Alvin Dive 3351

Transcript: Ken Macdonald stbd observer

Macdonald/ Boyle/ Heintz;

LAUNCH POINT: 18º 08.30' S, 113º 20.5' W

Lava Lake 18 08-18 18S first dive in area.

Did two 360º spins for mag calibration at depth 1000m, 2683m, on bottom, in age 3-3.5 pillows at target 1

0935 130º, 2680m, stopping for rock sample 1 in age 3-3.5 pillow lavas.

0942 225º, 2685m; underway again, age 3 pillow lavas; underway to target 2

0944 225º, 2683m age 3 lobates and pillows, perhaps lobates are a bit older.

0946 231º; 2695m; younger looking lobates here, age 2.5?, then onto talus of pillows and lobates; the talus is fresh

0948 turning right to follow along the wall which is producing this talus. Crossing two N-S fissures each ~1/2m wide.

  • on top of horst, top is age 2 lobates; turning back left again heading S. Horst about 5m high, fresh talus on both sides and at S end of horst, or is this actually a lava lake remnant? The way it abruptly stops has me thinking it is more likely to be a lava lake remnant.
  • Age 2.5 pillows; active hydrothermal vent sighted by Matt.
  • maneuvering around active vent site; at least a dozen inactive chimneys and one active black smoker which is down in a crack. No temp. taken because we only have the low temp probe.
  • 0956 sampling top of inactive chimney about 2m high, sample 2
  • 148º; 2695m no major biological community here; only alvinella worms in the active chimney edifice and some crabs grazing
  • getting rock sample 3 (later called sample 3b), top of small dead chimney.

    • 1006 rock sample 4 top of ~ 6m high dead chimney.

    1024 2696m just collected top of the active vent; put in bio box with sample 3b of inactive chimney, so this sample is #3; now leaving field of one active and many inactive hydrothermal sulfide vents; built on top of a high standing ridge of pillow lavas.

    1027 226º heading to waypt 2; age 2.5 pillows and lobates, could even be age 2; talus

    1029 224º; 2700m; transition to age 2 pillow lavas. Crossed 1m wide fissure trending N-S.

    1031 221º, 2697m; N-S fissure 1/2m wide, age 2-2.5 pillow lavas and fresh talus.

    1032 on top of dead hydrothermal ridge.

    1035 at least a dozen dead hydrothermal sulfide chimneys atop this ridge. The ridge itself appears to be a lava lake remnant, perhaps a linear array of pillars?? A "hydrovolcanic" edifice?

    1042 still on this hydrovolcanic edifice, heading off to waypt 4 now.

  • ; 160º; 2696m; age 2 pillows and lobates, 1/2m wide fissure.
  • ; two half m wide fissures, trending N-S. age 2 pillows.

    • 1048 another N-S 1/2m wide fissure (note; on tape I was turned around and said the fissures were E-W)

     

  • talus, coming up on wall, truncated pillow lavas; appears to be a horst ~ 6m high, its down on both sides. 146º; 2693m on top of horst. Horst trends N-S.
  • 154º; 2688m; now on age 3 lobates and pillows. Lots of sediment.
  • 153º; 2684m, heavy sediments, age 3-3.5 lobates.

    • 1055-1100; collected rock sample 6; heading to waypt 4

    1102 156º; 2694m; bottom drops ~12m; part of a N-S horst; age 3 lobates

  • 156º; 2705m; contact now age 2 jumbled sheet flows. Collapses within lobate flows too. Possible lava channel heading across our track.
  • 155º; 2704m; another hydrovolcanic ridge about 3m high by 1-2m wide; sheet lavas and old hydrothermal sulfides on top, talus at the base
  • back onto age 2 lobates
  • 167º; 2708m; contact with older age 3 pillows and lobates
  • collapse area in age 3 lobates and sheet flows.

    • 1115 old sulfide mound

  • 242º, 2712m, collecting rock sample 7 in age 3 lobates

    • 1119 6 old dead sulfide chimneys

    1120 220º; 2708m; fresh talus and pillows age 2.5

  • age 2.5 pillows, contact with fresh talus
  • on top of intensely autobrecciated horst.
  • 198º 2699m; age 2.5 pillow lavas
  • 200º 2698m age 2.5 pillows

    • 1136 198º 2700m; pillows on top of lobate lava, age 2.5

    ll44-7 stop for sample 8 in age 2.5 pillows and lobate lava

    1148 underway 090, 2698m it is 500m to target 7going up east wall.

    1151 starting steep ascent of east wall, lots of fresh talus

    1152 094º, 2684m; old lava lake remnant and bathtub rings within the debris going up east wall, talus is fresh. Two fissures, one 1m and one 1/2 wide on east side of a ~10m wide sliver of crust which is calving off the face of the east wall much like the slabs of ice that calve off the face of a glacier.

    1153 age 3 lobates and pillows on bench within east wall, 2683m, 090º

    1156 stopping at edge of 3m wide N-S fissure. Fresh talus, truncated pillow lavas in exposed face. Another 3 slivers of extrusive crust tipping in toward valley floor. There are also some intact pillow lavas along the edge of the fissure, perhaps lava drained into this fissure at some earlier time?

  • 306º, 2686m maneuvering around to get rock sample 9. Lots of fresh talus here.

    • 1209 090º very fresh angular fault talus

  • 2672m crossed 3 1/2m wide N-S fissures, age 3 pillows
  • 2m wide fissure , truncated pillows in face
  • ditto, 2667m 090º

    • 1216 2662m , turning to 180 to head to waypt 8 about 200 m before getting to waypt 7

  • 210º age 2.5 pillows

    • 1225 10m vertical drop to west (according to mesotech)

  • 190º 2682m old sulfide mound in age 3 pillows on top of one of these faulted slivers.

    • 1233 1/2m wide N-S fissure in age 3 pillows; on mesotech, floor of fissure ~10m deep

  • 203º 2687m age 3 pillow lavas
  • 200º 2689m going S along jagged edge of scarp facing west , age 3 pillows on top, truncated pillows on face.
  • that was ~15m scarp dropping back down into valley floor.

    • 1240 back in floor of valley sheet flows and a few lobates, age 2-2.5, a few short pillars only ~1-2m high.

  • several 1-2m high pillars supporting a lava lake remnant age 2-2.5 sheet flows. This is a linear array of pillars, these don’t have any sulfides on them but perhaps linear arrays of pillars like these give rise to the linear hydrothermal deposits we saw earlier.
  • —46 2699m rock sample 10
  • 242º 2690m toward target 9, going up 2m scarp truncated pillows in face, lobate lavas on top, several small collapses. Age 2.5
  • collapses and lava lake remnants
  • 200º age 3 lobates, collapses, pillow lavas on top, slightly younger?

    • 1252-54 stopped for sample11 , nice drained out lava tube here

    1255 mostly lobates age 3

    1300 204º 2697m change from pillows back to lobates age 3

    1306 2692m 207º contact with age 2 pillows, ascending flow front of elongate pillows, perhaps on the side of a pillow mound. Very little sediment, some glass.

  • 2683m 207º rock sample 12 from this elongate pillow flow front of age 2, some hydrothermal staining here

    • 1322 2691m rock sample 13 at top of pillow mound? must head back to surface even though we have lots of power left because of bad weather topside.

    1419-25 doing two 360s for magnetometer calibration.