Homework #3               Glaciology, GEOL 4888,  Spring 2022                        Humphrey

Some practical glaciology questions, based in Wyoming:

1. On the lee side of Medicine Bow Peak, the wind in the last storm has deposited a 1 meter deep snow drift with a temperature of -15C. This week the sun will melt about 2cm of water equivalent from the surface. Is there enough energy in the melt water to ripen the snow pack to 0C? Assume the snow has a density of 300kg/m3. Hint, use the snow cold content Index we discussed in class. I include the index here since apparently some of you didn’t take notes carefully: Iindex ~ C * M / (D*T), where M is the melt in water equivalent depth, D is the snow depth and T is the average snow temperature, the coefficient C is about 600 for fairly fresh snow and 400 for firn. You must use the same length units for M and D.

2 Use google earth: Find the Dinwoody Glacier in the Wind river mtns. Use the ‘path’ menu, with the ‘show profile’ options to get the surface slope of the north flowing, east arm of the glacier (avoid the rock covered moraines). What is the approximate depth of the glacier?

3 Also in the Wind River area, find in google earth the ‘Whiskey mountain conservation camp’ south of Dubois: This valley was occupied and deepened during the last glaciation by a large valley glacier coming from the Gannett peak area. Find the valley slope in the region of the camp (use about 2kilometers of valley to average over roughness), assume this is about the same as the glacier surface slope. The ridge on the south-east side of the valley is a glacial moraine, put there by the glacier. Is the height of the moraine reasonable (was the glacier about that thickness?). What was the glacier thickness?

4 The Gannett Glacier is steep, and gets almost 2x steeper near its lower end, creating a small ‘icefall’ or heavily crevassed region. In the flow direction distance of 200m, the ice velocity goes from about 5m/yr to nearly 25m/yr.

a What is the approximate longitudinal strain rate in this region?

b (Hard, requires Glen-Nye flow law) Assume there are no other stresses in the ice, and that the ice is ‘Temperate’ (For the ‘A’ softness parameter you can use 5x10^-24 per sec per Pascal cubed, which is appropriate for warm ice.) What is the approximate longitudinal stress in the ice from this strain?

c (Only answer if you are hardcore cryosphere nerd, no points) Assume the basal shear stress is 100,000Pa, how much ‘softer’ is the ice near the bed because of this extra stress?

5 How deep are the crevasses in the ‘icefall’? You need the answer from part 4b. (If you couldn’t do that question use 100,000Pa for the longitudinal stress.)