What’s happening under and inside the masses of ice in the polar regions is of great interest to scientists. Recently researchers in West Antarctica have found that one ice stream–a region of the ice sheet that moves faster than the surrounding ice—jerks along in an earthquake-like pattern equivalent to a magnitude 7 quake.

Their findings ran counter to the general belief that ice streams moved in a creeping motion. Instead, they found that the ice moved in a stick-slip movement, caused by the base of the stream alternating between sticking to the bed and then sliding over it.

In the ice stream studied, the jerking stick-slip motion occurs twice a day and seems to be related to the tides in the Ross Sea. When a slip occurs, a part of the Whillians Ice Stream 60 by 120 miles and almost 2,000 feet thick moves as much as 2.2 feet in about 25 minutes.

Douglas Wiens of Washington University in St. Louis, and leader of the research team, says, “A big puzzle is why this particular ice stream shows this slip-stick behavior and others don’t and we don’t really understand why. Our results show that the stick-slip motion originates from a sticky region on the bed of the ice stream where friction is higher, perhaps due to the absence of water.” Adding to the puzzle is the fact that this particular ice stream is slowing down.

The researchers stress that these findings do not immediately have implications for global warming, but are significant because they add to the understanding of ice dynamics. Scientists need more information about the conditions beneath glaciers and ice streams to model and predict sea level during climate change.

Other members of the team were from Penn State University, and the University of Newcastle in Great Britain.