Testing the temperature dependence of erosion using novel applications of cosmogenic nuclides

Mean annual temperatures in the European Alps have warmed roughly 2 °C over the last century and a half, and are expected to continue increasing well into the next several centuries. As they warm, the mechanisms by which these regions erode, and consequently the rate at which they erode, may also change. A considerable portion of my PhD work has investigated both the rates and mechanisms of erosion in these steep and pre-dominantly bedrock landscapes, as well as their dependence on temperature. Our method of choice? Cosmogenic nuclides.

Cosmogenic nuclides are rare isotopes produced when cosmic rays (yes, cosmic rays) from exploding supernovae (yes, exploding supernovae) interact with specific elements in minerals found on the surface of Earth. Because the energy from these rays dissipates (attenuates) as they permeate into the crust, most cosmogenic nuclides form only in the uppermost few meters of the Earth’s surface. For decades, researchers in many fields of natural and physical science (mathematics, physics, geoscience) have worked diligently to understand how cosmogenic nuclides are formed, and at what rate. They are now a standard tool in the geoscientist’s toolkit for determining the age of certain features in the landscape, as well as the rates at which landscapes are eroded, sculpted, and modified.

My PhD has centered around three of these nuclides, Be-10, He-3, and C-14, all of which are formed in the mineral quartz. We are exploring the utility of using these nuclides to investigate the erosion rate (Be-10), the erosion style (C-14), and the long-term environmental temperatures (He-3) in cold, high-alpine regions. Applying cosmogenic nuclide-based methods in these regions is not straightforward, because many of the simplifying assumptions that are made when interpreting cosmogenic nuclide concentrations as erosion rates (like the assumption of a uniformly-eroding surface) are not possible.

As part of this project, I wrote the Stochastically-eroding in-situ cosmogenic nuclide (STEIN) model, which was the basis for our study exploring the suitability and sensitivity of these three cosmogenic nuclides to the kinds of erosional regimes and environmental temperatures expected in high-alpine regions. We outline these findings in our paper Dennis & Scherler (2022): A combined cosmogenic nuclides approach for determining the temperature-dependence of erosion.

Another study, applying the cosmogenic nuclide approach described in that paper to samples collected from the central Mont Blanc massif, is forthcoming.