Cryosphere Reception and Inaugural Nye Lecture
At the AGU Fall Meeting
Moscone Convention Center, Room 130
San Francisco, California
1800 hrs, Saturday, 7 December 2002
General information about the Fall Meeting of AGU is available at:
http://agu.org/meetings/fm02/
Bob Bindschadler will be the guest lecturer for the inaugural Nye
Lecture, followed by the Cryosphere Reception (There will be finger food
and a cash bar at the Reception)
Consider an Ice Stream
Bob Bindschadler
NASA Goddard Space Flight Center
Forty years ago, John Nye was one of the leaders who introduced the
rigors of classical physics to glaciology. His elegant treatments
frequently took advantage of the then recent discovery that ice could be
approximated as a plastic material. With this viewpoint, Nye was able to
explain the shape of ice sheets and glaciers, to predict the expected
pattern of stress and velocity within a glacier, and to derive the
advance and retreat of a glacier from the record of accumulation and
ablation. These advances have given generations of glaciologists tools
to interpret the excellent observational record of glacier behavior and
variation. In the 1980s, glaciologists, weaned on these works of Nye and
of other similarly adept colleagues, carried their lessons to West
Antarctica to study ice streams, the vast conveyor belts of ice that
discharged nearly as much Antarctic ice as the much larger East
Antarctic ice sheet. Ice streams were a glaciological conundrum. Despite
the gently sloping surface, these broad features roared along, moving
fastest when the gravitational impetus was least. After two decades of
research, ice streams still have not given up all their secrets, yet
much is now known. Internal deformation is negligible. Basal friction is
frequently nil leaving the shattered margins as the primary means to
avoid rapid wastage of the ice sheet. Within the margins, the resistive
force results from a delicate balance of heat and evolving ice fabrics.
Nevertheless, the bed beneath an ice stream cannot be ignored. It is
ultimately the state of the underlying marine sediment that determines
whether the ice stream can slide at all. There too, the heat balance is
critical with an influx of water required to keep the bed wet enough to
let the streams glide along. Ice stream research has been the portal
through which glaciologists have seen and identified the complexities of
West Antarctic ice sheet dynamics. Remarkably, nearly all time scales
seem important. Ice stream positions in past millennia conform to
radically different flow patterns while on the scale of hours an ice
stream's motion is halted completely, then released to move at
surge-like speeds, in tempo with the tides. Explaining these
complexities constantly reminds us that the rigorous physics applied to
ice so effectively by Nye still work.