Supraglacial Lakes Are Not Destabilizing Greenland’s Ice Sheet, Yet

A recent study published in the Annals of Glaciology provides the first account of supraglacial lakes, which form on surfaces of glaciers in Greenland. The paper was a collaboration between University of Cambridge’s Alison Banwell and the University of Chicago’s Douglas MacAyeal and Grant Macdonald. Supraglacial lakes have been studied in detail in Antarctica, where they were found to accelerate glacier melting and thinning while triggering ice shelf instability and break-up upon formation. However, this recent study documents a different pattern in Greenland.

Location of the Petermann Tongue and the study sites
Location of the Petermann Tongue and the study sites (Source: MacAyeal et al, 2018).

The research was conducted at Petermann Glacier’s floating tongue, a long and narrow sheet of ice protruding off the coastline. An ice tongue forms when a valley glacier advances rapidly out into the ocean. It has similar characteristics to an ice shelf, a feature more commonly found in Antarctica. Based on Landsat 8 satellite images from 2014 to 2016, the team was able to view the lakes over the area and discern when the lakes formed, their movement, and changes in surface extent across time.

In an interview with GlacierHub, MacAyeal explained, “Petermann Glacier has one of the few remaining ice tongues in Greenland and has lakes forming on it in each year. The glacier is of particular interest to the community due to its size and catchment, and the notable recent large calving events.”

The Petermann tongue underwent severe volume losses of up to 40 percent during two calving events in 2010 and 2012, for example. Fortunately, the grounded upper portion of the Petermann Glacier remains dynamically stable and showed little change in velocity or thickness.

“Glaciologists believe that supraglacial lakes store water and can become ‘dangerous’ to the continued existence of floating ice, such as the Petermann ice tongue, but more importantly to the ice shelves of Antarctica,” MacAyeal told GlacierHub. These supraglacial lakes usually form in the summer as melting is induced by an increase in air temperatures and solar radiation receipt. In the case of Greenland, the lakes at the Petermann Glacier typically fill in June, reaching their peak in July. At this time, the lakes are largest in area and volume, with their numbers at the maximum as well.

Schematic diagram illustrating the side profile of ice shelves/tongues and their underlying geology
Schematic diagram illustrating the side profile of ice shelves/tongues and their underlying geology (Source: Julian Thompson/Andrill).

“The meltwater can fill cracks and cause them to extend through the ice. Also, when water flows into a depression and forms a lake, the lake is heavy and can cause the ice shelf to flex. Ice-shelf flexure can promote fracturing,” Macdonald further explained to GlacierHub. Fittingly, MacAyeal compares this to hydrofracking in the oil industry, except that this is a natural process when ice disintegrates as “heavy dense water fills crevasses and makes them crack farther open.”

Blue River, Greenland
Blue River flowing through the Petermann Glacier (Source: Pixohub/Pinterest)

As for the Petermann tongue, supraglacial lakes are less potent at inducing glacier thinning since lake drainage occurs relatively quickly. By July and August, even with the sustained high temperatures during the summer, total number, volume, and surface area of lakes were observed to have decreased. Drainage occurs in two ways: across the tongue surface and through the tongue. The former is enabled by the surface river system known as the Blue River which transports meltwater into the ocean across the tongue. The latter requires the process of rapid hydrofracking to occur, causing local lake drainage on the tongue. Overall, limited volume of meltwater storages on the tongue was noted, causing the research to lean toward the former mechanism.

Supraglacial lakes were under the spotlight when the formation of over 3,000 lakes caused the catastrophic disintegration of the Larsen B Ice Shelf in Antarctica in 2002. According to Grant, ice shelves are important as they shore up more than half of the Antarctic coast and several glaciers in Greenland. When this buttressing effect is removed the glaciers feeding the ice shelf accelerate. Without the ice shelves, more ice will enter the ocean at a faster rate, contributing to sea level rise.

Currently, the study indicates that supraglacial lakes cover less than 2.8 percent of the Petermann tongue, as compared to the 5.3 percent surface area prior to Larsen B’s collapse. However, there are warnings of higher density lakes with larger volumes that start developing earlier in the summer season due to higher air temperatures that could potentially destabilize ice shelves and tongues worldwide. “If we are to understand the future of ice shelves in a warming climate, we must understand supraglacial lakes,” Macdonald advised.

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Photo Friday: NASA’s Renewed Operation IceBridge

Since 2009, NASA’s Operation IceBridge embarks on an annual polar journey to document the Earth’s most remote and rapidly changing landscapes to better understand connections between polar regions and the global climate system. Using a fleet of research aircrafts to collect multi-dimensional images, IceBridge is dedicated to studying the annual changes in the thickness and position of sea ice, glaciers and ice sheets in Greenland and Antarctica.

This campaign, alongside the Oceans Melting Greenland, began ongoing deployments to Greenland in March. This Photo Friday, explore images from the IceBridge flights from last week’s deployments, and keep up with the latest photos and news from IceBridge through the NASA ICE twitter page.

The calving front of Northwest Greenland’s Petermann Glacier from last Thursday’s flight (Source: NASA ICE/Twitter).

 

A winding river through Alaska seen on Saturday’s flight (Source: NASA ICE/Twitter).

 

Sunlight breaking through the cloud cover over the Brooks Range in Alaska from Saturday’s flight (Source: NASA ICE/Twitter).

 

While flying back to the Thule Air Base last Tuesday, the team captured this winding route of a glacier (Source: NASA ICE/Twitter).

 

An isolated mountain in the Brooks Range of Alaska captured last Friday (Source: NASA ICE/Twitter).
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Roundup: Crack, Flood, Fight

Petermann Crack Develops

From Grist: “Petermann is one of the largest and most important glaciers in the world, with a direct connection to the core of the Greenland ice sheet. That means that even though this week’s new iceberg at Petermann is just 1/500th the size of the massive one that broke off the Larsen C ice shelf in Antarctica earlier this month, it could eventually have a much bigger effect on global sea levels. Scientists believe that if Petermann collapses completely, it could raise the seas by about a foot.”

Read more about the potential collapse of the Petermann here.

A satellite image from April 2017 shows existing and new cracks in the Petermann Glacier (Source: NASA).

 

Glacial Outburst Flood Rages in Iceland

From The Watchers: “A glacial outburst flood started in Iceland’s Múlakvísl river around midnight UTC on July 29, 2017. Electrical conductivity is now measured around 580µS/cm and has increased rapidly the last hour, Icelandic Met Office (IMO) reported 10:14 UTC on July 29. Increasing water levels of this river are an important indicator of Katla’s upcoming volcanic eruptions.”

Read about safety concerns associated with the flood here.

The Múlakvísl River appeared serene the day before the July 29 outburst flood (Source: Icelandic Met Office).

 

Conflict in the Himalayas

From The New York Times: “The road stands on territory at the point where China, India and Bhutan meet…The standoff began last month when Bhutan, a close ally of India, discovered Chinese workers trying to extend the road. Now soldiers from the two powers are squaring off, separated by only a few hundred feet. The conflict shows no sign of abating, and it reflects the swelling ambition— and nationalism— of both countries. Each is governed by a muscular leader eager to bolster his domestic standing while asserting his country’s place on the world stage as the United States recedes from a leading role.”

Learn more about the geopolitics of this standoff here.

A border post in Nathula, a mountain pass in the Himalayas that connects Sikkim and Tibet (Source: Indrajit Das/Wikimedia Commons).

 

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Don’t Step on the Crack at Petermann Glacier

A satellite image of the crack in Petermann Glacier (Source: Stef Lhermitte/Twitter).

Cracks in ice shelves have appeared in disaster movies as ominous signs of global warming. One memorable instance occurs in The Day After Tomorrow when a paleoclimatologist is drilling ice cores at the Larsen Ice Shelf. The shelf breaks apart, leading to a series of cataclysmic climate events that disrupt the North Atlantic Ocean circulation. In July, a real- life crack appeared at Petermann Glacier in Greenland and has been growing steadily ever since. Two scientists, Andreas Muenchow and Keith Nicholls, are investigating the crack and hypothesize that it is caused by an increase in air and ocean temperatures.

An image of ice breaking off the Petermann Glacier in 2012 (Source: NASA Goddard Space Flight Center/Flickr).

Petermann Glacier connects the Greenland ice sheet to the Arctic Ocean at 81°N. It is approximately 43 miles long and nearly 10 miles wide. This is not the first crack or full break of ice at Petermann Glacier, according to a Washington Post article by Chris Mooney. Since 2010, entire slabs of the Petermann glacier have broken off.

In fact, during two occasions, the glacier lost an area of ice six times the size of Manhattan, according to Mooney. This loss raises enormous concern because the glacier serves to slow down the flow of ice downhill from the Greenland ice sheet into the ocean. For this reason, experts call Petermann a “floodgate.” If the glacier that sits behind Petermann melts, it could raise sea levels by about a foot.

A close-up view of the new crack in the Petermann Glacier (Source: NASA Operation IceBridge/Facebook).

A recent paper published in the Geophysical Research Letters describes this type of calving at Petermann as common. The authors explain that it is usually assumed that ocean-ice dynamics are not involved. However, evidence from the Pine Island Glacier in West Antarctica found that ocean forcing can play a role in the melting.

Muenchow and Nicholls expect similar dynamics are occurring with Petermann Glacier. They have been on several expeditions to the glacier in order to measure ocean temperatures underneath the shelf itself. They want to see if rising ocean temperatures are also detrimental to the glacier and causing the melting from below.

If warm ocean water were melting the base of the glacier, it would only accelerate the destruction of Petermann. While it is extremely difficult to know definitively, they hypothesize Petermann’s river and the channel beneath it are playing a role in the melting.

Data from 2015 and 2016 demonstrates that the temperatures of the warm Atlantic layer in the ocean have increased. With both air and ocean temperatures getting warmer, it is unclear how much longer Petermann Glacier will be intact, leaving frightening implications for the melting of the enormous glacier behind it. The crack in the Petermann Glacier and the possible ensuing events show that news from the ice can sometimes be just as scary as the scenes in disaster movies.

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