The 2015 Eruption

Sunday, August 16, 2015
By Bill Chadwick

Weather: Overcast skies clearing to bright sun, with light winds, which are forecast to build up to 30 knots over the next few days.

What's happening today?  This morning the Jason and Sentry Groups completed their overnight navigational calibration north of Axial Seamount’s caldera. We transited to the North Rift Zone and launched AUV Sentry just after lunch. Medea was launched for the Jason Group to test a new winch cable and the rest of the evening was spent in preparation for our first ROV Jason dive, due at midnight tonight!

Map of the Ocean Observatories Initiative’s Cabled Array in the NE Pacific.  (Image courtesy of University of Washington.)

An exciting aspect of this expedition is that we are heading out to explore and sample new lava flows at Axial Seamount that are less than 4 months old. How do we know that Axial recently erupted? Because it is now a "wired volcano." Over the last several years the National Science Foundation has funded the Ocean Observatories Initiative (OOI), which is enabling new ways to study, observe, and understand our oceans. One component of the OOI is a fiber-optic cable network that extends from the Oregon coast to areas offshore, including Axial Seamount. About a year ago, the University of Washington finished deploying most of the monitoring instruments on this Cabled Array and it started sending data back to shore. On April 24, nearly 8000 earthquakes were suddenly detected and the seafloor dropped by 2.4 meters (almost 8 feet), signaling that something big was happening at Axial Seamount.

Axial Seamount 2015 Expedition video of Drs. Bill Chadwick and Scott Nooner discussing their work monitoring the volcano. Video by Jesse Crowell in association with Saskia Madlener at 77th Parallel Productions. Music by James Andrew Menking

Axial Seamount has two previous known eruptions in 1998 and 2011. What was different this time was that the OOI Cabled Array enabled a community of scientific researchers from many different disciplines to look at the data coming in and debate what it meant, each contributing their own valuable perspectives and interpretations. Often scientists work alone or in small groups, but in this case a diverse group came together in a collaborative way to discuss the event and try to figure out what was happening as it was unfolding. It was exciting!

From the drop in seafloor, it was clear that magma had moved from beneath the summit of the volcano, but it wasn't obvious at first whether or not it had reached the seafloor to erupt as lava. But over the next few weeks, explosion-like seismic signals were recorded from Axial's north rift zone, and unusual temperature increases began to be recorded at several of the OOI monitoring instruments in the summit caldera. Both of these were seen as a "smoking gun" for an eruption, but exactly what was causing them was unclear. More conclusive evidence for an eruption was collected just a few weeks ago by our colleagues at University of Washington. During an expedition to Axial Seamount to do maintenance work on the OOI Cabled Array, they were able to remap the summit and north rift

Map of depth differences (up to 127 meters) between the 2013 and 2015 bathymetric surveys due to the 2015 lava flows (created by Susan Merle, Oregon State University).

zone with multibeam sonar, which revealed depth changes up to 127 m (417 feet), and a short ROV dive on one of these areas confirmed that they were due to thick new lava flows. Since then, more detailed analysis of the new bathymetry and comparison to previous surveys by colleagues at the Monterey Bay Aquarium Research Institute (MBARI) has revealed additional thinner lava flows, both on the NE caldera floor and on the northern caldera rim. There may also be other thin lava flows that are still undetected that we may find on this expedition.

On this cruise, we'll be exploring and sampling the new lava flows in more detail. We plan to collect high-resolution bathymetry over the eruption sites with the AUV Sentry to better understand how the lava was emplaced. We'll make dives with ROV Jason to collect samples of the new lava that will be analyzed later for precise dating and chemical analysis. Since the lava flows are probably still warm and cooling, we expect to find new hydrothermal vents to sample. These could include "snowblower vents" that have such high densities of microbes that they look like snow coming out of the seafloor. We'll be looking for evidence of explosive activity during the eruption, which would leave small particles of ash on the surface of the new lavas. In short, we still have lots of questions about what happened during the eruption. We're a bit like detectives trying solving a mystery by looking for clues that will help us better understand what happened. It's fun and that's what science is all about!

Before-and-after multibeam bathymetric maps, showing the 2015 lava flows on Axial’s north rift zone outlined in black (created by Susan Merle, Oregon State University).