@article{PAR00009628,
  title = {{S}igmoidal particle density distribution in a subplinian scoria fall deposit},
  author = {{E}ychenne, {J}. and {L}e {P}ennec, {J}ean-{L}uc},
  editor = {},
  language = {{ENG}},
  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. {T}o 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 {T}ungurahua volcano in {E}cuador. {S}ix componentry classes, including pumice and scoria, have been identified in our sample collection. {W}e determined the class of 300 clasts in each 0.5{I} center dot fractions from -4.5{I} center dot to 3.5{I} center dot and carried out water pycnometry density measurements on selected size fractions. {R}esults 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 1.5{I} center dot. {T}he density of scoria and pumice increases between -3 and 1{I} center dot, while dense particle density is sub-constant with grainsize. {W}e 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. {T}hese 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 = {{D}ensity distributions ; {S}igmoidal law ; {C}omponentry proportions ; {V}olume-to-mass conversion},
  booktitle = {},
  journal = {{B}ulletin of {V}olcanology},
  volume = {74},
  numero = {10},
  pages = {2243--2249},
  ISSN = {0258-8900},
  year = {2012},
  DOI = {10.1007/s00445-012-0671-4},
  URL = {https://www.documentation.ird.fr/hor/{PAR}00009628},
}