Glaciers: the moving giants
Glaciers seem to be immutable, frozen in their eternal snowy. But don’t believe any of that, these ice giants are continually moving, slowly but surely. With Luc Moreau, glaciologist and associate member of the CNRS Edytem laboratory, explore their bluish depths and discover how they work.
Fascinated by the slow but inexorable movement of these ice monsters, Luc measures, studies and photographs some of the most famous glaciers in the world, particularly those on the Mont Blanc massif, at the foot of the emblematic “Sea of Ice”, where he has been based since 1986.
Luc, what conditions and ingredients are needed to create a glacier?
To make glacier ice, snow that falls has to not melt completely at the end of the summer and accumulate over several years, to make ice. In the Alps, for example, this process takes place above 3000m altitude, where the balance is positive: i.e. there is always more snow falling than melting. This area known as the “accumulation zone” is where glaciers start to form. Of course in the tropics you have to get above 6000m altitude to find these conditions. Conversely, in polar areas, glaciers start forming almost at sea level.
But how does it switch from snow to ice?
Mainly by compaction. Under the effect of its respective weight, layers of snow accumulate, get denser and are transformed into impermeable ice. The ice might stay cold and dry, stuck to rock if it does not melt, as is the case at the summit of Mont Blanc or at the centre of the polar ice caps! If melting occurs, water soaks up the névé* and the ice becomes tempered. When this happens it can slide downstream like a sledge and reach very low and very far!
Does that mean that cold and dry ice is not moving?
No, even if cold glaciers stay stuck to the rock, this does not mean that they’re not moving, because ice has plastic deformation properties a bit like metals.
So, regardless of the type of ice, are all the glaciers in the world constantly moving?
Exactly. It’s hard to see this with the naked eye, but if you take a picture every day, at exactly the same place, you can see this movement. The ice changes shape and slides every day, every minute, simply under the effect of its weight. From the source of a mountain glacier to its front, it’s like a real life natural treadmill which keeps going downhill, without stopping.
To observe the changes in the glaciers that he studies Luc Moreau uses a time-lapse camera. The shots taken automatically by his cameras (2 to 4 photos per day) mean that he can see the daily movements of the ice. Luc has used his cameras in France, Nepal, Patagonia and Greenland as you can see on the following video! More images and videos can be found on www.moreauluc.com.
To read the full interview of Luc, to know more about the effect of heat on glaciers, to discover the “treasures” buried in the ice and to learn how crevices and moraines are shaped, go page 21 of the 10th issue of Hiking on the Moon!