This simulation models how a volcano's eruption style emerges from the physics of its plumbing: magma viscosity, dissolved water, chamber pressure and conduit size. A chamber cross-section, a Hagen-Poiseuille conduit, a fragmentation (Deborah number) criterion, a buoyant plume, a Jeffreys lava flow and wind-blown ash fall are computed with real equations and drawn over a rock section textured in Blender. It shows why runny, gas-poor basalt flows gently while stiff, gas-rich magma fragments into towering Plinian columns.
The model derives the viscosity of the melt from silica, temperature and water, finds the depth where the foam fragments, computes the conduit flux and mass eruption rate from the chamber overpressure, and classifies the eruption (Effusive, Hawaiian, Strombolian, Vulcanian, Sub-Plinian, Plinian) from a Deborah number. Plume height uses buoyant plume theory and is checked against the Mastin fit; the erupted volume gives the VEI.
Choose a preset or drag the sliders for silica, temperature, water, chamber depth and volume, conduit radius, rupture pressure, recharge rate, wind and lava-channel width. Pressure builds in the chamber, the eruption starts at the rupture overpressure and the readouts, six live graphs and the VEI update. Use Trigger eruption now to skip the wait, and the 3D link for the full island with a cutaway.
The Volcanic Explosivity Index is logarithmic: each step up represents roughly a tenfold increase in erupted volume. The 1991 Pinatubo eruption rated VEI 6, while the Yellowstone supereruptions reached VEI 8, ejecting over 1,000 cubic kilometres of material.
It is mainly the balance between magma viscosity and dissolved gas. Low-viscosity, gas-poor magma lets gas bubbles escape easily, producing gentle effusive lava flows. High-viscosity, gas-rich magma traps gas until pressure shatters it, driving explosive eruptions. The simulation captures this with an explosivity ratio proportional to gas content divided by viscosity.
The chamber overpressure drives Poiseuille flow up the conduit: flux grows with the fourth power of the conduit radius and falls with viscosity and conduit length. The mass eruption rate sets the plume height through buoyant plume theory (height rises roughly as the fourth root of the rate), and the Volcanic Explosivity Index is a logarithmic scale of the erupted bulk volume, from VEI 0 to VEI 8. These are simplified relationships, not full fluid-dynamics solutions.
Silica, temperature and dissolved water set the magma viscosity and gas content. Chamber depth, volume and the rupture overpressure set how much magma can erupt and how fast; the conduit radius sets the flux; the recharge rate sets how quickly pressure builds between eruptions. Wind and lava-channel width shape the ash fall and the lava flow. Changing them changes the eruption style label, the plume and the lava.
It is a qualitative educational model rather than a research-grade simulator. The trends it shows are correct: viscosity and gas content really do govern eruption style, and VEI really is logarithmic. However, the exact equations are simplified approximations, and the particle system is a visual stylisation rather than a true computational fluid dynamics solution of magma ascent.
Silica content controls viscosity: more silica means longer polymer chains and thicker, stickier magma. Rhyolitic and dacitic magmas are extremely viscous, so exsolving gas cannot escape and instead builds enormous pressure. When the conduit finally fails, the magma fragments violently into ash and pumice, feeding the Plinian columns seen at the high end of the viscosity slider.