The forces of climate change and plate tectonics have been raging against each other since the Earth formed, with the former cutting the land down to size and the latter pushing it towards the sky – but which of the two is more powerful? According to a new study published in the Proceedings of the National Academy of Sciences, rapid erosion to mountainous regions by glacial process overcomes the uplifting, buoyant forces of plate tectonics, effectively meaning that mountains can be worn down faster than they can be built.
The interactions between climate change and plate tectonics, in particular the generation of mountains and huge basins, is a huge unknown in the geosciences. The complex nature of a wide range of processes, including continental drift, chemical weathering and mechanical erosion, mean that pinning down the exact nature of the balance between the two opposing forces has proved incredibly difficult.
The lead authors of this new study decided to look at the behavior of mountain ranges across a selection of glacial maximums – times of peak glacial cover – within the Pleistocene geological epoch, which lasted from around 2.6 million to 12,000 years ago. During this epoch, the total length of ice ages switched from being “short” (lasting around 40,000 years) to long (lasting up to 100,000 years).
The formation and migration of glaciers across mountain ranges causes varying degrees of erosion depending on how severe their associated glacial maximum was – the more severe a maximum, the more erosion of mountaintops that will occur. By analyzing specific geological regions during this time, researchers can potentially calculate a wide range of erosion rates, before comparing them with the simultaneous tectonic uplift.
For their ten-year-long study, the researchers employed cutting-edge seismic imaging and marine coring techniques in an attempt to measure the total amount and average flow rates of sedimentary material from the St. Elias Mountain Range on the Alaskan coast. As the rate of plate tectonic movement in the region has been roughly consistent over the last 6 million years, these mountains provided an excellent location to measure erosion rates.
Image credit: Periods of extreme glacial cover heavily erode mountain ranges, faster than they can be built. Ksenia Ragozine
Much of the sediments were deposited in features called fans. Sedimentologists can analyze the finer characteristics of the fan to give an estimate to how quickly it formed through erosional processes higher up the mountain range. They found, as expected, that the mountain ranges dynamically respond to the Earth’s climate, with glacier action causing their erosion over time.
More significantly, however, the sediments here were far younger than the researchers anticipated, indicating that the rates of sediment production – and thus, erosion – were far higher than expected. In fact, their results actually suggest that the mountain-building processes taking place during these glacial maximums were overwhelmed by the forces of glaciation, not just causing them to erode, but erode so fast that they began to actively shrink in size.
Remarkably, since the transition between short and long glacial maximums during the mid-Pleistocene, the erosion of material has outpaced the upward movement of the mountains by as much as 80 percent.