Seismic Clues to Surging Glaciers
Far from being static features of the landscape, glaciers are dynamic rivers of ice, flowing and carving earth beneath them in a diverse range of rates. There are fast-flowing glaciers, slow or stagnant glaciers, and surging glaciers that periodically accelerate and slow down again.
It's long been thought, Zhan notes, that liquid water at the base of glaciers might be acting as a lubricant, speeding glaciers up and along, but it is difficult to fully characterize what is taking place under many meters of ice. In a recent study published in Geophysical Research Letters, Zhan details the results of a new approach that offers a work-around.
Zhan's insight was to make use of two seismological stations set up astride the surging Bering Glacier in Alaska. Zhan examined station data for a 12-year period, which included a surge that lasted from 2008 to 2010, measuring changes in the speed of background seismic waves as they passed through the glacier. He found that waves slowed down during the surge, indicating they were traveling though softer material—water rather than ice or rock.
Zhan thinks that the bottom 10 or 20 meters of a glacier crack during a surge, with those cracks running perpendicular to the direction of the glacier's flow. Water, he says, rather than simply pooling at the base of the ice, fills these cracks. Zhan measured two types of seismic waves, Rayleigh and Love waves, to reach this conclusion.
Zhan would also like to extend his technique in future studies, perhaps adding additional seismological stations at different orientations across the glacier to better test his hypothesis.
Click here to read the full article in EOS.