giovedì 1 settembre 2011

Peterson Glacier Breakup Continues

In August 2010, part of the Petermann Glacier about four times the size of Manhattan island broke off. This is a huge island which would take years to melt and move south. Researcher Alun Hubbard, of the Centre for Glaciology at Aberystwyth University, U.K.has indicated that another section of the glacier, about twice the size of Manhattan, appeared close to breaking off. Alun Hubbard: "Although I knew what to expect in terms of ice loss from satellite imagery, I was still completely unprepared for the gob-smacking scale of the breakup, which rendered me speechless." ... "What the breakup means in terms of inland ice acceleration and draw-down of the ice sheet remains to be seen, but will be revealed by the GPS data recovered, which we are now processing at Aberystwyth."

Petermann Glacier is a large glacier located in North-West Greenland to the east of Nares Strait. It connects the Greenland ice sheet to the Arctic Ocean near 81 degrees north latitude. The tidewater glacier consists of a 43 mile long and 9.3 mile wide floating ice tongue whose thickness changes from about 2,000 feet at its grounding line to about 98—260 feet at its front. Rough mass balance estimates using these scales suggest that about 80% of its mass is lost as basal meltwater, yet little oceanographic data are available to connect Petermann Glacier to its fjord and adjacent Nares Strait. Even the sill depth and location is largely unknown as modern soundings of the fjord are still lacking. A series of satellite images from 2002 through 2009 illustrate that the terminus of the glacier has advanced towards the ocean, however, several lateral rifts have developed also. The distance of this rifts or cracks back from the terminus has diminished for this time period also and may serve as a pre-cursor to natural ice calving from Petermann Glacier. In response to the question: How abnormal is this event? Jason notes: "The August 2010 ice calving at Petermann is the largest in the observational record for Greenland" Falkner et al. (2011) scoured the observations and found no evidence of an event this large in scattered observations since 1876. Johannessen et al. (2011) identified the next largest observed Petermann calving event ocurring in 1991, being 58% as large as the 2010 event. Hubbard said the large rift, which the researchers have dubbed "The Big Kahuna," was getting bigger. He was cautious about predicting when it would create a new vast ice island, but said it could happen "maybe next year, something like that."

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