River deep, mountain high

Interactions between landslides and erosion caused by rivers explain why some mountain ranges exceed their expected lifespan, scientists from the University of Melbourne and Aarhus University in Denmark have discovered.

Study co-author Mike Sandiford of the School of Earth Sciences at the University of Melbourne says the study has answered the quandary as to why there was fast erosion in active mountain ranges in the Himalayas and slow erosion in others such as 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,” Professor Sandiford says.

“This study provides into the origins and topography of our globe’s mountainous landscape.”

Mountain ranges are expected to erode in the absence of tectonic (earthquake) activity but several ranges, such as the Appalachians in the USA and the Urals in Russia, have been preserved over several hundred million years.

Co-author, Professor David Egholm from Aarhus University says the new study, published recently in the journal Nature, 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,” he says.

The researchers say rivers can cut through bedrock and this process is thought to be the major controlling factor in 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 landscape evolution.

The study revealed landslides affected river erosion rates in two ways. Large landslides overwhelm river transport capacity and can protect the riverbed from further erosion; conversely, landslides also deliver abrasive agents to the streams, thereby accelerating erosion.

Feedback between these processes can help stabilise the rates of erosion and increase the lifespan of mountains, the authors say.

The study forms part of broader research program led by Professor Sandiford into the origins of mountains. 

His team works across southern Asia in Timor, Indonesia, New Guinea, the Himalayas and the Kunlun mountains in western China, focussing on the interplay of the processes that creates mountains, such as earthquakes, and the processes that destroy mountains, such as landslides.

Along with that of international colleagues, his work is leading to new insights into earthquake and landslide risks, and is delivering new databases and geological maps, as well as information about the fundamental processes responsible for the remarkable landscapes in some of the most rugged parts of our planet.

The work in remote parts of Asia is particularly important in providing better understanding of the risk of natural hazards, as well as basic geoscience data, essential for emerging nations such as East Timor. 

It is all part of an initiative led by Professor Sandiford to create a Graduate School in Asian Geoscience promoting engagement between Australian and Asian geoscience organisations, through student research exchanges and mentoring, and through the development and sharing of basic geoscience data. 

www.earthsci.unimelb.edu.au