Subaerial Liquefied Flow of Volcaniclastic Sediments, Central Japan

  1. William McCaffrey,
  2. Ben Kneller and
  3. Jeff Peakall
  1. K. Nakayama

Published Online: 17 MAR 2009

DOI: 10.1002/9781444304275.ch17

Particulate Gravity Currents

Particulate Gravity Currents

How to Cite

Nakayama, K. (2001) Subaerial Liquefied Flow of Volcaniclastic Sediments, Central Japan, in Particulate Gravity Currents (eds W. McCaffrey, B. Kneller and J. Peakall), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304275.ch17

Editor Information

  1. School of Earth Sciences, University of Leeds, Leeds, LS2 9JT, West Yorkshire, UK

Author Information

  1. Department of Geoscience, Shimane University, Matsue, 690-8504 Japan

Publication History

  1. Published Online: 17 MAR 2009
  2. Published Print: 24 APR 2001

ISBN Information

Print ISBN: 9780632059218

Online ISBN: 9781444304275

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Keywords:

  • subaerial liquefied flow of volcaniclastic sediments, central Japan;
  • volcaniclastic deposits formed by variety of sedimentary processes and mechanisms;
  • dispersive pressure equivalence;
  • Souri tephra bed - within fluvial Mio-Pleistocene Tokai Group;
  • liquefied flow of volcaniclastic sedimentation;
  • hydraulic settling equivalence and dispersive pressure equivalence during grain transport using methods of Cole and Stanley;
  • depositional succession of subaerial liquefied flow

Summary

Subaerial liquefied flow of reworked volcaniclastic sediments is identified by analysis of grain-size distributions and settling velocities, combined with field observation of mudflow deposits of the Pliocene Souri tephra bed within the fluvial Tokai Group, central Japan. The tephra consists predominantly of volcanic glass particles and pumice grains. Subaerial liquefied flow has previously been considered impossible, but this study shows it may occur when grains have relatively low settling velocities due to their surface roughness and/or low density. Experimentally determined settling velocities for these tephra grains show that the transition from laminar to turbulent flow is promoted at a lower grain Reynolds number than for smooth spherical particles of equivalent volume. The typical flow unit is divided into subunits A, B and C, in ascending order. Grains in subunit A were supported under hydraulic settling equivalence, and hence both glass particles and pumice grains having the same settling velocity were deposited simultaneously from suspended sediment dispersion. The grain-support mechanism of subunit B is autofluidization, because the superficial escape velocity of fluid released from subunit A can be greater than superficial fluid velocity at minimum fluidization for grains in subunit B. Subunit C consists of comparatively finer grains, which are elutriated from the fluidized part, and deposited as suspension fallout. This is the first quantitative and qualitative description of subaerial liquefied flow, and the succession described can be considered representative of such deposits.