Tsunami: Causes, History, and Modern Warning Systems

A tsunami is a wave or series of waves, sometimes of great height, triggered by the sudden displacement of water due to an earthquake, volcanic eruption, landslide, or the like. Tsunami waves are not particularly high in deep water, but they move at up to 500 miles an hour and gain in height as they reach shallower water. If the trough, or low point, beneath the tsunami’s crest reaches land first, it draws water back from the shoreline for a short period before the crest strikes the shore. Also known as seismic waves, tsunamis are capable of inflicting enormous damage on seacoasts.

Approximately 80 percent of tsunamis occur in the “Ring of Fire,” a tectonically and volcanically active belt extending around much of the Pacific Basin. They are particularly common in Japan, and their name itself is Japanese, combining the Japanese characters for tsu, meaning “harbor,” and nami, meaning “wave.”

One of the deadliest tsunamis of all time was triggered by a 9.1- to 9.3-magnitude earthquake—the third-largest ever measured—in the seabed off the Indonesian island of Sumatra on December 26, 2004. Its waves (technically known as a “wave train”) reached 100 feet in height and raced more than two miles inland in many locations. The combined disasters took the lives of at least 230,000 people, most of them Indonesians, and inflicted an estimated $10-billion worth of damage. A number of witnesses captured scenes of the tsunami on their cell phones, allowing the rest of the world to see the cataclysm and ensuing devastation.

A tsunami generated by a 9.0-magnitude undersea earthquake struck the east coast of Japan on March 11, 2011. The tsunami’s waves surged 6 miles inland and flooded more than 200 square miles, eventually washing some 5 million tons of debris back into the Pacific Ocean. The tsunami also damaged the cooling system of the Fukushima Daiichi Nuclear Power Plant, creating a meltdown that led to hundreds of tons of radioactive water leaking into the ocean. Although the country’s early warning system undoubtedly saved a number of lives, more than 18,000 people were killed. The total damages from the quake and tsunami were estimated to be $300 billion.

On occasion, tsunamis appear to have altered the course of human thought and even history. One of the most famous occurred in 1755 on All Saints’ Day—November 1. That morning, an 8.5-magnitude earthquake in the Atlantic Ocean rocked the coast of Portugal, including the country’s capital city of Lisbon at the mouth of the Tagus River. As the resulting tsunami raced upriver, fires broke out in the sections of the city built on higher ground, and within a short time, Lisbon had been destroyed and some 60,000 of its residents had perished. Subsequently, a number of philosophers took up the larger issues involved in the disaster, including Voltaire (1694-1778), who touched upon the destruction in his novel Candide (1759) to satirize the concept that humankind live in the best of all possible worlds.

One of the most powerful and destructive tsunamis of all time may have taken place in the Mediterranean Sea in the second millennium BCE when the Greek island of Santorini (Thera) was virtually destroyed by a volcanic eruption. This eruption appears to have created a tsunami that struck the northern coast of nearby Crete, possibly contributing to the decline of the Minoan civilization centered there.

Seismologists fear that a severe earthquake may occur off the coast of the Pacific Northwest in the near or intermediate future. If so, it could be a repetition of a quake of 8.7 to 9.2 magnitude that took place in the same location in 1700, producing a tsunami noted in Japanese records of the time. Such a combination of events in the twenty-first century could devastate the large coastal cities of Oregon, Washington, and British Columbia. In hopes of mitigating the impact of this and other potential threats, the US National Oceanic and Atmospheric Administration maintains National Tsunami and Pacific Tsunami warning centers that monitor seismic data and issue emergency alerts through various telecommunication systems. Agencies in Australia, India, and Indonesia provide similar services. Recognizing the grave danger that the deadly phenomenon pose, the United Nations designated November 5, 2016, as the first World Tsunami Awareness Day.

FURTHER READING: Berlin, Jeremy. 2016. “Tsunami Memories.” National Geographic 229 (3): 124-31.

Hadingham, Evan. 2008. “Minoan Tsunami.” Discover 29 (1): 8-14.

Henderson, Bonnie. 2014. The Next Tsunami: Living on a Restless Coast. Corvallis: Oregon State University Press.

Parker, Bruce B. 2010. The Power of the Sea: Tsunamis, Storm Surges, Rogue Waves, and Our Quest to Predict Disasters. New York: Palgrave Macmillan.