In April 2006, extraordinary observations of a deep-sea explosive (Strombolian) volcanic eruption were made at NW Rota-1, a submarine volcano in the Mariana arc of the western Pacific. This research funds a return to the volcano to collect observational and analytical data and its subsequent on-shore data analysis and interpretation. Instruments including hydrophones, chemical sensors, current meters, and plume sensing devices will be deployed at the eruption site for one year. During the cruises, visual observations will made. A time-series collection of lava, gas and fluids at the active volcanic vent will also take place. Vent fluids and biological specimens from local hydrothermal vent sites will also be sampled. In terms of scientific impact, the research provides an opportunity to learn about volcanological process that have been impossible to study directly until now. Owing to the high viscosity of water, compared to air, closer and more specific observation and sampling of a Strombolian eruption can take place at Rota 1 than can be accomplished in subaerial settings. As a result, this work reveals critical proceses that help unravel eruptive mechanism of a highly destructive type of explosive volcanism. Broader impacts include public outreach via the media. The work also involves inter-Agency participation, an interdisciplinary inter-institutional collaboration, and the training a graduate student.

Project Report

We live on a volcanically active planet where approximately 70% of the volcanic activity takes place beneath the ocean surface. Explosive eruptions near the sea surface havve been observed over several centuries, but eruptions in the deep sea have been hidden and were not directly observed until 2004, when a remotely operated vehicle photographed intermittent explosive activity at NW Rota-1 undersea volcano, located about 110 km NE of Guam in the Western Pacific. NW Rota-1 is one of the hundreds of discrete volcanoes that form above the subduction zone where the Pacific Ocean plate is recycled back into the Earth's mantle. Initial exploration of NW Rota from 2003-2006 indicated that it was in a prolonged, slow, gas-rich eruption phase (a 'Strombolian' eruption, named for Stromboli volcano in Italy) at 500 meters below the sea surface. Our study was designed to learn about how a deep-sea eruption changes over time and how eruptions affect ocean chemistry and deep-sea ecosystems, including microbes that live off of the chemical energy produced by the interaction of seawater with lava and magmatic gases. Monitoring instruments show that NW Rota continued to be very active between 2008 and 2010, with eruptive intensity varying significantly. A large eruptive episode recorded in August 2009 resulted in a major landslide changing the topography of the southern half of the volcano. We observed and sampled the eruptive vents on NW Rota in 2009 and 2010 with the remotely operated vehicle Jason. Using a specialized sampling instrument (see figure 1), we sampled hot gases, water, and sulfur particles directly over the surface of erupting lava. This has only been done at NW Rota and one other deep volcano, West Mata in the NE Lau basin near Fiji. We also sampled warm water at various distances from the eruptive vents to characterize their chemistry and microbiology. Our findings indicate that sulfur chemistry is central to understanding the effects of erupting arc volcanoes. With a new method of preservation and analysis, we made the first measurements of sulfur dioxide (SO2) in the deep sea. We found that the abundant magmatic gas emitted at the eruptive vents is composed primarily of water, CO2, SO2, H2, and trace gases. SO2 gas quickly dissolves into seawater and reacts to form elemental sulfur (native sulfur, or 'brimstone') and sulfuric acid. The acid quickly dissolves the fresh volcanic rock, adding the major rock-forming elements (iron, aluminum, silicon) to the acidic hydrothermal fluids and injecting them up into the overlying ocean water, along with billowing clouds of fine particulate sulfur (see figure 2), at times obscuring the entire summit of the volcano in a massive particulate cloud. Molten elemental sulfur is very common around the eruptive vents (see figure 3). Essentially all of the hot magmatic water-steam and the sulfur gases dissolve quickly into seawater, while CO2 and H2 form gas bubbles that rise through the water and slowly dissolve into the ocean, as shown in figure 4 from a paper published in Geology. The strong acid and high levels of sulfur dioxide and hydrogen emitted by erupting arc volcanoes near subduction zones produce conditions for microbial and animal communities that are quite different from mid-ocean ridges where ocean plates are initially formed. This research project was one important step in understanding how geological processes and chemistry influence deep ocean ecosystems.

National Science Foundation (NSF)
Division of Ocean Sciences (OCE)
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Barbara L. Ransom
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University of Washington
United States
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