Secret to Greenland’s ‘Vanishing’ Lakes

ENVIRONMENT

Huge lakes atop Greenlandic glaciers are vanishing. Now, scientists know why. (Washington Post)

Look below Greenland’s “vanishing ice” with our terrific map.

Teachers, scroll down for a quick list of key resources in our Teachers’ Toolkit, and don’t forget to take this week’s current events quiz!

Click to enlarge this lovely illustration of a worrying phenomenon. The mysterious draining of Greenland’s supraglacial lakes—illustrated on the left—has only recently been throughly explained. Illustration by Alejandro Tumas, National Geographic

Click to enlarge this lovely illustration of a worrying phenomenon. The mysterious draining of Greenland’s supraglacial lakes—illustrated on the left—has only recently been throughly explained.
Illustration by Alejandro Tumas, National Geographic

 

Here’s another look at Greenland’s fast-moving ice sheet. Illustration by National Geographic

Here’s another look at Greenland’s fast-moving ice sheet.
Illustration by National Geographic

Discussion Ideas

  • According to the Washington Post, Greenland’s ice sheet and supraglacial lakes melt unevenly. Where is the ice sheet more likely to decay? Take a look at the illustrations above for some older evidence, and the Washington Post article for some newer research.
    • Old and new evidence both point to fast-moving coastal regions as more likely to decay than the thicker inland portion of the Greenland ice sheet. Here’s why:
      • Old evidence: The third item in the second illustration above says “thinner ice has a weaker grip on the land and can’t hold the accelerating glacier.”
      • New evidence: Meltwater from inland lakes runs along the surface of the ice sheet before pooling in coastal lakes and draining through moulins to the base of the ice sheet and out to sea.

 

 

  • Greenland’s “vanishing” lakes are largely a negative reflection of climate change, but the new research includes some good news as well. What is it?
    • Geography to the rescue! According to the Washington Post, the research “suggests that meltwater lakes do not simply vanish of their own accord or under their own weight. Rather, they probably have to lie in a region where there’s another preexisting pathway for water to get under the ice in large amounts.”
      • MIT News puts it another way: “[I]t’s unlikely that inland lakes would drain, as there are fewer moulins near inland lakes, which prevents water from getting to the ground locally. Without these trigger channels, larger fractures would not form in the lake basin, and lakes would stay intact, simply refreezing in the winter or overflowing into a surface stream.”

 

A National Geographic writer crosses a supraglacial lake above a moulin 96 feet deep. Meltwater lakes like this one may become more familiar parts of the Greenlandic landscape. Photograph by James Balog, National Geographic

A National Geographic writer crosses a supraglacial Greenlandic lake. The deep, dark region of the lake is a moulin (crack in the ice) 29 meters (96 feet) deep. The Greenland ice sheet is up to 3 kilometers (1.9 miles) thick, and is the second-largest body of ice in the world. (The Antarctic ice sheet is the largest.)
Photograph by James Balog, National Geographic

 

TEACHERS’ TOOLKIT

Washington Post: Scientists finally have an explanation for why huge lakes atop Greenland are vanishing

Nat Geo: Vanishing Ice

Nat Geo: What is an ice sheet?

Nat Geo: What is a glacier?

(extra credit!) Nature: Greenland supraglacial lake drainages triggered by hydrologically induced basal slip

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