Friday, December 7, 2012

Operations at derwael ice rise

It took 22 hours of travel with two Prinoth trains to Derwael ice rise. Departure was delayed due to a few mechanical problems and we arrived by 7 am on Monday at the camp spot. It didn’t take long to get everything into place which meant that the science activities started later on the day (December 3, 2012). The weather has been very nice, warm and mostly cloudy with light snow fall. Ideal weather to pursue the activities. After three days, ROB1 was installed on the snow (or better dug in into the snow), which involved a lot of digging and snow removal. The GNSS antenna pole was put at a depth of 2m below the snow surface.

Drilling operations went rather smoothly, thanks to extensive testing at PEA. After three days, a depth of almost 60m was reached. Only few melt layers were detected in the upper firn part.

All radar profiles around Derwael were swiftly run. The first day (4 December), 70 km of low-frequency radar data were collected, clearly showing the different aspects of the Raymond bump, as well as a side bump to the south of the ice divide (the highest point on the ice rise where the major bump is situated). The origin of these bumps are due to the ice rheology. Ice deformation underneath an ice divide is essentially due to longitudinal stretching of the ice layers, while away from the divide, vertical shearing becomes more important. Due to the nonlinear nature of the flow law for ice, this leads to a higher effective viscosity under the divide, making the ice less easy to deform under the divide compared to the flanks. The result is that ice layers on the flanks are at greater depth on the flanks compared to the divide, leading to an upwarping of layers under the divide. This effect has been theoretically put forward by Charlie Raymond in the 1980s, but only observed for the first time with radar almost 20 years later. It is therefore commonly known as the Raymond effect. As a result of this effect, the ice core will reveal ice of an older age at depth compared to a position situated on the flanks.

Today, December 7, the Be:Wise team is ready to move their advance camp to the Roi Baudouin ice shelf.

No comments:

Post a Comment