Fossil Fjords in Namibia

#Sneeuw & IJs, #Droogte, #Image in the news, #Afrika

Gepubliceerd op 15 september 2021

Ice that carved a network of valleys 300 million years ago has long since disappeared, but the original shapes of the valleys remain.

Northwestern Namibia is not your typical desert landscape. Valleys dissect plateaus, creating striking vistas across the hot, dry region in southwest Africa. While these valleys are extremely old—with origins dating back hundreds of millions of years—they are remarkably well preserved.

New research indicates that the valleys are ancient relics of a time long before dinosaurs walked the Earth—when Africa was close to the South Pole, still part of the supercontinent Gondwana, and covered with ice. The flow of the ice cut into the land and eventually carved out long, narrow valleys that filled with seawater and formed fjords. Somehow, these ancient fjords have avoided being erased by erosion, uplift, and other geological processes that usually level off this kind of terrain. In fact, the area is so well preserved that scientists call it a “fossil glacial landscape.”

“One who looks at these valleys has a snapshot of what the fjords looked like 300 million years ago, except that the ice here has long disappeared,” said Pierre Dietrich, a scientist at University of Rennes and lead author of the study published in Geology.

Some of the region’s U-shaped “fossil fjords” (called paleofjords by geologists) are visible in this map, composed from elevation data from the Shuttle Radar Topography Mission (SRTM). The map is false-color to emphasize the topography; red areas are the highest elevations, and blue areas are closer to sea level.

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