What makes a mountain grow, and what keeps it from reaching unimaginable heights? Mount Everest, rising 8,848.86 metres above sea level, offers a case study in the interplay of tectonics, erosion, climate, and state-of-the-art measurement technology-skirting an intricate dance of forces that has been unfolding for tens of millions of years.
The origin of Everest lies in a colossal tectonic collision. About 200 million years ago, the supercontinent Pangea fractured, sending the Indian plate drifting northward across the Tethys Ocean. This plate moved at geologically rapid speeds-nearly 9 metres per century-until, about 45-50 million years ago, it slammed into Eurasia. The dense oceanic crust beneath the Tethys was subducted, scraping limestone and sediments from the seabed and crumpling them into the rising Himalayas. Unlike oceanic crust, the buoyant continental plate resisted sinking, forcing the surface to buckle and thicken, creating a mountain chain that still ascends today. India continues to push northward by roughly 5 cm annually, giving Everest an uplift of about 4 mm per year, although neighbouring peaks such as Nanga Parbat grow even faster.
This tectonic rise is complicated by erosion. Wind, rain, avalanches, and rivers gnaw at Everest’s flanks, sometimes cutting deep gorges at rates of 4–8 mm per year. Glaciers contribute their own abrasive power, dragging rock fragments across the surface in a sandpaper-like process. In Alaska’s Saint Elias Mountains, scientists have studied how glacier thickness and movement accelerate erosion, offering analogues for Everest’s slow battle between uplift and decay.
A remarkable twist in Everest’s growth story comes from the nearby Arun River. Geological modeling indicates that about 89,000 years ago, the Arun captured another Tibetan river in a process known as river piracy. This had the effect of increasing its erosive power, carving away an immense volume of rock and soil. The loss of that mass triggered isostatic rebound in which the crust flexes upward much like a boat rising when cargo is removed. The result has been to add an estimated 15–50 metres to Everest’s height-about 10% of its current annual uplift-and similarly affects neighbors Lhotse and Makalu.
Now, climate change is tilting the balance. In just 25 years, the South Col Glacier, near Everest’s summit, has lost 55 metres of thickness, melting up to 80 times faster than the centuries it took to form. As snowpack thins, the underlying ice absorbs more solar radiation, accelerating melt and sublimation. This is leaving more bare rock exposed to weathering, potentially increasing erosion and making climbing routes even more hazardous. According to researchers, glacier retreat in the Himalayas could be destabilizing slopes, setting off more avalanches, and even threatening base camps.
It calls for formidable logistical and technical challenges to measure Everest’s height with modern precision. Early surveys in the 19th century, using trigonometry-gauging angles from distant peaks, were used. Today, expeditions deploy GNSS receivers capable of millimetre accuracy, along with GPR to calculate snow and ice thickness. In 2019, Nepal’s surveyors carried lightweight GNSS units-just over 1 kg-and a specially designed tripod to the summit, recording for over an hour in temperatures near -26°C. GPR scans revealed about 4 meters of snow and ice atop the rock.
These measurements are tied to refined geodetic reference frameworks, requiring extensive networks of survey marks, gravity measurements, and temporary Continuous Operating Reference Stations (CORS) at high altitudes. Nepal’s campaign involved 298 survey marks and eight CORS stations, many installed by helicopter. Processing GNSS data from multiple satellite constellations-GPS, GLONASS, Galileo, and BeiDou-guaranteed robust results despite the short summit window.
Even the definition of “height” is complicated: Sea level depends on gravity pulling in and the general shape of Earth, making orthometric heights dependent upon accurate models of the geoid. Measured from Earth’s centre, Ecuador’s Chimborazo outdoes Everest at 10,920 metres; measured from the ocean floor, Hawaii’s Mauna Kea takes the record at over 10,000 metres. Off Earth, Mars’s Olympus Mons towers above them all at 21 km high and 624 km wide, its incredible size made possible by low gravity and the absence of plate tectonics that allowed lava flows to build up unchecked.
Everest will never rival Olympus Mons. Active weather systems on Earth, abundant water, and eventual mantle cooling prevent the building of mountains of such scale. At some point, [the mountain] becomes so steep that it’s unstable and chunks start falling off, says Aurora Elmore, a geologist who helped install the world’s highest weather station on Everest. For now, tectonics, erosion, river capture, and climate change will continue their tug-of-war, subtly reshaping the summit that remains an icon of human endurance and scientific curiosity.
