Days 21 & 22 High Seas and Earthquakes

The early morning (middle of the night) piston core was postponed because of winch problems and everyone took an opportunity to sleep—except for the grad students who rarely sleep and are looking a bit worn. Tom C., the transponder expert, stayed up with the ship’s crew to release and retrieve the transponders.

We say good-bye to Conical Seamount and head back south. We will return to most of the seamounts where we did the DSL-120 surveys. Hopefully, we will visit each with Jason-2 before this expedition ends.

Back at Pacman Seamount, the Jason Team has decided it is too rough to launch Jason-2 so we picked up the transponders we had left here from our previous visit. We spend 5 hours doing a piston core to get an 8-inch sample of sediment but this short sample does tell us that there is chimney growth in the area.

Then we’re off to Quaker Seamount. Jason is set for an 1800 launch but it is still too rough. Not a minute is lost—if Jason isn’t in the water, we’re coring—if we’re not coring, Patty gives Nathan a course to continue collecting bathymetry data to fill in the gaps in the maps of the sea floor.

We spend 2 hours rigging the piston core and another 5 hours to deploy and retrieve at the mound east of Nip and Blip that we call Dip. The geologists are anxious for a sample here because bathymetric data hints at deep serpentine mud close to the Mariana Trench. This piston core comes up with less than a foot of sediment. That’s a lot of work for a few inches of dirt! (Sorry Patty, I mean sediment and mud.) The trigger core had more sediment than the piston core. When we took the plastic liner out of the steel core pipe, we found that it was shattered. It hit something so hard that it imploded. There was sediment in the liner but as it reached the surface, we watched it flow from the pipe because the piston couldn’t hold suction in the shattered liner.

Everything is looking good for a midnight launch of Jason at Quaker Seamount.

Back in the Main Lab, Jim is still playing in the mud. Fifteen feet of mud in the core, or 2 inches, he is there taking detailed notes of every component. He then flushes the fine silt and clay from the sample in sieves until he is left with grains large enough to study under the microscope or with the naked eye.

Jim is looking for anything and everything, but he is most interested in metamorphosed rocks from the subducted plate that sometimes rise with the serpentine mud. Jim is also interested in carbonate crystals. Some of the metamorphic rocks can be identified visually but some will have to be analyzed chemically back on land. Rocks that go down with the Pacific Plate are subjected to changes in pressure and temperature. Once Jim identifies the metamorphic rock, he can determine the approximate pressure and temperature at which it formed. From pressure, he can calculate the depth and then he will know the approximate temperature of the plate at that depth.

The temperature of the Pacific Plate as it subducts is still a mystery and that is the focus of Jim’s studies. As the plate is being subducted it is in contact with the Philippine Sea Plate above it. As the plates move past one another, is there friction creating heat? Or is the plate coated in serpentine mud allowing it to slide without much friction and hence, less heat?

Some of the biggest earthquakes on Earth occur at subduction zones. Jim’s studies will lead to a better understanding of subduction and perhaps, someday, allow for predictions of the size and cause of these Earth-shaking events.

Science Summary - Day 21 & 22, April 12 & 13th

Science Objectives, Day 21:

The twenty-first day of the cruise, Apr. 12, as rising winds and seas from the tropical storm to our south continue to preclude lowering the Jason2/Medea ROV system, we will evaluate sea conditions for launch at first light and if still bad will collect bathymetry data for an additional two hours until the winds begin to abate, as they normally do in the later morning. If conditions permit us to launch at that time, we will do a lowering at the summit of Quaker Seamount, if not, we will perform a piston core. The core location will depend on an evaluation of a potential protrusion of serpentinite mud several kilometers east of Quaker Seamount, along the fault trace that controls the position of the seamount.

Science Objectives, Day 22:

The twenty-second day of the cruise, Apr. 13, as the weather is deemed unacceptable for launch of the Jason2/Medea system because of predictions that a swell from the tropical storm will worsen, we will perform a piston core at the small serpentinite protrusion we nicknamed Nip. After the core at Nip, if weather still precludes the ROV launch, we will do a bathymetric survey of a feature that appears similar to Nip but lies further east along the same fault trace. If the bathymetry suggests similar morphology we will do a piston core on that mound as well.

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