USGS/Cascades Volcano Observatory, Vancouver, Washington
Geology of Interactions of Volcanoes, Snow, and Water:
Mt. Spurr (Crater Peak), Alaska
Pyroclastic flows interact with snowpack
During each of the three 1992 eruptions of Crater Peak at Mount
Spurr volcano in Alaska, hot debris interacted with snowpack to
form mixed flows. Some flows were mostly of snow that slightly
melted to make them mobile; others were mostly of pyroclasts
whose snow component entirely melted to make the flows more
mobile than normal dry (so-called "pyroclastic") flows. Some hot
flows were large enough to substantially melt and erode glacier
ice to generate a flood. On the volcano flanks there were a range
of hybrid flows between conventional pyroclastic flows and muddy
floods (so-called "lahars"). The hybrid flows from Crater Peak
resemble some formed by swift snow melting at Mount St. Helens,
Washington during explosive eruptions between 1980 and 1991; at
Nevado del Ruiz, Colombia in 1985; at Mt. Augustine, Alaska in
1976 and 1986; and at Mt. Redoubt, Alaska in 1989-90. Wet flows
are hazardous insofar as their reduced internal friction projects
destructive flows down valleys beyond the reach of dry
("pyroclastic") currents.
Waitt, R.B., 1995, Hybrid wet flows formed by hot pyroclasts
interacting with snow during Crater Peak (Mt. Spurr) eruptions,
summer 1992: U.S. Geological Survey Bulletin 2139, p.107-118.
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11/03/97, Lyn Topinka