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Ellen McCallie's Diary

Day 22: Speed and Melt of the Glacier

Some folks get to spend the night on a glacier during this program. Unfortunately, I'm not one of them. Any chance I could get some plants to grow up there by tomorrow?

So, what's the challenge this time? Mike B. and I are responsible for determining if the glacier is advancing or retreating over the next couple of days. We are also supposed to make portable warming devices.

In order to see results, we set up the glacier movement equipment today. We'll work on concocting portable warmth tomorrow.

Photo: the glacierSo, how do you measure if a glacier is advancing or retreating?
Background: A glacier is a "river" of ice that moves downhill because of gravity acting on the glacier's great mass. So we know a glacier is always moving and it is moving downhill. Whether it is advancing or retreating is another story. This has to do with the amount of melting that occurs at the end of the glacier vs. the amount of ice that is pushed down each day. If more melting occurs than ice moving down to replace the melt, then the glacier "retreats", actually it shrinks by melting. If more ice moves down the valley that is melted away at the end, then the end of the glacier is pushed farther down the valley, so the glacier is advancing.

In either case, the glacier ice is always moving downward. We are in the temperate zone and this glacier extends below the snowline, so glacial ice is always melting. (Snow and ice melts below the snowline.)

What is going on now? From walking up the glacial valley, we could see several indications that the glacier was once much longer that it is today. First, we saw striations in bedrock where large boulders, carried by the glacier, had scraped against bedrock, making deep grooves. Rock is hard stuff. Rivers carve out rock, they don't make scrape-marks, so we can be certain that at some point in the past the glacier, carrying large boulders, scraped rock against rock. Second, as we looked around the valley, tall, mature forests were found up high, while younger forests were found lower down. The closer to the valley bottom, the younger the trees. This indicates that the glacier has recently covered the lower area and has only retreated recently, which allowed the trees to germinate and grow. The fact that the youngest trees are at the bottom and they get older as one looks higher on the cliff faces, says to me that the glacier once filled the valley to very high up and slowly melted. As the area became exposed, trees grew. The last area to be exposed from the ice is at the bottom.

So we know that compared to today the glacier was well advanced in the past, probably a couple hundred years ago. Maybe even up to 500 years, based on the age of the trees.

What are we measuring to get an idea of what is going on with the glacier now?

We are set up to take two different kinds of measurements. To measure how much (in distance) the glacier is advancing or retreating right now, we set up a "triangle-broomstick" contraption. Basically, we mounted the base triangle on bedrock (something that will not move) and then marked on the stick the distance to the current edge of the glacier. Because we are using a stationary base, bedrock, we will be able to tell if more ice is moving down the valley than is melting (advancing). Or, if ice is melting faster than ice is moving down from the glacier (retreating).

Photo: Ellen and Mike B sticking skewer sticks into the iceThe second setup allows us to visualize the ice melting at the end of the glacier. No matter if the glacier is advancing or retreating, ice is always melting. We stuck several skewer sticks into the ice (with a drill). We put them 5 cm down into the ice and from 2 to 6 cm from the edge of the glacier. This will allow us to see how much of the ice at the current edge of the glacier melts, both from the edge and from above. I think this has the potential of being really cool as well as complementing our actual challenge.

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Photo: Ellen McCallie
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