Volcano Eruption Lab
Explore how magma viscosity and dissolved gas content control eruption style. Adjust the sliders to see how basaltic magma produces gentle lava flows while rhyolitic magma drives catastrophic Plinian explosions. Observe the Volcanic Explosivity Index (VEI) and record data across eruption types.
Guided Experiment: Viscosity and Eruption Style
If you increase magma viscosity while keeping gas content constant, how will eruption style change? Will it become more or less explosive?
Write your hypothesis in the Lab Report panel, then click Next.
Cross-Section View
Controls
Presets
0 = Basaltic (fluid) → 10 = Rhyolitic (viscous)
0 = Dry magma → 10 = Highly gassy
Eruption Data
Eruption Type
Vulcanian
Andesitic magma
Data Table
(0 rows)| # | Viscosity Index | Gas Content Index | Magma Type | VEI | Eruption Type | Column Height (km) | Primary Hazard |
|---|
Reference Guide
Magma Viscosity
Viscosity measures a fluid's resistance to flow. In magma, silica (SiO2) content is the primary control. Silica forms long polymerized chains that tangle and resist movement.
- Basaltic (45-52% SiO2): Very fluid, lava flows easily
- Andesitic (52-63% SiO2): Moderate viscosity
- Dacitic (63-68% SiO2): High viscosity, slow flows
- Rhyolitic (68-77% SiO2): Extremely viscous, near-solid
Temperature also affects viscosity. Hotter magma flows more easily. Magma can be 600-1300 degrees Celsius depending on composition.
VEI Scale
The Volcanic Explosivity Index (VEI) is a logarithmic 0-8 scale measuring eruption size. Each step represents roughly 10 times more eruptive material than the previous.
The 1991 Pinatubo eruption (VEI 6) injected 20 million tonnes of sulfur dioxide into the stratosphere and cooled global temperatures by 0.5 degrees Celsius for two years.
Eruption Hazards
Different eruption styles produce different hazards. Hazard type depends on eruption style, not just size.
- Lava flows: Slow-moving, mainly destroys property
- Volcanic bombs: Ballistic fragments ejected up to 5 km
- Pyroclastic flows: Fast-moving gas and ash, up to 700 km/h
- Ash fall: Can collapse roofs, disrupt aviation
- Lahars: Volcanic mudflows, triggered by rain or ice melt
- Volcanic gases: SO2, CO2, H2S toxic in confined areas
Pyroclastic flows (VEI 5+) are the deadliest volcanic hazard. The 79 AD Vesuvius eruption that buried Pompeii was a VEI 5 event.
Gas and Explosivity
Dissolved gases (water vapor, CO2, SO2) are the primary driver of explosive eruptions. As magma rises and pressure decreases, gases exsolve and expand.
In low-viscosity basaltic magma, bubbles can escape freely. In high-viscosity rhyolitic magma, bubbles are trapped until pressure builds enough to fragment the magma into fine ash.
This fragmentation produces the fine glass shards that make rhyolitic ash particularly dangerous for aviation and lung health. Volcanic ash particles are typically less than 2 mm in diameter.
