Hunga Tonga-Hunga Ha’apai update, 20 March 2009

Above: MODIS image from NASA Aqua satellite captured at 01:30 GMT on 20 March 2009. The island of Tongatapu is at the lower edge of the image. The site of the eruption is marked by the yellow arrow: a small plume can be seen extending ENE, and floating ash is staining the sea around the volcano greenish-blue. [source]

Eruptive activity at Hunga Tonga-Hunga Ha’apai appears to have declined somewhat over the last 12 hours, according to the latest advisory from Wellington VAAC (10:29 GMT 19 March 2009). The VAAC advisory, based on pilot observations and satellite imagery, reports ‘no more active eruptions, steaming to 6000ft [1800 metres]’, with ‘white and wispy ash haze extending to large areas ENE blw 5000ft [below 1500 metres]’. An earlier advisory (17:58 GMT 19 March 2009) reported frequent eruptions and ash clouds to FL130 (13000 feet, 4000 metres), with a plume extending 300 miles (480 kilometres) ENE.

At 01:30 GMT today NASA’s Aqua satellite captured a MODIS image which showed only a small plume extending less than 10 kilometres ENE of the volcano (from the NASA MODIS Rapid Response site: original image is here, detail reproduced above).

The BBC has some fresh video of the eruption from the inspection trip made by Tongan geologists yesterday. CBS News has the AP report of the eruption, with added video, pictures, and the usual mad/dumb/hilarious comments from the visiting public; they also have a short photo essay on the eruption (titled, in typically odd CBS fashion, ‘Undersea Volcano Erupts Photos’). And the Boston Globe’s ‘Big Picture’ feature lives up to its name with spectacular big, big pictures of the eruption.

As if this eruption wasn’t enough of a reminder that Tonga is situated in a geologically highly active part of the planet, there was a magnitude 7.9 earthquake in the Tongan Arc yesterday. There is no reason to suspect a direct link to the eruption. A tsunami alert was issued following the earthquake, but was later cancelled because it was ‘a tiny tsunami … nothing to worry about’.

UPDATE: Lousy science reporting from the BBC, who are asserting on the basis of no evidence at all that ‘An earthquake may have triggered an underwater volcano to erupt’. Nice video, clueless commentary: Quake may have caused eruption. Additional update, Dr Klemetti at Eruptions is also irritated by this stuff: ‘absolutely terrible “science” journalism … silly note of dread … all conjecture’.

For all our coverage of the Tonga eruption: Tonga « The Volcanism Blog.

News
Undersea volcano making waves in the Pacific – CBS News, 19 March 2009
Volcano shatters Pacific calm around Tonga – The Independent, 20 March 2009
South Pacific volcano inspected – BBC News, 20 March 2009

Information
Global Volcanism Program: Hunga Tonga-Hunga Ha’apai – summary information about Hunga Tonga-Hunga Ha’apai (0403-04=)
Tonga volcanoes and volcanics – overview from the USGS