Today’s Landsat post leads us to Algeria.
The yellow streaks crossing this picture show us Erg Iguidi. This erg is part of the Sahara. If you direct your view on the fascinating background, you can distinguish between black sandstone in the middle and sand plains as seen on the lower left. Take a really close look, then you might as well see some white and light blue areas. Those are mineral and chalk deposits left behind by water that evaporated here.
But seriously what is an erg?
Honestly, I have never heard about ergs before. First of all we need the right climate. If we take a look between 20? to 40? either north or south on our Earth should do. Simply put, we need the trade winds and the heat to help us stir up some sand. One main criterion for an erg are ?aeolian? sediments, those are sands that were transported by air. Additionally, we need a super-arid environment, so less than 150mm of precipitation per year is necessary. Most ergs are downwind some source of loose sediments like dry riverbeds or lakes. This sand usually builds up to huge dunes wandering downwind. These dunes will be stopped by some sort of barrier or even wind converging at a certain point. Now you just have to wait at least a million years for the erg to build up.
But this huge streak of sand isn’t all. Dunes wander the flanks of the erg, reaching tremendous heights up to 500m. The extension of Erg Iguidi itself is 300km in length. Due to their loose sediments and high mobility ergs serve as an excellent water storage. On the sides of ergs often wells can be found.
However, tours through deserts will usually avoid ergs. The loose sediments, as well as, steep dips on lee of the dunes on the erg (20? – 30?+) make it difficult to cross.
See place 4 of the big NASA & USGS vote for yourself: http://amplt.de/l8