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Title: Submarine deposits from pumiceous pyroclastic density currents traveling over water: An outstanding example from offshore Montserrat (IODP 340)

Pyroclastic density currents have been observed to both enter the sea, and to travel over water for tens of kilometers. Here, we identified a 1.2-m-thick, stratified pumice lapilli-ash cored at Site U1396 offshore Montserrat (Integrated Ocean Drilling Program [IODP] Expedition 340) as being the first deposit to provide evidence that it was formed by submarine deposition from pumice-rich pyroclastic density currents that traveled above the water surface. The age of the submarine deposit is ca. 4 Ma, and its magma source is similar to those for much younger Soufrière Hills deposits, indicating that the island experienced large-magnitude, sub-aerial caldera-forming explosive eruptions much earlier than recorded in land deposits. The deposit's combined sedimentological characteristics are incompatible with deposition from a submarine eruption, pyroclastic fall over water, or a submarine seafloor-hugging turbidity current derived from a subaerial pyroclastic density current that entered water at the shoreline. The stratified pumice lapilli-ash unit can be subdivided into at least three depositional units, with the lowermost one being clast supported. The unit contains grains in five separate size modes and has a >12 phi range. Particles are chiefly sub-rounded pumice clasts, lithic clasts, crystal fragments, and glass shards. Pumice clasts are very poorly segregated frommore » other particle types, and lithic clasts occur throughout the deposit; fine particles are weakly density graded. We interpret the unit to record multiple closely spaced (< 2 d) hot pyroclastic density currents that flowed over the ocean, releasing pyroclasts onto the water surface, and settling of the various pyroclasts into the water column. Our settling and hot and cold flotation experiments show that waterlogging of pumice clasts at the water surface would have been immediate. The overall poor hydraulic sorting of the deposit resulted from mixing of particles from multiple pulses of vertical settling in the water column, attesting to complex sedimentation. Slow-settling particles were deposited on the seafloor together with faster-descending particles that were delivered at the water surface by subsequent pyroclastic flows. The final sediment pulses were eventually deflected upon their arrival on the seafloor and were deposited in laterally continuous facies. This study emphasizes the interaction between products of explosive volcanism and the ocean and discusses sedimentological complexities and hydrodynamics associated with particle delivery to water.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ;  [9] ;  [10]
  1. National Oceanography Centre, Southampton (United Kingdom); Univ. of Otago, Dunedin (New Zealand). Dept. of Geology; Univ. of Tasmania, Hobart, TAS (Australia). School of Physical Sciences and Centre of Excellence in Ore Deposits (CODES)
  2. Univ. of California, Berkeley, CA (United States). Dept. of Earth and Planetary Science
  3. Univ. of Otago, Dunedin (New Zealand). Dept. of Geology
  4. National Oceanography Centre, Southampton (United Kingdom)
  5. Univ. of New Hampshire, Durham, NH (United States). Climate Change Research Center
  6. Univ. of Birmingham (United Kingdom). School of Geography, Earth and Environmental Sciences
  7. Johannes Gutenberg Univ., Mainz (Germany). Inst. of Geosciences
  8. Univ. of Southampton (United Kingdom). School of Ocean and Earth Science
  9. Univ. Paris Diderot, Paris (France). Inst. de Physique du Globe de Paris
  10. National Inst. of Advanced Industrial Science and Technology (AIST), Ibaraki (Japan). Geological Survey of Japan
Publication Date:
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Geological Society of America, Bulletin
Additional Journal Information:
Journal Volume: 129; Journal Issue: 3-4; Journal ID: ISSN 0016-7606
Publisher:
Geological Society of America
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES
OSTI Identifier:
1480776

Jutzeler, M., Manga, M., White, J. D. L., Talling, P. J., Proussevitch, A. A., Watt, S. F. L., Cassidy, M., Taylor, R. N., Le Friant, A., and Ishizuka, O.. Submarine deposits from pumiceous pyroclastic density currents traveling over water: An outstanding example from offshore Montserrat (IODP 340). United States: N. p., Web. doi:10.1130/B31448.1.
Jutzeler, M., Manga, M., White, J. D. L., Talling, P. J., Proussevitch, A. A., Watt, S. F. L., Cassidy, M., Taylor, R. N., Le Friant, A., & Ishizuka, O.. Submarine deposits from pumiceous pyroclastic density currents traveling over water: An outstanding example from offshore Montserrat (IODP 340). United States. doi:10.1130/B31448.1.
Jutzeler, M., Manga, M., White, J. D. L., Talling, P. J., Proussevitch, A. A., Watt, S. F. L., Cassidy, M., Taylor, R. N., Le Friant, A., and Ishizuka, O.. 2016. "Submarine deposits from pumiceous pyroclastic density currents traveling over water: An outstanding example from offshore Montserrat (IODP 340)". United States. doi:10.1130/B31448.1. https://www.osti.gov/servlets/purl/1480776.
@article{osti_1480776,
title = {Submarine deposits from pumiceous pyroclastic density currents traveling over water: An outstanding example from offshore Montserrat (IODP 340)},
author = {Jutzeler, M. and Manga, M. and White, J. D. L. and Talling, P. J. and Proussevitch, A. A. and Watt, S. F. L. and Cassidy, M. and Taylor, R. N. and Le Friant, A. and Ishizuka, O.},
abstractNote = {Pyroclastic density currents have been observed to both enter the sea, and to travel over water for tens of kilometers. Here, we identified a 1.2-m-thick, stratified pumice lapilli-ash cored at Site U1396 offshore Montserrat (Integrated Ocean Drilling Program [IODP] Expedition 340) as being the first deposit to provide evidence that it was formed by submarine deposition from pumice-rich pyroclastic density currents that traveled above the water surface. The age of the submarine deposit is ca. 4 Ma, and its magma source is similar to those for much younger Soufrière Hills deposits, indicating that the island experienced large-magnitude, sub-aerial caldera-forming explosive eruptions much earlier than recorded in land deposits. The deposit's combined sedimentological characteristics are incompatible with deposition from a submarine eruption, pyroclastic fall over water, or a submarine seafloor-hugging turbidity current derived from a subaerial pyroclastic density current that entered water at the shoreline. The stratified pumice lapilli-ash unit can be subdivided into at least three depositional units, with the lowermost one being clast supported. The unit contains grains in five separate size modes and has a >12 phi range. Particles are chiefly sub-rounded pumice clasts, lithic clasts, crystal fragments, and glass shards. Pumice clasts are very poorly segregated from other particle types, and lithic clasts occur throughout the deposit; fine particles are weakly density graded. We interpret the unit to record multiple closely spaced (< 2 d) hot pyroclastic density currents that flowed over the ocean, releasing pyroclasts onto the water surface, and settling of the various pyroclasts into the water column. Our settling and hot and cold flotation experiments show that waterlogging of pumice clasts at the water surface would have been immediate. The overall poor hydraulic sorting of the deposit resulted from mixing of particles from multiple pulses of vertical settling in the water column, attesting to complex sedimentation. Slow-settling particles were deposited on the seafloor together with faster-descending particles that were delivered at the water surface by subsequent pyroclastic flows. The final sediment pulses were eventually deflected upon their arrival on the seafloor and were deposited in laterally continuous facies. This study emphasizes the interaction between products of explosive volcanism and the ocean and discusses sedimentological complexities and hydrodynamics associated with particle delivery to water.},
doi = {10.1130/B31448.1},
journal = {Geological Society of America, Bulletin},
number = 3-4,
volume = 129,
place = {United States},
year = {2016},
month = {9}
}