Logbook: September 28, 2004

Cruise Summary
Bill Chadwick, Chief Scientist

Sunset at sea from the R/V Thomas Thompson.

The NeMO 2004 expedition has been a great success, thanks to good weather, the hard work of the science party, and excellent support from the ROPOS group and the crew of the Thompson. Here’s a brief summary of our results this year:

1) We made 5 ROPOS dives at Axial Volcano this year and had one full day of instrument deployments and recoveries. Between dives we conducted 6 CTD (conductivity, temperature, and depth) casts or tows to survey the hydrothermal plumes in the water above the bottom. In addition we collected EM300 multibeam sonar data to update and extend our survey of the bathymetry around the volcano.

2) Two of the ROPOS dives were devoted to collecting fluid samples from hydrothermal vents at Axial for chemical and microbiological analysis. We sample many of the same sites each year to look for changes that might be signal changes in the behavior of the volcano. Some of the hydrothermal vents showed temperature decreases this year. The Marker 33 vent looks about the same as last year, but nearby Cloud vent definitely had reduced temperature and flow. The ASHES vent field looks about the same, but one of the vents there, Virgin, seems to have a lower temperature than in previous years.

3) We made our ROV-based pressure measurements at five seafloor benchmarks again this year, in order to look for volcano inflation at Axial. This year we made some changes to the way we collected the pressure data and we were able to improve our repeatability at each site by about an order of magnitude (9 mm this year vs. 7 cm last year)! The data show that all the stations in the caldera were uplifted since last year and the center of the caldera continues to go up at a rate of about 20 cm/yr.

4) The NeMO Net buoy and the Remote Access Sampler (RAS) were replaced, but we are taking the new Bottom Pressure Recorder (BPR) back with us because it was having data transmission problems. Hopefully, it can be fixed and redeployed during another expedition soon. The RAS that was put down last summer worked perfectly and was full of vent fluid samples when we recovered it.

Overall, our monitoring shows that Axial Volcano continues to gradually build up toward its next eruption, but we do not know exactly when that next eruption will happen. We continue to monitor the volcano and its hydrothermal sites with the aim of anticipating future activity and documenting the changes that occur when that eruption finally occurs