A volcano's shape and eruption style are set mostly by one property of its magma: viscosity — how easily it flows — together with how much gas is dissolved inside it. Runny, low-gas basaltic magma spreads into broad, gently sloped shield volcanoes like Mauna Loa. Thick, gassy andesitic-to-rhyolitic magma traps pressure until it fails catastrophically, building steep stratovolcanoes like Fuji or Vesuvius from alternating lava and ash layers. Very gassy magma erupting fast from a single vent instead sprays fountains of cooling lava that fall back as cinders, piling into a small, steep cinder cone in days to months.
The three volcano types sit on a rough continuum, not in strict boxes: many real volcanoes (like Etna) show mixed behaviour, building composite cones with occasional fluid lava flows when magma composition or gas content shifts between eruptions.
A cutaway 3D volcano whose shape, layering and eruption style are driven entirely by magma viscosity and dissolved gas content — the two properties that separate broad shield volcanoes from steep stratovolcanoes and small cinder cones.
Higher viscosity narrows and steepens the cone and adds visible strata; higher gas content shifts the eruption from an effusive lava flow toward an explosive ash column, matching real shield/stratovolcano/cinder-cone behaviour.
Pick a volcano type preset or drag the viscosity, gas and eruption-rate sliders yourself, then hit "Trigger eruption" to watch lava fountains, flows and ash columns respond to the current settings.
Mauna Loa's shield slopes rarely exceed 10°, while stratovolcanoes like Mount Fuji can reach over 30° — almost entirely because their magmas differ in silica content and viscosity, not because of different eruption sizes.