Why is Mount Everest so big? New study highlights river of injustice, but deeper forces are at work

Mount Everest (also known as Chomolungma or Sagarmatha) is famous for being the tallest mountain in the Himalayas, and indeed on Earth. but why?

At 8,849 meters above sea level, Mount Everest is about 250 meters higher than the other great mountains of the Himalayas. They also grow by about 2 mm each year, which is roughly twice the long-term average growth rate.

In a paper published in Nature Geoscience, a team of Chinese and British scientists say that Everest’s unusual height and growth is influenced by the Arun River, which flows through the Himalayas. They argue that about 90,000 years ago, the river changed its course, eroding the rock that was pressing down on Everest, and the mountain rose in response by some 15 to 50 meters.

Although the authors argue for the contribution of rivers, they acknowledge that the “fundamental cause” of the peak’s size is the tectonic movements that form the mountain. To understand what’s going on, we need to understand the forces that created the Himalayas in the first place and the movements that allowed them to grow so high.

mass of tibet

In the 19th century, British surveyors showed that the southern boundary of the Himalayas traced an arc that corresponded exactly to a small circle on Earth. This is pretty amazing.

The only reasonable way you can explain it is if you have the Eurasian tectonic plate to the north, the Indian plate to the south, and in between is a viscous mass (Tibet) that spreads southward while slowly collapsing due to gravity.

The depths of the Tibetan Plateau are like hot syrup, and the cold upper crust must be exhibiting faults and earthquakes, swept away by the slow northward movement of the Indian tectonic plate. The exact nature and depth of this hot syrup is debated, with geologists variously comparing it to crème brûlée or a jelly sandwich.

Overall, the India-Eurasia collision is characterized by a “mega-fault” in which the Indian plate gradually slides beneath the Eurasian plate. The entire giant thrust does not move at the same time. Generally, in a series of “upthrust earthquakes”, the Earth tilts forward little by little.

Narrow bands of these thrust earthquakes are found where the spreading mass of Tibet meets India. What happens in that narrow band ultimately determines the height of the world’s highest mountain.

How do mountains rise and sink?

Why is the Tibetan plateau north of Everest so flat, but next to this narrow band of earthquakes are mountains where the collapsing mass connects with the advancing Indian subcontinent?

The answer lies in how to support the mass of the mountain.

Imagine the pile is a pile of debris piled up on a thin plastic table. Since the top board does not have any inherent strength, it will sag downward, causing a pile of debris to sink. Just like an iceberg, only part of the chunk sticks out.

Now imagine that there is a thick, sturdy board at the end of the table. Here, the rubble pile is supported by the bending strength of the plates, allowing it to rise much higher than the ground. Therefore, the mountains can be much higher here. This is what happens when one tectonic plate slides over another as the descending plate creates a more powerful region.

Naturally, there is a balance. When the movement of plates causes earthquakes, mountain peaks break apart and huge avalanches move the crumbled rock into adjacent river systems.

This debris fall may reduce the absolute height of the mountain, as well as its relative height compared to adjacent valleys, but this is dependent on how far the river moves the debris downstream. It depends on how efficiently you move it.

Then, as this chunk of rock moves downstream, the upstream area becomes somewhat lighter. For our plastic table model, one might expect the table surface to have less deflection and the rubble apex to be slightly higher.

This is what a new study claims, but it’s basically earthquakes that push mountains up. When giant thrusts rupture where tectonic plates meet, mountains rise. However, how high a mountain rises depends on the strength of the rock that supports it below.

What is special about Everest?

The important question (as indeed the authors acknowledge) is why Everest stands out.

The boundary between collapsing Tibet and advancing India is demarcated by a huge megalithic fault. Some parts of this fault have remained unbroken for a very long time, perhaps centuries or more. These areas can have a lot of strain built up, and when they eventually break, the consequences can be disastrous.

However, the section of the giant thrust beneath Everest seems to be destroyed periodically, perhaps once or twice a century. The last major earthquake there caused partial destruction of the existing one.

With each break, Everest can get a little higher. Therefore, it is no wonder that compared to mountain peaks located in the quiet part of the giant thrust, Everest is able to maintain its advantage.

It’s entirely possible that ferocious rivers influence Everest’s size, as a new study suggests, but much of the mountain’s height is due to the pattern of earthquakes along the Himalayan fault. It still seems likely.

The challenge for the scientists involved is how to separate the individual contributions to height from the various factors. One is rebound erosion, new research suggests, but tectonic movements such as the movement of the central thrust and the slow creep of the southern Tibetan fault beneath which earth’s highest peaks were excavated There is also.

This article is republished from The Conversation under a Creative Commons license. Read the original article.