Seamounts Cruise 2004

Cruise History and Purpose

Cruise Dates: April 27, 2004 - May 8, 2004
Cruise Location: Offshore Seamounts
Ship: R/V Western Flyer
Chief Scientist: David Clague

Scheduled Start Time: 2004-04-27 0600 Local Moss Landing time
Scheduled End Time  : 2004-05-08 1700 Local Moss Landing time
(Subtract 7 hours during PDT to convert to local time, subtract 8 hours during PST)


The primary objective of the cruise is to continue volcanic rock sampling on the series of elongate seamounts off the west coast. At least some of these seamounts formed along spreading centers abandoned when the San Andreas fault system formed, although the seamounts we have studied so far are significantly younger than the time of fault initiation. These seamounts appear to young to the south, so we are anticipating thinner Mn-oxide crusts to obscure the outcrops. Many of these seamounts grew to shallow depths and several were islands, so they also are excellent locations to study the transition from submarine to subaerial explosive volcanic activity. Most of the lava flows on seamounts sampled to date are low-temperature melts that form thick pasty lava flows and volcaniclastic deposits. We expect more of the same, but with fresher samples with more abundant glass due to the younger ages of the seamounts to the south. We will also continue to characterize the fauna on these seamounts and have plans to collect clams (for genetic studies), bamboo corals (for paleoclimate studies), paragorgia (for genetic studies), crinoids (for taxonomic studies), predatory tunicates (taxonomic and genetic studies), and anything else that appears new or different.  

Required Equipment: Benthic sled with Kraft manipulator and drawer with partitions, push cores on swing arm rack, biojars along front of drawer, suction hose with screen but no sampler, bioboxes that fit drawer partitions, sediment scoops (no more than 2 per dive), Niskin bottles on vehicle

Planned track/Site: Transit from Moss Landing to San Juan Seamount (approximate location 33°N, 121°W, 240 nm transit) for the first dive, following dives will be at San Marcos Seamount (approximate location 32.7°N, 121.8°W), Little Joe Seamount (approximate location 31.9°N, 120.1°W), North east Bank (approximate location 32.3°N, 119.6°W), and along the Patton Escarpment (approximate location 33.1°N, 120.7°W). The final dive will be on Rodriguez Seamount (approximate location 34°N, 121.1°W) followed by a roughly 180 nm transit back to Moss Landing for arrival by 5 pm May 8.

Participants: David Clague (wf1), Alice Davis (wf2), Jenny Paduan (wf3), Lonny Lundsten (wf4), Joe Jones (wf5), Jim Hein (US Geological Survey) (wf6), Brandie McIntyre (US Geological Survey) (wf7), Kathie Marsaglia (Cal State University Northridge) (wf8), Tessa Hill (UC Santa Barbara) (wf9). [Note: A temporary email address is listed after each name. Add suffix "at mbari dot org," which is spelled out to reduce spam.] 

Cruise History and Background

This is a continuing project (See also the expedition logbook from Seamounts 2003). Our work on explosive volcanism along mid-ocean ridges, submarine rift zones in Hawaii, and seamounts along the California margin will continue to explore the range of environments, compositions, and depths under which explosive basaltic eruptions can occur. Such knowledge is critical to understanding the hazards such eruptions pose and the inputs of magmatic volatiles, dominated by carbon dioxide, into the hydrosphere. To date we have established that pyroclastic eruptions driven by loss of magmatic volatiles can fragment magma ranging from normal mid-ocean ridge basalt at depths as great as 3800 m to strongly alkalic basalt at depths as great as 4300 m. We will continue to examine the composition and structure of giant Hawaiian landslides offshore Oahu, Molokai, and Hawaii. With post-doctoral fellow Jody Webster now working on nearly 500 samples from drowned coral reefs around Hawaii, we expect to make significant progress in understanding how the reefs form and drown, as well as the implications for island subsidence and paleoclimate. Our work on the formation of seamounts offshore California has resulted in recognition that these seamounts also had explosive eruptions and that they formed by infrequent eruptions over long time periods. We will continue to publish results from MBARI's 2001 expedition to Hawaii and of Hawaiian dives with Pisces and JAMSTEC submersibles and ROVs, from MBARI dives to the Gorda and East Pacific Rise mid-ocean ridges, and from Davidson Seamount. In 2002 and 2003 our project requested and was awarded minimal dives while we completed our analytical work on the samples collected during the Hawaii expedition. In 2004 we are again ready to undertake more extensive field programs to extend our studies of submarine volcanism.

We propose to expand our studies of seamounts offshore central California southward by sampling and mapping on Rodriguez, Northeast Bank, San Juan, and San Marcos Seamounts, offshore Pt. Conception. Similar to Davidson, Guide, Pioneer, and Gumdrop, but slightly younger in age, these volcanoes are examples of a previously unrecognized kind of oceanic volcanism (Davis et al., 2002), reflecting changes in plate boundaries as the Pacific-North American boundary shifted from a convergent to a transform margin. The seamounts have unique structure of parallel elongate volcanic ridges with intervening basins, which reflects the fabric of the underlying ocean crust. Absence of collapse structures like calderas or pit craters suggest that the seamounts formed during multiple episodes of volcanism by intermittent eruptions occurring over long time periods (more than 4 million years for Davidson). Absence of collapse structures and presence of mantle xenoliths suggest that lavas rose from upper mantle depths without being stored in shallow magma chambers. The summits of these volcanoes have fragmental deposits that formed during explosive eruptions. Since some of these seamounts emerged above sea level before final submergence, they provide the rare opportunity to study the transition from submarine to subaerial eruption.