March 13, 2001 to June 2, 2001
Monterey to Hawaii and back
May 14, 2001: Leg 4; Day 6
Dave Clague writes: We started later than usual today following the marathon day and night yesterday. The ROV hit the water at 8:45 am and then had a slow descent as the engineering department made adjustments to the level-wind on the drum that handles the tether for the ROV. The dive was located on a series of submarine vents starting at about 2050 meters depth. The cones are related to the rejuvenated stage Koloa Volcanics on the south flank of Kauai, and are located close to the site of the dive on May 10.
The main objectives of the dive were to sample glassy basalt for volatile analyses and to observe the eruptive deposits on the cones to understand more about submarine eruptions. The first cone was an immediate surprise in that its surface was almost entirely covered by agglutinated spatter instead of the expected pillow basalt and hyaloclastite. The next two cones consisted almost entirely of hyaloclastite, some containing dense basalt clasts, and some spatter. We finally found pillow lava on a ridge at the base of the fourth cone we observed. However, the main cone appears to be of hyaloclastite yet again, although we only saw the base of the cone before ending the dive.
In processing the rock samples in the lab this evening we found that one sample has a breadcrust texture and another appears to be a volcanic bomb. We are finding that submarine eruptive products are more similar to those of subaerial eruptions than is generally believed and that spatter, previously undescribed from the submarine environment, may be a common submarine eruptive product. We collected yet another new sea star (nine-legged), a large sponge and a blue-purple sea cucumber. The cucumber was quite a troublesome critter, floating from the biology box and having to be recaptured. We have enough video of this particlar sea cucumber and his capture (twice) to make a short comedic movie! Tomorrow we will return to a flat-topped cone in the channel between Oahu and Kauai, where we attempted to dive on our first day but were stymied by strong winds and currents and high seas.