Homework #5 Glaciology, GEOL 4888, Spring 2014 Humphrey
1.
Two
approximately spherical rock clasts, 25cm in diameter,
are pressed together under the ice with a force of 1KNewton. The rocks are assumed to be very rigid, but
have a crush strength of about 20MPa (above that
stress the rock material tends to break into small chips). Calculate the diameter of the resulting
contact area.
2.
The
Parks Service in Yosemite (if you haven’t been there, look it up on Wikipedia)
has some nice displays showing how the valleys were carved by glaciers. We have talked a little about glacier
erosion; in particular we noted that the erosion coeff.
for granitic rocks is about 10-6 (vertical
rock erosion for each meter of basal glacier sliding). The deep U-shaped valleys in Yosemite are
about 1000m deep. Typical mountain
glacier sliding velocities are 10m/yr to somewhat
less than 100m/yr. The question is: do
you think the Parks Service displays are telling the public an accurate story,
and of course you have to explain why or why not?
3.
We
did a regelation experiment in class. We
used a copper wire with a thickness of .5mm.
We loaded a 2kg weight on each side of the wire, and hung it over a
piece of ice that had a diameter of 7cm.
Look back through your notes and you will find a scaling expression for
regelation. On the basis of your scaling
equation: should the wire have regelated through the
ice by the end of class or not?
4.
Here
is a puzzle for you. When rivers flow
around bends, the outside water in the bend flows faster than the inside. When a glacier flows around a bend, does the
ice on the inside or outside of the bend flow faster (and why)?
5.
Final
Question: What are you thinking about
for your project? Include at least one
source material resource in your answer (eg. Where are
you going to find information?)