May 3, 2004, Day 7
Today, we returned to Northeast Bank for a second dive. The first dive explored the eastern flank of the volcano and today we dove on the south flank. The locations for these dives were partly controlled by the locations of modern bathymetry, which is quite sparse on the volcano. We repeated the plan from the previous dive, working our way up the slope, onto the nearly flat summit, and then back down about 50 meters below the break-in-slope. From there we drove along a specific depth, collecting samples about every 150 meters or so. With this plan we sampled numerous lava flows that had crossed the break-in-slope when the volcano was active and the break-in-slope was the shoreline. It is critical to understanding the origin of the magmas that formed the volcano to sample as many eruptions as possible, so our strategy was designed to do just that. We also hoped to find another shoreline deposit with corals or other evidence that the break-in-slope really was the shoreline. Today, we did not find fossil deposits, despite two locations where we thought we had done so. One of these turned out to be some bamboo coral segments and the other, numerous shell fragments of the deep-sea clams we have been collecting for Joe for genetic study. Each caused quite a bit of excitement at the time, but neither turned out to be what we were looking for. We did, however, find some evidence that the break-in-slope marks the shoreline of an ancient island. We saw a deposit of large round beach cobbles and boulders scattered down the slope and an outcrop of conglomerate consisting of cemented rounded cobbles. We also collected, right at the break-in-slope, a beach-rock sample that contained numerous rounded pebbles. Now we know that Northeast Bank was an island, and we just have to figure out when. The biology was less exciting today, in part because we saw pretty much the same animals on the bottom that we had seen a few days ago. We did observe a squid that appeared to be feeding on the rocks (quite bizarre behavior), ran across an exotic deep red ctenophore, found a hatchet fish, and saw some large and colorful snail fish (liparids) . Snailfish (see photo), related to eelpouts, are unusual in that they have a pair of fins (pelvic) located near their head that is modified to act as a suction disc. Snailfish have very smooth skin and have no scales. Each caused a stir in the control room!
A bloody-belly comb jelly (the ctenophore, Lampocteis) drifts by a lava outcrop. (George Matsumoto of MBARI described this animal for the first time in the zoological literature.)
Another shot of the comb jelly. The flashes and rainbows of light are not bioluminescence, but are refractions of the ROV's bright lights by the crystalline hairs, or ctene rows, it uses like oars to propel itself.
In yesterday's dive, we saw a pair of Humboldt squid hunting a rattail fish. During today's dive, we saw several different types of large squid. One of these squid showed an unusual behavior in that it repeatedly darted in and out of the rock outcrops. We think that this squid was looking for small animals to eat.
We are within range of Los Angeles radio stations and coastal fog. The
ship's fog horn sounded this evening for the first time this trip (much
like ops in Monterey Bay!) Most of the day was clear and sunny, however.
We saw a large Nereocystis (bull kelp) float by the ship, which is
consistent with our suspicion that some of the cobbles with continental
rock compositions (such as granite, quartz sandstones, and blueschist)
we find on the seamounts may be erratics that rafted from the coast with
kelp hold-fasts, and did not somehow erupt out here.
Our dive today traversed what is probably a rift zone of the volcano
that is Northeast Bank. We saw many repeated sequences that we think
were channelized a'a flows cascading down the flank of the volcano,
separated by talus chutes. During the vigorous phase of the flow, thinly
layered levees built up on the sides of the channel. Then the flow
finally solidified as a massive, columnar-jointed unit between the
levees. Dave showed me these forms on Kilauea Volcano during our
expedition to Hawaii in 2001.
Thinly bedded lava levee (the flow channel was on the right) is now home to brisingid stars and sponges.
Thorny-head rockfish (Sebastolobus) nestled up to a corroded metal cylinder of unknown origin, one of six we observed in the area.
Another species of clam that lives like a brachiopod. It is new to us and probably related to the ones we have previously found on the seamounts (see the cruise log on April 29), but is larger and has a striated, more fragile shell.