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Logbook
July 7, 1999

Contents:

• News from Thompson
• Participant Perspective
• Logbook from Teacher at Sea
• Question/Answer from shore to sea

Science Report - Wednesday, July 7
Ships Location: 46 00.9/130 01.5

ROPOS collected Imagenex data all night as dive 496 continued into the morning when it cut the anchor line holding down the rumbleometer.

Rumbleometer safely on deck of the Thompson after surviving a lava flow.

When it came to the surface, there were many lines hanging from the instrument from our past attempts to rescue it, and these had to be cleared before it could be brought on board. It was very satisfying to see the rumbleometer brought on board the ship - the final stage in its bizarre odyssey (photo right). It was interesting to examine the instrument on deck. The bottom side of several of the yellow plastic "hard hats" that protect the glass ball flotation had melted slightly (photo below left) and had chips of basalt glass embedded in them, which happened when 1998 lava flowed under the instrument. But overall, it is amazing that the instrument appears to be in pretty good shape despite having been trapped in a lava flow! This is apparently because the temperature at the bottom of the ocean is just above freezing (2 degrees C), basically like an ice bath, and there is an unlimited supply of that cold water.

Slight melting of the Rumbleometer's floatation.

When molten lava erupts into this cold seawater, it immediately starts forming a crust on its upper surface, and once the solid crust grows thick enough it becomes a good insulator, so that the solid crust of an active lava flow is much cooler than its molten interior. This is how the rumbleometer instrument could have survived a close encounter with the 1998 lava flow without being completely cooked (as it undoubtedly would have if the same thing happened on land)! The data from the instrument will not be downloaded until it is returned to Seattle.

This evening, ROPOS went back in the water for dive 497, this time on Axial's north rift zone to recover and deploy acoustic extensometer instruments with the elevator, and then to visit CASM, a high-temperature vent site at the northern end of the caldera, for biological and slurp sampling and to recover temperature probes deployed there last year.

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Paul Johnson
University of Hawaii

Aloha from the North East Pacific Ocean. The first thing I must admit is that the cold grey Pacific ocean which we are currently working in is quite a change from the warm blue Pacific waters around Honolulu, Hawaii where I live. I work as a marine geologist for the Hawaii Mapping Research Group (HMRG) at the University of Hawaii. HMRG specializes in the both the science and engineering behind designing, building, running, and interpretation of data of systems that map the ocean floor. My job at HMRG, whether we are working at the University or out somewhere at sea, is to process the data from these system and to then generate maps from this data.

Before working at HMRG I worked for the Dr. Embley and Dr. Chadwick in Newport, Oregon as a Research Assistant doing work on the Juan de Fuca Ridge. So when they asked me if I wanted to come along, I jumped at the chance. I was especially intrigued about the opportunity of being able to do a comparison of the Hawaiian style volcanic features, which I have had the pleasure to watch form as the molten rock was erupted out of the earth, and the types of features we would find during our dives on this cruise.

My role on this cruise is as one of the three navigators. Using a network of transponders set out on the seafloor we are able to determine the location of ROPOS as it moves along the seafloor. We monitor the ROV's movement, determine the quality of the navigation that we are collecting, and relay information to both the ROPOS team and the bridge of the ship on where different vents or features are located. This turns out to be a pretty interesting role as you are involved with the some of the operations of the dive, instead of just being an observer. However, no matter how interesting it is, getting up for my first shift of the day at 3:30am is sometimes just a little bit too painful.

Today actually proved to be a very exciting days for me personally as I was involved with the small boat recovery of the rumbleometer which we freed from grips of the lava flow last night. If you have ever seen a small boat launch from a ship of this size, you would know that it is a pretty neat sight. You get into the boat on the level 2 deck of the ship, the boat then drops on a harness and descends something like 30 feet to the water below, where you then start up the engines and take off......pretty cool. Once on the water we had a spectacular view of the R/V Thompson with nothing but the Pacific around it (why, oh why, did I forget my camera). Our job in the small boat was to remove all of the loose lines and gear from the rumbleometer (after it made it to the surface), so that after we towed it back to the ship it would make pulling it out a whole lot easier. This turned out to be quite a bit of work as all of the lines were crossed and fouled on the top of the rumbleometer. After some pretty hard work of yanking and tugging on lines we had almost all of the lines either off the rumbleometer or secured. The rumbleometer was then lifted up on the deck of the ship using the crane, and we then zoomed in next to the ship and the entire small boat was picked up by the harness and hauled back up. All in all, a pretty great day.

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Thompson Teacher at Sea Log Teachers log #17 7/7/99

What a morning! Under gray skies and calm seas, ROPOS successfully cut the anchor tether line holding the recently released rumbleometer from its 20 month stay on the seafloor. While it slowly floated to the surface, ROPOS was brought aboard (photo left). The small recovery boat successfully collected the rumbleometer and towed it to the Thompson. After it was secured on deck it was examined and we noticed that small areas of melting were visible on the yellow plastic floats and some had lava fragments embedded in them. Chief Scientist Bob Embley and staff began removing the instrumentation following their inspection. The seismic data collected will be fully analyzed back on shore. Dive 496 included some biological sampling and Imagenex surveying in addition to the rumbleometer recovery and was a huge success.

ROPOS is being prepared for another complicated dive along the North Rift Zone and a vent called CASM. Dr. Bill Chadwick is planning to deploy one new extensometer (photo right) and retrieve four that were left at this site last year.

Bill Chadwick preparing the extensometer's electronics for deployment.

Extensometers, first deployed in 1996, help determine the movement of the plates that border each side of the rift zone. They are positioned in a line running across the rift zone so that they can communicate with each other with acoustic signals. In a programmed pattern, one extensometer will send a signal and wait for it to be returned by the receiving extensometer. Each of the instruments is capable of sending and receiving. The time between when the signal was sent and the time it was received can be used to determine the distance the sound signal traveled within about 1 cm. With each extensometer recording data when it is a signal sender, the actual position of each can be determined and the extent of any crustal movement can be determined. Data analyzed from last year indicated a small decrease in the distance between them caused by deflation of the volcano summit at the time of the 1998 eruption, which the rumbleometer located in the caldera also showed. Once this data is collected it will be downloaded on board the ship and the extensometer will be redeployed for another year. This type of monitoring uses measured changes in the physical shape of the volcano to learn about magma movements beneath the seafloor.

The extensometer inside the elevator preparing for deployment

The elevator used earlier in the cruise has been specially set up to carry the extensometers (photo left). Large corrugated tubes have been attached so that the extensometers can be carried down to the ocean floor and brought to the surface safely. After positioning the new instrument, ROPOS will collect the four from the bottom and place the long cylindrical instruments into the tubes. As with any technology used in science, researchers are always looking for ways to improve it. They next generation of extensometers are already in the works. It is hopeful that they can stay at the bottom longer and relay the data they collect from the ocean floor to a ship directly via acoustic modem.

Remember that when using the elevator we need to have calm seas and good weather, so keep your fingers crossed. Dive 497 is on its way to the bottom now to deal with the extensometers. Stay tuned for an update tomorrow.

Bye for now.

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