Why isn’t Everest taller if it ‘grows’ every year?

The Himalayas were formed about 60 million years ago when the continents of India and Eurasia collided. Since the bark of both has a similar density, neither of the two goes under the other. They collide and, so to speak, wrinkle, rising higher and higher. «That’s why they are called collision chains. The Pyrenees were also formed in this way,” explains Professor Apraiz. But if the convergence occurs between two plates of different densities, the denser one will slide underneath to enter the Earth’s mantle, generating large amounts of magma that give rise to “subduction chains”, which have great volcanic and seismic activity. This is what happens in the Andes or in the South Pacific, where the so-called ‘Pacific Ring of Fire’ is located, a strip of 40,000 kilometers that concentrates the largest number of volcanoes in the world.

Everest, like the rest of the mountains, has several ‘enemies’ that slow down its growth. One is Earth’s gravity. This causes it to flatten “just as a ball of bread dough slowly flattens when placed on a table,” explains Humphreys, who does not mention that it could be much worse: without going any further, the pressure on Venus is 90 times higher than that of the Earth, the equivalent of being one kilometer under the sea. The other is erosion. The wind, the rivers and, above all, the glaciers. These tongues of ice that rest on their walls pierce them slowly but inexorably. «They are like saws that wear down the mountains. “Glacial erosion creates a steep mountain which is then prone to landslides,” adds Humphreys. Both factors mean that “the higher a mountain is, the greater the pressure it suffers from gravity and the stronger the tendency to collapse. In the case of Everest, it could have risen higher but its south face seems unstable,” he continues.

The growth of volcanoes

The way that would have made possible a height even above ten kilometers would have been for Everest to be a volcano. These grow when they erupt. The lava accumulates on its walls as it cools, allowing them to gain height. This is how Mount Olympus, on Mars, has reached its colossal size, which with its 25 kilometers of altitude is the highest in the Solar System. This has an added advantage over terrestrial volcanoes. There are no tectonic plates on the Red Planet, which means that this giant will always have “the heat point” under its bowels, unlike what happens on Earth. «Our planet is the only one we know of that has plate tectonics. As these continue to move, there comes a time when the heat point moves. Thus one volcano ‘dies’ but others are generated,” corroborates the expert from the University of the Basque Country.

Now, even Olympus has limits to its growth. Its enormous height and gravity can prevent the magma from reaching the mouth of the volcano. “You can think of a volcano basically as a pipe that you’re trying to pump lava through. If it is too high, there may come a time when you do not have enough strength to make it reach its upper end,” explains Briony Horgan, a planetary scientist at Indiana University cited by journalist JoAnna Wendel. And that’s assuming it’s still active, because no activity has been detected recently.

The Himalayas, and with it Everest, will stop growing when India’s push against Southeast Asia stops. Until then, it will continue to gain height, but not too much.