The door to the basal ice

Friday 23rd March. Posted by Mathieu Tachon

Now the work is starting to get wet! Our main task now consists of melting the ice from the research shaft.

This was firstly to replace load cells which are inlaid in the bedrock and that we use to measure the pressure of the ice at the interface between the glacier and the bedrock. We also want to map the bedrock topography under the ice with the Xbox Kinect to get useful data for helping in getting a better understanding of basal sliding and other processes at the base.

Before starting, we needed to open the door that leads to the basal ice. This door was made up of some kind of metallic beams in order to stop the glacier flowing into the tunnel. Then, we turned on the water pump down by the laboratory and also a large hot-water heater that will help with the melting.

The hot water took a while to come up to the research shaft through the different pipes and then into the hose. Before coming to SVARTISEN subglacial laboratory, I had first thought that creating tunnels in a glacier would be simply to spray hot water onto the ice but it is not quite as simple as that. The basal ice, that is the layer directly in contact with the bedrock, is rich in sediment.

This is due to the strength and the pressure that the glacier applies at the base and which leads to the incorporation of sand, gravel and even large rocks into the ice. Therefore, a lot of shovelling is necessary to clear away the enormous amount of sediments that are released while spraying with hot water. To make the melting easier, we fixed the hose on a tripod so we didn’t have to hold it continuously.

Because the ice tunnels close due the pressure of the glacier above and because digging out the sediment proves to be quite tiring, we did several shifts to make sure the water kept flowing and to change the position of the hose if necessary. We started after the pump tests ended, at around 2:30 am and worked until 11:30 to reach the load cells and to have enough space to remove them.

We used a large drill to remove the cement around the load cells and in the boreholes where the cables from the load cells to the datalogger were going down to the main tunnel.

Top picture: Mathieu Tachon trying to clear the borehole. Behind his is clear glacier ice (at the base of 200 m of ice), and to the left of him the more sediment-rich ice is visible.

Bottom picture: Mathieu Tachon and Pierre-Marie LeFeuvre trying to clear the borehole.