Surveying the Lemon Creek Glacier
Isabel Suhr, Lewis & Clark College
A few days ago I got the opportunity to help Scott McGee with the GPS surveying project. Our goal for the day was to complete six profiles on the Lemon Creek Glacier below Camp 17: five transverse profiles (across the glacier) and one longitudinal profile (from the top to the bottom of the glacier). Each profile consists of between fifteen and thirty GPS points, and our task for the day was to take a GPS measurement at each point, to measure the elevation of the glacier there. Combined with previous years’ data, this gives a record of the thickness of the Lemon Creek glacier over time.
To survey the glacier, Scott and Bjorn first set up a GPS base station over a benchmark on the ridge at Camp 17. Since the benchmark had been previously surveyed, we could use its known latitude and longitude to calculate the error in our GPS measurements for the day. The base station then communicates the error correction to the two backpack GPS units we took into the field. With the base station set up, we collected the two GPS backpacks and headed down onto the glacier to begin our day’s work. We split up at the center point, with Bjorn, Ella, and Jolon heading to the lower glacier while Scott, Joel, and I headed toward the upper.
Surveying GPS points is kind of like playing a video game while on skis—really fun, but a little hard to coordinate at first. Once you pick a point to survey, the screen of the GPS tells you which direction you need to go and how many meters away from the point you are. Once you get within a meter or two, your location and the GPS survey point location both show up on the screen, and the goal is to plant the antenna pole in the snow within half a meter of the surveyed point. Once you’ve lined that up, you take a GPS measurement of the elevation of the glacier at that point, and move on to the next point on the profile.
The profiles we surveyed took us all over the upper Lemon Creek glacier, from the middle of the glacier all the way up to the shores of Lake Linda at the very top, and from the flat center to the steep slopes at either side (including one point where we had to scramble up some steep rocks past the edge of the glacier). It was a beautifully clear day, and from high up on the edges of the glacier we could watch the tiny dots of the other survey party making their way across the lower glacier, and of other JIRPers digging mass balance pits and practicing skiing. In between breaks to appreciate the view and put on more sunscreen, it was easy to get into a rhythm across each transect. Shuffle forward to the next point, plant the antenna pole, level it, take the measurement, and shuffle on to the next point. By the end of the day, the GPS group had shuffled our way across the entire glacier, and had another year’s worth of GPS points to add to the record. And beyond that, we had the chance to learn to use GPS equipment and experience a day of field work!