Monterey Bay Aquarium Research Institute

West Coast Expedition
DATES: July 20 - August 30, 2002
LOCATION: West Coast of North America

Cruise Description

NEPacificGorda2002.jpgThe cruise is divided into three legs. The first leg includes a combination of 11 dives for four groups. Four dives are for the MBARI Submarine Volcanism Project for David Clague. Three of the dives are funded by NURP for Rob Zierenberg and Jim McClain to explore two active hydrothermal vent sites, and one dive is for the MBARI Midwater Biology Project for Jeff Drazen. The submarine volcanism dives continue work on eruption of vesicular mid-ocean ridge basalt and submarine strombolian eruptions and ejecta dispersal. The final dive is to determine the geochemical variations in lavas exposed within the caldera-bounding faults on one of the President Jackson Seamounts. The objective of the NURP-funded hydrothermal dives is to collect water samples from two previously sampled hydrothermal vent sites to evaluate changes over time and to map the extent and structural setting of the Seacliff hydrothermal site. The Midwater Biology dive is to observe brooding blob sculpins and to determine if abundant octopuses in the same area are also brooding eggs.

cleft segmentThe second leg, composed of four dives, is under the direction of Dr. Debra Stakes. This leg continues a study of the Cleft ridge axis started in 2000 to examine the formation history of the southernmost segment of the Juan de Fuca Ridge. Models for the formation of oceanic crust assume that the uppermost portion of the seafloor form from seafloor eruptions right at the spreading axis. Narrow ridges of piled up pillow basalts would then be split in half by the forces of seafloor spreading. This so-called “split-ridge” hypothesis is the primary focus of our rock-collecting program. Our work from 2000 suggested that much of the upper crust forms on the ridge flanks, several kilometers from the axis. This would extend the zone of young volcanism to several kilometers from the mid-ocean ridge, also extending the zone of potential hydrothermal vents and subsurface microbial habitat. On the first dive we plan to revisit one of the active ridge-flank vent sites to sample fluids and collect precipitates that might yield evidence of microbial activity.

Endeavour SegmentThe third leg is funded by the Keck Foundation and will be guided by Dr. John Delaney (University of Washington). The goal of the Keck project is to contemporaneously measure earthquakes, fluid flow and microbial activity across the northern Juan de Fuca plate to assess their interrelationships. The two sites that will be instrumented are the Endeavour Segment of the Juan de Fuca Ridge and the intersection of the Nootka Fracture Zone and the Cascadia Subduction zone. This is the first field effort of this project and the locations of the seismometer array will be determined during the expedition. Boreholes will be made in the basaltic basement at the Endeavour Ridge to provide well-coupled deployment sites for short-period seismometers. Broadband sensors require a meter of thick sediment for burial and we will also search for deposits 2-3 km from the Endeavour spreading axis. The instruments will be deployed in 2003. Endeavor Observatory


 

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