What an avalanche is, how it kills, and the ten worst death tolls in recorded history.
Eight backcountry skiers are dead in the Sierra Nevada. A ninth is missing and presumed buried under a wall of snow over 100 yards in length near Castle Peak, above Lake Tahoe.
Six survivors owe their lives to iPhone satellite signals and rescue crews who skied two miles through conditions the Nevada County sheriff called “pretty horrific.”
This is the deadliest avalanche in modern California history, but will not be the last.
The group of fifteen — eleven clients and four guides from Blackbird Mountain Guides — had been finishing a three-day backcountry expedition from the Frog Lake huts, a popular destination tucked below Castle Peak at about 9,100 feet. They were heading back to the trailhead on Tuesday morning when someone in the group spotted the slide coming.
They were all close together. Most never had a chance.
What Is An Avalanche?
An avalanche is not simply snow falling off a mountain. It is a structural collapse.
Snow accumulates in layers over time. Each storm deposits a new blanket with its own density, temperature, and crystal structure. Between storms, the existing snowpack changes. Fluctuating temperatures force water vapor to migrate through the layers, creating what scientists call facets — tiny, angular crystals that stack like a house of dominoes.
When new snow loads onto that weak foundation — especially when combined with wind, which compresses and redistributes the weight unevenly — the structure reaches a tipping point.
A skier, a snowmobiler, sometimes nothing more than a gust crosses the slope, the weak layer collapses, and the slab above loses its grip.
What follows is physics at its most lethal. Hundreds of thousands of tons of snow accelerate downhill, reaching speeds that can exceed 100 miles per hour, dragging trees, rock, and ice with it. The debris does not settle like fresh powder. It sets like concrete. A buried person cannot move a millimeter. Breathing creates a small pocket of warm air that quickly ices over. The victim is effectively sealed inside a freezing, airless tomb.
Heinz Mueller, a Swiss mountain guide who survived two and a half hours buried under thirty feet of snow in a 1993 avalanche in the Alps, described the sensation: “It is like breathing into a plastic bag while encased in concrete. You cannot hear rescuers above you. You cannot signal. You wait, and your body temperature drops, and the window closes.”
In the Sierra Nevada this week, the conditions were textbook. A prolonged dry spell in late January and early February had allowed the existing snowpack to deteriorate into that dangerous faceted layer. Fresh snow arrived on February 10, followed by freezing rain that added weight. Then a massive atmospheric river slammed into California. Nearly three feet of snow accumulated at Donner Peak in 48 hours. Wind gusts exceeded 100 miles per hour along the ridgelines. Avalanche warnings had been issued since Sunday.
The Sierra Avalanche Center rated the danger as high. Blackbird Mountain Guides posted a video on Sunday acknowledging that a weak snow layer in the area could lead to “unpredictable avalanches.” The group went out anyway.
An average of 27 people die in avalanches each year in the United States. Most of those avalanches are triggered by the victims themselves. The rare ones — the ones triggered by nature alone — are, as one expert put it, “just a matter of bad luck, just being in the wrong place at the wrong time.”
The Sierra Nevada slide is a small event measured against the full history of avalanche catastrophe. Mountains have been burying human beings for as long as human beings have been climbing them.
The Ten Deadliest Avalanches in Recorded History
The scale of destruction an avalanche can achieve is almost incomprehensible. Here are the ten worst.
1. Huascarán, Peru — May 31, 1970 — Estimated 22,000 dead.
An undersea earthquake destabilized the north face of Mount Huascarán in the Andes. A chunk of glacier 910 meters wide broke free and roared down the mountain at nearly 200 miles per hour, picking up rock, dirt, and water as it descended. The towns of Yungay and Ranrahirca were obliterated. More than ten villages were destroyed. Estimates of the dead range from 22,000 to as high as 70,000. It remains the deadliest single avalanche event in human history.
2. White Friday, Italian Alps — December 13, 1916 — Estimated 2,000 to 10,000 dead.
During World War I, Austro-Hungarian and Italian soldiers were dug into positions on and around Monte Marmolada in the Dolomites during the heaviest snowfall of the twentieth century in the Tyrolean Alps. On December 13, a series of massive avalanches struck military encampments on both sides. The single deadliest slide buried the barracks of the 1st Battalion, Kaiserschützen Regiment III, killing between 270 and 330 soldiers in one stroke. Over the following days, avalanche after avalanche swept the front. Recent scholarship puts the combined toll at roughly 2,000. Older estimates, long repeated but now disputed, claimed 10,000.
3. Huascarán, Peru — January 10, 1962 — Approximately 4,000 dead.
Eight years before the earthquake-triggered catastrophe, a massive chunk of glacier broke from the same mountain and buried several villages in the Rio Santa Valley below.
4. Winter of Terror, Alps — January to March 1951 — 265 dead
A three-month siege of extreme snowfall along the Austrian-Swiss alpine border produced 649 recorded avalanches. Nearly 15 feet of snow fell in a three-day span in some areas. Over 265 people were killed, 500 cattle buried, and 900 buildings destroyed. The disaster transformed avalanche science and led to modern forecasting systems across Europe.
5. Afghanistan — February 2015 — Approximately 310 dead
A series of avalanches struck four northeastern provinces over four days, with the Panjshir Province — 60 miles northeast of Kabul — suffering the worst damage. Over 100 homes were destroyed. Roads were blocked, power was cut, and rescue efforts were crippled by continuing storms.
6. Lahual Valley, India — March 6, 1979 — Approximately 254 dead. Intense snowstorms triggered avalanches that buried villages in the Lahual Valley under nearly 20 feet of snow.
7. Afghanistan — February 2012 — 201 dead. Another devastating series of avalanches across Afghanistan’s mountainous provinces in a country where high-altitude communities remain perpetually vulnerable.
8. Siachen Glacier, Pakistan — April 7, 2012 — 138 dead. An avalanche struck the Gayatri Military Base in the disputed Siachen region, killing soldiers and civilian employees of the Northern Light Battalion. The disaster intensified international pressure on India and Pakistan to resolve the Siachen dispute.
9. Kolka Glacier, Russia — September 20, 2002 — 125 dead. A partial collapse of the Kolka glacier on the northern slopes of the Kazbek massif in North Ossetia sent a wall of ice and debris through the valley, burying the village of Nijni Karmadon. Among the dead was a 27-person film crew, including the prominent Russian actor Sergei Bodrov Jr.
10. Wellington, Washington — March 1, 1910 — 96 dead. The deadliest avalanche in United States history. Two Great Northern Railway passenger trains had been stranded for days in heavy snow near the town of Wellington in the Cascade Mountains. An avalanche swept the trains off the tracks and into a gorge 150 feet below. Some passengers had walked to town before the slide, saving their lives. The disaster led to the construction of the longest railroad tunnel in North America.
What the Mountain Teaches
Before this week, the deadliest avalanche in California history was the 1982 Alpine Meadows disaster, which killed seven people at a ski resort near Lake Tahoe. A 22-year-old ski-lift operator named Anna Conrad survived five days buried in a collapsed building before rescue dogs found her. “You just keep pushing,” she said from her hospital bed, “knowing that eventually, sometime, you’re going to make it.”
Eight people near Castle Peak did not make it. The mountain does not negotiate. It does not care about experience, equipment, or intention. The backcountry is beautiful, as Sheriff Shannan Moon said. But to Mother Nature, it doesn’t seem to matter.
The bodies remain on the mountain tonight. More snow is falling. Rescue crews cannot go back until the weather breaks and the avalanche risk subsides. Eighteen more inches are expected on the ridgelines by Friday.
The ninth skier has not been found. Officials say the conditions are not survivable.
The mountain keeps what it takes.
