Tsunamis

When they approach land, where the water is much shallower, their true height and power is seen. First, the water recedes from the coast, often by a distance of hundreds of metres. Then the wave arrives. At its maximum, the 2011 Japanese tsunami was 40 metres high.

The main defence against a tsunami is to evacuate as many people as possible before it arrives, which is not easy as sometimes there is little warning. Evacuation may be to get people inland or simply getting them as high as possible in a tsunami-proof building. Building high sea walls could also help. When a tsunami is created close to a coastline, there may be only a few minutes warning. It might be possible to out-run the wave in a motor vehicle on a straight road but on foot, there is no chance, they move rapidly.

The primary effects of a tsunami are the destruction of property and flooding. The secondary effects are much greater and can include both short- and long-term events. For example, after the Japan tsunami, the oyster fishing industry was destroyed in the area, there were fires from burst gas pipelines, people left the area forever in fear of future tsunamis and large amounts of floating debris entered the Pacific ocean with the backwash from the tsunami.

After any natural disaster, there are both short-term (e.g. rescuing injured or stranded people, erecting temporary housing and putting out fires) and long term responses. The long-term responses are mainly about cleaning up and rebuilding, together with improving early warning systems and other tsunami defence infrastructure like sea walls.