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.

8. The 1981-1991 Lava Flows at the "Floc Site"

The 1994 deep-towed camera survey delineated a series of young, glassy lava flows extending for 7 km along a ridge ~500 m west of the actively venting fissure swarm at the Floc site (Figures 8, 9, and 10). The lava erupted along a preexisting ridge; in some locations it flowed down the east side of the ridge and at other places down the west side (Figure 10). Application of the SeaBeam differencing technique revealed a small but distinct depth difference anomaly (up to 25 m) between the 1981 and 1991 surveys which coincides exactly with the young lava mound delineated by the towed camera at 46°17.5N, 129°43.3W. Note that this SeaBeam anomaly is different than the "southern 1981–1991 SeaBeam anomaly" tentatively identified at 46°26.2N by Chadwick et al. [1995], which our 1994 camera tows revealed to be false. The Floc site anomaly discussed here was also assumed to be an artifact [Chadwick et al., 1995] because it was relatively small in area and did not have any photographic groundtruthing at the time. The absence of additional SeaBeam difference anomalies coinciding with the other areas of glassy lavas mapped by the towed camera suggests that most of the 1981–1991 lava flows at the Floc site are thinner than ~5–15 m, which is the vertical resolution of this technique [Fox et al., 1992]. The SeaBeam differencing results do not allow age discrimination between the 1982–1991 lava flow at the Flow site and this one at the Floc site. However, close examination of Alvin hand-held photographs of the two sites suggests that the Floc site pillow mounds are slightly older because they have small sediment pockets and do not have as vitreous a luster as the northern lavas (compare Plates 2f and 3f). The towed camera imagery and video traverses made with the submersible Alvin show that neither of the 1981–1991 flows were fractured, nor were they colonized with sessile organisms.

Return to previous section or go to next section

PMEL Outstanding Papers

PMEL Publications Search

PMEL Homepage