The remotely operated vehicle (ROV) had a major hydraulic leak, so we rock-crushed all day and had a chance to catch up a bit. It was not too hot and I found myself in a reflective mood.
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. We tease what we can from the mute rocks; our investigations are akin to forensics. You have heard in these cruise logs about what the lava chemistries, eruption styles, and subsequent fracture patterns may mean.
But we also enjoy the beauty of this landscape and marvel at the power of the processes that shaped it. In the birthing of new seafloor, lavas pave the surface with tremendous outpourings of sheet flows and slow pulses of pillows. Their final throes are frozen in place, and their morphologies are a testament to the awesome violence or the resolute insistence of their emplacement. Their residual heat drives fluids that build spectacular hydrothermal chimneys and nourish bacteria and animals, and are hot enough to scorch to black the wooden dowel supporting our temperature sensor.
But over time, the heat in the lava wanes, hydrothermal fluid flow ceases, and the chimneys crumble. The flow features are covered by new flows, or busted up by tectonic fracturing of the plates pulling apart. They are dusted, then buried in the sediment that rains down through the water column year after year. The beautiful lava forms are smothered and lost to time. The crust cools and subsides as it is transported slowly away from the heat of the ridge crest, and the only trace of its having been at a ridge is the magnetic anomaly.
The life of molten lava is brief. The frozen forms remain a bit longer, but over the span of geologic time, they too are ephemeral. Our human time scale intersects with their time scale just here, at the ridge.
In my previous log entry, I talked about the relative age and structural relationships we’ve seen between the fractures and lava flows that we are studying during this leg of the expedition. Today, as our ROV-diving journey progresses along the Alarcón Rise we have continued to discover, and also be amazed by, the extent and pervasive distribution of the faults and fractures which strike sub-parallel to the ridge axis. I cannot help thinking about the fact that these geological features are important, not only because they are an intrinsic geomorphologic component of this dark and yet beautiful landscape, but because these structures accommodate part of the deformation that results as the Pacific and North American tectonic plates diverge and slide past each other in different directions.
The set of fractures located to the north of the Alarcón’s ridge axis lie strictly on the Pacific Plate, whereas the fractures to its south lie on the North American Plate! Therefore, in a general sense, the underwater fractures that we are seeing during this expedition can be viewed as a small portion of the broad tectonic boundary between these two major tectonic plates.
By definition, faults and fractures are brittle structural features capable of producing earthquakes. To find out the size (magnitude) and distribution (location of epicenters) of earthquakes along the Alarcón Rise, the reader is prompted to visit the IRIS seismic monitor webpage. In general, it is widely accepted that earthquakes at mid-ocean ridges, such as the Alarcón Rise, are relatively small (magnitude of less than 4.9) as compared to the medium (magnitudes between five and 7.9) and large (greater than eight) magnitude earthquakes that can be generated along strike-slip and subduction zones, respectively. However, given the relative young age of the seismic networks around the world, and the fact that mid-ocean ridges are mainly located in remote and non-populated areas, I cannot help but wonder about whether or not we could possibly be underestimating the size, and potential damage, of earthquakes that can be generated at these tectonic boundaries. Perhaps the most recent example of how we can be underestimating the potential size of an earthquake, in relation to the type of fault capable of producing it, would be the April 11, 2012 strike-slip earthquake off of Sumatra (8.6 magnitude).
The MBARI 2012 expedition to the Gulf of California will provide a wide community of scientific researchers with valuable information about the biological, geological, and tectonic processes which are presently occurring in a rather inaccessible place such as the Alarcón Rise. The autonomous underwater vehicle (AUV) mapping will provide a powerful tool to map in great detail the length, offset, distribution, and temporal relationships of faults and fractures on the seafloor. This information will bring insight not only into the volcanic history and structural behavior of this mid-ocean ridge, but also into the magnitude of scarp-forming events.
In the meantime, I am thrilled to be able to watch in real time, during our ROV dives, the spectacular geomorphology, vast biology, and astonishing volcanic and tectonic features at the Alarcón Rise.
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.