Talus Cone Formation: Frost-Wedging & Angle of Repose

Frost-Wedging Weathering

Frost cycles 14 / min

Angle of repose 35°

Fragment size Medium

Talus Cone State

Measured slope

0.0°

Target repose

35°

Deposited volume

0.00 m³

Fragments released

How it works

Water seeps into cliff joints, freezes, and expands about 9% in volume. Repeated freeze–thaw cycles wedge fragments loose — the classic mechanical-weathering process that feeds every scree slope. Each release is a discrete event drawn at the current frost-cycle rate; fragment volume follows a sphere of radius r drawn from the size slider's range:

V = (4/3)πr³
event interval ≈ 60 / rate  (s), ±40% jitter

Once a fragment lands at the cliff base it doesn't stay where it fell — it rolls and settles until the local slope can no longer support it. This is simulated with a cellular angle-of-repose relaxation identical in spirit to the sandpile automata used in real reduced-complexity landscape models: any two adjacent cells whose height difference exceeds tan(θ) × cell-width topple, moving the excess halfway to the lower cell, applied outward from the cliff and laterally along it:

unstable if  (h₁ − h₂) / Δx  >  tan(θ_repose)
→ move  ((h₁−h₂) − Δx·tanθ) / 2  from cell 1 to cell 2

Frost cycles — how often a weathering event dislodges a new fragment.
Angle of repose — the maximum stable slope for loose, angular rock debris (real scree sits around 30–40°, set by interparticle friction); raising it lets the cone stand steeper before toppling.
Fragment size — the mean radius of released rock, which sets how much volume each event adds.

Run it long enough and the measured slope converges on the target repose angle — the same self-organizing equilibrium that keeps real talus cones at a remarkably consistent angle regardless of how tall the cliff feeding them is.

Cliff face Talus cone Falling fragment

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