The Waterfalls of Greenland

December 2, 2019

Above, a moulin recorded in Southwest Greenland, summer 2014.

Washington Post:

A cerulean lake consisting of glacial meltwater on the surface of the Greenland ice sheet, located about 18 miles from where the Store Glacier meets the sea in west Greenland, briefly became one of the world’s tallest waterfalls during the course of five hours in July 2018.

The waterfall, like many others on the ice sheet’s surface, was triggered by cracks in the ice sheet. In the case of this one meltwater lake that scientists closely observed in July 2018, the water cascaded more than 3,200 feet to the underbelly of the glacier, where the ice meets bedrock. There, the water can help lubricate the base of the ice sheet, helping the ice move faster toward the sea.

The observations of scientists, armed with aerial drones and other high-tech equipment, of the partial lake drainage that resulted could help researchers better understand how surface melting of the ice sheet could affect its melt rate, and improve global sea level rise projections.

Scientists are keenly interested in how meltwater on the surface of the Greenland ice sheet — the largest contributor to global sea level rise — acts to speed up the movement of ice toward the sea by lubricating the underside of the ice surface. The new study, published Monday in Proceedings of the National Academy of Sciences, suggests that scientists are underestimating the number of melt ponds that partially, and rapidly, drain into the ice sheet each year. This means tweaks may be needed to the computer models used to predict sea level rise from Greenland.

This is the first study to show that partial lake drainage can occur through cracks in the ice, rather than overtopping or other mechanisms, which was previously the assumption. This means even more water is reaching the base of the ice sheet than previously thought.

For example, rapidly draining lakes in fast-moving areas of the ice sheet could provide a time-limited burst of speed for glaciers to dump more ice into the sea. The new study showed a sudden but brief increase in ice flow as the lake drained, from seven feet per day to 16 feet per day, though it slowed down again thereafter.

Using computer models, the study found that the lake in question is what the researchers term a “trigger lake,” which can result in a chain reaction of sorts, causing more lakes as far away as 62 miles to subsequently drain.

The researchers observed a sudden, partial draining of the lake they termed “Lake 028” during a span of five hours on July 7, 2018. At its peak, the lake was draining the equivalent of one Olympic-size swimming pool every three seconds, according to the study’s lead author, Thomas Chudley of the University of Cambridge.

To put it differently, the meltwater was enough to fill one U.S. Capitol rotunda every two minutes and 19 seconds.

The researchers measured the lake’s changes using about 900 photos collected by autonomously flying drones outfitted with GPS equipment. The images were stitched together to form 3-D surface elevation models.

The sudden injection of water from the lake also helped raise the surface of the ice by about 1.8 feet, which suggests the water got between the ice and the base of the ice sheet via cracks in the ice known as hydrofractures. When water pours into these fractures, which originally form under stress, it can create moulins, which are vertical channels or caverns in the ice formed by flowing water. The presence of moulins sets up glaciers for further ice melt from surface lakes in the future, the study finds.

“It’s like a highway to the bottom of the bed,” Chudley said in an interview.

In the case of Lake 028, the 2018 partial drainage occurred along a fracture in the ice that originally formed in 2017 and then moved along with the ice flow.

Study co-author Poul Christoffersen, a glaciologist at the University of Cambridge, said the passage of water to the ice bed is key, because more surface melt ponds are forming as temperatures increase in response to climate change, and the water adds heat to the ice sheet’s base, causing melting there.

For example, a spike in Greenland temperatures during the summer led to hundreds of melt ponds forming even at higher elevations on the ice sheet.

Christoffersen said the study breaks new ground by detailing the mechanisms by which surface water is transported to the bed of the ice sheet in a rapidly flowing part of a glacier.

UPDATE:

4 Responses to “The Waterfalls of Greenland”

  1. Keith McClary Says:

    Time lapse video of lake draining:
    https://phys.org/news/2019-12-drone-images-greenland-ice-sheet.html

    From a distance, so not spectacular, you can see a bit of spray blowing up from the fracture.

  2. redskylite Says:

    Interesting study as the Arctic continues it’s journey to a new equilibrium. More and more changes being reported at the other end of our planet too.

    This from National Geographic today: –

    Why is an ocean current critical to world weather losing steam? Scientists search the Arctic for answers.

    Meanwhile, the warming and ice loss spiral continues. De Steur’s moorings find temperatures in the polar water flowing into the Fram Strait have climbed nearly 1 degree F over the past 17 years, while the Atlantic water has warmed nearly half a degree. If the trend continues, it could dampen deepwater formation and throttle the conveyor belt’s engine just like freshening will, she says.

    If our planet-warming emissions aren’t seriously cut, and soon, she says, “I am worried that these changes are unstoppable and cannot be reversed.”

    https://www.nationalgeographic.com/science/2019/12/why-ocean-current-critical-to-world-weather-losing-steam-arctic/

    • redskylite Says:

      and a further, somewhat disquieting, study from deep down south:

      Antarctica’s thinning ice shelves causing more ice to move from land into sea.

      “There are other processes in play as well, but we can now state firmly that the observed changes in ice-shelves do cause significant changes over the grounded ice, speeding up its flow into the ocean.”

      A critical element of the findings was the speed at which the ice flowed from the sheet into the ocean as a result of the thinning ice shelves.

      https://www.sciencedaily.com/releases/2019/12/191202124622.htm


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