Rivers cut notches in glacial valleys

7 Dec 2010

Again, can be found at www.physorg.com/print210777849.html ... a geological conumdrum as rivers form steep inner gorges in some broad glacial valleys in the Alps. The U shaped valleys were formed by slow moving glaciers, eroding the bedrock over hundreds and thousands of years. When the glaciers receded rivers carved V shaped notches, or inner gorges, into the flow of the glacial valleys. However, geologists disagree over whether such gorges are erased by later glaciations and reform all over again when the glaciers retreat once more - an important point as it bears on the dating of such landscap features. In the uniformitarian model rivers do not carve out gorges in a short period but it is a process that takes an enormously long period of time. New research purports to show that later glaciations fill the gorges with ice and rock debris and this protects them from being scoured away as the glacier slowly grows. Somewhat later, when it recedes once again, the river returns and washes out the debris and begins to flow through the same gorge. The paper is published in the December 5th issue of Nature Geoscience. The problem they were faced with is that if the gorges were carved out since the last glacial it would have required a faster rate of erosion than theory allows. The erosion rate would be much too fast, the author declares. We can expect such V shaped valleys in other parts of the world, such as the Himilayas, will be explored in order to find similar evidence.