6 December 2012

Rocky “Bumps” Anchor Antarctic Glaciers

Posted by kramsayer

Antarctica's Thwaites Glacier is currently stabilized by a rocky ridge underneath its base. (Credit: NASA / Jim Yungel)

When glaciers have rock to cling to, they hold on tight. Luckily for us, a ridge of rock lines the edge of an expansive Antarctic glacier that might otherwise – without the ridge – be rapidly retreating and raising global sea level.

Richard Alley, a glaciologist from Penn State University, presented these findings Tuesday morning at the 2012 AGU Fall Meeting in San Francisco on behalf of co-author Byron Parizek, who could not attend the session.

Alley showed that a ridge of mud and rock has stabilized west Antarctica’s Thwaites Glacier by both providing a solid surface for the ice to hold on to—rather than slippery mud—and by blocking seawater from seeping under the glacier and melting it.

His team created a model simulating scenarios that should jeopardize the glacier’s stability, including ice thinning and sea level rise. But in most cases, the ridge kept the glacier stable.

“Ice loves bumps,” Alley said during his talk. “The ice is sensitive to [changes], but there are not huge scary things going on because it is just sitting on top of that bump.”

The “huge scary things” Alley alluded to, which are not currently happening, include rapid ice retreat and sea level rise.

But a potential looming force that could still pull the glacier down this scarier road is sneaky seawater that seeps past the bumps and warms the glacier’s base. It gets there during low tide, as the glacial tongue droops downward, and the inland ice compensates by arching up. This arch creates space for water to seep in and pool under the glacier.

For now, this has not caused catastrophic melting because once high tide arrives, the glacial tongue floats back up and the inland ice settles, squeezing the water out. In the process, the glacier compacts sediment underneath the ice, cementing a muddy ridge that actually further stabilizes ice.

This tidal see-sawing effect remains stable now, but the team’s research shows that, if seawater reaches a large enough region under the ice with forecasted sea-level rise, the glacier could rapidly destabilize.

“If [the glacier] gets off that hard zone, then you’re in something really soft and it can run away in a hurry,” Alley said during his talk.

Alley emphasized that it’s hard to predict how stable glaciers will be in the coming years. His team hopes to improve the accuracy of their models forecasting glacial movements, with higher-resolution radar data showing clearer images of these savior bumps, and better field-based data of oceanic and atmospheric conditions that affect glacial conditions.

-Laura Poppick is science communication graduate student at UC Santa Cruz