In-situ study of submarine volcanism using 1m-resolution AUV-based seafloor mapping with targeted lava and sediment sampling using ROVs

Monday, 30 January 2017: 08:30
Sovereign Room (Hobart Function and Conference Centre)
David A Clague1, Jennifer Brophy Paduan1, David W Caress1, Brian M Dreyer2 and Ryan A Portner3, (1)Monterey Bay Aquarium Res Inst, Moss Landing, CA, United States, (2)University of California Santa Cruz, Santa Cruz, CA, United States, (3)Brown University, Providence, RI, United States
Abstract:
In-situ study of volcanic terrain and processes during the past 20 years revolutionized the study of submarine volcanism. Technology and methods evolved rapidly with the advent of GPS navigated surface ships with higher-resolution multibeam mapping systems, improved ultra-short baseline bottom-tracking of vehicles, widespread adoption of remotely operated vehicles (ROVs), and autonomous underwater vehicles (AUVs) equipped with high-precision navigation, CTDs, multibeam and sidescan sonars, and sub-bottom seismic reflection profilers. These technologies now allow scientists to map and sample select areas of the seafloor at scales comparable to working on land.

ROV-push coring led to recognition of widespread pyroclastic debris on the MOR, and now offers a means to obtain minimum eruption ages through radiocarbon dating of foraminifera. The cores provide chemostratigraphy of glass shards of eruptions near the sampling site. We have mapped historical lava flows at 1-m resolution including 1993 and 1982-1991 CoAxial; 1986 North Cleft; 1996 North Gorda; 1998, 2011, and 2015 Axial Seamount; and 2008 NE Lau Spreading Center; and at Endeavour, Gorda Ridge, and Alarcon Rise. The maps define individual flows and their morphologies, and are combined with minimum flow ages and compositions to reconstruct volcanic and tectonic history.

We present three examples of application of these new methods and technologies. The axial graben at Endeavour formed ~4.3 kyr ago as the ridge shifted from a magmatic to an extensional tectonic phase. Magmatic activity slowly resumed ~2 kyrs ago and continues. The tectonized crust supports intense hydrothermal circulation. At Axial, caldera formation ~1.1-1.3 kyr ago coincided with eruption of voluminous flows on the deep S rift, and likely with summit phreatomagmatic eruptions as seawater penetrated into the volcano along caldera-bounding faults. Crystal-rich, primitive, depleted lava erupted when effusive activity resumed a few hundred years later. Lava compositions shifted to less-depleted, less-primitive, aphyric compositions ~400 yrs ago. The 2015 lava is the most primitive to erupt in 400 yrs. At Alarcon Rise, the northern third of the ridge erupted evolved andesite, dacite, and rhyolite from 19-2 kyr, but then returned to more typical mid-ocean ridge basalt eruptions.

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