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Logbook
September 4, 1998

Contents:

Daily Science Report - Sep 4

ship's location = 45 56.0N/130 00.8W (directly over ASHES vent field)

The ROPOS dive that started yesterday (dive 465) to investigate the possible eruption site 3 miles south of Axial's caldera (at 45 52.0/130 00) lasted 5 hours and was a great success. We suspected that lava had erupted at this site in January because a bathymetric re-survey (collected by scientists from the Monterey Bay Aquarium Research Institute) in May had shown up to 25 m of depth change on the south rift zone (link shows bathymetry difference on right maps). But you never know until you get down to the bottom and look. But when ROPOS got to the bottom, it quickly found a thick pile of new "pillow-lava", a kind of underwater lava flow that forms big round or tubular "pillows". This new flow had extensive evidence of having had warm water flowing through it as it cooled, including extensive staining and fluffy, orange bacterial mats deposited on it (like we've seen up in the caldera on other dives), but it seems to have all stopped by now because we saw no warm water actively venting. Finding the lava flow and mapping its extent was very satisfying because it was *exactly* were we thought it was, and confirms the accuracy of our methods for remotely detecting the locations of seafloor eruptions. The interval between dives again included CTDs and rockcores, and this time was notable because during one rockcore (which usually only samples a few grams of rock during each core) a huge rock came up to the surface with the corer, wrapped up in the wire that the corer is lowered on! What a spectacular sample!

ROPOS is now back on the bottom again (dive 466), this time at the ASHES vent field, which is near the SW caldera wall. This will be our first dive of many at ASHES - up until now all our dives have been in the SE part of the caldera on the upper south rift zone where lava was erupted in January (though we will be returning for more dives there as well). ASHES has many high-temperature "smoker" chimneys in addition to extensive areas of more diffuse venting and vent animal colonies. Water and biological sampling are scheduled.

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John Chadwick
Graduate Student, University of Florida

Once upon a time there was a geologist named John Chadwick, who spent a month on a big ship called the Ronald Brown. John was handsome, smart, honest, hard-working, resourceful, and very, very modest. One day our hero was taking samples of the sea floor using a heavy, torpedo-shaped device that collects tiny pieces of glassy rock that form when hot basaltic lava is quenched by the cold ocean water. The chemistry of this glass holds important clues to the origin and evolution of the lava that has erupted from Axial volcano and other related volcanoes on the rifted zone to the south of Axial. The torpedo device is sent down to the ocean floor, sometimes more than a mile down, on a long steel cable.

Well on one particular day, instead of tiny slivers of rock that weigh less than a typical dust bunny, the cable had tangled itself around a rock the size of a small house. OK, maybe I'm exaggerating a little, it would have to be a VERY small house. The rock was in fact about three feet long and weighed in at about 100 pounds! That's about one-quarter the weight and size of those really big-boned people you see at the mall! Everyone on the ship was so excited about the big rock that someone was actually overheard saying, "Look. A rock."

The geology of the Axial volcano area is actually very interesting, because the volcano lies at the intersection of a mid-ocean ridge and a chain of hotspot volcanic islands. Mid-ocean ridges are places where new oceanic crust is forming by volcanic processes, and are interconnected around the Earth like the seams on a baseball. Hotspots are where hot plumes of magma from deep in the Earth's mantle come to the surface, creating chains of volcanoes like the Hawaiian Islands. These two volcanic processes are overlapping here at Axial volcano, a situation that is very similar to Iceland. All of these processes are driven by heat coming from within the Earth, heat created by the decay of radioactive elements and heat leftover from the Earth's formation 4.6 billion years ago. All this volcanism is just the result of the Earth cooling itself off and releasing heat, very similar to the hot air that politicians release during a speech. The interesting things that some of the other scientists on the Brown are studying, like the hydrothermal vents and the strange creatures that form around them on the ocean floor, all owe their existence to these underlying thermal and geologic forces that have created Axial volcano.

Our hero will continue to doggedly pursue his tiny pieces of rock, and the occasional boulder. He will study their chemistry upon his return to the University of Florida and try to unravel some of the mysteries of this interesting volcano. He is thoroughly enjoying the experiences aboard the ship, his first ever voyage to explore the geology under the sea. The sunsets and sunrises out in the Pacific are some of the most vivid and dramatic he has ever seen. The sun, clouds, and sea perform a mystical alchemy that cannot be matched on land. Dark blue waves and shimmering white clouds march by the ship like powerful legions in arms heading for a distant war. The ship is about the size of a typical hotel, so you'd think that claustrophobia might be a problem (The ship is in fact quite large (our hero still hasn't found the Men's bathroom.) Thank goodness for the Poop Deck!)). But outside, you can see 360 degrees of horizon, so one might also experience, well, whatever the opposite of claustrophobia is. Big-outside-phobia is the technical term, I believe.

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