Stationed at the Vailulu’u seamount, we continued to take CTD readings directly over the crater.  At about 1:30AM we retrieved the CTD because the Pinger (a device that uses sonar to measure the distance from the CTD to the bottom) was low on batteries.

The normal procedure for retrieving the CTD is fairly simple, though it requires some good hand-eye coordination, especially when trying to attach lines to the CTD while it is swinging from the crane.  The procedure is as follows:  The CTD is raised to the surface of the water, if the Pinger is attached (on the cable about 20 feet above the CTD) it is removed.  The CTD is then raised to deck level and lines are attached using large latching-hooks that are held in place at the end of a large pole (kind of like a marlin spike).  After the two lines are attached and tensioned, the crane moves the CDT into position over its pad and slowly lowers it into position.  Once on deck, the CTD is firmly secured.  If it is not going back in the water, the cable is removed and the CTD is rolled into its hanger for storage.

Unfortunately, just after the CTD made contact with its platform, the winch died.  The captain and engineers broke out the schematics and started pouring over it, trying to figure out what was wrong.  During this time we moved to a position just NW of the crater rim, to the location where we were to re-deploy the CTD.

Two or three hours later, the winch was operational again, though no one could define what the problem was or how they fixed it.  Not wasting time, we deployed the CTD (minus the Pinger) and soon it was on its way down to 1070 meters.  Once there it was brought back up to 400 meters, and then sent back down to 1070.  One cycle, or “Cast”, takes about 15 minutes to complete.  This process was repeated over and over for 14 hours so that we could get data from a full tidal cycle. 

The data that we collect here will help us understand the flow of water around Vailulu’u which will give us a better picture of the volcanic activity that is occurring.  Using the CTD we can see the change in the temperature of the water, and the particulates that are present. 

The implications of the data are not yet clear, and analysis is a large part of what we are doing now.  We found that there was a dense layer of particulates in the crater, but the water was clear outside the crater rim.  This is different from what was observed during the cruise in 2000 where there was a dense ring around the whole volcano. It appears that the particulates are rising out of the crater and then sinking instead of forming a ring like the one previously observed.

Blake English onboard the R/V Kilo Moana.