Lava is emitted at the crater as discrete packets at temperature Terupt = 1150°C. Each packet cools toward the solidus Tsol = 980°C at the rate set by the cooling slider, and its viscosity follows a Shaw-style log-linear (Arrhenius) law: μ rises smoothly from a fluid ~10 Pa·s near eruption temperature toward ~107 Pa·s as it approaches the solidus, where it effectively freezes in place.
μ(T) = μmax · 10^(3·(Tsol−T)/(Terupt−Tsol))
u = ρ·g·sin(α)·h² / (3μ) (Jeffreys' laminar sheet-flow law)
That velocity u (ρ=2600 kg/m³, sinα=0.40, h=1.5 m) advances each packet down the flank; the flow-front readouts show the newest, hottest, fastest packet still moving. Ballistic ash and lava bombs launched from the crater follow ordinary projectile motion x(t)=v₀cosθ·t, y(t)=v₀sinθ·t−½gt², with launch speed v₀ set by the eruption-force slider. Ash density scales both the plume's opacity and its Stokes settling speed ― denser ash falls out of the plume sooner. Animation time runs ~25× faster than the physical process it models so a lava flow visibly reaches the base within a minute.