Day 6: An endless array of volcanic formations
August 15, 2013
The clouds and drizzle have moved back in but without the winds of a squall. Today's remotely operated vehicle (ROV) dive was on the South Rift Zone of Axial Volcano, approximately 25 kilometers from where we have been working in the caldera. Comparison of bathymetry data collected from ships in 1998 and 2011 (both times following eruptions at Axial), indicated that a pillow ridge was erupted here sometime between the surveys. It most likely was associated with the 2011 eruption, as instrumentation has been in place in the caldera to monitor the volcano since the 1998 eruption, and other than the April 2011 eruption, no other large events have been recorded. We verified that the lavas inside the area of changed bathymetry are young. We collected lavas from this flow, which we will analyze for chemistry and Ken Rubin will try to date, to confirm if they are from the 2011 eruption. We also collected lavas from flows nearby and push cores to 14C date the foraminifera in the sediment to give approximate ages of those older flows.
Contact between pillow lavas of an older flow (left) and the presumed 2011 flow (right).
Today we were the first humans to see the youngest lavas on the Axial Volcano South Rift Zone, which were recently erupted roughly 25 kilometers away from, and 500 meters deeper than the summit caldera of the volcano. The best information we have says this bit of seafloor lava was probably erupted around the same time as the 2011 summit eruption, as a long ridge of young lava that was piled up to 120 meters tall. This is really thick for a typical submarine eruption deposit! Today was the first occasion for people to view these south rift zone lavas, but they were discovered two years ago, after the 2011 Axial Volcano summit eruption. See Jenny's blog for a discussion of the discovery, from a comparison of 1998 and 2011 sonar surveys of the sea bed over the southern sector of the volcano.
Were we excited before today's dive to the pillow ridge? You bet we were! It is always exciting to investigate a new piece of seafloor, to see the types of volcanic landforms there, the potential for hydrothermal activity and colonization by organisms, and the relationships between new lavas and older volcanic structures.
Were we disappointed? Not in the least. We saw spectacular volcanic landforms in both the new lava and older surrounding terrain, including steep pillow lava walls, frozen lava cascades, deep fissures cut into the older terrain, and orange microbial mat communities in cracks and crevices of the new lava, confirming their relative youth. We took 13 samples of young lava, nine samples of older lava, and several sediment cores.
With five kilometers of volcanic deposits stretched out along a series of mounds and ridges to explore, our plan has been to explore this eruption deposit over two ROV Doc Ricketts dives. Stay tuned for tomorrow's dive results.
Staining from hot fluids that emanated from cracks between lava pillows at the peak of a pillow mound is an ephemeral sign that the eruption was recent.
Elongate pillows of a lava cascade frozen on a vertical face of the presumed 2011 pillow ridge. Orange stains on the rocks are remnants of bacterial growth associated with fluids heated by the cooling lava.
Wide fracture in a neighboring flow attests that it has been around for a while on this spreading ridge.
(A) Various long-lived deep-sea corals growing on pillow lava. Deep-sea corals are long-lived, so are an indication that this lava they are attached to erupted many years ago. Small brittle stars typically perch on the corals to take advantage of small food particles floating in the water. (B) Some of the pillow lavas had dense polyps (zoanthids) covering them, and had spike-like carnivorous sponges as well.
(C) The beautiful Venus' flower basket is a hexactinellid sponge, which produces a glass matrix. It certainly takes a long time for one of these to grow. (D) The Pacific white deep-sea skate (Bathyraja spinosissima) swims fluidly just above the lava surface. They are one of the largest skates we see in the deep ocean and this male was nearly six feet (two meters) wide. (E) There are a number of other fishes here, but Antimora microlepis is one of the rarer ones. (F) The seastar Solaster has numerous arms and a mouth that faces the sediment. This juvenile is feeding on something as evidenced by the “hump” in the center disc. (Caption from Linda Kuhnz)