Activity 6. The Puu Oo and Mount St. Helens Eruptions(Grades 9-12)

Activity 9.6 compares and contrasts the current eruption of Kilauea Volcano with the 1980 eruption of Mount St. Helens. The eruptions are compared in an article by Montana (1992). The Puu Oo eruption began as a fissure eruption that became localized at a single, central vent. The Mount St. Helens eruption was at a central vent. Puu Oo is a vent on a shield volcano. Mount St. Helens is a stratovolcano. The current eruption has had 53 episodes over a 10 year period. Mount St. Helens erupted explosively six times and then built a dome. Puu Oo erupted tephra (cinder, reticulite, Pele's hair, Pele's tears, see lesson 15) and lava. Mount St. Helens erupted ash. Puu Oo is on the flank of Kilauea. Mount St. Helens erupted at its summit. The current eruption of Kilauea is in its eleventh year. Intermittent seismicity, small explosions, and the release of gas and small volumes of ash continue at Mount St. Helens. During the current eruption of Kilauea, one person has died and property losses total $61 million. During the 1980 eruption of Mount St. Helens, 57 people died, and property damage totaled $1.1 billion. Both volcanoes are still active. Kilauea is gentle, non-explosive, and relatively safe. Mount St. Helens is violent, explosive, and dangerous. In 11 years, Kilauea has erupted 0.2 cubic mi (0.9 cubic km) of tephra and lava. In May 1980 Mount St. Helens erupted 0.3 cubic mi (1.25 cubic km) of unconsolidated ash. Puu Oo lava fountains reached heights of 1,300 feet (400 m). Mount St. Helens erupted ash to 15 miles (24 km). Kilauea is above a hot spot. Mount St. Helens is above a subduction zone. Kilauea erupts basalt. Mount St. Helens erupted dacite (lesson 13). Both volcanoes are visited by millions of tourists each year. The viscosity of Hawaiian lava is low. The viscosity of lava at Mount St. Helens is high. Hawaiian magmas contain 0.5-1 weight percent gas. Magmas from stratovolcanoes contain 3-4 weight percent gas. Click here for the handout for Activity 6. 
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