Chadwick William W.

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William W.

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  • Article
    Axial Seamount
    (Oceanography Society, 2010-03) Chadwick, William W. ; Butterfield, David A. ; Embley, Robert W. ; Tunnicliffe, Verena ; Huber, Julie A. ; Nooner, Scott L. ; Clague, David A.
    Axial Seamount is a hotspot volcano superimposed on the Juan de Fuca Ridge (JdFR) in the Northeast Pacific Ocean. Due to its robust magma supply, it rises ~ 800 m above the rest of JdFR and has a large elongate summit caldera with two rift zones that parallel and overlap with adjacent segments of the spreading center.
  • Article
    Waning magmatic activity along the Southern Explorer Ridge revealed through fault restoration of rift topography
    (John Wiley & Sons, 2013-05-29) Deschamps, Anne ; Tivey, Maurice A. ; Chadwick, William W. ; Embley, Robert W.
    We combine high-resolution bathymetry acquired using the Autonomous Underwater Vehicle ABE with digital seafloor imagery collected using the remotely operated vehicle ROPOS across the axial valley of the Southern Explorer Ridge (SER) to infer the recent volcanic and tectonic processes. The SER is an intermediate spreading ridge located in the northeast Pacific. It hosts the Magic Mountain hydrothermal vent. We reconstruct the unfaulted seafloor terrain at SER based on calculations of the vertical displacement field and fault parameters. The vertical changes between the initial and the restored topographies reflect the integrated effects of volcanism and tectonism on relief-forming processes over the last 11,000–14,000 years. The restored topography indicates that the axial morphology evolved from a smooth constructional dome >500 m in diameter, to a fault-bounded graben, ~500 m wide and 30–70 m deep. This evolution has been accompanied by changes in eruptive rate, with deposition of voluminous lobate and sheet flows when the SER had a domed morphology, and limited-extent low-effusion rate pillow eruptions during graben development. Most of the faults shaping the present axial valley postdate the construction of the dome. Our study supports a model of cyclic volcanism at the SER with periods of effusive eruptions flooding the axial rift, centered on the broad plateau at the summit of the ridge, followed by a decrease in eruptive activity and a subsequent dominance of tectonic processes, with minor low-effusion rate eruptions confined to the axial graben. The asymmetric shape of the axial graben supports an increasing role of extensional processes, with a component of simple shear in the spreading processes.
  • Article
    Flux measurements of explosive degassing using a yearlong hydroacoustic record at an erupting submarine volcano
    (American Geophysical Union, 2012-11-29) Dziak, Robert P. ; Baker, Edward T. ; Shaw, Alison M. ; Bohnenstiehl, DelWayne R. ; Chadwick, William W. ; Haxel, Joseph H. ; Matsumoto, Haru ; Walker, Sharon L.
    The output of gas and tephra from volcanoes is an inherently disorganized process that makes reliable flux estimates challenging to obtain. Continuous monitoring of gas flux has been achieved in only a few instances at subaerial volcanoes, but never for submarine volcanoes. Here we use the first sustained (yearlong) hydroacoustic monitoring of an erupting submarine volcano (NW Rota-1, Mariana arc) to make calculations of explosive gas flux from a volcano into the ocean. Bursts of Strombolian explosive degassing at the volcano summit (520 m deep) occurred at 1–2 min intervals during the entire 12-month hydrophone record and commonly exhibited cyclic step-function changes between high and low intensity. Total gas flux calculated from the hydroacoustic record is 5.4 ± 0.6 Tg a−1, where the magmatic gases driving eruptions at NW Rota-1 are primarily H2O, SO2, and CO2. Instantaneous fluxes varied by a factor of ∼100 over the deployment. Using melt inclusion information to estimate the concentration of CO2 in the explosive gases as 6.9 ± 0.7 wt %, we calculate an annual CO2 eruption flux of 0.4 ± 0.1 Tg a−1. This result is within the range of measured CO2 fluxes at continuously erupting subaerial volcanoes, and represents ∼0.2–0.6% of the annual estimated output of CO2from all subaerial arc volcanoes, and ∼0.4–0.6% of the mid-ocean ridge flux. The multiyear eruptive history of NW Rota-1 demonstrates that submarine volcanoes can be significant and sustained sources of CO2 to the shallow ocean.
  • Article
    The magnetization of an underwater caldera: a time‐lapse magnetic anomaly study of axial seamount
    (American Geophysical Union, 2022-09-03) Fluegel, Bailey ; Tivey, Maurice ; Biasi, Joseph ; Chadwick, William W. ; Nooner, Scott L.
    Axial Seamount in the northeast Pacific erupted in 2015, 2011, and 1998. Although monitored by the Regional Cabled Array of the Ocean Observatory Initiative, few magnetic surveys have been conducted over the region. This study uses high‐resolution magnetic data over the seamount collected by autonomous underwater vehicle Sentry during three years (2015, 2017, and 2020). The goal is to investigate whether there are temporal changes in the near‐surface magnetic field observable over the time scale of one volcanic cycle. We compare magnetic maps from repeated tracklines from each year. We find maps of the yearly difference in magnetization show coherent patterns that are not random. The central region of the caldera has become more magnetic during recent years, suggesting cooling of the surficial lava flows since 2015. Sentry data are more sensitive to shallow crustal structure compared to sea surface data which show longer wavelength anomalies extending deeper into the crust.Plain Language SummaryAxial Seamount is an active underwater volcano located off the coast of Oregon that has recently erupted in 2015, 2011, and 1998. Though Axial is monitored by many seafloor instruments, the magnetism of the region and how it changes with time has not been studied. However, we believe studying the magnetics of Axial can provide powerful insights into the internal structure of the volcano. Specifically, volcanic rocks contain magnetic minerals called magnetite. Above a certain temperature, called the Curie temperature, these minerals become non‐magnetic. Thus, magnetism may be able to detect changes in the high temperature areas of the volcano between eruptions, such as the magma chamber or young lava flows. Here, we perform the first study analyzing three separate years of high‐resolution magnetic data collected using an autonomous underwater vehicle over Axial seamount. We create magnetic maps using repeated vehicle tracklines to highlight differences between each year and compare our findings with broader surveys of the region. Our results indicate the central region of Axial has become more magnetic during recent years, suggesting cooling of the lavas erupted in 2015 and their associated subsurface feeder zones.Key PointsRepeat magnetic surveys at active submarine volcanos image temporal change in thermal structure related to geologic and volcanic processesHigh resolution magnetic data can be used for low‐cost volcano monitoring in the marine environment over relevant timescales
  • Article
    Hydrothermal discharge during submarine eruptions : the importance of detection, response, and new technology
    (The Oceanography Society, 2012-03) Baker, Edward T. ; Chadwick, William W. ; Cowen, James P. ; Dziak, Robert P. ; Rubin, Kenneth H. ; Fornari, Daniel J.
    Submarine volcanic eruptions and intrusions construct new oceanic crust and build long chains of volcanic islands and vast submarine plateaus. Magmatic events are a primary agent for the transfer of heat, chemicals, and even microbes from the crust to the ocean, but the processes that control these transfers are poorly understood. The 1980s discovery that mid-ocean ridge eruptions are often associated with brief releases of immense volumes of hot fluids ("event plumes") spurred interest in methods for detecting the onset of eruptions or intrusions and for rapidly organizing seagoing response efforts. Since then, some 35 magmatic events have been recognized and responded to on mid-ocean ridges and at seamounts in both volcanic arc and intraplate settings. Field responses at mid-ocean ridges have found that event plumes occur over a wide range of eruption styles and sizes, and thus may be a common consequence of ridge eruptions. The source(s) of event plume fluids are still debated. Eruptions detected at ridges generally have high effusion rates and short durations (hours to days), whereas field responses at arc volcanic cones have found eruptions with very low effusion rates and durations on the scale of years. New approaches to the study of submarine magmatic events include the development of autonomous vehicles for detection and response, and the establishment of permanent seafloor observatories at likely future eruption sites.
  • Article
    Eruptive modes and hiatus of volcanism at West Mata seamount, NE Lau basin : 1996–2012
    (John Wiley & Sons, 2014-10-31) Embley, Robert W. ; Merle, Susan G. ; Baker, Edward T. ; Rubin, Kenneth H. ; Lupton, John E. ; Resing, Joseph A. ; Dziak, Robert P. ; Lilley, Marvin D. ; Chadwick, William W. ; Shank, Timothy M. ; Greene, Ronald ; Walker, Sharon L. ; Haxel, Joseph H. ; Olson, Eric J. ; Baumberger, Tamara
    We present multiple lines of evidence for years to decade-long changes in the location and character of volcanic activity at West Mata seamount in the NE Lau basin over a 16 year period, and a hiatus in summit eruptions from early 2011 to at least September 2012. Boninite lava and pyroclasts were observed erupting from its summit in 2009, and hydroacoustic data from a succession of hydrophones moored nearby show near-continuous eruptive activity from January 2009 to early 2011. Successive differencing of seven multibeam bathymetric surveys of the volcano made in the 1996–2012 period reveals a pattern of extended constructional volcanism on the summit and northwest flank punctuated by eruptions along the volcano's WSW rift zone (WSWRZ). Away from the summit, the volumetrically largest eruption during the observational period occurred between May 2010 and November 2011 at ∼2920 m depth near the base of the WSWRZ. The (nearly) equally long ENE rift zone did not experience any volcanic activity during the 1996–2012 period. The cessation of summit volcanism recorded on the moored hydrophone was accompanied or followed by the formation of a small summit crater and a landslide on the eastern flank. Water column sensors, analysis of gas samples in the overlying hydrothermal plume and dives with a remotely operated vehicle in September 2012 confirmed that the summit eruption had ceased. Based on the historical eruption rates calculated using the bathymetric differencing technique, the volcano could be as young as several thousand years.
  • Article
    Volcanic eruptions in the deep sea
    (The Oceanography Society, 2012-03) Rubin, Kenneth H. ; Soule, Samuel A. ; Chadwick, William W. ; Fornari, Daniel J. ; Clague, David A. ; Embley, Robert W. ; Baker, Edward T. ; Perfit, Michael R. ; Caress, David W. ; Dziak, Robert P.
    Volcanic eruptions are important events in Earth's cycle of magma generation and crustal construction. Over durations of hours to years, eruptions produce new deposits of lava and/or fragmentary ejecta, transfer heat and magmatic volatiles from Earth's interior to the overlying air or seawater, and significantly modify the landscape and perturb local ecosystems. Today and through most of geological history, the greatest number and volume of volcanic eruptions on Earth have occurred in the deep ocean along mid-ocean ridges, near subduction zones, on oceanic plateaus, and on thousands of mid-plate seamounts. However, deep-sea eruptions (> 500 m depth) are much more difficult to detect and observe than subaerial eruptions, so comparatively little is known about them. Great strides have been made in eruption detection, response speed, and observational detail since the first recognition of a deep submarine eruption at a mid-ocean ridge 25 years ago. Studies of ongoing or recent deep submarine eruptions reveal information about their sizes, durations, frequencies, styles, and environmental impacts. Ultimately, magma formation and accumulation in the upper mantle and crust, plus local tectonic stress fields, dictate when, where, and how often submarine eruptions occur, whereas eruption depth, magma composition, conditions of volatile segregation, and tectonic setting determine submarine eruption style.