Tsunamis 101 | National Geographic

A tragic scene: entire cities flooded, entire towns inundated, an unending stream of floating debris—buildings, cars, people swept away in an unstoppable wave. It's a brutal reminder tsunamis are dangerous and unpredictable.

But what causes these giant waves, and what can be done to minimize their impact? Tsunamis can strike with little warning because they're usually triggered by a sudden displacement of ocean water, like volcanic eruptions, landslides, meteorites, or the most common culprit: earthquakes.

In the deep ocean, a typical tsunami wave is barely noticeable and poses little threat. However, the waves can spread out thousands of miles, rolling across the ocean at speeds up to 600 mph. As the rolling water reaches the shoreline, the wave's friction against the shallower floor slows it down and raises its height.

By the time it reaches the shore, the wave can be as tall as 100 ft. Unlike ordinary waves, a tsunami wave doesn't crest and break; instead, it moves forward like a solid wall of water that crashes over the coastline, obliterating almost everything in its path. And just when you think the danger is over, it recedes, dragging everything back to the ocean.

Tsunamis have multiple waves, which can continue to hit the shore for several hours, causing even more destruction. The word "tsunami" originates from Japan, a country that sits on a geographic location that makes it an easy target for these natural disasters. In 2011, it was struck by a tsunami that claimed nearly 16,000 lives.

But the deadliest tsunami in history is believed to be the Indian Ocean Tsunami of 2004. The U.S. Geological Survey estimated that tsunami released the energy equivalent of 20,000 to 23,000 Hiroshima-type atomic bombs. An earthquake created an estimated 600-mile rupture on the ocean floor; this caused the tsunami to form and then travel at the speed of a jetliner, reaching over 11 countries and traveling over 3,000 miles, killing more than 220,000 people.

Because they can strike so quickly with such deadly force, tsunami warning centers around the globe are on constant alert, monitoring underwater earthquakes large enough to trigger massive waves. Their ultimate goal is to alert vulnerable coastlines and give residents time to seek higher ground before a tsunami hits.