Monday, November 7, 2011

Tsunamis in Australia

A tsunami is a wave, or train of waves that have been generated by a large scale displacement the ocean. This is usually caused by an undersea earthquake, but can also be the result of landslides, volcanic activity and more rarely, the impact of meteors.

As we have seen in recent times tsunamis can be devastating and immensely lethal. The Boxing Day tsunami of 2004 was one of the great disasters of modern history with over a quarter of a million people losing their lives as giant waves crashed along the coasts of Indonesia, Thailand, Sri Lanka and India. More recently, on March 11 2011, a tsunami struck the coastline of eastern Japan, killing over 13,000 people and producing many billions of dollars worth of damage.

Devastated township in Sumatra following the Boxing day tsunami of 2004. (Image from Wikipedia Commons – click to enlarge)

As a result of these tsunamis, a question commonly asked today is “Can Australia be struck by a tsunami”? The answer is certainly yes and indeed several such events have been recorded over the last 200 years.

However, the threat posed by tsunamis to the Australian coast varies markedly according to location. The risk is low along the southern coastline of the mainland, including South Australia, but moderate along the northwest coast of Western Australia because of its exposure to the geologically active area around Indonesia.

In August 1977 a large earthquake near Indonesia produced a tsunami at Cape Leveque, on the Western Australian coast to the north of Broome, that generated rises in sea level of 6m above the norm.

The Boxing Day Tsunami of 2004 was detected right along the Australian coastline as was another tsunami in May 1960, when a massive earthquake occurred in Chile. This latter event also produced a surge of water along the NSW coast, and boats were torn from their moorings in Sydney Harbour, Newcastle and Evans Head.

Going back further, another massive Chilean earthquake on 14th August 1868 was also detected in South Australia but produced a far greater effect in Newcastle Harbour on the NSW coast, as the tsunami finally reached the area. A contemporary newspaper report described the scene:

"An extraordinary tidal disturbance has been experienced here this morning since half past 6 o'clock, - the vessels at the coal shoots broke from their moorings, one nearly losing her masts; the ship “Lucibelle”, 1000 tons, was swung round four times, although a strong ebb tide was running; and the vessels in harbour swung round in all directions".

Newcastle Harbour – hit by the tsunami of 1868 (Image from Wikipedia Commons – click to enlarge)

In order to alert the Australian public about any tsunami activity approaching the Australian shoreline, the Joint Australian Tsunami Warning Centre was established in 2007, operated by the Bureau of Meteorology and Geoscience Australia.

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