Secrets Beneath the Himalayas

The Himalayas: A New Understanding of Their Formation

The Himalayas, the highest mountain range on Earth, have long fascinated scientists. For over a century, researchers believed that the region’s towering heights were primarily supported by a thickened crust beneath the mountains. However, recent findings challenge this long-standing theory, offering a new perspective on how these monumental peaks have been formed and sustained.

The Old Theory: Crust Alone Holds Up the Himalayas

For many years, the prevailing belief was that the Himalayas and the vast Tibetan Plateau were supported by the doubling of the Earth’s crust. This idea originated from the work of Swiss geologist Émile Argand in 1924, who proposed that the collision between the Indian and Asian tectonic plates caused the crust to thicken, extending to depths of 45 to 50 miles (70 to 80 km). According to this theory, the thickened crust provided enough support to carry the massive weight of the mountains.

However, there were inherent issues with this theory. As the crust thickens deeper below the surface, temperatures rise to the point where rocks become molten, turning into a ductile substance at around 25 miles (40 km). Pietro Sternai, the lead author of the study and an associate professor of geophysics at the University of Milano-Bicocca, explained this phenomenon with a simple analogy: “If you’ve got 70 km of crust, then the lowermost part becomes ductile… it becomes like yogurt — and you can’t build a mountain on top of yogurt.” This analogy calls into question the viability of relying solely on the crust to sustain the Himalayas.

A New Discovery: The Mantle’s Role in Supporting the Himalayas

Pietro Sternai and his colleagues have proposed an entirely new model, suggesting that there is an additional, unexpected layer between the two crusts: the mantle. Their simulations showed that when the Indian plate slipped beneath the Eurasian plate, some of the mantle material did not just flow beneath the Asian crust as once thought. Instead, blobs of the mantle rose and were sandwiched between the crusts, providing necessary support.

“The mantle material doesn’t liquefy at the same temperature as the crust, and this layer of mantle adds strength to the region,” said Sternai. The new model suggests that the combination of the two crusts with a layer of mantle beneath them provides both mechanical strength and buoyancy, sustaining the weight of the Himalayas and the Tibetan Plateau.

Simone Pilia, a co-author of the study, explained that the mantle sandwich helped to resolve several geological oddities. “Things actually start to make sense now,” Pilia said. “Observations that seemed to be enigmatic are actually now more easily explained by having a model where you have crust, mantle, crust.”

The team’s model also better matches seismic data and direct observations of the region, reinforcing its credibility.

Why This Matters: A New Perspective on Tectonics and Mountain Building

The implications of this discovery are profound, not only for understanding the Himalayas but for tectonics in general. Historically, any new data about the region had been interpreted through the lens of the double-thickened crust theory. Sternai noted, “Historically, any data that would come along would be interpreted in terms of a single, double-thickness crustal layer.” However, with the addition of the mantle layer, the puzzle pieces now fit together more logically.

The findings raise new questions about the forces that shape mountain ranges worldwide. How many other mountain ranges might have similar structures? Could the presence of mantle material beneath other tectonic boundaries be the key to understanding their uplift?

This new model not only enhances our understanding of the Himalayas but also opens up new avenues for research into the broader mechanisms of tectonic activity. It challenges existing assumptions and encourages scientists to reevaluate long-held theories in light of new evidence. As research continues, we may uncover even more insights into the dynamic processes that shape our planet.