The 2015 Mount Everest avalanche was triggered by a magnitude 7.8 earthquake that struck Nepal at 11:56 local time on April 25, 2015. The quake, with its epicenter about 67 km northeast of Bharatpur at a shallow depth of just 8.2 km, rattled glaciers and ice formations along a ridge west of Everest, sending a massive wall of ice, snow, and rock into South Base Camp. It killed at least 18 climbers and Sherpas on the mountain, with over 70 more injured, making it the deadliest single event in Everest’s history at that time.
The Earthquake That Started It
The 7.8 magnitude quake was the strongest ever recorded in the region. Its shallow depth, only 8.2 km below the surface, meant the shaking was intense and focused. Across Nepal, the earthquake killed more than 5,200 people in the days that followed, flattening buildings and cutting off entire villages. But on Everest, the consequences arrived in a different form: the violent shaking destabilized hanging glaciers and ice formations on the ridgeline just west of the summit, particularly on and around Mount Pumori, which overlooks Base Camp.
An estimated 1,000 climbers and support staff were on the mountain that day. Late April is peak climbing season, and Base Camp was crowded with expedition teams preparing for summit attempts. The timing could hardly have been worse.
How the Avalanche Reached Base Camp
The earthquake shook loose enormous volumes of ice and snow from the ridge west of Everest. This debris accelerated downhill toward South Base Camp, gathering mass and speed. But the avalanche itself was only part of what hit. Research from the University of Toronto, based on data from a weather station near Base Camp, revealed that a massive plume of snow and ice crystals accompanied the slide, plunging the area into near-total darkness for three to four minutes as the cloud blocked out sunlight.
The weather station also captured something unusual about the wind patterns. Rather than a single blast moving in one direction, the instruments recorded chaotic, gusting winds that shifted direction rapidly. Researchers interpreted this as the turbulent wind field created by a powder snow avalanche, a type of avalanche where airborne snow and ice move almost like a fast-moving storm rather than a simple downhill slide. This chaotic blast of wind, snow, and debris is what tore through the tents and structures at Base Camp.
Some researchers have proposed that the earthquake may have triggered not one avalanche but a swarm of smaller avalanches from multiple points along the ridge, all converging on Base Camp in rapid succession. This would help explain the variable wind directions and the wide area of destruction.
The Toll at Base Camp
The avalanche killed at least 18 people at Base Camp, including both Sherpas and international climbers. Some sources place the total mountain death toll at 22 when accounting for casualties at other points on Everest. More than 70 people were injured, many seriously enough to require evacuation by helicopter.
Rescue operations were complicated by the fact that Nepal itself was in crisis. Roads were destroyed, hospitals were overwhelmed, and aftershocks continued. Despite this, an ad hoc rescue chain formed at Base Camp within hours. Climbers and expedition doctors triaged the wounded on-site, and the next day helicopters began ferrying injured patients down to Pheriche at 4,300 meters, where the nearest undamaged medical clinic operated. From there, patients were flown to the small hospital at Lukla and then onward to Kathmandu for definitive care. The entire evacuation from Base Camp to the capital took less than 30 hours, a remarkable feat given the circumstances.
Why Everest Was So Vulnerable
South Base Camp sits at roughly 5,300 meters on the Khumbu Glacier, directly below steep terrain loaded with ice. In normal conditions, the primary hazard comes from the Khumbu Icefall, a slow-moving but unstable stretch of glacier between Base Camp and Camp I where house-sized blocks of ice (called seracs) can collapse without warning. Just one year earlier, in April 2014, a serac collapse in the Icefall killed 16 Sherpas in what was then the mountain’s worst single disaster.
That 2014 avalanche had no earthquake trigger. It was simply gravity acting on an unstable ice formation. The 2015 event was fundamentally different: a powerful seismic shock destabilized ice across a broad area all at once, producing a much larger and more widespread avalanche that reached all the way to Base Camp rather than being confined to the Icefall. The scale of destruction was something no one at Base Camp had planned for, because an earthquake of that magnitude had not struck during climbing season in living memory.
The End of the 2015 Season
Within days, the climbing season was over. The Tibetan Mountaineering Association officially closed all 8,000-meter peaks in Tibet, and operations on the Nepal side of Everest shut down as well. Expedition teams that had spent months preparing and acclimatizing found themselves evacuating instead. As one expedition doctor wrote from Base Camp, “Hopes of continuing the climb gradually morphed into a strange emotional limbo of conflicting desires and the realization that extraneous forces would probably call the last shot.”
For the second consecutive year, no climbers summited Everest from the south side. The back-to-back disasters of 2014 and 2015 forced a broader reckoning within the mountaineering community about the risks of concentrating so many people in such an exposed location, and about the safety infrastructure available when things go wrong at extreme altitude.