EMU Today

YPSILANTI — Eastern Michigan University associate professor of geography and geology Eric Portenga has contributed to scientific studies in Earth’s topography for the past 15 years. Portenga recently gathered data and collaborated with other researchers to discover the history of the Laurentide Ice Sheet in Isle Royale National Park. Their study can help scientists understand the relationships between climate change, ice on Earth, sea-level rise, and the strength of ocean currents. 

In 2018, Portenga, associate professor of geoscience at Northland College David Ullman, and EMU alumnus Stephen Ogden spent three days on Isle Royale looking for rocks left behind after the ice sheet melted, also known as glacial erratics. After hiking Mt. Desor, they discovered 11 suitable rocks to collect samples from. A rare form of the element, beryllium, was extracted from each sample at the University of Vermont Community Cosmogenic Facility, and the amounts of beryllium were measured at the Purdue Rare Isotope Measurement (PRIME) laboratory. Portenga and his colleagues used these data to determine when each erratic was exposed under melting ice.

“In our study, we interpret the average exposure age of erratics on Isle Royale to suggest that the Laurentide Ice Sheet was still covering parts of the island until about 10.1 thousand years ago, which is hundreds of years later than previous studies thought,” said Portenga. “We hope these findings can help scientists learn more about the routes taken by meltwater from the ice sheet through the Great Lakes to reach the oceans.”

After discovering these findings, Portenga and his colleagues published their work in Geochronology. This international open-access journal highlights the research EMU faculty and students achieve and allows people everywhere to read his work. 

Portenga was born and raised in West Michigan, so his interests lie in the state’s landscapes. After joining EMU faculty in 2017, he got to work researching Isle Royale and securing an EMU Faculty Research Fellowship, which provided funds for travel. In March 2022, after receiving the beryllium data from PRIME Lab, he ran an independent study for Earth science majors to focus the study's narrative. He also incorporates his data into geomorphology courses and hopes these findings will inspire his students to become interested in the natural world.

“As a born-and-raised Michigander, I am excited that our research will be out there because it shows that new information can be gleaned from an otherwise small, isolated dataset. I hope it will lead to more glacial work for myself and my students in the Great Lakes region,” said Portenga.

Currently, Portenga is wrapping up a multi-year project on erosion in the Santa Monica Mountains in California caused by the 2018 Woolsey Fire, funded by the National Science Foundation. He also continues his interest in glacial landscapes by mentoring a professional geology major on research to develop a framework to estimate the ages of undated glacial landforms in the Great Lakes.

Visit the website to read Portenga’s complete publication, Early Holocene ice retreat from Isle Royale in the Laurentian Great Lakes constrained with 10Be exposure-age dating, featured in Geochronology. Visit the webpage to learn more about EMU’s geography and geology program.

About Eastern Michigan University
Founded in 1849, Eastern is the second oldest public university in Michigan. It currently serves more than 14,000 students pursuing undergraduate, graduate, specialist, doctoral and certificate degrees in the arts, sciences and professions. In all, more than 300 majors, minors and concentrations are delivered through the University's Colleges of Arts and Sciences; Business; Education; Engineering and Technology; Health and Human Services; and its graduate school. National publications regularly recognize EMU for its excellence, diversity, and commitment to applied education. Visit the University’s rankings and points of pride websites to learn more. For more information about Eastern Michigan University, visit the University's website. To stay up to date on University news, activities and announcements, visit EMU Today.