River Piracy Boosts Mount Everest’s Height #

Mount Everest, known as Chomolungma (‘Goddess Mother of the World’ in Tibetan), stands at 29,031.69 feet (8,848.86 meters) above sea level, making it one of Earth’s tallest mountains. The Himalayan mountain range, including Everest, began forming 40-50 million years ago when the India Plate and Eurasian Plate collided.

Recent GPS measurements have shown that Everest is growing at a rate of about 0.08 inches (2 millimeters) per year, which is twice the expected rate. New research suggests this extra growth is due to a geological event called river piracy.

Approximately 89,000 years ago, the Kosi River in the Himalayas captured part of the Arun River, a tributary. This river piracy set off a chain of geological events that reshaped the landscape. The strengthened Kosi system began eroding more rock from the valleys below Everest. As rocky mass crumbled away, other parts of the Himalayas shifted upward to compensate for the loss, a process known as isostatic rebound.

This rebound lifted Everest and two nearby peaks - Lhotse and Makalu - by an estimated 49 to 164 feet (15 to 50 meters). While the main driver of Everest’s height remains plate collision, this discovery adds a new dimension to understanding mountain formation.

The connection between river erosion and peak uplift has been studied in various locations worldwide. Usually, rivers and mountains reach an equilibrium where erosion and uplift balance each other. However, when a river suddenly changes course, it can dramatically alter this balance, triggering rapid erosion and subsequent mountain uplift through isostatic rebound.

The findings address two anomalies in the Himalayas: the unusual heights of Everest, Lhotse, and Makalu compared to neighboring peaks, and the unique path of the Arun River from southern Tibet towards the Kosi River in Nepal.

While some instances of river capture and landscape remodeling began millions of years ago, others are happening today. Evidence of ancient river capture can be seen around the edges of the Himalayas, where deep gorges were eroded, causing significant uplift in certain regions over millions of years.

The research team’s investigation began with questions about the unusual course of the Arun River and the discovery of ancient lake sediments in the Arun River Basin. Computer simulations suggested that river capture would have dramatically increased water flow in the Kosi’s lower segments, leading to deeper erosion and subsequent uplift of nearby peaks.

River capture can occur rapidly in geological terms, sometimes within just a few years or decades. A recent example was observed in Canada’s Yukon Territory, where glacier melt was rerouted from one river to another in just four years.

While Everest continues to grow due to these geological processes, it is also being worn down by extreme weather and glacier movement. The mountain’s future height will depend on the balance between these opposing forces.

Understanding the formation of iconic landscapes like Everest helps scientists grasp Earth’s dynamic evolution. As the planet faces changing climates and shifting weather patterns, this knowledge could aid in predicting how landscapes might evolve in the future.