The secret life of ice sails

In Abstract

Unravelling the mystery of giant ice protrusions in the high mountains

A rare and somewhat esoteric feature of debris-covered glaciers is the phenomenon of `Ice Sails’. Ice Sails are imposing clean ice structures that protrude out of the surface of debris-covered glaciers.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, primarily 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.

Now, researchers from the University of Manchester (in partnership with the University of Cambridge, the Bavarian Academy of Sciences and Humanities and the University of Innsbruck) have produced the first ever analysis of Ice Sails. In so doing, they have created an inventory of their global spread, 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 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 the melt-rate of the Ice Sail, at which point the Ice Sail decays. From mathematically modelling this profile, the team were able to show that the existence of an Ice Sail is critically dependent upon both the glacier topography and the thickness of the debris cover of the glacier. By combining their model with satellite images, the team were able to estimate the age of some Ice Sails to be in excess of one hundred years.

To read the full article click here - DOI https://doi.org/10.1017/jog.2017.72