Summary of pre-1980 tephra-fall deposits erupted from Mount St. Helens, Washington State, USA

Field-trip guide for exploring pyroclastic density current deposits from the May 18, 1980, eruption of Mount St. Helens, Washington

“…3; from Doukas, 1990). Layers include deposits from lahars and dilute pyroclastic currents, alternating with deposits from concentrated pyroclastic currents, fallout tephra, and lava flows that traveled down the Muddy River-Pine Creek fan (for more details, see Mullineaux, 1986Mullineaux, , 1996. Note that this river-bank exposure is affected annually by winter floods and the quality of the exposure varies from year to year.…”

Geologic map of the Mount Adams volcanic field, Cascade Range of southern Washington

“…There have been no historical eruptions in the Mount Adams volcanic field, and none of the Holocene lava flows has been demonstrated to be younger than 3500 yr B.P., the age of a widespread and distinctive ash layer (layer Ye) erupted from Mount St. Helens (Mullineaux, 1986}. Among the eight Holocene eruptive units mapped, only the windswept lavas of units agg and abr, high on barren ridgecrests, are conceivably younger than the 3500-yearold ash.…”

“…The scoria fall and three of the four ash lenses also overlie ash layers of set P from Mount St. Helens (approximately 2500 years old}, but all underlie St. Helens layer We (A.D. 1482;Mullineaux, 1986). None of these late Holocene tephras, which apparently represent the most recent eruptions of the Mount Adams volcanic field, has been tied to a specific eruptive vent.…”

Notes on historical aspects on the earliest known observations of noctilucent clouds

“…The eruption was characterized by the explosive Plinian phase, followed by several minor explosions (Crandell et al, 1975;Yamaguchi, 1983;Carey et al, 1995;Siebert et al, 2010). The eruptive characteristics have been estimated based on detailed field investigations of fall deposits, dispersal of lithic clasts, and have been derived from theoretical models of tephra dispersal which are capable of calculating eruption column height, magma discharge and wind velocity from dispersal characteristics of fall deposits (Mullineaux, 1986;Carey and Sparks, 1986;Wilson and Walker, 1987).…”