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Woods Hole Oceanographic Institution

Samuel A. Soule

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Projects
» Seawater-lava interaction

» EPR Volcanism

» Deccan Flood Basalts

» Subaerial lava flows


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Lava drip (stalagtite) on the interior surface of a lobate lava crust collected at the Galapagos Spreading Center. Drips can be delicate, bulbous, or flange-like and reflect the presence of a seawater-derived vapor layer that has collected beneath the quenched crust of a lava flow. (Adam Soule)


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The interior surface of lava crusts that have interacted with a seawater-derived vapor phase are mantled by crystallites that have formed from the melt with contributions from the vapor. Sodium (Na) rich plagioclase feldspar are the the larger crystals at the center of the image. Dioposide are the smaller crystals coating the interior surface of the crust. (Adam Soule)


Incorporation of seawater into active submarine lava flows: impact on lava chemistry and dynamics

Collaborators:
Dan Fornari (WHOI) Mike Perfit (U Florida) Mark Reed (U Oregon) Joe Cann (U Leeds) Ian Ridley (USGS)

Evidence for the interaction between seawater and lava during emplacement can be observed in solidified flows at a variety of scales including rapid quenching of their outer crusts and the formation of lava pillars through the body of the flow. Recently, an additional interaction, incorporation of heated seawater (vapor) into the body of a flow, has been proposed. Large voids and vesicles beneath the surface crust of lobate and sheet MOR lava flows and lava drips found within those cavities have been cited as evidence for this interaction, but cannot rule out magmatic vapor as a plausible source of the vapor. The voids resulting from this interaction contribute to the high porosity of the shallow ocean crust and play an important role in crustal permeability and hydrothermal circulation at mid-ocean ridges, and thus it is important to understand their origin. We investigate samples from the fast-spreading East Pacific Rise and intermediate-spreading Galapagos Spreading Center to characterize this reaction, identify the source of the vapor, and investigate the implications of a vapor layer on submarine lava flow dynamics. We find that samples that have interacted with a vapor have a zone of increased vesicularity on the underside of the lava crust and a crystal fringe (i.e., coating of precipitate minerals) that are distinct in form and chemistry from those crystallized from the melt. We use thermochemical modeling to simulate reaction between the lava and a vapor and find that only with seawater can we reproduce the phase assemblage we observe within the crystal fringe. Model results suggest that large-scale contamination of the lava by mass exchange with the vapor is unlikely, but we observe local enrichment of the lava in Cl that has resulted from the incorporation of a brine separated from the seawater. We suggest that high eruption rates are necessary for seawater incorporation to occur, but the mechanism by seawater enters the flow has yet to be resolved. A persistent vapor phase may play an important role in how lava flows are emplaced by inhibiting the collapse of lava flow roofs during natural waxing and waning of lava levels during emplacement. In addition, we illustrate the potential for a persistent vapor layer to increase local flow rates within submarine flows by up to a factor of three.

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