Bristol blows its top

Posted by lcb14 at Jul 18, 2016 03:45 PM |
Professor John Smellie, a volcanologist in the Geology Department, working with Peter Fretwell of the British Antarctic Survey, is using satellite images to document an eruption on one of the world’s most remote and least visited volcanoes: Mt Sourabaya, on Bristol Island in the sub-Antarctic South Sandwich Islands.
Bristol blows its top

Ice-clad Mt Sourabaya, formed by a line of small steaming volcanic cones, photographed by John Smellie in 1997

The volcanic archipelago is situated c. 2000 km SE of the Falkland Islands and a similar distance north of the Antarctic continent. The islands suffer from a very hostile climate and are ice-bound for much of the year. As most also lack beaches, boat landings are difficult and rare. Eruptions on Bristol Island have been observed on only two previous occasions: in 1935 and 1956. During an expedition for the British Antarctic Survey led by John in January 1997, the summit region was visited for the first and only time. He determined that the 1935 site was a small volcanic cone a few hundred metres east of Mt Sourabaya whereas the 1956 site was a line of fresh-looking steaming cones at Mt Sourabaya itself.

Sampling rocks during a quick visit to Mt Sourabaya by John Smellie and British Antarctic Survey colleagues in 1997
Sampling rocks during a quick visit to Mt Sourabaya by John Smellie and British Antarctic Survey colleagues in 1997
The Mt Sourabaya volcano suddenly and unexpectedly blasted into life earlier this year and it may be developing into an interesting eruption characterised mainly by emission of lava flows. The two satellite images shown below illustrate how the eruption is evolving. The earliest, taken in April, clearly shows the summit crater as a hot red circle – the crater is brim-full of lava. The second image, taken in June, shows expanded activity on the island, but many details are obscured by steam clouds. One interpretation is that several new vents have started erupting along an east—west fissure. Alternatively (and more likely) there has been expanded eruption of lava flows, the first of which was observed in May. The fringing ‘moats’ seen at the left side downslope of the steam clouds suggest melting of the snow and ice by radiant heat ahead of three lavas rather than explosive activity at new vents. However, ash covers the snow and ice on the east side of the island where the prevailing wind has deposited it. Unfortunately it is the wrong time of year to visit the region to make closer observations due to extensive sea ice now present (it is winter there). Other South Sandwich volcanoes with activity observed in recent years are Mt Michael on Saunders Island with its semi-permanent lava lake, and Mt Belinda on Montagu Island which erupted several large lava flows from a small summit cone between 2001 and 2007 and constructed a new promontory of land on the island’s north coast. If, as seems likely, the new lavas flowing out of Mt Sourabaya reach the coast, more new land will be created. In a very real sense, British Overseas Territories are likely to be growing in size in the near future, providing fresh substrates for the local wildlife (mainly penguins) to colonise - once the new land cools down, that is!

Satellite view of Bristol Island. The central red coloration is the Mt Sourabaya crater brim-full of lava; Landsat 8, 8 April 2016
Satellite view of Bristol Island. The central red coloration is the Mt Sourabaya crater brim-full of lava; Landsat 8, 8 April 2016
Satellite view of Mt Bristol showing several likely lavas flowing west out of Mt Sourabaya; WorldView1 Quicklook, 20 June 2016. Image courtesy of Digital Globe.
Satellite view of Mt Bristol showing several likely lavas flowing west out of Mt Sourabaya; WorldView1 Quicklook, 20 June 2016. Image courtesy of Digital Globe

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