By Bill Chadwick
Chief Scientist
Our research expedition to Axial Seamount was a great success, thanks to the combined efforts of the crew of the R/V Revelle, the Jason and Sentry teams, and the science party. We were able to complete 5 Jason ROV dives, 5 Sentry AUV dives, 3 CTD casts, and we deployed 4 instrument moorings and we recovered 5 of them that had been out collecting data for the last 2 years. It was a big relief to feel we accomplished all our goals as we returned to Newport, OR, but the work of analyzing data and samples will continue for many months from now.
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| Scientists on the expedition.
| R/V Revelle returning to Newport, OR.
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Two of the Jason ROV dives were mainly devoted to making pressure measurements at an array of seafloor benchmarks to measure how much the volcano has re-inflated since our last survey two years ago. We found the center of the caldera has risen 80 centimeters (nearly 3 feet) in the last two years, and 1.25 meters (over 4 feet) since the end of the 2015 eruption. That means the volcano has recovered half of the deflation that occurred during the last eruption in just two and a quarter years, but during that time the rate of re-inflation has also slowed substantially, from initial rates of 80 cm/yr to current rates of about 20 cm/yr. That means the second half of re-inflation will take longer than the first and the next eruption is probably not due before 2020 or 2021, depending on how the inflation rate varies between now and then. We’ll be keeping an eye on it through the
real-time data from the OOI Cabled Observatory, and will be attempting to
forecast the next eruption as it gets closer.
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| Blue mat at Marker N3 Vent site. |
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| "Mini-smoker" on Axial's north rift zone. |
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| Piece of hollow pillow crust with lava drips that had been extending down. |
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| Map of AUV Sentry navigation. |
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Two of the other Jason ROV dives were devoted to sampling vent fluids and sulfide chimneys for chemical and microbiological analysis. One of those dives was in the caldera at vent sites that had been visited many times before, and we discovered that the “blue mat” has returned to the Marker N3 Vent site, which was paved over with new lava during the 2011 eruption. It’s remarkable that there is something unique about the chemistry of the vent fluid at that site that the blue mat (a protozoan ciliate) really likes. The other chemistry dive was to a new vent site discovered just a year ago by an MBARI-led expedition making dives on Axial’s the north rift zone. There they found “mini-smokers” that are very unusual in that they are high-temperature (we measured up to 321°C), but are located on top of the thick 2015 lava flows. We found these vents have a very different chemistry than the other hydrothermal vent sites in the caldera. The final Jason ROV dive was made along a graben (a narrow down-faulted block) along the NE rim of the caldera that traces the path of the dike that connects the 2015 lava flow on the NE caldera floor to another one on the rim. These parts of the 2015 eruption had not been visited previously, so we collected 14 new lava samples to fill in that gap. It’s always fun to get to explore new areas, and it’s fun that Axial Seamount still can surprise us even after all these years!
