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Geology of Lake Superior

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Lake Superior, and the spectacular scenery around it, is the result of a huge geologic structure known as the Midcontinent Rift. This is a 1.1 billion–year–old, 1800-mile-long scar, where tectonic forces tore apart the North American continent in a fashion much like a giant volcanic scissors opening. Many of the rocks around Lake Superior are part of the long belt of igneous, mostly volcanic rocks left by the rift. Despite the rift’s size, it is mostly covered by younger sedimentary rocks. However, basaltic lava flows from the rift can be seen in many places along Minnesota’s north shore, and in Michigan’s Porcupine Mountains Wilderness State Park. The Pictured Rocks National Lakeshore, also in Michigan, contains good examples of the sediments deposited after the volcanic rifting. (Source: National Park Service.)
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Tim Hawkins
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Lake Superior, and the spectacular scenery around it, is the result of a huge geologic structure known as the Midcontinent Rift. This is a 1.1 billion–year–old, 1800-mile-long scar, where tectonic forces tore apart the North American continent in a fashion much like a giant volcanic scissors opening. Many of the rocks around Lake Superior are part of the long belt of igneous, mostly volcanic rocks left by the rift. Despite the rift’s size, it is mostly covered by younger sedimentary rocks. However, basaltic lava flows from the rift can be seen in many places along Minnesota’s north shore, and in Michigan’s Porcupine Mountains Wilderness State Park. The Pictured Rocks National Lakeshore, also in Michigan, contains good examples of the sediments deposited after the volcanic rifting. (Source: National Park Service.)