Almost end of stay

Sunday March 25th. Posted by Pierre-Marie (Pim) Lefeuvre

Almost the end of our stay in the subglacial lab. Every single muscle is sore. The work has been intense and yesterday started late and finished late but we achieved quite a lot.

After a short night, Miriam removed the time lapse camera (that didn’t work) from the ice cave and straight away I started melting and shovelling. We had to release enough space for the Kinect© and the total station to reach the load cells. Some shovelling later, I left the research shaft to help Miriam check the load cells that were going to be installed later that day.

The load cells were showing a slight deviation from their zero frequency: 0.3 bars instead of 0.05 bars normally. This is nevertheless rather small compared to the 19 bars that they are going to endure, hopefully for more than 15 years. In April, we are going to check that the zero has remained stable.

Joined by the rest of the team, we took with us the two chosen load cells to the research shaft. The main issue with installing these sensors is to make sure that the cables do not get stuck in the borehole. As we didn’t have a ‘cable mouse’ that could carry them for us to the other side of the borehole (where a cheese could have been standing!), we just attached a 5 m wire-thread with a weight to the end of the cables. Again, every thing went slowly. Every hour, the cave is becoming smaller and smaller. This attempt had to work straight away.

The cables were passed in the auxiliary borehole that connects the load cell to the main borehole. Brought back to the surface with some difficulties, we tightened the wire with the weight to the load cell cable. The weight going down smoothly, we went down to the tunnel to see if it had gone through the borehole. The wire wasn’t long enough. Not discouraged, we started to push from the top the cable, which is more than 15m long, cm by cm. To facilitate our work, the cable was twisting all the time, slowing us down. I don’t know how much time it took but it was long and I lost track of time. With Mathieu, we went down again to see how much cable went through and found that Miriam was pulling the load cell cable (that helped substantially!).

The cement ready, we finally placed the load cells and blocked the main borehole with a wooden plug. The glacier did not help to make the cement drying. Under a temperate glacier, the ice at the bed is at pressure-melting point, which is why we all wear good raingear. Despite some protection (wood and rock), some water dripping from some massive creeping ice let a nice ring in the cement. You have to imagine that being in that cave is like being in a constant, small but thick drizzle. Thus, we used our amazing red umbrella that I called “Lady Engabreen”. Although it is not in its best shape, it did the job very efficiently!

Later we went up again with the Kinect© and started mapping the bedrock upstream of the load cells. We set up a grid of cubes that were actually quite hard to keep stable on the steepest part. For the latter, some sticks maintained them up. This is going to be used for matching the different images together. We were taking one picture with four cubes and then another one with just three or two cubes, so that we could get the bed topography underneath them. For the Kinect© set up, the sensor was placed on one end of a 1 m long bar and on the other side was standing the battery, acting as a counter weight. This bar was screwed on a tripod, which we tried to maintain as more horizontal as possible. The sensor was cabled to a sealed box, where we had a small, portable PC.

We used the free software RGB-Demo to visualise what we were going to map and the fakenect command record to store the raw data. The small size of the ice cave constrained our motion quite a lot. We managed to obtain 26 images of the bed and covered a surface of about 4 square metres. Freezing and wet, we stopped when the laptop ran out of battery.

Before leaving, we left the time-lapse camera facing toward the entrance to film the closure of the ice tunnel. While Alex was looking at the camera settings and testing it, I was holding the umbrella to protect the camera from the freezing melting ice. Once back in the living quarters we looked at photos of our day, the images from the Kinect and ate a late dinner.

What a day!

I am looking forward to seeing the outside world and resting a bit in Oslo!

PiM

Photo 1: Alexandra and Pierre-Marieset up the time lapse camera, using an umbrella to help

keep it dry

Photo 2: Setting up a time-lapse camera under the ice

Photo 2: