Summary: When we first saw bottom, approximately 1.3
km west of the axial trough near 17°27'N, it was composed
of flat-lying, Macdonald age 1.5 lobes. In the process of landing,
we drifted onto a constructional slope (30-40°) of decorated
pillows and lobes. The combination of macro- and microtopography
made it appear that the constructional slope had less sediment
cover than the flat-lying lobate lavas, although no contact was
observed. We traveled upslope, and we observed a jumbled sheet
flow which had been dramatically autobrecciated while flowing
down the steep pillow slope. This jumbled flow also contained
clots of lava that appeared to have been accreted while rolling
in a lava channel; these clots were roughly 3 m in diameter.
We crossed the contact into the "young lava" approximately
1.1 km west of the west wall of the axial trough at this latitude.
We identified the young lava on the basis of it's
spotty sediment cover and fresh, black glass. The western margin
of this flow is characterized by decorated pillows and buds.
There are lineated and jumbled channels observed approximately
800 m west of the axis. These channels originate in small collapse
features, and are onlapped by lobate lavas. This suggests that
the first outpouring of lava during the eruption were high-effusion
rate channeled flows, which were buried by subsequent lobate flows
as the effusion waned.
Approximately 500 m west of the west axial wall (near the 2610
m SeaBeam contour line) we crossed a contact into Macdonald age
1.5-2.0 pillows and lobes. This increase in sediment cover corresponded
with an observed increase in vent fauna (especially crabs, fish,
and dandelions) and increased turbidity of the water. However,
the superposition relations are obvious, and there is no doubt
that the Macdonald age 1.5-2.0 pillows and lobes are a kipuka
of older material, and not merely the result of increased hydrothermal
sedimentation. The eastern boundary of this kipuka is not clearly
defined, however. It appears that the sediment cover gradually
decreases until ~200 m west of the axis (near the 2600 m SeaBeam
contour), where the young lava can be observed clearly.
We followed a lineated, smooth, and jumbled channel up to the
axis. The channel is bounded by collapse features at either margin,
and ends in a ~2-4 m high collapse feature (capped by lobate lavas)
located 10 m west of the axial wall.
We crossed the axis, and found the Gumbo black smoker, where we
sampled tube worms for Cindy. The axial floor is filled with
pillars, rubble, and lineated and chaotically folded sheet flows.
The wall of the axial trough have an irregular planform, and
are coated with bathtub rings. The axial wall locally projects
several meters into the trough, in narrow "peninsulas"
that may be 5 or more meters long but only 1-2 m wide. The axial
trough is 8-10 m deep both here and farther to the south.
We followed a channel down the eastern flank of the axis, marked
by folded and lineated lavas. This channel disappears by diving
underground at an ~2-m-high collapse in lobate lavas, roughly
350 m east of the axial wall. A short distance farther east (~75
m), we encountered a series of elongate, aligned collapses floored
with rubble, as well as folded and lineated lavas, which we interpret
to be the surface expression of a lava tube.
As we turned back west to go back to the axis, we encountered
2 more kipukas of older pillows and lobes. These were not associated
with any increased hydrothermal activity, and it is possible that
these kipukas represent 2 different lava ages.
Lava channels are not as common on the eastern side of the axis
as they are on the western side, as suggested both by our dive
observations and by the DSL-120 data. However, we did follow
a lineated channel a short distance up to the eastern wall of
the axis. It ended in a ~3-m-high collapse feature within lobate
lavas approximately 10 m away from the axial wall. Unfortunately,
we could not see through the collapse to the axial trough.
Within the axis near 17°27.2'S, we collected portions of 2
pillars, approximately 100 m apart, as well as a portion of chaotically
folded sheet flow from the axial floor. Although hydrothermal
sediment was common on the pillars and especially on the piles
of talus at the base of the axial wall and at the bases of pillars,
we did not observe any present hydrothermal activity. Spaghetti
worms were common all along the axial walls, and serpulid shells
were common along the axial floor. Finally, orange and white
hydrothermal staining was visible in the cracks and pockets of
lava flows along the entire dive track, varying slightly in abundance.
Sample Locations:
Time Number X Y Depth Lat(-17) Lon(-113) 957 1 -1245 -3603 2709 27.033 13.556 1029 2 -760 -3617 2631 27.041 13.282 1154 3 367 -3462 2592 26.957 12.646 1243 4 1232 -3624 2601 27.045 12.157 1253 5 1247 -3841 2607 27.162 12.149 1323 6 288 -3951 2567 27.222 12.690 1415 7 208 -3929 2567 27.210 12.736 1423 8 245 -4030 2572 27.265 12.715 1432 9 245 -4030 2572 27.265 12.715 1453 10 225 -4050 2577 27.276 12.726
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