Alivin dive 3346 - Feb 5, 1999

Observers: Rodey Batiza (transcript) and Karl Gronvold (transcript)

Pilot: Matthew Heintz

Launch: 18° 40.00' S, 113° 25.33 W


  • Determine whether the boundary between the fissured (south) and less fissured (north) axis corresponds to the southern extent of the "animal Farm" flow
  • Determine whether there is a significant difference in age or flow morphology across this kink
  • Study flows at the axis and on the flanks of the axial high to map patterns of flow morphology. Are AF-type flows found south of the kink?
  • Collect 13 marvelous lava samples (and of course, bugs)
  • Plan:

  • Plan is for a south to north zigzag patteren across the axis, encompassing a small kink in the trend of the axis at 18°39.2'S (006° vs 017°). South of the kink, the axis is heavily fissured, whereas north of the kink the axis is less fissured or even resurfaced. Despite the kink in the overall trend of the axial high, fissures and axial lineations trend 016° to 017° on both sides of the kink.
  • 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

    Navigation Plot (GMT)