On March 11, 2011, a 9.0 magnitude earthquake shook the floor of the Pacific Ocean. The earthquake triggered a tsunami that devastated Japan. Although tsunamis do not occur often, when they do, they can be deadly.

A tsunami is a series of large, fast-moving waves caused by an earthquake in the ocean. Other events that can cause tsunamis include: meteorite impacts, volcanic eruptions, and landslides. Tsunami waves can race across the ocean at hundreds of miles per hour. A tsunami moves in all directions from its source, possibly reaching land at multiple locations.

At first, tsunami waves may not appear dangerous. Tsunami waves may pass under a ship floating on the ocean and go unnoticed by the crew. This is because the distance between wave crests can be many miles long. Plus, the wave may only be a few feet high in the deep ocean waters. However, as the tsunami travels over the shallow ocean floor approaching land, its height grows and speed slows. The waves then collapse upon the land, flooding the low-lying coast. Tsunami waves may be tens or even a hundred feet high when they make landfall. Multiple waves crash along the coast as the tsunami makes impact. These waves may come minutes or even hours apart.

Tsunami warning systems are in place around the world. Seismic detectors monitor for ocean earthquakes. Ocean buoys track changes in sea level heights. When a tsunami threat is identified, advisory and warnings are issued. If you are ever an area where a tsunami warning has been issued, move to higher ground and inland. Advanced warning may come only minutes or an hour before the tsunami hits land.