Pick a real volcano (Mauna Loa, Stromboli, Parícutin, Mount Fuji, Vesuvius or Mount St Helens) or change the silica and gas yourself to go from gentle lava flows to an explosive Plinian eruption with an ash column and pyroclastic flows. Move the village and switch on the hazard zones to see who is in danger.
- What are the parts of a volcano?
- The magma chamber (a store of molten rock in the crust), the main vent (the pipe magma rises through), the crater at the top, secondary vents on the sides, and the cone itself, built from layers of ash and solidified lava.
- Why do volcanoes erupt?
- Magma is less dense than the rock around it, so it rises. Gas dissolved in it comes out as bubbles as the pressure drops, like opening a fizzy drink. When the pressure of magma and gas is greater than the strength of the rock above, the volcano erupts.
- What are the three main types of volcano?
- Shield volcanoes (wide and gentle, built from runny basalt lava, like Mauna Loa), composite or stratovolcanoes (tall and steep, with layers of ash and lava, like Mount Fuji and Vesuvius) and cinder cones (small, steep piles of cinders, like Parícutin).
- Why are some eruptions explosive and others gentle?
- It depends on the magma. Runny, low-silica basalt lets gas escape easily, so it pours out as lava. Sticky, high-silica magma traps the gas until it shatters into ash, giving explosive eruptions with ash columns and pyroclastic flows.
- What is a pyroclastic flow?
- A fast-moving avalanche of hot ash, gas and rock that races down a volcano at over 100 km/h and more than 500 °C. It is the deadliest volcanic hazard and destroyed Pompeii in AD 79.
- What is the VEI?
- The Volcanic Explosivity Index measures how big an eruption is, mainly by the volume of material it throws out. It runs from 0 (gentle Hawaiian lava flows) to 8 (super-eruptions); each step is about ten times bigger.