For over a hundred years, geologists have relied on Émile Argand’s influential theory to explain one of Earth’s grandest features—the Himalayan mountain range. His idea was elegant in its simplicity: as the Indian and Asian continental plates collided, their crusts thickened dramatically, folding and stacking to form the towering peaks of the Himalayas and the vast Tibetan Plateau. According to Argand, the sheer bulk of this doubled crust—estimated at 70 to 80 kilometers thick—was enough to support the massive elevation.
This vision of crustal thickening became the bedrock of geological understanding, inspiring textbooks, shaping research, and becoming the standard story of how continents collide. For decades, it stood largely unchallenged. But science is never static. It thrives on questioning, testing, and refining. Over the years, cracks began to appear in Argand’s model.
When the Puzzle Pieces Don’t Fit
The first doubts emerged from physics itself. Crust thicker than about 40 kilometers, scientists argued, should not be able to support a plateau as vast as Tibet without collapsing under its own weight. The Himalayan-Tibetan system, under Argand’s model, required nearly twice that thickness—something that seemed mechanically implausible.
Then came the whispers from the Earth itself. Seismic studies suggested that mantle rocks—normally buried far below—were appearing much closer to the surface than Argand’s framework could explain. Geochemical evidence reinforced the suspicion: Argand’s story, though beautiful, might not match the reality hidden beneath the mountains.
The Himalayas, it seemed, were keeping a deeper secret.
A New Lens Into the Deep Earth
In a recent study published in the journal Tectonics, researchers sought to peel back the mystery. Their approach was ambitious. Instead of relying solely on observation, they combined state-of-the-art computer simulations with real-world seismic and geochemical data.
They created more than 100 two-dimensional numerical models, tweaking the properties of crust and mantle, and then tested which scenarios best matched what scientists could actually measure under the Himalayas. Each simulation was like running a miniature Earth in fast forward, watching plates crash together, melt, and deform.
What emerged was a radically different vision—one that may rewrite how we understand the world’s tallest mountains.
The Crust-Mantle-Crust Sandwich
The simulations revealed that the collision between India and Asia did not merely produce a monstrously thick stack of crust. Instead, something more intricate occurred. As India plunged beneath Asia, its crust slid under not just Asian crust, but under the entire Asian lithosphere—crust and upper mantle together.
At those crushing depths, the Indian crust began to partially melt, softening into a buoyant layer. Rather than vanishing into Earth’s depths, pieces of this molten crust rose upward, lodging beneath the Asian mantle. The result was a geological “sandwich”: Indian crust below, Asian mantle in the middle, and Asian crust above.
This process, known as viscous underplating, suggests that it is not ultra-thick crust alone holding up the Himalayas, but the buoyant force of the underplated Indian crust, reinforced by the strength of Asian mantle above.
In other words, the Himalayas are not simply a colossal pile of crustal rock—they are the product of a dynamic partnership between buoyancy and rigidity, melt and strength, crust and mantle.
Why This Model Fits Better
This new theory does more than offer a fresh metaphor. It aligns with evidence that has puzzled geologists for decades. Seismic signals showing mantle rock closer to the surface now make sense: the Asian mantle sits sandwiched between layers of crust, exactly as the model predicts. Geochemical signatures of rocks exposed at the surface can also be explained by crustal material that melted and rose during underplating.
Crucially, the new model avoids the mechanical improbability of Argand’s ultra-thick crust. Instead of imagining a Himalayan system teetering on impossible foundations, we now see one supported by a more balanced and elegant mechanism.
Implications Beyond the Himalayas
If correct, this theory doesn’t just reframe the story of the Himalayas—it reshapes our understanding of mountain building everywhere. The mechanisms at play beneath Tibet could also be relevant to other continental collision zones, past and present.
It forces geologists to rethink debates about how crust flows within continents and about the strength of Earth’s lithosphere. Where earlier models emphasized the Asian crust’s dominance, this new vision highlights the buoyant Indian crust’s role in lifting and sustaining Earth’s mightiest peaks.
Perhaps most strikingly, the theory underscores the idea that mountain ranges are not static monuments but living systems, shaped by deep, dynamic interactions between layers of the Earth we cannot see.
The Emotional Weight of Mountains
The Himalayas inspire awe not only for their staggering height but for the mystery they embody. To stand before them is to feel the raw power of Earth’s forces, the clash of continents frozen in stone. For generations, they have been symbols of permanence. And yet, what science shows us is that even mountains are born, grow, and evolve from forces still active beneath our feet.
The new theory reminds us that beneath the timeless peaks lies a restless, molten, ever-shifting planet. It reveals that the Himalayas are not a finished masterpiece, but an ongoing story—a story of continents colliding, of crust melting and rising, of mantle rock giving strength to mountains that seem eternal.
A Future of Discovery
Science advances by challenging the comfortable truths of the past, and the Himalayas are no exception. Argand’s model, though flawed, laid the groundwork for generations of inquiry. The new crust-mantle-crust model doesn’t erase his contribution—it builds upon it, sharpening our view of reality.
As research moves toward even more detailed three-dimensional modeling, scientists will uncover further nuances. Each discovery will bring us closer to answering profound questions: How do mountains grow? How do continents endure? And how does the restless Earth sculpt landscapes that define entire civilizations?
For now, we can look at the Himalayas with fresh eyes. We can see not just peaks of stone, but a dynamic collaboration between hidden layers, a balance of strength and buoyancy, an unfolding symphony beneath the “Roof of the World.”
The Himalayas, it turns out, are not simply held up by thickened crust. They are held up by the restless creativity of the Earth itself.
More information: P. Sternai et al, Raising the Roof of the World: Intra‐Crustal Asian Mantle Supports the Himalayan‐Tibetan Orogen, Tectonics (2025). DOI: 10.1029/2025TC009057
