It’s Not the Earth’s Crust Holding up the Himalayas — Experts Point to a Surprising Geology

The thick outer crust of Earth has zillions of wafer-like pieces interlocked and held together like a cork trapping the molten hot mantle. The blizzard-like forces agitating inside the mantle continue to catalyze these plates in a recurring metamorphosis as they shift, slip, collide, and crash into each other. As a result, they give birth to volcanoes and mountains, dig up ocean basins, bury carbon, and erupt trapped carbon into the air.

Around 40 million years ago, one such interaction between two tectonic plates pushed the crust upwards, which is how the great towering beast called the Himalayas materialized into the skies. However, in a new report published in Tectonics, geoscientists revealed that it wasn’t just these tectonic plates that caused these mountains to rise. There was so much more going on.

The stretch where the great Himalayas are today was just a patch of dense tropical forests around 55 million years ago, according to PBS Eons. The forests fringed with trees of fig, maple, and ironwood. Wild animals roamed and lived in these forests. But then, the flames smoldering within the magma of the planet’s mantle, along with other magnetic forces, triggered a clash between the Indian plate and the Eurasian plate. The two continental plates crashed into one another. But since both the plates were formed of hard crust, instead of slipping below the other plate, the crust of the Indian plate folded and created faults.

The aggressive dance pushed the crust upwards, giving rise to the Himalayas. Over time, violent rains soaked up the rising plateau, eating away the rocks and carving deep valleys and canyons that shaped and sculpted the mountains. Lashed by chemical-dripping monsoons, the rocks soon became rigid and mountainous. A 1924 research published by the Swiss geologist Emile Argand reported that the Indian and the Eurasian crusts stacked atop each other, together stretching for about 45 to 50 miles deep beneath Earth’s surface. But lately, scientists have caught a big discrepancy in this hypothesis.

Around 25 miles deep, the high temperature of the magma turns the rocks molten and viscous, and mountains can’t sit atop a slurry of liquid. "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," Pietro Sternai, an associate professor of geophysics at the University of Milano-Bicocca in Italy and the lead author of a new study, proposed and shared with Live Science. According to Sternai and his team, there is a piece of mantle sandwiched between the Indian crust and the Eurasian crust, the glue that holds together the Himalayas on its head.

This middle mantle portion is the reason why the mountain range continues to stand tall and grow taller day after day. Sternai and his team arrived at this conclusion after simulating the ancient plate collision on their computers. According to their model, when the Indian plate slipped beneath the Eurasian plate, it started to liquify. Blobs of this molten plate rose and clung, not to the base of the Eurasian plate, but to the lithosphere itself, the outer rigid crust of the planet. Today, this additional mantle fragment between the two plates offers all the mechanical strength and resistance needed by the mountains to stand as they are.

“You've got all the ingredients you need to uplift topography and sustain the weight of the Himalayas and Tibetan plateau," he explained. So, it’s not actually a crust-crust model, but rather a crust-mantle-crust model. Which means, the next time you plan a toilsome hike at Mount Everest, remember that it’s not just the hardy crust that is holding the mountain. The credit also goes to the squishy molten mantle that keeps the slippery relationship between the crusts going.