What are ice sails, and why?

At the  recent European Geosciences Union (EGU) General Assembly conference Geoff Evatt was interviewed about his latest work on ‘ice sails’. “What are they then?” I hear you ask. Well they are clean ice structures that protrude out of the surrounding debris-covered glacier. They can be up to 20 meters in height, with widths of up to 90 meters, and generally have flat-sided faces. Early observers of them referred to them as ice sails as they looked like a flotilla of white-sailed boats floating along the glacier surface.

First off, here is a photo of some ice sails taken in 1929 by C. Visse and provided by Christoph Mayer of the Bavarian Academy of Sciences. They do kind of look like they are floating on top the glacier, no?


The curious thing about them is that they are remarkably persistent over a number of decades, and this was what motivated the research – to try and understand why they form and how come they can hang around so long. Geoffs PhD student Amy Mallinson did an incredible detective job of looking at a lot of satellite images to see if there was a geomorphological or topographic control on these sails and to identify if they can be tracked along the glacier surface. On this point it seems that because the individual shape of each sail is largely preserved, they can be tracked for a number of years and therefore might be a useful way of measuring the horizontal displacement of the surface of glaciers. What Geoff presented was a simple numerical model that explains the conditions under which a 3-sided pyramid form can persist. The model results indicate that it needs to be dry, the balance of the melt rate between the debris-covered surface and the included faces of the sail needs to be just right. The ice sails form when these conditions are met and once the sails are transported by ice flow to a location when these conditions are no longer met then they fade out of existence.

Jonathan Amos of the BBC prepared a nice article on this topic, featuring interviews with Geoff on ice sails and myself on the topic of debris covered glaciers in general, which can be found here.

The debris covered glacier session at the EGU this year was particularly vibrant and you can check out the research that was presented on the conference website, where some of the authors have uploaded their posters and talks. Navigate to session CR4.3 and then click on Orals or Posters to see the contents of each session. You can download the full set of submitted abstracts here: EGU2016-CR4-3-Abstracts.

About lindsey

Environmental scientist. I am glaciologist specialising in glacier-climate interactions to better understand the climate system. The point of this is to understand how glaciated envionments might change in the future - how the glaciers will respond and what the impact on associated water resources and hazard potential will be.
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