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GEOREF RECORD

Hybrid fall deposits in the Bishop Tuff, California; a novel pyroclastic depositional mechanism

Colin J. N. Wilson and Wes H. Hildreth
Hybrid fall deposits in the Bishop Tuff, California; a novel pyroclastic depositional mechanism
Geology (Boulder) (January 1998) 26 (1): 7-10

Abstract

Hybrid fall deposits in the Bishop Tuff show features common to both archetypal fall and surge deposits. Like normal-fall deposits, they have an overall plane-parallel bedding and flat-lying pumice clasts but also, like surge deposits, they show variable development of cross-bedding, some crystal and pumice sorting, and some rounding of pumice clasts. All variations exist from normal-fall deposits, through streaky material with incipient development of cross-bedding, to the hybrid fall deposits with well-developed cross-bedding. The streaky and hybrid deposits are interpreted as fall material contemporaneously redeposited by strong (up to 40 m/s) swirling winds, comparable to firestorm whirlwinds, generated by air currents associated with coeval emplacement of pyroclastic flows. Recognition of hybrid fall deposits is important in interpreting the dynamics of explosive eruptions and correctly assessing volcanic hazards. However, although such deposits may be commonly produced by explosive eruptions, especially where pyroclastic flows accompany fall activity, they are likely to be overlooked, or wrongly interpreted as surge deposits or secondary, reworked material.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 26
Serial Issue: 1
Title: Hybrid fall deposits in the Bishop Tuff, California; a novel pyroclastic depositional mechanism
Affiliation: Institute of Geological and Nuclear Sciences, Taupo, New Zealand
Pages: 7-10
Published: 199801
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 18
Accession Number: 1998-019155
Categories: Igneous and metamorphic petrologyQuaternary geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sketch map
N37°30'00" - N37°30'00", W118°30'00" - W118°30'00"
Secondary Affiliation: U. S. Geological Survey, Menlo Park, CA, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 199808
Program Name: USGSOPNon-USGS publications with USGS authors
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