Tuesday, 10 June 2014

The tsunami count is updated: WA holds record

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The largest recorded tsunami inundation in Australia was a 7.9m wave that hit Steep Point (pictured) near Shark Bay, following an earthquake off Java in July 2006. The largest recorded tsunami inundation in Australia was a 7.9m wave that hit Steep Point (pictured) near Shark Bay, following an earthquake off Java in July 2006. Image: Finn Propper

WESTERN Australia has been hit by 19 tsunamis since 1838 with Perth, Albany, Geraldton and the Pilbara all copping at least one of the waves, according to an update of the Australian tsunami database.

The state holds the record for the largest historical tsunami inundation in Australia, a 7.9m wave that hit Steep Point, near Shark Bay, following an earthquake off Java in July 2006.

Another tsunami that hit the Swan River in 1838 reached an estimated maximum height of 6.0m above sea level and is thought to have been caused by a meteorite.

Tsunamis differ from regular waves in that they have a very long wavelength—sometimes hundreds of kilometers, and this can make tsunamis initially resemble a rising tide.

UNSW Australia professor of tsunami science James Goff, who authored the database, says the main concern for WA is tsunamis generated by earthquakes south of Java, in Indonesia.

“If there’s an event just off Java, that fires tsunamis directly towards places like Steep Point, potentially to a lot of those coastal communities where we have some fairly significant infrastructure for iron ore extraction and oil,” he says.

Professor Goff says the fact that the record 2006 tsunami at Steep Point was generated by a moderately small earthquake and produced a moderately small wave “raises a flag on the play”.

“If that’s happened in fairly recent historic time… then perhaps we’ve had bigger events that have happened in the past,” he says.

The tsunami database updates an earlier database from 2007 and takes the number of tsunamis in Australia from 57 (including two erroneous events) to 145.

He says most of the tsunamis that happened before the late 1950s were discovered simply by trawling through old newspaper records.

Many of the more recent tsunamis in the database had a wave height of only a few centimetres and were discovered because of anomalies in tide gauge data that could not be explained by cyclones or large storms.

The database details 23 tsunamis known to have hit WA.

The state also holds the record for the oldest tsunami in the world, a wave that hit the Pilbara following an asteroid impact 3.47 billion years ago.

Professor Goff hopes to make the full Australian tsunami database available online.

He also wants to see the databases of different countries put together so events can be linked, such as an 1870 tsunami that destroyed much of the town of Westport in New Zealand but was only recorded in the Kiwi database following the discovery of a “minute blip” in Sydney tide gauge data.

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