New mechanism of erosion revealed
Local surface uplift can block rivers, particularly in mountainous regions. The impounded water, however, always finds its way downstream, often cutting a narrow gorge into the rocks.
Geländearbeit in der Schlucht des Da’an Chi in Taiwan. Die ein Kilometer lange und bis zu 20 Meter tiefe Schlucht hat sich in weniger als 10 Jahren nach dem Jiji-Erdbeben im Jahr 1999 gebildet. Der Felssporn in der Bildmitte wurde während eines Hochwassers 2012 im Zeitraum von einer Stunde weggespült. (Foto: Kristen Cook, GFZ)
Subsequent erosion of the rocks can lead to a complete eradication of this initial incision, until not a trace is left of the original breakthrough.
In extreme cases the whole gorge disappears, leaving behind a broad valley with a flat floodplain. Previously, the assumption was that this transition from a narrow gorge to a wide valley was driven by gorge widening and the erosion of the walls of the gorges.
A team of scientists from the GFZ German Research Centre for Geosciences in Potsdam has now revealed a new mechanism that drives this process of fluvial erosion (Nature Geoscience, 17.08.2014). The geoscientists analyzed the development of a gorge on the Da'an Chi river in Taiwan over a period of almost ten years.
There, uplift that was caused by the Jiji earthquake of 1999 (magnitude 7.6), and that runs transverse to the river, had formed a blockage. Earthquakes of that size occur there every 300 to 500 years. "Before the quake there was no sign of a gorge at all in this riverbed, which is one and a half kilometers wide", explains Kristen Cook of the GFZ.
"We have here the world's first real-time observation of the evolution of gorge width by fluvial erosion over the course of several years." Currently the gorge is roughly a kilometer long, 25 meters wide and up to 17 meters deep. Initially, the gorge walls were eroded at a rate of five meters per year, and today are still retreating one and a half meters per year.
The scientists identified a hitherto unknown mechanism by which the gorge is destroyed. "Downstream sweep erosion" they termed this process. "A wide braided channel upstream of the gorge is necessary," explains co-author Jens Turowski (GFZ).
"The course of this channel changes regularly and it has to flow in sharp bends to run into the gorge. In these bends, the bed-load material that is transported by the river hits the upper edge of the gorge causing rapid erosion."
This mechanism gradually washes away all of the bedrock surrounding the gorge and, therefore, is the cause for the planation of the riverbed over the complete width of the valley. Assuming the current erosion rate of 17 meters per year, it will take here at the Da'an Chi River only 50 to 100 years until again a flat beveled channel again fills the valley.
In contrast, lateral erosion in the gorge would be too slow to eradicate the gorge in the time of one earthquake cycle. The newly discovered downstream sweep erosion is far more effective.
Kristen L. Cook, Jens M. Turowski and Niels Hovius: "River gorge eradication by downstream sweep erosion", Nature Geoscience, Advance Online Publication, 17.08.2014, DOI: 10.1038/ngeo2224
F. Ossing | Eurek Alert!
Clouds and climate in the pre-industrial age
30.05.2016 | Goethe-Universität Frankfurt am Main
Researchers find higher than expected carbon emissions from inland waterways
25.05.2016 | Washington State University
Physicists of the Laboratory for Attosecond Physics at the Max Planck Institute of Quantum Optics and the Ludwig-Maximilians-Universität Munich in collaboration with scientists from the Friedrich-Alexander-Universität Erlangen-Nürnberg have observed a light-matter phenomenon in nano-optics, which lasts only attoseconds.
The interaction between light and matter is of key importance in nature, the most prominent example being photosynthesis. Light-matter interactions have also...
A biological and energy-efficient process, developed and patented by the University of Innsbruck, converts nitrogen compounds in wastewater treatment facilities into harmless atmospheric nitrogen gas. This innovative technology is now being refined and marketed jointly with the United States’ DC Water and Sewer Authority (DC Water). The largest DEMON®-system in a wastewater treatment plant is currently being built in Washington, DC.
The DEMON®-system was developed and patented by the University of Innsbruck 11 years ago. Today this successful technology has been implemented in about 70...
Permanent magnets are very important for technologies of the future like electromobility and renewable energy, and rare earth elements (REE) are necessary for their manufacture. The Fraunhofer Institute for Mechanics of Materials IWM in Freiburg, Germany, has now succeeded in identifying promising approaches and materials for new permanent magnets through use of an in-house simulation process based on high-throughput screening (HTS). The team was able to improve magnetic properties this way and at the same time replaced REE with elements that are less expensive and readily available. The results were published in the online technical journal “Scientific Reports”.
The starting point for IWM researchers Wolfgang Körner, Georg Krugel, and Christian Elsässer was a neodymium-iron-nitrogen compound based on a type of...
In the Beyond EUV project, the Fraunhofer Institutes for Laser Technology ILT in Aachen and for Applied Optics and Precision Engineering IOF in Jena are developing key technologies for the manufacture of a new generation of microchips using EUV radiation at a wavelength of 6.7 nm. The resulting structures are barely thicker than single atoms, and they make it possible to produce extremely integrated circuits for such items as wearables or mind-controlled prosthetic limbs.
In 1965 Gordon Moore formulated the law that came to be named after him, which states that the complexity of integrated circuits doubles every one to two...
Characterization of high-quality material reveals important details relevant to next generation nanoelectronic devices
Quantum mechanics is the field of physics governing the behavior of things on atomic scales, where things work very differently from our everyday world.
24.05.2016 | Event News
20.05.2016 | Event News
19.05.2016 | Event News
31.05.2016 | Power and Electrical Engineering
31.05.2016 | Life Sciences
31.05.2016 | Information Technology