Alvin Dive 3359 - 20 Feb. 1999

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
  • Navigation Plot (GMT)
  • Navigation Plot (dot cloud)
  • Depth + Altitude
  • Heading
  • Temperature