October 11- October 17, 2003
October 15, 2003
David Clague writes:
We continued our exploration of more of the volcanic cones that dot the lower flanks of Rodriguez Seamount today. We again got a later-than-normal start since we recovered the acoustic beacon used for the navigational tests at dawn and then steamed to the dive location before launching the vehicle. Today’s dive was very smooth as everyone has learned their duties and the team is now playing in near-World Series form. We explored 5 separate cones today, working our way up the slope from the base to the summit, making observations and collecting samples and then gliding through the water column to the base of the next cone and repeating the process. We elected to forego the observations we could collect on the downhill part of each cone for the simple reason that it is slow and difficult to work downhill using either a manned submersible or a remotely operated vehicle like Tiburon. The main problem is that the camera is high off the bottom in order to avoid dragging the stern of the vehicle on the bottom if one drives downhill. One way to avoid this is to “crab” down the slope, but progress is fairly slow in this mode of operation. We elected to have brief periods of midwater “observations” (in quotes since there is no midwater geology!) in order to get to more volcanic cones. We collected 32 rock samples, including some large samples (the pilots kid me that I have never seen a rock that is too big to try to collect!) The vehicle was completely loaded when we ended the dive with no place left to put any samples and such a weight load that we had a slow ascent back to the surface. Several of the recovered samples are erratics and do not belong on the seamounts. In the far northern Pacific and Atlantic, such rocks arrive in icebergs that drop rocks as they melt. Off central California, other transport mechanisms must be sought. Two that appear to be important are as kelp holdfasts and as beach cobbles swallowed by sea lions and elephant seals (as ballast?) that are later expelled. Over the millions of years that have passed since the seamounts formed, quite a number of such stones have accumulated on their surfaces. In any case, such erratics are common on all the seamounts near the California margin that we have studies so far, although we observed fewer on Rodriguez than on Pioneer, Davidson, or Guide Seamounts.
We have now recovered so many biologic specimens that we have just about run out of preservatives and jars. Many of these animals are recovered attached to the rock samples but others are specifically collected to identify the native species. Still other animals are collected to become part of ongoing studies by colleagues. As an example, several years ago we rediscovered a clam that lives among the rocks on Davidson Seamount. I say rediscovered because this particular clam was last recovered more than 50 years ago. Since our rediscovery, we have found the same clam on a seamount west of Eureka, and on this cruise on both Pioneer and Rodriguez Seamounts. Genetic markers are being used to evaluate if the clams from different locations are closely related. There are always surprises when you collect anything. Today, we collected a predatory tunicate, another animals being studied by a colleague, only to find that it was partly filled with well-developed fish eggs. These eggs are being incubated in a cold seawater tank to see if they can be hatched.
Tomorrow will be our final dive before the long steam back to Moss Landing. We will have a short dive since we need to be on our way by 3 pm to arrive late Friday afternoon. We have elected to return to the summit, but to start the dive in the headwall of a landslide on the northeastern flank of the seamount. One characteristic of large oceanic volcanoes is that their flanks fail as large landslides. We hope to learn about such landslides by examining a smaller scale landslide structure.