We definitely saved the best, or strangest, for last today. After much discussion and hashing out dive plans over and over we chose to go back to the silica-rich volcanic unit in the northern part of the ridge axis. What caused us to make this change? Detailed examination of a small sample of ash (glassy volcanic sand) we collected three days ago revealed an abundance of frothy, bubble-rich grains, some having exotic chunks embedded within them. All in all, this sample contained a huge variety of particles that really got us excited, in light of the fact that this type of material is rarely, if ever, described from mid-ocean ridges.
Mid-ocean ridges are dominated by silica-poor rocks, namely basalt. The silica-rich rocks that have been described from mid-ocean ridges are typically found in deep drill holes or in rare uplifted portions of the lower oceanic crust. They generally form way below the ocean seafloor as the final “crud” left over after all the silica-poor rocks have been formed, and do not get to erupt to form volcanic rocks. In addition to high silica contents, silicic volcanic rocks commonly have high gas contents, which cause the largest and most dangerous eruptions on land. So we thought it would be a good idea to get back to the silicic volcanic unit on Alarcón Rise and sample it in detail to better understand how these strange rocks and ash deposits form along mid-ocean ridges.
Although we had a very detailed one-meter resolution map of the area we dove on today, the extremely rugged nature of the silicic-complex proved to be very challenging to navigate through. The remotely operated vehicle flew a very sinuous course to cover the area in detail, going up and down very steep valleys, across knife-like ridges, and around the headwalls of bowl-shaped features. To give you an idea, our mapping autonomous underwater vehicle (AUV) crashed two times in this area trying to get through it, despite only crashing once before on many, many dives. One area on the map where the AUV crashed left a big, blank gap in the data. We traversed this “data-hole of no return” to find a vertical wall tens of meters high. Our very skilled ROV pilot team was continually checking our position relative to the boat to make sure our tether did not drag over the top of these vertical scarps. It would be analogous to climbing and navigating through a glaciated high alpine terrain in a snow storm with a flashlight and having your partner attached to you on a rope.
Our extensive sample collection that we gathered during the dive confirmed our suspicions that this complex was indeed silicic. Time will tell when the rocks are analyzed in the lab. Much work is yet to be done on these very interesting and rare rocks. How do they form deep below the surface? How explosive were their eruptions? What style of particle dispersal did they have? You would not want to have been there when this place was active. Boulders and blocks the size of cars and small houses were not uncommon. The slopes were littered with gravelly debris that would have been deposited via large avalanche-like deposits. A few ridges were composed of very strange, steeply dipping, lineated flows very different from the pillow-style morphology of deep-sea basalt. An enormous amount of gas would also have been released, evidenced by the bubbly nature of most particles.
All the excitement about this incredible place had our punk-rock-crushing wax head going bonkers!
Some of the previous log entries mention young/ old relationships, so today I’m going to explain how we determine this relationship using what we call relative dating.
To get familiar with relative dating I’m going to use an example; If we ask an average person what he did yesterday, and we ask this person to tell us the activities in a random order, maybe he will come up with a list like this one: dinner, breakfast, run, television, restaurant, wake up early, come home, take a shower, work, going to sleep and work again. These words really don’t make any sense. But, if we ask this person to tell us exactly what he did from the moment he woke until the moment he went to sleep, maybe he will tell the next story: Woke early in the morning and went running then went back home to have breakfast; after that I showered and went to work, had lunch in a restaurant, and went back to work; after work I went back home and had dinner; after that, I watched television and then went to sleep. Now, this history really makes sense and this person actually is making a relative dating, he is putting the activities that he did during the day in chronological order.
The people who study earth history do the same thing to know the order in which geological events or processes took place. So now let’s make a geological relative dating! Suppose that someone asks us to do a relative dating of the events that form the features observed in Figure 1.
We are going to start by saying that the first thing (event) that happened was the deposition of strata A to E, with strata A the oldest (first to deposit) and E the youngest (latest strata deposited, Figure 2).
Then an earthquake took place and displaced the strata along a fault in a vertical way as shown in Figure 3.
We can make a list of events that led to the appearance of the block shown in Figure 1:
So this is what relative dating is all about. In this way we can get answers to questions like: When did the fault actually take place? The answer will be, after strata E was deposited. How old is the fault? And the answer will be, older than the age of strata E because the fault is displacing all the strata including E, so this strata must have been deposited before the fault took place. See how important relative dating is when it comes to putting in order geological events or processes that help us to understand earth history?
Now that you know how to establish the young/old relationships with relative dating, you must be wondering if you can actually put an age on these events. That would be neat, yes?
Geologists also work to put an age on these events, so we will know when things happened. It is called absolute or radiometric dating. This technique of dating is based on the use of radioactive isotopes. When minerals form, some of the atoms that end up in the rock are radioactive. Many can be used as a clock that can tell us the approximate age of the rock.
Imagine buying a watch; when you put in the battery the clock starts ticking and begins measuring time, and when the battery life is finished the watch will stop. Suppose that the battery only lasts 12 hours, and we put the battery in the watch at 12:00 noon. In the afternoon of the same day we want to know the time, so we look at our watch and it reads 6:00 p.m. Another way to find out what time it is to take the battery out and measure the amount of charge it still has; if it has half the charge then, we know that is 6:00 p.m. because we put in the battery fully charged at 12:00 noon (and remember that the battery has a life of 12 hours) and now it is only 50 percent charged, so six hours must have passed. The radioactive isotopes contained in minerals work the same way; they start "ticking" when the lava solidifies and forms a rock. In our relative dating example, if we are lucky enough to have rocks in each strata containing radioactive isotopes, we can date these rocks and actually assign an age to each strata. Then we can know how things happened (relative dating) and when it happened (radiometric dating). This is exactly what the scientists aboard the Western Flyer are trying to do in order to figure out the volcanic history of the Alarcón Ridge.
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.