Category: General Article
Friday, August 28, 2015
Submitted by Rachel Teasdale
Summary: Rachel summarizes the last ROV Jason dives of the cruise which ended by looking at 2015 lava flows.
Following the successful of the pressure dives (J2-823 and 824) and a quick turnaround by the Jason crew, dive J2-825 was launched Wednesday morning at the Marker 33 Vent in the southeast part of the caldera. This vent has been active since before the 1998 eruption and vent samples have been collected there nearly continuously, making it one of the best time-series sites in the caldera. Fluid samples were collected for the second round of incubator experiments and for chemical analysis and microbial culturing on the ship.
Following the fluid sampling, Jason transited to the NE caldera rim where we explored more of the 2015 lava flows that we had not yet seen or sampled. We targeted this area because some of the earlier CTD tow-yos above northeast rim of the caldera (see CTD blog) had revealed high turbidity and multi-layered hydrothermal plumes above the seafloor, suggesting that 2015 lavas, or perhaps new hydrothermal vents, were emitting vent fluids. We spent several hours exploring the northeast caldera rim and sampling the 2015 lava flows along the North Rift Zone (NRZ).
Eight lava samples were collected for geochemistry and dating Polonium isotopes that could provide precise ages of the samples to constrain the timing of the emplacement of lavas, possibly within the day or week of the eruption. Such precision will help understand the eruption dynamics and rates of lava flow emplacement. These 2015 lavas include many lava morphologies, including ropy surfaces (lavas take on a rope-like appearance), jumbled flow surfaces (lavas take on a very craggy appearance) and have numerous collapse areas.
Samples includes pillow lavas (thick lavas with many pillow-shaped masses), sheet flows, inflated areas and a pillow bud — the branching point where a pillow formed and then branched off.
Examples of all these lavas can be seen in the slideshow on the righthand sidebar.
The last dive of the expedition was J2-826, which focused on collecting rocks and fluids from the 2015 lava flows of the north rift zone (NRZ), continuing the exploration of the area we started during our first Jason dive.
The first task during the dive was to position the Remote Access Sampler (RAS), which is a set of water bottles that will collect vent fluid samples in a time-series over a year when the RAS will be recovered. The RAS was deployed from the ship earlier today by placing it in the water and letting it free-fall to the seafloor with weights that increase its descent rate and remain on the seafloor. On recovery, Jason will return to manually release the anchor attached to the RAS so that glass floats attached above the RAS can lift it back to the surface.
For the rest of the dive we continued a move across the thick 2015 lava flows on the North Rift Zone, continuing where we left off during our first Jason dive to collect samples of the 2015 lavas and any vent fluids discovered where the flows are so thick they are still cooling.
We continued exploring the 2015 lavas of the NRZ as long as we could before it was time to recover Jason and head for home. As usual, there is always more we would like to do if we had more time, but that’s what also keeps us coming back to Axial Seamount! We headed to the surface with lots of samples and a much better idea of the diversity and distribution of the 2015 lava flows than we started with. Next stop, Seattle!
Images of the 2015 Axial Team.