A recent finding has altered the history of the evolution of Himalayas. Evidences revealed in a new study suggest the presence of an ancient canyon buried deep in south Tibet, carved by an ancient river million years ago. On observing the rivers flowing in the region, the researchers from the China Earthquake Administration and the California Institute of Technology (Caltech) concluded that an arcane canyon, having a depth of thousands of feet in places, once ran along the Yarlung Tsangpo River in south Tibet, north of the eastern end of the Himalayas. The new finding has changed the current view about the formation of massive and picturesque gorges of the Himalayas, which have became so steep so fast. The study has been reported in the journal Science.
Lead researcher Jean-Philippe Avouac of Caltech said “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.” Geological deformations are usually studied by using tools like GPS and seismology but in order to uncover the occurrences of millions of years ago, geomorphic signatures left behind by rivers are more helpful, which demonstrates the interaction of waterways and land during geological transformations.
Avouac elaborated “In this case, we used a paleocanyon that was carved by a river. It’s a nice example where by recovering the geometry of the bottom of the canyon, we were able to say how much the range has moved up and when it started moving.” For the study, the researchers drilled into the valley floor at five locations along the Yarlung Tsangpo River and discovered gravel and larger rocks cemented together at a depth of 800 meters. This indicates that once a river flowed here. The lowest sediment layer had two isotopes, beryllium-10 and aluminum-26, and their examination revealed that it was around 2.5 million years ago when the bedrock turned to depositing sediments.
On the basis of the depth and age of the paleocanyon and the geometry of the valley, the geologists have concluded that about three million years ago, there existed a river. But with the continued collision of the Indian and Eurasian plates the Himalayan mountain range pushed northward, damming the river. This also resulted in filling up of the canyon with sediments and gradually veiling its existence on Earth.