: Dr R.
W. Johnson, Ms S. van Rose, Dr C. Kilburn and Dr D. Tedesco.
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