The work, presented online May 27 in Nature Geoscience, shows that once the angle of a slope exceeds 30 degrees – whether from uplift, a rushing stream carving away the bottom of the slope or a combination of the two – landslide erosion increases significantly until the hillside stabilizes.
The Landsat satellite image at left shows a huge lake on the Tsangpo River behind a dam created by a landslide (in red, lower right of the lake) in early 2000. The image at right shows the river following a catastrophic breach of the dam in June 2000. Credit: U.S. Geological Survey/NASA
"I think the formation of these landscapes could apply to any steep mountain terrain in the world," said lead author Isaac Larsen, a University of Washington doctoral student in Earth and space sciences.
The study, co-authored by David Montgomery, a UW professor of Earth and space sciences and Larsen's doctoral adviser, focuses on landslide erosion along rivers in the eastern Himalaya region of southern Asia.
The scientists studied images of more than 15,000 landslides before 1974 and more than 550 more between 1974 and 2007. The data came from satellite imagery, including high-resolution spy satellite photography that was declassified in the 1990s.
They found that small increases in slope angle above about 30 degrees translated into large increases in landslide erosion as the stress of gravity exceeded the strength of the bedrock.
"Interestingly, 35 degrees is about the same angle that will form if sand or other coarse granular material is poured into a pile," Larsen said. "Sand is non-cohesive, whereas intact bedrock can have high cohesion and should support steeper slopes.
"The implication is that bedrock in tectonically active mountains is so extensively fractured that in some ways it behaves like a sand pile. Removal of sand at the base of the pile will cause miniature landslides, just as erosion of material at the base of hill slopes in real mountain ranges will lead to landslides."
The researchers looked closely at an area of the 150-mile Tsangpo Gorge in southeast Tibet, possibly the deepest gorge in the world, downstream from the Yarlung Tsangpo River where the Po Tsangpo River plunges more than 6,500 feet, about 1.25 miles. It then becomes the Brahmaputra River before flowing through the Ganges River delta and into the Bay of Bengal.
The scientists found that within the steep gorge, the rapidly flowing water can scour soil from the bases, or toes, of slopes, leaving exposed bedrock and an increased slope angle that triggers landslides to stabilize the slopes.
From 1974 through 2007, erosion rates reached more than a half-inch per year along some 6-mile stretches of the river within the gorge, and throughout that active landslide region erosion ranged from 0.15 to 0.8 inch per year. Areas with less tectonic and landslide activity experienced erosion rates of less than 0.15 inch a year.
Images showed that a huge landslide in early 2000 created a gigantic dam on a stretch of the Po Tsangpo. The dam failed catastrophically in June of that year, and the ensuing flood caused a number of fatalities and much property damage downstream.
That event illustrates the processes at work in steep mountain terrain, but the processes happen on a faster timescale in the Tsangpo Gorge than in other steep mountain regions of the world and so are more easily verified.
"We've been able to document the role that landslides play in the Tsangpo Gorge," Larsen said. "It explains how steep mountain topography evolves over time."
The work was financed by NASA, the Geological Society of America, Sigma Xi (the Scientific Research Society) and the UW Quaternary Research Center and Department of Earth and Space Sciences.
For more information, contact Larsen at 206-265-0473 or firstname.lastname@example.org, or Montgomery at 206-685-2560 or email@example.com
Vince Stricherz | EurekAlert!
A promising target in the quest for a 1-million-year-old Antarctic ice core
24.05.2018 | University of Washington
Tropical Peat Swamps: Restoration of Endangered Carbon Reservoirs
24.05.2018 | Leibniz-Zentrum für Marine Tropenforschung (ZMT)
The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.
Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
25.05.2018 | Event News
02.05.2018 | Event News
13.04.2018 | Event News
25.05.2018 | Event News
25.05.2018 | Machine Engineering
25.05.2018 | Life Sciences