Glossary

Pyroclastic Flow

A pyroclastic flow is a mixture of scorching gas, ash and rock that races down the slopes of a volcano. It can exceed 100 km/h and several hundred degrees.

It is the deadliest volcanic hazard. It cannot be outrun once it starts, hence the importance of evacuating in advance. It destroyed Pompeii in AD 79 and Saint-Pierre in Martinique in 1902.

Examples on the Map

• Vesuvius
• Pinatubo

Other Definitions

• Tectonic Plate
• Subduction
• Mid-Ocean Ridge
• Transform Fault
• Fault
• Earthquake, Epicentre and Hypocentre
• Magnitude
• Intensity (Mercalli Scale)
• Aftershock
• Tsunami
• Active Volcano
• Stratovolcano
• Shield Volcano
• Caldera
• Volcanic Explosivity Index (VEI)
• Lahar
• Hotspot
• Tropical Cyclone, Hurricane, Typhoon
• Saffir-Simpson Scale
• Aurora and Kp Index