Yellowstone National Park is a forested wonderland speckled with crystal lakes, thermal features and magnificent geysers. These natural phenomena are a sight to behold, but why are they there and how were they created? Answers to this question lie within the rocks found in the fertile Snake River Plain that sits hundreds of miles to the southwest of the park.
The geography of the Snake River Plain suggests that it was once an active hot spot full of volcanic activity. Scientists believe that a mantle plume, or column of very hot rock that rises up through the Earth’s mantle, sits below the present day yellowstone Caldera, which lies within the boundaries of the national park, and angles back far beneath the Snake River Plain. As the Earth’s crust passes over the hot spot, which is the mantle plume, it is heated to its melting point, resulting in volcanic activity.
As plate tectonics pulled the North American continent westward, a chain of volcanic activity on the Earth’s surface was created, resulting in the Snake River Plain. When these volcanic episodes occur, molten rock spewed from holes and fissures in the crusts hardens in the form of rhyolite, usually a light-colored rock with high silica content. When rhyolite is found, it implies that a hot spot once was there.
Enter John Shervais, USU professor of geology. Since 2005, Shervais has been meeting with a consortium of geologists and geophysicists from around the world called the ICDP, or International Continental Drilling Program, to study the Yellowstone plume and understand the volcanic history of the Snake River Plain. In 2009, the project was funded, and in 2010, Shervais and James Evans, also a USU professor of geology, formed a team of geologists, students and a drilling crew begin their exploration of the lithosphere that lies beneath the Snake River Plain.
“We want to know if there is indeed a hot spot under the Snake River Plain,” said Shervais. “If so, how hot is it, and can we harness that heat for geothermal energy?”
One of the overarching goals of the project is to find the existence of a geothermal source associated with this volcanic system and discover a way to harness that energy. The drilling team of project Hotspot, as it is called, drills around the clock, carving deep into the Earth to bring out core samples that are analyzed to, first and foremost, understand the volcanic history of the Yellowstone-Snake River Plain. The team is also looking to confirm or deny whether the Yellowstone-Snake River Plain. the team is also looking to confirm or deny whether the Yellowstone-Snake River volcanic system results from a deep mantle plume, and if it does, study the nature of that plume.
The drilling started on September 27, 2010, on a site in Kimama, Idaho, which is the first of three separate holes at three separate drilling sites that will be used during the duration of the project. The drilling team is a non-profit consortium called the Direct Observation and Sampling of Earth’s Continental Crust, or DOSECC. The drilling team works in twelve-hour shifts, from midnight to noon and noon to midnight, to keep the drill running and pulling up core non-stop.
When the core samples are pulled by a wireline out of the ground, they are immediately logged by the day, time, hole depth and physical description. Each sample is then packed into boxes and stacked for future analyzing and photographing. So as not to upset the geologic history being discovered by placing a core upside down in the box, one red and one blue vertical line is drawn along the core, with red always on the right.
“This is an unparalleled opportunity for students to be involved in drilling and research,” said Evans. “Nowhere else can they get such an intense, hands-on experience that is directly career related.”
The extracted core samples show geologic layering of various rock types that tell a story of the history of the plain. Classically, in volcanic regions such as this, the rhyolite layers, which erupted first from the volcano, are buried beneath layers of basalt.
“We expected to reach layers of rhyolite around 3,000-4,000 feet in depth,” said Shervais. “Now at 6,275 feet, we are still in basalt, with no signs of rhyolite.”
Rhyolite does exist in the Snake River Plain and can be seen in the Snake River canyon at Twin Falls, Idaho, a mere 200 feet down the canyon wall. Twin Falls sits in between two of the team’s drill sites, which gives encouragement to the search for rhyolite.
Sightings of rhyolite would have secured the idea of a hot spot because it has a higher heat gradient, which means it has been heated to a greater degree at some point. The minerals they have found in the rocks so far suggest that the rocks get “hotter” as the hole gets deeper, but still no rhyolite.
“This just goes to show that we understand a lot less about the Snake River Plain than we thought we did,” said Shervais. “We are on a voyage of exploration now, with greater knowledge as our goal.”
The hole at Kimama is now complete, and the hoped-for rhyolite was never found, but a wealth of information was still gathered from the core samples. The geologists have become explorers of pristine underground terrain and are embarking in new territory with their findings. Their samples and research will be used to create new geophysical models for this area and will be studied by countless researchers for years to come.
The team is now moving to Kimberly, Idaho where they will drill to a target depth of 6,000 feet, with high hopes of finding rhyolite and answers to their questions. The final hole will be drilled at Mountain Home Air Force Base in Idaho this coming May.
“Nowhere else can students get such an intense, hands-on experience that is directly career related.”