The tsunami as a secondary hazard

When a powerful earthquake strikes beneath the sea, the shaking is often only the beginning. The sea itself can rise and surge inland as a tsunami. The wave floods coastlines, sweeps away buildings and kills people, including people some distance from where the earthquake happened.

Geographers call the tsunami a secondary effect. It is triggered by an earthquake or a volcanic event rather than being the event itself. Of all the secondary effects, it is the best known, and it is often more destructive than the earthquake that set it off.

smoke over burning port after 2011 Japan tsunami — Black smoke rises over the burning port and industrial area of Sendai after the tsunami, 12 March 2011. U.S. Navy photo, public domain, via Wikimedia Commons

Look at the photo from Japan in 2011. The main damage visible is fire spreading through a port and its industry, a disaster set off by the arrival of the water. One tsunami can start a chain of further harm along a whole coastline. The wider list of secondary effects, such as landslides and lahars, is covered in the lesson on causes and consequences of tectonic activity.

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