Erosion

While looking for data comparing the amount of earth moved by human processes with that moved naturally, I came across this beautiful image and its related story. The picture shows a curl of sand and dust from the Sahara desert blowing west over Africa and across the North Atlantic before heading north at the Cape Verde islands. The Sahara contributes about half of all of the dust dumped into the atmosphere every year.

According to research reported in the New Scientist, much of this dust comes from a single valley in the Sahara and ends up fertilizing the Amazon basin.

The trees and plants in the Amazon rainforest rely on nutrient-rich dust from a single valley in the Sahara desert for sustenance, researchers have discovered.

Scientists know that millions of tonnes of mineral dust are blown from the Sahara desert to the Amazon basin each year. The dust helps keep the Brazilian rainforest soils fertile.

Now, researchers have found that 56% of this dust comes from one place: the Bodélé depression in Chad, Africa. They also showed that three times more dust than previously thought is transported each year from the Sahara to the Amazon - over 40 million tonnes.

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The Bodélé valley is 200 times smaller than the Amazon basin, and forms only 0.2% of the Sahara itself. The reason the valley supplies so much dust is its location between two mountain ridges. It forms a funnel that accelerates the flow of air, not unlike a wind tunnel, allowing more dust to be carried. In winter, the valley produces an average of 700,000 tonnes of dust per day.

For more details, see Environmental Research Letters (DOI: 10.1088/1748-9326/1/1/014005)