From: Kevin Bluck (kevin.bluck@mail.com)
Date: Sat Jul 27 2002 - 22:55:34 MDT
At 05:10 AM 7/27/2002, you wrote:
>The following site thinks the numbers are slightly different:
>http://pubs.usgs.gov/factsheet/fs133-99/gl_vol.html
>
>It claims the maximum sea level rise potential if the Ross Ice Shelf were
>to completely melt would be 1 cm.
I admit to some imprecision in my comments.
Technically, the Ross Ice Shelf consists only of the floating mass over the
Ross Sea that forms due to the discharge of several ice streams. Since the
shelf is floating, practically all of its volume is already displacing
seawater, and so its fracture or melting would have only a minor effect on
sea levels --- if that was the limit of the change. In my "underice
volcano" scenario, I was lumping in portions of the grounded Western ice
sheet immediately behind the Ross ice shelf that would be fairly likely to
lose traction under certain conditions and "push" the Ross ice shelf before
it as it cascaded into the Ross Sea. It is those grounded portions that
would be responsible for significant sea level changes.
The situation in Western Antarctia is precarious, geologically speaking. It
is very active geothermally. Much of the Western ice sheet is grounded on
bedrock that is below sea level. If an underice volcano were to erupt in
the right (or wrong, if you prefer) spot near the grounding line, it could
allow seawater to infiltrate under the ice sheet. If a wide enough zone
became thus "lubricated", a large portion of the sheet could literally
"fall off" the continent. The goodly portion near the Ross Sea could flow
off in a matter of days, and the remainder of the West sheet, deprived of
its natural "holdback", could follow over the course of a few years,
virtually clearing western Antarctica of ice all the way to the spine of
the Transantarctic Range that divides the continent. There is considerable
geological evidence that similar scenarios have occurred in the past, and
western Antarctica has alternated many times between glaciation and open land.
It is unclear what effect global warming might have on such a process. It
may in fact be irrelevant, and a suitably large eruption would cause this
catastrophe even if we somehow completely eliminate human impact on the
climate. On the other hand, maybe human impact will be the final straw. We
don't really know.
I think it is safe to say, however, that a rise in sea level of up to 6
meters over the course of a decade or so would be a worldwide catastrophe.
--- Kevin
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