DATES: April 27, 2004 - May 8, 2004
LOCATION: California Seamounts
This expedition will expand on 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.
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.
Click on the links above to find out more about this exciting cruise!