2015 Geodynamics Program: Geologic Study Tour To The Greater Yellowstone Geoecosystem
June 25 - July 3, 2015
This year’s study tour highlighted various stages in the evolution of the Snake River Plain–Yellowstone Plateau bimodal volcanic province, and associated faulting and uplift, also known as the track of the Yellowstone hotspot. The 17-Ma Yellowstone hotspot track is one of the few places on Earth where time-transgressive processes on continental crust can be observed in the volcanic and tectonic (faulting and uplift) record at the rate and direction predicted by plate motion. Recent interest in young and possible renewed volcanism at Yellowstone along with new discoveries and synthesis of previous studies, i.e., tomographic, deformation, bathymetric, and seismic surveys, provide a framework of evidence of plate motion over a mantle plume.
The trip was organized to present an overview into volcanism and tectonism in this dynamically active region. Visits included a tour of the Cretaceous copper and Mo porphyry mines at Butte, MT, the young (2000-15,000-year old) basaltic Craters of the Moon volcanic field, exposures of 12–4 Ma rhyolites and edges of their associated collapsed calderas on the Snake River Plain, and exposures of faults which show an age progression similar to the volcanic fields. The geology of both Grand Teton and Yellowstone National Parks is profoundly affected by processes associated with the Yellowstone hot spot track. The Parks are located in the youngest parts of the Snake River Plain-Yellowstone Plateau, a time- and spatial-transgressive volcanic-tectonic province which has developed over the last 17 Ma in response to the southwest movement of the North American plate over a fixed melting anomaly. The track of the Yellowstone hot spot is represented by a systematic northeast-trending linear belt of silicic, caldera-forming volcanism that arrived at Yellowstone around 2 Ma, was near American Falls, Idaho about 10 Ma, and started about 17 Ma near the Oregon-Nevada-Idaho border. Uplift and faulting have migrated to the northeast in advance of volcanism; this pattern of volcanism, faulting, and uplift along the Snake River Plain-Yellowstone Plateau province now defines the 750-km-long Yellowstone hotspot track (Pierce and Morgan, 1992, 2009).
Pre-generals students are required to carry out a research project related to this year’s theme - preferably something outside their current field of research. They will be required to write this work up in an 8-10 page report, due at our last class meeting. In addition, they will give a 12-15 minute oral presentation at the end of the course, reporting the results of their findings.
Some project ideas have been solicited from seminar quest speakers, WHOI staff and falculty and posted below. Students can also come up with their own project idea. Please notify this year's science organizers of your project topic.
Thermo-mechanical behavior of fountaining geysers
Supervision: Rob Sohn, Geology and Geophysics
In the first lecture I laid out a thermo-mechanical framework for understanding the behavior of fountaining geysers. Eruptions occur when rapid depressurization of a bubble trap triggers an instability wherein the volume flux of vapor generated in the trap exceeds the volume flux of liquid discharged from the eruption conduit. A key, unresolved aspect of this problem concerns the energy balance that governs the evolution of this instability and the meta-stable condition associated with steady, fountaining behavior. For this project, the student will work with me to solve this energy balance, and apply the model to data acquired from the Lone Star and Old Faithful geysers in Yellowstone National Park. The system energy is partitioned into internal components and dynamic components associated with flow. The project will involve some background reading to familiarize oneself with two-phase flow, formally stating the energy conservation equation(s), using correlations found in the literature to estimate the individual terms in the equation(s), and then using data from Lone Star and Old Faithful to constrain the sub-surface conditions at these geysers. Most of the work can be done with pen and paper, but familiarity with Matlab will be helpful for applying the model to the geyser data.
- Ultrasonic measurement of flow-induced microcracking
Supervision: Rob Sohn, Geology and GeophysicsHydrothermal fluids interact extensively with the host rock matrix, and some of these interactions fracture the rock. Serpentinization of peridotite is an important example of this phenomenon. Serpentinite outcrops typically exhibit high-levels of fracturing and veining, and laboratory experiments have shown that the volume change associated with serpentinization opens microfractures in peridotite samples. I am presently working with Frieder Klein (WHOI, MCG) to develop an experimental apparatus capable of measuring acoustic emissions from microfracturing events that occur during laboratory serpentinization experiments. The crux of the project is integrating an ultrasonic hydrophone into the high-pressure/high-temperature serpentinization rig in Jeff Seewald’s lab. Ultrasonic sensors are required to capture acoustic emissions from very small microfracturing events, and we have recently purchased a novel sensor that utilizes an optical fiber to make the necessary type of high-resolution acoustic measurements. This project will involve testing and calibrating the fiber-optic ultrasonic sensor, and, time permitting, integrating the sensor into the experimental rig. Some background reading on ultrasonic sensors will be required, but most of this project will be spent in the lab working with the sensor. As such, the student will be required to work with an oscilloscope/function generator and other electronic equipment, and will be expected to calibrate the optical-fiber sensor response over the frequency range of interest (~100 kHz – 50 MHz). Some experience with laboratory equipment will be very helpful.
- Analysis of seismic records from flow-induced microcracking at the Rainbow hydrothermal fieldSupervision: Rob Sohn, Geology and GeophysicsHydrothermal fluids interact extensively with the host rock matrix, and some of these interactions fracture the rock. Serpentinization of peridotite is an important example of this phenomenon. Serpentinite outcrops typically exhibit high-levels of fracturing and veining, and laboratory experiments have shown that the volume change associated with serpentinization opens microfractures in peridotite samples. However, microearthquakes from serpentinization have never been observed in the field. I recently deployed a network of six ocean bottom seismometers in a tight cluster around the Rainbow hydrothermal field, where high-temperature fluids with compositions indicating reaction with peridotite (high H and CH4 concentrations) discharge from an ultramafic outcrop. Preliminary analyses indicate that these instruments detected ubiquitous levels of very small seismic events with waveforms that are consistent with volume change, instead of shear displacement, source mechanisms. Thus, these records may well contain the first field observations of serpentinization-induced cracking. This project will involve analyzing these seismic records to generate a complete catalogue of event detections, and, time permitting, localization of the fracturing events in the subsurface. The project will involve use of Antelope seismic analysis software, Matlab, and Unix scripting (i.e., Python, perl, etc.), and thus will be computer intensive with an emphasis on signal processing.
- Human Induced SeismicitySupervision: Jeff McGuire, Geology and Geophysics
Earthquakes are now being routinely induced across the entire U.S. as a result of various energy industry activities. One of the clearest examples of human induced seismicity is the Salton Sea Geothermal field in California which is of particular concern because of its proximity to the San Andreas fault. Recent studies have claimed that the probability of a damaging M8 earthquake in southern California is significantly increased by the geothermal plants based on statistical models but the physical mechanism connecting the geothermal wells with the plate boundary fault is complicated. The project would involve using seismology to detect changes in fault properties as a result of geothermal pumping.