Dike / magma
Dense deep crust
Light shallow crust
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Most magma generated in the mantle never becomes an eruption — it freezes underground as an intrusion. This simulator models the real two-stage journey a dike must survive to reach daylight. First it has to nucleate: the chamber's overpressure has to concentrate enough stress at a small starter crack to exceed the host rock's fracture toughness, or nothing happens at all. Then, once cracked, it has to keep climbing against gravity — buoyancy from the density contrast between magma and the rock it is splitting apart, integrated all the way up from the chamber. Because real crust gets less dense toward the surface, that buoyancy can flip sign partway up, stalling the dike at its neutral buoyancy level where it spreads sideways into a sill instead of erupting. Tune chamber overpressure, magma density, rock toughness and the near-surface density contrast to explore every outcome: no nucleation, a stalled sill, or a full eruption breaking the surface.