Monday, May 2, 2016

Trails explore Split Rock State Park geology

Split Rock Lighthouse sits atop a massive 1,1-billion-year-old block of rock.
Split Rock’s great scenery would not exist if not for 1.1 billion-year-old lava flows that formed when North America began to separate into two, creating what today is called the Mid-Continent Rift. The rift extends all across the Great Lakes to as far south as Kansas.

In Minnesota, those lava flows along Lake Superior are known as the North Shore Volcanic Group. Occurring over millions of years, the flows can run up to 30,000 feet in the region.

Much of the state park sits atop a single, large block of anorthosite. A buoyant mineral, it floated atop the magma as the rift grew. The mineral is also quite resistant to erosion – so resistant that during the early 1900s the Minnesota Mining and Manufacturing Company (now known as 3M) mistakenly thought the rock there might by corundum, which is used in abrasives.

Fast forward to 10,000 A.D. After eons of being buried by sediment, the great glaciers of the last ice age had scraped off most of the terrain, leaving only the basalt and a thin layer of till over them. Cold Lake Superior is merely what remains of a melted glacier in a low spot of the 1.1 billion-year-old rift, and the rivers along the North Shore are carving through the remaining till and sediment and exposing the underlying basalt.

Some great trails to explore Split Rock’s geology include:
Corundum Mine Trail
Split Rock River Trail
Day Hill Trail
Palisade Head Trail

Learn about trail guidebooks available in the Hittin’ the Trail series.