Friday, December 26, 2014
The ice-core drilling challenge
Ice core drilling is challenging and therefore, very exciting. This season, we had set the objectives very high for the ice core drilling team, Jean-Louis Tison, PhD student Morgane Philippe, and mechanic Kristof Soete, who were all very happy to take that challenge! If you remember well, in 2012, we drilled 120 meters in 11 days, and we encountered some problems on which IPF and Eclipse Ice Drill have been working since then. This year, we planned to drill 3 boreholes: two shallow-firn cores of 30 meters and one ice core of about 160 meters, in 17 days.
After setting up and being stuck for 2 days by the first storm, we could finally start drilling the first 30 meters at Derwael Ice Rise on the 3rd of December. This drilling and the next one went really smooth. Almost every run yielded a 1.40m beautiful piece of firn core, with very few thin ice layers (less than 1mm). The two 30m boreholes were drilled within 3 days, just before the second storm hit us. These boreholes were also “televiewed” which means that we recorded a digital image of the borehole with a special camera, at very high resolution.
On the Roi Baudouin Ice Shelf, drilling the third hole was not such an easy task. There are several reasons for that: one of them is the number of ice layers, sometimes 20 cm thick that the drill encounters regularly during its progression. Another reason is that we reached ice much faster on the shelf, (~30 meters) and the firn – ice transition is always a difficult part to go through, since we have to adjust many parameters. For example, we had to change to more powerful core dogs, designed by IPF, otherwise the drill head could not break the cores anymore.
But the real problems started at 54 m, when the drill got stuck at the bottom… after trying all we could do without damaging the drill (blowing the fuses, using the hand crank, leaving the cable under tension for one night), we decided that we would need to poor diluted antifreeze down the hole, as it has been done in other drilling programs. It was done within 24 hours thanks to a very efficient logistical help from IPF and a tube transport system. To everyone’s relief, the drill was loose the next morning. Surprisingly, the core was in very good state in the barrel, so we decided to try restart in the same hole, and it worked! From that moment, we worked non-stop during two days and two nights, with the whole team taking turns to drill as deep as possible, slowly removing the leftover antifreeze at the same time. Unfortunately, time was running out and we could not miss our plane, unless we wanted to stay in Antarctica until February. We managed to go down to 107m, instead of the 155 meters needed to reach the ocean, but this already represents a lot of valuable material, as well as a very informative televiewer image of the borehole, showing precisely every single ice layer, a signature of about 200 years of the surface melting history in this typical place on the ice shelf. We will soon compare it with all the other data: those from the different radars used in the IceCon project, but also the data from the Benemelt project.