|GLACIAL LANDFORMS IN MICHIGAN (AN OVERVIEW)
Landforms--the mountains, hills, valleys, plains, and coastlines--are the foundation on which the modern state of Michigan was created. Glacial landforms dominate the surface of the whole state except the western half of the Upper Peninsula, where eroded remnants of some of the oldest mountains on earth are found.
The landforms of Michigan are largely a result of the activities of the extensive glaciers of the Pleistocene period (from about 2 million years ago until 10,000 years ago). There were several stages of ice advance and retreat. The entire Pleistocene period covered about 2 million years, but it was the most recent ice advances during the Wisconsin stage that, by and large, sculptured the current Michigan landscape. As the ice moved south, it leveled off the existing hills, filled in valleys, blocked the drainage of the rivers, gouged out major basins such as those now filled by the Great Lakes, and in general, changed the existing surface by grinding, eroding, leveling, and depositing.
Several stages of the continental glaciation affected the state, but the most important was the most recent Wisconsin stage, which retreated from Michigan about 9,500 to 15,000 years ago. Todays water, landforms, and soil characteristics and patterns are related to the nature and results of the glacial processes.
Glacial ice is a semi-plastic medium that is capable of deforming and "flowing" under gravity and pressure. When thick accumulations of snow are compacted under great pressure, ice forms. This ice can flow like a plastic, or break like a solid. Although ice is soft, it is capable of eroding soil and hard rock, because it picks up rocks and uses them as "tools".
Largely responsible for our topography, landforms, and our conglomeration of soils were the glaciers which covered Michigan. Six major landform types emerged from the maelstrom of forces that were operative in our state during recent geologic time: moraines, till plains, outwash plains, lake clay plains, lake sand plains, and rock outcrop areas with little or no glacial drift upon their surfaces.
When the glacier melted from North America it left a mass of "heterogeneous" rock debris (loosely termed "glacial drift") over the area it had covered. Of all the glacial landforms, moraines best tell the tale of the retreat of the ice from the surface of Michigan. They mark the lines of halt and with their accompanying till plains, the lines of retreat. They reveal the halting retreats and slight readvances of the glacier; they show us where the ice held its position for thousands of years. Each glacial lobe built up its own set of moraines which can be mapped and more or less definitely set apart one from the other, and as mappable units have been given names of localities prominent on them.
What is a moraine? When the ice front halted, that is, when the glacier could push forward no faster than the ice melted or backward melting equaled forward push, the melting ice dumped its load of rock waste which was added to by the forward-moving ice. Thus a ridge of hummocky hills made of all kinds and sizes of unsorted rocks and ground-up rock debris was piled high along the ice front at every succeeding "halt". Thick ice with a heavy load of drift built higher moraines, cleaner and thinner ice built low, smoother moraines. Occasionally, and in places, melting ceased and the glacier again advanced over or onto its own entrenching ridge, pushed it higher, added more rock debris to it mass. The great ridge of hummocky hills extending from Illinois to Long Island marks the most southerly position of the ice sheet and is known as the glaciers terminal moraine.
So, in summary, glacial end moraines are belts of rolling or rugged hills with intervening swales, swamps and lakes that enhance the beauty of the countryside. Morainic soils, however, consist of materials ranging from boulders to fine clay and silts, with all possible gradations of rock derivatives from coarse gravel to fine sand intervening between the two extremes. Our morainic areas contain much good soil and much that is either too poor or too steep for cultivated crops.
Till plains, or ground moraine, are gently undulating lands. They are generally fertile, with soils that are predominately clay loams and sandy loams, capable of supporting diversified agriculture indefinitely, provided they are handled properly.
Frequently during meltback, blocks of ice broken from the ice front were buried in glacial debris and did not melt until long after the ice had passed. On final melting they left deep, steep-sided depressions, some of which later became filled with water. Such depressions are named "kettles". Such kettles, as well as the depressions caused by unequal bulk of deposited morainic material, account for the hundreds of lake basins we now find in the state. Not all the basins currently have lakes in them, for thousands have been drained in the past 10,000 years; many kettle lakes are drying up now or their water levels lowered in times of decreased rainfall.
Outwash plains occupy extensive areas in northern Michigan and constitute the poorest soils, with the exception of exposed or almost barren rock. The sandy hardwood and jack pine plains of the northern half of the Lower Peninsula are typical. These have been the problem lands of Michigan. Forty to 50 years ago large scale attempts were made to clear and farm these lands, but the thin forest humus overlying infertile sand was soon exhausted and thousands of hopeful pioneer farmers starved out and their lands reverted. Ownership records indicate that some of these farms went through the tax reversion wringer two or three times before they finally came to rest in public ownership.
The lake (lacustrine) plains, which are typical of Saginaw, Huron, Monroe and other counties bordering lakes Huron and Erie, comprise our richest agricultural lands, but they require drainage and careful handling. Sandy areas on the lake plains, with dune lands and ancient beach ridges, are of low fertility and often wet. Like the outwash plains, they help supply our need for wood and vast areas of wildlife habitat.
The rock outcrop areas of Michigan are most prominent in the Upper Peninsula. There are two types of landforms in this category: the rugged hills and mountains found in the western half of the peninsula, and flat limestone and sandstone outcrops, typical of Drummond Island and certain sections of the eastern half of the peninsula. The rocks are frequently covered with a thin layer of glacial drift and humus that is capable of supporting a vigorous stand of northern hardwood and coniferous trees.
None of these basic landmarks is homogeneous. For example, in the Lower Peninsula moraines occur in concentric ranges parallel to the shores of Saginaw Bay, Lake Erie, Lake Huron and Lake Michigan, but others occur in irregular patterns which seemingly have no relations to the outlines of the Great Lakes. Till plains and outwash plains commonly fill in the space between the hill formations. Lake plains occupy much of the Saginaw River Valley, and the broad belt of flat land surrounding the "Thumb" and extending southward along the shores of Lakes Huron, St. Clair and Erie.
A large part of Michigans northern land has moderate limitations as far as agriculture is concerned. It consists of rugged hills, shallow rocky soils with rock outcrops, rolling sandy plains, extensive swamps, inland lakes and streams. This is Michigans public and private forest and recreation land. This is the land that makes Michigans tourist industry second only to the automotive industry in dollars-and-cents value. This is the land that was logged and destroyed by fire. This is the land that has come back from desolation as a result of forest management, good forest fire control and intelligent land-use planning. However, not all of northern Michigan is bad, agriculturally. Scattered areas of fair to good farmland may be found throughout this part of the state. Northern Michigan has also produced the major share of Michigans mineral wealth: limestone, gypsum, copper, iron, oil and gas. This rugged northern, mineral-laden land has supplied the crude materials for heavy industry in the great industrial cities of the world.