60 Fun Facts About Avalanche

What are the two general forms of avalanche?

Slabs of tightly packed snow release when a weak layer beneath collapses; loose snow avalanches start from a point.

What is the most common cause of natural avalanches?

Melting from solar radiation is the second-largest cause; contrary to legend, sound pressure is far too small to trigger one.

Can a loud sound trigger an avalanche?

Skiers, snowmobiles and explosives are real artificial triggers.

Slab avalanches account for roughly what share of avalanche deaths?

Slabs can range from a few centimetres to three metres thick.

What is the fracture at the bottom of a slab avalanche called?

The crown fracture is at the top of the start zone and the flank fractures on the sides.

Powder snow avalanches can exceed what speed?

They can carry a million tons of snow and even run uphill for short distances.

Wet snow avalanches typically travel at what speed?

They are slow but enormously destructive because of their mass and density.

An avalanche's starting point typically occurs on a slope of what angle?

The track usually runs at 20-30 degrees and the runout zone below 20.

At what slope angle are human-triggered avalanches most frequent?

Slopes flatter than 25 or steeper than 60 degrees see fewer avalanches.

What is the rule of thumb about which slopes can avalanche?

Normalized for use, hazard rises uniformly with slope angle regardless of exposure direction.

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

Terrain is where, weather creates the snowpack, and snowpack is the structure that fails.

Where relative to a ridge does more snow accumulate, along with wind slabs and cornices?

Windward slopes are usually much shallower.

Which shape of slope is less stable, because of the gap between snow's tensile and compressive strength?

The difference lies in the disparity between snow's tensile and compressive strength.

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

They form when the gradient exceeds 10 °C per vertical metre for more than a day and become a persistent weak layer.

What do large, angular crystals in the snowpack indicate?

They have fewer bonds per unit volume than small rounded crystals that pack tightly.

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

Top-loading occurs when wind blows over a summit and deposits snow down the lee side.

When do most avalanches happen?

Rain acts like heavy snowfall, adding load and lubricating layers.

What are the three parts of an avalanche path?

The debris deposit is the accumulated snow at rest in the runout; trim lines mark paths through forest.

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

Many small slides run each year without covering the path's full length.

Which type of terrain is highly unlikely to produce avalanches?

Full-depth avalanches are actually more common on smooth ground like grass or rock.

On average, how many people die in avalanches each winter in the United States?

From 1950-51 to 2020-21, 1,169 people died in US avalanches.

Globally, about how many people die in avalanches each year, according to a 2001 report?

People caught in avalanches die from suffocation, trauma or hypothermia.

A 1996 study found what share of recreational-setting avalanches were caused by the victims themselves?

Accidents in residential, industrial and transport settings were all due to natural avalanches.

A Swiss study of buried skiers found survival drops from 92% within 15 minutes to what after 35 minutes?

Chances are near zero after two hours, when victims die of injuries or hypothermia.

What is considered the minimum equipment for companion rescue?

France's ANENA also recommends Recco reflectors for off-piste skiers.

Avalanche transceivers operate on which international standard frequency?

It was adopted in 1986; early units transmitted at 2.275 kHz.

The first effective avalanche transceiver, sold from 1971, carried what brand name?

John Lawton invented it at Cornell Aeronautical Laboratory; the name comes from the Norse goddess Skaði.

Explosive avalanche control charges may be delivered by which of these?

Hand-tossed charges, Gazex concussion lines and air cannons are also used.

What is the simplest active preventive measure against avalanches?

Boot-packing, ski-cutting and machine grooming all disrupt weak layers.

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

Rigid steel or concrete snow fences are effective but expensive and unsightly.

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

It closes barriers and traffic lights within seconds of detecting a slide.

The Rutschblock test isolates a block of snow how wide?

'Rutsch' means slide in German; the result is rated on a seven-step scale.

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

In France most deaths occur at levels 3 and 4; in Switzerland at 2 and 3.

On the European scale, what incline defines a 'steep' slope?

'Very steep' is over 35° and 'extremely steep' over 40°.

The 1910 Wellington avalanche, the deadliest in US history, killed how many people?

It struck two Great Northern Railway trains at Stevens Pass and threw them 150 feet into the Tye River valley.

Three days after Wellington, 62 railroad workers died in an avalanche at which Canadian pass?

Both March 1910 disasters struck the Cascade and Selkirk ranges.

An estimated how many soldiers died in avalanches on the Austrian-Italian front in the First World War?

Many were triggered by artillery fire; some 10,000 died in December 1916 alone.

The deadliest 'White Friday' avalanche of December 1916 struck barracks on which mountain?

It killed 270 soldiers; the event is commemorated each 13 December, Saint Lucy's Day.

The 'Winter of Terror' of 1950-51 saw about how many avalanches across the Alps in three months?

They killed around 265 people, with Austria suffering the most, and Andermatt was hit by six avalanches in an hour.

The Blons avalanches of January 1954 killed 125 people in which Austrian state?

Fifty-seven died in the village of Blons itself.

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

Rock, ice and snow from Huascarán buried the town of Yungay; the toll is put at 66,794 to 70,000.

Which Peruvian town, buried by the 1970 Huascarán avalanche, became a national cemetery?

31 May is now Peru's Natural Disaster Education and Reflection Day.

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

It remains one of the deadliest mountaineering accidents ever.

The 1993 Bayburt Üzengili avalanche that killed 60 people occurred in which country?

Üzengili is a village in Bayburt province.

After the 1999 Montroc avalanche killed 12 people, who was convicted of second-degree murder?

He received a suspended sentence for failing to evacuate; 300,000 cubic metres of snow slid at about 100 km/h.

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

The avalanche was exceptionally large and flowed right into the village.

The 2003 Tatra Mountains avalanche swept away students heading for which summit?

Nine of a thirteen-member group from a Tychy high school were caught.

The 18 April 2014 ice avalanche in the Khumbu Icefall killed how many climbing Sherpas?

Sherpas then refused to work on Everest for the rest of the season.

The 2015 Everest Base Camp avalanche, triggered by the Nepal earthquake, originated on which nearby peak?

At least 24 died, making it the deadliest disaster on the mountain.

A serac collapse on which Italian glacier killed 11 alpinists on 3 July 2022?

Ice avalanches behave more like rockfalls and are almost impossible to mitigate.

Barry, the rescue dog who saved 40 lives in the early 1800s, worked from the hospice on which pass?

His byname Menschenretter means 'people rescuer'; he was smaller than the modern St Bernard breed.

What kind of climate change effect is predicted to make avalanche burials more deadly?

Denser debris cuts the time a buried person has before oxygen runs out.

What is an ice avalanche most analogous to?

They occur when a serac or calving glacier falls, as in the Khumbu Icefall.

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

The gap between that and cold air above creates the gradient that grows depth hoar.

What is the effect of a rapid rise in temperature well above freezing on a snowpack?

Gentle freeze-thaw cycles, by contrast, tend to strengthen the pack overnight.

Which Swiss glacier system has an early warning system that can foresee ice avalanches days ahead?

Interferometric radars, cameras and motion sensors track unstable areas for months or years.

On the European scale, what counts as a 'heavy' additional load on a slope?

A single boarder linking turns smoothly counts as a light load.

Consolidated snow is a necessary condition for which type of avalanche?

Newly fallen snow needs time to bond with the layers beneath, especially in cold, dry conditions.

An engineered avalanche dam on Mount Stephen protects which Canadian mountain crossing?

Avalanches typically follow drainages downslope, sharing paths with summer watersheds.

What is the vertical fracture wall at the top of a slab avalanche's start zone called?

Flank fractures run down the sides, and the crown and flanks together outline the snow that broke away from what stayed on the slope.