60 Fun Facts About Avalanche

After an avalanche comes to rest, the debris holding a buried person is often likened to which material?

Concrete. The debris locks solid the instant it stops, so a buried person usually cannot move even a hand and has to be dug out by others.

What is the most common cause of natural avalanches?

Increased load from snowfall during storms. A quick deluge of new snow overloads the layers beneath until one gives way, so the riskiest time is during a storm and just after it.

Which of these supposed causes of an avalanche is actually a myth?

A loud shout. Swiss researchers calculated that sound presses on the snow at least a hundred times too weakly to matter, so it sets off avalanches, as one veteran forecaster put it, only in the movies.

What do avalanche forecasters dig into a slope to read a winter's snowfall layer by layer?

A snow pit. Its wall shows the whole winter stacked up like the layers of a cake, and tests on it reveal which layer is likely to give way.

Avalanche researcher André Roch famously warned skiers that the avalanche doesn't know you are what?

An expert. Roch, a Swiss pioneer of avalanche science, spoke from experience: he was caught in three avalanches himself, and his son was swept away by one while skiing with him and survived.

Roughly how fast can the fastest powder snow avalanches travel?

300 km/h. Most begin as an ordinary sliding slab, and when the drop is long enough so much snow is whirled into the air that it becomes a racing powder cloud.

Which avalanches are usually slower than most, yet leave very dense, destructive debris?

Wet snow avalanches. Rain or strong spring sunshine soaks the snowpack until it loses its strength, so they tend to release on their own in warm weather late in the season.

Most avalanches start on slopes about as steep as what?

A black diamond run. Slopes of roughly 30 to 45 degrees are gentle enough to hold deep snow yet steep enough for it to slide, and they are also the pitch backcountry skiers like best.

Why are big slab avalanches rare on mountain faces steeper than about 60 degrees?

New snow keeps sluffing off in small, frequent slides before a deep slab can build. Gentle slopes rarely release for the opposite reason: gravity cannot overcome the friction holding the snow in place.

What do avalanche forecasters call a gully or cliff that makes even a small slide far more dangerous?

A terrain trap. A gully funnels the debris into a deep pile instead of letting it fan out, so a slide too small to matter on an open slope can bury someone completely.

Which three primary elements of avalanches did Doug Fesler and Jill Fredston identify?

Terrain, weather and snowpack. In the triangle the pair drew for their 1984 handbook Snow Sense, terrain decides where a slide can run, weather builds and loads the snow, and the snowpack's layers decide whether it fails.

Where relative to a ridge does more snow accumulate, forming deep drifts and wind slabs?

In its lee. Wind slows as it crosses the crest and drops the snow it is carrying, so the sheltered side where you would hide from a gale is the one being loaded.

What do backcountry skiers call a convex slope that steepens as it drops away?

A rollover. Snow is stretched rather than squeezed where a slope bends over, which is why shallow, soft slabs tend to crack right at the roll.

What are the angular, poorly bonding snow crystals formed by a persistent strong temperature gradient called?

Depth hoar or facets. Skiers call it sugar snow because its grains refuse to stick together, and once it forms it can linger all season, letting a slope slide weeks after it was buried.

What is the overhanging lip of wind-packed snow that builds out from a ridge crest called?

A cornice. Some grow larger than a bus, and when one snaps off, its impact can set off a slab avalanche on the slope beneath.

What is the term for wind depositing snow parallel to a slope, forming slabs that are hard to spot?

Cross-loading. Wind blowing across a slope drops its snow into the gullies and hollows that run down it, so slabs can form in pockets far below the ridgeline.

What do avalanche forecasters call the sudden collapse of a buried snow layer under a person's weight?

A whumpf. The name copies the muffled thump of the layer giving way, and on a slope steep enough to slide the same collapse often releases a slab avalanche.

What are the three parts of an avalanche path?

Start zone, track and runout zone. Below the tree line the track often shows as a treeless stripe, because repeated slides strip the trees and stop them growing back.

What is the 'return period' of an avalanche path?

How often avalanches form there. Like a flood's return period, it is used to judge risk: small slides may run every winter, while planners keep buildings out of reach of the rare big ones.

Which type of terrain is highly unlikely to produce avalanches?

Dense forests. Closely spaced trunks anchor the snowpack and break up its layers, whereas scattered trees and boulders do the opposite, growing weak spots in the snow around them.

Since national records began in 1950, which US state has had the most avalanche deaths?

Colorado. Its high, dry Rockies get a thin, cold snowpack that grows weak, sugary layers, so slopes there can still be triggered long after a storm has passed.

Cold is rarely what kills someone buried by an avalanche; what causes most of the deaths?

Suffocation. A Canadian review of 204 deaths put it at three in four and trauma at nearly all the rest; buried victims run short of air long before they could freeze.

Who or what triggers about nine in ten avalanche accidents?

The victims' own group. The snowpack usually rests in balance until a person's weight collapses a weak layer beneath them, so most victims set off the very slide that buries them.

For about how long after burial do avalanche victims keep a better than 90% chance of survival?

15 minutes. A Swiss study of 422 buried skiers found survival falling from 92% then to about 30% by 35 minutes, so a victim's best hope is the companions already on the slope.

What is considered the minimum equipment for companion rescue?

Beacon, shovel and probe. The beacon's signal leads searchers to the right patch of snow, the probe pinpoints the person beneath it, and the shovel does the slowest job of all: digging.

What does an avalanche transceiver do all day while its wearer is simply skiing?

Sends out a constant radio pulse. Only after a burial do the others switch to search mode and home in on it, and because every brand shares one frequency, 457 kHz, any unit can find any other.

Skadi, the first effective avalanche transceiver, took its name from a ski-borne goddess of which mythology?

Norse. Skadi hunts on skis in the myths; the early device named after her simply made a tone in an earphone, and searchers walked toward wherever it grew loudest.

Why do ski patrols and highway crews fire explosives into loaded avalanche slopes?

To trigger slides while it's safe. Charges are thrown by hand, dropped from helicopters or fired from howitzers, so the snow comes down in small planned releases with nobody underneath.

What do ski patrols call tramping up and down a steep slope on foot to break up weak snow layers?

Boot-packing. It is the simplest avalanche control there is: crews walk a slope again and again as the snow builds, so weak layers are broken up before deeper snow can bury them.

Landscaped barriers that stop or deflect avalanches with their weight are called what?

Avalanche dams. Snow nets hold the snow in place high on the slope so that no slide begins, whereas a dam waits at the bottom to stop, split or steer one that is already moving.

A radar-based alarm system protects the only access road to which Swiss resort?

Zermatt. Two radars watch the avalanche gullies above the road, and within seconds of spotting a slide they drop the barriers and turn the traffic lights red.

What loads the snow block in a Rutschblock test?

A jumping skier. 'Rutsch' is German for slide: the tester steps onto the block, flexes, then jumps harder and harder, and the sooner it slides, the weaker the slope.

The European avalanche risk scale, adopted in 1993, runs from what to what?

1 to 5. The deadliest level is the middle one, 'considerable': Swiss records put about half of avalanche deaths there, far more than at the two top levels, which are forecast on only a few days a winter.

Avalanche airbags keep a skier on top through the effect that brings which nuts to the top of a shaken tin?

Brazil nuts. Shake any mix of grains and the biggest pieces work their way upward, so an inflated airbag turns its wearer into the largest 'nut' in the flowing snow.

America's deadliest avalanche swept two trains off a Cascade mountainside at Wellington in 1910, in which state?

Washington. The trains had waited nearly a week in blizzards below Stevens Pass when the slide hit after midnight, throwing them 150 feet downhill and killing 96 people.

Three days after Wellington, an avalanche killed 58 railway workers clearing the track at which Canadian pass?

Rogers. The crew was digging the line out from one slide near midnight when a second swept down from the opposite side of the valley and filled the trench they were working in.

Avalanches killed thousands of soldiers holding a mountain front between Italy and Austria during which war?

First World War. Both armies kept men on the high peaks through the winter, and in December 1916 avalanches killed thousands of them within days, some reportedly set off by shellfire.

A NASA orbiter has photographed avalanches in mid-fall on the polar cliffs of which other world?

Mars. In 2008 the HiRISE camera caught four at once pouring off a cliff near the north pole, each still trailing a cloud of ice and dust as it fell.

The 'Winter of Terror' of 1950-51, when avalanches killed more than 200 people, struck which mountain range?

The Alps. Two storm cycles each piled up metres of fresh snow within days, far more than the slopes could hold, and Austria suffered worst, losing 135 people.

Which US state capital ran on diesel generators for weeks in 2008 after avalanches wrecked its main power line?

Juneau. The slides destroyed three pylons carrying its hydroelectric supply, and for the weeks it took to rebuild them electricity prices in the Alaskan capital rose roughly fivefold.

The world's deadliest avalanche, in 1970, was triggered by an earthquake off which country?

Peru. The quake shook loose part of Huascaran, the country's highest peak, and the mass of ice and rock buried the town of Yungay, which was left untouched as a national cemetery.

What are people caught in a flowing avalanche taught to do to stay near the surface?

Swim hard. A person is denser than the flowing snow and sinks in it, so the advice is to fight upward the whole way down, using a backstroke with the feet pointing downhill.

An earthquake-triggered avalanche in 1990 wiped out a climbing camp on which Central Asian mountain?

Lenin. The earthquake struck deep beneath Afghanistan's Hindu Kush, hundreds of kilometres away, yet the slide it set off buried the camp and killed 43 climbers.

English borrowed the word 'avalanche' in the 18th century from which language?

French. Alpine dialects had an older word, something like 'lavanche', whose sounds were apparently swapped around under the pull of 'aval', a French word for downhill.

After the 1999 Montroc avalanche killed 12 people in their chalets, who received a suspended prison sentence?

The mayor of Chamonix. In July 2003 Michel Charlet was given a three-month suspended sentence over his handling of the days just before the slide, when the chalets were not evacuated.

The 1999 avalanche that killed 31 people in a village thought to be in a safe zone struck where?

Galtür, Austria. It struck the village's 'green zone', where homes needed no reinforcement, because the slide kept gathering fresh snow as it fell and ran farther than any on record there.

The 2017 Rigopiano avalanche in central Italy buried what kind of building, where survivors were found two days later?

A mountain hotel. Guests had gathered downstairs to be evacuated after a day of earthquakes when the snow hit; nine people, four of them children, were later pulled out alive from the wreckage.

In 2014 an avalanche killed 16 guides on which stretch of Everest's standard route?

The Khumbu Icefall. A huge block of ice broke off the slope above the guides as they readied the route for paying clients, and the surviving Sherpas then refused to work on Everest for the rest of the year.

In 2015 an earthquake sent a deadly avalanche through which part of Mount Everest?

Base Camp. The quake broke an ice cliff off the ridge beside the neighbouring peak Pumori, and the blast flattened the tents below on what was the deadliest day in Everest's history.

A huge chunk of which Italian glacier broke away in July 2022, killing 11 climbers below?

Marmolada. It gave way in a heatwave at the start of summer, after 10 °C was recorded at the summit and a dry winter had left the ice without its usual protective blanket of snow.

Barry, the rescue dog credited with saving some 40 lives in the early 1800s, worked from the hospice on which mountain pass?

Great St Bernard. A dog at the hospice has been named Barry in his honour ever since, but the famous brandy barrel is a myth, the monks say: their rescue dogs never wore one.

A long-term wildlife study found avalanches to be a leading cause of death for which North American animals?

Mountain goats. The steep ground that puts them out of reach of predators is also where avalanches run, and in some ranges snow slides kill more of them than predators do.

What do mountaineers call a tower or block of glacier ice that can topple without warning and start an ice avalanche?

A serac. The name is borrowed from an Alpine cheese, which a glacier shattered into such blocks was thought to resemble.

What is the ground temperature usually at the base of a snowpack?

Around 0 °C. A snowpack is warmest at the ground and coldest at its surface, and when the air is bitterly cold that contrast between top and bottom slowly weakens the snow in between.

During a run of sunny spring days and clear nights, when is avalanche danger usually at its lowest?

Early morning. A cold, clear night refreezes the day's meltwater into a strong crust, and the danger climbs again as the sun softens it; after a mild, cloudy night that respite may never come.

A 2021 study explaining the Dyatlov Pass hikers' deaths as a small avalanche borrowed its snow-simulation code from which animated film?

Frozen. Avalanche scientist Johan Gaume so admired the film's snow that he visited its animators and adapted their code, then showed how a small slab sliding onto the tent could cause the hikers' injuries.

What counts as a 'high additional load' on the snowpack under Europe's avalanche danger scale?

Two skiers close together. Their weight bears on the same patch of snow at once, whereas a party spaced at least ten metres apart loads the slope one person at a time.

Which future king narrowly escaped a 1988 avalanche at the Swiss resort of Klosters that killed a friend in his ski party?

Charles III. Then Prince of Wales, he was skiing off-piste with five others when the snow broke away above them; he got clear and helped dig for the two who were swept off, but Major Hugh Lindsay died.

Before electronic transceivers, what did ski mountaineers trail behind them so rescuers could trace them under avalanche debris?

A long red cord. It was tied to the wearer in the hope that a stretch would stay on the surface, and markers every metre or so showed rescuers which end led to the buried skier.

What is the vertical fracture wall at the top of a slab avalanche called?

The crown. Investigators go back to it afterwards, because the height of that wall of snow shows how thick the slab was when it broke away.