How to cross a crevasse zone on the Antarctic ice sheet
We are back at the CTAM (Central Trans Antarctic Mountain) camp.
Over the last several days we take stock in that we accomplished the first major goal of our trip. That is, to study the glacier deposits at Mount Howe, the southernmost rock outcrop on Earth. We found (what we think are) deposits left behind by the ice sheet when it was bigger, at several different time periods in recent Earth’s history. We can tell in a preliminary way, before we have carried out the laboratory work back home, that the glacier deposits must be of different ages because they are different ‘colors’ – red for more oxidized (rusted). They also show other signs of varying in age such as the weathering of the rocks and landforms, which increases away from the ice sheet (=older). This means that there will be a record of the glacier leaving behind different types of rocks over a period of time, likely well before the last ice age. It was an important goal to find such deposits for our sampling.
We quickly regroup our stuff over the next few days at the CTAM camp and start to get ready for the next major camp move, to Mount Achernar. For this stage of our trip, which is only about 25 kilometers from the CTAM camp, we are hoping to get there by snowmobile. We will use 4 snowmobiles pulling 6 sleds (two snowmobiles will pull two sleds each). This will allow us to move our entire camp, set it up for more than a week near the site, work, and then come back to CTAM after 8 days or so. However, there is a small problem. There is a crevasse shear zone in the ice sheet between the CTAM camp and Mount Achernar. So, we must figure out where to cross the crevasse zone. We do this two ways. First, we take a helicopter trip from CTAM for an hour (they are quick) to scope out or reconnaissance the area (a “reconn”). On the helicopter, we think we figure out where we might be able to cross the crevasse zone. The helicopter trip also allows us to see the whole area of Mt Achernar and where we want to camp. Camp ideally has to be on a snow patch so we can stake the tents down and in a spot not too windy.
The second way we figure out how to cross the crevasse zone is to go to it, by snowmobile on just a day trip from CTAM (another “reconn”). Mike R (Roberts), our mountain guide, shows us how to link the snowmobiles by ropes, in case one falls into a crevasse. We also put on climbing harnesses and rope ourselves to a second set of ropes between the snowmobiles. This is so that if we fall in, we can either climb out or be pulled out by others.
We get to the crevasse zone which starts at about 15 miles from the CTAM camp. The first few crevasses seem quite bad – each about 2 to 5 feet cross. Although they all seem to have natural ‘snow bridges’ that cross the top of the crevasse, which we can drive across, we need to be confident that they will not collapse due to the weight of the machine. Mike R slowly investigates each crevasse we cross to see how strong the overlying snow bridges are and how wide each crevasse is. After about an hour, we start thinking maybe there are just too many crevasses (every few hundred feet we are finding another one) and it would take too long to figure out how to get across the entire crevasse zone. Mike R suggests we park and get off the snowmobiles, link up with ropes and slowly walk for a while to see how much longer the bad crevasses continue. This seems easier at the moment then stopping and starting the snowmobiles every time we reach another crevasse. To our surprise, the crevasses quickly get smaller and disappear just as we start walking! We did it ! We found a reasonable and quick way to get across the crevasse zone which is less than a 1 mile wide at its bad part. We put flags next to each one so that we can easily see where they are when we come back through on the way to Mount Achernar site to do our work.
Mike Kaplan, Kathy Licht, Nicole Bader and Mike Roberts