Glaciers Slowed by 'Sticky Spots'

April 12, 2007 — New research into what makes glaciers suddenly change their ebb and flow is revealing that it all depends on "sticky spots" on glaciers' underbellies, say an international team of researchers.

Rocky patches and freeze-ups are among the sort of sticky spots that can lock up and slow down a glacier. Getting a better understanding of how they work is key to grasping how fast giant glaciers, called ice streams, will unload Greenland and Antarctic interior ice into the oceans and raise sea levels.

The details of how ice streams collapse are among the biggest areas of uncertainty in international efforts to forecast the effects of global warming.

"One of the big unknowns is the stability of Greenland and Antarctica," said ice stream researcher Chris Stokes of the University of Durham in the U.K. "That collapse would lead to several meters of sea level rise."

Stokes and his colleagues are investigating the ancient beds of long-gone ice streams in the Canadian Arctic to learn more about how and where the bedrock and softer glacial "till" sediments slowed and sped up the ice, with the help of melt water.

The hope is that the ancient ice stream data, along with data gathered by glaciologists working on today's glaciers, will lead to better simulations to predict what ice streams will do.

It's even possible such simulations could lead to glacier surgeries by geo-engineers to drain off melt water, which lubricates and unsticks glaciers. That way they might be able to increase the number of sticky spots and slow down misbehaving ice streams, Stokes said.

He and his colleagues from the United States and Canada have published a review of sticky spot research in the April issue of the journal Earth-Science Reviews.

"We can reasonably well model a normal, well-behaved ice sheet," said Stokes. But the ice streams of most concern are those in Greenland and Western Antarctica that are moving many times faster than their siblings — not normal at all.

"There's been a real evolution of thinking about how the bed of a glacier matters," said glaciologist Sridhar Anandakrishnan of Pennsylvania State University.

For years, ice stream beds had been considered nearly frictionless — devoid of sticky spots.

But then the idea of lumps and bumps, and the role of melt water in lubricating the bed, became better understood, Anandakrishnan explained. Now it appears that an ice stream's speed may be entirely a function of how many sticky spots lie beneath it.