Gulf of California 2012

Volcanoes and Seamounts

April 17-May 1, 2012

Alarcon Rise is a 50-kilometer-long, asymmetrically spreading mid-ocean ridge segment bounded at the ends by the Pescadero and Tamayo transform faults. The ROV dives on Alarcon Rise will observe and sample the volcanic terrain along the ridge axis, with the primary objective to test the hypothesis that the shallowest central portion of the ridge segment experiences more frequent eruptions and has more vigorous hydrothermal discharge than the deeper portions towards the transform faults that bound the ridge segment.

Using data that will be collected with the mapping AUV on the R/V Zephyr as a separate part of this expedition, we will focus our ROV dives on any newly discovered hydrothermal vent structures and the youngest, least sediment-covered lava flows. We will examine the style of eruptions from ROV observations and samples, and evaluate the frequency of the eruptions by dating samples of the lavas and of fossils in sediments that blanket the flows. A secondary objective on these dives will be to characterize and collect non-vent and vent organisms, should any active hydrothermal vents be discovered.

The Alarcon Seamount ROV dives are planned to make geological observations relevant to understanding caldera formation and explosive eruptions on these near-ridge type of volcanoes. As we have done at the Taney, President Jackson and Vance Seamounts, we will collect samples of lava and pyroclastic deposits from the caldera walls and rims at the Alarcon Seamounts, which rise to 800 meters (2,625 feet) depth.

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Further Reading

Further reading

Alarcon Rise
Castillo, P.R., J.W. Hawkins, P.F. Lonsdale, D.R. Hilton, and A.M. Shaw (2002) Petrology of Alarcon Rise lavas, Gulf of California: Nascent intracontinental ocean crust. Journal of Geophysical Research, 107(B10), 2222, doi:10.1029/2001JB000666. [Abstract] [Article]

Mid-ocean ridge eruptions
Clague, D.A., J.B. Paduan, A.S. Davis (2009) Widespread strombolian eruptions of mid-ocean ridge basalt, Journal of Volcanology and Geophysical Research, 180: 171-188, doi:10.1016/j.jvolgeores.2008.08.007. [Article]

Davis, A.S., D.A. Clague (2003) Got glass? Glass from sediment and foraminifera tests contribute clues to volcanic history, Geology, 31:(2): 103-106. [Abstract] [Article]

Near-ridge seamounts
Clague, D.A., J.R. Reynolds, and A.S. Davis (2000) Near-ridge seamount chains in the northeastern Pacific Ocean, Journal of Geophysical Research, 105(B7): 16,541-16,561. [Abstract] [Article]

Davis, A.S. and D.A. Clague (2000) President Jackson Seamounts, northern Gorda Ridge: tectonomagmatic relationship between on- and off-axis volcanism, Journal of Geophysical Research, 105(B12): 27,939-27,956. [Abstract] [Article]

Staudigal, H., D.A. Clague (2010) The geological history of deep-sea volcanoes: biosphere, hydrosphere, and lithosphere interactions. Oceanography 23(1): 58–71. [Article]

Logbook

The ROV manipulator collecting a sample of a drained lava pillow rind.

GOC 2012: May 1

Chief scientist Dave Clague summarizes the achievements of the submarine volcanism group's research in the Gulf of California.
Figure 3: After the sediment strata were deposited, an earthquake took place and displaced the strata along a fault as shown.

GOC 2012: Apr 30

We definitely saved the best—or strangest—for last today.
An amazing feature formed by a fault scarp. A portion of the face of a fault-scarp truncates a set of pillow lavas (center), with its characteristic radial fractures giving the pillow a “wagon-wheel” shape.

GOC 2012: Apr 29

We have been mapping and collecting images and samples of the lava flows to be able to understand as much as possible about the eruptions here at Alarcón Rise.
Hot, mineral rich water spews from a hydrothermal vent on the seafloor. Also known as black smoker, the mineral rich water appears as a column of black smoke rising from the seafloor. White, floculent bacterial mat is seen on the surface of the chimney below the black smoker.

GOC 2012: Apr 28

Today we dove on five active hydrothermal vents and several more inactive chimneys.
Our Second Mate, Andrew McKee, took this photo of the remotely operated vehcile (ROV) Doc Ricketts being recovered this morning. He lowered a camera from the bow aimed back between the ship's hulls, and snapped the photo as the vehicle was being lifted through the moon pool at the center of the ship.

GOC 2012: Apr 27

The wind has begun to blow and is cooling us off a bit, which is welcome. The seas have picked up too, so the ship is moving around under our feet for the first time this trip.
Basalts are black volcanic rocks that compose most of the ocean crust. This particular chunk of basalt has a lot of white plagioclase crystals. Plag- refers to the plagioclase mineral; phyric- means that there are large visible crystals in the rock.

GOC 2012: Apr 26

Check out that awesome plag-phyric basalt sample!
The yellow mineral that shines in the sample is pyrite.

GOC 2012: Apr 25

Rocks can tell us many things. We just have to know what and how to ask, and then listen carefully to the answers.
White coral (Chrysogorgia sp.) and a small crustacean (galatheid crab) behind the coral on the right side of the image.

GOC 2012: Apr 24

We have started the day with big expectations; there's a possibility to find hydrothermal vents and chimneys.
This portion of a fault scarp has been overrun by lava, which dripped down the nearly vertical face of the scarp as elongate pillows (center of the picture). These structures indicate that at the time of eruption, this scarp was already present.

GOC 2012: Apr 23

During today's remotely operated vehicle (ROV) dive on the southern Alarcón Rise, we came across a series of spectacular structural features.
A close-up view of the vent tube worms (Riftia). If you look closely you’ll see several fish hiding in among the worms. The little black spots covering the worm casings are limpets.

GOC 2012: Apr 22

As the ROV descended, the control room was abuzz with anticipation; today we were diving on one of strangest environments in the deep sea.
Figure 1: Alarcón seamounts showing today's dive track on the middle seamount, starting in a smaller crater (see below) and ending on the rim of a large caldera.

GOC 2012: Apr 21

Alarcon seamounts showing today's dive track on the middle seamount, starting in a smaller crater and ending on the rim of a large caldera.