Fact: Although this is true in Hawaii, the hazards differ at the more than 150 volcanoes in other parts of the United States.
Principal hazards outside Hawaii include:
1. Volcanic ashfall resulting from explosive-style eruptions. Volcanic ash, the shattered remnants of volcanic rock, rises into the atmosphere, where it is a hazard to aircraft and affects large areas downwind when it falls back to earth. Where it falls in sufficient quantity, it can cause difficulties for vehicles, machinery, and utilities, and can be injurious to human health.
2. Volcanic mudflows (lahars) resulting from the sudden melting of snow and ice during eruptions. Lahars can inundate river valleys tens of miles distant, destroying bridges, highways, and other types of development, as well as endangering people.