The 2009 northern expedition allowed MBARI volcanologist David Clague and his group to add important data and samples to those collected at several eruption sites on expeditions over the previous four years: Axial Seamount (1998 eruption), the CoAxial (1993 and 1982-91 eruptions) and North Cleft (1986 eruption) segments of the Juan de Fuca Ridge, and the northern Gorda Ridge (1996 eruption). Two key elements of these sites are the presence of a historic lava flow and the geochemical similarities of all the flows erupted at each site.
The AUV map produced at the CoAxial site in 2009. Superimposed on the map are dive tracks for three dives, T882 in 2006 using ROV Tiburon, and D77 and D78 in 2009 using ROV Doc Ricketts. Tectonically fractured and fissured flows and pillow mounds are older than unfractured flows that are covered lightly with sediment. The pillowed margins of flows can be identified in the one-meter-resolution data, and in most cases, their superposition can be determined based on which flow overruns other flows. The volumes of the mapped flows, particularly pillow flows, can be calculated from the map data. Pillow flows from slow eruptions are easily distinguished from rapid-eruption sheet flows. Radiocarbon ages of foraminifera from sediment on three prehistoric flows under the historic flows are roughly 1,000, 4,000, and 6,500 years old and suggest a surprisingly long eruptive history in the more recent volcanic zone, despite the presence of two historic lava flows separated by less than 11 years.
Similar work is underway for three locations at Axial Seamount, around the 1986 North Cleft eruption, and around the 1996 North Gorda site. Over the next five years, eruptive histories should be constructed for each of these sites, as well as a few additional sites in the Gulf of California and the southernmost Gorda Ridge, which will allow Clague’s group to critically determine temporal changes in lava chemistry, hydrothermal activity, and eruptive volumes, rates, and styles.
 Ropy whorls of lava were eddies in the surface of a rapidly-advancing sheet flow. These vigorous eruptions are mildly explosive and produce abundant volcanic glass particles known as “limu o Pele” © MBARI 2009 |
Rust-colored hydrothermal stains in cracks of a lava pillow mound are just one indication that this is a recent flow. © MBARI 2009
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Several biologists participated in the expedition, including former MBARI postdoctoral fellow Craig McClain. Discerning the processes that influence geographic distributions of species remains one of the central goals of ecology, directly speaking to the conservation of biodiversity. Little is known about the fauna that inhabit newly created seafloor lava flows, one of the few ways new unoccupied habitat is created in the deep ocean. Submarine lava flows literally wipe the slate clean so that subsequent recruitment occurs on pristine substrate devoid of animals. As the volcanic substrate ages and accumulates sediments, biological colonization and succession continue. How quickly species can colonize newly erupted seafloor and the order and timing of ecological succession remain unknown in the deep sea.
Shelves of lava were flow surfaces in a three-meter-wide lava tube now exposed in the wall of Axial Caldera. The margin of the tube is visible in the extreme right. Tube-fed flows are better insulated against the cold sea water so the lava can travel great distances. Dating flows at the base of the caldera wall will give an idea of how fast the volcano grows. © MBARI 2009 |
Very top of the hydrothermal vent “El Guapo” at Axial Volcano, to which MBARI researchers returned with the ROV Doc Ricketts. The vent was discovered in 2006 on an ROV dive to explore terrain newly mapped with the MBARI AUV. Axial’s vents have been studied for years, but this one had been missed. It stands 13 meters tall and vents water hotter than 330°C, both new records at Axial. © MBARI 2009 |