Observers: Rodey Batiza (transcript)
and Karl Gronvold (transcript)
Pilot: Matthew Heintz
Launch: 18° 40.00' S, 113° 25.33 W
Objectives:
Plan:
Summary: Dive 3346 explored the EPR axis and flanks
of the axial high between ~18°40'S and 18°39"S. We
began the dive at ~2725m (2750m on seabeam maps) on the west flank
of the axial high, made three zig-zag crossings of the axis and
ended at 2740m on the east flank of the axial high. The flanks
of the axial high, up to a depth of ~2700m are dominated by lobate
flows and pillow lava. Pillows appear to be younger than the lobates,
but it is also possible that high standing pillows were inundated
by lobate lava flows. In some places, lobates are the dominant
flow type, but in others pillow lava is most abundant. Although
rare pillows were found throughout the dive, the flanks of the
axial high are the only areas we visited where pillows can be
the dominant flow type. The transition zone between the axial
summit and flanks is marked by the appearance of significant amounts
of pillow lava. Based on sediment thickness, the flanks of the
axial high have an age of 1.5 to 2.0, older than lavas at the
axis (sediment age 0.5-1.0 on the Macdonald scale).
The axis in the southern part of the dive area is heavily fissured,
whereas the northern part is dominated by collapse features with
bathtub rings and pillars at the margins and sheet flows or rubble
in the floors. Fissures vary in width from several tens of cm.
to over 5 m and in general have thin-bedded lobate flows exposed
in the walls. A fairly sharp transition occurs at 18°39.50'S,
but the axial flows on either side do not appear to be different
in age. This suggests that the fissuring occurred since the eruption.
At the axis, flow morphology is dominated by lobate flows, with
folded sheet flows next most abundant, and lineated and jumbled
sheets least common. Pillows are rare but do occur, especially
at the margins of the axis. All these flow types appear to belong
to the same eruptive event. Transitions between flow types are
generally abrupt. One region of unusually diverse flow morphology
occurs at 18°39.60 near the first turn (~11:20 L). Although
only a single diffuse hydrothermal vent (4.4°C) was found
in the area, there are widespread signs of previous active hydrothermal
venting, including an inactive chimney, dead organisms at several
sites, and very widespread hydrothermal straining on rocks.
Sample list :
Sample time depth* X Y Lat. Long. description
3346-1 0938 2725 1193 1816 18°41.98 113°25.32 pillow bud
3346-2 0955 2709 1411 1985 18°42.07 113°25.19 pillow bud
3346-3 1012 2701 1546 2083 18°42.13 113°25.12 folded sheet
3346-4 1038 2680 1932 2359 18°42.27 113°24.90 lobate
3346-5 1059 2679 2318 2592 18°42.40 113°24.68 lobate
3346-6 1105 2678 2318 2592 18°42.40 113°24.68 folded sheet
3346-7 1123 2688 2467 2673 18°42.44 113°24.59 sheet flow
3346-8 1143 2685 2451 2816 18°42.52 113°24.60 lobate
3346-9 1229 2683 1900 3800 18°43.05 113°24.91 lobate
3346-10 1245 2676 2314 4016 18°43.17 113°24.68 lobate
3346-11 1316 2679 2446 4099 18°43.22 113°24.60 pillar (top)
3346-12 1317 2679 2446 4099 18°43.22 113°24.60 pillar (middle)
3346-13 1318 2679 2446 4099 18°43.22 113°24.60 pillar (base)
3346-14 1331 2677 2603 4273 18°43.31 113°24.51 lobate
3346-15 1406 2671 2700 4800 18°43.60 113°24.46 lobate
3346-16 1438 2730 3599 4827 18°43.61 113°23.95 lobate
3346-17 1513 2739 3706 4816 18°43.61 113°23.89 bud
* depths are Alvin pressure depths
