This article was written by Jeffrey Lu
As winter descends upon us once again, cast a thought to an even colder time when vast forces shaped the landscape. This distant past was the Ice Age. Though it may feel like it has little effect on us in modern times, the Ice Age profoundly changed the lands of Minnesota, dictating how we live today.
The Ice Age is a familiar but poorly understood topic for many people. It was a time period when massive glaciers, up to two and half miles thick (over 16 times as tall as the tallest building in Minneapolis, the IDS Center!), covered much of the Northern Hemisphere, including almost all Minnesota. “The Ice Age” is actually the fifth ice age Earth has experienced and began around two and a half million years ago for reasons geologists are still studying. Proposed explanations include changing ocean currents altered by continental drift and shifts in Earth’s tilt and orbit relative to the sun. The most recent Ice Age was also not uniformly cold but experienced several “interglacial” periods where the planet temporarily warmed up again for several thousand years. The last glacial period ended around 11,000 years ago, and we are currently living in an interglacial.
The Ice Age glaciers’ paths in Minnesota can be seen in the land today and effect where and how we humans live in the state. As the glaciers inched along, they scoured the soil and rock down to the extremely hard bedrock. Consequently, very old volcanic stone normally buried deep underground can be found at the surface in northeastern Minnesota. The granite, greenstone, basalt and gabbro rocks around Lake Superior are dated by geologists to be between 2.7 billion and 600 million years old, predating the oldest known multicellular life. The namesake ore of the Iron Range is only accessible because of the glacier’s scouring of the overlaying rock.
The glaciers were critical to another of Minnesota’s major industries. As the ice melted away 11,000 years ago, it dropped tremendous amounts of silt, sand and clay which became the fertile soil where we farm our crops today. Also left behind were thousands of boulders called “erratics” which now pepper the state. Hills in this rich earth are often glacial landforms like moraines, eskers and drumlins.
The waters of Minnesota where we drink, fish and swim are also creations of the Ice Age. Many of Minnesota’s famous 10,000 lakes and boundless wetlands are depressions scooped out by the glaciers called kettles filled in by water and plant matter. Another particularly dramatic glacial landscape is the Minnesota River Valley which was carved out at the end of the last glaciation when meltwater came blasting through in a tremendous river up to five miles across.
The one part of Minnesota untouched by the glaciers is the Driftless Area near Red Wing, explaining why its geography of valleys, ridges, peaks and spires is unique in the state. Without the coming and going of the ice, Minnesota’s landscape and the lives of the people living on it would be very different today.
If you want to see the footprints of the glaciers for yourself or learn more about Minnesota’s fascinating geology, grab a guide like Minnesota Underfoot by Constance Jefferson Sansome (which was used to help write this article) or Roadside Geology of Minnesota by Richard W. Ojakangas and go exploring! A great place to start is St. Anthony Falls, which were initially formed by the great river which blasted out the Minnesota River Valley.
Sources for this article are the University of Minnesota, the University of Utah, Minnesota Underfoot by Constance Jefferson Sansome, and the Minnesota River Basin Data Center.
Join us for upcoming programs at Kroening Nature Center! Browse and register for all programs at minneapolisparks.org/activities-events/nature-activities or call 612-370-4844.
Highlighted programs this month:
Black to Nature: Science and Beauty of Snow · Sunday December 4, 1-3 p.m. | Free | All Ages | Activity #140336 | Learn how snow forms and what conditions in Minnesota create different types of snow. Hear snow tales from local artists and make your own paper snow crystal to take home.
Mni Memories: Nature and Singing Memory Care · Every Tuesday noon-1:30 p.m., until December 13 | Free | All Ages | Light lunch provided | Activity #140337 | Mni means water in Dakota; Jayanthi Kyle, a local musician, and naturalists are bringing nature and singing together in a joyful and healing environment. This program is for those experiencing memory loss and their caregivers, but all are welcome.
Winter Solstice Celebration · Wednesday, December 21 | $5 / person | All Ages | Two sessions: 5-7 p.m., Activity #129517and 7-9 p.m., Activity #129518|Rejoice the coming of longer days with an evening of celestial fun. Take a nature walk along a glowing luminary trail, then make your own luminary to bring home. Play winter themed games and enjoy the warmth of a bonfire.