Guide to Geologic Hazards in Alaska - Glossary

Volcano hazards
Alaska contains over 130 volcanoes and volcanic fields which have been active within the last two million years. Of these volcanoes, about 90 have been active within the last 10,000 years (and might be expected to erupt again), and more than 50 have been active within historical time (since about 1760, for Alaska). Volcanoes produce a wide variety of natural hazards. Some, such as ash clouds and pyroclastic flows, occur as eruption processes. While others, such as water contamination and lahars (mudflows) can occur even when a volcano is quiescent.