Is Shangri La a place to be
How Shangri-Las are made
With a new simulation, geologists are massively shortening the Earth's history, which lasted millions of years. In doing so, they are turning previous explanations for the formation of high valleys in the southeasternmost tip of the Tibetan highlands on their heads.
The southeastern part of the Tibetan highlands is an extraordinary mountain landscape. So high peaks rise steeply and steeply to over 7000 meters above sea level. Large rivers, including the Yangtze, Mekong and Saluen, have cut deep into the bedrock. But next to it lie almost lovely high valleys with rolling hills, large lakes and meandering rivers, nestled between mountain ridges. These landscapes inspired James Hilton to create his mysterious Shangri-La, a heavenly and peaceful place, which he anchored in the minds of the western world with his novel "Lost Horizons".
Earth scientists consider the region a little less romantic. For them, this is especially geologically extremely interesting and they want to find out how high valleys of the Shangri-La form were formed.
Uplifting flat land is questionable
Until now, it was assumed that these high valleys are relict landscapes, created in the lowlands that literally lie at the feet of the Himalayas. Only the collision of the Indian with the Asian plate and the associated raising of the Tibetan plateau ensured that parts of the lowland were raised and reached their current level between 2000 and 5000 meters above sea level. Their landscape characteristics are said to have been preserved there.
Geologists at ETH Zurich have now used a new model to simulate the formation of these high valleys on the computer; the simulations are a kind of time-lapse to understand the geological processes of the last 50 million years. This brings them to a completely different conclusion, as shown in a study just presented in the journal “Nature”.
Faults interrupt the water network
In their simulation, they could not trace the rise of the lowlands into the highlands. However, they showed that the gentle high valleys must have been created on the spot - in situ - due to interruptions in parts of the river network due to tectonic movements.
In this simulation (and derived from it also in reality) in the area of today's Yunnan province, the northeastern corner of the Indian plate collides with the Asian and "dents" the eastern part of the Himalayas and the Tibetan plateau. This creates strong tensions that are accompanied by numerous earthquakes. These deform the earth's surface along faults that “cut up” the landscape.
These surface deformations force rivers into other beds or even interrupt rivers, so that rivers lose part of their catchment area. For example, if there is no inflow, the previous river will carry less water. This reduces the erosion and sediment transport capacity along its route; this in turn reduces the steepness of the river banks. But also on the adjacent slopes the erosion is slower, as the river "gnaws" less aggressively and undermines them less quickly. This makes slopes less steep and landslides less frequent. In this way, landscapes similar to those in the valley are formed over millions of years in the middle of the mountains. For the co-author of the study, ETH Professor Sean Willett, the case is clear: "Our simulations clearly show that these high valleys must have developed on site and are not relics of former lowlands."
Willett rules out that glaciers created the gentle shapes. The glaciation in the study region was limited to the highest peak regions. She may have helped to erode high mountains and extensive slopes. Only rivers are responsible for the formation of the valleys.
Engadin like Shangri-La?
The results of the study apply not only to the eastern Himalayas, but also to other mountain ranges. The ETH professor cites the Engadine as an example of the Swiss Alps. The valley floor is at great sea level, but is flatter than one would expect from a pure glacier valley. There is much to suggest that the Engadine high valley just like the high valleys of the southeastern Tibetan highlands could have formed on site at this altitude. "The Malojapass is not a real pass, as it has no incline on the Engadine side," says Willett. "It looks like the beginning of the valley has been cut off."
An upcoming study will clarify whether the Engadine and other high alpine valleys actually correspond to the current model of the earth scientists.
Yang R, Willett S, Goren L. In situ low-relief landscape formation as a result of river network disruption. Nature, published online April 22, 2015; DOI: 10.1038 / nature14354
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