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Tephra Isopach Map: Crosswind Fallout Fan

Interactive 2D top-down tephra isopach map: ash and lapilli of different grain sizes settle under a real gravity-drag terminal-velocity balance while a wind shear profile advects them downwind and genuine turbulent crosswind diffusion spreads them sideways, building the actual thinning-and-fining fallout fan volcanologists map in the field.

Climate, Ecology & Environment2DAdvanced60 FPS📱 Mobile-adapted⇄ 3D version

Where the 3D version of this sim shows a side-on slice through the falling ash column, this 2D companion looks straight down on the ground: a genuine top-down isopach map built from the same gravity-drag terminal-velocity balance and altitude wind shear, but with real turbulent crosswind diffusion added — each clast's sideways drift is an independent random walk whose ensemble spread follows the textbook Gaussian-plume law σ_y(t) = √(2Kt). Because fine ash spends far longer aloft than coarse lapilli, it accumulates far more crosswind spread by the time it lands, so the simulated deposit naturally widens from a narrow proximal fan near the vent into a broad distal fan downwind — the same wedge-shaped thinning-and-fining fallout pattern volcanologists map with real isopach and isopleth lines after an eruption.

⚙ Under the hood

Top-down 2D isopach map of a volcanic ash fallout: clasts settle under the same gravity-drag terminal-velocity balance and altitude wind shear as the 3D column view, but genuine turbulent crosswind diffusion (a per-clast random walk, sigma_y = sqrt(2Kt)) spreads them sideways, building a real wedge-shaped deposit fan that is narrow near the vent and widens far downwind.

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2D · HTML5 Canvas 2D · 60 FPS target · runs fully client-side, no install