by Lindsey Valich
Oct 26, 2010
Earthquakes triggered as glaciers break apart in Greenland can be felt as far away as South Dakota.
Seismologist Meredith Nettles knows their force firsthand because she has measured them during field trips to Greenland’s melting ice castles.
Although no one can physically experience them shaking the ground of Sioux Falls, instruments can pick up the seismic waves of these quakes.
The glacial quakes, in turn, offer scientists clues to current rising sea levels and warming sea temperatures as they relate to global climate change, said Nettles, assistant professor of Earth and Environmental Science at Columbia University’s Lamont-Doherty Earth Observatory.
Glacial earthquakes occur when large ice masses break off glaciers in a process called calving, Nettles told scientists the 2010 Comer Conference on abrupt climate change, held this fall in Wisconsin. When calving occurs, it reduces overall resistance to glacier flow, causing the glacier to gain velocity and often accelerating the calving.
Calving takes place naturally, but Nettles and her colleagues have demonstated in a series of high-tech observations the alarming increases in that acceleration and the rate of erosion at the edges of glaciers.
“We do see that these big changes are happening,” Nettles said.
With a process she describes as “very time and resource intensive,” Nettles and her colleagues placed global positioning systems (GPS) on the ice and were able to track the movement of glaciers over time to get an estimate of glacier velocity. This information is used to recognize the link between changing environmental conditions and the erosion at the edges of glaciers. Before this, many glacier models assumed that the vulnerable edges of glaciers were not important.
“This is a piece of information that you can use to make a more sophisticated model of ice flow,” Nettles said. “It is a step forward in understanding overall how changes in environmental conditions will affect glaciers and ice sheets.”
The rate of melting is a critical component for scientists to predict how fast and how much ocean levels may rise, posing risks to coastal areas. Estimates for the rise vary widely but at least a meter of escalation is expected in coming decades.
Nettles has been studying glacial quakes in Greenland since 1993 and just completed a five-year series of studies funded in part by the Comer Science and Education Foundation and the National Science Foundation. Many of the quakes that Nettles studied are registered as magnitude 5 in Greenland and humans can feel earthquakes of smaller magnitudes if they are nearby.
In addition, these quakes typically last for 50-60 seconds, versus the typical 2 seconds of magnitude 5 earthquakes that occur along fault lines. A 5.4 magnitude earthquake centered in Southeastern Illinois in 2008 was enough to cause some local damage.
Nettles likens the glacial quakes in Greenland to the movement of an elevator. People in an elevator usually feel the elevator starting and stopping, but not the slow motion in between floors.
She said she seeks to respond to doubts about global warming by simply showing others the data she has collected. Sitting in an airplane, a man next to her asked about the data she was analyzing on her computer. When she told him what she was researching, he voiced skepticism regarding climate change.
“Let me show you the data,” she offered, and proceeded to let the information speak for itself.
“Part of it is that people just haven’t seen the data,” Nettles explained regarding those skeptical of climate change. “The noise gets conveyed, but it’s surprising how unlikely it is that someone has seen those basic data records. The dialogue gets distorted by not separating out, for example, the actual observation of what’s changing from whose fault it is.”
This philosophy of open information is something she has extended to the village of Tasiilaq in Greenland, approximately 100 kilometers away from the sites where she and her colleagues set up their stations. In Tasiilaq, Nettles has begun working with students in the village school to spur their involvement in the data-collecting process occurring in their country.
“I want them to know science is something they can do,” Nettles said.
This is not a view in which Nettles herself felt any confidence as she majored in political science as an undergraduate at Harvard University. She said she was interested in science but found it a very lofty ambition.
“I always felt like that was a job for people way different than me,” Nettles said. At the same time, however, she was a research assistant to a seismologist and fell in love with the science. “You can make a contribution even if you’re not Newton. That is something I try to convey to the kids in the schools.”
Nettles’ impact is a lot like the glacial quakes—making reverberations that make rapid climate change hard to ignore.