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The Gorda Ridge is an oceanic spreading center located off the coast of northern California and southern Oregon. The geologic setting and tectonics of the ridge were summarized by Clague and Holmes (1987) and Fisk and Howard (1993).The ridge axis has the typical deep axial valley of slow-spreading ridges. More recently a detailed description of the ridge structure, based on comprehensive SeaBeam bathymetry, was presented by Chadwick et al. (1998). They divide the ridge into five segments named, from south to north, the Escanaba, Phoenix, Central, Jackson, and North Gorda segments, offset from one another by transform offsets. The ridge has a complex history due to spreading rate changes, intraplate deformation of the Gorda plate, and reorientation of the ridge axis (Wilson, 1986, 1989). Davis and Clague (1987, 1990), Nielsen et al. (1995), and Rubin et al. (1998) have studied the petrology of lavas erupted along the four northern segments. Disequilibrium U-Th-Ra studies have established the ages of some of these lavas (Goldstein et al., 1992; Volpe and Goldstein, 1993).
In the 1980s, NOAA discovered hydrothermal plumes in the water column above the North Gorda segment (called the GR14 site, Collier et al., 1986, Baker, 1994). Subsequently, extensive mapping and sampling was conducted in the North Gorda segment in search of the source hydrothermal vents (Rona and Clague, 1989; Clague and Rona, 1990). These vents were subsequently discovered using the SeaCliff submersible (named after the SeaCliff hydrothermal field, Rona et al., 1990; Zierenberg et al., 1995). These vents are highly unusual in that they are not located in the axial valley, but instead are about 300 meters above the valley on the east wall. Scientists from MBARI and the University of California at Davis returned to these vents in 2000.
In 1996, a seismic swarm occurred along the North Gorda segment (Fox and Dziak, 1998). Investigations in the area demonstrated that an eruption had occurred at the site (Chadwick et al., 1998). Po-Pb analyses show that young lavas collected from the proposed eruption site did in fact erupt in 1996 (Rubin et al., 1998). A special issue of Deep Sea Research II (Cowen, 1998) presents the results of a wide range of studies done to investigate the eruption.
The new high-resolution data presented here provide more detailed views of the constructional features in the axial valley and the block faults that make up the valley walls. In particular, the morphology of numerous individual vents can be seen clearly. Similarly, the valley walls commonly include partial vent structures that have been dismembered by faulting. The new high-resolution data also provide more detailed maps of the SeaCliff hydrothermal field and the 1996 eruption site
|Index Map||Axial Volcano||Gorda Ridge||Cleft Segment||Taney Seamounts|
|Guide, Gumdrop, Pioneer Seamounts||Mendocino Fracture Zone||President Jackson Seamount||Davidson Seamount||Vance Seamounts|