11 February, 2016 by Staff Reporter
A seismic study by scientists across the West Antarctica and Marie Byrd Land has resulted in the discovery of a ‘hot zone’ beneath the West Antarctic Rift System, thought to have a major influence on ice streams, according to new research by Washington University in St. Louis.
The research, published in the Journal of Geophysical Research, used recordings from seismometers deployed in the region during the 2009-10 Antarctic summer to create maps of seismic velocities beneath the rift valley. It is the first time seismologists have been able to deploy instruments rugged enough to survive a winter in this part of the frozen continent, and is the first detailed look at the Earth beneath this region.
The next step is to study the geological structure under the Thwaites and Pine Island glaciers, which lie closer to the coastline than the Bentley Subglacial Trench, where ice flow surges could theoretically cause the rapid disintegration of the entire West Antarctic ice sheet. Another 10 seismic stations were deployed in this region during the 2014-2015 Antarctic summer.
Superheated rock was found about nearly 100km beneath Mount Sidley, the last of a chain of volcanic mountains in Marie Byrd Land, east of the Ross Ice Shelf. They also reveal hot rock beneath the Bentley Subglacial Trench, part of the West Antarctic Rift System.
Hot rock beneath the region indicates that this part of the rift system, a linear zone where the Earth's crust and upper mantle are being pulled apart, was active quite recently.
“We didn’t know what we’d find beneath the basin,” says Doug Wiens, PhD, professor of earth and planetary sciences and a co-author on the paper. “For all we knew it would be old and cold. We didn’t detect any earthquakes, so we don’t think the rift is currently active, but the heat suggests rifting stopped quite recently.”
The rift system is thought to have a major influence on ice streams in West Antarctica. “Rifting and ice flow occur on completely different time scales, so rifting is not going to suddenly make the ice sheet unstable,” says Andrew Lloyd, a graduate student in earth and planetary sciences in Arts & Sciences at Washington University in St Louis. “But to accurately model how quickly the ice is going to flow or the rock to rebound, we need to understand the ‘boundary conditions’ for ice models, such as heat flow from the mantle.”
“Seismic surveys like this one will help inform models of the ice sheet,” Wiens said. “Modellers need an estimate of the heat flow, and they need to know something about the geological conditions at the bottom of the ice sheet in order to estimate drag. Right now, both of these factors are very poorly constrained.”
While heat flow through the Earth’s crust has been measured at least 34,000 different spots around the globe, in Antarctica it has been measured in less than a dozen places. In July 2015, scientists reported the heat flow at one of these spots was four times higher than the global average. Ever since then, scientists have been wondering why the reading was so high.