Hawaii Cruise Report for May 9, 2001
We departed Honolulu at 8 a.m. today and
steamed west and then north along the
west coast of Oahu in calm seas and low winds. Our target site
for the first dive of leg 4 was about 5 hours
steam from Honolulu to the northwest of
Oahu. The target was a flat-topped lava cone that has a small
cone on its top and an apparent water column anomaly suggestive of
bubbling or hot water discharge. Either
possibility would be consistent with
recent volcanic or hydrothermal activity, suggesting that the cone
might be volcanically active. As we rounded the
northwest point on Oahu we could see a
wind line and white caps beyond. The sea state increased and
the winds rose to nearly 30 knots before we arrived at our target.
With surface currents of about 1 knot in
addition to the seas and wind, we were
unable to hold station with the ship and had to move on to an
alternate site. We had previously selected
several interesting sites on blocks in
the upper part of the Waianae landslide, but these turned out
to be located within a military explosive dump
site and we decided we had already seen
enough ordinance on this trip. We steamed to the northwest
to a site in the deeper part of the channel between Oahu and Kauai
where, at about 4 p.m., we began a dive on several small rejuvenated
stage volcanic cones at a depth of about 2900
m.
The dive began in a moderately sediment
covered region, but fragments of lava
projected through the sediment. Each block of lava had a
trail of gravel behind it, showing the orientation of the strong
bottom currents in the region. We continued
downslope with little change in bottom
characteristics, crossed through a small valley between two cones
and then started up the slope on the second cone. The bottom remained
gentle with low lava outcrops and gravel in a surface mainly of
fine sediment. The SeaBeam bathymetry indicated
that the cone was low and broad, but we
found it to be smaller across and steeper. The steep slope
consisted on sheet-like lava flows with shallow channels. During
this short dive the Kraft manipulator began to
misbehave (it developed a jerky
movement) that made sampling challenging, to say the least. We
decided to end the dive and try to repair the
arm. The dive recovered 14 samples of
lava from two volcanic vent structures and established that both
these cones are quite old, having moderate sediment cover and thick
Mn-oxide crusts on the rock samples. We will
cut these samples today and determine
whether we succeeded in collecting volcanic glass that would allow
us to characterize the volatile and rare gas components of these
lavas. The day ended about midnight when we
finished the initial laboratory
processing of the samples. Overnight we will steam to the south
flank of Kauai where we will dive on a series of similar rejuvenated-stage
volcanic cones related to the Koloa Volcanics on Kauai.
-Dave
Clague
