An integrated study of the driving forces and deposits of shallow water eruptions of volatile-rich basalt: Socorro 1993 revisited

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Shallow water submarine volcanism plays a critical role in the formation of oceanic islands and is associated with hazards to both human populations and marine biological communities. One of the most rarely observed styles of these eruptions is the production of giant floating lava blocks that are filled with gas. When they rise to the sea surface these "lava balloons" often explode and then settle back down to the seafloor. Little is known about this unusual style of submarine volcanism due to the lack of direct observation as only five such eruptions have been documented, all of which occurred at oceanic islands associated with volcanic hotspots such as Hawaii, the Canary Islands, the Azores, and the Revillagigedo archipelago in Mexico. This research develops a better understanding of how these floating gas filled lava blocks are formed during relatively shallow water volcanic eruptions. The project focus on "lava balloon" samples and other associated explosive volcanic products, like ash and other pyroclastic material, erupted from vents off the shores of Mexico's Socorro Island in the eastern Pacific in 1993. During a 2017 oceanographic exploration by the ship, E/V Nautilus, high-resolution video was collected by a submersible, remotely-operated vehicle called Hercules in the area of the eruption at a location where floating gas filled lava blocks were observed while the volcano was active. Other samples of the volcanic material and deposits were also collected and their trace element geochemistry, volatile content, melt inclusions, and the depositional characteristics of the resulting volcanic ash and ejecta layers were targeted for analysis. Objectives of the research include (1) defining the morphology, structure, and nature of the 1993 Socorro vent site based on ultrahigh-resolution bathymetric surveys from the Hercules; (2) carrying out geochemical analyses on the samples to characterize their magmatic composition, volatile content and degassing history, their magma viscosity, and source characteristics; and (3) developing an eruption model for the 1993 event using degassing simulations with inputs from geochemical and textural analyses. Broader impacts of the work include student training at the graduate and undergraduate levels, leveraging unique samples collected at great cost, characterization of a newly designated UNESCO World Heritage Site, and interaction with the Ocean Exploration Trust which is has a major public and K-12 outreach program showcasing the cruise and science coming from the associated research. A video that will have wide dissemination, documenting seagoing research exposing the public to the life of a marine geologist at sea and the wonders of exploring submarine volcanic environments, will be created and there is international collaboration with scientists from Mexico. The work will also contribute to hazard evaluations around the coasts of volcanically-active oceanic islands.Volcanic ejecta of sizes from microns to meters and deposits of these that resulted from the 1993 explosive submarine eruption of Socorro Volcano off the western coast of Mexico will be characterized geochemically and texturally to determine the conditions of eruption and deposition of explosive debris around the vent site. Geochemical analyses will include mineral and glass analyses via electron microprobe, a New Wave 213 nanometer laser ablation system coupled to a Thermo X-Series II inductively coupled mass spectrometer, and a Thermo Nicolet iS50 Fourier Transform Infrared (FTIR) spectrometer. Resulting trace element data will be modeled and new FTIR data will provide minimum values of pre-eruption gas contents for the Socorro magma. CO2/H2O degassing paths, determined from melt inclusion volatile analyses, will provide specific information about whether degassing occurred under closed- or open-system conditions and allow predictions of vesicularities under different degassing scenarios to be made. Magma ascent rates will be modeled using volatile diffusion profiles in glass embayments and phenocrysts in the volcanic ejecta. For very small volcanic particles, a scanning electron microscope (SEM) will be used to examine surface features to evaluate the role of explosive magma/seawater interactions in the eruption process. Another important goal of the research will be development of a well-constrained facies model (scale, morphology, deposit types) for shallow water eruptions of this style, with these samples and this site providing a modern analogue for the paleo-environmental interpretation of ancient, highly vesicular submarine basaltic sequences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.