U.S. Dept. of Commerce / NOAA / OAR / PMEL / Publications

Recent eruptions on the CoAxial segment of the Juan de Fuca Ridge: Implications for mid-ocean ridge accretion processes

R. W. Embley,1 W. W. Chadwick,2 M. R. Perfit,3 M. C. Smith,3 and J. R. Delaney4

1Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Hatfield Marine Science Center, Newport, Oregon 97365
2Cooperative Institute for Marine Resources Studies, Oregon State University, Hatfield Marine Science Center, Newport, Oregon 97365
3Department of Geology, University of Florida, Gainesville, Florida, 32611
4School of Oceanography, University of Washington, Seattle, WA 98195

Journal of Geophysical Research, 105(B7), 16,501–16,525 (2000).
Copyright ©2000 by the American Geophysical Union. Further electronic distribution is not allowed.

2. Sources of Data

2.1. Multibeam Bathymetry

The initial SeaBeam surveys of the axis of the Juan de Fuca Ridge were collected in 1981–1982 on the NOAA ship Surveyor and were navigated by Loran-C, which provided good relative positioning for swath matching but only approximate geodetic control. These data were subsequently shifted to geodetic "space" using Transit satellite fixes taken during the original surveys. Following the 1990 discovery of the young eruptive mounds on the southern Juan de Fuca Ridge [Chadwick et al., 1991; Fox et al., 1992] another survey of the entire neovolcanic zone of the Juan de Fuca Ridge was made from the NOAA ship Discoverer in 1991. A third survey with GPS navigation over the northern portion of Axial Volcano and the CoAxial segment was made immediately after the 1993 eruption. These three surveys were the basis for the SeaBeam differencing calculations presented by Chadwick et al. [1995]. The database used for the SeaBeam base maps in this manuscript is a combination of the older Loran-C/Transit navigated data and the 1993 GPS survey.

2.2. Side-Scan Sonar

Data from two types of side-scan sonar systems, SeaMARC II and AMS-60, are used in this study to provide an excellent regional structural context within which to view higher-resolution data sets. The SeaMARC II system is a surface-towed side-scan sonar system operating at 12 kHz. The SeaMARC II data used in this study were collected in 1983 and 1985 by the Canadian Pacific Geoscience Center, the USGS, the University of Washington, and the University of Hawaii. These surveys were navigated by Loran-C and Transit satellite fixes. In 1996, comprehensive surveys of the neovolcanic zone of CoAxial and the north rift zone of Axial Volcano were made using an AMS-60 (60 kHz) deep-towed side-scan operated by Williamson and Co., Seattle, Washington, towed from the NOAA ship Discoverer. The position of the side-scan sonar was calculated using the setback of the towfish from depth, wire out, and the GPS position of the ship. The AMS-60 side-scan data were processed to a resolution of 1 m using the USGS Mini Image Processing System (MIPS) software. The AMS-60 side-scan data provides information on the morphology, structure, and texture of the seafloor and can be used to distinguish young volcanic terrain from older tectonized seafloor.

2.3. Submersible and Camera Tow Data

These data were collected using the NOAA Pacific Marine Environmental Laboratory (PMEL) and the USGS deep-towed camera systems (1993–1994), ROPOS (1993), and the manned submersible Alvin (1993–1995). The ROPOS and Alvin data used in this paper include video and still photographs and microbathymetry (derived from adding the pressure depth and altimeter output). The deep-towed camera data consist of color 35-mm film, color video, and temperature from the USGS system and monochrome video, color 35-mm film, temperature, and microbathymetry from the NOAA camera system. The seafloor images were digitized and characterized according to the scheme of Fox et al. [1988]. All of the Alvin dives and most of the deep-towed camera data were collected within long-baseline transponder nets that provide a positional accuracy of ~20 m. These near-bottom observations were used to delineate the location of the neovolcanic zone on both the CoAxial segment and the north rift zone of Axial Volcano.


Return to previous section or go to next section

PMEL Outstanding Papers

PMEL Publications Search

PMEL Homepage