Mountain Erosion Rates Increased as Climate Cooled

A topographical investigation of global cooling and glaciation over the last 2- to 3 million years has led to a new understanding of the balance between tectonics, climate and their interaction through erosion.

A research team from the University of Tübingen Geoscience Department and other institutions compiled bedrock thermochronometric data from around the world to make their assessments. Thermochronometry is the study of a mineral, rock or geological region using radiometric dating of two or more different minerals with different closure temperatures, or the temperature at which the crystal structure of a mineral has formed and cooled sufficiently to prevent diffusion of isotopes.

The thermochronometric analysis revealed that mountain erosion rates have increased since 6 million years ago, with the most rapid increase occurring within the last 2 million years.

Moreover, alpine glaciers, the researchers suggest, play a significant role in erosion rates under a cool climate.

To reach their conclusions, the researchers collected data from more than 18,000 rock samples, which allowed them to globally estimate temporal and spatial variations in erosion states.

"During mountain erosion rocks travel from about 10 kilometers depth in the crust to the Earth's surface. During this process, the rocks cool from great depths to the surface," the researchers said in a statement. "Thermochronology exploits that small quantities of radioactive uranium contained in the rock decay in a time-dependent process. Below a given so-called closure temperature rocks accumulate the products of radioactive decay."

By calculating the decay process, the researchers are able to determine the time it took the rock to reach the surface and ultimately erode.

The researchers said that because their research was global in scale, the slight regional variations observed at individual sites were able to be reduced, painting a clearer overall picture of erosion rates around the world.

Overall, the researchers concluded there is a strong correlation with global climate change and erosion rates over the last several million years.

"On a global scale erosion rates span four orders of magnitude in the last eight million years from one hundreth of a millimeter up to ten millimeters a year," said Todd Ehlers of the University of Tübingen.

The most substantial erosion changes were seen at latitudes greater than 30°, in places such as the European Alps, Patagonia, Alaska, the South Island of New Zealand and The Coast Mountains of British Columbia.

Each of these areas are highly variable in their tectonic activity, but they have all been glaciated in the past few million years. "This change with increased activity of glaciers and higher sediment flux shows a clear temporal correspondence with further Late Cenozoic cooling," Ehlers said, adding that the results have implications for improving our understanding of the coupling between climate and erosion.

The research is published in the journal Nature.