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Submarine Volcanism

Volcanism on the seafloor may account for >75% of all global volcanic activity. As we continue to increase exploration of the seafloor, we learn more about volcanic activity miles below the ocean's surface and the make-up of the oceanic crust.

Samuel's research aims to understand how submarine eruptions differ from those on land, and how deep volcanic activity can still have impacts at or near the surface.

Eruption dynamics and submarine clast cooling

Microtextures of volcanic rocks (glass, crystals and vesicles) can be used to interpret styles and intensity of volcanic eruptions on the seafloor. Measurements of hydroxyl (OH) in volcanic glass can be used to identify clast quenching conditions (pressure and temperature) as shown within previous research.

Vesicle and microlite size distributions and number densities have been used to interpret shallow conduit conditions, magmatic decompression, and how large pumice blocks are produced during submarine eruptions. A recent study also compared tube and spherical vesicles in pumice to assess strain conditions within a submarine volcanic conduit.

Other research has focused on fragmentation mechanisms of the 2012 eruption of the Havre submarine volcano, showing how pumice is produced in a "non-explosive" style as magma had insufficient cumulative strain or viscosity to result in magmatic fragmentation.

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Secondary hyrdation of volcanic glass

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Measurements of H2O in volcanic matrix glasses and melt inclusions are commonly used to interpret magma storage depths, magma ascent rates, processes within the shallow conduit, and clast quenching. However, these geochemical records can be altered by diffusion of external water into glass over a range of timescales and temperatures.

Previous research used H2O speciation (molecular H2O and OH), acquired by FTIR spectroscopy, to show how rapid rehydration can be identified in submarine glasses. High molecular-H2O/OH ratios can be used as a proxy for rehydrated glasses, and H2O diffusion profiles can be used to determine likely timescales of rehydration if quenching temperatures are known.

However, H2O speciation does not identify the source of rehydration, so we must rely on isotopic measurements of H and O in glass. More recent research (in revision) uses D/H measurements to identify multiple sources of H2O within submarine glasses from a variety of ages, eruptive styles and depths. Measurements of 18O/16O from silicate, and water in glass, can be used as a geo-thermometer to identify likely temperatures of rehydration.

Why do pumice sink or float in water?

Research currently in review compares clasts within oceanic pumice rafts with clasts taken from the seafloor produced by the same eruption. Subtle difference in microtextural properties (vesicle connectivity, pore throat diameters, and vesicle number densities) ultimately control how gas may become trapped within pore space in pumice.

Previous research by colleagues demonstrated experimentally that large volumes of gas can be trapped within high porosity pumice. The connectivity of pore space also controls how water in ingested into pumice and how vapor may escape during submarine pyroclast cooling.

Future research will aim to constrain how submarine clast textures may be identifiable from subaerial pumice microtextures, which helps with identifying paleoenvironments in ancient pyroclastic sequences.

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