|This footprint and others preserved in the muddy ash deposits of Kilauea's explosive eruption in 1790 are believed to be those of Hawaiians who survived the hot explosion cloud. (Photograph by James F. Martin, National Park Service.)|
Infrequent explosive activityExplosive eruptions that deposit large volumes of pyroclastic debris over large areas -- like the May 1980 eruption of Mount St. Helens -- are rare at Hawaiian volcanoes. The term "pyroclastic" -- derived from Greek pyro (fire) and klastos (broken) -- is a general term to describe all types of fragmented new magma or old solid rock ejected during explosive eruptions. Less than 1 percent of Hawaiian eruptions have been violently explosive, based on the scarcity of pyroclastic deposits. In contrast, some volcanic chains formed along the convergent boundaries of the Earth's tectonic plates contain 90 percent or more pyroclastic material.
In 1790, a series of major explosive eruptions, which probably lasted a few days
to a few weeks, deposited a blanket of pyroclastic debris up to 30 feet thick in
and around Kilauea summit.