This so-called "ice diamict" was deposited on both the north and south volcano flanks. The northside icy flows reached as far from the vent as 14 km (9 mi) laterally over an altitude drop of 2.3 km (7540 ft) and covered an area of about 5.7 km2 (2.2 sq. mi). On Crescent Glacier on the south volcano flank a composite ice diamict is as thick as 20 m (66 ft). It travelled laterally 4.3 km (2.7 mi) while dropping 1.7 km (5575 ft).
Erupting, fragmenting hot juvenile lava triggered and turbulently mixed with snow at covering the glacier heads. These flows rapidly entrained more snow and ice blocks from the crevassed glacier. On the north flank, a trailing watery flood swept over the new icy deposits. The last floods reworked valley- floor snowpack and swept 35 km (22 mi) downvalley to the sea.
Similar flows of mixed ice grains and fragmented hot erupted debris resulted from the 13 November 1985 eruption of Nevado del Ruiz volcano in Colombia (20,000 killed), as well as from eruptions of snowclad Mount St. Helens between 1982 and 1984. Such deposits at snowclad volcanoes soon become extensively reworked and hard to recognize in the geologic record. Hazards to people and property from these events are thus greater than the preserved geologic record suggests.
Waitt, R.B., Gardner, C.A., Pierson, T.C., Major, J.J., and Neal, C.A., 1994, Unusual ice diamicts emplaced during 15 December 1989 eruption of Redoubt Volcano, Alaska: Journal of Vocanology and Geothermal Research, v. 62, p. 409-428.
