What Causes a Tsunami?
What causes a Tsunami? Many people worldwide can recall watching footage of the devastation caused by the 2004 Indian Ocean earthquake, a colossal 9.3 magnitude quake that triggered a chain of deadly tsunamis. Beginning with an initial surge of about 108 feet, the tsunami killed almost a quarter million people, making it the deadliest tsunami in recorded history.
Water is life’s most vital resource, a necessity for humans, animals and plants alike. Yet, when provoked into the form of a tsunami, it has killed millions and obliterated towns and cities throughout the centuries, each time raising the question: how does life’s sustaining liquid turn into a destructive force?
The Causes of Tsunamis
Tsunamis are generated by sudden displacements of large volumes of ocean water caused by volcanic activity, shifts in the sea floor, landslides and–most frequently–undersea earthquakes. These movements push the overlying water around to create the initial waves of a tsunami. As the waves spread outward, 360 degrees from the quake’s epicenter, they swiftly grow into the frequently seen 30-foot waves that damage coastal settlements.
In the deep ocean, these first waves are just small undulations, but they become increasingly larger and more dangerous as they move toward shore. When the waves hit shallower water, the shallow depth both slows and bunches them together, significantly increasing their height. By the time they approach the coast, they can be enormous waves that wield ravaging potential. Tsunami is a Japanese word that derives from this situation: “tsu” means harbor and “name” means wave, creating a literal meaning of “harbor wave.”
Just three years ago, a 9.0 magnitude earthquake off the coast of Japan triggered catastrophic tsunami waves that grew to heights of 133 feet. It was a quake so powerful that it altered the planet’s axis by 6.5 inches and relocated Japan eight feet closer to the United States. In some areas, these waves traveled more than six miles inland. The destruction to Japan was considerable, damaging over a million buildings and killing almost 16,000 people while injuring another 6,000.
Japanese Prime Minister Naoto Kan called the tsunami the worst crisis for Japan since World War II, and the World Bank estimated the economic cost to Japan at $235 billion, the most expensive natural disaster in recorded world history.
Because tsunamis travel at an astonishing speed–one comparable to that of a jet airliner–coastal towns near an undersea earthquake suffer the worst damage. Though natural disasters like tsunamis cannot be avoided, the consequences can be very different depending on the wealth of the region.
“Most of the people killed by the tsunami died because they are poor,” says Michael Clemens, a research fellow at the Center for Global Development. “Even with improved warning systems, little can be done to prevent natural disasters from becoming massacres as long as people’s livelihoods, infrastructure and public health conditions are precarious.”
A high magnitude quake and tsunami in the Northern Pacific Ocean costs fewer lives and wreaks less infrastructural damage since that oceanic area is surrounded by wealthy nations like the U.S. and Japan, who maintain high-tech detection and monitoring systems. Additionally, these prosperous countries have stronger, more durable buildings and infrastructure than poor coastal towns and countries. In poor countries, a tsunami can throw millions below the poverty line by destroying homes and livelihoods.
“To minimize the death toll in future disasters, we need to do a much better job of supporting long-term economic development in these countries,” added Clemens.
– Annie Jung
Sources: Voice for America, Geology, Beach Safe BBC, NOAA Center for Tsunami Research, NY Daily Times, Center for Global Development
Photo: WeatherWatch12