Axial Seamount seafloor-mapping expedition

The captain and crew of the R/V Rachel Carson, the AUV team, and the science party gather next to the AUVs on the aft deck of the Rachel Carson for a group photo.

MBARI Expedition #719-720

Expedition goal: For this expedition we returned to Axial Seamount to conduct AUV mapping to repeat long survey lines over the summit as part of long-term monitoring of the volcano’s inflation toward its next eruption and to extend our coverage of the volcano and its rift zones, among other goals.

Expedition dates: August 17—September 3, 2019

Ship: R/V Rachel Carson

Research technology:  Mapping AUV

Expedition chief scientist: David Caress

Overview of expedition by Jenny Paduan, Emery Nolasco, Dave Caress, and Hans Thomas

Map showing the location of Axial Seamount relative to our home port in Moss Landing. Between legs of the cruise we went to Newport, Oregon to resupply.

The R/V Rachel Carson just returned from a successful 18-day, two-leg expedition to Axial Seamount, performing geological mapping of the seafloor in support of several different projects for MBARI Principal Engineer David Caress and Senior Scientist David Clague.

Twelve surveys were accomplished using MBARI’s two seafloor-mapping autonomous underwater vehicles (AUVs) in weather that was at times was challenging and other times glorious. We heartily thank Captain Aaron Gregg and the crew of the R/V Rachel Carson, AUV Supervisor Hans Thomas, and the entire AUV team, for a job well done.

Our departure was delayed by two days to avoid heading out into a gale. The 3.5-day transit from Moss Landing was still quite bouncy, but could have been worse. When we arrived at Axial, the tail end of a storm was blowing through and we launched the first AUV in upwards of 30-knot winds. Our first deployments of the second leg were similarly exciting. But we got the vehicles back and the data are beautiful!

Axial Seamount is an underwater volcano about 470 kilometers (290 miles) off the coast of Oregon, on the Juan de Fuca mid-ocean ridge, which is the spreading boundary between the Pacific and Juan de Fuca tectonic plates. The volcano erupted in 2015, 2011, 1998, and many times before that, as our research has shown.

Jenny processing data after the AUV returns.

Because of its frequent volcanic eruptions and accessibility to west-coast ports, Axial Seamount is an ideal location to study the processes associated with the creation of the oceanic crust, which comprises two-thirds of the Earth’s surface. Over the last two decades, MBARI researchers have performed many remotely operated vehicle (ROV) dives and AUV mapping surveys on the seamount using MBARI’s ships, and as part of collaborators’ research cruises.

Many monitoring instruments have been installed in the caldera of Axial Seamount as part of the U.S. Ocean Observing Initiative (OOI) cabled observatory. MBARI’s MARS observatory in Monterey Bay served a testing platform for some of these instruments.

One intriguing discovery during this expedition was a lava flow with a texture that we and our collaborators had never seen before (see below). The unusual texture could indicate an unusual lava chemistry. Perhaps there will be time next summer for the ROV Jason to dive on this area and collect some lava samples.

Unusual lava flow textures appear in a flow on the southeastern flank of the volcano (middle and lower right portion of image). Flow lobes consisting of the usual inflated sheet flow morphology from more recent eruptions have overtopped it from the northwest (upper left).

We spent the expedition mapping different parts of Axial Seamount. We had a number of goals, all of which were met. These included:

  • Repeat mapping over the summit to measure the deformation of the seafloor as the volcano’s magma chamber reinflates before its next eruption. This is part of a multi-year NSF-funded project with MBARI Adjunct Bill Chadwick (Oregon State University and NOAA) and Scott Nooner (University of North Carolina, Wilmington).
  • Testing the terrain-relative navigation capability of the AUV. This system enables the AUV to maintain its track in real time relative to an existing bathymetric map, which greatly improves our ability to precisely repeat long survey tracks. The system was developed by MBARI Adjunct Steve Rock and MBARI engineers Rob McEwen and Rich Henthorn. The software will be ported to the AUV Sentry (operated by Woods Hole Oceanographic Institution) next year.
  • Preparing 0.5-meter (1.6-foot) horizontal resolution base maps of hydrothermal-vent fields, to be used in planning and carrying out ROV dives next summer. Although the black-smoker vents in these fields are visually dramatic, much of the heat and chemical flux from hydrothermal-vent fields comes out through broad areas of diffuse, low flow-rate venting, which are often covered with bacterial mats and associated fauna. Actually measuring the amount of diffuse venting has been difficult. During next year’s Doc Ricketts dives, we will be mapping the vent fields at 1-centimeter resolution using MBARI’s Low Altitude Survey System (multibeam sonar, lidar, and stereo cameras). We will also use Kakani Katija’s Deep-PIV (particle image velocimetry) system to directly measure fluid flow at selected diffuse venting sites.
  • Extending the AUV mapping coverage we already have on the flank of the volcano, so now the seafloor above the entire subsurface magma chamber has been mapped at 1-meter (3-foot) lateral resolution.
  • Extending our mapping coverage of the South Rift Zone of the volcano, down which the dike will probably propagate during the next eruption.
  • Extending our coverage of enormous lava flows that erupted about a thousand years ago on the South Rift Zone and spilled into the graben of the Vance Segment, which overlaps the ridge segment that Axial Seamount is on and is actively propagating northward. This is in collaboration with former MBARI Postdoctoral Fellow Morgane LeSaout, now at Geomar in Germany, who is studying the segmentation and broad tectonic structures of the ridge system.