Northern 13, Leg 2-3 – Seafloor lava flows

The MBARI mapping autonomous underwater vehicle (AUV) D. Allan B. has collected high-resolution data mapping Axial Volcano’s caldera, flanks, and south rift zone, and several other sites along the Juan de Fuca mid-ocean spreading ridge, where eruptions have occurred in the past 30 years (which are called here “historic flows”). These new maps are at a resolution that allows mapping of individual sulfide chimneys, lava pillars,

channels in sheet flows, eruptive fissures and faults, and flow margins.

During this expedition, MBARI will return to these sites with the remotely operated vehicle (ROV) Doc Ricketts to collect video observations and samples. Cruise objectives for both legs of the expedition are to use push cores and vibracores to collect the pyroclastic (volcanic ash and glass particles) sediment sequences on the caldera rim of Axial Seamount, image the caldera wall at Axial with ROV video, collect more samples of the Axial 2011 lava flows and other flows discerned on our high-resolution AUV maps using the ROV and a wax-tipped corer, and collect samples and sediment cores for radiocarbon dating at other sites along the Juan de Fuca Ridge. These data will be combined to evaluate timing of eruptions and changes in lava geochemistry and eruption style as a function of spatial location and age.

Specific targets for Leg 2 will be at the summit of Axial Seamount, pillow ridges emplaced on Axial’s south rift during the 2011 eruption, and some cones on Axial’s north and south rift made of lavas containing high concentrations of magnesium (more primitive melts that erupted at higher temperature than most lava found at Axial or elsewhere along the Juan de Fuca Ridge).

Targets for Leg 3 will be on the summit of Axial Seamount, andesite (more evolved melts than usually found at Axial or along the Juan de Fuca Ridge) cones near Axial’s north rift, historic flows on the CoAxial segment of the Juan de Fuca Ridge that erupted in 1993 and between 1982 and 1991, and a large perched lava pond on Axial’s south rift.

Part A shows bathymetry at 100-meter contour intervals of the continental margin offshore of Eureka, California, and locations of Eel River, Mendocino Fracture Zone (MFZ) and Eel Canyon. The location of the classic Eel River seeps are indicated with an X. The area indicated with the red box is shown in more detail in Part B. Part B shows multibeam bathymetry of the area where six huge water column plumes were discovered (black dots; Gardner et al., 2009). Two emanate from slide scars to the south of Eel Canyon, and four emanate from the seafloor and northern flanks of Eel Canyon. Arrows indicate steps within the canyon floor. Part C is a detailed map of the slide scar area where a feature similar to the Santa Monica mounds occurs (black arrow).