Al Trippel – The Geology of Cook County Minnesota: Oceans, Volcanoes, and Glaciers, Oh My!

Al Trippel lives in Grand Marais and Minneapolis-St. Paul, Minnesota. He grew up around rocks in the Midwest and the Western US. From a childhood hobby to a high school job, to a career in mining, and now a passion during retirement (actually it’s “refirement”), rocks continue to awe and inspire. Much of his lapidary and jewelry-making utilizes rocks and minerals found along the way. The Geology of Cook County, Minnesota – Oceans, Volcanoes, and Glaciers, Oh My! Cook County is home to a variety of rock types, some common and some extremely rare on Earth. We will look at where we sit in the regional big picture of the so-called Canadian Shield stable craton. The county straddles two rock terrains: older deep ocean greenstones and granites, and younger volcanic basalt lavas and intrusions of gabbro. Much more recently, 1-2 mile thick continental ice sheets scraped and carved the landscape into what we now see as the Sawtooth Mountains and countless inland lakes and hills. A thin veneer of glacial gravel and sand covers much of the land. Highly unusual rocks and features include: • Gunflint banded iron formation (BIF) early life forms • Sudbury asteroid impact debris layer • Mid-Continental Rift that failed • Hydrothermal (hot springs) Lake Superior Agates and Thompsonite • Glaciers of immense power scraped, sculpted, and bulldozed the landscape topography • Eagle Mountain, other high knobs, and numerous water falls are the tallest in Minnesota • Lake Superior is the largest lake on Earth, and its deepest point is 1000 ft below sea level This presentation will be held at the Chik-Wauk Nature Center. All presentations are family-friendly and free to the public. Donations are always appreciated. Take your time driving up the Gunflint Trail National Scenic Byway! Presentations are sponsored by Visit Cook County and the GTHS Gift Club!