R. Batiza (transcript), Milene Cormier (transcript), and Steve Faluotico (pilot)
Summary: The purpose of this dive was to map and sample the southern termination of the early 90's flow in the northern (17°30') study area and to determine whether the small isolated outcrops of "very fresh" (age zero) lava at the axis found during 1994 Shenkai dives and 1996 Argo survey were related to the early 90's flow. Unfortunately these young isolated outcrops were not found/recognized during the dive, so this question remains open. The southern end of the early 90's flow has an age of ~0.5 on the Macdonald scale and is about 300m wide at 17°33.6, near the northern end of the dive track. We followed this flow about 1 km south to about 17°34.2'S where it ends. At this point it is less than 10m wide. The young flow consists of lobate lava with pillow facies near it margin. The axis south of the fresh flow is dominated by lobates, with occasional pillows, until ~17°35.2'S where pillows dominate. The appearance of abundant pillows corresponds roughly with the appearance on DSL 120 sidescan records of "mounds". The axial region south of the young flow is moderately fissured, as is the southern terminus of the young flow itself. At ~17°34.5'S the axis has two geomorphic ridges on the sidescan records which turn out to be vertically tilted lava plates. These appear to be very steep-sided tumuli that developed on previous lobates and folded sheet flows. The lower reaches of the tilted lava plates are obscured by younger axial lobate lava that laps up to the tilted plates. Both tumuli have long axes oriented N-S parallel to the axis. During the dive, we found a previously unreported diffuse venting site at ~17°33.8'S, and visited an active black smoker site at ~17°35.2'S, presumably the site "Hobbs" of the Lilley/Von Damm cruise. The axis between 17°33.8'S and ~17°35.6'S, seen on this dive, has abundant signs of previous hydrothermal activity, including sites without obvious flow of shimmering water, but still with fairly abundant biota.
Sample Locations Sample Time Depth*Latitude (S)Longitude (W) 3359-1 0951 2609 17°33.55'S 113°14.16'W 3359-2 1014 2598 17°33.60'S 113°14.29'W 3359-3 1034 2591 17°33.64'S 113°14.37'W 3359-4 1055 2605 17°33.69'S 113°14.51'W 3359-5 1117 2597 17°33.84'S 113°14.45'W 3359-6 1149 2596 17°34.07'S 113°14.43'W 3359-7 1233 2589 17°34.53'S 113°14.58'W 3359-8 1251 2592 17°34.73'S 113°14.67'W 3359-9a,b 1409 2591 17°35.36'S 113°14.78'W 3359-10 1436 2593 17°35.53'S 113°14.79'W *- all depths are Alvin pressure depths- these are ~26-27m shallower than Seabeam depths