Its chilly underbelly may be snagging on large rises in the underlying ground, according to a seismic survey.
The Thwaites Glacier, a sheet of ice the size of Florida that is melting and presently contributing roughly 4% of the rise in global sea level, is the subject of mostly negative headlines. However, there might be some positive news to report.
Glaciologist Coen Hofstede reported on December 12 at a press conference during the American Geophysical Union fall meeting that a seismic survey of the bed beneath an upstream section of Thwaites glacier has revealed rough high-rises of earth beneath the Antarctic glacier, comparable in height to the Manhattan skyline. It’s possible that these jagged elevations are snagging the glacier’s underside, halting its flow toward the ocean and reducing the rate of sea level rise worldwide.
While considerably slower than rivers, glaciers flow in similar ways. Thwaites glacier joins a floating ice shelf that partially restrains and supports the glacier when it empties into the ocean. It was stabilized when that ice shelf was anchored to an undersea mountain (SN: 12/13/21). Erin Pettit, a glaciologist at Oregon State University in Corvallis, stated at the news conference that the shelf has become so degraded that it is essentially unhitched at this point.
Fortunately, however, in part because of the discoveries made upstream, the glacier “is not going to suddenly flow off land,” according to Pettit, who was not involved in the discovery.
In order to investigate the Thwaites glacier’s underside, Hofstede and associates carried out a seismic investigation more than 70 kilometers inland from Thwaites’ ice shelf.
A daisy-chain of seismometers measuring 1.5 kilometers in length was fastened by the team to a car fitted with a vibrating plate. Then, employing the plate to create seismic waves and seismometers to record the waves’ reflectance off the soil and ice layers below, they drove a section of the glacier that was about 200 kilometers long. Hofstede of the Alfred Wegener Institute Helmholtz Center for Polar and Marine Research in Bremerhaven, Germany, compared it to radar.
Seismic waves exposed rises beneath Thwaites glacier that are ten to twenty kilometers long and include chunks of silt arranged in a serrated pattern. These blocks extended horizontally for several kilometers and rose to a height of up to 100 meters above the rises.
According to the data, there may be layers of distorted ice within the glacier above the rises, and the upstream faces of these blocks appear to be under more strain than their downstream sides. Hofstede speculates that Thwaites’ flow is being slowed down by the rises and barriers because the ice is pressing against them.
The Thwaites glacier “gets hung up on tall features,” according to computer simulations of its flow, according to glaciologist Ben Smith of the University of Washington in Seattle, who was not involved in the work.
According to Hofstede, the elevations are most likely connected to a rift system, which is a region where tectonic pressures have torn the earth apart. Like speed bumps on a road, these rifts run under Thwaites about perpendicular to the glacier’s ice flow.
According to Hofstede, the results will enable more accurate simulations of the glacier’s history, which are essential for comprehending the rates of sea level rise.