Two pontoon sessions were needed to accomodate the number of participants for GLC board member and geologist Daniel Lizzadro-McPherson’s geo-tour at Gratiot Lake.
From the pontoon boat and at the GLC Preserve participants viewed the amazing topography of Gratiot Lake, a 10,000-year-old glacially formed plunge pool carved out of 960-million-year-old Jacobsville sandstone. The lake’s mountain-backed northeastern shoreline marks an important geologic boundary, the Keweenaw Fault. One-billion-year-old lava flows (known as the Portage Lake Volcanics) sitting high above the Gratiot Lake have been thrust up and over the younger Jacobsville sandstone. The Keweenaw Fault is inferred from the sharp change in topography and bedrock.
From the boat, Daniel was able point out the evidence of powerful forces that formed what on that summer day seemed a placid landscape. The group also visited the Gratiot Lake Conservancy land to identify shoreline pebbles and boulders and to picnic at the Noblet Field Station.
Daniel is in the process of mapping this specific segment of the fault as part of his Master’s thesis at Michigan Tech. He has done work on Keweenaw GeoHeritage, fieldwork on the Keweenaw fault to enhance the USGS EdMAP, and is a GIS analyst at Michigan Tech’s Great Lakes Research Center.
Part of the tour was put on YouTube by participant Robin Mueller and can be viewed at