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A tsunami, the Japanese word for “large harbor wave,” is a series of large waves made by a sudden vertical shift of water. Aquatic earthquakes are the most common cause, but volcanic activity, landslides and impacts of meteorites may also create tsunamis. Earthquake-generated tsunamis develop when tectonic plates shift quickly in a vertical direction and the overlying water is displaced. Waves created by this motion move away from the source. In deep waters, the surface disturbance of water can be subtle and only create a gentle wave. As the wave reaches shallow waters along the coast, it rises above the surface related to the amplitude of the underwater waves.

Tsunamis have the ability to cause significant loss of life, injury and damage. The 2004 Indian Ocean tsunami caused more than 225,000 deaths across twelve nations, and the 2011 Japan tsunami caused an estimated 28,000 deaths. The objective of a Public Library of Science study was to describe the impact of tsunamis on humans.

Data on the impact of tsunamis from 1900 to mid-2009 was collected via a review of tsunami events from multiple databases and a literature review of publications. Between 1900 and 2009, 94 tsunamis that affected human populations were recorded. There were 255,195 deaths and 48,462 injuries as a result of these tsunamis. Tsunami frequency and deaths were concentrated in the Western Pacific, Southeast Asia, and Americas regions, each of which accounted for almost one third of tsunami events and deaths, but Southeast Asia accounted for 52 percent of the tsunami-affected population from 1900 through 2009 and 95 percent of the tsunami affected population from 1980 through 2009. An estimated 2.5 million people were affected by tsunamis during this time.

The average distance tsunamis travel from source was 74 miles, and the average wave height was 22 feet. The majority of the tsunamis reported were due to earthquakes (95.5 percent), followed by landslides (3.0 percent), volcanoes (0.8 percent), and meteorological events (0.8 percent). The average magnitude for earthquake-generated tsunamis was 8.1 and is considered “great.”

The majority of deaths (89 percent) and injuries reported during this time were attributed to the 2004 Indian Ocean tsunami. The main cause of tsunami-related mortality is drowning, and females, children and the elderly are at increased risk of death. In both Indonesia and Sri Lanka, significantly higher death rates were reported among females who were 1.4 to 2.1 times more likely to die than males. Significantly increased risk of death was also observed in children (1.8 to 4.3 times) and older adults (2.1 to 3.1 times) when compared with younger or middle age adults. Other risk factors included education which was inversely associated with death risk, fisheries-based livelihoods, being indoors at the time of the tsunami, and destruction of the home and physical environment.

A typical tsunami caused 218 injuries. The most common types of injuries were wounds due to physical impact with debris, fractures, and near drowning and/or aspiration. As compared to other types of natural disasters, tsunamis often result in relatively high death rates but have lower rates of injury

There were substantial differences in numbers of deaths by World Health Organization-defined region, with the majority of tsunami events that occurred in the Americas resulting in low (less than 10) deaths and 50 percent of events in the South East Asian region resulting in high (greater than 75) deaths. Areas with low income levels in relation to Gross Domestic Product were significantly associated with higher tsunami mortality. The majority of tsunamis in high income countries resulted in ten or fewer deaths, a considerably greater number of events in low and lower-middle income countries resulted in greater than ten deaths.

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