Impulse Lab
From slide kinematics to run-up in milliseconds
The empirical chain engineers use for screening: an energy-line impact velocity, the Heller–Hager impulse product parameter P, the wave it generates and how that wave decays, and two run-up laws. Then 4,000 Monte Carlo draws over the uncertain inputs ask how often the chain reaches the observed 481 m.
Centroid drop, slide thickness, width and impact depth are assumptions bracketed in the Monte Carlo.
Impact velocity Vs
78m/s
Impulse product P
1.67
Max amplitude a_M
134m
Max height H_M
168m
Run-up envelope
248–495m
Wave decay with distance
Heller & Hager (2010) 2D laws: H(x) = ¾[P(x/h)^−⅓]^⅘ h and a(x) = ⅗[P(x/h)^−⅓]^⅘ h. The dashed line marks the run-up shore.
Run-up estimators vs observation
Two waves (decayed H(x) at the shore, and the impact-zone maximum H_M as an upper bound) fed to Müller (1995) and Synolakis (1987). The red band is the observed trimline range.
Monte Carlo: Tracy Arm input uncertainty
4,000 draws · seed 2025Uniform draws: volume 55–100 M m³ (Science study to USGS preliminary upper bound), centroid drop 400–700 m, δ 15–25°, α 35–50°, thickness 70–130 m, width 0.7–1.1 km, depth 150–300 m, shore distance 2–4 km, β 35–50°. Impact velocity follows from the energy line. Two estimators bracket the result: Müller with the decayed wave (lower) and Synolakis with the impact-zone wave (upper).
These laws come from 2D wave-channel experiments (granular slides, P = 0.17–8.13). A fjord is close to that confinement but not equal: bends, the side arm at Sawyer Island and lateral spreading all matter. Near-field run-up of a 100 m breaking wave also mixes splash and bore run-up that no single regression captures, which is why the twin reports an envelope rather than a single number.