UNIVERSITY PARK, Pa. — The processes that happen in the first few feet of soil can have large impacts on agriculture and water resources. To better understand these processes, a team of graduating Penn State geoscience majors mapped the subsurface at a research site in Penn State's Stone Valley Forest.

“The critical zone, which extends from the treetops to the groundwater, is important because it controls soil production and groundwater flow, and it’s closely tied with human processes such as agriculture and building,” said Chad Cole, a recent Penn State geosciences graduate. “It’s responsible for sustaining terrestrial life on earth.”

The team set up a 328-foot seismic line with 24 geophones spaced 6.5 feet apart at the Susquehanna Shale Hills Critical Zone Observatory. The observatory is part of a National Science Foundation-funded network established to investigate the processes that occur at Earth’s surface. In between each geophone, the team struck a steel plate with a sledgehammer, creating a seismic wave. The geophones measured the return times of the waves, and the researchers used those times, much like CT scanning, to create an image of the subsurface to a depth of about 45 feet.

“The quicker a wave reaches a geophone, the faster the velocity,” said recent Penn State geosciences graduate Nick Schuler. “At the very top near the surface are slower velocities and then the farther down you go the velocities increase because the rock is more in place and intact, so the waves go faster.”

They also ran another survey with electrodes and a resistivity meter to identify water flow direction in the subsurface. The meter uses electrical currents to measure resistance. Less resistance means more water is present. The project is part of a larger time-lapse resistivity survey to monitor water flow at Shale Hills over a three-month period.

“The critical zone is a major area of research,” Schuler said. “We want to know more about the first couple feet because that’s where humans get their life-sustaining resources: water and food.”

The students said the project provided valuable hands-on field experience and opportunities to solve problems when issues arose in the field.

“I’ve worked in a lot of labs and taken many classes, but this was the first time I actually had to go out in the field and collect data,” Cole said. “It can be really messy, and things go wrong. But it has given me the opportunity to problem solve and think critically about something specific that no one has done before, and I think that’s really interesting and a great opportunity.”

The researchers named Andy Nyblade, professor of geosciences; Dave Yoxtheimer, assistant research professor in the Earth and Environmental Systems Institute at Penn State; and former Penn State postdoctoral scholar Natalie Accardo as important mentors during this project.

“Four years ago, I would never have guessed that I would become as fascinated by geophysics as I am now to go into grad school,” said Schuler, who will continue his studies at Louisiana State University in the fall. “I’m working with a geophysics adviser at LSU all because of this project.”

Before graduating, Cole received a job offer from a civil engineering firm in Emmaus, Pennsylvania, and was also pursuing opportunities with AmeriCorps in Utah and the National Park Service at New River Gorge, West Virginia.

Joseph Grant, a recent Penn State geosciences graduate, also participated in the project.