June 27, 2013
Why Have Some Mountain Ranges Exceeded Their Expected Lifespan?
Lee Rannals for redOrbit.com - Your Universe Online
Interactions between landslides and erosion has helped scientists understand the reasons behind the lifespan of some of the world's iconic mountains. Researchers say this study answers questions as to why there was fast erosion in active mountain ranges in the Himalayas and slow erosion in others like the Great Dividing Range in Australia or the Urals in Russia.
"We have shown that links between landslides and rivers are important in maintaining erosion in active or ancient mountain ranges," said co-author Professor Mike Sandiford of the School of Earth Sciences at the University of Melbourne. "This study is a great insight into the origins and topography of our globe's mountainous landscape."
Mountain ranges should theoretically erode away over time in the absence of tectonic activity. However, several ranges, like the Appalachians in the US and the Urals in Russia, have been preserved over several hundred million years. The latest study provides a plausible mechanism for the preservation of tectonically inactive mountain ranges.
"Computational simulations performed for the study revealed that variations in mountain erosion may relate to a coupling between river incision and landslides," said co-author, Professor David Egholm from Aarhus University.
The scientists said rivers can cut through bedrock and this process is thought to be a major factor in controlling mountain erosion. However, the long-term preservation of some mountains is at odds with some of the underlying assumptions regarding river erosion rates in current models of river-based landscape evolution.
The most recent study revealed landslides affected river erosion rates in two ways. In the first example, large landslides overwhelm river transport capacity and protect the riverbed from further erosion. The second example shows how landslides also deliver abrasive agents to the streams, accelerating erosion. Scientists said feedback between these processes helps to stabilize the rates of erosion and increase the lifespan of mountains.
One region of the Appalachian Mountains seems to be vastly different from the rest of it. Scientists reported in February that this location could have undergone a "geological facelift." The area looks more like younger mountain ranges instead of the older, rounded ones. The team determined that the earth's mantle had been helping the older region look a lot younger than it really was.
"The earth's outer shell is the crust, but the next layer down - the mantle - is essentially a very viscous fluid," said Karl Wegmann, an assistant professor of marine, earth and atmospheric sciences at North Carolina State University said. "When it's warm it can well up, pushing the crust up like a big blister. If a heavy portion of the crust underneath the Appalachians 'broke off,' so to speak, this area floated upward on top of the blister. In this case, our best hypothesis is that mantle dynamics rejuvenated the landscape."