Snow avalanche dynamics shows how a buried weak layer beneath a fresh-snow slab can fail under its own weight. Adjust slope angle, snow load and weak-layer strength to see the driving stress and stability index respond live, then trigger a slab release to watch particles fracture away and slide into a fanning runout zone.
A simplified Mohr-Coulomb-style stability criterion: driving stress τ = ρ·g·h·sin θ·cos θ from the slab's weight, compared against the weak layer's shear strength to compute a live stability index SI.
Drag the slope-angle, snow-load and weak-layer-strength sliders to push SI toward or away from 1. Press "Trigger avalanche" or let extreme settings release the slab automatically.
Most human-triggered avalanches occur on slopes between 30° and 45° — flatter slopes rarely generate enough driving stress, and steeper slopes tend to sluff continuously rather than store dangerous stress.
This canvas-based simulation models a slab avalanche using a simplified Mohr-Coulomb-style stability criterion. A fresh-snow slab sits atop a buried, weaker "weak layer" on a sloped mountainside. The slab's own weight resolves into a downslope shear component — the driving stress τdriving = ρ·g·h·sinθ·cosθ — while the weak layer resists with a shear strength τstrength set by the user. Their ratio, the stability index SI, tells you whether the slope is likely to hold or fail.
Push the slope angle or new-snow load higher, or drag the weak-layer strength down, and SI falls toward 1; below that threshold the slab fractures automatically, or you can trigger it manually. Released particles accelerate downhill under gravity minus friction, then fan out and decelerate in a flatter runout zone at the base — mirroring how real slab avalanches propagate from a fracture line to a debris field. This mirrors the real-world snow-science practice of testing buried weak layers before entering avalanche terrain.
What is the Mohr-Coulomb-style stability criterion used here?
It compares the shear stress trying to slide the snow slab downhill (driving stress) against the shear strength of the buried weak layer that resists that motion. When the resisting strength is smaller than the driving stress, the weak layer fails and the slab releases — the same logic used in real slope-stability analysis, simplified for an interactive model.
What is a "weak layer" in a snowpack?
A weak layer is a thin band within the snowpack, often made of loosely bonded or faceted snow crystals, buried beneath later snowfalls. It has much lower shear strength than the denser slab above it, so it acts as a sliding surface once the load on top becomes too great.
How is driving stress calculated?
Driving stress uses τ = ρ·g·h·sinθ·cosθ, where ρ is snow density, g is gravitational acceleration, h is the slab's depth, and θ is the slope angle. It represents the component of the slab's weight acting as shear along the slope, resolved from the two sine/cosine projections of gravity onto an inclined plane.
What triggers a real avalanche?
Common triggers include the added weight of a skier, snowmobiler, or explosive charge, rapid new snow loading, rain-on-snow events, and temperature swings that weaken bonds. All of these effectively increase driving stress or reduce weak-layer strength, pushing the stability index below 1, just as the sliders do in this simulation.
The slope-angle slider changes θ, directly affecting driving stress through sinθ·cosθ; the new-snow-load slider changes slab depth h, increasing both driving stress and the number of particles released; the weak-layer-strength slider sets τstrength; "Trigger avalanche" forces an immediate release; and "Reset" restores default slope conditions.
The simulation continuously recomputes the stability index SI = τstrength / τdriving. If your slider adjustments push SI below 1 — for example by steepening the slope or piling on new snow while the weak layer stays weak — the slab fractures on its own, just as an overloaded real slope can avalanche without a human trigger.
Once triggered, particles fracture from the upper slab and accelerate down the slope with a = g·(sinθ − μ·cosθ), where μ is a friction coefficient. As particles reach the flatter runout zone at the base, the slope-parallel acceleration drops, friction dominates, and lateral spreading fans the debris out, matching how real avalanche debris decelerates and spreads at the bottom of a track.
It is a simplified, stylised model that captures the core Mohr-Coulomb-style comparison of driving stress and shear strength, plus basic Newtonian sliding dynamics, but it does not model snow fracture mechanics, cornice failure, or terrain-specific effects in full detail. It is designed to build correct physical intuition about the balance of forces behind slab avalanches.