On The Ice Sheet, Hairline Cracks Become Moulins Overnight, Shaking Our Understanding Of Greenland's Stability

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Alun Hubbard in The Conversation:

I’m striding along the steep bank of a raging white-water torrent, and even though the canyon is only about the width of a highway, the river’s flow is greater than that of London’s Thames. The deafening roar and rumble of the cascading water is incredible – a humbling reminder of the raw power of nature. As I round a corner, I am awestruck at a completely surreal sight: A gaping fissure has opened in the riverbed, and it is swallowing the water in a massive whirlpool, sending up huge spumes of spray. This might sound like a computer-generated scene from a blockbuster action movie – but it’s real. A moulin is forming right in front of me on the Greenland ice sheet. Only this really shouldn’t be happening here – current scientific understanding doesn’t accommodate this reality. As a glaciologist, I’ve spent 35 years investigating how meltwater affects the flow and stability of glaciers and ice sheets.

This gaping hole that’s opening up at the surface is merely the beginning of the meltwater’s journey through the guts of the ice sheet. As it funnels into moulins, it bores a complex network of tunnels through the ice sheet that extend many hundreds of meters down, all the way to the ice sheet bed. When it reaches the bed, the meltwater decants into the ice sheet’s subglacial drainage system – much like an urban stormwater network, though one that is constantly evolving and backing up. It carries the meltwater to the ice margins and ultimately ends up in the ocean, with major consequences for the thermodynamics and flow of the overlying ice sheet.



Scenes like this and new research into the ice sheet’s mechanics are challenging traditional thinking about what happens inside and under ice sheets, where observations are extremely challenging yet have stark implications. They suggest that Earth’s remaining ice sheets in Greenland and Antarctica are far more vulnerable to climate warming than models predict, and that the ice sheets may be destabilizing from inside.

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In a new paper, Dave Chandler and I demonstrate that ice sheets are littered with millions of tiny hairline cracks that are forced open by the meltwater from the rivers and streams that intercept them. Because glacier ice is so brittle at the surface, such cracks are ubiquitous across the melt zones of all glaciers, ice sheets and ice shelves. Yet because they are so tiny, they can’t be detected by satellite remote sensing. Under most conditions, we find that stream-fed hydrofracture like this allows water to penetrate hundreds of meters down before freezing closed, without the crack’s necessarily penetrating to the bed to form a full-fledged moulin. But, even these partial-depth hydrofractures have considerable impact on ice sheet stability.

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https://climatecrocks.com/2024/01/02/greenlands-hairline-fractures-magnify-melting-mystery/