Glacier Quakes

Meredith Nettles of Lamont-Doherty Earth Observatory, a scientist studying glacier dynamics in Greenland, sent a link to her project Web site the other day. There, in addition to basic information on her NSF-funded study, you can find a few pictures from the first of two field trips this year and a sheaf of photos from previous years as well. The team accesses its monitoring sites via helicopter, landing on the scarred surface of the glacier. Source: Nettles Web site

Nettles and colleagues Gordon Hamilton (University of Maine) and Jim Davis (Smithsonian), along with Danish and Spanish colleagues and technical experts from UNAVCO, have placed Global Positioning Systems (GPS) networks on two of Greenland’s most active outlet glaciers, Helheim and Kangerdlugssuaq, both on the island’s southeastern coast.  These glaciers dump massive quantities of fresh water into the Arctic Ocean, and back around 2005 scientists noticed that they (and other glaciers in Greenland’s south) seemed to be flowing a lot faster all at once:  a statue placed on Helheim Glacier in January 2002 would have advanced an impressive six kilometers toward the ocean by year’s end; but during 2005 the same statue would have raced seaward some 11 kilometers—about half a football field a day, Gordon Hamilton estimated.  In addition to accelerated advance, the science team observed that the glacier—about 700 meters (nearly half a mile) thick from muddy bottom to tumbled top, seemed to be thinning rapidly as well, which suggested further destabilization.

The calving front of Helheim Glacier, 2006. Photo: Meredith Nettles

The seasonal processes driving these changes are what the Nettles collaboration is attempting to discover. For the past few years, researchers have gone to one or both of the glaciers and placed GPS instruments on the ice to create the monitoring networks. (On the Helheim, the team has also placed time-lapse cameras and instruments to monitor climate, seismic and tidal activity.)  These have then collected precise information about the glaciers’ movements, sending data via radio signal to a collecting station on a rock outcrop which in turn sends data back to the Nettles lab via Iridium phone.

Here researchers install a GPS instrument in the middle of nowhere--actually a northern section of the Helheim). Photo: J. Vilendal Petersen

The networks have captured information about so-called glacier quakes, phenomena discovered less than a decade ago by Nettles and colleagues monitoring other seismic information. The team noticed that seismic signals were being recorded in clusters around the coast of southern Greenland, an area traditionally associated with little seismic activity. Further study revealed that the seismic activity was caused by sudden, fierce movement of glaciers lurching forward, but the physical processes where not known.

Since then, Nettles and others have learned a bit about these quakes. Nettles talked with Popular Mechanics earlier this year, explaining how glacier quakes work:

“We saw a couple last summer from our helicopter, near the calving front. We were at the outlet to the Helheim glacier, in a system of fjords with sheer rock walls that are 500 meters [more than 1600 ft] tall. Typically, you start to see a rift open up in the glacier and then this big block of ice starts to roll over. The block that breaks off might be a couple of kilometers long and it's the full thickness of the glacier, which is about seven hundred meters—mainly underwater. . . . It takes a couple of minutes to fall, and as it's rolling, it has to move this thick melange of ice and water that's in front of it out of the way. You start to see the icebergs moving very, very fast down the fjord or, if they're close to the calving front, you see them being popped up, straight towards the helicopter. Then you see just tons of water streaming off of the new iceberg as it is being formed. We have instruments to detect the resulting tsunami about 35 or 40 kilometers away.”

Not for the faint of heart.

Instruments located on Helheim Glacier, Greenland.

After capturing a season’s worth of data on the GPS networks, the Nettles team is back in the field this week removing the Kangerdlugssuaq network and winterizing that on the Helheims. She indicated that she is pleased with the data capture. See for yourself by clicking “Telemetry Status” on the project Web page.