MBARI Ridges 2005 Expedition

Juan de Fuca Leg: August 7–18, 2005
Gorda Leg: August 22–September 2, 2005

September 1-2 update - Posted by Dave Clague

On our way back to Moss Landing, the winds subsided considerably, so were able to complete one last dive on Pioneer Seamount. The dive was a continuation of one we began two years ago, but had to abort due to bad weather. It seemed fitting that we could complete it after having been unable to dive at the epicenter of the June Eureka M7.2 earthquake due to poor weather.

Pioneer Seamount is one of a group of seamounts (underwater volcanos) off the central California coast that consist of a cluster of parallel volcanic ridges or cones. These ridges are aligned parallel to oceanic spreading centers that became inactive when the San Andreas fault system formed, some 20-24 million years ago. We have been working on these seamounts for the past 5 years, so the opportunity to add another dive on Pioneer was welcome.

In previous years, we were not able to dive near the summit of Pioneer Seamount because a submarine cable is draped over the seamount, and we were concerned about entangling the ROV or its tether with the cable. However, over the last few years, MBARI performed ROV dives along the cable to map its route, and we discovered that we can, in fact, dive safely in this area.

After the spectacular lava forms we saw on the Juan de Fuca and Gorda Ridges, the rocks on the seamount were relatively dull and quite uniform. Most of the dive showed a sea bottom made up of volcaniclastic flows of breccia and sandstone, with some fragmental lava flow surfaces. Some sediment was draped over the rock surfaces, but currents have prevented sediment from accumulating very thickly during the roughly 12 million years since the volcano was active.

Left image: On one part of Pioneer Seamount, we found large numbers of delicate bamboo corals, which are rare elsewhere. Right image: Although the volcaniclastic rocks on Pioneer Seamount looked soft and unconsolidated, they were actually very hard and it was difficult to collect samples that were attached to outcrops. In many places the outcrops were dotted with a variety of colorful corals and sponges.

In contrast to the rather dull geology, large, impressive marine animals were abundant on the seamount. On each volcanic cone we observed different animal communities, so we saw a wide variety of animals during the dive. For example, the first cone we traversed had abundant bamboo corals, but all subsequent cones had few if any these corals. Another cone had abundant crinoids (the kind that swim), but these were nearly absent on all the other cones. A third cone had abundant Solaster (10-armed) sea stars, which were rare or absent elsewhere.

Left image: On some parts of Pioneer Seamount, we had a hard time collecting rock samples because the sea floor was covered with the remains of dead sponges, which apparently collected over long time periods. The pink mushroom-like organisms are a type of soft coral, which are growing on top of the dead-sponge "reef" along with some crinoids and a white sponge that is still alive. Right image: Near the tops of the volcanic cones, we saw "gardens" of large sponges, many of which were over a meter across. On one ridge top, the sponges were covered with crinoids (the orange fringed creatures in this picture). On other ridges, we saw no crinoids, but lots of small crabs living in and on the sponges.

During the course of the 12-hour dive, we collected rock samples from seven different cones and managed to recover both lava-flow fragments and volcaniclastic rocks. The lava fragments will be anlayzed in detail to determine their chemical makeup and ages. We hope that the volcaniclastic rocks will contain unaltered fragments of volcanic glass that we can analyze to determine the composition and volatile content of the original volcanic magma. The analysis of volatiles will help us determine whether the top of the seamount ever reached the sea surface, forming an island, or if the volcanoes only erupted underwater.

We started our dive a little before noon on Thursday, and continued into the evening. ROV Tiburon was back on board the Western Flyer about midnight and we were still processing samples in the laboratory at 2 am. Later that morning (September 2), the Western Flyer traveled the last hundred kilometers or so, arriving back at MBARI a little after 10 am. When we arrived at the dock, we spent several more hours packing all of our samples and equipment, then moving them from the boat and into our lab on shore. We finshed this process by about 1 pm on Friday.

Left image: This photo, taken around 1 am on our last night at sea, shows Jim and Lionel describing one of the more than 35 rocks that we brought back to the surface from Pioneer Seamount. Right image: We collected these fragments of dead bamboo coral for DNA analysis.

As we approached Moss Landing harbor, we could see the smoke stacks of the Moss Landing power plant in the distance. We were happy that the expedition had achieved most of is goals, but we also looked forward to seeing our friends and families back on shore.

This expedition has been a great success thanks to the dedication and professionalism of the crews of the R/V Western Flyer and ROV Tiburon, working under Captain Ian Young and Chief Pilot Buck Reynolds, to whom we are grateful and appreciative. They make working at sea both productive and great fun.

The success of the two cruise legs was also due to the contributions and hard work of all the scientific staff who participated. On the first (Juan de Fuca) leg of the expedition, I was joined by MBARI employees Alice Davis, Jenny Paduan and Linda Kuhnz as well as Bill Chadwick from Oregon State University; Gillian Clague from Willamette University; Brian Cousens and Laura Karrei from Carleton University in Ottawa; Nick Delich from NOAA in Seattle; Bob Embley from NOAA in Newport, Oregon; and Fred Pleijel from Goteburg University in Sweden.

During the second (Gorda Ridge) Leg, MBARI employees Alice Davis and Jenny Paduan continued to work on the ship, and were joined by MBARI employees Kim Fulton-Bennett, Joe Jones and Amanda Jones. In addition, we benefitted greatly from the presence of Jim Head from Brown University; Larry Mastin from the Cascade Volcano Observatory of the US Geological Survey; Stephanie Ross from the Coastal and Marine Geology Program of the US Geological Survey; Lionel Wilson from Lancaster University in England; and Rob Zierenberg from the University of California at Davis.

NOAA’s National Undersea Research Program (NURP) funded the instrumental work conducted during the first leg by Bill, Bob, and Nick, while the remainder of the program was funded by MBARI through a grant from the David and Lucile Packard Foundation.

I hope you have found our daily reports interesting and informative. We have tried to convey a sense of what is involved in running an expedition, what it is like to be at sea, and what we have been finding. Much of the hard work still remains to be completed back in our laboratories, but the field program has been very successful in collecting the data and samples we were after.

Dave Clague


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