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Submarine volcanic vents and pumice rafts...

  1. Mar 25, 2017 #1
    How deep can a submarine volcanic vent be and still generate a significant pumice raft ?

    Sadly, Wiki is a stub, and most of the relevant literature is pay-walled.

    As I understand it, deep vents may generate a lot of pumice, but it never reaches the surface, just stays on the vent's flanks. The famous mega-rafting in 'South Pacific' came from a transient volcanic island, clearly visible on the bemused yachties' photos. Unlike Surtsey, it didn't endure...

    Would a kilometre-submerged rifting event, eg in Canary chain, produce significant, persistent rafting ??
     
  2. jcsd
  3. Mar 25, 2017 #2

    jedishrfu

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  4. Mar 26, 2017 #3

    OmCheeto

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    The paper that the Wired article references does:

    Rapid, Long-Distance Dispersal by Pumice Rafting
    Scott E. Bryan , Alex G. Cook, Jason P. Evans, Kerry Hebden, Lucy Hurrey, Peter Colls, John S. Jell, Dion Weatherley, Jennifer Firn
    Published: July 18, 2012


    The main eruption appears to have been driven principally by magmatic explosivity, with hot pumice and ash largely excluded from the shallow water column by the erupting jet. Airborne cooling of the pumice in the eruption column was therefore important to cool pumice to form the floating pumice raft as experimental studies have shown hot pumice rapidly ingests water, becomes negatively buoyant and sinks.

    I've never heard of "pumice" being associated with deep sea vents.
    But I'm not a geologist, so that doesn't mean much.

    @davenn and @billiards , have you ever heard of such a thing?
     
  5. Mar 26, 2017 #4

    davenn

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    no, nor have I. From all I have so far read, the pumice isn't formed unless the eruption breaches the ocean surface

    ...
    The publication date of that article made me do a double take and reread of the contents ... the research in that article was referring to eruptions in ~ 2006 in the Tongan Isl. region.
    That publication date happens to correspond to a more massive eruption 1000km or so further south in the southern Kermadec Isl. region that was very much deeper undersea and produced large pumice rafts. The approximate depth to the top of the Havre Seamount is around 1100m. The eruption was not initially reported and it was only the pumice rafts, observed by several aircraft crossing the area on the 20th July, 2012, that has scientists going back over prior days satellite images to find the eruption imagery. They also found corresponding seismograms of some 157 events that were centred around the Havre Seamount.

    From everything I have so far been able to find, this is the deepest undersea eruption that has produced pumice. BUT the main point being that the eruption was large enough to breach the ocean surface and produce pumice.

    I haven't found any publication, so far, that suggests that pumice can be produced below sea level in the absence of an atmosphere.
    I would be interesting to see if anything can be found to confirm or deny that :smile:


    Dave
     
  6. Mar 26, 2017 #5

    OmCheeto

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    Wow! I didn't see that number in my research. This kind of reminds me of the numbers from the "Gulf Spill" back in 2010.

    [ref: PF, younger Om]

    Things sure get weird when you move things from a high pressure area to a lower one.

    Fun topic.

    I just found this article:
    Havre Seamount
    October 2012 cruise confirms Havre as pumice source. On 26 October 2012 the New Zealand National Institute of Water and Atmospheric Research’s (NIWA) Research Vessel Tangaroa mapped Havre submarine volcano. NIWA ocean geology scientist Joshu Mountjoy announced finding a new volcanic cone which has formed on the edge of the volcano, towering 240 m above the crater rim that was first mapped in 2002 (Wright and others, 2006). The 2012 Havre eruption was strong enough to breach the ocean surface from a depth of more than 700 m by producing an ash plume, thermal alert, and a pumice raft that covered an area of 22,000 km2, all visible by satellite.

    Sounds like a homework problem from hell.
     
    Last edited: Mar 26, 2017
  7. Mar 28, 2017 #6
    Here's the abstract that piqued my curiosity...
    http://geology.gsapubs.org/content/38/5/391.abstract
    Paywalled, of course

    My understanding of the erudite comments and linked articles in this thread suggest that, for significant pumice rafting, you'd need either a volcanic island, however transitory, or a submerged eruption that sent something resembling a pyroclastic flow all the way to the surface. The former is photogenic provided you can keep engine intakes clear. The latter is surely a 'Be Not There' event...

    Fortunately, this is not a homework question. I began wondering about the first indications if the hypothesised embryonic subduction zone off Gibraltar 'went live'...
    http://geology.gsapubs.org/content/early/2013/06/05/G34100.1.full.pdf+html
    Paywalled, of course, of course...
     
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