Region 1: Soils of the Superior Upland

The Superior Upland region of the Midwest reveals a vibrant record of tropical seas, violent volcanic eruptions, and huge glaciers. Sand deposited over 400 million years ago provides some of the purest quartz deposits in the US, which are used in the glass and foundry industries today. Ten to twenty thousand years ago this area was covered by glaciers, and the deposits those glaciers brought with them—either directly or indirectly—make up most of the parent material of the soil today. Agriculture is big here, although not as prolific as in Region 2 due to the mountainous topography, near-surface bedrock, and cooler climate. However, the soil here does supports over 1.5 million acres of mixed hardwood and coniferous forests in, among other places, the Chequamegon National Forest (Wisconsin), the Nicolet National Forest (Wisconsin), and the Porcupine Mountains (the Upper Peninsula of Michigan). This region is part of one of the oldest mountain ranges in the world, a range composed of resistant igneous and metamorphic rocks that includes the 3.6-billion-year-old Morton Gneiss of Minnesota, some of the oldest exposed rock in the world.

See Chapter 2: Rocks for more about the formation of the Morton Gneiss and other Midwestern rocks.

The climate, the hardwood and conifer forests, and the numerous wetlands provide the conditions for producing the dominant soil of the region, a Spodosol, or more specifically the Spodosol of suborder Orthods (Figure 8.5). This soil is typical of cold, wet climates and, frequently, sandy parent material. The spruce and fir forests and the bogs of the north are typical ecosystems for this soil.

Mineral mining is also big in this region. In northeastern Minnesota, the Minnesota Iron Range holds the largest deposit of iron ore in the nation, and it is composed of the Mesabi, Cuyuna, Vermilion, and Gunflint mountain ranges. The eastern end of the region is also home to many iron mines near Ishpeming and Negaunee in Michigan. These deposits color the local soils and sand deposits with a noticeable red hue due to the rusting iron.

About 13,000 years ago, the Laurentide Ice Sheet, which covered most of Canada at the time, began to melt at its southern border. In its prime, the Laurentide was more than 5 kilometers (3.1 miles) thick at its thickest point on what is now the Hudson Bay. This sheet of ice weighed so much that it depressed the crust, allowing for an expansive lake to form as the ice melted. This lake developed in an area that separates the Mississippi watershed from areas that drain northward. Lake Agassiz was born, and it is said to have been the largest lake ever to exist, the volume of which, today, could contain all the water in all the lakes on Earth. As glaciers continued to melt at the end of the last ice age, several modern river valleys were carved out by the waters spilling over from Lake Agassiz, including the Minnesota River and the Red River Valley, the latter of which was formed from silt deposited from the lake. Much of the water from Lake Agassiz was drained into what are now the Minnesota and the Mississippi Rivers and also into Lake Superior. These sediments provided the parent material for many of the soils in these northern river valleys and were also the source for some of the loess deposits common to the region.

Loess deposits are found throughout the Midwest, including the Superior Upland region, and although wind brought these materials to the area, water erosion is now the primary reason these soils are being washed away. Methods to combat the loss of the soil in this area include the use of “no till” farming and the planting of cover crops, which are crops planted after a main crop is harvested that help to decrease runoff, increase soil quality, and also provide habitat for animals during the winter.