(On-axis, Animal Farm at 18°36.5'S to 18°37.4'S)

Observers: Cindy Van Dover and Milène Cormier
Pilot: Steve Faluotico

Summary

The objective for the first part of the dive was to locate and sample a mussel bed at Animal farm for biodiversity comparisons. We returned to the coordinates of the mussel bed sampled on Dive 3343 (Animal Farm Site 1; x=3525, y=8433), measured temperature (ambient=1.74°C; within mussels=1.84°C), and collected one large (2-liter) box of mussels using a scoop. Subsequent to this sampling, we undertook a short survey of the area in search of a mussel bed with more vigorous water flow and healthier mussels. Not finding this, we returned to within 20m of our site (Animal farm Site 2; x=3530; y=8420) where there was a larger (10m vs 4m max dimension) mussel bed. Maximum temperature measured in this mussel bed was 2.6°C. We tested one mussel pot sampler but it failed due both to the single layer of mussels making up the bed and to a snag in the cinch line. Five scoop samples (each of ~2 liter volume) were collected from this site as well as an incidental rock sample which was given a sample number post-dive.
The objective for the second part of the dive was to survey the system of right-stepping en echelon fissures visible in the DSL-120 side scan record along the ridge axis. We proceeded southward from the Animal Farm site and zig-zagged across the fissures to assess their nature, width, and dimensions. All the lava flows encountered were very glassy, with only a light dusting of sediments; sessile macrofauna was present almost continuously, and anemones were a common sight. We estimate a relative age of the lavas of 1.0 on the Macdonald age scale, similar to previous age estimates for the Animal Farm lava flow. Each crossing of the fissures revealed similar features. The depths of the fissures estimated from Alvin's pressure sensor and down-looking sonar vary between 5 and 9 m. Their widths are estimated to be 40-60m (although all crossings were oblique to their strike, DSL 120 records suggest a strike of N010° near 18°36'S). Untectonized lobate flows occurred a short distance from the fissures, sometimes grading into sheet flow and jumbled sheet flow near their rims. The walls of the fissures never exposed fresh break (= these fissures are eruptive fissures). Sheet flows draping down the walls of the fissures like waterfalls were observed on several occasions. The upper crust of these cascading sheet flows is fragmented into imbricated pieces in the upper reaches of the wall (= the fragments are still plastered on the cascading sheet flow, frozen-in-action). Down in the face of the walls, fragmented sheet flows were common, and behind the draped flow, "bathtub-ring-like" layering a few cm thick. Lava pillars have been observed only near 18°36.8'-36.9'S. Most of the time, the floor of the fissure was lined by lineated sheet flow (with lineations striking sub-parallel to the trend of the fissure), and jumbled, fragmented sheet flow. These observations suggest a high eruption rate which infilled the fissure and flooded the flanks with lobate flows, followed by a drainback so rapid that the lavas just erupted on the rims cascaded back down to the bottom of the fissure.

Samples collected

# 	      Time	 Latitude(S) Longitude(W)Depth (m)	Site	Description
3349-1	10:37	18°36.439'	113°24.025'	2677	Animal Farm	mussel bed sampled with "mussel pot" (turned out to be empty)
3349-2	10:48	18°36.433'	113°23.993'	2677	Animal Farm	~2 liters of mussels; fragments of jumbled sheet flow
3349-3	11:51	18°36.433'	113°23.993'	2677	Animal Farm	~2 liters of mussels
3349-4	12:06	18°36.433'	113°23.993'	2677	Animal Farm	2 liters of mussels
3349-5	12:20	18°36.433'	113°23.993'	2677	Animal Farm	2 liters of mussels
3349-6	12:59	18°36.431'	113°23.997'	2677	Animal Farm	2 liters of mussels
3349-7	13:02	18°36.431'	113°23.993'	2676	Animal Farm	2liters of mussels
3349-8	13:37	18°36.431'	113°23.993'	2676	Animal Farm	2 liters of mussels 
3349-9	13:54	18°36.664'	113°23.958'	2672	east of ASC	large slab of lobate flow
3349-10	14:39	18°37.081'	113°24.152'	2679	bottom of ASC	3 pieces of sheet flow
3349-11	15:03	18°37.165'	113°24.167'	2679	bottom of ASC	small piece of sheet flow

Transcript of the video tapes (Milène Cormier)

Nota:
- X,Y coordinates are referenced to a net origin of 18°41'S, 113°26'W, using the 1866 Clark spheroid.
- Depths indicated are total water depths (= Alvin depth + Alvin altitude)
- These depths are shallower than SeaBeam 2000 depths by about 25 m
- Somehow, the location of the fissuresn reported on the SeaBeam 2000 chart appears systematically shifted west of the topographic ridge crest by about 100m. This may be real, or it may indicate a problem with the registration of the SeaBeam 2000 gridded data (Navigation errors are unlikely; both the SeaBeam 2000 data and the transponders were navigated with continuous P-code GPS precision)
- Alvin remained within ~50 m of the "Animal Farm" site between 10:00 and 13:20
- The lava flows were all very glassy, with only a light dusting of sediments; sessile macrofauna was abundant throughout the dive. This corresponds to a relative age of 1.0 on the Macdonald age scale.

Time Course X,Y Depth(m) Comments

Cindy Van Dover on port, Milène Cormier on starboard for first part of dive

09:53 On bottom, slightly west of topographic ridge axis. Sheet flow, light dusting of sediment, age 1.0

09:54 180° 3549,8550 2679 Jumbled sheet flow. Step down into what may be a lava channel; This step is striking ~WNW

09:57 188° 2677 At bottom of presumed channel. Jumbled sheet flow, occasional draped flow, cloudy water; seafloor sloping down to the west.

09:58 206° 2678 slowly ascending beautiful lineated flow flowing approximately to the NNE, which turns into a draped flow upslope

09:59 209° 2678 Slope steepens a lot. Near the top, wall is draped with what looks like flow drips. Total height is about 4 m.

10:00 217° 3537,8455 2674 Just passes over the rim of the presumed channel. Sheet flows, draped and jumbled sheet flow

10:02 214° 3526,8438 2675 water is cloudy, fauna becomes more abundant (serpulides, clams, mussels, anemones). Arriving at the Animal Farm site, evaluating prospect for bio sampling.

10:06 174° 3533,8428 2677 Mussel bed on jumbled sheet flow with a few meters of relief: This is definitely the "Animal Farm" site

10:09-11:02 on station 3525,8425 2677 Biological samples 3349-1 and 3349-2
(lots of mussels)
Perform low T measurement in mussel bed

11:02-06 _80°-220° 3521,8413 2678 wandering slowly southward over Animal Farm;
jumbled sheet flow, a few lobates; lineated sheet flow flowing downslope to the west

11:07 112° 3578,8369 2676 Lobates on port, anemones and dead clams; Steps down 5 m over a ledge striking approx. NNE.

11:08 034° 3578,8369 2678 lineated sheet flow at the bottom, flowing in ~NS direction

11:10-12 241 3573,8399 2678 Large (a few meters high?) inactive chimney covered with serpulides and with scattered mussels at its base

11:13 334° 3573,8399 2677 cloudy water, shrimp

11:14 030° 2676 jumbled sheet flow with occasional spaghetti worms;
flat sheet flow, fissured, striking NE

11:15 355° 3578,8423 2674 ascending a steep slope, 3-4 m high, draped by jumbled sheet flow; (fish)
Just passed a lava channel?

11:16 324° 3579,8423 2676 sheet flow , lineated NW-SE (drainback along eruptive fissure?); scarps a few meters high on starboard with bathtub rings

11:18 340° 3559,8481 2676 lobate flows, some collapsed; lineated sheet flow

11:20 turning cw ? 2677 topographic low; jumbled sheet flow with a few meters of topography.
We may actually be going over the same area seen 10 minutes ago;? Heading is continuously changing as we explore for better mussel beds

11:22 201° ? 2678 lots of "stuff" in the water. Jumbled sheet flow and draped flow intermixed, sloping to the east; sheet flow seems to be coming from the south.

11:24 200° ? 2678 lineated sheet flow, lineation strike NW-SE

11:26 briefly on station 3539,8435 2675 jumbled sheet flow covered with mussels and clams. Some snails and anemones

11:28 210° 3539,8435 inactive chimneys spotted ahead, not visible from starboard side; mound is surrounded by mussels.

11:32 184° 2676 jumbled sheet flow

11:34 198 3527,8332 2673 jumbled intermixed with lobates; some lobates are collapsed.
anemones

11:35-36 106° 3527,8326 2674 jumbled sheet flow; arriving to edge of a 4 m drop-off striking NNE; looking down at lineated lava at bottom of channel; flow direction is about NS
anemones everywhere

11:37 Back on jumbled sheet flow

11:43 on station 3528,8424 2676 Biological sample 3349-3
Back to "Animal Farm"
mussel bed on jumbled sheet flow

END OF TAPE 1

11:54 START OF TAPE 2

11:55 to 13:21 on station 3526,8423 2677 Biological samples 3349-4 through 3349-7
Lots of mussels

13:22 Switch port/starboard observers:
Cindy V.D. on starboard, Milène C. on port

13:23 121° 2678 Jumbled sheet flow

13:24 142° 2673 ascending low slope covered with sheet flow

13:25 181° 2677 lineated sheet flow coming down toward Alvin (to the NW); Broken fragments of sheet flow

13:26 177° 2677 fallen chimney visible to port, and 3 inactive chimneys standing up

13:27 178° 2677 lineated sheet flow, oriented about NS;
a whole field of "Homer Simpson" creatures visible on starboard

13:28 215° 3562,8296 2678 lineated sheet flow oriented NNW-SSE;
10-15 cm-wide crack in sheet flow parallel to lineation

13:29 143° 3580,8280 2678 jumbled sheet flow; talus of broken fragment of sheet flow or lobate flow

13:30 128° 2676 coming to edge of fissure; 2-3 m deep. Lineated sheet flow on bottom.
cloudy water and anemones

13:31-32 128°-209° 3603,8253 2676 within fissure; flat sheet flow and draped flow; anemones

13:33 183° jumbled sheet flow and draped flow over Slowly ascending slope (switch to SIT camera)

13:34 3606,8179 2675 Sheet flow is draping down the wall of the fissure

13:35-39 on station 3608,8169 on top of eastern edge of fissure; stop briefly to start up CTFM
Smooth sheet flow with hairline cracks. Galatae, dead snails, anemones, starfish, ...

13:41 207° 2675 draped and jumbled sheet flow; Topography slightly down to the south. crabs

13:42 248° 2674 Reaching the east side of fissure again. Drop-off is 5-6 m. Lineated sheet flow drapes down into the fissure. Large collapse to port with jumble sheet flow; slope is down to port (S)

13:43 245° Along the rim of the fissure, the thin crust of the sheet flow becomes fragmented as it drapes down the wall. Other wall dimly visible ahead.

13:44 170° 2681 At bottom of fissure. Smooth sheet flow with hairline cracks; small fissure about 50 cm wide. Anemones.
Broken fragments of sheet flow.

13:45 203° 2681 Draped flow at base of wall. Water becomes more cloudy and fauna increases: fish, mussels, polychates, clams, worms, crabs.

13:46 217° 2681 relatively smooth, draped sheet flow, down toward Alvin (NNE)
mussels, clams, crabs, serpulides, fish
Unfortunately, changed course to SE before reaching the west side of the fissure

13:47 c/c 130° 2680 Reaching east side of fissure again. Base of the wall is covered with draped flow; fragmented sheet flow are plastered on the wall and near the top; lineated sheet flow on what appears later on to be a bench halfway up the wall rather than the summit. fish

13:48 125° 3549,8027
? 2678 lineated sheet flow oriented about NS;
still climbing east wall; thin fragments of sheet flow are draping down the wall.

13:49 140° 2674 Reached top of east wall of fissure. Total height is ~ 9 m. At rim, beautiful draped sheet flow transitions into lobates

13:50 162° 3583,8007 2671 lobate flow

13:51-14:00 on station 3588,8002 2672 lobate and sheet flow
Geological sample 3349-9

13:55 END TAPE 2
BEGIN TAPE 3

14:01 200° 2672 untectonized lobate east of eruptive fissure. Lobates are 2-3 m across. Some collapses on the lobates are a few meters across

14:02 2671 lobates transition into sheet flow

14:03 2671 sheet flows transition back into lobates; small collapse a few meters deep on port side

14:04 244° 2671 Reaching E edge of eruptive fissure again; wall is raggedy: sheet flow and jumbled sheet flow drape the wall of the fissure, and talus at base of wall. Lineation on sheet flow at bottom are oriented ~NS. Encounter talus as we approach the west side of the fissure. Total height of wall is ~9 m.

14:06 240° 2680 climbing the W wall of fissure; lineated sheet flow cascading down the face of the wall

14:07 224° 2680 lineated sheet flow draping the W wall of the fissure. No obvious bath-tub rings? water is cloudy, fishes, crabs and worm-like things on the wall.

14:09 170° 2675 Near top of eruptive fissure, jumbled sheet flow and fragmented pieces of sheet flow are plastered on the wall, "frozen-in-action". Climbing out of eruptive fissure; jumbled sheet flow near west rim. fishes, crabs

14:11 221° 3455,7771 2673 west side of fissure. Intermittent lobates among jumbled sheet flow; some collapse pits a few m across.

14:12 turning ccw 2672 draped sheet flow, jumbled sheet flow, and lobate

14:13 collapse about 10 m across on port side, with 1-2 m high pillars inside; lobates are mostly intact, but some have collapses a few meters across.

14:14 152° 2671 Approaching again W edge of eruptive fissure. Again, sheet flow becomes fragmented near the edge of the fissure and on the upper part of the wall; lineated sheet flows drapes the wall, and draped flow cover the lower slope.

14:15- 151° 3489,7680 2676 looking down into fissure with SIT camera; mixed sheet flow and jumbled sheet flow; broken fragments plastered on upper wall and loose on lower slope. Total height is about 7 m.

14:16 153° 3494,7680 2678 Reaching east edge of fissure; similar structure of the bounding wall; fine layering in the wall visible through the fragmented sheet flow.

14:17-18 153°-180° 2677 skirting E wall of fissure; jumbled sheet flow, talus; lobate flow to the edge of fissure. These are broad lobates, with some occasional collapse 1-2m across.

14:19-20 223° 3501,7611 2677 This section of the fissure contains many pillars and up-and-down topography. Vertical drops between remnant lobates topping pillars varies between 2 and 6 m; lots of fragmented sheet flow; draped flow cascade down the wall of the fissure to the bottom; sheet flow on bottom
Beautiful pink "dumbo eared octopus" drifting by on port side

14:21 222° 3474,7580 2673 collapse pits within the fissure;
climbing steep west wall of fissure

14:22 221° 2670 lobate flow on west side of fissure; some lobate with collapsed top. Not much fauna.

14:23-25 223 2672 uniform lobate flows; lobates are untectonized a few to several meters across

14:26 181° 3391,7475 2673 lobates; cc to the south
broad lobates change to draped and jumbled sheet flow at 14:26.3

14:27 185° 3394,7447 2669 lobate flow, some lobates are collapsed.
spaghetti worms

14:30 227° 3398,7396 2672 broad lobates; octopus

14:31-35 227° 3359,7353 2674 lobates (a few to several m across),
occasional drapes
sediment cover seems to increase slightly? There are some sediment pockets between drapes at around 14:34

14:35 226 3296,7280 2678 reaching E rim of eruptive fissure; jumbled sheet flow intermixed with lobates near the edge; sheet flow and draped flow on bottom of fissure; 4-7 m deep; broken fragment of sheet flow on bottom and jumbled sheet flow.

14:36 197° 3255,7230 2679 reaching W rim of fissure.

14:37-47 on station 3247,7227 2678 geological sample 3349-10
pieces of jumbled sheet flow, within what turns on later to be only part way up the W wall of fissure rather than its summit

14:48 216° 2678 back in bottom of fissure. chaotic jumbled sheet flow with lots of topography.

14:49 c/c 180° 3374,6926 2678 c/c 180°; jumbled sheet flow at bottom of fissure.

14:50-51 181° 3436,7140 2674 Probably skirting east side of fissure. Jumbled sheet flow, at times lineated NNE-SSW, less shattered than earlier; slowly climbing up slope; draped sheet flow cascading down the wall; interlocked sheet fragments. At top of fissure, lobates and draped sheet flow. Total height is ~6m.

14:52 181° 3244,7140 2672 reached top of east side of fissure. transitioning from lobate flow to draped flow and back

14:53 223° 2671 jumbled sheet flow; some collapses; crossing over a trough about 2-3 m deep; draped and jumbled sheet flow

14:54 220° 3222,7075 2679 jumbled, shattered sheet flow; bottom drop again; must have been on a ledge on east-facing wall; narrow fissure on bottom.

14:56 205° 3214,7063 2679 jumbled sheet flow

14:58-15:07 on station 3208,7046 2679 geological sample 3349-11
fragment of jumbled sheet flow near base of east wall sampled just before lift off.

15:08 Lift off....