Time-lapse, satellite imagery shows how meltwater plumes trigger calving ice

By Kala Hunter
Medill Reports

As Greenland’s glaciers melt from an abruptly warming climate, scientists are studying how mammoth glaciers are losing their ice. The research is urgent to better predict the speed of global glacial retreat that leads directly to sea level rise across the globe.

“You study Greenland because it’s the future of Antarctica,” said glaciologist Richard Alley, Ph.D., professor of Geosciences at Penn State University and co-author of a study.

Greenland ice has been melting significantly over the past two decades. Greenland is losing an average of 279 gigatons per year, says Sierra Melton, Ph.D. candidate at Penn State University and

One gigaton is about the size of New York’s Central Park in length and width, and as high as some of the tallest skyscrapers.

Melton and Alley reported their findings of the Helheim glacier in Greenland at the annual Comer Climate Conference this fall.

“Greenland could contribute up to sea level rise if its entire ice sheet melts,” Alley said.

The accelerating melt of Greenland in the Northern Hemisphere shows triggers of ice loss that could apply to the much larger ice sheets of Antarctica in the Southern Hemisphere.

Melton and her colleagues published their latest findings in 2021 to highlight how often meltwater plumes and calving are occurring, and why and where they are happening at Helheim glacier. Calving means huge masses of ice break off the ice sheet and tumble into the sea.

According to Melton, Helheim is terminating at a rate of up to 25 meters per day.

Video courtesy of NASA

A phenomenon of meltwater plumes has been occurring over the past two decades due to warming temperatures across the globe and in Greenland. Temperatures are rising due to higher concentrations of carbon dioxide from fossil fuel emissions. As greenhouse gases that are embedded in all facets of industrialized systems rise, so do temperatures.

Fig.1

At the base of the Helheim glacier terminus, there is a mix of sea ice and floating icebergs, known as the mélange. Due to the difficulty and danger of observing these directly, Melton used time-lapse and satellite images to draw conclusions about how meltwater plumes impact calving events.

Video courtesy of Sridhar Anandakrishnan/Penn State

When water melts at the top of the glacier, it travels down to the base of the glacier. It then goes from the base of the glacier towards a mélange and pops up in front of the glacier terminus — where the glacier ends — creating a meltwater plume from the pressure of the surfacing water. (See Fig. 1.)

Time-lapse imagery and satellite imagery from 2011-19 revealed a pattern of plume location. This suggests the meltwater’s path from the top of the glacier to the bottom has created a subglacial channel.

Pressure from the base of the glacier is a key indicator of how the glacier will respond. Melton’s study found that higher pressure from the base of the glacier will cause the glacier to calve (break off) instead of forming a plume, while just low pressure from the base of the glacier creates a plume.

Fig. 2 Location and visualization of Helheim glacial retreat. Colored circles depict the locations of all 21 plumes observed in satellite imagery from 2011 to 2019, and lines represent where the glacier ended.

Plumes and calving are, as Melton puts it, “separated in time and space.”

Calving stopped when a plume appeared and started again when the plume disappeared. Yet the plumes can weaken the ice they are holding back.

“Time-lapse revealed that when the plume disappeared after many months that the calving occurred within a few hoursMelton said.

The calving events contribute to enormous ice mass loss. As plumes and calving appear around Helheim, geoscientists and glaciologists will be able to look at this work to better understand how they may react and predict the future of Greenland and unlock predictions about the ice on Earth’s largest ice mass, Antarctica.

As for the future of Greenland’s ice, Melton isn’t sure of studies that point to when Greenland’s ice will fully melt. Scientists can only speculate on the future of Greenland based on past and current studies.

“It is unlikely that Helheim will be gone anytime soon. Helheim is one of the major outlets from the Greenland Ice Sheet to the ocean, so as the Greenland Ice Sheet loses mass, a lot of the ice is draining through Helheim,” Melton said.

Sources:
Melton, S., Alley, R., Anandakrishnan, S., Parizek, B., Shahin, M., Stearns, L., . . . Finnegan, D. (2022). Meltwater drainage and iceberg calving observed in high-spatiotemporal resolution at Helheim Glacier, Greenland. Journal of Glaciology, 68(270), 812-828. doi:10.1017/jog.2021.141

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