Key Moments
The Terrifying Real Science Of Avalanches
VeritasiumKey Moments
Avalanches are complex natural phenomena driven by snowpack instability, with slab avalanches being the most dangerous. Prevention and rescue tools are crucial for survival.
Key Insights
Avalanches occur when the bonds between snow crystals break, and gravity overcomes friction, with slab avalanches being the most deadly due to their cohesive nature.
The snowpack is layered, with different conditions affecting its structure; weak layers (like surface hoar or facets) form from temperature gradients and can be buried, creating instability.
Slab avalanches can be triggered remotely by skiers or snowboarders, often on slopes between 34-45 degrees, and can travel at high speeds.
Avalanche control in resorts involves intentionally triggering smaller avalanches using explosives to prevent larger, more destructive ones from forming.
Backcountry safety requires essential gear: a beacon (transmitter/receiver), probe, and shovel. Time is critical for rescue, with survival rates dropping significantly after 10-15 minutes.
Avalanche airbags can increase a skier's buoyancy, reducing deep burial and providing a larger air pocket for survival during rescue efforts.
UNDERSTANDING AVALANCHE FORMATION
Avalanches are primarily caused by the failure of crystalline bonds between snow crystals, where gravity's pull overtakes the frictional forces holding the snow in place. The snowpack is not uniform; it's a layered structure built up over time, with each layer's properties influenced by atmospheric conditions like temperature, humidity, sun, and wind. Temperature gradients within the snowpack are particularly crucial, as they can transform snow crystals, creating weak layers that are prone to failure under stress.
TYPES AND TRIGGERS OF AVALANCHES
Avalanches are categorized by size and type. Loose avalanches, involving unconsolidated snow, are generally less dangerous, often referred to as 'slough' by skiers. The more lethal type is the slab avalanche, where a cohesive layer of snow breaks off. These are most common on slopes between 34 and 45 degrees. A terrifying aspect of slab avalanches is their potential for remote triggering; a skier on a gentler slope can destabilize a steeper section above them, with avalanches capable of reaching speeds up to 120 kmph.
WEAK LAYERS AND SNOWPACK INSTABILITY
The critical element in dangerous avalanches is the presence of weak layers within the snowpack. Surface hoar, formed from condensation on cold, clear nights, and facets, which are transformed snow crystals due to strong temperature gradients, are common examples. If these fragile layers are buried by subsequent snowfall before they can break down, they create a devastating foundation for slab avalanches. The stiffness of the overlying slab also plays a role; stiffer slabs resist initial triggers but lead to more significant propagation when they fail.
NATURAL AND HUMAN INFLUENCES ON AVALANCHES
While natural events like storms and wind can increase avalanche risk, human recreation is the most common trigger for fatal avalanches, accounting for 93% in the US. Storms add weight to the snowpack, potentially triggering deep weak layers. Strong winds can form unstable 'wind slabs' by compacting snow. Cornices, large overhanging masses of wind-blown snow, pose a significant threat as their collapse can trigger massive avalanches. In ski resorts, a proactive approach is taken to manage this risk.
AVALANCHE PREVENTION AND CONTROL
In ski resorts, avalanche control work is paramount to ensure skier safety. Ski patrols intentionally trigger avalanches in treacherous areas before they open to the public, using explosives like bombs and artillery shells. This ensures that any avalanches are small and manageable. Roads passing through avalanche-prone areas, such as parts of the Trans-Canada Highway, also undergo similar artillery control measures to prevent devastating snow slides from blocking or destroying the route.
BACKCOUNTRY SAFETY AND RESCUE PROTOCOLS
For backcountry travel, carrying essential safety gear—an avalanche beacon, probe, and shovel—is non-negotiable. In the event of a burial, a beacon aids in locating the victim. The probe is used for pinpointing the exact location, and the shovel for excavation. Survival rates plummet rapidly after burial; being uncovered within 10 minutes offers an 80% survival chance, dropping significantly thereafter. Time is the most critical factor in avalanche rescue.
ADVANCEMENTS IN AVALANCHE RESCUE TECHNOLOGY
Beyond basic rescue tools, modern technology offers enhanced survival chances. Avalanche airbags, activated by pulling a cord, rapidly inflate to increase a skier's buoyancy, helping them stay higher in the snow and reducing the likelihood of deep burial. Newer models use battery-powered fans for inflation. If burial does occur, the deflating airbag can also create a larger vital air pocket, extending the window for rescue and increasing the chances of survival.
Mentioned in This Episode
●Products
●Companies
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●Concepts
●People Referenced
Avalanche Safety: Do's and Don'ts
Practical takeaways from this episode
Do This
Avoid This
Avalanche Size Scale
Data extracted from this episode
| Size | Description |
|---|---|
| 1 | Not large enough to bury a person |
| 5 | Involves 100,000 cubic meters of snow traveling many kilometers, causing massive destruction |
Slab Avalanche Slope Angles
Data extracted from this episode
| Slope Angle | Likelihood of Dangerous Slab Avalanche |
|---|---|
| Under 25° | Unlikely |
| 34°-45° | Common for dangerous slab avalanches (75% occur here) |
| Over 50° | Unlikely (snow accumulation is difficult) |
| Black Diamond run (~30°) | Best conditions for skiing and avalanches |
| Double Black Diamond run (~40°) | Best conditions for skiing and avalanches |
Avalanche Burial Survival Rates
Data extracted from this episode
| Time to Rescue | Chance of Survival |
|---|---|
| First 10 minutes | 80% |
| 15 minutes | 40% |
| 30 minutes | 22% |
Avalanche Fatality Causes
Data extracted from this episode
| Cause | Percentage |
|---|---|
| Trauma (hitting objects, falls) | 25% |
| Asphyxiation (lack of oxygen, CO2 buildup) | The rest (approx. 75%) |
Common Questions
The deadliest known snow avalanches occurred in the Dolomites in December 1916 during WWI, where between 2,000 and 10,000 soldiers died. Another significant event was in May 1970 in Yungay, Peru, where an earthquake-triggered avalanche and landslide killed an estimated 30,000 people.
Topics
Mentioned in this video
Location of North America's largest ski resort, where avalanche control work was demonstrated.
A location in the Dolomites where an avalanche in December 1916 wiped out an Austrian Barracks, killing at least 275 people.
A town destroyed in May 1970 by an avalanche triggered by a major earthquake, which also caused a landslide.
A mountain pass along the Trans Canada Highway known for its high avalanche risk and active control measures.
A mountain near Rogers Pass where Parks Canada and the Canadian Army conduct avalanche control.
A mountain range in Northern Italy where thousands of troops died in snow avalanches during World War I.
A type of avalanche where the top layer of snow becomes a cohesive slab that releases in big chunks. These are often more deadly.
A type of weak layer in snowpack formed by condensation on cold, clear nights, which can become dangerous if buried.
Snow crystals that become angular due to a strong temperature gradient in the snowpack, forming a weak layer.
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