Can you spot the glacier on the picture above? Not that easy… Glacier Noir is a debris-covered glacier located in the French Alps. Contrary to clean-ice glaciers which are shiny white or blue ice masses, debris-covered glaciers are ice masses with a layer of rock debris on the top which makes them look like their surrounding environment: they are the “chameleon glaciers”. They are currently called debris-covered glaciers but in the early 2000s, you could hear “debris-mantled glaciers” and even “buried glaciers” in the 1960s. They are often confused with rock glaciers. There are a lot of names and confusion around debris-covered glaciers. Why? Simply because they are difficult to find, define and study as you can imagine from the picture above.
Debris-covered glaciers represent around 5% of all mountains glaciers in the world. So why is it important to study them – there are many more clean-ice glaciers, aren’t there? Yes, debris-covered glaciers are a small fraction of all glaciers but like any other glacier, the melting of debris-covered glaciers contributes to sea level rise and there is currently huge uncertainty about how fast they melt compared to clean-ice glaciers. In addition, in the Himalayas, they make up a greater proportion of the glaciers and in many valleys, debris-covered glaciers are the main and often the only source of drinking water, like for example the famous Khumbu Glacier just below Mount Everest on the Nepal side.
Some debris-covered glaciers, like the Tasman Glacier, the biggest glacier in New Zealand, are very large features that can be the origin of risks and hazards. The debris layer creates numerous ponds filled with meltwater on the surface of glaciers. These ponds can hold monumental volumes of water that can be suddenly and brutally drained through crevasses in the ice or a breach on their edge. This drainage can create an outburst flood and submerge the valley below.
Debris layers on top of glaciers can come from rock falls, like for the Sherman Glacier in Alaska. This rock cover modifies the dynamics of the ice by slowing down the melting happening underneath. This insulation process creates various phenomena, like thickening of the ice under the debris, building hills of ice slowly moving down the glacier or advancement of the glacier’s tongue. These two phenomena can block or deviate water streams and again generate massive floods.
A less obvious reason to study debris-covered glaciers is that if glaciers on Mars exist, they are debris-covered. So studying debris-covered glaciers on Earth can contribute to space conquest and the human adventure on Mars. In the same vein, studying current debris-covered glaciers and their behavior in the face of climate change can help us understand and interpret the climate of the past. There is an example of a potential misinterpretation of the Waiho Loop moraine in New Zealand in front of the Franz-Joseph Glacier: 12000 years there was a worldwide cooling event (called Younger Dryas) that might have led to the formation of the very large moraine of Waiho Loop. Or, a massive rock avalanche landing on Franz-Joseph Glacier triggered its advance and the deposition of the moraine.
I’ve already described a few examples of debris-covered glaciers: Glacier Noir, Khumbu Glacier, Tasman Glacier, Sherman Glacier and maybe Franz-Joseph Glacier. But where else can you find debris-covered glaciers? They can actually be found in every mountain range: from the Miage Glacier (Italy) in the European Alps with to the Inylchek Glacier (Kyrgyzstan) or Langtang (Nepal) glaciers in the Asian High Mountain; from the Black Rapids Glacier (Alaska) in the Rocky Mountains and the Dome Glacier (Canada), to the Andes with Grosse and Exploradores glaciers in Patagonia (Chile). There are debris-covered glaciers even in Antarctica in the Dry Valleys, such as the Mullins Glacier.
So understanding debris-covered glaciers is an international problem. This is my final reason to study them. I study debris-covered glaciers and their past, present and future evolution. I focus more on glacier-wide aspects like length, surface area and volume change to model their future behavior.
They do not make up a large number, but debris-covered glaciers are important. In the face of climate change, debris-covered glaciers may be the last standing glaciers, as their evolution is slower. But at the current pace, they will still end up like all other glaciers: ice chunks melting in the sun…
Pierre is a PhD student at the Centre for Glaciology at Aberystwyth University, Wales, UK (started 2013). His Earth Sciences Master degree from the University of Grenoble, France and his 4 years as a surveyor in the National Institute of Geographic and Forestry Information (IGN) drove his research interests toward field observation techniques, remote sensing and glacier-wide digital modeling. His current project is entitled “Predicting the effect of climate change on debris-covered glaciers evolution”.
Find Pierre on the net:
Blog: Ice & Rock
University Profile: http://www.aber.ac.uk/en/iges/staff/phd/pfl4/