Over the past few years MBARI researchers have been combining the one-meter horizontal resolution maps acquired by the MBARI mapping AUV with ROV observations and sampling. They can outline the flow boundaries and identify old/young relationships in the maps and confirm these relationships with ROV observations of contacts between the flows and chemical compositions of collected lava samples. They can target the sampling of individual lava flows, other volcanic structures, and hydrothermal chimneys with a precision undreamed of until recently. They have found that lavas on the floor of the caldera at Axial volcano, lavas on the rim from eruptions that flowed away from the summit prior to collapse of the caldera, as well as the flows exposed in the caldera walls, are chemically and mineralogically distinctive.
A major piece of the puzzle has been to establish some time constraints for the changes in lava chemistry and for when the many flows on the caldera floor erupted. They have developed a technique that is analogous to constraining ages in young lava fields on land (where flows are commonly dated by collecting and radiocarbon dating charcoal from burned vegetation beneath flow edges). Under water, there of course is no charcoal produced and it is not possible to excavate below the flow margins, so they do the next best thing, which is to collect short push cores of the sediment on top of the flows. For the entire Juan de Fuca region MBARI researchers have found that enough sediment concentrates that it can be collected, especially among pillow basalts, for flows older than about 300 years. Foraminifera tests (shells) are extracted from the bottom centimeter of the core for radiocarbon dating, which yields a minimum age of the flow beneath. This will be a major objective of the CoAxial and some of the Axial dives.
Another objective is to determine the time of formation of the caldera. The rim is buried under as much as two meters of volcaniclastic (ash and volcanic glass fragments) debris that the team has tried, with varying success, to core several times. The goal is to try to build a chemical stratigraphy of the pyroclasts in the section and time-constrain this stratigraphy by dating foraminifera in the sediment layers between the pyroclastic units, which represent the quiet periods between the violent eruptions.
Finally, an eruption occurred at Axial Seamount in April 2011 that MBARI mapped with the AUV and dove on with the ROV in August 2011. The differences in the “before” and “after” high-resolution AUV mapping allowed precise calculation of the eruption’s area and volume, details of the evolution of flow morphology along the flow, and unexpected characteristics such as the reuse of old eruptive fissures and flow channels. Samples collected in 2011 have lava chemistry similar to the 1998 flow. More samples will be collected on this expedition on parts of the flow not sampled in 2011, to examine the changes in lava chemistry and degassing of volatiles as the eruption progressed down the fissure system and across the width of the flow. Two pillow ridges on the south rift zone will be sampled, one that is partially covered in the AUV mapping and is certainly from the 2011 eruption, and another 20 kilometers down-rift that was detected by comparing lower-resolution ship-mounted multibeam data collected in 2011 and in 1998. This pillow ridge has only been dredged, and the possibility exists that it is not from the 2011 eruption.
The 1993 CoAxial eruption, a collection of papers in Geophysical Research Letters, 22, No. 2 in 1995. These papers describe the mega-plume emitted during the CoAxial eruption, the seismic swarm that accompanied the eruption, and initial results on the character of the eruption.
The 1998 Axial Seamount eruption, a collection of papers in Geophysical Research Letters, 26, No. 23 in 1999. Same sort of collection for the 1998 Axial eruption.
Caress, D.W., D.A. Clague, J.B. Paduan, J.F. Martin, B.M. Dreyer, W.W. Chadwick Jr., A. Denny, D.S. Kelley (2012) Repeat bathymetric surveys at 1-metre resolution of lava flows erupted at Axial Seamount in April 2011. Nature Geoscience, 5(7): 483-488. doi: 10.1038/NGEO1496. See also other papers in this volume.
Chadwick, J., Perfit, M., Ridley, I., Kamenov, G., Chadwick, W.W., Embley, R.W., le Roux, P., and Smith, M. (2005) Magmatic effects of the Cobb hot spot on the Juan de Fuca Ridge, Journal of Geophysical Research, 110, doi:10.1029/2003JB002767. Petrology of Axial Seamount, mainly based on samples from the south caldera and south rift zone.
Chadwick, W.W., Jr., Scheirer, D.S., Embley, R.W., and Johnson, H.P. (2001) High-resolution bathymetric surveys using scanning sonars: Lava flow morphology, hydrothermal vents, and geologic structure at recent eruption sites on the Juan de Fuca Ridge, Journal of Geophysical Research, 106: 16,075-16,099. Describes the North Cleft and CoAxial eruption sites.
Clague, D.A. and Paduan, J.B. (2009) Submarine basaltic volcanism, In: Submarine Volcanism and Mineralization: Modern through Ancient, B. Cousens and S.J. Piercey (eds.), Geological Association of Canada, Short Course 39-30 May 2008, Quebec City, Canada, p. 41-60.
Clague, D.A., Paduan, J.B., and Davis, A.S. (2009) Widespread stombolian eruptions of mid-ocean ridge basalt, Journal of Volcanology and Geothermal Research (2009) 180: 171-188. Describes the fragmental eruption products of strombolian bubble-burst activity on Pacific mid-ocean ridges, including Gorda and Juan de Fuca ridges, near-ridge seamounts, and a few back-arc basins.
Embley, R.W. Chadwick, W.W., Perfit, M.R., Smith, M.C., and Delaney, J.R. (2000) Recent eruptions on the CoAxial segment of the Juan de Fuca Ridge: Implications for mid-ocean ridge accretion processes, Journal of Geophysical Research, 105: 16,501-16,525. A synthesis of what was known at that time about the 1993 and an adjacent pillow ridge emplaced between surveys done in 1982 and 1991.
Embley, R.W., Murphy, K.M., and Fox, C.G. (1990) High-resolution studies of the summit of Axial volcano, Journal of Geophysical Research, 95: 12,785-12,812. Best overall description of the caldera and summit of Axial volcano.
Helo, C., D.A. Clague, D.B. Dingwell, and J. Stix (2013). High and highly variable cooling rates during pyroclastic eruptions on Axial Seamount, Juan de Fuca Ridge. Journal of Volcanology and Geothermal Research, 253: 54-64. doi: 10.1016/j.jvolgeores.2012.12.004.
Helo, C., Longpre, M.-A., Shimizu, N., Clague, D.A., and Stix, J. (2011) CO2 rich magmas from Axial Seamount - A link to explosive eruptions on mid-ocean ridges?, Nature Geoscience, doi:10.1038/NGEO1104.
Rubin, K.H., S.A. Soule, W.W. Chadwick Jr., D.J. Fornari, D.A. Clague, R.W. Embley, E.T. Baker, M.R. Perfit, D.W. Caress, and R.P. Dziak (2012) Volcanic eruptions in the deep sea. Oceanography 25(1): 142–157, doi: 10.5670/oceanog.2012.12. Overview of what is known about deep-sea volcanic eruptions and how they are studied.
Yeo, I.A., D.A. Clague, J.F. Martin, J.B. Paduan, and D.W. Caress (2013) Pre-eruptive flow focussing in dikes feeding historical pillow ridges on the Juan de Fuca and Gorda Ridges. Geochem. Geophys. Geosyst., doi: 10.1002/ggge.20210.
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