Glaciation responsible for accelerated erosion

19/Dec/2013

This image shows a frosted landscape.

Researchers from the University of Lausanne and ETH Zurich funded by the Swiss National Science Foundation (SNSF) have shown that glaciation is clearly responsible for accelerated erosion over the past millions of years. Their study has answered a question that has been the subject of debate for over 20 years.

During the past millions of years, the Earth has been subject to glaciation and erosion has increased massively at a global level. Has this glaciation been responsible for the erosion? Or is erosion the result of increased tectonic activity? The Earth sciences community has been debating this question for more than two decades. A study (*) recently published by a team of researchers led by Frédéric Herman, from the University of Lausanne, has shown that the acceleration in erosion is indeed caused by glaciation.

The compilation and interpretation of some 18,000 thermochronometric data records taken from local studies has given them access to global information on the average speed of mountain erosion during periods with cold climates. This information shows not only that processes of erosion started to accelerate with the onset of glaciation, but also that this acceleration is much greater in high latitudes and at high altitude, where most glaciers can be found.

Painstaking work

Finding these local studies, making them comparable and compiling the data was truly painstaking work, according to Frédéric Herman. "We started the task four years ago," he explained. "Our main leap forward came when we had gathered all of the data and ran it through a novel interpretation method that allowed us to improve our modelling of the phenomenon of rock travel from deep down below ground, up to the surface."

Their study took advantage of thermochronometry, a thirty-year old technique. It is based on the principle that the closer a rock comes to the surface, the lower its temperature becomes. This change in temperature is recorded in minerals such as zircon and apatite. By determining the thermal history of these minerals (their age on reaching a certain temperature), the researchers are able to calculate the amount of time that the rock in which they are contained has taken to reach the surface, and thus deduce the speed of erosion.

Erosion and the CO2 cycle

The results of this study should also improve understanding of the links between erosion and the CO2 cycle. "The more a rock is broken up into small pieces, the more these pieces react chemically with the atmosphere and carry CO2 that they trap on the ocean floor. The fact that glaciation accelerates the processes of erosion means that this cooling plays a complex role in the carbon dioxide cycle, as a greenhouse agent and in terms of its development through the ages," explained Frédéric Herman. This is obviously an important aspect at a time at which so much effort is being applied to improving models of climate change and greenhouse gases.

(*)Frédéric Herman, Diane Seward, Pierre G. Valla, Andrew Carter, Barry Kohn, Sean D. Willett and Todd A. Ehlers (2013). Worldwide acceleration of mountain erosion under a cooling climate. Nature online: doi: DOI: 10.1038/nature12877 (Available to journalists in PDF format from the SNSF: com@snf.ch)

legend: blue indicates erosion of less than 0.01 mm p.a.; red indicates erosion of more than 7 mm p.a.

Contact

Prof Frédéric Herman
Institute of Earth Sciences
University of Lausanne
CH-1015 Lausanne
Phone +41 21 692 44 24
E-mail Frederic.Herman@unil.ch