Meltwater drainage, break-away icebergs linked at shrinking Helheim
Glacier

Date:
March 31, 2022
Source:
Penn State
Summary:
Dark patches of open sea that appear in the ice-choked water around
Helheim Glacier may reveal new clues about how a rapidly changing
Greenland glacier loses ice, according to scientists.



FULL STORY ==========================================================================
Dark patches of open sea that appear in the ice-choked water around
Helheim Glacier may reveal new clues about how a rapidly changing
Greenland glacier loses ice, according to a Penn State-led team of
scientists.


========================================================================== "Greenland is losing a lot of ice, and it drains from the interior of the
ice sheet to the ocean through outlet glaciers like Helheim," said Sierra Melton, a doctoral candidate in geosciences at Penn State. "Understanding what's happening at these glaciers is important." During warm periods,
enough meltwater drains from underneath Helheim that plumes of buoyant
fresh water rise to the surface of the sea in front of the glacier and
are visible as patches of open water, the scientists said.

Tracking these plumes using satellite and time-lapse images, the
scientists found when the plumes were visible on the surface that
large icebergs stopped breaking away, or calving, from the glacier near
the plumes.

"We'd see a lot of calving happening, and then it would stop when the
plume was visible and start again after the plume disappeared," Melton
said. "And when calving did occur, it happened away from the plume. They
were always separated by space and time." Calving at Helheim involves
large chunks of ice breaking off from behind the cliff at the front of
the glacier, which is up to 300-feet tall in some locations. Helheim
once ended in a floating extension called an ice shelf or ice tongue,
like larger Antarctic glaciers, but that ice has already broken off and
melted, exposing the cliff. Calving accounts for about half of the ice
loss from the Greenland Ice Sheet and is a significant contributor to
sea level rise, the scientists said.



========================================================================== "Sierra's work, including this paper, is an important contribution
to the larger effort to understand how iceberg calving really works
and what controls its speed, so we can do a better job of projecting
what will happen in Greenland, as well as Antarctica, and what that
will mean for sea-level rise and costal people," said Richard Alley,
Evan Pugh University Professor of Geosciences at Penn State, Melton's
adviser and a co-author on the paper.

While the relationship between the plumes and calving was previously
observed at Helheim, making direct observations is difficult because of impassable terrane on the glacier and ice in the sea. The scientists
conducted a more comprehensive study using high-resolution satellite
images and thousands of time-lapse photos from cameras stationed around
the glacier from 2011 to 2019.

The findings, reported in the Journal of Glaciology, suggest that changes
in hydrology and pressure beneath the glacier are responsible for the relationship between meltwater discharge and calving.

During melt season, water begins pooling in crevasses and forms lakes
on the glacier surface. Some meltwater drains to the glacier bed,
where it begins to fill up cavities and form a network between them,
the scientists said.

"The way a subglacial drainage system evolves is if there's not very
much water under the glacier, then there is low water pressure," Melton
said. "As the water increases under the glacier, the pressure starts
to increase with it." As more water flows to the bottom and the water
pressure rises, the speed of the glacier's march toward the sea increases
and cracks can form in the ice, making it more vulnerable for calving,
the scientists said.



==========================================================================
But eventually under this pressure, and if enough water is present at
the glacier bed, the water can carve channels in the bottom of the ice
that direct meltwater into the sea, acting as a kind of relief valve
that reduces the water pressure under the glacier ice, the scientists
said. These channels can release enough fresh water for plumes to be
visible at the surface of the sea.

"We think this lower pressure configuration inhibits the large calving
because the fractures in the bottom of the ice can't form," Melton
said. "So basically, the system that supports the plume existence should suppress the calving." Also contributing from Penn State were Sridhar Anandakrishnan, professor of geosciences and Melton's co-adviser, and
Byron Parizek, professor of mathematics and geosciences.

Leigh Stearns, associate professor and Michael Shahin, doctoral candidate,
at the University of Kansas, and Adam LeWinter, physical scientist,
and David Finnegan, director of remote sensing, at the Cold Regions
Research and Engineering Laboratory, also contributed.

The National Science Foundation, U.K. Natural Environment Research
Council and Heising-Simons Foundation supported this research.


========================================================================== Story Source: Materials provided by Penn_State. Original written by
Matthew Carroll. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Sierra M. Melton, Richard B. Alley, Sridhar Anandakrishnan, Byron R.

Parizek, Michael G. Shahin, Leigh A. Stearns, Adam L. LeWinter,
David C.

Finnegan. Meltwater drainage and iceberg calving observed in high-
spatiotemporal resolution at Helheim Glacier, Greenland. Journal
of Glaciology, 2022; 1 DOI: 10.1017/jog.2021.141 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220331121246.htm

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