What is the average avalanche slope angle range?

• A. 15-25 degrees
• B. 5-15 degrees
• C. 45-60 degrees
• D. 30-45 degrees

Answer: (D)

Avalanches tend to release on slopes where the driving force of gravity along the slope overcomes the snowpack’s resistance, and this balance shifts into failure most commonly on moderate-to-steep terrain. As the slope angle increases, the gravitational component that pulls snow downslope grows (roughly following the sine of the angle), so the snowpack becomes less stable. Real-world observations show that starting zones for dry-snow avalanches are typically found on slopes around 30 to 45 degrees, where there’s enough driving stress to propagate a fracture through a weak layer without the slope being so steep that failure behaves differently or is less common. Slopes well below 30 degrees are usually too stable for spontaneous avalanches, while slopes well above 45 degrees, though capable of avalanching, are less common as starting zones. That’s why the 30-45 degree range best represents the average avalanche slope angle.