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The interplay among clast size, vesicularity, postfragmentation expansion, and clast breakage: An example from the 1.8 ka Taupo eruption


Mitchell, SJ and Biass, S and Houghton, RF and Anderson, A and Bonny, E and Walker, BH and Mintz, BG and Turner, NR and Frank, D and Carey, RJ and Rosenberg, MD, The interplay among clast size, vesicularity, postfragmentation expansion, and clast breakage: An example from the 1.8 ka Taupo eruption, Field Volcanology: A Tribute to the Distinguished Career of Don Swanson, Geological Society of America, MP Poland, MO Garcia, VE Camp and A Grunder (ed), United States, pp. 375-383. ISBN 9780813795386 (2018) [Research Book Chapter]

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Copyright 2018 The Geological Society of America

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DOI: doi:10.1130/2018.2538(17)


Field studies of tephra-fall deposits traditionally use the density of juvenile pyroclasts to determine vesicularity of the host magma at the point of fragmentation. A range of pyroclast sizes between 16 and 32 mm has commonly been chosen for this purpose. Larger pyroclasts outside this range may undergo postfragmentation vesiculation due to slow cooling of the interior of the clasts, while smaller pyroclasts may be too small to represent accurately the distribution of the largest vesicles. The assumption of this method, of course, is that the 16-32 mm size range is representative of the fragmented magma. We explore, in detail, variations in density over a size range of 4-128 mm from Unit 2 pyroclasts of the 1.8 ka Taupo eruption and make inferences about the roles of postfragmentation vesiculation and secondary breakage of pyroclasts. We find (1) there is a clear threshold for onset of postfragmentation vesiculation at >32 mm, and (2) there are broken small pieces of the largest pyroclasts in the sample that artificially skew the density distribution for smaller size fractions. We constrain uncertainty associated with vesicularity measurements and offer best-practice recommendations in the hope of improving consistency of field sampling and laboratory processing of pyroclast populations for vesicularity studies.

Item Details

Item Type:Research Book Chapter
Keywords:grainsize, field studies, volcanology
Research Division:Earth Sciences
Research Group:Geology
Research Field:Volcanology
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the earth sciences
UTAS Author:Carey, RJ (Associate Professor Rebecca Carey)
ID Code:129337
Year Published:2018
Funding Support:Australian Research Council (DE150101190)
Deposited By:Earth Sciences
Deposited On:2018-11-23
Last Modified:2019-03-14

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