Why ‘the roof of the world’ collapses

The roof of the world in Tibet is collapsing, and now we know why. A team of Earth Scientists, led by VU Professor Wouter Schellart, has demonstrated that the solution lies some 4000 kilometres eastward, at the boundary between the Pacific Ocean and the continental margin of East Asia.

10/02/2019 | 11:35 AM

The highest mountains on Earth are located in Tibet and around its edges, including the Himalaya, Karakoram and Kunlun Shan. The Tibetan Plateau is most peculiar, as its average elevation lies an astonishing 5 kilometres above sea level, higher than the highest peaks in the Alps and the Rockies. Apart from its exceptional elevation, Tibet is also very large, with a surface area exceeding two million square kilometres, about the same size as Greenland.

Too high to sustain itself?
Geologists have known for long that Tibet and its surrounding ranges resulted from the continental collision between India and Asia, which started some 50 to 60 million years ago and is still active today. The collision has folded, fractured and thickened the Asian crust, thereby uplifting the Tibetan Plateau to its current height.

There are multiple lines of evidence, however, that, as Tibet and the Himalaya are being squeezed and shortened in a north-south direction, the plateau is extending and collapsing eastward. In earlier research to explain such collapse, it was argued that the plateau was simply too high to sustain itself, thereby triggering the collapse. But such an argument does not explain why the plateau is only collapsing eastward and not westward.

East Asia is moving millimetres to centimetres per year
New research by a team of Dutch, Chinese, French and Portuguese scientists, published 2 October in Nature Communications, shows that the mechanism driving this collapse is located at the eastern and south-eastern boundaries of the Eurasian tectonic plate. These plate boundaries are marked by enormous subduction zones, places where an oceanic plate dives (subducts) below another tectonic plate into the Earth’s interior. Using geodynamic laboratory experiments, the scientists have demonstrated that the subducting Pacific and Australian plates pull the Eurasian plate towards themselves by dragging at its borders and its base.

“The result is that East Asia is slowly moving eastward and southward, at millimetres to centimetres per year, and is being torn, stretched and fragmented along the way”, says Wouter Schellart, the team’s leading scientist. The westernmost expressions of this tearing are found in Tibet, where numerous north-south striking valleys are flanked by major extensional faults, and in Siberia, where the deepest lake on Earth, Lake Baikal, formed as a major tear in the Eurasian plate.

The collapse of Tibet and the break-up of Asia started many millions of years ago, and the end of these processes is not nearly in sight. Eventually, the Tibetan Plateau will disappear altogether, thanks in part also due to erosion. If humanity will be around to bear witness of this is still up in the air, as it is likely to take many tens of millions of years to come.
Topography of a geodynamic experiment showing the India-Asia collision, as well as the formation of the Tibet-Himalaya mountain ranges north (right) of India (in yellow-brown), and the break-up, tearing and stretching of East Asia and Tibet as a consequence of subduction along the eastern and southeastern borders of Asia.