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Bulletin of Volcanology

, Volume 74, Issue 10, pp 2243–2249 | Cite as

Sigmoidal particle density distribution in a subplinian scoria fall deposit

  • Julia EychenneEmail author
  • Jean-Luc Le Pennec
Short Scientific Communication

Abstract

A general expression to describe particle density distribution in tephra fall deposits is essential to improve fallout tephra mass determination and numerical modelling of tephra dispersion. To obtain particle density distributions in tephra fall deposits, we performed high-resolution componentry and particle density analyses on samples from the 2006 subplinian eruption of Tungurahua volcano in Ecuador. Six componentry classes, including pumice and scoria, have been identified in our sample collection. We determined the class of 300 clasts in each 0.5ϕ fractions from −4.5ϕ to 3.5ϕ and carried out water pycnometry density measurements on selected size fractions. Results indicate that the mean particle density increases with ϕ up to a plateau of ~2.6 g/cm3 for clasts finer than 1.5ϕ. The density of scoria and pumice increases between −3 and 1ϕ, while dense particle density is sub-constant with grainsize. We show that the mean particle density μ of the vesicular fractions is a function of grainsize i (ϕ scale) given by a sigmoidal law: \( \mu (i)={{{K+\beta }} \left/ {{\left( {1+\alpha {e^{-ri }}} \right)}} \right.} \), where K, β, α and r are constants. These sigmoidal distributions can be used to determine accurately the load of each componentry class and should be applicable to many tephra deposits and for modelling purposes.

Keywords

Density distributions Sigmoidal law Componentry proportions Volume-to-mass conversion 

Notes

Acknowledgements

This work is part of a PhD project by J Eychenne and has been completed in the context of a project entitled “Volcanic hazards associated with open-system activity” (Action Incitative of IRD). L Gailler and A Delcamp carried out a great part of the tedious grain counting and pycnometry analysis, and are warmly acknowledged. The authors thank C Bonnadona and J-C Komorowski for comments on an earlier version of the manuscript. Reviews of the manuscript by V Manville and A Durant and editorial handling by J White are warmly acknowledged. This is Laboratory of Excellence ClerVolc contribution no. 32.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2012

Authors and Affiliations

  1. 1.OPGC, Laboratoire Magmas et Volcans, Clermont UniversitéUniversité Blaise PascalClermont-FerrandFrance
  2. 2.CNRS, UMR 6524, LMVClermont-FerrandFrance
  3. 3.IRD, R 163, LMVClermont-FerrandFrance

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