GLIMS feedback as requested

[Bruce Raup]

Matthias, et al.

Sorry to be a bit slow at responding to this.

On 2001-06-13 11:05 +0200,  Matthias Braun wrote:

> Dear Bruce,
>
> I agree that this is a fundamental question and I would generally support the
> definition suggested for land based or tide water glaciers. However, how
> shall
> we treat ice shelves?
> Are they single glaciers as long as they do not fall apart or do we delimit
> tributaries and use e.g. the grounding line as lower boundary of the
> glaciers and
> treat the shelf area separately?
> Treating them as single glaciers might be difficult as they are often fed by
> several glacial systems from different areas e.g. Wilkins Ice Shelf or how do
> we deal with the Larsen A, untill break-up as single glacier and afterwards?
> In this case we would lose continuity in the database. Both ideas have their
> advantages and difficulties.
>
> Any better ideas/suggestions?
>
> Regards,
>
> Matthias

My inclination would be to consider the ice to be "glacier" up to the
grounding zone, and treat the ice shelf separately.  Flow lines are
frequently (usually?) identifiable in ice shelves (see
http://nsidc.org/NSIDC/ICESHELVES/larsen_aux_images.html for an example on
the Larsen), so there might be the temptation to keep track of source
glacier for each part of the ice shelf.  However, this could be very
complex in situations where different sources fluctuate wildly, as is the
case along the Siple Coast.

Difficultly in defining the grounding zone can be handled by the analyst
doing the best job possible, then assigning an appropriate uncertainty to
that segment of the outline.

The Wilkins is an interesting case.  In addition to the many glaciers
feeding it, much of its accumulation is due simply to snow accumulation,
according to Ted Scambos.  Its horizontal velocities are quite slow.

I think most glaciologists think of ice shelves as different systems from
the glaciers that feed them.  Certainly the dynamics are different.

More comments or ideas?

Bruce

--
Bruce Raup
National Snow and Ice Data Center                     Phone:  303-492-8814
University of Colorado, 449 UCB                       Fax:    303-492-2468
Boulder, CO  80309-0449                            Bruce.Raup at colorado.edu