The Indecisive River
By Anne Pawsey
As the largest river in the world, the Amazon gives an impression of permanence. In actual fact nothing could be further from the truth, quite aside from changing course slightly every year the Amazon used to run completely in the other direction.
Graduate student, Russell Mapes, and his supervisor, Dr. Drew Coleman, from the University of North Carolina have just completed a mammoth field trip covering 80% of the Amazon Basin and have found conclusive proof that the Amazon used to run east to west before changing direction and running into the Atlantic.
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The evidence for this change of direction can be found in the sedimentary rocks of the river basin. The river transported minerals from its source and deposited them in the basin, studying where and when these rocks started out gives a picture of the river. It turns out that in the Cretaceous period (65-145 million years ago) the river ran east-west, over time a low central ridge formed and the river began to run from the centre out, in effect splitting in two. Towards the end of the Cretaceous the Andes started to grow and the river was forced to flow back east. Eventually the basin between the Andes and the central ridge was filled and the river broke though forming the Amazon as we see it today.
Click the image to enlarge
Graduate student, Russell Mapes, and his supervisor, Dr. Drew Coleman, from the University of North Carolina have just completed a mammoth field trip covering 80% of the Amazon Basin and have found conclusive proof that the Amazon used to run east to west before changing direction and running into the Atlantic.
The evidence for this change of direction can be found in the sedimentary rocks of the river basin. The river transported minerals from its source and deposited them in the basin, studying where and when these rocks started out gives a picture of the river. It turns out that in the Cretaceous period (65-145 million years ago) the river ran east-west, over time a low central ridge formed and the river began to run from the centre out, in effect splitting in two. Towards the end of the Cretaceous the Andes started to grow and the river was forced to flow back east. Eventually the basin between the Andes and the central ridge was filled and the river broke though forming the Amazon as we see it today.
Click the image to enlarge
Title image: Joseph Reganit/SXC
Diagram: Russell Mapes
Diagram: Russell Mapes
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