Tsunami are unpredictable hazards, yet for many years geographers like myself have been attempting to educate residents of tsunami-prone areas with what to do if warned that the arrival of a tsunami is imminent.
The standard advice for coastal residents that feel an earthquake or who have been issued with a tsunami warning is to get up high. Preferably this should be interpreted as meaning get to higher ground, but on coastal lowlands the advice is to go into the upper floors of buildings and even in some countries the advice is to adopt a palm tree and climb to the top of it to get above the flow of the tsunami! One shouldn't try to escape inland unless the ground rises quickly as tsunami can penetrate many kilometres inland on coastal lowlands travelling at the speed of a 30mph car - it's difficult to outrun if roads are jammed with traffic or debris from any preceding earthquake.
In the Indian Ocean tsunami of 26 December 2004 this advice served well in many places away from the earthquake epicentre, except Banda Aceh, with even hotels located on the beach surviving the tsunami strike and people who managed to get upstairs on the whole were OK; it was people who were stranded on beaches or in streets or on coastal plains that sadly made up the majority of the c. 250,000 victims.
Friday's 8.9 magnitude earthquake and tsunami in Japan made most of this advice almost useless. Eyewitnesses have reported that tsunami warning sirens sounded within a minute of the earthquake, so the warning system worked well. But what were residents supposed to do in response?
Within a few ten’s of minutes, due to the close proximity of the coast to the earthquakes epicentre, the tsunami quickly mounted the coastal lowlands near the city of Sendai in northeast Japan. High ground is kilometres inland in this region so the only survival tactic available to the residents was to go into the higher floors of buildings. However, the height, speed and power of the tsunami was so great that it demolished many buildings in its path.
Each building the tsunami destroyed contributed to the debris it had armed itself with as it progressed inland from the shore. So with boats, shipping containers, cars, and building debris, the tsunami effectively became a bulldozer flattening all in its path. Only a few tall buildings, such as the five-storey hospital in Shizugawa remained standing, but even here staff evacuated patients from the lower floors up into the third floor only for the tsunami to submerge that floor and the fourth floor above! Only the fifth floor and roof top stayed above the torrent. Fleeing inland was also difficult as the tsunami apparently penetrated around 10km inland in some places.
Interactive Google Map of the area around Sendai, northeast Japan. The earthquake epicentre is located c. 130km to the east.
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