Volcanoes can cause damage and loss of life.
One famous example is the eruption of Vesuvius in 79 AD, which buried the roman towns of Pompeii and Herculaneum.
Many of the people killed in that eruption were killed by pyroclastic flows, which are hot clouds of gas full of tiny particles of volcanic rocks.
These clouds rush down at high speed.
The towns were buried in volcanic ash, and excavation has revealed buildings and streets.