March 13, 2001 to June 2, 2001
Monterey to Hawaii and back
April 5, 2001: Leg 2; Day 5
Kyra Schlining writes: When the samples come back on board we form an assembly line to label them, scrub them, measure & sketch them, then photograph them. Using the rock saw, we isolate a slab (thin section billet) from each sample to make thin sections from after the cruise. Some of the slabs are pretty interesting inside. We will be sure to send photos soon. Then we lay the rocks out on the deck to dry (image). And as Dave Clague noted in his log, they do not smell like roses.
Buzz Scott & Buck Reynolds caught an enormous mahi mahi (at least 20 kgs?) off the back deck. I imagine that we'll be dining on that tomorrow! For once we are done early. What a treat!
Dave Clague writes: We remained in the Kona coast region again today, waiting for the strong trade winds to diminish. We again had some trouble with strong surface currents, but managed two excellent dives, one more to another section of the 400 m reef, and a second on the -690 m reef. The first dive was located close to our first dive on the reef in an area where the height of the reef face is greatest (620 m at the bottom and 410 m at the top), so we could get the most complete section of rocks exposed. We found much more coral on this dive than the previous dives and found a lava flow that apparently covered the reef while it was growing, so that lava cobbles were common below 530 m depth and absent above that. We think the reefs grow in multiple short bursts of rapid growth interleaved with periods of emergence above sea level and then by rapid drowning, as sea level fluctuates with the global glacial cycles. The lava flow may have occurred during a period when the reef was not actively growing, since the rocks are rounded like beach cobbles. We found corals all the way to the top of the reef on this dive, and in contrast to the earlier dives here all the reef material at the top was algal. This reef, like active modern reefs, is extremely complex.
The second dive went to a previously unsampled reef at 690 m depth. This reef is thought to have drowned about 245 thousand years ago. This dive turned out to have many surprises - the first being that we had a hard time finding white carbonate reef rocks for the first half of the dive. The slope was completely mantled by cobbles and finer gravel of basalt. Carbonate boulders began to appear about halfway up the slope. At one point we found a thick lava flow with a thin carbonate reef deposit on top, covered by another lava flow. Lava from the overlying flow had dribbled between heads of coral. Above this, coral and algal reef rocks were much more abundant, but basalt persisted until we had reached the top of the reef face and crossed the upper reef flat for several hundred meters. We collected all the lava flows and found many corals from multiple levels in the reef that should be suitable for radiometric dating. Such dating will confirm the age estimated from sea level changes during the Pleistocene.
At the end of the second dive, we completed one more rock crusher drop on another of the volcanic cones aligned with the cones we dove on on our first dive in the region. The sampling was successful and recovered volcanic glass that will allow us to compare this sample with the other cones. The weather forecast is for trades changing to light Kona winds from the south tomorrow, so we are now steaming south for Loihi Seamount, where trade wind conditions are commonly very rough. Hope the weatherman has this right as it is 100 nautical miles to Loihi and there are no other high-priority nearby dive sites in protected waters to substitute