What Holds Up the Himalayas?
Scientists havediscovered that a 100-year-old theory about Earth’s highest mountain range iswrong.
The Himalayas wereformed when the Asian and Indian continents collided around 50 million yearsago. Tibet was squeezed so hard it crumpled and shrank. Eventually, Indiaslipped under the Eurasian tectonic plate, which doubled the thickness of Earth’scrust beneath the Himalayas and Tibet.
Until now, the theoryhas been that this extra-thick crust carries the weight of the Tibetan Plateauand the Himalayas. In 1924, geologist Emile Argand published research showingthe 2 crusts stacked on top of each other, stretching 45-50 miles (70-80 km)deep under Earth’s surface.
But researchers now saythat rocks in the crust turn molten about 25 miles (40 km) down because ofextreme temperatures. The lowermost layers become like yogurt, which won’tsupport a mountain.
New research says thereis a piece of mantle sandwiched between the 2 crusts. The mantle is a layerthat usually sits directly beneath the crust. Being denser than the crust, itdoesn’t liquify at the same temperatures. The crust is buoyant, similar to aniceberg. It lifts higher the thicker it gets.
A computer simulationof the collision between the Asian and Indian continents showed that as theIndian crust began to liquify, blobs of it rose and attached to the base of therigid outer layer. This means there is a rigid layer of mantle between thestacked crusts, which solidifies the structure beneath the Himalayas. While the2 crusts give buoyancy to the region lifted, the mantle material providesmechanical strength.
Then the researcherscompared their simulation with seismic data and information obtained fromrocks. They found that the mantle sandwich matched previous evidence thatArnand’s theory couldn’t explain. Enigmatic observations are more easilyexplained with this model. This study presents strong evidence, but it iscontroversial because Arnaud’s theory has been widely adopted.
These results explain anumber of geological oddities in the region. The scientists ran lots ofsimulations using different thicknesses for the layers, and they always got abit of mantle sandwiched between the 2 crusts.
