Our dive today was a little farther to the northeast of the previous dives, along the neovolcanic zone of the Alarcón Rise, using the maps from the autonomous underwater vehicle (AUV) to guide our dive. As on previous dives, we observed and collected rocks and sediment push cores from numerous lava flows we identified in the AUV maps. Our goal is to determine their relative ages, morphologies, and whether some small cones were pillow mounds or old sulfide deposits (they were all steep pillow mounds today), and to examine fracture patterns.
If you were to sit in the control room with us during one of our dives you would hear us repeating terms such as “lobate flow,” “jumbled sheet flow,” “elongate pillow lava,” “truncated pillows,” and “Ooo... what a nice plag-phyric glassy basalt!” And, if you hang around with us long enough, you may even begin to understand these terms, too. It is true that geologists seem to be speaking in another language—well, most of the time—but there is a reason to use a unique and consistent set of terminology. We need to be able to rely on our notes to accurately reconstruct the morphology of the seafloor. Morphology refers to the shape and structure of the landscape. Each of those terms I mentioned above are used to describe a specific type of lava flow or feature observed along the Alarcón Rise.
There are two main lava morphologies to note: sheet flows and pillow lavas.
Sheet flows are flat (or flattish) sheets of solidified lava. Depending on the shape of the underlying seafloor and the rate of the eruption, different sheet flows can look very different. Swift-moving flows will have well defined flow lines and will look like a solidified river of lava like in the above picture. If the flow gets fracture and jumbled we then call it a jumbled sheet flow. As the flow gets further from the source, it cools and slows. The morphology of the flow changes as well; the flow will become more lobate. If the rate slows even further, pillow lavas will begin to form.
Pillow lavas look like rounded blobs of solidified lava. They are formed as lava extrudes slowly out of the seafloor and the outer edge is cooled very quickly by the cold seawater. Think about squeezing toothpaste out of a tube, but instead of it flowing freely, the outer skin of the toothpaste hardens as soon as it touches air. Pillow lavas come in a variety of sizes and shapes and each of these shapes can tell us a bit about the eruption that formed them. Today, as we were surveying flows near fissures (or large cracks) in the seafloor we saw both what we call elongate pillows and truncated pillows.
The type of pillow flow observed across a fissure can indicate the order in which the features formed. If there are elongate pillows flowing over the edge and into the fissure, we know that the flow occurred after the cracking of the seafloor. If the pillows are truncated, we know that the flow occurred before the cracking of the seafloor. These are the types of relationships that are impossible to infer from the AUV mapping data and are essential if we are going to successfully reconstruct the volcanic history of the ridge.
One of our main objectives is to develop a map of all the different lava flows present along the Alarcón Rise and place these flows in order of their relative ages. This is no small task. We have to first identify all of the boundaries between the flow units and then determine the age relationships along each of these boundaries along the entire 60-kilometer (37-mile) ridge segment! To do this we need to use both the AUV mapping data and the direct observations from the dives. Changes in the lava flow morphologies, as described above, often indicate a boundary between two separate flows. These different flow morphologies can be roughly inferred from the AUV maps. Additionally, the edge of a flow will often be marked by a small change in seafloor height. Think about squirting ketchup (a new lava flow) on a plate, the edges of the pile of ketchup (the new lava flow) will be slightly higher than the surrounding plate. We can see these small changes in bathymetry on the AUV maps and can infer the edges of the lava flows.
However, there is a caveat: a single eruption will likely display all the different flow morphologies and could have multiple flow lobes layered on top of each other. From the maps, we identified 22 potential flow units along our dive track. During the dive we marked the location and took video of each of the contacts between flows.
These visual observations will help to improve our confidence in the flow boundary that was drawn using the AUV maps. Additionally, we took rock samples and push-core samples from each flow unit to confirm that each identified flow was, in fact, a separate flow.
Check out that awesome plag-phyric basalt sample!
Volcanoes & Seamounts
The R/V Western Flyer is a small water-plane area twin hull (SWATH) oceanographic research vessel measuring 35.6 meters long and 16.2 meters wide. It was designed and constructed for MBARI to serve as the support vessel for ROV operations. Her missions include the Monterey Bay as well as extended cruises to Hawaii, Gulf of California and the Pacific Northwest.
ROV Doc Ricketts is MBARI's next generation ROV. The system breaks new ground in providing an integrated unmanned submersible research platform, with many powerful features providing efficient, reliable and precise sampling and data collection in a wide range of missions.
A push-core looks like a clear plastic tube with a rubber handle on one end. Just as its name implies, the push core is pushed down into loose sediment using the ROV's manipulator arm. As the sediment fills up the core, water exits out the top through one-way valves. When the core is pulled up again, these valves close, which (most of the time) keeps the sediment from sliding out of the core tube. When we bring these cores back to the surface, we typically look for living animals and organic material in the sediments.
Niskin bottles are used to collect water samples as well as the tiny bacteria and plankton in that volume. The caps at both ends are open until the bottles are tripped, when the caps snap closed.
The box fits in a partition in the sample drawer. It is shown open, with an animal being placed into it by the ROV's manipulator. When the lid is closed, the box will hold water to protect the animals inside.
This device is used to collect volcanic glass fragments from the surface of a flow. It is made of about 450kg of lead and steel and is launched over the stern of the ship on a wire. Fragments of rock that break off of the lava flow on impact are trapped in wax-tipped cones mounted around the crusher. The wax is melted in the lab to liberate the rock particles for analysis.
The benthic toolsled is attached to the bottom of the ROV for our geology dives. Its components are the manipulator arm and the sample drawer. The sample drawer is shown open on deck, full of rocks. Normally it is closed when the vehicle is operating and is opened only when a sample needs to be stowed. Partitions in the drawer help us keep the rocks in order. The rocks often look alike, but the conditions and chemistries of the eruptions are different so it is important that we know where each came from.
This equipment is used to vacuum glass particles and larval animals from cracks and crevices. The carousel of small plastic jars fitted with wire mesh will be mounted in the benthic toolsled. The hose will be held by the ROV's manipulator and a suction will be drawn by the pump.
Canvas bags on a T-handle for collecting gravel or other materials that fall out of a push-core.
Held by the ROV's manipulator, the wire on the right is placed into the fluid emitted from a hydrothermal vent to record the temperature.
Vibracoring is a common technique used to obtain samples from water-saturated sediment. These corers work by attaching a motor that induces high frequency vibrations in the core liner that in turn liquefies the sediment directly around the core cutter, enabling it to pass through the sediment with little resistance.
R/V Western Flyer
ROV Doc Ricketts
Dave's research interests are nearly all related to the formation and degradation of oceanic volcanoes, particularly Hawaiian volcanoes, mid-ocean ridges, and isolated seamounts. Topics of interest include: compositions of mantle sources for basaltic magmas and conditions of melting; volatile and rare-gas components in basaltic magmas and their degassing history; chronostratigraphic studies of eruption sequence and evolution of lava chemistry during volcano growth; subsidence of ocean volcanoes and its related crustal flexure, plate deformation, and magmatic activity; geologic setting of hydrothermal activity; origin of isolated seamounts; and monitoring of magmatic, tectonic, and hydrothermal activity at submarine and subaerial volcanoes.
Jenny works with Dave Clague in the submarine volcanism project, processing the high-resolution MBARI mapping AUV data and interpreting the maps using ROV observations and samples from our research sites. On this cruise, she will stand watches in the ROV control room, help with rock and sediment sample workup and curation once the vehicle is on deck, and coordinate these cruise logs. She is now quite solidly a marine geologist, but her degrees are in biochemistry (Smith College) and biological oceanography (Oregon State University). She is thankful for the opportunities that have led her to study volcanoes, and loves being involved with the research and going to sea. She looks forward to discovering more about how Earth works.
On this cruise, Lonny will be in charge of biological sample collection and processing and video data management. This work entails identifying unique biological and geological features that will be seen during the dive, while using MBARI-designed software to log the observations. He is especially excited about this expedition, because no one has surveyed this particular seamount before, and he expects to find many new species on this cruise.
Julie works with the submarine volcanism group, where she currently produces high resolution maps of the seafloor that are used to identify geologic features along submarine ridges and seamounts. Her research interests also include modeling of volcanic ash from sub-aerial, large-scale explosive eruptions.
Ryan's work with the submarine volcanism project primarily focuses on the formation and distribution of volcaniclastic deposits on active and extinct seamounts and mid-ocean ridges. By categorizing the diversity in these deposits with respect to volcanic landforms he hopes to better understand the underlying controls on explosive vs. non-explosive deep marine eruptions. His background research on deep-marine gravity flow deposits preserved in sedimentary-volcanic successions exposed on land lends a comparable platform to study similar deposits of the modern oceans.
Julie is a Research Associate and Staff Scientist with the Institute for Rock Magnetism at the University of Minnesota. As a paleomagnetist, Julie studies variations in Earth's magnetic field and how those variations get recorded in rocks and sediments. One of Julie's particular interests involves using paleofield variations recorded in mid-ocean ridge lava flows to place age constraints on the flows. On this expedition, Julie is interested both in using this technique to try to date some of the young lava flows and in gaining a better understanding of how the Earth's field has varied in this particular location.
Pat is a Professor of Geology at the Scripps Institution of Oceanography, University of California, San Diego. His research interests include petrology and geochemistry of magmas produced within and along divergent and convergent boundaries of tectonic plates, magmatic and tectonic evolution of continental margins and mantle geodynamics. On this expedition, Pat is interested in the petrologic and tectonic evolution of the newly formed oceanic basement in the Gulf of California.
Brian studies the recent magmagenesis and petrology of the Juan de Fuca Ridge. His interest in mid-ocean ridges began during his postdoctoral fellowship with MBARI's submarine volcanism project; there, he utilized uranium-series disequilibria within individual lavas of Axial Seamount to clarify eruption and petrogenetic timescales. At mid-ocean ridge systems globally, Brian is interested in a) how variability in lava morphology, geochemistry, and petrology reflect deeper mantle-melting and magmatic processes and their complex interplay with tectonism and b) improving the chronological framework of the ridge magmatic plumbing systems. Brian received his Ph.D. in Earth and Planetary Science from Washington University in St. Louis in 2007.
Rigoberto Guardado is a teacher and research scientist with the Facultad de Ciencias Marinas (Marine Sciences Faculty) at the University of Baja California in Mexico. As a oceanographer, Rigoberto studies sedimentation processes in the ocean. On this expedition, Rigoberto is interested in learning more about the sediments in this area of the Gulf of California.
Ronald Michael Spelz Madero
Ronald Spelz earned his Ph.D. in earth sciences from Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE) in 2008. His research interests are mainly focused in the structural geology and tectonic geomorphology of fault bounded basins and mountain range-fronts in northern Baja California. He is also part of the multidisciplinary research team studying the origin and effects of the El Mayor-Cucapah 7.2 magnitude earthquake which struck northern Baja in April 4, 2010. Ronald presently works in the Marine Sciences Faculty at the Universidad Autónoma de Baja California.
Hiram Rivera is part of the Coastal Management group and teacher in the Faculty of Marine Science at Universidad Autónoma de Baja California. Since 2008 he has worked as a technician with geographic information systems (GIS) applied to fisheries resource management. From 2010 to now he has worked with his students in public participation geographic information systems (PPGIS) 3D models applied to the use of GIS to broaden public involvement in policymaking. His interest for this cruise is to learn about the techniques associated with digital cartography of the Gulf of California.