Mixing Zephyr Program
Dive 3000

Port Observer: Delaney
Starboard Observer: Kelley
Pilot: Hickey
Date: 9/20/95

Summary

Dive Goals: The goal of this dive was to explore and map out the Salty Dog vent field that was discovered in June of this year and which lies north of the main Endeavour vent field. The second objective was to examine the terrain 200-300 m north of this area and to determine the nature of small aligned features that were observed in this area by side scan sonar.

Dive summary: We landed about 100 m N of the Salty Dog target in a small basalt filled depression and then drove south to the target. The Salty Dog site was offset ~100 m west from the grid determined in June. At Salty Dog, the vent at marker AF was vigorously venting and was sampled with gas tight bottle #5, major #6 with an ALVIN probe temperature of 317°C. A video survey around the multi-flanged structure was completed as was a vertical transect. We drove slightly SE ~ 75 m and came upon a new large massive sulfide structure that we named Grendl, which is joined to the NW by another massive sulfide structure by a small saddle. Grendl is highly complex, composed of a series of composite and stair step flanges that are roofed by abundant small pinnacles. Diffuse flow from underlying reflecting ponds is extremely common as are tube worms that form a ringing fringe around the flange tips. Under one of these flanges a temperature of 297-299°C was measured from a pool a couple of cm deep. We sampled a second reflecting pool with bottle major #10 and gas tight #6 and measured a temperature with the ALVIN probe of 295.6°C. Marker # B3000 was dropped near this flange structure. A small inactive chimney spire subadjacent to Grendl was sampled for sulfide and biota studies, in addition, Niskin samples were taken above the flange structure at 1, 5 , and 10 m, respectively. We then dropped down to the base of Grendl that has a distinctive small ridge lined by a forest of small spires that looks like a Christmas tree forest. The base of this structure is bounded by heavily sedimented sulfide talus that grades down slope into intercalated oxidized sulfide and basalt talus and sediment. We traversed around this structure following the sulfide, sulfide-talus basalt-sediment contact making a full circle around the field with 7- 8 distinct massive sulfide structures observed. Except for Salty Dog and Grendl, these other structures were not actively venting and only rarely was diffuse flow observed. The boundary of this composite feature is bounded by pillow and platy sheet flows with only very minor fractures. Upon closing the traverse back to marker B3000 we sampled a third flange structure on Grendl for old sulfide and took gas tight samples from bottle #2 & 7, and double major 4 & 5. A detailed Mesotech survey was then completed from 6475 to 6775, and 9700 to 9850 using 7 E-W lines spaced 25 m apart with a 30° swath, and an 8th line running at ~300 NW across the field to intersect the large sulfide structures. The Mesotech survey, coupled with the traverse that followed the sulfide-basalt/sediment contact, indicates that the field is L-shaped with the lower leg extending ~150 m to the SE and the upper leg extending at least 150-200 m to the NE. Salty Dog to the west is distinct from this feature and is separated by a small low. After completion of the survey we drove north into a large field of collapsed lava lakes marked by extensive collapse pits, abundant pillars, bathtub rings, and talus. We sampled 2 basalt samples from one of the pillars and returned to the surface.