We had previously found evidence for the repeated build-up and collapse of the ash and lava around Brimstone vent at NW Rota, leading to landsliding down the steep southern flank. To try to capture these kinds of events, last year we deployed 4 moorings with temperature and turbidity sensors, current meters, a fluid sampler, and a hydrophone to monitor activity at the volcano between then and now.
In fact, we have discovered on this trip that the volcano experienced a major landslide between last year and this year. Such an event is exactly what we had hoped to capture, except that this one was far larger than anything we had anticipated and appears to have caught all four of the instrument moorings. After an extensive search, we have only been able to communicate from one of the moorings. This one was deployed downslope from the summit at a depth of 1500 m, and it was moved about 1 km downslope (to ~1830 m) by the landslide and the acoustic release reports that it is horizontal. We plan to make a Jason dive on this mooring to see what instruments survived and might be recovered. The data it recorded could be fascinating, but it is deeply disappointing that the other moorings appear to be lost, both for the loss of valuable equipment but also for the lost scientific data. We plan to search with Jason for all of them during subsequent dives, so we have not yet given up all hope of finding them.
The changes in the summit area are equally staggering. The volcano summit is still in the same place and at the same height (probably a resistant lava plug), but the landslide event eroded back the summit ridge about 100 m to the north on either side, and one of the ridges SE of the summit has been replaced by a large landslide scar (on the 2nd map, the red line is the new summit ridge and the green dots are the mooring locations).
-Bill Chadwick, Oregon State University