Logbook: September 3, 2006

Position: 45°56.0'N, 130°01.0'W
Axial Volcano

The MBARI AUV is recovered on board the R/V Thompson after an all-night mapping mission. (click image for larger view)

Today ROPOS dive R1013 is focused on vent fluid sampling in the ASHES vent site.

During the 2006 NEMO cruise on the R/V Thompson, the Monterey Bay Aquarium Research Institute (MBARI) Mapping Autonomous Underwater Vehicle (AUV) has been deployed for 6 dives on Axial Seamount. The objectives of the surveys were to investigate the geologic history of the summit of Axial Seamount and produce higher resolution maps of the volcanic terrain in and around the caldera than have ever been made before. Another goal is to locate optimal fiber-optic cable routes for a future observatory.

The mapping AUV is a torpedo-shaped vehicle designed and constructed by MBARI. The vehicle is equipped with a suite of instruments and sensors for seafloor mapping, and a very sophisticated inertial navigation system. The AUV can survey for up to eight hours at 3 knots and it can dive to depth of up to 6000 meters (~20,000 feet). At Axial, the first AUV deployment suffered a malfunction and the vehicle veered off the planned mission and was recovered after surfacing after the mission aborted. After evaluating and remedying the problem, we launched a sequence of 5 successful missions, one each night after the ROPOS ROV was recovered and the daily CTD cast completed. These surveys covered parts of the caldera rim and floor, and produced some spectacularly detailed maps.

The surveys have a resolution of one meter so that large individual lava pillars and hydrothermal chimneys can be seen, fissures stand out clearly, and the regions of collapsed lobate lava flows can be mapped. Many of the flows, including the 1998 flow, have dramatic drained lava ponds and channel distributary systems that closely resemble on-land flow channel. The northeast rim of the caldera is cut by numerous fissures, some of which served as eruptive vents for post-caldera flows that are on top of the volcaniclastic deposits. The north rift zone has prominent fissures near the caldera, but within about 1.5 kilometers of the caldera rim, the fissure system is less obvious, having been buried by young flows. The survey of the northern part of the caldera floor covers the deepest part of the caldera, the only large cone within the caldera, and the CASM hydrothermal vent site. The five AUV surveys during this expedition have mapped all of the known hydrothermal vent sites in and near Axial caldera. As we have time to examine the new maps in detail, we expect to find new chimneys and undiscovered hydrothermal fields. These dives have also shown the value of high-resolution mapping in studies of young volcanic terrain and provide the clearest views ever of this active submarine volcano.