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The ability of climate to influence tectonics has been of growing interest for more than a century. Likewise, the dramatic effect of rainfall on the evolution of mountainous landscapes is a subject of debate among geologists.
In a new study, scientists at the University of Bristol calculated the impact of rain, providing detailed information on how peaks and valleys have developed over millions of years. The study, which focused on the most powerful mountain ranges, the Himalayas, could predict the possible impact of climate change on landscapes and, in turn, on human life.
Their study also shows that rain can actually move mountains.
Lead author Dr. Byron Adams, Royal Society Fellow Dorothy Hodgkin Fellow at the university’s Cabot Institute for the Environment, said: “It may seem intuitive that more rain can shape mountains by making rivers turn to rocks faster. But scientists have also believed that rain can erode a landscape fast enough to essentially ‘suck’ rocks out of the Earth, effectively lifting mountains very quickly. Both theories have been debated for decades because the steps required to test them are painstakingly complicated. That’s what makes this discovery such an exciting breakthrough, as it strongly supports the notion that reliable terrestrial and atmospheric processes are intimately connected. “
The study was based on the central and eastern Himalayas of Bhutan and Nepal. Using cosmic clocks inside grains of sand, the scientists measured the speed at which rivers erode the rocks below them.
Dr. Adams said: “When a cosmic particle from outer space hits Earth, it is likely to hit the grains of sand on the slopes as they are carried into rivers. When this happens, some atoms within each grain of sand can transform into a rare element. By counting how many atoms of this element are present in a bag of sand, we can calculate how long the sand has been there and, therefore, how quickly the landscape has eroded ”.
“Once we have the erosion rates for the entire mountain range, we can compare them to variations in the slope of the river and rainfall. However, this comparison is enormously problematic because each data point is challenging to produce and the statistical interpretation of all the data together is complicated. “
The scientists met this challenge by combining regression techniques with numerical models of how rivers erode.
They tested various numerical models to reproduce the erosion rate pattern observed in Bhutan and Nepal. Fascinatingly, one of the models accurately predicts the measured erosion rates. The model also allowed them to quantify how rainfall affects erosion rates on rugged terrain.
Research collaborator Professor Kelin Whipple, professor of geology at ASU, said: “Our findings show how critical it is to take rainfall into account when assessing patterns of tectonic activity using topography, and they also provide an essential step in addressing how much the rate of slip on tectonic faults can be controlled by weather-driven erosion in the surface. “
The study findings also have significant implications for land use management, infrastructure maintenance, and hazards in the Himalayas.
In the Himalayas, there is an ever-present risk that high rates of erosion could dramatically increase sedimentation behind dams, jeopardizing critical hydroelectric projects. The findings suggest that major rains can undermine hill slopes, increasing the risk of debris flows or landslides, some of which may be large enough to dam the river and create a new hazard: flooding. sudden from the lake.
Dr. Adams added: “Our data and analysis provide an effective tool for estimating erosion patterns in mountainous landscapes such as the Himalayas, and thus can provide invaluable information on the hazards that affect the hundreds of millions of people who live in and at the foot of these mountains. . “
The research was funded by the Royal Society, the UK Natural Environmental Research Council (NERC) and the US National Science Foundation (NSF).
Magazine reference:
- BA Adams et al. Climate Controls of Erosion in Tectonically Active Landscapes, Science Advances (2020). DOI: 10.1126 / sciadv.aaz3166
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