This simulation models how a volcano's eruption style emerges from three physical inputs: magma viscosity, dissolved gas content and chamber pressure build rate. A particle system spawns lava blobs, incandescent pyroclasts and drifting ash from the vent, while a simplified geophysical model computes eruption rate, column height and a Volcanic Explosivity Index (VEI). It shows why runny, gas-poor basalt flows gently while stiff, gas-rich magma fragments into towering Plinian columns.
The sim derives an explosivity ratio of roughly gas content times ten divided by viscosity, classifying the eruption as Effusive, Hawaiian, Strombolian, Vulcanian or Plinian. Eruption rate scales with gas and pressure but falls with the square of viscosity; column height follows a power law of that rate, and VEI approximates log10 of the eruption rate. Particles are drawn as lava, pyroclasts or ash with different gravity and lifespan.
Drag the Magma Viscosity slider (1 to 10, from very low to rhyolitic), the Gas Content slider (0.5 to 8 per cent) and the Pressure Build Rate slider (1 to 10). The telemetry panel updates viscosity, gas, chamber pressure in MPa, eruption rate in cubic metres per second, column height in km and VEI live. Press Reset Volcano to clear particles, lava flows and accumulated pressure.
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.
Eruption rate rises with gas content and pressure build rate but falls with the square of viscosity, so stiff magma chokes the conduit. Column height follows a power law of that rate, and the Volcanic Explosivity Index is approximated as roughly the base-ten logarithm of the eruption rate, clamped between 0 and 8. These are simplified relationships, not full fluid-dynamics solutions.
Magma Viscosity (1 to 10) sets how resistant the magma is to flow, from very low to rhyolitic. Gas Content (0.5 to 8 per cent) sets the dissolved volatiles that drive explosivity. Pressure Build Rate (1 to 10) controls how fast chamber pressure accumulates, raising the eruption rate. Adjusting them changes the eruption style label and the particle behaviour at the vent.
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.