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SYFY WIRE Bad Astronomy

A dust storm over… Greenland?

By Phil Plait
Winds pick up and blow glacial flour, very fine powder ground by glaciers moving over rock, creating a dust storm over Greenland.

OK, so this I was not expecting: ESA’s Earth-observing Sentinel-2 satellite took an amazing image showing a dust storm blowing over a fairly unusual location on the planet… and by unusual, I mean Greenland. Yes, Greenland.

And by “dust”, I mean flour. Glacial flour.

Yeah. This whole thing is weird. But it makes sense, and bonus: The image of the storm is gasp-worthingly lovely.

Winds pick up and blow glacial flour, very fine powder ground by glaciers moving over rock, creating a dust storm over Greenland.

This was taken on September 29, 2018 as Sentinel-2 orbited the Earth above the northeastern part of Greenland. The dust is glacial flour: Extremely fine powder formed as a glacier moves over rock. The ice generates enough pressure to grind up rock as it moves over the land, creating what’s called till: rocks in size from boulders down to sand and smaller. This stuff is generally all mixed together (what geologists call unsorted) and is left as debris when the glacier retreats.

In this case, though, it looks like the valley formed by the glacier has had multiple streams running through it, all meandering this way and that (called a braided stream). Running water can sort rocks, arranging them by size, carrying finer sediment downstream before depositing it. That means the flour, the extremely powdery stuff, is dumped right where the flowing water meets the sea.

And that’s just where we see the dust blowing. The streams have dried up, letting the winds pick up the flour and blow it to the east.

Here’s a before-and-after shot, showing the same region less than a week earlier:

An image from NASA’s Terra satellite compares an area of Greenland (top, taken on Sep. 23, 2018) to the same area taken by ESA’s Sentinel-2 satellite (bottom) during a dust storm of glacial flour blown by high winds.

I’m not 100% sure but the green stuff in the “before” image may be algae or some other wee life form. It highlights the terminuses of the streams.

This is pretty far north, at 71° north latitude (as the Earth Observatory Image of the Day site (where I found this image) notes, this is farther north than the northern coast of Alaska). If you go to Google maps and zoom out, head north along Greenland’s east coast and you can see a myriad of intertwining glacial valleys, and the glaciers themselves, too.

When I think dust storm I think… well, Mars, actually. But on Earth I tend to think of deserts like the Sahara, or haboobs in the United States southwest. Greenland doesn’t come right to mind, but in hindsight it all fits together. In late summer the glaciers retreat, the waters stop flowing, the flour dries up, and a decent wind can blow it for hundreds of kilometers.

The Earth Observatory site also notes that it’s pretty rare to get a good view of these because they aren’t very common, they don’t last long, not too many people live in this area to get ground data, and satellite views are often blocked by clouds. Winds can carry fine particles a long way, and in fact it’s becoming clear that soot from wildfires in the US can be swept up and dropped in Greenland. This is making the ice darker, which means it absorbs more sunlight, which means it melts faster than it otherwise would. Coupled with warmer and longer melt seasons care of global warming, this spells very very big trouble.

The Sentinel-2 image of the flour storm is lovely, certainly. But I can’t help being reminded that even as that flour blows over the Greenland Sea north of Iceland and on to Scandinavia, every bit of our planet is in some way connected to every other bit. And if you muck up one part, well, no other place is untouched.