Thursday, September 5, 2013

Measuring Pressure

Weather: The last 24 hours have been calm and sunny with sparse clouds. The sea is relatively calm, which is a great help for deck work involved in launching and recovering instruments

Science Update:
Today’s objectives:
1) Deploy 3 BPR moorings - check!
2) Release and recover 2 OBHs - check!
3) Deploy Jason on first dive of this cruise (dive J2-726)- check!  

Measuring Pressure Chief Scientist Bill Chadwick describes what a BPR is and what it does to help monitor submarine volcanoes like Axial Seamount and you can see footage of one being deployed on Sept 5th in the video below. Chadwick and colleague, Scott Nooner (University of North Carolina, Wilmington) use BPRs to collect and record pressure data that are used to better understand the inflation and deflation patterns at Axial Seamount. The BPR instruments are deployed on the seafloor for as much as two years before being recovered.

Each BPR (shown at above) has a set of buoys attached to them and an acoustic release that can be activated from the ship to release the anchor that holds the BPR to the seafloor. The buoys help float the instrument back to the surface when it’s time for the instrument to be recovered and data downloaded.
 In addition to the continuous pressure measurements collected by BPRs, a long dive (5½ days) will be dedicated during this cruise to complete pressure measurements with Jason at an array of sites (green dots on map at left) to determine the spatial distribution of inflation. These measurements are collected for 20 minutes at each site, and circuit of all the sites will be completed 4 times during the dive. The ROV-based measurements document long-term gradual inflation, whereas the BPRs are better for rapid short-term events.

Chadwick and Nooner have collaborated on monitoring Axial Seamount for more than 10 years. Together they have deployed and recovered BPRs at Axial and studied the pressure data to understand the long-term inflation and deflation cycle at the volcano. They are looking for repeatable patterns that might help forecast future eruptions.

During the pressure dive, sites will include those used in previous surveys, as well as several new stations, which we are deploying on this cruise. The ROV-based pressure measurements are made on a cement benchmark (see photo at right, of a benchmark being deployed, and one on the seafloor in the image below from a 2010 survey). Research by Chadwick and Nooner at Axial Seamount is funded by the National Science Foundation.