This is a 2D cutaway cross-section of a stratovolcano: a magma chamber below ground, a conduit up through the cone, and a crater vent. It is the pressure-cycle companion to the 3D flyover simulation — a distinct model driven by a chamber-pressure ODE rather than a fixed particle-emission rate.
dP/dt = supplyRate (dormant, recharging)
dP/dt = supplyRate − ventWidth·k·P (erupting, venting)
Once P reaches the eruption threshold, the vent opens and pressure bleeds off exponentially until it falls under ~18% of threshold, at which point the vent closes and the chamber recharges for the next cycle — the same rise-trigger-relax pattern used for real seismic/deformation eruption forecasting, simplified to one state variable.
- Viscosity controls how the released magma partitions: viscous (rhyolitic) magma traps gas and fragments explosively, so more of the released volume becomes ballistic ejecta and ash — the real reason silicic volcanoes are more violent than basaltic ones. Runny (basaltic) magma instead mostly feeds an effusive lava flow.
- Lava flow front advances as dFront/dt = effusiveFlux / (viscosity·(0.3 + front)) — it slows both with higher viscosity and as the flow lengthens and cools, matching the qualitative behavior of real gravity-driven lava flows (Jeffreys-type thinning).
- Vent width sets how fast the chamber can vent (bigger vent → shorter, more frequent, milder eruptions) and how many ejecta the vent can pass per second.
- Eruption style is classified live from peak pressure and viscosity into effusive / Strombolian / Vulcanian / Plinian-like bands, mirroring the qualitative VEI ladder.