Caltech geologists: Himalaya gorge not formed by water erosion

tsangpo gorge canyon himalaya tibetGeology and most people would assume that most Himalayan gorges were formed by river water erosion or glacier action.

A recent study by Chinese (China Earthquake Administration) and Caltech (California Institute of Technology) geologists with new data and modeling has suggested that Tsangpo Gorge was formed by movement of the rock, or rapid uplift as they like to call it.

The Yarlung Tsangpo Valley close to the Tsangpo Gorge, where it is rather narrow and underlain by only about 250 meters of sediments. The mountains in the upper left corner belong to the Namche Barwa massif. Previously, scientists had suspected that the debris deposited by a glacier in the foreground was responsible for the formation of the steep Tsangpo Gorge -- the new discoveries falsify this hypothesis.

rapid rock uplift water glacier erosionA team of researchers from Caltech and the China Earthquake Administration has discovered an ancient, deep canyon buried along the Yarlung Tsangpo River in south Tibet, north of the eastern end of the Himalayas. The geologists say that the ancient canyon—thousands of feet deep in places—effectively rules out a popular model used to explain how the massive and picturesque gorges of the Himalayas became so steep, so fast.

"I was extremely surprised when my colleagues, Jing Liu-Zeng and Dirk Scherler, showed me the evidence for this canyon in southern Tibet," says Jean-Philippe Avouac, the Earle C. Anthony Professor of Geology at Caltech. "When I first saw the data, I said, 'Wow!' It was amazing to see that the river once cut quite deeply into the Tibetan Plateau because it does not today. That was a big discovery, in my opinion."

yarlung tsangpo river gorge tibetThe team's new hypothesis also rules out a model that has been around for about 15 years, called tectonic aneurysm, which suggests that the rapid uplift seen at the Namche Barwa massif was triggered by intense river incision. In tectonic aneurysm, a river cuts down through the earth's crust so fast that it causes the crust to heat up, making a nearby mountain range weaker and facilitating uplift.

The model is popular among geologists, and indeed Avouac himself published a modeling paper in 1996 that showed the viability of the mechanism. "But now we have discovered that the river was able to cut into the plateau way before the uplift happened," Avouac says, "and this shows that the tectonic aneurysm model was actually not at work here. The rapid uplift is not a response to river incision."
Geologists discover ancient buried canyon in South Tibet

yarlung tsangpo valley gorge south tibet

Tsangpo Gorge not formed by water erosion

Could they now find other gorges, canyons and valleys in the Himalayas or other mountain ranges on the Earth that are not formed by the result of water or glacial erosion and action?

The Himalayan mountains are dissected by some of the deepest and most impressive gorges on Earth. Constraining the interplay between river incision and rock uplift is important for understanding tectonic deformation in this region ... By reconstructing the former valley bottom and dating sediments at the base of the valley fill, we show that steepening of the Tsangpo Gorge started at about 2 million to 2.5 million years ago as a consequence of an increase in rock uplift rates. The high erosion rates within the gorge are therefore a direct consequence of rapid rock uplift.

Rapid tectonic uplift was responsible for the immense Tsangpo Gorge on the eastern edge of the Tibetan plateau 2.5 million years ago ... The constant river gradient strongly suggests a rapid uplift event created the gorge, rather than river incision as previously believed.
Tectonic control of Yarlung Tsangpo Gorge revealed by a buried canyon in Southern Tibet

Links:
Tectonic aneurysm model explanation