March 13, 2001 to June 2, 2001
Monterey to Hawaii and back
April 27, 2001: Leg 3;Day 7
Connor writes: It's Friday and we're off the north side of Molokai with the wind and waves picking up. We launched Tiburon approximately 6:30 a.m. to dive into a submarine canyon 3460 meters deep--our deepest dive on the Hawaii expedition so far. It took two hours for the ROV to reach the seafloor.
Gary Greene searched for rock outcrops in the muddy seafloor and found layered volcanic outcrops including the one pictured. Sediment covered most vertical rock surfaces, including a shallow depression in a rockwall with trails of sediment. We also encountered a couple of purple pelagic holothurians--surely the most graceful of the sea cucumbers.
Right now, DJ Osborne has a CTD cast down at 3500 meters and when that returns to the surface, we may head for the lee of Molokai to get out of these winds and swells.
Gary Greene writes: Dive 307 was the deepest dive made on Leg 3 to date. The dive transect started at 3435 m near the base of the northern flank of the island of Molokai, in one of the largest submarine canyons that cuts this slope. This canyon is the most westerly submarine canyon that erodes the slope and is located due north of Mokio Point on the island of Molokai. In sticking with our submarine canyon origin and processes theme, we selected this canyon to dive in because it heads far out on the island shelf and does not appear to be connected with any substantial stream onshore. In addition, this dive is located where the scar of a massive ancient landslide, that displaced a few thousand cubic kilometers of material into the deep-sea, is believed to occur. This landslide is among the largest that is known to occur anywhere in the world. Our intent was to examine the characteristics of the rocks associated with this massive slope failure and the relationship of the canyon to the slope failure.
Eight rock samples, 2 push cores and continuous sampling of water for radium analyses were collected. Little life was seen on this dive with the exception of a few deep-sea fishes and stalked spider-like crinoids.
The sea floor at the start of the dive, in the center of the canyon, was muddy with scattered rubble and shallow linear groves that are similar to trawl marks. In places, patches of fine-grained angular gravels oriented parallel to the canyon axis were observed. Much of the bottom and rubble here is covered with very fine sediment.
At 3424 m depth the lower northern wall of the canyon was encountered which is composed of a well-lithified (hard) volcano-clastic rock. In many places the rock appeared to be composed of an angular breccia, perhaps generated from tectonic shearing associated with the landslide. Outcrops of this lithology formed the steeper faces to a depth of 3331 m where the dive was terminated. Between the outcrops were extensive sediment draped slopes. Much of the rock outcrop is dusted with mud while the intervening areas appear to have about 10-20 cm of mud cover over the bedrock. Near the end of the transect more finely bedded sedimentary rock was exposed and thin beds of apparent volcanic sandstone are differentially eroded.
The apparent dip of the well-bedded volcano-clastic rocks at the base of this section is 15° to 20° to the west. The upper part of the transect was along a slope of about 45°. The slope here (~3245 m) appears to be a bedding dip slope with an apparent dip toward the northeast. These observations suggest that there is a major structure within this sequence.
The dive was prematurely terminated at 3331 m because of deteriorating weather conditions on the surface. During the recovery, it was discovered that several tight turns were in the cable. After recovery, a severe kink existed in the cable which required the umbilical to be cut and reterminated. Thus, the rest of the day was spent conducting hydrocasts to ground truth the radium sampling efforts
Jenny Paduan writes: Today a series of kinks was inadvertently put into the ROV's tether. The tether is the umbilical to the vehicle, and carries power and commands from the ship down to the vehicle and video and data back up from it. If the tether is damaged, we could lose telemetry and control of the vehicle, and in the worst case, lose the vehicle entirely. The winds had risen to 40 knots, so the recovery was dicey even without the added vulnerability of the tether. Fortunately the damage was only to the metal fibers that are the strength members, not to the optical fibers, so they were able to control the vehicle for the entire ascent from 3,400 meters depth. The ROV pilots then worked to reterminate the tether. It will be a late night for them tonight. We expect to be able to dive again tomorrow morning!