Following the tsunami which devastated the island of Samoa in the South Pacific earlier this week, we explore the phenomenon that can leave lives and entire countries destroyed.
What causes a tsunami?
Tsunamis occur when there is a large-scale disturbance of the sea. The most common causes are earthquakes, but volcanic eruptions or landslides can also have the same effect, forcing a vast amount of water suddenly upwards, creating enormous waves which can hit land at up to 45mph, often with devastating effect.
Tsunami - the deadly wave
Tsunami means ‘harbour wave’ in Japanese, but they’re not the sort of friendly wave you'd want to tussle with on a surfboard. These monster waves can travel at speeds of up to 500mph at sea, slowing to around 50mph as they reach land, often with a height of around 40 feet.
Those that hit Samoa this week were up to 15ft high. In the 2004 Indian Ocean tsunami, waves of up to 100ft high were reported.
A tsunami waves’ enormity can make them hard to detect when in deep sea, as can the fact they generally don’t break, instead hitting the shore like a tidal bore. The waves often travel for up to five miles inland, destroying everything in their path. Around 80 per cent of the world's tsunamis occur in the Pacific Ocean.
Warning signs
There are dedicated centres around the world whose job it is to monitor earthquakes and sea pressure, in order to predict impending tidal waves.
A Pacific Tsunami Warning System in Hawaii is among a number of facilities using pressure sensors and computer mapping to watch for earthquakes which might trigger a tsunami.
How to survive a tsunami
There are warning signs to look out for outside of a tsunami watch centre. The main thing to watch out for is drawback - when the water along the shoreline recedes dramatically, exposing normally submerged areas. This is usually accompanied by a sucking noise. If you witness drawback seek high ground immediately.
It has also been reported that animals head for the hills before an impending tsunami, so keep an eye on the wildlife too.
Disastrous tsunamis
Tsunami: Samoa, September 2009
Destruction caused: At least 100 people killed and entire villages destroyed in Samoa.
An 8.3 magnitude earthquake was the cause of the tsunami which has just battered the islands of Samoa and American Samoa in the South Pacific. The four waves which hit the coast were around 20 metres high, with waves reaching as far as Japan.
Thanks to an early radio warning, many thousands of residents managed to flee to higher ground in time.
Tsunami: Indian Ocean, December 2004
Destruction caused: Around 230,000 people were killed, making this one of the worst natural disasters in recorded history.
Hitting Thailand, Sri Lanka, Indonesia and India, the 2004 Tsunami was utterly cataclysmic, with waves up to 100 feet high battering the coasts and causing floods which lead to a staggering loss of life.
The earthquake which caused it measured over 9.0 on the Richter scale, making it the second largest ever recorded.
Tsunami: Papua New Guinea, July 1998
Destruction caused: Around 2,000 people killed, with a further 9,500 made homeless
This Tsunami wasn’t directly caused by an earthquake – the one that hit offshore Papua New Guinea measured only around 7.1 on the Richter scale.
It did, however, create the landslide which triggered waves of around 15 metres high and which destroyed a number of villages in their path.
Tsunami: Hokkaido, Japan, July 1993
Destruction caused: 250 people killed
In July 1993, an earthquake of 7.8 magnitude struck the coast of Hokkaido and within minutes the Japanese authorities had issued emergency warnings.
Sadly they weren’t quick enough to save the residents of the island of Okushiri which neighboured the epicentre, and from which around 200 of the 250 deaths came. It took a mere 17 minutes for the waves to destroy Okushiri.
Tsunami: Tumaco, Ecuador, December 1979
Destruction caused: Around 250 people dead, a further 800 injured
An earthquake off the coast of Colombia and Ecuador started this tsunami, which caused most destruction to Colombia, in particular the coastal city of Tumaco.
As well as wrecking a number of small fishing villages, the waves claimed around 250 lives and wounded another 800, wreaking havoc in the city and surrounding towns.
Tsunami: Moro Gulf, Philippines, August 1976
Destruction caused: Approximately 5,000 killed, 2,000 missing and 9,000 people injured
The Moro Gulf coastline in the Philippines felt the full impact of a tsunami caused by an earthquake in Mindanao, with around 700 kilometres of coastline battered by waves which claimed over 5,000 lives. As well as the casualties, the impact on such a large area left nearly 100,000 people homeless and entire towns in ruins.
The final Curious © phrase:
“Did you know that the word "tsunami," which is now being used worldwide, is a Japanese word? This is indicative of the extent to which Japan has been subject to frequent tsunami disasters in the past”
(Junichiro Koizumi)
