Eyewitness to the Landslide

Today, we successfully recovered the hydrophone mooring that we deployed last year at NW Rota to record the sounds of eruptive or landslide activity. We had not been able to communicate with the mooring since we arrived this year, so we feared it had maybe been swept away by the landslide. We didn’t know if it was still there or not. Today, we decided to find out by driving to its deployment location with Jason. We were able to quickly find it with Jason’s sonar and confirmed that it was still intact. Fortunately, it was located well north of the new landslide scar and so survived the event. After finding it, we sent the release code from the ship while Jason watched on the bottom, the release function worked, the mooring floated to the surface, and the ship recovered Jason and then the mooring including the hydrophone.

ROV Jason II witnessesd the release of the hydrophone mooring as the signal was sent from the ship to the release device pictured on the left. In the next instance, the hydrophone mooring was released to the surface and only bubbles from the wake remained (right image).

It's a relief to get the hydrophone back after not knowing if it survived the landslide. It will be a few weeks before the data are examined and analyzed, but it surely will be a fascinating record because it can tell us when the landslide occurred and how it was related to NW Rota's eruptive activity. This is probably the first ever near-field recording of a landslide on a submarine volcano, and it will help us better understand a lot of what we are seeing on the bottom this year with Jason.

The actual hydrophone instrument was pulled on board the R/V Kilo Moana after being released from the ocean floor. The hydrophone should contain data documenting the landslide event.

-Bill Chadwick, Oregon State University.

Arrival at Brimstone

March 18, 2010

We arrived at NW Rota seamount late yesterday and the question on
everyone’s mind was “would it still be erupting?” On the one hand,
the volcano has been found to be active every time it’s been visited
over the last 7 years, but on the other hand, how long could the
volcano keep this up? After we arrived, the first thing we did was
resurvey the summit of the volcano with the ship’s multibeam sonar
system, and the bathymetry showed some major morphologic changes
around the summit since last year. Next, we performed a vertical
cast with the CTD (an instrument package that measures conductivity,
temperature, depth, and optical backscatter) to look for evidence of
hydrothermal activity, and it showed that there was a strong plume
over the seamount. We’re now in the middle of making our first Jason
dive at NW Rota, and we’re seeing some big changes on the seafloor

2010 Brimstone at NW Rota-1 Volcano, Mariana Arc

since last year. First of all, the volcano is still erupting, which
I must admit still amazes me. Ash is being vigorously thrown out of
the vent along with a billowing sulfur-laden plume. But to our
surprise, we found 2 eruptive vents instead of 1. Also, the
submarine landscape is completely altered since last year. The main
eruptive vent is 25 m deeper than last year, and there appears to
have been both major landsliding (removing the large cone we saw last
year and parts of the surrounding area) followed volcanic re-
construction (which is gradually building a new cone over the
eruptive vent). What a dynamic landscape this is!
Every year we
have seen something different, which gives us the rare opportunity to
learn about how active submarine volcanoes work. We’re all excited
to learn more about what the volcano is up to this year. Stay tuned…

- Bill Chadwick, Chief Scientist, Oregon State University