Australian Tsunami

Tsunami is a Japanese word - tsu meaning 'harbor' and nami meaning 'wave'. It was coined several hundred years ago by fishermen who came back from sea to discover the harbor devastated by waves, even though there had been no wind and no unusual wave action observed in the open ocean.

 Unlike wind-generated waves which cause movement of water near the sea surface, tsunami are waves generated by sudden movement of the sea floor, mostly by undersea earthquakes which cause the entire overlying water column to move vertically. The resulting wave spreads outwards from the source and has wavelengths of 100 kilometers or more. Submarine landslides and, less frequently, a volcano or meteorite impact also can cause tsunami. Although such impacts are rare, it has been suggested that tsunami generated by meteorites or comets may have reached Australian shores in prehistoric times

In Australia, public advice on any tsunami threat is being provided by the Bureau of Meteorology and Geo science Australia. The agencies continue to establish extensive networks of seismic and sea level monitoring instruments which are being integrated with sophisticated computer systems designed to detect and forecast the arrival of tsunami. However, because of the proximity of Australia to known earthquake zones off Indonesia and between New Guinea and New Zealand, the travel time for a tsunami from the nearest danger zones is around three to four hours. This provides some limited time to analyse the potential threat and issue warnings. For countries closer to an earthquake source, a tsunami may arrive in less than 15 minutes, allowing limited time for warnings to be issued. On 26 December 2004, strong currents and sea level variations were observed along Australia's west and southern coasts with around 35 people being washed out to sea and subsequently rescued.
           
While the overall risk from tsunami to the Australian population is lower than it is for many parts of the world, some preliminary assessments by the Australian Government indicate that the north-west and east coast have the potential to be affected by a damaging tsunami resulting from a large earthquake. A recent relatively significant event was the 17 July 2006 Java tsunami, which achieved a run-up height of eight meters above sea level on isolated sections of the Western Australian coast. Although earthquakes are seen as the most likely source for tsunami in the region, there are at least five active volcanic source regions capable of generating tsunami which could affect Australia

REFERENCES

Bryant E, (2001) Tsunami: The Underrated Hazard,

Dominey-Howes D, Marine Geology, 239 (1), pp. 99-123, April 2007

Rynn J and Davidson J, (1999) ‘Contemporary assessment of tsunami risk and implications for early warnings for Australia and its island territories’, Science of Tsunami Hazards, 17(2):107-125

Australias volcanic activity

There has not been any eruptions in Australia in this century. The most recent eruption in Australia was at Mt. Gambier, a shield volcano in the Newer Volcanic Province, Victoria. The Newer Volcanics Province in Victoria Australia is made of four shield volcanoes and associated vents: Red Rock, Mt. Napier, Mt. Schank, and Mt. Gambier. They last erupted between 5850 and 2900 B.C. The eruptions were explosive and some generated lava flows. It is impossible to say if the volcanoes will erupt again. However, there have been rare earthquakes in the area, most recently in 1976. There are numerous volcanic islands north and east of Australia including North Island, New Zealand, the islands of Vanuatu, the Solomon Islands, New Britian, and Indonesia. There are numerous interesting volcanic provinces in Australia. There are flood basalts of Cambrian age (about 650 million years old) northeast of Halls Crossing in northern Australia. Volcanism commenced about 70 million years ago at volcanic centers in southeast Queensland and northeast South Wales. Compositions range from basalt to rhyolite and includes shields, plugs, and domes. In north Queensland there are some very long basaltic lava flows. For example, at Undara a flow is 100 miles (160 km) long.

Geo science Australia monitors seismic data from more than 60 stations on the Australian National Seismograph Network and in excess of 300 stations worldwide in near real-time, 24 hours a day, seven days a week. Most of the 40 samples per second data are delivered within 30 seconds of being recorded at the seismometer to Geo science Australia’s central processing facility in Canberra through various digital satellite and broadband communication systems. This allow the government the ability to give advanced warnings of potential eruptions.

Sources of Information:
Johnson, R.W., 1976, Volcanism in Australia: Elsevier, New York, 405 p.

Johnson, R.W., Knutson, J., and Taylor, S.R., 1989, Intraplate volcanism in eastern Australia and New Zealand: Cambridge University Press, Cambridge, England, 408 p.

Simkin, T., and Siebert, L., 1994, Volcanoes of the world: Geoscience Press, Tucson, Arizona, 349 p.