During today’s remotely operated vehicle (ROV) dive on the southern Alarcón Rise, we came across a series of spectacular structural features, which include fissures, fractures, and fault scarps. These structures, some of them several hundred meters long, and some with vertical offsets of a few meters, represent a very powerful geological tool to reconstruct the tectonic and volcanic history along this important spreading center in the boundary of the Pacific and North American Plates.
Today’s observations showed that in some places the fractures appear to be relatively recent, as evident by the apparent young age of the fractured flows, based on having few sessile (fixed in place) organisms, or relatively thin sediment cover. In contrast, fractures and fault scarps elsewhere were observed to have been partially or totally overrun by lava flows, suggesting their preexistence and relatively older age.
The best way to closely visualize the relative time relationships between rocks and scarps during today’s dive is with the aid of our detailed seafloor map, generated with data collected by our autonomous underwater vehicle (AUV). Analyses of the sediment and rock samples that we collected during this dive, and the dives to come, will help us constrain the time when the features formed. Furthermore, the detailed mapping describing the time and space distribution of these tectonic features will allow us to explore deeper into the history, and perhaps the magnitude, of scarp-forming earthquakes in this area. Today is still only the beginning of an amazing journey and, since we have only visited a relatively small portion of the rift, I’m looking forward to the upcoming dives on the Alarcón Rise.
Today’s dive focused on examining the relationships between older and younger lava flows. Our objective is to better understand the processes controlling how ocean crust is made and how seafloor morphology evolves though time. At oceanic spreading centers, lava erupts in discrete locations along the spreading axis over a several-kilometer-wide zone, called the neo-volcanic zone. It is not uncommon for lavas that erupted over a large range in time, up to several thousands of years, to be in direct contact with each other. We use maps and observations to construct a relative chronological framework. For example, older lava flows at mid-ocean ridges tend to have a higher abundance of fractures than do younger lavas, and we can often resolve many “older/younger” relationships with our high-resolution maps created with the AUV D. Allan B. Adjacent older and younger lava flows are clearly visible along the Alarcon Rise.
To resolve more subtle differences in ages of lava flows, direct visual observation of lava contacts is key, and the MBARI submersible ROV Doc Ricketts allows this more detailed view. This is often sufficient to figure out how the newest crust is generated and evolves, but we would also like to know how fast these processes happen. This requires obtaining absolute ages on at least a few lava flows in order to pin down the relative age relationships.
One method of dating older lava flows involves using push cores to collect sediment deposited on top of the flow. This sediment, which accumulates slowly through time, commonly contains small, carbon-rich fossils, and a radiocarbon date of the fossils at the base of the push core gives a minimum age for the lava flow. We have applied this method on the lavas from the Juan de Fuca Ridge for several years, and this is our initial attempt on the Alarcón Rise. On today’s dive, we collected geological observations and lava and sediment samples from more than a dozen flows.
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.