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Field goals

An intensive joint field school gives geosciences students hands-on application of field data acquisition and interpretation methods.

By Graham Chandler

Early in the afternoon of Friday the 13th of May this year, undergraduate and graduate university students from Imperial College London and Colorado School of Mines, along with their staff and faculty loaded up trucks and vans at the Colorado School of Mines to get an early Saturday morning start to a month-long geosciences learning adventure. After an overnight stopover, by Sunday they were at Neal Hot Springs in Vale, Oregon. There they met up with their counterparts from Boise State University, who had already set up tents and were ready for the field. The BSU students had been asked to bring along sturdy outdoor gear, from rain suits and hiking boots to good gloves and day packs.

For the first three days, the students learned the local geology and hydrology—stratigraphy, structural overview, and groundwater flow and fracture patterns. Then on Thursday the practical side started: laying out lines and learning safety in anticipation of the massive Veritas vibrator trucks arriving. Friday and through the weekend they practiced surveying, gravity & magnetics, deep EM, deep seismic, DC resistance, hammer seismic, vertical seismic profiling, even audio-magnetic tellurics and marine-streamer seismics. On the seventh hectic day the vibrator trucks left and the students pulled together a summary of the field methods and data they acquired. By Thursday the 26th the camp was left spotless and the tired bunch had packed for the trip home. 

They were back in time to enjoy the Memorial Day weekend—if they could spare the time for that. The fresh-air activities were over but there was now the job of reducing the data and interpreting it to tell the story of all that geology. There was a lot more work to do before grades could be handed out. Ten days after Memorial Day, the full final report was due for presentation.

The annual geophysical field camp is co-hosted by Boise State University, Colorado School of Mines and Imperial College London, and is sponsored by the Department of Energy and the Society of Exploration Geophysicists. It’s a 4-credit course called GEOPH486 and a requirement for the undergraduate geophysics degree. The syllabus involves everything from vibroseismic imaging for basement structure, to near-surface characterization for a better understanding of the geology and geothermal resources. The 4-week program is split roughly equally between field work and data processing/interpretation.

“Students go on a three-day geology investigation to start the camp, forming hypotheses on the subsurface structure based on surface observations,” explains Kasper van Wijk, Assistant Professor in Boise State’s Department of Geosciences who heads up the field school with his colleague Lee Liberty. “They then design, with their faculty, geophysical investigations to test these hypotheses.”

Dr. van Wijk currently serves as the Program Coordinator of graduate studies in geophysics at Boise State University. So he’s well-versed in all the methods the students came to practice in this spectacular slice of Oregon.

He explains the camp’s uniqueness. “What makes this geophysics camp special is the link between research and education,” he says. “Unlike most other geophysics camps—and there are only a few that I know of—we move around for our field camp targets. It has been a tectonic target, a drinking-water target, and for the last few years it has been a geothermal target.”

What’s equally unique is that Vale was chosen largely because its complicated geological structure presents a real challenge for students. In addition, it is the location of active developments for geothermal power generation by US Geothermal. Here, students will encounter more variation in one place than most other parts of the world.

This area of eastern Oregon is highly arid and sits in a setting of complex and intersecting fault trends. It’s described as a succession of basin fill sediments and intercalated lava flows repeatedly broken by episodes of basin formation and extensional faulting. This subsidence and deformational history has resulted in a complex map pattern of intersecting faults and fault blocks comprised of inter-layered sedimentary rocks and lava flows. Within this realm, the most recent faulting appears to have defined a down-faulted half-graben with a basin fill of Late Miocene lacustrine strata faulted against a heavily silicified and brecciated NW-SE striking normal fault. This fault zone is deeply dissected by two local creeks: Cottonwood and Bully. Where the commingled streams cross the fault, defining the lowest exposure in the area, there is a surface hot spring with temperatures near the boiling point. Extensive surface alteration and silicification suggest the hydrothermal system has been in place for a long time, perhaps millions of years.

The coincidence of the large catchment with ample water and the deep seated fault with its brecciated and permeable character provide a logical set of parameters that may serve to localize the hydrothermal system there today. It’s no surprise that it is under active consideration and study for commercial geothermal power generation.

So it’s easy to see the challenge for the students to interpret their newly-acquired data. Their geophysical investigations are based on the hypothesis that cold meteoric waters arriving by regional drainage are saturating the fault zones in the area and that once waters have descended to depths of 1000 to 1500 meters, they will heat to almost boiling and rise through convection and emerge as hot springs.

“The current project is a real challenge, because often geothermal targets go hand in hand with complex and beaten-up geology,” summarizes van Wijk. “Geophysical characterization is complicated by large amounts of heterogeneity: an inherent mix of sedimentary and volcanics.”

Assistance with the field data reduction and interpretation came from Jonathan Glen of the United States Geological Service (USGS). “[He] graciously agreed to help us learn how Oasis montaj could be used as a tool in potential field applications,” says Clinton Colwell, one of the few master’s level students who came along with the undergrad seniors to learn.

Copies of the software were provided under the Geosoft Education Program. “As a tool for teaching, Oasis montaj is very powerful,” says Colwell. “The georeferencing (shadow cursor tool) feature is invaluable for identifying magnetic and gravity field responses to the different mapped geologic units. It is amazing to pan along a gridded magnetic survey and see that the magnetic gradients do in fact lie directly above magnetic contacts.”

Many of the rock units in the Vale area are strongly magnetic volcanic rocks, so are easily mapped with ground based magnetic surveys. However, gravity data are not tightly spaced enough to resolve individual rock units, says Colwell. “But the same georeferencing tool allows for large scale mapped structures to be tested immediately. To me this feature is incredibly useful for teaching purposes because it allows visual first order analysis to happen almost instantly. As for it being a good tool to use within my career, I think the fact that respected scientists from all around use Oasis montaj as a main program in their geophysical research speaks for itself.” He reckons they wouldn’t use it if it didn’t work well.

Students say the camp was a good blend of fun and learning, says Colwell. “I think the field camp has been very fun and useful,” he says. “I enjoyed the field work portion of the camp, and I have enjoyed the processing and interpretation side of the camp also. I believe that many of the students at the camp have some geophysical data acquisition experience, but I doubt that any of us students had experienced all of these different methods. I know I had not.”

Colwell adds that the camp was valuable for learning how to work with others, including other nationalities—important for budding geoscientists expecting to work worldwide. “Since I am a new BSU student, I did not know anyone when I first showed up to camp,” he says. “There were three different schools, and I think thirteen different nationalities present so I met many different people and needed to productively work with all of them. This is an important lesson which was completely unrelated to geophysics.”

After the intensive data processing and interpretation phase, students wrapped up the course with the grand finale: a solid two-hour presentation at the Boise State campus on Friday June 20th which was followed by a pizza lunch hosted by the geosciences department. It attracted a good turnout, from the geosciences department, US Geothermal and several parties interested in geothermal and renewables. “It was a team effort,” says van Wijk. “And I am very proud of the end result.”

And from the students, too: “I don't think I will have another learning experience quite like this again,” says an enthusiastic Colwell. “I surely haven’t up until this point.”