A study into climate controls on erosion has quantified the impact of rainfall on the development of mountain ranges across millions of years.
The study – ‘Climate controls on erosion in tectonically active landscapes’ – was published in Science Advances and conducted in the Himalayas.
Dr Byron Adams, the lead author of the study and a Royal Society Dorothy Hodgkin Fellow at Bristol University’s Cabot Institute for the Environment, said the study used the cosmic clocks within sand grains to study the speed at which rivers in the central and eastern Himalaya of Bhutan and Nepal eroded the rocks beneath.
“When a cosmic particle from outer space reaches Earth, it is likely to hit sand grains on hillslopes as they are transported toward rivers,” Adams explained.
“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 been eroding.”
The Himalaya region is one of the most used landscapes for scientists studying erosion rates.
Comparing erosion rates
Adams’ research team, which included collaborators from Arizona State University and Louisiana State University, compared the erosion rates across the mountains using regression techniques and numerical models.
“Once we have erosion rates from all over the mountain range, we can compare them with variations in river steepness and rainfall,” he said. “However, such a comparison is hugely problematic because each data point is very difficult to produce and the statistical interpretation of all the data together is complicated.
“We tested a wide variety of numerical models to reproduce the observed erosion rate pattern across Bhutan and Nepal.
“Ultimately only one model was able to accurately predict the measured erosion rates. This model allows us for the first time to quantify how rainfall affects erosion rates in rugged terrain.”
The study shows that rainfall should be factored in to the assessment of tectonic activity patterns using topography. It will also help determine the level of climate-driven surface erosion that impacts the slip rate on tectonic faults.
According to Bristol University, high erosion rates in the Himalaya increase sedimentation behind dams, with the study also showing that increased rainfall can increase the risk of landslides.
“Our data and analysis provides an effective tool for estimating patterns of erosion in mountainous landscapes such as the Himalaya, and thus, can provide invaluable insight into the hazards that influence the hundreds of millions of people who live within and at the foot of these mountains,” Adams said.