To: bentway who wrote (367844 ) 1/22/2008 1:03:18 PM From: combjelly Read Replies (1) | Respond to of 1577338 Volcano found under Antarctic ice Active volcano may contribute to rapid glacial melt. Quirin Schiermeier Radar surveys from the air can image what's under the ice.Radar surveys from the air can image what's under the ice.Carl Robinson/British Antarctic Survey Scientists have found an active volcano beneath Antarctic ice that last erupted just 2,000 years ago. The hotspot lies beneath the Pine Island region of the West Antarctic Ice Sheet, where glaciers are retreating more quickly than elsewhere on the continent. The dramatic find might help to explain this particularly rapid loss of ice. Although the Antarctic is often thought of as a huge, sedate expanse of snow, the continent is known to host several active volcanoes, some of which poke out of the ice. Mount Erebus, on Ross Island in the Ross Sea, is the area’s most famous active volcano and its continuous activity has been observed since the 1970s. This volcanic activity has led some geologists to suspect that volcanoes lurking beneath the ice might affect how glaciers melt and flow on the continent. But no such hot-spots have been confirmed until now. Hugh Corr and David Vaughan of the British Antarctic Survey, which is has its headquarters in Cambridge, UK, analysed radar data from an airborne survey of the area conducted three years ago. They were stunned by an exceptionally strong signal showing the radar reflecting from a mid-depth layer in the ice — a stronger reflection than that from the bed rock lower down. The only valid explanation for this is that the ice contains a layer of ash from a recent volcanic eruption, they conclude in Nature Geoscience 1. “This is a small sensation,” says Karsten Gohl, a geophysicist at the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany. “We did suspect active volcanism in the region, but now we have solid evidence.” Blow hole The British team estimate that between 0.019 and 0.31 cubic kilometres of ‘tephra’ – lose fragments of volcanic ash — erupted around 325 BC. “It was probably the biggest volcanic eruption in Antarctica during the last 10,000 years,” says Vaughan. “It must have blown a huge hole in the ice sheet and generated a 12 kilometre-high plume of ash and gas.” The ashes, deposited over an area roughly the size of Wales, were subsequently buried by snowfall. The team determined the date of the eruption by modelling the rate at which snow would have accumulated on top of the ash, and looking at the depth of ice present on top of the ash today. The estimate of the eruption’s size is only a rough one, they admit. “It’s only a best estimate,” says Vaughan. “One day I hope we will able to drill a bore hole and check.” Other sub-glacial eruptions could have occurred recently in the vicinity as well, but evidence for this might be hard to find. Most ash layers would probably have been carried to sea by the fast-retreating ice. Gohl says that during a planned expedition in 2010 to western Antarctica he will search for traces of volcanic material in ocean sediments. Hot bottom The Pine Island Glacier shrinks in length by more than a kilometre every year, and thins by several vertical metres, as glaciers flow out to sea. In the unlikely event that all ice in this huge glacier region melts, it would raise the global sea level by 1.5 metres. Scientists think that most glacial melting occurs as the result of warmer ocean waters, which accelerate the calving of icebergs into the sea. But the existence of active volcanism in this part of western Antarctica suggests that geothermal heat, which warms the glaciers from below, might also play a big role in this fast-melting region. “A very basic condition – how hot is it under the glaciers – has changed with this finding,” says Sridhar Anandakrishnan, a glaciologist at Pennsylvania State University in University Park. “Anyone who wants to model the ice flow of West Antarctica in future must take this into account.”nature.com