@article{fdi:010064109,
  title = {{N}ature and velocity of pyroclastic density currents inferred from models of entrainment of substrate lithic clasts},
  author = {{R}oche, {O}livier},
  editor = {},
  language = {{ENG}},
  abstract = {{D}eposits of pyroclastic density currents ({PDC}s) often contain accidental lithic clasts of typical size of 0.1-1 m captured from an underlying substrate by the parent flows at distances up to several tens of kilometers from the eruptive vent. {I}n order to gain insights into the nature of {PDC}s, this study investigates the conditions required for entrainment of particles from a granular substrate by a gas-particle density current, with special emphasis to ignimbrite-forming currents whose dynamics are controversial. {T}he two types of physics of emplacement of {PDC}s proposed in literature are considered. {T}he first model deals with a hydraulically rough, dilute turbulent {PDC} of bulk density of similar to 1-10 kg/m(3) and considers that entrainment through both traction and saltation is controlled by a {S}hield criterion at high (>10(4)) particle {R}eynolds number. {T}he second model considers entrainment by a {PDC} consisting of a dense basal flow of bulk density of the order of 10(3) kg/m(3) and with high interstitial gas pore pressure. {T}his model involves uplift of substrate particles, caused by an upward pressure gradient at the flow-substrate interface, and then transport and deposition on the aggrading basal deposit of the flow as demonstrated by recent laboratory experiments. {R}esults show that a dilute {PDC} can entrain blocks of maximum size of similar to 10-15 cm (for a block density of 2000-3000 kg/m(3)) if maximum current velocities up to similar to 100 m/s are taken into account. {T}his, in turn, suggests that larger (heavier) blocks found in deposits were captured by {PDC}s if these had a dense basal flow. {T}he dense flow model predicts that {PDC}s have the potential to entrain metric blocks, whose maximum size (up to similar to 2-5 m) decreases with decreasing atmospheric pressure (i.e. increasing altitude). {A}pplication of the model considering published data on the characteristics of accidental blocks in several well-studied ignimbrites indicates that the velocity of the parent dense {PDC}s was up to similar to 25-30 m/s.},
  keywords = {pyroclastic density currents ; substrate entrainment ; erosion ; accidental blocks ; ignimbrite ; flow velocity},
  booktitle = {},
  journal = {{E}arth and {P}lanetary {S}cience {L}etters},
  volume = {418},
  numero = {},
  pages = {115--125},
  ISSN = {0012-821{X}},
  year = {2015},
  DOI = {10.1016/j.epsl.2015.03.001},
  URL = {https://www.documentation.ird.fr/hor/fdi:010064109},
}