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Tephra-fall deposits from the 1992 eruption of Crater Peak, Alaska: implications of clast textures for eruptive processes

January 1, 1998

The 1992 eruption of Crater Peak, Mount Spurr, Alaska, involved three subplinian tephra-producing events of similar volume and duration. The tephra consists of two dense juvenile clast types that are identified by color, one tan and one gray, of similar chemistry, mineral assemblage, and glass composition. In two of the eruptive events, the clast types are strongly stratified with tan clasts dominating the basal two thirds of the deposits and gray clasts the upper one third. Tan clasts have average densities between 1.5 and 1.7 g/cc and vesicularities (phenocryst free) of approximately 42%. Gray clasts have average densities between 2.1 and 2.3 g/cc, and vesicularities of approximately 20%; both contain abundant microlites. Average maximum plagioclase microlite lengths (13-15 ??m) in gray clasts in the upper layer are similar regardless of eruptive event (and therefore the repose time between them) and are larger than average maximum plagioclase microlite lengths (9-11 ???m) in the tan clasts in the lower layer. This suggests that microlite growth is a response to eruptive processes and not to magma reservoir heterogeneity or dynamics. Furthermore, we suggest that the low vesicularities of the clasts are due to syneruptive magmatic degassing resulting in microlitic growth prior to fragmentation and not to quenching of clasts by external groundwater.

Citation Information

Publication Year 1998
Title Tephra-fall deposits from the 1992 eruption of Crater Peak, Alaska: implications of clast textures for eruptive processes
DOI 10.1007/s004450050208
Authors C.A. Gardner, K.V. Cashman, C.A. Neal
Publication Type Article
Publication Subtype Journal Article
Series Title Bulletin of Volcanology
Series Number
Index ID 70020831
Record Source USGS Publications Warehouse
USGS Organization

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