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Tonga boulders may be evidence of volcanic tsunami 25 September 2008

Posted by admin in current research, geoscience, natural hazards, Pacific, submarine volcanism.
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Seven huge coral boulders standing on the western shore of Tonga’s main island Tongatapu may be evidence of a tsunami produced by a volcanic eruption, according to University of Texas researchers. The boulders, which are up to 9 metres high and weigh up to 1600 tonnes, are made of coral similar to that which makes up the offshore reefs of Tongatapu; their coral was formed about 122,000 years ago. They were clearly not formed in their present location and could not, on largely flat Tongatapu, have rolled downhill from somewhere else. The conclusion is that they were torn from the reef and hurled inland by a tsunami generated by a submarine eruption, probably from one of the volcanic centres in the northern section of the nearby Tonga-Kermadec Arc.

‘These could be the largest boulders displaced by a tsunami, worldwide’, says Matthew Hornbach of the University of Texas Institute for Geophysics. ‘We think studying erratic boulders is one way of getting better statistics on mega-tsunamis. There are a lot of places that have similar underwater volcanoes and people haven’t paid much attention to the threat’.

UPDATE: Dr Erik Klemetti at Eruptions takes a cautious look at the Tonga boulders: ‘it will be interesting to see what evidence they have for the deposit being from a volcanically-triggered event’.

UPDATE: National Geographic News has published an article on the Tonga boulders, which has been added to the list of links below.

[Found via Geology News.]

World’s largest tsunami debris discovered – ScienceDaily, 25 September 2008
Boulders on Tonga may have been dumped by tsunami – Reuters, 25 September 2008
Tongan coral may hold key to ancient tsunami – Radio Australia, 25 September 2008
Boulders in Tonga evidence of largest tsunami debris found – Geology News, 24 September 2008
The big boulders of Tonga – Eruptions, 25 September 2008
Ancient tsunami carried giant boulders to TongaNational Geographic News, 30 September 2008

Global Volcanism Program: Tonga Islands – volcanoes of Tonga and vicinity
New Zealand American Submarine Ring of Fire 2005 – studying submarine volcanism in the Tonga-Kermadec Arc
Bathymetry of the Tonga Trench and Forearc: a map series – article, with maps, from Marine Geophysical Researches, vol. 21, no. 5 (2000)

The Volcanism Blog


1. Melissa - 26 September 2008

After reading my first natural disaster book by Gordon Gumpertz titled TSUNAMI, I became so much more aware of the affects of such an astronomical storm. I have since then been searching the web for more information. I am curious to learn more about the connection between volcanoes and tsunamis. The study of erratic boulders sounds interesting.

2. fevah - 7 December 2008

I live in Tonga on the Island of ‘Eua and know of these boulder of which you write and of more on our Island as well, however I didn’t know of the interesting story behind them.
I am new to the internet and just started a blog yesterday myself.
I am very impressed by your site. I am of course very interested in volcanism and are very aware that where I live supports a lot of seismic and volcanic activity, so If you ever need so up to date info as it happens over here I would only be to happy to help.

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