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Volcanic eruption of the mid-ocean ridge along the East Pacific Rise crest at 9°45–52′N: Direct submersible observations of seafloor phenomena associated with an eruption event in April, 1991

Dawn J Wright; R. Haymon; Dawn J Wright; Michael Perfit; D. Fornari

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  <identifier identifierType="DOI">10.5281/zenodo.268748</identifier>
      <creatorName>Dawn J Wright</creatorName>
      <affiliation>Environmental Systems Research Institute</affiliation>
      <creatorName>R. Haymon</creatorName>
      <creatorName>Dawn J Wright</creatorName>
      <affiliation>Environmental Systems Research Institute</affiliation>
      <creatorName>Michael Perfit</creatorName>
      <affiliation>University of Florida</affiliation>
      <creatorName>D. Fornari</creatorName>
    <title>Volcanic eruption of the mid-ocean ridge along the East Pacific Rise crest at 9°45–52′N: Direct submersible observations of seafloor phenomena associated with an eruption event in April, 1991</title>
    <subject>Earth Sciences</subject>
    <subject>Mid Ocean Ridge</subject>
    <subject>Physical sciences</subject>
    <subject>High Temperature</subject>
    <subject>Earth and Planetary Science</subject>
    <subject>Hydrothermal Vent</subject>
    <subject>Phase Separation</subject>
    <subject>High Density Concrete</subject>
    <subject>Volcanic Eruption</subject>
    <subject>Critical Temperature</subject>
    <subject>Heat Loss</subject>
    <date dateType="Issued">1993-05-20</date>
  <resourceType resourceTypeGeneral="JournalArticle"/>
    <alternateIdentifier alternateIdentifierType="url">https://zenodo.org/record/268748</alternateIdentifier>
    <rights rightsURI="https://creativecommons.org/licenses/by/4.0/legalcode">Creative Commons Attribution 4.0 International</rights>
    <rights rightsURI="info:eu-repo/semantics/openAccess">Open Access</rights>
    <description descriptionType="Abstract">In April, 1991, we witnessed from the submersible Alvin a suite of previously undocumented seafloor phenomena
accompanying an in-progress eruption of the mid-ocean ridge on the East Pacific Rise crest at 9°45'N-52'N. The volume of
the eruption could not be precisely determined, although comparison of pre- and post-eruption SeaBeam bathymetry
indicate that any changes in ridge crest morphology resulting from the eruption were &amp;lt; 10 m high.
Effects of the eruption included: (1) increased abundance and redistribution of hydrothermal vents, disappearance of
numerous vent communities, and changes in characteristics of vent fauna and mineral deposits within the eruption area
since December, 1989; (2) murkiness of bottom waters up to tens of meters above the seafloor due to high densities of
suspended mineral and biogenic particulates; (3) destruction of a vent community by lava flows, mass wasting, and possible
hydrovolcanic explosion at a site known as 'Tubeworm Barbecue' in the axial summit caldera (ASC) at 9°50.6'N; (4)
near-critical temperatures of hydrothermal vent fluids, ranging up to 403°C; (5) temporal variations over a 2 week interval in
both temperatures and chemical/isotopic compositions of hydrothermal fluids; (6) unusual compositions of end-member
vent fluids, with pH values ranging to a record low of 2.5, salinities ranging as low as 0.3 wt% NaCI (one-twelfth that of
seawater), and dissolved gases reaching high concentrations (&amp;gt; 65 mmol/1 for both CO 2 and H2S); (7) venting at
temperatures above 380°C of visually detectable white vapor that transformed to plumes of gray smoke a few centimeters
above vent orifices; (8) disorganized venting of both high-temperature fluids (black and gray smoke) and large volumes of cooler, diffuse hydrothermal fluids directly from the basaltic seafloor, rather than from hydrothermal mineral constructions;
(9) rapid and extensive growth of flocculent white bacterial mats (species unknown) on and under the seafloor in areas
experiencing widespread venting of diffuse hydrothermal fluid; and (10) subseafloor downslope migration of magma normal
to the ridge axis in a network of small-scale (1-5 m diameter) lava tubes and channels to distances at least 100-200 m
outside the ASC.
We suggest that, in April, 1991, intrusion of dikes in the eruption area to &amp;lt; 200 m beneath the ASC floor resulted in
phase separation of fluids near the tops of the dikes and a large flux of vapor-rich hydrothermal fluids through the overlying
rubbly, cavernous lavas. Low salinities and gas-rich compositions of hydrothermal fluids sampled in the eruption area are
appropriate for a vapor phase in a seawater system undergoing subcritical liquid-vapor phase separation (boiling) and phase
segregation. Hydrothermal fluids streamed directly from fissures and pits that may have been loci of lava drainback and/or
hydrovolcanic explosions. These fissures and pits were lined with white mats of a unique fast-growing bacteria that was the
only life associated with the brand-new vents. The prolific bacteria, which covered thousands of square meters on the ridge
crest and were also abundant in subseafloor voids, may thrive on high levels of gases in the vapor-rich hydrothermal fluids
initially escaping the hydrothermal system. White bacterial particulates swept from the seafloor by hydrothermal vents
swirled in an unprecedented biogenic 'blizzard' up to 50 m above the bottom. The bacterial proliferation of April, 1991 is
likely to be a transient bloom that will be checked quickly either by decline of dissolved gas concentrations in the fluids as
rapid heat loss brings about cessation of boiling, and/or by grazing as other organisms are re-established in the biologically
devastated area.</description>
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