Homework #7              Glaciology, GEOL 4888,  Spring 2017             Humphrey

1. Glaciologists often attempt to measure the ‘mean annual’ air temperature above a glacier by measuring the temperature of the ice at 10m depth below surface, where the temperature is assumed to be constant. Give an estimate of the size of error that could be introduced between measuring in winter vs measuring in summer, if there is a 20C swing between summer and winter at the surface. You can use the scale we developed in class for the fractional change in temperature with depth and time.

K – thermal conductivity

t – time since temperature changed

r (should be rho ice) – density of ice

C – heat capacity of ice

L – thickness of ice for the heat to flow through

2. This method is known to give errors when the mean temperature gets close to 0C. Consider if there is a 20C yearly temperature swing, but the mean air temperature is -5C. Will the 10m depth temperature in the ice, give the mean temperature? Will it be colder or warmer?

3. Make a plot of a parabolic profile for the Greenland ice sheet, using the parabola we developed in class. Assume the ice sheet divide is 700km from the margin.

4. Using your plot from 3, find the ice depth at 100km inland. Compare that with Greenland. Use Google Earth and go to the west coast of greenland at about 67 degres North (near the town of Kangerlussauq). Find the ice edge, and go in about 100km and find the surface elevation. The bed of the ice sheet in the region is relatively flat and only a few 100m above sea level. Does the Parabola from 3 give a reasonable number? (I have drilled the ice at 45km inland, and it was 825m, is this reasonable?)