Eychenne J. auteur aut IRD Le Pennec Jean-Luc auteur aut IRD text journalArticle eng text/pdf born digital access 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 0.5I center dot fractions from -4.5I center dot to 3.5I center dot and carried out water pycnometry density measurements on selected size fractions. Results indicate that the mean particle density increases with I center dot up to a plateau of similar to 2.6 g/cm(3) for clasts finer than 1.5I center dot. The density of scoria and pumice increases between -3 and 1I center dot, while dense particle density is sub-constant with grainsize. We show that the mean particle density mu of the vesicular fractions is a function of grainsize i (I center dot scale) given by a sigmoidal law: , where K, beta, alpha 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. specialized Density distributions Sigmoidal law Componentry proportions Volume-to-mass conversion 064 020 74 10 2243-2249 2012 0258-8900 https://www.documentation.ird.fr/hor/fdi:010058196 10.1007/s00445-012-0671-4 0258-8900 [F B010058196] https://www.documentation.ird.fr/hor/fdi:010058196 https://www.documentation.ird.fr/intranet/publi/2012/12/010058196.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2013-01-09 2017-08-23 fdi:010058196 fre