The mountain grows about 4mm per year due to tectonic uplift. But GPS measurements show the 2015 Nepal earthquake dropped it by 2.5cm in seconds, the first time a mountain was caught shrinking.
Rdevany, CC BY-SA 3.0, via Wikimedia Commons
A mountain in motion
Mount Everest exists because of a geological collision in slow motion. The Indian tectonic plate is sliding northwards into the Eurasian plate at a rate of about two centimeters per year. This immense pressure forces the Earth's crust to buckle and rise, creating the Himalayan mountain range. This process of tectonic uplift pushes Everest's rock upwards by about 4 millimeters annually. The mountain also moves horizontally, drifting northeast at about 4 centimeters per year.
This constant, gradual growth is the mountain's default state. For decades, surveyors and scientists focused on refining their measurements to account for this slow rise. Early efforts, like the British Great Trigonometrical Survey in the 1850s, used theodolites from over 150 kilometers away to calculate the height. They arrived at a figure of 8,840 meters (29,002 feet). A 1954 Survey of India measurement of 8,848 meters became the widely accepted official height for many years.
An earthquake's impact
On April 25, 2015, a magnitude 7.8 earthquake struck Nepal, with its epicenter just 60 kilometers northwest of Kathmandu. The event, known as the Gorkha earthquake, was a sudden release of the accumulated stress between the Indian and Eurasian plates. While the quake caused widespread devastation and triggered a deadly avalanche on Everest that killed at least 17 people at Base Camp, it also had a direct, measurable effect on the mountain itself.
Satellite data and GPS readings from a station near the summit indicated that the planet's highest peak had shrunk. The earthquake caused the rock to relax and subside, resulting in a loss of height of about 2.5 centimeters, or one inch. This event marked a rare moment where the forces of an earthquake momentarily overpowered the long-term tectonic uplift. The same earthquake also shifted the mountain about 3 centimeters to the southwest, reversing its usual northeasterly drift.
The earthquake prompted a new effort to definitively measure the mountain. In a joint project, survey teams from Nepal and China ascended the peak in 2019 and 2020. They used a combination of modern and traditional techniques. A GNSS (Global Navigation Satellite System) receiver was placed on the summit to communicate with GPS and Beidou satellites, while ground-penetrating radar measured the depth of the snow and ice cap. Simultaneously, surveyors at surrounding ground stations took measurements using laser theodolites.
On December 8, 2020, the two countries jointly announced the new official height: 8,848.86 meters (29,031.7 feet). This figure, which includes the snowpack, is now the globally accepted elevation and reflects the interaction between steady growth and sudden geological shifts.
💡Fun Facts
The rock at Mount Everest's summit is Ordovician limestone, formed from the fossilized remains of marine creatures that lived in a shallow sea around 450 million years ago.
The first measurement in 1856 calculated the height as exactly 29,000 feet, but it was publicly declared as 29,002 feet to avoid the impression that the number was just a rounded estimate.
The mountain was first identified as the world's highest peak in 1852 by Indian mathematician and surveyor Radhanath Sikdar.
The peak is named after Sir George Everest, a former Surveyor General of India, though he had no direct involvement in its discovery as the world's highest point.
The mountain is accessible during the main climbing seasons, typically March-May and September-November. The surrounding Sagarmatha National Park has regular hours.
Admission
Accessing the mountain requires expensive climbing permits ($11,000+ per person) and numerous other fees. Trekking within the national park also requires permits.
Accessibility
The terrain is extremely rugged. Reaching Base Camp requires a multi-day trek at high altitude. The summit is only accessible to highly experienced and well-equipped mountaineers.
