Vance Expedition
July 24 - August 6, 2006

August 1, 2006
Tiburon dive T1010, Axial Seamount

Sheet flow of very fluid lava that erupted since the thick volcaniclastic sediments were deposited. This flow was very difficult to sample because the thin sheets were pure volcanic glass that shattered easily.
Dave Clague writes: We continued our exploration of the clastic volcanic deposits on Axial Seamount today with a dive on the northeast side of the summit caldera. We began the dive on the floor of the caldera so that we could observe the rock units exposed in the caldera wall on our way to the first vibracore location. Talus of mostly angular massive lava flows has accumulated at the base of the caldera wall, but upslope the wall consists of outcrop of massive jointed flows, pillow flows, and lobate flows. Every small shelf is covered with sand and gravel sized glass fragments. The massive flows form vertical sections up to perhaps 5 meters thick, but the pillow and lobate flows form less steep slopes. The entire section has been extensively fractured. Near the top we encountered several fractures that parallel

Drained lava pond. This was a pool of lava that filled and then subsided. The remaining walls and roofs are held up by pillars that formed when vaporized seawater made vertical channels through the lake and cooled the lava around them.
the caldera wall where arcuate blocks are leaning back into the caldera. The top section is a series of steps bounded by small vertical offsets, always stepping up away from the caldera. The top several of these blocks are covered by the thick volcaniclastic units we came to sample to determine thickness of the deposits as a function of distance to the caldera. We began collected vibracores every 100 m and the first three cores were nearly full 2-meter cores. The deposit quickly began to thin and the next few cores were roughly a meter long, perhaps somewhat less.

As we continued to move away from the caldera, we were surprised to find a young flow with only a small sediment cover. This flow, and perhaps others, erupted from fissures parallel to the caldera wall, but located at least 1 kilometer from the wall. Such circumferential eruptive vents are known from many volcanoes, but were previously unknown on Axial Seamount. These flows produced large, deep lava lakes at or near their vents. This was an exciting discovery as it reveals one more aspect of activity at Axial Volcano. However, these young flows also cover the volcaniclastic unit we came to sample. We sidestepped around the north edge of the flow several times and finally located

John witnessed his first "limu o Pele" with our dives at Axial Volcano! Here he is looking through our microscope at pieces that are up to 1 cm long.
sediment once again, to the north of our initial transect line. Further exploration revealed that young flows covered an extensive area away from the caldera and we decided to return towards the caldera to use our final vibracore. Once again, young flows covered the clastic unit and we ended up with one unused core barrel, but an appreciation of the frequency of such eruptions along circumferential (ring) fissures.

Although there are aspects of the study we undertook that we were unable to determine, such as the distribution of the deposit as a function of distance from the caldera, other parts turned out better than expected. These include our discovery of eruptions along circumferential (ring) faults around the caldera and that the clastic deposit on the northeast side reaches at least 2 meters thick. The vibracores remain in their aluminum core barrels since we are not equipped to split them at sea, so we really do not know yet what we have recovered, except that there is a lot of it! We have processed some of the sediment scoop samples and pushcores tonight and know that the sands and gravels near the surface contain abundant glass particles produced during pyroclastic eruptions, including Pele’s hair and limu o Pele (bubble wall fragments). In several of the cores, the bottom of the core is an unusual grey-green silty sediment, identical to material we found last year. The color reflects abundant greenish hydrothermal clay fragments. This green clay in the cores recovered last year is what led us to try to understand the formation of such deposits at Axial and their possible relationship to caldera formation.

Four of us in the small boat to recover the elevator (I'm in the midst of taking the accompanying photo!)

Tomorrow, we will return to the Vance Seamounts where we will explore a different seamount located between the two we explored last week.

John Stix writes: Yesterday we sampled rocks and creatures on the flank of Axial volcano from near the caldera rim westward. Axial is a very interesting volcano in many respects; since it sits astride the actively spreading Juan de Fuca Ridge, it is an active volcano which erupts frequently, most recently in 1998. It also has a big caldera at the top, which makes the volcano even more interesting. We want to know what happens when a caldera forms underwater, and these samples from Axial will help us unravel the story. Are the eruptions explosive? How do magma and seawater interact as the caldera subsides? Does the magma form sufficient gas bubbles quick enough to tear the magma apart and fragment it? Stay tuned for the answers!

The samples we collected yesterday are fascinating indeed. The material consists mainly of small shards and fragments of basaltic volcanic glass. This is amazing stuff. Glass forms when magma, which is at a temperature of about 2000 degrees F or 1200 degrees C, is rapidly cooled and quenched to a solid. Of course the marine environment is an ideal place for glass to form, due to the abundance of very

The elevator surfaced just off the starboard bow of the Western Flyer about a half hour after the ROV released it from its anchor at the bottom. We freed the yellow tow line coiled at its top edge (visible on the right) and brought the elevator around to the stern so it could be winched aboard. The water was so clear you could see the ship's props turning from just aft.
cold seawater. The amazing thing about our samples is the abundance of delicate glass fibers, called Pele’s hair after the volcano goddess of Hawaii, which are present in our samples. The presence of Pele’s hairs is an indication that as the magma was erupted, it was able to be contorted and stretched into very thin strands, and then blown apart while still in a plastic state. This implies that the magma was not being frozen to glass instantaneously, and that there was time for the hairs of Pele to form. What this information tells us about eruptive conditions in the submarine environment is a focus of our current and future research.

Jenny writes: I got to ride in the RHIB (rigid hull inflatable boat) to retrieve the elevator today! Erik (2nd Mate) and Kim (Deckhand/Oiler) did the line handling, Benny (Able Seaman) was our skipper, and I photographed and tried to stay out of the way.

Rachel writes: Today we visited the other side of Axial Seamount's caldera. It is amazing how different this young lava looks from the old, crusty stuff we have found on the Vance Seamounts. Basaltic glass is some beautiful stuff!!! The rock samples we brought up had some really interesting features: folding, bubbles, tiny crystals in the glass, and lots more. The vibracores came up early today...the elevator conveniently surfaced just feet away from the ship! I also heard there might have been some hijinks with a pink flamingo...

View of the stern of the R/V Western Flyer from the small boat. The cable hanging taut between the hulls is the tether hanging through the moonpool for the ROV working on Axial Volcano 1.5 km below. The crane (to port) is for recovering the small boat. The elevator (in the water at left) is being winched in to the A-frame (centered over the stern).

Liz, Kristen, and I spent most of the day doing what geologists do best...smash up rocks!!!! This is also known as sub-sampling, a way to get only the part we need for chemical analysis. We did some pretty good damage. Kristen searches on for the lost bag of colored markers, an essential tool for creation of the smushed cups. Derek continued to impress us with his wonderful cuisine, some of us even when back for seconds of dessert. All in all, a good day, looking forward to another great dive tomorrow!

Liz writes: I have finally settled into a nice routine: my first shift in the control room was from 9-10:30 (note taking). Then there is time before lunch to watch the dive on the TV in my room or do some other I did laundry. The boat has a washer and dryer outside on the top deck. It was a warm, sunny day, and aside from the diesel exhaust, doing laundry was quite pleasant. Lunch was from 11:30-12:30, today Derek outdid himself with a delicious stir-fry with peanut sauce. Then it was off to the wet lab for rock smashing duty. Rachel and I have been chipping off pieces of glass from each rock sample (they will be used for chemical analysis). We had a boat drill today at 1:00. We grabbed our survival suits and gathered in the wet lab. The crew put out a 'fire' in the area where the ROV is stored. All went well and it was back to work. My second shift in the control room was from 1:30-3:00 (GIS annotations). A little more rock chipping and the it was up to the exercise room (a.k.a the top deck). There is a nice elliptical machine (very popular), weights, and yoga mats. I got in a good workout before dinner (5-6:00). The ROV came up early today (it surfaced around 6:00) because the pilots had to take the vibracorer off the vehicle. Everyone is very busy at this time...taking samples out of the ROV drawer, taking any critters off of the rocks first, then the geologists get their turn. Rachel and I are still on rock scrubbing duty. Since the ROV was up early, and we had only 14 rocks today, we are done now and it's only 8:30! Time to watch a movie in the control room...old first-class airline seats, and two large screen TVs!

Kristen searched and searched for our multi-color set of permanent markers, last seen two nights ago, so she could decorate some more styrofoam cups. How many places on a ship this size can something be hidden? She made the sign shown here, describing the missing items and offering a reward, and hung it in the galley. The markers magically appeared, with the sign taped to the bag!

Rachel and Liz chipping volcanic glass from the rocks collected yesterday. Major and trace elements will be analyzed by Liz, and radiogenic isotopes will be analyzed by Rachel, for their master's thesis projects.

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