PRESSURE-MELTING OF ICE: While-U-Wait Bill Locke, Dept ...
PRESSURE-MELTING OF ICE: While-U-Wait
W. W. Locke, Dept of Earth Sciences, Montana State University, Bozeman, MT 59717; [email protected]
Ice is weird!
Ice < Water
Pressure drives solid ice
(PMP) drops 0.7 C/
vertical km of ice
Melting point under
5-km thick Antarctic
Ice Sheet -3.5 C
Fill bottle with water
Make loop of wire to hang bottle on ice cube
Arrange mount on table to suspend fork above pan
Demo detail. Note
wire resting on top
of ice cube on fork.
Place ice cube (near room temperature) on fork
Hang full bottle from ice cube by fine wire loop
Ask students to pose multiple working hypotheses as to the
Wait ~15 minutes while discussing principles (listed to the left)
Most basal ice is at PMP
Cant cool further because
of thermal gradient
Cant warm further because
of ice; basal melting
Maximizes melt @ bed!
affects basal ice processes
Wire cuts through ice cube (pressure melt)
Ice refreezes behind it (regelation)
Melting cube can be picked up and held by its end!
A septum of bubble-free regelation ice marks the healed track.
Demo half-complete. Note wire
disappearing into middle of ice
wire resting on fork
edge, but not yet to
the base of the
(melting) ice cube.
to the bed
2-liter soda bottle
32-guage rust-resistant craft wire
Mount (fork and C-clamp)
Drainage collection pan
Is ice too weak (100 kPa shear strength) to resist wire; if so,
why did the ice heal?
Does ice heal as refreezing because of residual cold from the
freezer; if so, why did it melt at first?
The actual stress can be calculated from wire diameter, ice
cube width, and bottle weight.
Demo finale. Note wire
resting on fork and the
ability to pick
up the shrinking
Pressure-melt is a phenomenon that occurs at scales of time,
space, and force that can readily be duplicated in the classroom
it is of widespread importance beneath glaciers and ice
Demo Grand Finale! Note
that the ice cube, although
smaller, is intact. Healed
septum is barely visible.
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