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The science
Pressure at depth z is P = P0 + rho g z, so water can stay liquid well above 100 C at the bottom of a conduit. The boiling temperature follows Clausius-Clapeyron: 1/Tsat = 1/T0 - (R_v/L) ln(P/P0) with L = 2.257 MJ/kg and R_v = 461.5 J/kg/K (accurate to a few kelvin up to 15 bar).
The heater warms the bottom cells (dT/dt = Q/(m c)) while convection mixes neighbours. When any depth reaches its boiling temperature, water flashes: a lower column pressure lets more water flash and an eruption results. Flash steam fraction x = c (T - 100)/L; the work x R_v T ln(P_bottom/P0) times a calibrated jet efficiency gives the exit speed and height h = v^2/(2g).
Honest simplifications: a one-dimensional column, a single lumped efficiency (not a two-phase flow solution), constant L, no real conduit geometry or side chambers. The numbers are plausible for an Old Faithful-type geyser but are not fitted to a specific one. The 3D page is a particle visualisation of the same eruption cycle.
What to try
- Raise the depth: pressure is higher, so the eruption waits for a hotter column and the jet is taller.
- Use Well mixed: heat spreads upward, so eruptions come earlier and weaker.
- Halve the heat input and compare the interval with the readout estimate.