LARHYSS Journal
Volume 19, Numéro 3, Pages 7-41
2022-09-28
The Bodélé Depression (chad): When The Venturi Effect Propelles Dust From The Sahara Towards The Amazon Basin
Authors : Remini Boualem .
Abstract
This paper answers the question: How can a region as small as the Bodélé Depression continuously supply large amounts of dust to the Amazon Basin? To answer this question, you must know that millions of tons of dust to fly over more than 4000 km must first be lifted into the upper atmosphere. Such a criterion can only be satisfied by the existence of very violent winds that last several days. This condition was dictated by the geography and geomorphology of the Bodélé region. The adequate layout of the Tibesti and Ennedi mega-obstacles upstream of the Bodélé offers the most beautiful Venturi on the planet. In a very rare case, 3 pass areas participate at the same time to increase the wind speed. These are the passes of Tibesti (south-east), Ennedi (north-west) and Bembéché (under the Venturi effect). The harmattan wind from Libya and Egypt rushes into the Borkou tunnel and escapes from Bembéché (the pass) with much greater speed. The detachment of the air streams from the obstacles takes place in the detachment area (Largeau), which is accompanied by gigantic vortices, thus lifting the dust into the atmosphere. Thus, during the last 20 years, approximately 503 dust uplifts have been recorded at the level of the Bodélé depression, i.e., 58% of the total number of uplifts recorded in the Sahara. The great storms we have called effective upheavals. These are long-lasting dust lifts that exceed 7 days. These storms can send fine particles toward the Amazon. Each year, 2 to 3 effective uprisings per year are recorded in the Bodélé depression.
Keywords
Amazonia ; Sahara ; Dust rising ; Dust plume ; Bodélé ; Tibesti ; Ennedi
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