Anatomy of an Avalanche

Infinite Variety,
Unimaginable Power

Propelled by gravity, snowslides have the power to rip through forests leaving distinctive cuts often mistaken for ski runs. Like the snow crystals that give them birth, slidepaths mark the landscape with an endless variety of shapes and sizes. Some paths thunder with snow many times a winter, others may lurk quietly for centuries.

Two types of snow avalanches What makes snow avalanche?

Glacier National Park
1997-0-064 Glacier National Park, BC, April 1980. © Parks Canada, John G Woods.

There are 2 types of avalanches: Slab and loose snow avalanches. Download (MP4) (0.4 MB) Download (WEBM) (0.3 MB)

Recipe for an Avalanche

Recipe for
an avalanche

When snow and slope combine with a hidden weakness beneath the surface, you have set the stage for an avalanche waiting to be triggered.

Learn more

Controlled Avalanche
Controlled avalanche at Bear Pass, BC. Revelstoke Museum & Archives 5529. © BC Ministry of Transportation and Infrastructure.

How much snow?

There is no exact answer. On a smooth slope 30 cm is enough to create an avalanche.

Slope

Ingredients

  • Snow

Deep
Yearly snowfall often exceeds 10 m in Rogers Pass. Here men saw and slide huge chunks of the winter’s snow accumulation from the roof of the Glacier House Hotel, circa 1926. © Whyte Museum of the Canadian Rockies V263 / NA – 1360, Byron Harmon.

How steep?

Avalanches have run down slopes from 10° to nearly 90°. Most recreational avalanche accidents have happened on slopes between 30° and 35°.

Weak layer

Ingredients

  • Snow
  • Slope

All in a Day's Work
Chief Avalanche Forecaster V. G. (Fred) Schleiss takes a moment to marvel at the beauty of his workplace high above the Trans-Canada Highway, in the trigger zone of Lanark Slidepath circa 1979, Revelstoke Museum & Archives 5563. © Parks Canada, John G. Woods.

Why layers?

Storms deposit snowfall in layers. The crystals within these layers, as well as on the surface, are always changing. This results in layers of different strengths—some weaker, some stronger.

Trigger

Ingredients

  • Snow
  • Slope
  • Weak Layer

Snow Science
Some crystals cling together, others are as loose as sugar. Avalanche professional John Tweedy looks for weak layers in the snow that could provide a sliding surface for an avalanche. Revelstoke Museum & Archives 5331. © BC Ministry of Transportation and Infrastructure.

What triggers?

Falling snow, drifting snow, temperature change, rain, a mountain goat, a skier, a snow machine, an explosion…

"The next thing I knew was all of the snow on the mountainside was in motion and it was coming down towards us... and the only thing that saved us was pure blind luck". Jim Bay, 2013.

Transcript Transcript Download MP3 (2:11 2.0MB) Download OGG (2:11 1.7MB)

Ingredients

  • Snow
  • Slope
  • Weak Layer
  • Trigger

Close-call

Play/pause

"The next thing I knew was all of the snow on the mountainside was in motion and it was coming down towards us... and the only thing that saved us was pure blind luck". Jim Bay, 2013.
Transcript Download MP3 (2:11 2.0MB) Download OGG (2:11 1.7MB)

Trigger
Any force that initiates a facture at a weak layer in the snowpack. Avalanche professional Jim Bay, Valhalla Range, BC, 2013. Revelstoke Museum & Archives 5532. © Jim Bay

Digging Deeper

How experts dig deeper into the anatomy of the snowpack.

Observing Weather

Transcript Download MP4 (38.6 MB) Download WEBM (31.1 MB)

Avalanche technicians for Parks Canada discuss snow and how weather affects snow and avalanche activity.

Mount Fidelity Research Station, Glacier National Park, BC 2013. Revelstoke Museum & Archives A2013.18.1. © Parks Canada

Finding Hidden Layers

Transcript Download MP4 (63.1 MB) Download WEBM (47.8 MB)

Avalanche technicians for Parks Canada study a snowpack.

Mount Fidelity Research Station, Glacier National Park, BC 2013 Revelstoke Museum & Archives A2013.18.2. © Parks Canada

Probing Snowpack Layers

Transcript Download MP4 (28.5 MB) Download WEBM (19.5 MB)

Avalanche technicians for Parks Canada describe how they study temperatures and snow crystal structure within the snowpack.

Mount Fidelity Research Station, Glacier National Park, BC, 2013. Revelstoke Museum & Archives A2013.18.3. © Parks Canada

Testing Snowpack Strength

Transcript Download MP4 (25.4 MB) Download WEBM (18.4 MB)

Avalanche technicians for Parks Canada discuss snow density and demonstrate a compression test

Mount Fidelity Research Station, Glacier National Park, BC, 2013. Revelstoke Museum & Archives A2013.18.4. © Parks Canada

Big, Powerful, Fast

Big

Railway Station in Rogers Pass

Black and white photograph of 6 passengers waiting at small railway station on wooden platform in summer, with mountain range in background.
An avalanche demolished this railway station killing seven people including two children. The station was rebuilt in an avalanche-free area.

This was the first station on the Canadian Pacific Railway over Rogers Pass. BC. The railway was built in 1885 and the avalanche struck on January 31, 1899. © Revelstoke Museum & Archives 1683

Greenslide, South of Revelstoke, BC

Black and white photograph of men clearing huge amounts of avalanche debris from covered railway.
This railway near Revelstoke was dug out from under a huge volume of avalanche snow.

This slide has deeply buried a now-abandoned line of the Canadian Pacific Railway. © Revelstoke Museum & Archives 2548.

Avalanche Blocks Roadway

4 men pose for black and white photograph at large slide covering road.
Snow avalanche deposits can dwarf humans.

This slide at Greenslide, South of Revelstoke, BC, has deeply buried a public roadway April 28, 1972. © Revelstoke Museum & Archives 5558, Brian Gawiuk.

Powerful

Avalanche on the Trans-Canada Highway

Black and white photograph of truck thrown on to its side after being tossed through the air by avalanche. Rescuers in background.
An avalanche hurled this semi-transport truck through the air and tossed smaller trucks aside. The highway was closed for days.

The vehicles included a semi-transport truck, two pick-ups, and an army vehicle towing a 105 mm Howitzer. Trans-Canada Highway, Rogers Pass, Glacier National Park, BC 1974 Revelstoke Museum & Archives 5533. © Jim Bay Collection

1910 Tragedy in Rogers Pass

Black and white photograph of 10+ rescuers on site of avalanche, which shows a rotary snow plough pushed off the railway tracks and uphill.
An avalanche flung this rotary snow plough weighing more than 100,000 kg off the railway tracks and uphill.

Fifty-eight workers died and the Canadian Pacific Railway was closed for days in Canada's worst avalanche accident. Rogers Pass, Glacier National Park, BC, 1910. © Revelstoke Museum & Archives 257

Fast

Loose Snow Avalanche

Transcript Download MP4 (32.1 MB) Download WEBM (21.5 MB)

Avalanches can travel at speeds greater than 216 km/hr—double the maximum speed limit on any Canadian highway.

This avalanche raced towards Bear Lake after being triggered by explosives in an avalanche safety mission protecting Hwy 31A, BC, 2007. Revelstoke Museum & Archives A2013.24.1. © BC Ministry of Transportation and Infrastructure.

Precision observations and meticulous research are vital in our ongoing battle with snow avalanches.

Battling avalanches