By John M. Zawiskie, Geologist and Museum Educator, Cranbrook Institute of Science

Paleogeography during the time of the formation of the Birmingham Moraine ~13,800 years ago showing the position of ice lobes and early glacial Lake Maumee.

Have you ever wondered how Rochester Hills formed or where all of the strange surface rocks came from? How old is the Clinton River and how did the thick sandy bluffs that line its river valley get there? The local story is more incredible than any science fiction tale. It involves the most recent remarkable global swing in the Earth’s climate system, an ice age.

For the last two million years our planet has been in an ice age, typified by two steady climate states that mysteriously shift back and forth to the rhythm of slow, recurring and predictable changes in Earth’s orbit. During glacial periods the earth cools and giant continental ice sheets, two to three miles thick, expand and flow from high northern latitudes to engulf large areas of North America and Eurasia. The frigid glacial climate commonly lasts 100,000 years. These glacial periods are rapidly punctuated by geologically brief 10,000 to15,000 year warm interglacial periods, that cause the ice to melt and allow the biota to return. We’re currently about 10,000 years into a warm interglacial period.

During the most recent glacial episode massive glaciers flowed over Michigan, further widening preexisting river valleys into the Great Lakes basins. By 20,000 years ago the ice front reached as far south as Cincinnati before finally staring to melt.

Rapid global warming enhanced the melting and approximately 14,500 years ago a seam between two massive lobes of the ice sheet opened up in Oakland County, finally exposing the frozen land surface. Rochester and Auburn Hills formed along the southeastern edge of the seam in front of the Huron-Erie ice lobe as it melted back across the southeastern portion of the county. These hills are glacial landforms called moraines. A moraine develops when the ice temporarily stabilizes during its recession, depositing low-lying hills of haphazardly sorted sediments, containing exotic rocks of all sizes and types. This ice deposited sediment is called till.

Many of the rocks in the till of Rochester Hills were transported by ice from the ancient Ontario bedrock north of Lake Huron. They range in age from one to three billion years old and provide evidence for the former presence of extensive volcanism and Himalayan-sized mountains in the Great Lakes region.

The northeast to southwest oriented belt of moraines in the area between the Clinton River in Rochester Hills and Pontiac to the northwest are called the Fort Wayne and Defiance Moraines. They extend all the way to Fort Wayne, Indiana and Defiance, Ohio, respectively, before wrapping east around the southern margin of Lake Erie. These hills outline the former edges of the giant ice lobes.

The next moraine southeast of the Clinton River runs from the western part of Rochester to Birmingham. It formed in front of the ice sheet 13,800 years ago and is called the Birmingham Moraine. To the south and southeast of the Birmingham moraine, as the glacier continued to recede, a series of glacial lakes formed in front of the ice creating a flat muddy lake plain with old sandy beach ridges. This nearly flat gently sloping lake plain characterizes the southeastern portion of Oakland County and extends across Wayne County to the Detroit River.

The early stages of the present river systems of southeast Michigan also evolved during the glacial and glacial lake history before attaining the modern drainage pattern. James William Bay worked out this fascinating story in 1938. Initially, melt-water from the glaciers formed huge networks of braided streams that carried sand and gravel away from the glaciers and moraines into the central seam between the ice lobes. This sediment is referred to as glacial outwash and the vast plains of well-sorted sand and gravel in the center of Oakland County formed in this setting.

As the ice receded to the southeast rivers began to break through the moraines, but were always forced to flow to the southwest by the ice front. When the ice retreated from the position of the Defiance Moraine, around 14,000 years ago, the ancestral Clinton River cut across it, separating it from the Rouge drainage. However, the river was still forced to flow to the southwest by the ice front during the time of formation of the Birmingham Moraine. During this period the drainage from Stony and Paint Creek also flowed to the southwest after they joined the ancestral Clinton River.

When the ice melted back from the site of the Birmingham Moraine the Clinton River was no longer forced to the southwest and flowed to the northeast cutting cross the moraine and eventually across the southeasterly sloping glacial lake plain.

The base level of the river was affected by oscillating glacial lake levels until around 11,000 years ago. This accounts for some of the unusual widening and terraces along the river valley. The sandy bluffs along the northeasterly flowing portion of the Clinton River leading to Rochester are the 13,800 year old glacial melt-water stream deposits. My recent examination of the stratification in these sands with my colleague Nina Misuraca, an Oakland County environmental planner studying the potential for a public trail in this area, confirms that the sand was transported to the southwest exactly opposite the northeasterly flow direction of the modern river!

Tundra developed in the wake of the melting ice followed by cold boreal spruce forests with open meadows and swamps. Many large animals like mammoths, mastodons and black-bear sized beavers populated this habitat until they became extinct between 11,000 and 10,000 years ago. Paleo-Indians also entered this region by around 11,000 years ago.

So the next time you’re stuck in traffic just remember what a special place you’re at. The ordinary little Rochester Hills and the Clinton River are not so ordinary afterall. They’re children of the ice age!