The drastic effect that rain has on the evolution of mountainous landscapes is widely debated among geologists, but new research led by the University of Bristol, in the United Kingdom, and published this Friday in Science Advances, clearly calculates its impact, which broadens the understanding of how peaks and valleys have developed over millions of years.

Their findings, which focused on the most powerful of the mountain ranges, the Himalayas, also pave the way for forecasting. the possible impact of climate change on landscapes and, in turn, in human life.

Lead author Dr Byron Adams, Royal Society Fellow Dorothy Hodgkin, Cabot University Institute of the Environment, admits that “it may seem intuitive that more rain can shape mountains by causing rivers to fracture mountains. rocks faster. But scientists have also believed that rain can erode a landscape fast enough to ‘suck’ rocks out of the ground, which effectively lifts mountains very quickly. “

The central and eastern Himalayas of Bhutan and Nepal

“Both theories have been debated for decades because the measurements required to test them are painstakingly complicated,” he continues. That is what makes this discovery. such an exciting breakthroughas it strongly supports the notion that solid atmospheric and terrestrial processes are intimately connected. “

While there is no shortage of scientific models aimed at explaining how the Earth works, the biggest challenge may be making enough good observations to test which are the most accurate.

The study was based on the central and eastern Himalayas of Bhutan and Nepal, because this region of the world has become one of the most sampled landscapes for studies of erosion rates. Dr. Adams, along with collaborators from Arizona State University (ASU) and Louisiana State University, used cosmic clocks inside grains of sand to measure the rate at which rivers erode the rocks below them.

Erosion through rain

“When a cosmic particle from outer space reaches Earth, it is likely that hit grains of sand on the slopes while being transported to the rivers. When this happens, some atoms within each grain of sand can transform into a rare element, explains Adams. By counting how many atoms of this element are present in a sandbag, we can calculate how long the sand has been there, and therefore how quickly the landscape has eroded. “

“Once we have the erosion rates of the entire mountain range, we can compare them with the variations in the slope of the river and rainfall,” he continues. “However, such a comparison it’s hugely problematic because each data point is very difficult to produce and the statistical interpretation of all the data together is complicated. “

Dr. Adams overcame this challenge combining regression techniques with numerical models of how rivers are eroding. “We tested a wide series of numerical models to reproduce the erosion rate pattern observed in Bhutan and Nepal. Ultimately, only one model was able to accurately predict the measured erosion rates,” he adds. “This model allows us for the first time to quantify how the rains affect erosion rates in rugged terrain “.

Key to the dangers in the Himalayas

Research collaborator Kelin Whipple, a professor of geology at ASU, notes that the findings “show how critical it is to take rain into account when tectonic activity patterns are evaluated using topography, and they also provide an essential step in addressing the rate of slip where tectonic faults can be controlled by weather-driven surface erosion. “

The study findings also have important implications for land use management, maintenance from infrastructure and the dangers 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 also suggest that more rainfall can undermine 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: flash flooding. from the lake.

“Our data and analysis provide uAn effective tool for estimating erosion patterns in mountainous landscapes like the Himalayas and therefore can provide invaluable information on the dangers that affect the hundreds of millions of people who live in and at the foot of these mountains, “he adds.