Tiburon Dive 175

Western Blanco Fracture Zone at intersection with South Cleft

by Debra Stakes

The drop point for this dive was in 3200 meters of water at the RTI (Ridge- Transform Intersection). The intersection of the southernmost Juan de Fuca Ridge and the Blanco Transform zone is characterized by a series of ridges that bend around the corner and can be traced to the bottom of the transform. Our dive site includes an inspection of one of these ridges. This will be followed by a traverse up the wall of the transform approximately four kilometers off-axis.

The vehicle was in the water at 0655 local 21 July, (1355 GMT) for the first dive of this series. The remarkably clear blue water provided beautiful views of the ROV launch. The ROV was equipped with the coring sled that included four barrels. Along the starboard side of the coring sled was a manifold of holders for wax push cores (a great idea borrowed from Mike Perfit of the University of Florida) and the geocompass (provided by Maurice Tivey of Woods Hole Oceanographic Institute). During the descent, the vehicle had to be rebooted after hydraulics powered up.

One of the most surprising observations at the beginning of the dive was the abundance of benthic fauna, including crinoids, brittle stars, sponges, snails (Neptunia) and anemones. We used the corer to core into the ridge on the floor of the transform. Although it was heavily sedimented, the core included several pieces of old basalt. We assume that the ridge is a low angle fault. The software problem required us to reboot both before and twice after the drilling operation. We decided to terminate drilling operations unless the problem could be resolved. The dive continued with the collection of several geological and biological samples collected using the manipulator. There was mostly sediment-covered talus on the lower wall that gave way to intact, but sedimented pillow basalts on the upper wall. We also passed several NW-SE trending faults that appeared to curve into the transform. Two Tiburon wax push-cores appeared to work well.