Greetings, from our snowy o-WAIS-is! It is a bright sunny night here and our field work is finally underway. Yesterday afternoon, Anny, Rachel and I took our first radar measurements while Emilie and Erin finished up initial tests for our logging tool. The camp carpenters, mechanics and electricians were out with us all weekend setting up our logging tent and warming hut. The primary task was setting up the winch and cable that will lower our logging tools 3,405 meters down the borehole!
The borehole is protected under a huge aluminum arch, about 8 meters tall and 20 meters long. The arch was built during the extraction of the core to shelter the core and the drillers from outside elements. The core needed to be kept at -25degrees Celcius to preserve the crystal structure and chemistry, and the drillers needed to be kept toasty in their control room. Now, the arch is buried under several years of snowfall, and each season, the WAIS Divide Crew digs out a snow ramp running down to the arch doors. Our winch sits in a tent on the current snow surface above the arch. The cable runs from the winch to the roof of the arch where it’s lowered down an opening to the borehole below.
MVP of the week is our winch operator, Elizabeth! Elizabeth joined our team when we were in McMurdo because our original winch operator was unable to join us on the ice this season. Since arriving at WAIS Thursday night, she’s been tackling the winch and logging setup, making sure everything runs smoothly so we can have the most successful borehole logging possible.
The first borehole logging tool we will use is an acoustic televiewer. The acoustic televiewer is a two meter rod that is lowered into the borehole. It can tell us the shape of the borehole essentially using echolocation as it’s lowered down through the ice. We call it Batwoman.
When we lower Batwoman down the borehole, she sends out an ultrasonic ping. The ping bounces off the borehole wall and returns to a receiver within the tool. By dividing the ping’s travel time by it’s velocity, we can determine the distance it travelled and, in turn, the size of the borehole. To get the full picture of the borehole, a mirror inside the acoustic televiewer is constantly rotating, sending the ping off in a spiral as it moves down the borehole.
Now that Batwoman is set up, we have begun our 24 hour logging sessions for each run through the hole. One full log, from top to bottom to top, will likely take four to five days. The data we get from these logs will be compared to data from VeLveT Ice’s 2014-2015 season. We expect to see certain layers of ice closing in at a faster rate than others. In particular, we expect certain layers of the deeper ice in the borehole to deform more because of their “fabric” or microstructural properties, like ice crystal size and orientation.