Image by Thisisbadri/Wikimedia Commons (CC BY-SA 4.0)
The Himalayas are the largest mountain range in the world. Extending from northern India to Pakistan and Nepal, they give us such indelible global features as K2 and Everest. But other than the formidable heights of these different peaks, the Himalayas also offer an unusual natural history.
Unlike the world’s many other mountain ranges — the Cascades, Rockies, Alps, etc. — the Himalayas were formed from an unusually high-speed collision. This collision was between a prehistoric India and what is today Asia. The speed of this collision (and the stubborn nature of the continents involved) culminated in the greatest mountain range we know today.
An Ancient World
Geologic forces are constantly pushing and pulling at the rock beneath our feet. Oftentimes, these processes are so forceful that they will uproot other continents to create mountains. When they do, we study the process through a discipline called orogeny (oro meaning “high ground” and geny meaning “birth”).
The orogeny of the Himalayas is different than that for most other mountains. This is true for several reasons — the first of which has to do with the continents that made them.
When we rewind the clock of geologic time back 250 million years, we see that the Indian and Eurasian plate (what Indian plate eventually crashed into) were entirely separate. They were, in fact, different components of a larger “supercontinent” called Pangea.
As time progressed and geologic forces beneath the Earth’s lithosphere (the hard rock that makes up Earth’s tectonic plates) continued to churn, Pangea began to break apart. This process continued, unabated, eventually isolating India as its own continental island.
Not long after India became its own, it began to move northward toward other fragments of the now-broken Pangea. At the time, it was moving through a large body of water called the Tethys Sea, which separated India from what would later become Europe and Asia. While it took another 150 million years for the Indian plate to finally make contact with Eurasia, the collision eventually did happen. When it did, it would create quite the splash.
There are many unique features about the Indian-Eurasian collision. The most salient of these was the speed with which the Indian plate traveled toward its northern destination. Usually, continents move at a pace of around 2.4 inches a year. India, conversely, moved at a mind-boggling eight inches per year. That’s unprecedented in terms of continental movement.
The reasons for this speed, which were once elusive, have begun to get elucidated by the likes of scientists. What they have discovered is that there was once a mantle plume beneath the Indian plate, which helped to accelerate the speed at which the plate moved.
A mantle plume is modest eruption of magma from the Earth’s mantle pressing up against the lithosphere that lies above. When this magma presses up against the lithosphere, it induces the plates that they create to move faster than they would otherwise. In this case, it induced the Indian plate to travel with unprecedented speed northward.
The speed with which the Indian plate traveled, when combined with the composition of the plates involved in the collision, induced the creation of the largest mountain range currently in existence.
Normally, when two tectonic plates collide, one will subduct beneath the other. The result is a melting of the subducted plate, which causes a rise in geologic material (i.e., mountains). This causes the growth of mountains more inland. This is how we got the Cascades, Rockies, and other mountain ranges across the world.
The Himalayas are different.
When the Indian and Eurasian plate collided, neither plate was less dense than the other. Because of this, the two stubbornly refused to sink. The result of this stalemate was a greater thrust of the two plates upward. And, as you could have guessed, giant mountains were the result.
And thus, the Himalayas were formed.