Do you have a favorite place to go on vacation? Well, I do, and it’s a bit unconventional. I have spent almost a half a year of my life living in Antarctica! I lived on the Whillans Ice Stream, working hard researching the ice sheet there.
First, let me tell you about Antarctica. It’s a huge continent covered in thousands of feet of ice that accumulated as snow over many thousands of years. Did you know that ice flows (despite how solid it looks floating in your glass of iced tea)? This means that the huge pile of ice sitting on top of Antarctica is slowly flowing under its own weight towards the ocean, where it will break off into icebergs or melt into the ocean. How thick the ice sheet is depends on the balance between how much snow accumulates, and how much ice breaks off or melts into the ocean. If more ice breaks off or melts into the ocean than accumulates as snow, the ice sheet shrinks and sea level rises. If more snow accumulates, then the ice sheet grows, and sea level drops. So if you live near the beach (my other favorite place to go on vacation) and want to know how much sea level will rise in the next 50 years, you need to understand how the ice flows downhill towards the ocean. That’s what I’m studying.
What is an ice stream? An ice stream is essentially a glacier, but instead of flowing between rocky mountains like a glacier in the Alps, it is held on either side by more ice. The ice on either side barely creeps along, moving very slowly, while the ice in the middle flows really fast (1000 feet or more per year). In between the stationary ice and the moving ice, there are house-swallowing crevasses, or cracks in the ice (don’t go there!). Nobody is quite sure what is underneath, but it’s some mixture of mud, sand, water, and rock. Ice streams drain a huge portion of the interior of the Antarctic Ice Sheet.
The Whillans Ice Stream is one of five ice streams on the Siple Coast of West Antarctica, across the Ross Ice Shelf from McMurdo Station. This motley bunch of ice streams has some interesting behavior. MacAyeal, Bindschadler, and Mercer Ice Streams all behave “normally,” flowing out of the highlands of the West Antarctic Ice Sheet and into the Ross Ice Shelf. The Whillans is actually slowing down, and moves in fits and starts. And the Kamb Ice Stream is stopped entirely! How do you stop a river of ice??? (I wish I knew.)
When glaciers and ice streams move, they are sometimes deforming internally (like silly putty), sometimes they slide over their muddy beds, and sometimes they scrape along over harder bedrock. Each of these different kinds of interactions causes the ice to move slow, fast, or unpredictably. The Whillans ice stream falls into the “unpredictable” category. Most of the time, the Whillans is creeping along very slowly. But then, once or twice a day, in step with the tides beneath the Ross Ice Shelf, it suddenly lurches forward, moving a foot or two over fifteen or twenty minutes. Ok, not that exciting, only two feet?? Well, no other ice stream acts like this, so call me crazy, but I find it fascinating. Is this how you stop a river of ice?
Turns out, there are lots of tiny earthquakes (very very very tiny) that occur in certain “sticky” places at the bottom of the ice whileit lurches forward. So this river of ice is slowing down and scraping along the bottom while it does so. Could this be related to what’s causing the ice stream to slow down?
Last year, as part of the WISSARD project, I put a bunch of seismometers (usually used to measure earthquakes) out on the Whillans Ice Stream to study these tiny earthquakes that occur between the ice stream and its bed. My team drilled four holes deep into the ice to put seismometers as close as possible to these little earthquakes. I also have eighteen seismometers and twelve GPS on the surface of the ice, which will allow me to find where the tiny earthquakes are occurring, how big they are, and how the ice stream moves in response. Essentially, I’m using seismometers and GPS to “listen to” and “watch” the ice as it moves over its bed, which might help me figure out what’s so special about the ice stream bed in the stickiest parts of the Whillans Ice Stream story.
Some vacation, huh?
– Grace, University of California Santa Cruz, USA