Why the Mount Everest Keeps Growing

Mount Everest, at 8,849 meters above sea level, stands as the highest peak on Earth, towering over the surrounding Himalayan mountains. Despite the mountain’s prominence, the mechanisms behind its height and continuous growth remain a subject of scientific inquiry. A recent study published in Nature Geoscience sheds light on one of the factors contributing to Everest’s towering height, suggesting that erosion from a nearby river network has triggered an uplift effect, adding to the mountain’s elevation over thousands of years.

One of the key contributors to Everest’s height is the process known as isostatic rebound. This phenomenon occurs when the Earth’s crust loses mass due to erosion, causing the underlying mantle to push upwards, as the pressure from the liquid mantle below becomes greater than the downward force of gravity. In Everest’s case, erosion caused by the Arun River has played a significant role. Located about 75 kilometers from the mountain, this river has been carving out a gorge, gradually removing rock and soil over time. This loss of material has caused Everest to rebound upwards by as much as 2 millimeters annually, resulting in an estimated height increase of between 15 and 50 meters over the past 89,000 years.

The study, led by researchers from the University of California and the China University of Geosciences, attributes part of Everest’s continued growth to the merging of the Arun and Kosi rivers around 89,000 years ago. This event, known as drainage piracy, caused the Arun River to reroute and join the Kosi River system, which increased the erosive power of the rivers. As more material was washed away, Everest and neighboring peaks experienced isostatic rebound, pushing their heights even higher.

Co-author Dr. Adam Smith of University College London (UCL) explains that this discovery highlights the dynamic relationship between erosion and mountain growth. “Our research shows that as the nearby river system cuts deeper, the loss of material is causing the mountain to spring further upwards,” said Smith. The impact of this process is not limited to Everest alone. Neighboring peaks, such as Lhotse and Makalu, the world’s fourth and fifth highest mountains, respectively, also experience uplift due to this phenomenon.

While erosion-driven isostatic rebound explains part of Everest’s height, the primary driver behind the growth of the mountain range is tectonic activity. The Himalayas were formed as a result of the ongoing collision between the Indian and Eurasian tectonic plates. This collision causes the Earth’s crust to buckle and rise, forming the towering peaks we see today. Deep beneath Everest, the megathrust fault—a region where the Indian plate slides beneath the Eurasian plate—regularly ruptures, causing earthquakes that further push the mountain upwards.

Co-author Dr. Matthew Fox (UCL Earth Sciences) explains that the frequent seismic activity in this region plays a critical role in maintaining Everest’s height. “Mount Everest and its neighboring peaks are growing because the isostatic rebound is raising them up faster than erosion is wearing them down,” said Fox. These tectonic processes, combined with isostatic rebound, help Everest maintain its status as the tallest peak in the Himalayas.

Interestingly, the portion of the megathrust fault beneath Everest is more active compared to other sections of the fault line, breaking every few centuries. Each rupture in the fault pushes Everest higher, explaining why the mountain continues to rise while other peaks in quieter sections of the fault do not experience the same level of uplift.

The Arun River has long puzzled geologists due to its unusual course, which cuts through the highest mountain range on Earth. Researchers believe that the river’s current path is the result of a dramatic event in the past, when it merged with another river system through the process of river capture. This event likely occurred during a time of flooding, causing the Arun to erode its way through the mountains and join the Kosi River. This rerouting increased the erosion rates in the region, contributing to the isostatic rebound that has elevated Everest’s height.

The study’s findings are supported by models that simulate the capture event and the subsequent erosion, which have increased the Arun River’s capacity to carry away sediment. By removing vast amounts of material, the river allowed the Earth’s crust to rise, leading to an overall uplift of the mountains. However, some scientists, such as geologist Peter van der Beek of the University of Potsdam, caution that the timing of this river capture event remains uncertain, as the models used to estimate it are based on simplified assumptions of river behavior.

Estimating the exact contributions of different factors to Everest’s growth is complicated. While isostatic rebound and tectonic activity are well-established drivers, other elements, such as erosion rates and the effects of seismic activity, add complexity to the process. For instance, large earthquakes, such as the magnitude-7.8 earthquake in Nepal in 2015, can cause the mountain to temporarily subside. Over long periods, these quakes can alter the overall height of the mountains, making it difficult to determine the precise impact of each event.

Geologists also recognize that rivers like the Arun contribute to reducing mountain heights through erosion. As rivers transport material away from the peaks, they shape the surrounding landscape, lowering the height of the mountains in some areas while contributing to uplift in others.

The growth of Mount Everest is a complex interplay of forces, including tectonic uplift, seismic activity, and the effects of erosion and isostatic rebound. While the Arun River’s erosion has contributed to Everest’s height increase, the mountain’s ongoing growth is primarily driven by tectonic processes beneath the surface. As researchers continue to study the forces shaping the Himalayas, the exact mechanisms behind Everest’s towering height will become clearer, offering new insights into the dynamic processes that govern Earth’s surface.