Monterey Bay Aquarium Research Institute

Hawaii Cruise
March 13, 2001 to June 2, 2001
Monterey to Hawaii and back
Logbook

April 10, 2001: Leg 2; Day 10



Kyra Schlining writes: I'm sending a couple of random images from yesterday. Here are Jerry Winterer, Charlie Paull, Jenny Paduan, and Juli Morgan discussing various prize carbonate specimens. Also some very small dolphins bowriding (no idea who they are as I got out there just as they were leaving, this photo was taken by Buck). This is our second time we've seen dolphins. We've also had whales (humpbacks?) breaching way out in front of our ship on one day!

Dave Clague has been extremely busy picking Site A, Site B, Site C....Site X for each day to try to plan for high winds. 

Hard to believe there is less than a week left on our cruise.


A large vase sponge.

Dave Clague writes: Today began in similar fashion to the last few days - searching for a dive location where both the wind and currents would allow us to dive. The first several sites we went to had surface currents in excess of 1.5 knots, but the winds were acceptable. The next two sites had acceptable currents but the wind was too strong. Finally, on the fifth dive target, we found a place with acceptable wind and currents where we could dive on the 900-meter terrace (estimated age about 335 thousand years old). The dive began much like the previous dive on this terrace, in an endless sea of basaltic lava flows that draped the steep outer terrace slope. We drove along the top of the terrace, collecting the lava flows at intervals to map the different flows we encountered. After covering perhaps a kilometer along the terrace, we found a sandy region with reef limestone outcrops, many of which contained abundant corals. Farther along the dive track, we came to another area covered by lava flows. The setting was exactly like the sandy beaches on Hawaii Island, where lava headlands occur at each end of sandy beaches with coral reefs offshore.


A fan-shaped coral growing on a boulder of eroded limestone.

We did a second dive later in the day on the 400-meter terrace where it is crosscut by a fissure eruption that built several small volcanic cones. The dive began with a transect up the reef face where we found some corals and a nearly vertical section of massive limestone. The limestone at the top of the steep slope is deeply eroded so that it looks like swiss cheese. We think this material is mainly lithified carbonate sand. The first volcanic cone consisted of pillow lava, indicating its submarine eruption. We then traversed more of the reef top that consisted of sandy areas surrounding outcrops of the same swiss cheese limestone. We were heading for the last volcanic cone when the wind quickly picked up. By the time we reached the edge of the cone, we had gusts to 40 knots so we grabbed a few samples and quickly recovered the vehicle. Just before we started up, we came across an outcrop that showed the pillow lavas draped over the swiss cheese limestone, demonstrating that the volcanic activity postdates the reef.

We have now collected excellent corals from the 400, 585, 690, and 900-meter reefs and will be able to test previous models for the timing when these reefs drowned as sea level rose rapidly at the end of glacial periods. We are confident that some of these terraces (the 150, 400, and 1150-meter deep ones) are mainly reef constructs. We have also observed that some of the terraces (those at 585, 690, and 945-meters depth) are mainly composed of lava flows, with either patchy or continuous reefs on their tops. These terraces have been regarded as coral reef structures, but they appear instead to be formed as a change in slope that occurs as lava flows enter the ocean, as observed around the actively growing volcanoes Kilauea and Mauna Loa today. Such a model could explain the apparent absence of these intermediate depth terraces on the flanks of Kohala Volcano farther to the north, which was no longer erupting frequently when these terraces should have been forming. The relative roles of coral reefs and lava flows in forming the terraces has been the topic of lively debates on the ship! We are heading back to the south Kona landslides for a few more dives starting tomorrow, with hopes of understanding what materials are involved in the slides, and how the different pieces fit together.


Jennifer Paduan writes: Just before the ROV reached the bottom on dive 288, we had a fire and boat drill. I brought this little beastie down from our stateroom to participate in the drill. It already had its life-ring on but a PFD was made for an extra margin of safety. It later got caught up in the assembly line processing of samples, and here is its official lab photo for the samples database as sample number T288-A00.



A close-up of eroded limestone, showing a swiss-cheese texture.

A lobe of pillow lava that flowed over the lithified carbonate sand material below it, demonstrating that the volcanic activity postdates the reef.

 

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