How Mekong River Became So Deep

Posted: Oct 17 2018, 3:09pm CDT | by , Updated: Oct 17 2018, 3:11pm CDT, in Latest Science News


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How Mekong River Became So Deep
Credit: Gregory Wissink

Researchers have linked the formation of Mekong canyon to heavy Asian monsoon rain 17 million years ago.

Mekong River is the longest river in Southeast Asia. It originates in the Tibetan Plateau and runs through China, Myanmar, Laos, Thailand, Cambodia and Vietnam. The Chinese portion of the river (Lancang Jiang) harbors a spectacular canyon that is between 1 to 2 kilometers deep relative to its surrounding landscape. A new study suggests that the formation of this deep valley is likely caused by major intensification of the Asian monsoon that occurred in middle Miocene, about 17 million years ago. The finding lends support to the theory that erosion is responsible for this geologic feature in the landscape.

River incision is a natural process in which a river cuts downward into its bed. The incision is mostly attributed to tectonic uplift. But climate can also drive this process as climate system controls precipitation and triggers erosional mechanisms in rivers. The heavy precipitation eventually cuts bedrock and deepens the active channel.

“When the upper half of that river was established and at what point it incised the canyon it occupies today, as well as whether it was influenced by climate or by tectonics, has been debated by geologists for the last quarter century. Our work establishes when major canyon incision began and identifies the most likely mechanism responsible for that incision: an intensification of the Asian monsoon during the warmest period over the last 23 million years, the Middle Miocene climate optimum.” Co-author Gregory Hoke, associate professor and associate chair of Earth sciences, said.

To determine the cause, researchers extracted bedrock samples of Mekong canyon and modeled the history of erosion by the river. The results pointed towards a non-tectonic cause for incision.

Researchers found Mekong River began to cut fast and deep into the Tibetan Plateau about 17 million years ago. There is no evidence of major tectonic activity at that time, but the period was marked by an exceptionally intense East Asian summer monsoon rains. The model suggests that strong rain and erosion, rather than tectonic uplift, led to the formation of Mekong canyon.

“Here we report low-temperature thermochronology data from river bedrock samples that reveal a phase of rapid downward incision (>700 m) of the Mekong River during the middle Miocene about 17 million years ago, long after the uplift of the central and southeastern Tibetan Plateau. However, this coincides with a period of enhanced East Asian summer monsoon precipitation over the region compared with the early Miocene.” Authors wrote in the study. “Using stream profile modeling, we demonstrate that such an increase in precipitation could have produced the observed incision in the Mekong River.”

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<a href="/latest_stories/all/all/47" rel="author">Hira Bashir</a>
The latest discoveries in science are the passion of Hira Bashir (). With years of experience, she is able to spot the most interesting new achievements of scientists around the world and cover them in easy to understand reporting.




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