Saturday, July 22, 2017

The Last Dive

By Teresa Atwill

At about 3:30 am this morning, the Jason team began preparing Jason for its last dive of our expedition. At almost 4 am, the ships crew and the Jason winch operator and the rest of the Jason team lifted the ROV from the deck and lowered it into the water. After all systems are shown to be working then they added the 34 football floats and the transponder onto the cable. For this geology dive all of the chemical sampling equipment has been removed from Jason and extra milk crates with dividers have been added to Jason’s basket to hold the planned rock samples.

New 2015 lava draping over older lavas on the NE rim of Axial.
At about 5:20 am the bottom was reached and we found one of the lava flows that erupted in 2015. I have spent a lot of time in Hawaii on Kilauea Volcano and the features seen here look very familiar to me. We see glassy lava with ropy features and thin flat crusts that have rafted into each other. In some areas the lava is jumbled and broken up. We collect samples with Jason’s manipulator arms and this is hard to do as the glassy surface of the new lava breaks so easily and the gripper jaws on Jason’s arm are made to be strong, not delicate. The Jason pilot on this watch, Jimmy, manages to get a piece of lava into one of the sample boxes, but some of the samples are easier to collect than others. It is hard to design a manipulator arm that can be strong, withstand the pressure in the deep ocean, and yet can also delicately pick up fragile rocks.

We see some cool pillow lavas from the 2015 eruption flowing down over the jumble of rocks and boulders at the base of the caldera wall. We collect another rock sample and Jason begins to rise up the side of the caldera about 65 meters high. Some of the caldera wall is a sheer rock face and we can see features like lava tubes and pillows that have been cut in half as if by a giant knife. This reminds me so much of road cuts along the Hawaii National Park Chain of Craters Road, but here we are a mile underwater.

Collecting 2015 lava sample.
At the top of the caldera rim we begin to move along a large graben (a down-dropped block between two faults) with deep fractures running northward. There is no fresh lava here. These features are similar to those seen on rift zones in Hawaii. On both volcanoes the open fractures generally parallel the rift zones (areas where the lava moves outward from the under the central caldera), where over and over again new lava is injected in dikes and sometimes erupts out of fissures.

After several hours of zig zagging across the graben while driving Jason northward and looking at the fractures the Jason team shift changes. Everyone takes turns eating breakfast and returning to the control van. At about 8:15 am we see some 2015 lava in the crack of a fissure. This is where a dike, or magma filled crack, reached the surface and lava squirted out. Much of the magma stayed underground in this part of the rift zone. We see fissures, but not much fresh lava.

Control van view of lava pillar to be collected (center of large screen).
At about 8:30 am we reach an area that has 2015 pillow lavas and we take a sample. We continue up the graben toward where we know there are larger 2015 lava flows, but we are filling in a gap that has not been explored before. We are the first to see these features and to sample these lavas.

At times during the dive, as we sit in the control van, it feels like one of those virtual experience rides, where you sit in a simulator and they show you flying in a space craft. The R/V Revelle provides some dips and rolls that match with Jason’s video movements and you feel like you are in a submersible flying (although slowly) through the water. As we move into the area where more lava erupted on Axial’s North Rift Zone, we see larger areas that are covered by thin ropy lava. There are really interesting sites that have the new lava flowing under, around and on top of the sediments that were here before the eruption. We saw sea pickles all over the lava flow. They are not supposed to be here and never were before. Now they are everywhere. They belong in more tropical waters, so it is worrisome to see them here, and are another piece of evidence of changing ocean conditions.
Pillar collected in photo above right.

We saw a number of cool lava pillars and areas of lava-sediment interactions. We ultimately collected 14 rock samples from the 2015 lava flows, and it's time to head back to the surface. We all must be getting hungry, as a discussion of where to get the best pizza in port ensued.

Back on deck at noon.