Geoscience in the news: Here today, gone tomorrow? A gorge in Taiwan, cut through rocks raised by a 1999 earthquake, is now disappearing at an unprecedented rate and taking geological evidence with it. In a new paper in the journal Nature Geoscience, a team from the German Research Center for Geosciences demonstrate how rivers can respond to local surface uplift or depositional blockage by incision of a narrow channel, but the resulting gorges are often temporary features. Although fluvial downcutting, channel narrowing and gorge formation have been studied over a range of conditions, the eradication of bedrock gorges and the transformation of an incised gorge into a broad floodplain are poorly understood and have not been documented in a natural river. In order to evaluate mechanisms of gorge eradication, the authors studied the Daadn River bedrock gorge, formed in response to coseismic uplift in 1999. By mapping the width of channels in the gorge using aerial photographs and Lidar data from 2004 to 2010, they identify a mechanism they call downstream sweep erosion, which is rapidly transforming the gorge into a bevelled floodplain. This is happening through the downstream propagation of a wide erosion front located where the broad upstream channel abruptly transitions into a narrow gorge. The authors estimate that gorge erosion will remove the uplifted topography in as little as 50 years. The suggestion is that downstream sweep erosion can remove bedrock gorges, impose local valley widths based on upstream conditions, remove evidence of tectonic activity or depositional river blockages and therefore complicate the interpretation of channel morphology in terms of tectonic or climatic forcing. Watch a short video report on this work via the link to YouTube... For those with online access, the original paper can be found on: nature/ngeo/journal/vaop/ncurrent/full/ngeo2224.html#affil-auth. See also: bbc.co.uk/news/science-environment-28810357
Posted on: Sun, 24 Aug 2014 07:00:02 +0000
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