Lava Explosions Nearly a Mile Beneath the Oceans’ Surface: Axial Seamount

RCA : Lava Explosions Nearly a Mile Beneath the Oceans’

Surface Axial Seamount is a rare, “well-behaved” submarine volcano yielding the ability to forecast the next eruption based on inflation and seismicity relationships [1]. The April 24, 2015 eruption of Axial (Figure 24) was a spectacular event marked by a seismic crisis of >8000 earthquakes over a 24-hour period (Figure 24B) [2], coincident with a drop in the seafloor of 2.45 m [1]. The resultant lava flow on the northern rift reached 127 m in thickness (Figure 24A & D), the summit of which was covered by acres of microbes supported by nutrient-rich fluids emanating from the cooling lava flow [3-5]. I n total, 1.48 X 10 m3 of lava was erupted onto the seafloor [4]. Figure 24: A) Summit and northern rift zone on Axial Seamount showing location of the 2011 (purple-brown colored flow with delineating thickness) and 2015 flows that extend along the northern rift zone (red outline). Also shown is the location of RCA infrastructure. Bathymetry courtesy of D. Caress and D. Clague, MBARI. B) location of earthquakes (blue dots) and water born impulsive events interpreted to result from explosions on April 26, 2015 (Courtesy W. Wilcock) and location of seismometers (yellow-orange dots) and Primary node PN1B. C) Diffusive broadband and punctuated signals recorded by the RCA hydrophone at the Central Caldera site on May 2, 2015 [6, Figure 9]. d) Breached pillow basalt on the toe of the 127 m thick northern flow (UW/NSFOOI/CSSF V15). E) Ash deposit on the bottom pressure-tilt instrument at Central Caldera three months after the eruption (UW/NSF-OOI/CSSF V15). F) Fountaining of lava during an eruption of Kilauea volcano, Hawaii (courtesy of

Caplan-Auerbach et al., [6], postulate that a submarine eruption similar in style to a Hawaiian ash eruption occurred during the 2015 event based on analyses of continuous Regional Cabled Array hydrophone data (Figure 35C). Unlike the punctuated, water-borne impulsive acoustic signals that delineated >30,000 explosive events (Figure 24B &C) [2], prolonged diffusive broadband signals were detected over an ~ 20day period in May (Figure 24C) [6]. Caplan-Auerbach notes that these signals are reminiscent of those recorded during degassing and tephra production at the 50 NW Rota-1 and West Mata submarine volcanoes in the Marianas and Lau Basin systems, respectively.

The authors propose that the eruption of lava within the caldera and along the northern rift, resulted in the decompression of deeper-sourced, gas-rich magma and exsolution of gasses that had collected beneath the magma chamber roof. Primary magmas beneath Axial Seamount contain extremely high concentrations of CO2 [7] and have been linked to pyroclastic (ash) deposits at Axial containing Pele’s hair and limu o Pele [8]. These deposits have been attributed to implosion of gas-rich bubbles causing fragmentation and phreatic eruptions with transport of ash into eruption plumes [8]. The prolonged diffusive signals correlate well with a uniform increase in water temperature within the caldera that lasted for 40 days [6 & 9]. This increase has been hypothesized to reflect the release of heat during Hawaiian style explosive activity [6] or effusion of dense, warm brines stored in the subsurface [9]. Three months after the 2015 eruption, an ash deposit was observed on an RCA bottom-pressure tilt recorder at the Central Caldera site (Figure 24A & E), ~ 1 km away from the single flow in the caldera that reached a thickness of 13 m [10]. The addition of three NSF-funded CTD’s (PI W. Chadwick, OSU) within the caldera are providing new information about near bottom fluids with a focus on the next eruption. NSF funding (PI’s Manalang and Kelley, UW) directed at testing of a recently developed ADCP, at the Central Caldera site in 2021, through an RCA-Teledyne Marine partnership, with full water column imaging capabilities, may provide a new technology for the community to quantify syn-eruptive plume behavior

[1] Nooner, S.L., and Chadwick, W.W., Jr. (2016) Inflation-predictable behavior and co-eruption deformation at Axial Seamount. Science, 354, 1399-1403. [2] Wilcock, W.S.D., Tolstoy, M., Waldhouser, F., Garcia, C., Tan Y.J, Bohnenstiehl, D.R., Caplan-Auerbach, J., Dziak, R.P., Arnulf, A.F., and Mann, M.E. (2016) Seismic constraints on caldera dynamics from the 2015 Axial Seamount eruption. Science, 354, 1395-1899. [3] Kelley, D.S., Delaney, J.R., Chadwick, W., Philip, B.T., and Merle, S.G. (2015) Axial Seamount eruption: A 127 m thick, microbially-covered lava flow. American Geophysical Union, Fall Meeting, 2015, OS41B-08. [4] Chadwick, W.W., Jr., Paduan, J.B., Clague, D.A., Dryer, B.M., Merle, S.G., Bobbitt, A.M., Caress, D.W., Philip, B.T. and Nooner, S.L. (2016) Voluminous eruption from a zoned magma body after an increase in supply rate at Axial Seamount. Geophysical Research Letters, 43, 12,063-12,070. [5] Spietz, R.L., Butterfield, D.A., Buck, N.J., Larson, B.I., Chadwick, W.W., Jr., Walker, S.L., Kelley, D.S., and Morris, R.M, (2018) Deep-sea volcanic eruptions create unique chemical and biological linkages between the subsurface lithosphere and the oceanic hydrosphere. Oceanography, 31, 129-135. [6] Caplan-Auerbach, J., Dziak, R.P., Haxel, J., Bohnenstiehl, D.R., and Garcia, S. (2017) Explosive processes during the 2015 eruption of Axial Seamount, as recorded by seafloor hydrophones. Geochemistry, Geophysics, Geosystems, 18, 1761-1774. [7] Helo, C., Longpre, M-A., Schmizu, N., Clague, D.A. and Stix, J. (2011) Explosive eruptions at mid-ocean ridges driven by CO2-rich magmas. Nature Geoscience, 4, 260-263. [8] Portner, R.A., Clague, D.A., Helo, C., Dreyer, B.M., and Pauduan, J.B. (2015) Contrasting styles of deep-marine pyroclastic eruptions revealed from Axial Seamount push core records. Earth and Planetary Science Letters, 423, 2015-2019. [9] Xu. G. Chadwick, W.W. Jr., Wilcock, W.S.D., Bemis, K.G., and Delaney, J. (2018) Observation and modeling of hydrothermal response to the eruption at Axial Seamount, Northeast Pacific. Geochemistry, Geophysics, Geosystems, 19, 2780-2797. [10] Baker, E.T., Walker, S.L., Chadwick, W.W., Jr., Butterfield, D.A., Buck, N.J., and Resing, J.A. (2018) Post-eruption enhancement of hydrothermal