A billion years ago, the Upper Midwest once teemed with fiery geologic activity. Visitors can retrace the results of this billion-year-old story via cascading waterfalls, red sandstone sea caves, and towering cliffs
was formed. . The rift largely produced flows of basalt, runny lava that formed low-lying shield volcanoes. “You’d have fissures, these big long cracks,” Stewart says. “They might have been kilometers long with this runny basalt lava coming out of them.”
A cyclist takes in the scenery at Michigan’s Porcupine Mountains Wilderness State Park. Travelers can find traces of the Midcontinent Rift along the steep-sloped ridges running parallel to Lake Superior’s shore.Please be respectful of copyright. Unauthorized use is prohibited.—the lava didn’t make it far. “The Lake Superior area is a very unusual case,” says Tyrone Rooney, professor of igneous petrology and geochemistry at Michigan State University.
Regardless of the reasons why, over roughly 30 million years, the Midcontinent Rift produced more than 240,000 cubic miles of volcanic rock—44 times the volume of all the Great Lakes combined. “Below Lake Superior, it’s insane,” says George Hudak. The senior geologist at the describes how tens of kilometers of sedimentary rocks piled into the rift as it opened up, covering a molten, volcanic sea. “This was one of the biggest magmatic events to ever occur on Earth,” he says.
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