March 25, 2010

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.