Historical Event Review
Overall, an average of 3 (range 1-10) volcanic eruptions affecting human populations occurred annually. When trends in reporting were assessed by source, the number of events reported annually by NOAA (range 8-27) was more consistent than EM-DAT (range 2-53), where the frequency of reported events increased over time and in particular after 1970 (Figures 2 & 3). The impact of volcanic events across regions from 1979 - 2009 is summarized in Figure 4. The World Health Organization defined regions of the Western Pacific (WPRO), Americas (AMRO) and Southeast Asia (SEARO) each accounted for more than 20% of volcanic eruptions, while both the Africa (AFRO) and the European (EURO) regions each accounted for less than 10% of eruptions; no volcanic eruptions were reported in the Eastern Mediterranean (EMRO) region. When deaths were assessed, the vast majority occurred in the AMRO region, which had 73% of reported deaths for 1900-2008; significant minorities of deaths were reported in the SEARO (16%) and WPRO regions (8%). WPRO was the region with the largest affected, which comprised approximately half of the global affected population in each time period. The AMRO region, which reported the greatest number of volcanic events and deaths for both time periods, had less than 20% of the total affected population. The overall impact of volcanic events on human populations is summarized in Table 3.
Mortality and Injury. When mortality data from the three sources were combined, deaths were reported in 76% (n=237) of eruptions since 1900. Overall, 91,834 deaths (range 85,169-102,372) resulting from volcanic eruptions were reported in the historical event review. For eruptions where mortality was reported, there was a median of 6 (mean = 536; 5% trimmed mean= 117; range 1-30,000) deaths per eruption when using the highest reported death toll. The ten most deadly eruptions accounted for 81.1% of reported volcano mortality (Table 4). Deaths were concentrated in Martinique (30.3% or 31,023 deaths, 3 events), Colombia (23.5% or 24,099 deaths, 7 events), Indonesia (18.4% or 18,840, 70 events) and Guatemala (12.2% or 12,522 deaths, 10 events). Injuries were reported in 59 (18.8%) events where a total of 14,726 injuries (range 11,549-17,917) were documented. In eruptions where injuries were reported, there was a median of 11 (mean = 304; 5% trimmed mean=93, range 1-10,000) injuries per eruption when the highest reported figure was used. To estimate the total number of injuries due to volcanic eruptions, it was presumed that injuries would occur in events where deaths were reported. A total of 237 eruptions with fatalities occurred were reported; when the median and 5% trimmed mean for injuries were applied to the remaining 178 events with fatalities, it was estimated that between 1,958 and 16,643 unreported volcano related injuries may have occurred between 1900 and 2008.
Data to compute ratios of deaths to injured and affected populations was available for 58 and 130 historical events, respectively. Wide variation in ratios was observed, presumably because of variation in reporting quality. For 1900-2008, the median ratio of dead: injured was 0.63 (mean 2.53, range 0-36). When compared to the affected population, there was a median of 0 deaths per 1000 affected (mean = 96, range 0-6709). Point estimates for both ratios decreased by approximately half in the period of 1980 to 2008, which may suggest improvements in disaster response and preparedness; however, these changes were not statistically significant. Multinomial logistic regression for predictors of evacuation indicates that time period of the eruption (among other factors) is significantly associated with evacuation, where eruptions occurring in 1980 and later were 20.25 (CI: 8.01-51.21) more likely to have an evacuation reported as compared to those between 1900-1939, which also suggests improvements in preparedness and response (Table 5).
Affected Population and Other Impacts. An estimated 4.7 million people were reported to be affected by volcanoes between 1900 and 2009, including 4.2 million that were rendered homeless. However, these figures are likely to substantially underestimate the true impact of volcanoes on human populations because estimates of the total affected population and the homeless population were reported in 49.8% (n=156) and 43.3% (n=135) of events, respectively. The distribution of the affected population was highly skewed: on average 22,698 people were affected in an eruption, though the median affected population was significantly lower at 3,000. Other measures of effect on human populations reported by GVP included evacuation and damages in excess of one million dollars; these data were reported for 296 (94.6%) of events. Damage in excess of one million dollars were reported in 75.0% of events (n=222/296) and evacuation was reported in 56.5% (n=177/296) of events.
Eruptive characteristics were reported by GVP for 296 (94.6%) eruptions in the event file. When assessed by volcano type, proportions were as follows: stratovolcano 73% (n=228), complex volcano 13% (n=39); shield volcano 7% (n=22); caldera 4% (n=11); cinder cone 2% (n=4); and others 2% (n=4). VEI is a logarithmic scale (0-8) indicating the amount of mass ejected during an eruption and the size of the eruption column. 13
In general, VEI 1-3 events generate localized hazardous phenomena and VEI 4-5 events have the potential for disruption on a regional scale; VEI 6+ events can affect the entire planet via their impact on global climate 10
. The average VEI of eruptions was 2.60 (Table 6). In a multinomial regression model, an average of 362 additional deaths (CI: 57-667, p=.020) were associated with a one unit increase in VEI after controlling for evacuation.
Systematic Literature Review
A review by Tanguy (1998) estimates 221,907 deaths from major volcanic eruptions over the past two centuries (1783-1997), which includes 90% of recorded deaths throughout history. Volcano related mortality was attributed to primary volcanic phenomena (see table 7 for definitions) including ash and pyrolcastic flows (36%), mudflows or lahars (17.1%), volcanogenic tsunamis (16.9%), and post-eruption epidemics or famines (30.3%). Of the 79,286 deaths due to primary volcanic phenomena, 75.0% were attributed to pyroclastic flows or surges and magma-generated sector collapse, followed by debris avalanches (12.6%), ash fall including ballistic projectiles (11.6%), and lava flows (0.8%). Four volcanic eruptions (Tambora, 1815; Krakatau, 1883; Mt. Pelee, 1902; and Ruiz, 1985) accounted for more than 66% of deaths, and the principal causes of death, including famine, tsunamis, pyroclastic flows, and lahars varied in each event. While famine and epidemics were the principal causes of mortality in earlier volcanic events, they currently present much less of a risk due in large part to international relief and humanitarian assistance efforts 14
Another database developed by Witham (2005) considers all volcano-related incidents (n=491) with human impacts between 1900 and 1999, including 296 (60%), which were classified as disasters. Witham found the number of people impacted per event was substantially greater in middle income than in high income countries, with middle income countries reporting the highest numbers of volcano related deaths, injuries, and affected populations 2
. While fatalities were the most frequent outcome, observed in 53% of events, the largest consequence was displacement, which accounted for 94% of the affected population. Similar to historic findings, the study found fatalities to be concentrated in relatively few large events. The eruptions of Mt. Pelee (1902) and Nevado del Ruiz (1985), which together accounted for more than 50% of deaths, and the top ten events combine to account for more than 90% of deaths. During the 20th
century, pyroclastic flows were the primary cause of death followed by lahars (which were also the principal cause of injury), and tephra was a primary cause for evacuation and displacement 2
. Tephra, which includes fragmental material from volcanoes and volcanic ash, is also a common cause of trauma-related deaths either by projectile impact or collapse of ash-covered roofs 1
. The three main causes of direct mortality in recent volcanic eruptions include asphyxiation from ash, thermal injuries from pyroclastic flow, and trauma (Table 2) 15,16
. A review of health hazards from volcanic gases indicates that volcanic gases account for less than 1% to 4% of mortality, though this is a likely underestimate because studies neglect volcanic degassing when unassociated with eruptive activity, and because the extent of dispersion of volcanic gases is not always appreciated 17
. Historical estimates in the 20th
Century suggest that 2,000 deaths have resulted from volcanic gases, with the most hazardous volcanogenic gases being carbon dioxide, sulfur dioxide, hydrogen sulfide, mercury, and radon 18
Transient increases in trauma-related injuries resulting from traffic accidents and falls, and morbidity, primarily ocular irritations and respiratory symptoms, are observed following volcanic eruptions. Increases in communicable diseases and long-term health effects are not attributed to volcanic eruptions, however, volcanism associated morbidity is likely underestimated 9
. Ash fall can have health implications for populations as far as hundreds of kilometers away 19
. A recent review of the respiratory effects of volcanic ash suggests that they are short-lived and dependent on the mode of ash generation and particle size, among other factors 20
. De novo appearance of ash-related asthma has not been documented, though increases in respiratory symptoms are frequently reported. Higher levels of ash exposure have been associated with increased reports of respiratory symptoms among children 21
and in high-exposure occupation groups 22,23
. Increases in emergency room visits for respiratory problems have been observed following recent volcanic eruptions in the United States and Ecuador, where children under five 24
and individuals with pre-existing lung conditions such as asthma or chronic bronchitis were at increased risk for the development of respiratory symptoms 20,22,23
. Recently, adverse cardiorespiratory health effects have been associated with chronic exposure to volcanogenic gases in both Hawaii and Montserrat 25,26
and historically, where one study suggested that adverse health symptoms in Europe during the summer of 1783 was associated with volcanic gases and fogs 27
. Review findings indicate that volcanic eruptions are associated with short-term increases in morbidity, primarily ocular irritations and respiratory symptoms.