More than a million avalanches fall around the world every year. In the BBC documentary 10 Things You Didn't Know About Avalanches, geologist Iain Stewart travels across mountain ranges and glaciers to tell ten stories about them, from Hannibal's army in the Alps to the deadliest avalanche in history and the scientists who have gone inside moving avalanches to study them.
Iain Stewart and the BBC avalanche documentary
Iain Stewart, born in 1964, is Professor of Geoscience Communication at the University of Plymouth. His first BBC appearance was as an expert in a 2002 Horizon film about Helike, the ancient Greek city on the Gulf of Corinth that vanished in an earthquake, and he went on to present series such as Journeys from the Centre of the Earth (2004), Journeys into the Ring of Fire (2006) and How Earth Made Us (2010).
The avalanche episode of his BBC Four series 10 Things You Didn't Know About… was first shown in 2008. Its chapters cover how avalanches form, controlled avalanches, rock avalanches, the Kolka glacier collapse in the Caucasus and the "saltation layer" of bouncing snow inside a moving avalanche.
How avalanches form: slabs, loose snow and ice
In a slab avalanche, a cohesive layer of snow sitting on a weaker layer breaks away in one piece. Loose-snow avalanches start at a single point in poorly bonded surface snow and fan out as they fall. Ice avalanches, when part of a glacier breaks off, are a separate process and can be far larger.
Slope angle matters most. Avalanches usually start on slopes of 30 to 45 degrees, and the most dangerous angle for human-triggered slides is around 38 degrees, the pitch of a perfect powder run. In recreational accidents, about 83 percent of avalanches are triggered by the victims or members of their own group. Avalanche Canada's guide to avalanche types explains each kind with diagrams.
Hannibal, Huascarán and Kolka: avalanches in history
Hannibal, 218 BC. When the Carthaginian general crossed the Alps to attack Rome in late autumn, he started with more than 70,000 men and reached Italy with about 35,000. Polybius and Livy describe snow that melted by day and refroze at night, a steep descent on the Italian side where many men lost their footing, and a landslide that blocked the path until his soldiers rebuilt it. Stewart's documentary counts avalanches among the hazards that cost Hannibal so dearly.
Huascarán, 1970. On 31 May 1970, a magnitude 7.9 earthquake off Peru shook loose the north face of Huascarán. A mass of rock, ice and snow ran about 18 km at average speeds of 280–335 km/h and buried the towns of Yungay and Ranrahirca in a matter of minutes. It is considered the deadliest avalanche on record; the documentary's account puts the death toll at about 18,000 people in around three minutes.
Kolka, 2002. On 20 September 2002, the Kolka Glacier near Mount Kazbek in North Ossetia, Russia, collapsed. Ice, water and rock poured down the Karmadon valley, and the icy mudflow ran a further 12 km, reaching a height of up to 140 metres. At least 125 people died. The programme also looks at an aviation mystery in which an avalanche played a key role, and at how warming glaciers may make ice avalanches more frequent.
Avalanche science and staying safe in the mountains
The turbulence inside a powder avalanche is still poorly understood, which is why scientists have had to go inside active avalanches to study them. Their measurements feed into the forecasts and control work that keep ski resorts and mountain roads open, from explosives that bring snow down on purpose to permanent snow sheds and dams.
Read the avalanche bulletin before every day in the backcountry. Regional centres such as those listed by the US avalanche centers directory publish daily danger ratings, and every member of a group should carry a transceiver, probe and shovel and know how to use them.
Explore more: managed avalanche-control work; a dated East Vail rescue.
Sources
- Unofficial Networks, 10 Things You Didn't Know About Avalanches: unofficialnetworks.com
- IMDb, "10 Things You Didn't Know About..." Avalanches (2008): https://www.imdb.com/title/tt1722643/
- Wikipedia, Iain Stewart (geologist): https://en.wikipedia.org/wiki/Iain_Stewart_(geologist)
- Wikipedia, Hannibal's crossing of the Alps: https://en.wikipedia.org/wiki/Hannibal's_crossing_of_the_Alps
- Wikipedia, 1970 Ancash earthquake: https://en.wikipedia.org/wiki/1970_Ancash_earthquake
- Wikipedia, Kolka Glacier: https://en.wikipedia.org/wiki/Kolka_Glacier
- Wikipedia, Avalanche: https://en.wikipedia.org/wiki/Avalanche
- Avalanche Canada, types of avalanches: https://avysavvy.avalanche.ca/en-ca/types-of-avalanches
- Image: BBC / Iain Stewart avalanche documentary
Related reading:
- avalanches
- Scientists
- East Vail Avalanche Rescue: The December 22, 2013 Footage
- Avalanche Preparation: Training, Terrain, Equipment and Group Decisions
- Aymar Navarro’s Avalanche Incident in the Spanish Pyrenees
- Lightning Safety: Shelter Comes Before Survival Techniques
- Dub Roots: Dubsatch Collective’s Alta Ski Film
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