Northern 13, Leg 2-3 – Seafloor lava flows

August 10-September 1, 2013

The MBARI mapping autonomous underwater vehicle (AUV) D. Allan B. has collected high-resolution data mapping Axial Volcano’s caldera, flanks, and south rift zone, and several other sites along the Juan de Fuca mid-ocean spreading ridge, where eruptions have occurred in the past 30 years (which are called here “historic flows”). These new maps are at a resolution that allows mapping of individual sulfide chimneys, lava pillars,

channels in sheet flows, eruptive fissures and faults, and flow margins.

During this expedition, MBARI will return to these sites with the remotely operated vehicle (ROV) Doc Ricketts to collect video observations and samples. Cruise objectives for both legs of the expedition are to use push cores and vibracores to collect the pyroclastic (volcanic ash and glass particles) sediment sequences on the caldera rim of Axial Seamount, image the caldera wall at Axial with ROV video, collect more samples of the Axial 2011 lava flows and other flows discerned on our high-resolution AUV maps using the ROV and a wax-tipped corer, and collect samples and sediment cores for radiocarbon dating at other sites along the Juan de Fuca Ridge. These data will be combined to evaluate timing of eruptions and changes in lava geochemistry and eruption style as a function of spatial location and age.

Specific targets for Leg 2 will be at the summit of Axial Seamount, pillow ridges emplaced on Axial’s south rift during the 2011 eruption, and some cones on Axial’s north and south rift made of lavas containing high concentrations of magnesium (more primitive melts that erupted at higher temperature than most lava found at Axial or elsewhere along the Juan de Fuca Ridge).

Targets for Leg 3 will be on the summit of Axial Seamount, andesite (more evolved melts than usually found at Axial or along the Juan de Fuca Ridge) cones near Axial’s north rift, historic flows on the CoAxial segment of the Juan de Fuca Ridge that erupted in 1993 and between 1982 and 1991, and a large perched lava pond on Axial’s south rift.

bathymetry map

Part A shows bathymetry at 100-meter contour intervals of the continental margin offshore of Eureka, California, and locations of Eel River, Mendocino Fracture Zone (MFZ) and Eel Canyon. The location of the classic Eel River seeps are indicated with an X. The area indicated with the red box is shown in more detail in Part B. Part B shows multibeam bathymetry of the area where six huge water column plumes were discovered (black dots; Gardner et al., 2009). Two emanate from slide scars to the south of Eel Canyon, and four emanate from the seafloor and northern flanks of Eel Canyon. Arrows indicate steps within the canyon floor. Part C is a detailed map of the slide scar area where a feature similar to the Santa Monica mounds occurs (black arrow).

Logbook

yellow crinoid

Heading for port

A yellow crinoid (Family Crinoidea) is perched on the peak of a jumbled sheet flow block with its arms outstretched to trap food particles. This type of crinoid can swim by gracefully paddling its feathery arms and uses shorter appendages to grip the substrate.
crab

Lava pond

This crab (Macroregonia) calls the jumbled sheet flow home.
pillow lava eruption from 2011

Axial Volcano summit caldera

Pillow lava erupted in 2011 (at right in the central and top monitors) over-riding a 1998 jumbled sheet flow (left), from the perspective of an observer looking over the shoulder of the scientist at the main camera controls in the ROV control room on the ship.
Favorite picture of the day: a lobate lava at the rim of Cage Seamount has been broken open to reveal drainage shelves (horizontal layering) formed while lava was coursing through the pillow, and the mold of an adjacent pillow that formed against it and has since fallen away (just left of center).

Revisiting the 1993 lava flows

We returned to the CoAxial segment today to tie up some loose ends left from five ROV dives we did in 2005, 2009, and 2011, and an AUV mapping survey completed in 2009.
Elongated andesite lava pillows flowed down a steep pillow mound. One has cracked open and drained a twisted, elongate drip. These pillows are inhabited here by small red corals and an anemone (Actinostolidae).

Searching for rare lavas

One of the main objectives of our dive today was to see if we could locate these andesitic lavas, to document how they erupted, and to determine how they might be related to the normal mid-ocean ridge basalts that comprise Axial and the surrounding seafloor.
hematite stains on lava flow

Lava flow layers tell a story

Lava flows from hundreds of separate eruptions are exposed in cross-section in this wall, which resembles an enormous layered cake. The size and shape of each exposed lava flow (each layer) testify to the characteristics of the eruption that formed that flow.
Map - halfway to Axial Volcano

Transit to Axial Volcano

We began our transit this morning at 7 a.m. and are a little less than halfway to our destination.
dave prepping cores

Leg 2 wrap-up

It has been an eventful cruise that began with a two-day transit from Eureka, California to Axial Seamount, and is just wrapping up with a 29-hour transit from Axial Seamount to Newport.
piston corer being deployed

Designing a new corer

As we explained in a recent log, the sediment at Axial is particularly difficult to sample because of its unusual texture. Dave Clague asked me to join this cruise so that I could observe his coring method and possibly come up with a better solution.
red bacterial mat

Exploring the 2011 lava flow

After two full days cruising along the lava flow that was probably erupted in 2011 along the South Rift Zone of Axial Volcano, we are back to Axial Volcano’s summit, chasing lava flows that definitely came from the 2011 eruption.
Benthoctopus

Axial Volcano's South Rift Zone

Our exploration of the circa 2011 Axial Volcano South Rift Zone eruption continued today with remotely operated vehicle (ROV) Doc Ricketts dive 521. Today's dive targeted several large mound structures within the 2011 flow.
pillow lavas

An endless array of volcanic formations

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.
push core handle

Collecting core samples

This morning, we woke up to surprisingly nice weather: the wind was down and the sun out. The waves were still in the two meter range, but much better than yesterday. During the night, the ship had moved to our work site for the morning, the southwest side of the caldera (site C).
ROV manipulator arm collecting lava flow sample

Making the most of bad weather

A low-pressure system moved in last night and it has been raining and blowing more than 25 knots all day. The motion of the ocean has the ship moving about more than it has since we left Eureka, but everyone seems to have their sea legs and, as usual on this remarkably stable ship, my coffee cup stays where I put it.
talus blocks that fell from the caldera wall

Exploring a caldera

Today was our first day at Axial Seamount. The remotely operated vehicle (ROV) went into the water on time and we arrived on the bottom at 7:30 a.m.. We are investigating the northeastern wall of the caldera. The walls are full of information about the old days of Axial Seamount.
ROV doc ricketts

Halfway to Axial seamount

Since this is my first cruise, I wasn’t sure what to expect, but life at sea has turned out to be fascinating and unlike anything I’ve ever done. I had never before been beyond the sight of shore. You can walk around the lower deck of the R/V Western Flyer and see the ocean from all directions.
man overboard drill

Transit day one

We left the dock in Eureka, California, at 7:00 a.m. this morning and are steaming toward the northwest for almost 750 kilometers to Axial Seamount on the Juan de Fuca mid-ocean ridge. We anticipate that if the calm weather holds, we'll arrive Monday morning. First things first, as on every one of our cruises, the science party had a safety briefing and the ship's crew carried out a series of safety drills.