@article{fdi:010054363,
  title = {{C}auses and consequences of bimodal grain-size distribution of tephra fall deposited during the {A}ugust 2006 {T}ungurahua eruption ({E}cuador)},
  author = {{E}ychenne, {J}. and {L}e {P}ennec, {J}ean-{L}uc and {T}roncoso, {L}. and {G}ouhier, {M}. and {N}edelec, {J}. {M}.},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he violent {A}ugust 16-17, 2006 {T}ungurahua eruption in {E}cuador witnessed the emplacement of numerous scoria flows and the deposition of a widespread tephra layer west of the volcano. {W}e assess the size of the eruption by determining a bulk tephra volume in the range 42-57 x 10(6) m(3), which supports a {V}olcanic {E}xplosivity {I}ndex 3 event, consistent with calculated column height of 16-18 km above the vent and making it the strongest eruptive phase since the volcano's magmatic reactivation in 1999. {I}sopachs west of the volcano are sub-bilobate in shape, while sieve and laser diffraction grain-size analyses of tephra samples reveal strongly bimodal distributions. {B}ased on a new grain-size deconvolution algorithm and extended sampling area, we propose here a mechanism to account for the bimodal grain-size distribution. {T}he deconvolution procedure allows us to identify two particle subpopulations in the deposit with distinct characteristics that indicate dissimilar transport-depositional processes. {T}he log-normal coarse-grained subpopulation is typical of particles transported downwind by the main volcanic plume. {T}he positively skewed, fine-grained subpopulation in the tephra fall layer shares close similarities with the elutriated co-pyroclastic flow ash cloud layers preserved on top of the scoria flow deposits. {T}he area with the higher fine particle content in the tephra layer coincides with the downwind prolongation of the pyroclastic flow deposits. {T}hese results indicate that the bimodal distribution of grain size in the {T}ungurahua fall deposit results from synchronous deposition of lapilli from the main plume and fine ash elutriated from scoria flows emplaced on the western flank of the volcano. {O}ur study also reveals that inappropriate grain-size data processing may produce misleading determination of eruptive type.},
  keywords = {{T}ephra fall ; {B}imodal grain size ; {V}olcanic {E}xplosivity {I}ndex ; {E}ruption type ; {T}ungurahua volcano},
  booktitle = {},
  journal = {{B}ulletin of {V}olcanology},
  volume = {74},
  numero = {1},
  pages = {187--205},
  ISSN = {0258-8900},
  year = {2012},
  DOI = {10.1007/s00445-011-0517-5},
  URL = {https://www.documentation.ird.fr/hor/fdi:010054363},
}