Warning system worked but tsunami was too powerful
by Tryst Williams, Western Mail
Mar 16 2011
The devastating impact of the Japanese tsunami has highlighted the need for a review of the response to warning systems, says Professor Simon Haslett of the University of Wales
TSUNAMIS 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.
In some countries, such as Nicaragua, the advice has even been to adopt a palm tree and climb to the top of it to get above the flow of the tsunami. Indeed, a similar tactic served one Japanese man well when he is reported to have shimmied to the top of a pole and just managed to keep his head above water as the tsunami made landfall last Friday.
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 December 26, 2004 this advice to get up high served well in many places away from the earthquake epicentre 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 adjacent to the earthquake epicentre, such as Banda Aceh on the Indonesian island of Sumatra, that sadly made up the majority of the 250,000 victims. Friday’s magnitude 9.0 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?
The earthquake occurred at 2.46pm local time, with most adult inhabitants out at work, children in schools and colleges, and many of the elderly in their homes. At first the quake was estimated to have a magnitude of 8.8, but then through the day it rose to 8.9, and then just before I gave an interview on the 6 o’clock news on BBC News Channel it was revised upwards to magnitude 9.0 by the United States Geological Survey, which I was able to tell viewers around the world.
Due to the close proximity of the coast to the earthquake’s epicentre, within a few 10s of minutes to an hour and a half, the tsunami quickly mounted the coastal lowlands near the city of Sendai in north-east Japan. The areas worst affected included the Miyagi and Fukushima Prefectures, from Sendai in the south then north to the city of Kesennuma.
High ground is many kilometres inland in some areas in this region so the only survival tactic available to many 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. It has been estimated that the wave was up to 10m high in places and resembled a gigantic river flowing from the sea.
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.
Then as soon as the tsunami wave inundated the land it withdrew – in what is termed the backwash – back out to sea, taking with it some of the debris it collected and also people caught up in the wave. Indeed, one man was found 9km out at sea marooned on a floating rooftop. Many “before and after” photographs that are emerging on the internet clearly show that new channels have been created on the coast by the tsunami backwash draining the floodwater back into the sea.
But it may not all be over yet. The Japanese Meteorological Agency, the national organisation responsible for monitoring natural hazards, has said that there is a 70% chance of an earthquake in the magnitude of 7 or greater within the three days starting from 10am last Sunday, and a 50% within three days starting 10am today. A lethal tsunami is usually only generated by an earthquake of 7.5 magnitude or more, so unless another earthquake surpasses that then we hopefully won’t see another devastating tsunami.
What advice can coastal scientists give to residents living in such areas as north-east Japan and Banda Aceh?
Building high and sturdy refuge platforms may be an option, as have been built elsewhere, but even these may not have withstood the force of Friday’s tsunami. Scientists now need to think long and hard about how we might be able to better prepare, educate and protect people who live in coastal lowland areas like Sendai who face considerable risk from such an unstoppable tsunami.
Simon Haslett is Professor of Physical geography and Dean of the School of STEM at the University of Wales, and he is author of Coastal Systems (2008, Routledge)