Volcanic Eruption Types and Hazards

Volcanologists classify eruptions using several overlapping schemes, the most widely used of which is the Volcanic Explosivity Index (VEI), developed by Chris Newhall of the USGS and Stephen Self of the University of Hawaii in 1982. The VEI runs on a logarithmic scale from 0 to 8, based primarily on the volume of ejected material (tephra) and the height of the eruption column, so that each whole-number increase represents roughly a tenfold increase in erupted volume. A VEI of 0 to 1 describes gentle, effusive eruptions such as those typical of Hawaii's Kilauea, while a VEI of 8, the maximum recorded category, describes eruptions that expel more than 1,000 cubic kilometers of material, an event so rare that none has occurred in recorded human history.