The rapid loss of Hektoria Glacier’s grounded ice is visible
in these images acquired in October 2022 (left) and March 2024 (right) with the OLI (Operational Land Imager) on Landsat 8. The glacier retreated 8 kilometers in
November-December 2022, after having lost a 16-kilometer-long section of
floating ice earlier that year.
To say something moves at a glacial pace is to imply sluggish, unhurried
change. But what transpired over the course of 15 months at Antarctica’s
Hektoria Glacier was uncharacteristically quick. Between January 2022 and March
2023, the glacier lost about 25 kilometers (15 miles) in length. That included
a two-month period in which the terminus retreated more than 8 kilometers (5 miles)—the
highest rate of grounded glacial ice loss observed in modern history.
A team of scientists published an
analysis of Hektoria’s
collapse based on
a suite of remote-sensing data, finding that its particular geometry enabled
the rapid change. Like many glaciers on the Antarctic Peninsula, Hektoria
starts on land and extends to the sea, with the last section being a thick,
floating plate of ice, or “ice tongue.” The researchers determined Hektoria
lost both its ice tongue and an area of grounded ice spread over a flat
plain—the latter directly contributing to sea level rise. Although Hektoria is
relatively small as Antarctic glaciers go, scientists say that similar events
at larger glaciers could be much more consequential.
The images above capture the scale
of the loss of Hektoria’s grounded ice on the eastern Antarctic Peninsula. Note
that the right image was acquired about one year after the remarkable loss of
grounded ice; a cloud-free Landsat image showing the whole area was not
available from the previous March. Hektoria’s terminus remained relatively
stable after the sudden loss, the study reported, though the neighboring Green
Glacier continued to retreat.
The chain of events culminating in
Hektoria’s breakup goes back to early 2002. At that time, the Larsen B ice
shelf, which served as a backstop for Hektoria and neighboring glaciers, splintered and collapsed in short order. The glaciers then thinned and retreated for several years. In 2011, landfast sea ice in the Larsen B embayment near Hektoria’s terminus filled in enough
to allow the glacier to start advancing.
But after several years, the new
support for the glacier front was suddenly removed. Landfast ice in the
embayment broke up in January 2022, likely due to large, destabilizing ocean
swells. From that
point, rapid change at Hektoria was again underway. Throughout the rest of the
austral summer, the floating ice tongue disaggregated in a series of calvings,
resulting in a loss of 16 kilometers.
The glacier’s terminus stabilized
during the 2022 austral winter. However, satellite-based laser altimetry data,
including ice elevation measurements from NASA’s ICESat-2 (Ice, Cloud, and Land Elevation Satellite-2)
mission, revealed that the ice continued to thin during that winter.
The thinner remaining ice was still
grounded during the 2022 austral spring (left image, above), the study authors
concluded, based on the detection of earthquakes occurring beneath the glacier.
They determined the ice was spread out over a relatively flat area of bedrock,
forming an ice plain. This geometry allows seawater to infiltrate the glacier’s
bed during high tide and intermittently lift ice off the ground. When ice is
thin enough, large areas can lift and break away at once. The process, called
buoyancy-driven calving, is believed to have caused the second stage of
Hektoria’s rapid retreat, resulting in an additional loss of 8 kilometers in
length.
“New platforms, such as the NISAR and SWOT satellites developed by NASA and
partners, may aid in understanding rapid changes in glaciers.
Naomi Ochwat, a glaciologist at the University of Innsbruck and the study’s
lead author, is now looking into other glaciers that may be at risk of
destabilizing in a similar way. As the Antarctic Peninsula responds to warming,
more of its glaciers are losing their ice tongues, and their termini are now
resting on the seabed, as Hektoria's does. (Called tidewater glaciers, this type is common in Alaska and Greenland.) New technologies developed
by NASA and partners can aid in understanding rapid glacial retreat, said
Ochwat and study co-author Ted Scambos, a senior research scientist at the
University of Colorado Boulder.
The NISAR (NASA-ISRO Synthetic Aperture Radar) satellite,
for example, can detect the movement of land and ice surfaces down to the
centimeter. Its data will be “very useful for structural evaluations of
Hektoria and other glaciers in the region,” Scambos said.
“In addition to NISAR,” Ochwat
added, “I'm particularly interested in learning what SWOT can tell us about
rapid glacier changes.” The SWOT (Surface Water and Ocean Topography) satellite’s
primary mission is to observe the fine details of Earth’s surface water height.
But scientists are also exploring its applications to the cryosphere, such as
measuring surfaces of ice
shelves and sea ice.
At Hektoria Glacier, the days of
dramatic change are likely past, now to be replaced by slow retreat. Scambos
said he would not be surprised to see the ice slowing down. “The glacier has
lost so much elevation and mass that it simply can’t continue to maintain the
same output,” he said. “It’s on its way to being a fjord, not a glacier.”
NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Lindsey Doermann.
Source: Record-Setting Retreat of Hektoria Glacier - NASA Science
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