Antarctica: Giant River of Ice Triggers Massive Sesmic Signals

The earthquake problems afflicting places like California and Japan are nothing in comparison to those experienced daily in Antarctica. A seismologist at Washington University in St. Louis and colleagues at Pennsylvania State University and Newcastle University in the United Kingdom, have discovered that twice a day, a magnitude seven earthquake emanates from a giant river of ice in the southern land of ice.

Douglas A. Wiens, Ph.D., professor of earth and planetary sciences in Arts & Sciences at Washington University, along with colleagues, have combined seismological and global positioning system analysis to pinpoint that the massive earthquakes spawn from an ice stream some 60 miles wide and half a mile thick.

It is, in essence, a massive glacial ice stream. And, just as its source is glacial, so is its speed.

“Glacial earthquakes” were first reported in Greenland in 2003. They are essentially massive earthquakes, but instead of taking moments to pass, happen over several minutes. It is a high magnitude earthquake stretched in to 10 minutes.

Since their discovery, more and more have been found across the planet, as people know what to look for. For a long time scientists thought that this phenomenon came solely from calving, the massive break off of ice from a glacier in to the ocean around it. The Antarctic signals however are the first showcasing these glacial earthquakes taking place as a result of sudden sliding by large sheets of ice.

The glacial earthquake stems from the stop and start motion of an ice stream. The data show that the river moves approximately 18 inches within ten minutes, but then remains still for some 12 hours, before moving another 18 inches.

"By some measures, the seismic impact is equivalent to a very large earthquake, but it doesn't feel like it because the movement is much slower than a real earthquake," Wiens said. "The data look an awful lot like an earthquake, but the slip lasts for 10 minutes, while on the other hand an earthquake of this size would last for just ten seconds. I guess you could call it an earthquake at glacial speed. This is very strange behavior, and we need to understand more about it."

"The GPS shows us directly how the ice stream moves," Wiens continued. "The slip starts in a certain part of the ice stream and then it moves out, rather like a landslide might start at a certain point and then move out to envelope an entire mountainside. The GPS tells us which part moved first and what other parts moved next and so forth."

Scientists and glaciologists had already thought they understood how glaciers move, Wiens said, but with this new information indicating that they move with a fast slip, akin to an earthquake, their ideas have been thrown out the window. "This stick-slip phenomenon may provide a clue about what makes these ice streams move faster or slower," Wiens said. "This particular ice stream has been slowing down over the last few decades, and no one knows why.”

Posted by Josh Hill. Image credit: Harry Kokstra.