Regelation or Viscous Deformation?

This summer, in addition to five other interns, we also had four students through the Climate and Life program: Camille, Jeremy, Naomi, and Jennifer. They were looking at the difference between regelation (pressure melting and recrystallization) and viscous deformation, which could be mechanisms of flow at the base of glaciers under the right conditions. Mike built a frame to go with Rob's dead weight apparatus that the students assembled. They calculated the stress for each increment of weight to be added. 

They did a great job drawing the below schematic of the set up. The frame was used to apply a dead weight to the top of the ice, which was resting on top of spheres of various size and composition. The  hypothesis was that under some conditions regelation would dominate over viscous deformation and other conditions it would not. Since any melt formed would drop down below the balls due to gravity, we would be able to tell the difference. Also, in theory, regelation should be faster with spheres of higher thermal conductivity so we thought me might be able to tell the difference that way.

They printed up their motivations, methods, and results into a nice poster. Title was all their idea, and I love it!

And they did a great describing their project to the other interns and my colleagues at an informal poster session held on the last day.

With about a half hour left before the bus, they enjoyed some competitive stress concentration and particle interaction.

Also joining us in the lab this summer was Will, a local high school student. He worked on a pressure sensitive film project to quantify real area of contact changes of samples in the rig. After getting the method down on roughened teflon and PMMA, it was time to start working on ice.  Since he was looking at contact area change with time and normal stress (but zero velocity), we didn't need to use both pistons for his experiment. Working with Mike, they designed and built a special purpose cryostat with a wood frame and this green styrofoam for insulation.

The cryostat fit nicely into the apparatus, allowing it to be pre-chilled with circulating fluid and loaded with the prepared ice sample and forcing blocks. A small slot at the top allowed him to change the chilled pressure films in and out. 

With the horizontal hydraulic pistons, we applied 450 kPa normal stress at -2 degrees C and he measured the pressure on the films at 10 s, 100 s and 1000 s holds. The films were digitized and analyzed in ImageJ for %area. After lots of trouble shooting and trial and error to develop the protocol for this brand new method (for us anyway), his summer culminated in getting the below data set (Fig. b). It looks great! Well done, Will!