Vance Expedition
July 24 - August 6, 2006
July 29th, 2006
Got an early morning report from the Western Flyer that the ROV Tiburon has been launched and the dive has started!
July 29 update
Tiburon dive T1007
Dave Clague writes: Today, at long last, we did our first dive on the Vance Seamounts. We elected to start on the youngest large central volcano in the chain. This volcano is a circular, flat-topped volcano with a large central caldera and a second caldera that downdropped the entire southeastern portion of the volcano, leaving the impression of a doughnut with a bite missing. Our dive plan, which we followed quite closely, is shown on a bathymetric map of the volcano. The dive progressed from south to north, ending on the north rim of the central caldera.
Map of Vance F seamount with our dive track in black.
The dive began in the flank caldera floor, where we landed on lava flows erupted within the caldera after it formed. These flows drape several small faults that parallel the nearby Juan de Fuca Ridge axis, showing that the flows postdated all movement on these faults. We then drove northwest to the base of caldera wall, which was a large talus-covered slope for about half its height. The upper portion was a series of truncated pillow flows and massive lava flows, all capped by a thin layer of fine-grained volcaniclastite (a sedimentary rock composed of silt and sand sized volcanic particles). We crossed over a narrow septum between the two calderas and then dropped down into the second, and centrally located, caldera. Once again, the caldera wall consisted of a series of truncated pillow and massive flows under a thin cap of volcaniclastite, with the lower half of the slope buried in talus. At the base of the talus slope, the nearly flat caldera floor was buried beneath rippled sediment. As we crossed the caldera floor, outcrops of harder rock were spotted on the sonar and we found exposures of fine-grained volcaniclastite that formed the flat floor of the caldera. We proceeded north towards a hummocky deposit on the caldera floor that could have been either landslide debris or constructional volcanics. It turned out to be the latter, showing that effusive eruptions occurred on the caldera floors of both calderas after they formed. We ended this dive with one more traverse up the caldera wall, encountering the same sequence of units seen previously, with more abundant massive flows and less abundant pillow lava, and capped with volcaniclastite.
At the top of the caldera walls, we found thin beds of volcaniclastic (= broken up volcanic) material overlying the more massive flow units. Here at the very edge, a multitude of gorgonians and sponges are attached to the flow units, their fronds growing out, rather than the usual up, to take advantage of currents focused up the wall that carry particles of food. Note that nothing appears to be growing on the clastic material.
Pillow lavas overlain by a massive flow interior unit on the caldera wall. Stacks of these units were truncated and became a vertical cliff hundreds of meters tall when the caldera collapsed.
This single dive has documented that the volcano formed by accumulation of numerous pillowed and massive flows, followed by formation of the two calderas and explosive eruption of a thin layer of volcaniclastite, perhaps in direct response to collapse of the first, central, caldera. Small effusive eruptions on the caldera floors appear to be the final volcanic activity on this volcano. This remarkably clear sequence defines the major volcanic events in the history of this seamount. Samples collected from each phase of this activity will be used to determine how the magma compositions changed as the volcano grew and changed. In addition, sediments collected on top of each unit will be dated to place this evolution in a timeframe, to find out when this all took place and how long it took to occur.
During the dive we also collected a number of animals to characterize the biota living on this young volcano. In general, the talus slopes and sediment hosted sparse communities whereas lush complex communities occurred on the upper caldera walls. At one location on the caldera wall we collected 8 different gorgonian species as we waited for the ship to catch up to us so we could traverse down the inner caldera wall.
View from up by the ship's bridge of the ROV Tiburon being launched this morning.
Brian Cousens writes: It was a huge relief to finally see the ROV in the water this morning when I got up! Just three days ago, we were wondering if we were ever going to get here as we slogged at 2 knots through bad weather. But it was worth the slogging. Today we dove in Vance seamount “F”, one of the youngest of the seamount chain. We hoped that we might come across some active or dead hydrothermal vents, but none were seen. However, that was our only disappointment. This was the “elevator” dive – starting out on low ground, then up on top of one edge of the seamount summit, then back down into the caldera collapse area in the center of the seamount, then back up to its flat summit again to end the dive. We saw a huge variety of volcanic rock types, showing how the style of volcanic activity changed often as the seamounts grew. We also came across lots of animals, all competing for the best spots along rock walls to catch water currents with the most food. At one spot, there were so many coral types and sponges jammed together it was hard to see the rock wall they were attached to! Another interesting phenomenon that we commonly noted was that many of the areas covered in sediments had ripples on the sediment surface. You almost always see ripples in sediments on the bottom of rivers or at the beach where shallow waves or currents can move sand grains. We were seeing ripples at over 2 km beneath the surface of the ocean! The ripples we saw today are caused by deep ocean currents that can move sediment grains to form ripples, which means that these currents travel at pretty fast speeds! So this was a great day 1 of diving.
Rachel at the controls of the ROV Tiburon in the control room, with pilot Buzz nervously teaching her to drive.
Liz and Rachel write: Up early at 7:00 AM, but not early enough to watch the first launch of the ROV. However, we did catch the landing of the ROV on the seafloor...amazing! The control room was packed, standing room only, with the entire science team excited to finally be doing what we came here to do. Our job was to man the ArcView GIS and notetaking stations at various shifts during the day. In the afternoon, we graduated to 'pilots' of the ROV. We were travelling across a barren, muddy, flat area and the pilot allowed each of the students to sit in the pilot chair and 'drive' the ROV for a short period. It was one of the most stressful times in my life...thank goodness it didn't crash into anything. Another highlight of the day was the submerging and surfacing of the styrofoam cups we decorated last night. They shrank into tiny little thimbles under the pressure at the seafloor. The ROV surfaced around 8:00 PM and we removed all the samples from the compartments. While others were working, a few of us went outside the see the beautiful rainbow spanning the sky (and then we went back to work). All of the rocks were brought into the wet lab area. We were assigned to rock cleaning duty. Yes, there is such a thing as dirty and clean rocks. The goal was to remove all organic matter and seawater for better storage. As the rocks got cleaner, we got dirtier. But we got the job done. The first dive day was long, exciting, surreal, eventful, and we should be getting to bed soon so we can do it all over again tomorrow.
Kristin and Gill collecting small organisms from the rocks before the geologists scrub, photograph, describe, subsample, and pack up them up.
Mike preparing to smash (um, subsample) a rock.
Liz showing off the cups she decorated last night and shrunk on the Tiburon today.