Strange blue desert markings in Africa

[neilcreek]

This blue area in Chad, Africa sticks out like a sore thumb in the middle of the rest of the desert. Can anyone guess what it might be? It's not water, and it seems obviously windswept from the northeast. In fact, zooming in, there are some places where obvious sand dunes seem to shield the ground from the blue, with brown sand appearing behind the trailing edge, suggesting whatever the blue is, that it's carried on the wind. The scale of this feature is huge! Zoom out and you can clearly see it, even when viewing the entire African continent.

I'd love to know what this is!

[fishbne2]

That's a good one. After extensive searching, I came up EMPTY! According to everything I read there's nothing there but desert.

[grav8e]

I know that Lake Chad used to extend up into that area but has been "disappearing" over the past few decades. So I don't know if we are seeing remnants or if it is unrelated.

[fishbne2]

that's what I thought too, however the spot is way to high to be recents remnants of Lake Chad (IMHO)

[jamocorke]

Could this be a dried up lake leaving salt deposits.

[hypeserver]

Originally Posted by neilcreek

This blue area in Chad, Africa sticks out like a sore thumb in the middle of the rest of the desert. Can anyone guess what it might be? It's not water, and it seems obviously windswept from the northeast. In fact, zooming in, there are some places where obvious sand dunes seem to shield the ground from the blue, with brown sand appearing behind the trailing edge, suggesting whatever the blue is, that it's carried on the wind. The scale of this feature is huge! Zoom out and you can clearly see it, even when viewing the entire African continent.

I'd love to know what this is!

I learned about this in Science class. It's permafrost the driest of deserts can get it. It's the constant freezing of top soil. You have to remember that deserts may be hot by day but get to freezing by night. My best guess is its permafrost that may have drifted in the wind.

[Alex_UY]

it appears that the blue color is the result of a band combination in the base images. Look at 29º 13' 42.4"N - 19º 24º 23.8"E... in this area the low-res image has blue color but high res image not. Maybe salts accumulation?

Hope helps,

Alex

[hypeserver]

For some reason I still think it's drifted permafrost.

[punk_sandwich]

Don't think it is permafrost. Have a look at the definition of permafrost in wikipedia (http://en.wikipedia.org/wiki/Permafrost): continuously frozen ground for more than two years. Rather unlikely in a desert.
There might be frost in the desert overnight but we wouldn't see it in the satellite pictures as they are taken during daylight (and probably around noon to avoid long shadows). Given the daylight temperature in the desert any frost would have melted by that time.
Turning on the water layer in GE makes me think this was indeed water and are now minerals left behind (IMHO). A map of watersheds in Africa (http://earthtrends.wri.org/maps_spat...ct=294&theme=2)
shows a lake at the position of the blue structure.

Cheers, Mic

[Rwootton]

these appear to be salt flats or pans (like Lake Bonneville around Great Salt lake in Utah) formed by periodic heavy rainfall filling the basin followed by evaporation, leaving the mineral residue.

[grav8e]

Originally Posted by Rwootton

these appear to be salt flats or pans (like Lake Bonneville around Great Salt lake in Utah) formed by periodic heavy rainfall filling the basin followed by evaporation, leaving the mineral residue.

Which leads me back to my guess about Lake Chad. I'm still standing by that one... ;-)

[Rwootton]

Actually Lake Chad is 350 miles to the southwest at the border with Niger and Nigeria, You are correct though that Lake Chad is shrinking. But the salt flats are called Erg du Djourab

http://www.un.org/Depts/Cartographic...ofile/chad.pdf) :neutral:

[Arashi]

As Rwottoon said, Lake Chad is far to the southwest.

My Worldatlas sais this region is named Bod elé Djourab, that would indicate a saltflat.
The Atlas also shows that this region is a very low bassin and periodic rivers flow in there from the mountains in the north and east.
And thats the blue stuff is drifting with the wind indicates that its a rather light sediment, not water or stone.
And Salt was the Chads most important export product for long time.....

So I would say the blue colour truly results from salt and other sedimented minerals like cobalt or such stuff, brought by the rivers that dry out in summer.

[Genosse Pumuckl]

I had this strange idea, that we're seeing the sky being reflected in the sand, or in the lower hotter air

[Alf]

Enable Google Earth's "water-overlay-option".