What do the painted rock and Sigma Alpha Epsilon’s annual Mud Bowl football game have in common?
If you answered that they’re both beloved and messy U-M traditions on Washtenaw Avenue, then you’re right, up to a point. Their shared experience as crude sites for collegiate bonding extends only as far back as the mid-20th century; in a much older distinction, they are enduring remnants of Ann Arbor’s glacial past.
That deep history is easy to overlook amid the towering and fluid urban landscape of the present. From the recent rise of luxury apartment towers downtown, to the frequent opening and shuttering of businesses, our residential and commercial terrain undergoes constant transformations that threaten to obscure or obliterate the underlying landscape.
And yet, despite our cosmetic alterations of the land, much of the topography sculpted during the last ice age is still visible throughout the city. Between 110,000 and 10,000 years ago, toward the end of the Pleistocene Epoch, glaciers undertook their most recent series of advances and retreats across North America. This last and most recent period of glacial activity is known as the Wisconsin Stage (so named for the study of glacial deposits in the state of Wisconsin). The future Michigan then groaned underneath several thousand feet of dense ice, part of the Laurentide Ice Sheet, a continental glacier covering practically all of Canada and much of the upper Midwest.
According to experts, the ice blanketing Ann Arbor originated in Hudson Bay. The glacier was propelled forward by the weight of its frozen tonnage, which caused the bottom layers of ice to flow outward, bulldozing as they went, and picking up everything from grains of sand to boulders. All this power, and still a glacier follows the course of least resistance. The movement of the glacier into and across Michigan, to give an imperfect analogy, was not the uniform lowering of a mini-blind, but the irregular flow of chunky batter into a warped and dented pan. That pan was the Great Lakes region, and those dents and depressions the basins now occupied by Lake Michigan, Saginaw Bay, and the main body of Lake Huron. (Each was originally an ancient river valley, broadened and deepened by earlier glaciers.) The glacier, following these basins, pushed into Michigan in three enormous ice lobes: the Michigan Lobe, the Saginaw Lobe, and the Huron-Erie Lobe. This latter lobe descended from the northeast to cover Ann Arbor, and was responsible for much of our current surface topography.
About 14,000 years ago, as the climate began to warm, the Huron-Erie Lobe stalled over Ann Arbor, its forward movement pretty much equal to its melt. The western edge of the glacier, or ice margin, lay atop the west side of the city. Although the glacier was relatively stationary, the internal movement of the ice proceeded to dump massive quantities of glacial till–unsorted sediment including sand, gravel, silt, and clay–in a ridge known as an end moraine. This process of deposition built the sudden rise along Ann Arbor’s west side. If you’ve ever labored to bike up the incline on westbound Liberty between 7th and Stadium, or if you’ve ever sweated the walk up Spring Street to the northwest tip of Hunt Park, you’ve climbed this moraine, and have an idle glacier to thank for your rock-hard calves. It is formally known as the Fort Wayne Moraine, because it extends all the way to Fort Wayne, Indiana.
Glacial deposition also takes the form of erratics, or large, isolated rocks and boulders dropped by the ice. One notable erratic is the aforementioned painted rock. It did not come to rest at its current location, the corner of Hill and Washtenaw, via glacier, however; it was placed there in 1932 under the direction of city parks superintendent Eli Gallup, who, drawn to the limestone rock’s size and glacial striations, rescued it from a landfill with the hope of sharing it with the public. There are a few other Gallup erratics prominently displayed around town, including one on Huron near First, in honor of town founder John Allen’s settlement. You’ll also find one, spangled with rosy flecks of quartz, in the Bird Hills Nature Area, where steep, scenic trails crisscross the Fort Wayne Moraine.
There are also massive hunks of granite, gneiss, and limestone in the former gravel pit at the Fox Science Preserve near Delhi. Abandoned more than forty years ago, the mine is being recolonized by various plants, mosses, fungi, algae, and lichens. This landscape offers us a possible vision of Ann Arbor as it looked 11,000 years ago, after the scouring retreat of the glacier and the return of living things.
Other gravel mines dot the area, most of them now abandoned. Sepulchers to industry, these pits used to be hills containing deposits of gravel and sand that were mined for local construction. (Gravel from Olson Park and the Fox Science Preserve was used to build I-94.) These hills–known as kames–were created when glacial melt poured heavy sediments like sand and gravel into holes, crevices, and other openings in the ice; lighter sediments such as clay and silt were carried off by the water. Further melting of the glacier eventually dropped the sorted accumulation in heaps on the ground. One kame still stands in the Ruthven Nature Area, at the northeast corner of Huron Parkway and Geddes Rd.
—
Many of Ann Arbor’s low-lying areas are also the result of glacial action and deposition. The flat expanse of central and south Ann Arbor is what’s known as an outwash plain, neatly formed when streams and rivers of glacial melt weave across the land, laying down sediments in sorted deposits according to size. Outwash plains frequently contain depressions, or kettles, such as the one used for the Mud Bowl at the corner of Washtenaw and South University. A kettle forms when a large block of ice calves off a retreating glacier, is partially or wholly buried by deposited sediment, and then melts to leave behind a mold of itself. When kettles contain water, they’re called kettle lakes. Two pretty examples are the First and Second Sister Lakes in the Dolph Nature Area off of Wagner near Jackson Rd. A fishing and observation dock overlooks the First Sister Lake, the smaller of the two; its edges are laced with water lilies, duckweed, cattails, and other vegetation whose growth, according to the City of Ann Arbor’s Natural Area Preservation division, is gradually transforming this kettle lake into a bog.
As for the flowing waters of the Huron River, it originated as a glacial stream that began near the southeastern corner of modern-day Livingston County. The stream’s course changed and reversed over several thousand years, in response to the variable ice margin and the building up of moraines.
As the Huron-Erie Lobe continued its watery withdrawal from Ann Arbor, the weather cooled again, and the lobe’s western edge came to a standstill to the east of Ann Arbor. It laid down unsorted sediment in another ridge known as the Defiance Moraine, which runs parallel to the Fort Wayne Moraine and extends to Defiance, Ohio.
Moraine, kame, outwash plain, kettle, kettle lake: Ann Arbor has them all. Our topographically rich town is part of a larger interlobate region spread across the southern Lower Peninsula. According to MSU geography professor Randall Schaetzl, in his book Michigan Geography & Geology, this interlobate region–“where a sort of glaciological train wreck among the Michigan, Saginaw, and Huron-Erie glacial lobes left a tangled mass of sandy, glacial debris”–is unique among all the Midwestern states. As it turns out, this glacial landscape makes Ann Arbor one diverse and distinctive place–something we’ve recognized all along.
