* Astronomy

The most powerful earthquake in New Zealand's recorded history struck Wellington only 155 years ago. Still that city continues to expand along a major geological fault zone. A tsunami from Chile produced a 5.5m tsunami in Lyttelton Harbour on May 22-23, 1960 and affected other east coast harbours.
Tsunamis can also have their origins in space. Australian geographer, Ted Bryant, reminds us of the role of meteorite impact with the ocean, when, on February 22, 1491, a meteorite strike caused tsunami waves in excess of 130m high along the Australian coast.
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Supposed evidence Australia has been subject to prehistoric tsunamis up to 20m in height over the past 10,000 years could just be the result of Aboriginal occupation, a major conference is set to hear tomorrow.
Archaeologists from the Australian National University say the theory about the mega-tsunamis, which has influenced the development of emergency service plans in Western Australia, is not supported by evidence.
In 2003 Australian geological researchers suggested prehistoric tsunamis over the past 10,000 years were much larger than those recorded since European settlement, including findings of surges up to 20m in height affecting a 2500km stretch of the WA coast.

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Title: Cosmogenic mega-tsunami in the Australia region: are they supported by Aboriginal and Maori legends?
Authors: E. Bryant1, G. Walsh2 & D. Abbott3

1 Science Faculty Office, University of Wollongong, Wollongong, NSW, Australia, 2522 (e-mail: ebryant{at}uow.edu.au)
2 TAKARAKKA Rock Art Research Centre, 36 Bonros Place, The Gap, Queensland, Australia 4061
3 Lamont-Doherty Earth Observatory, Route 9W

Mega-tsunami have affected much of the coastline of Australia over the past millennium. Such catastrophic waves have left an imprint consisting predominantly of bedrock sculpturing of the rocky coastline and deposition of marine sediments to elevations reaching 130 m above sea level. One of the largest of these events occurred in eastern Australia in the fifteenth century. This event may be related to the Mahuika impact crater found at 48.3 S, 166.4 E on the continental shelf 250 km south of New Zealand. A comet at least 500 m in diameter formed the crater. Maori and Aboriginal legends allude to significant cosmogenic events in the region, while Aboriginal legends about tsunami are common along the eastern Australian coast. Evidence for legends that could describe the impact of a cosmogenic tsunami also exists in NW Australia. Here geological evidence of a single mega-tsunami as recent as in the seventeenth century covers 1500 km of coastline. We term this event Wandjina after the artwork related to the legends. More attention should be given to oral traditions in searching globally for other sites of significant mega-tsunami.

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The most reliable and widespread evidence of an impact is that of tektites. Tektites form when an impactor liquefies its target and sends the melt into the atmosphere. The Mahuika tektite field contains glassy tektites that appear orange, light green, and clear in visible light. The tektite field does not extend radially outward from the crater; instead, it appears to extend roughly thirty degrees to either side of a line drawn southwest from the centre. This shape suggests an impact that occurred at a very low angle relative to the earth’s crust. This oblique angle also agrees with Aboriginal legends that tell of a great fireball passing through the sky in south-eastern Australia. A great circle path that uses the north-western most sighting of the fireball and the location of the structure in the Tasman Sea, almost exactly bisects the field where tektites have been found.

Tektites have been found over 220 km from the crater. Despite these large distances the chemistry of the tektites is surprisingly similar. The tektites were analysed using energy dispersive x-ray analysis. Despite the inherent error in this technique, the analysis showed average weight percents of 48% O, 27% Si, 10% Fe, 3% Mg, 3% Al, 3% K and trace Ni.

In addition to similar compositions the tektites also have a very uniform size. All of the tektites range from 40-51 microns in diameter. This size range fits with the scaling predicted for a crater the size of the Mahuika structure. It is also important to note that the tektite field was mapped using dredges. If you assume a normal sedimentation rate of 1cm/thousand yrs, then the event happened within the last thousand years. The date of the event will become more constrained after a C-14 date is obtained from the fossils in surface samples.

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