Mathematicians Conduct Inventory of "Ice Sails"
Work conducted by researchers from the University of Manchester including Geoff Evatt, Matthias Heil and PhD student Amy Mallinson (in partnership with the Bavarian Academy of Sciences and Humanities and the University of Innsbruck) has produced the first ever analysis of Ice Sails.
A rare and somewhat esoteric feature of debris-covered glaciers, is the phenomenon of `Ice Sails’. These Ice Sails are imposing ice structures that protrude out of the surrounding debris-covered glacier. They can be up to 25 meters in height, with widths of up to 90 meters and generally have flat-sided faces. To date, they have only been observed on a small number of glaciers around the Karakoram mountain region of Pakistan; most notably the Baltoro glacier, which begins life at the very summit of K2. From a distance they look like the sails of a boat, hence their name.
The researchers created an inventory of the global spread of Ice Sails, and presented an explanation for their existence and rarity. They showed that Ice Sails melt out of areas of a glacier with thin, patchy debris coverage, where growth is possible due to the melt-rate of inclined clean-ice being smaller than that of the surrounding flat, thinly-debris-covered ice. But as the glacier flows downstream, this debris layer slowly thickens, causing the corresponding melt-rate of the underlying ice to decline. Eventually, the melt-rate of the debris-covered ice becomes lower than that of the Ice Sail’s melt-rate, at which point the Ice Sail decays. From mathematically modelling this profile, the team were able to show that an Ice Sail's existence is critically dependent upon both the glacier topography and the thickness of the glacier's debris cover. By combing their model with satellite images, the team were able to estimate the age of some Ice Sail to be in excess of one hundred years.
More detail can be found in a paper produced by those involved.