Great Lakes Literacy, Principle Two – natural forces formed the Great Lakes

Great Lakes Literacy is an understanding of the Great Lakes’ influence on you and your influence on the Great Lakes. Principle Two focuses on Great Lakes morphology.

This article is the third in a series of articles discussing what Great Lakes literacy means for residents of the state of Michigan and the Great Lakes region.

Great Lakes Literacy Principle One

Great Lakes Literacy Principle Three

Ancient igneous and metamorphic rocks form portions of the upper Great Lakes basin. Other rocks underlying the present day Great Lakes and surrounding watershed are sedimentary, originating during a time when shallow tropical seas covered the basin. Many of the rocks now exposed on land were deposited and shaped during the advance and retreat of glaciers.

Bedrock of Lake Huron BasinDuring the Ice Age, mile-thick sheets of ice covered the Great Lakes region multiple times, depressing the cruise with their weight. Ancient beach ridges mark previous lake shorelines, as can be clearly seen on Mackinac Island. Since glaciers retreated about 10,000 years ago, Earth’s crust has been adjusting upward in a process of isostatic rebound that continues today.

Lake level changes influence the physical features of the Great Lakes coast. Lake water levels show changes and patterns. These can be short-term variations due to weather conditions, seasonal variations with summer highs and winter lows, or variations that can be seen over millennia.

Erosion – the wearing away of rock, soil and other earth material – occurs in coastal areas as wind, waves and currents in rivers and the Great Lakes move sediments. Rates of erosion can vary tremendously depending on the type of material being impacted by natural forces.

Sediments are a product of erosion and consist of fragments of animals, plants, rocks, and minerals. Sediments re-classified by grain sizes from silt and clay to sand, cobbles, and boulders. Sediments are seasonally redistributed by waves and coastal currents and help maintain beaches and coastal wetlands.

MSU Extension and Michigan Sea Grant offer many opportunities to learn more about the Great Lakes, with educational opportunities such as the Great Lakes Education Program, Summer Discovery Cruises, and 4-H Great Lakes & Natural Resources Camp. If you are particularly interested in Great Lakes geology and morphology, look at the resources from our Great Lakes Rock! online workshop at the College of Exploration under the COSEE Great Lakes section. There you will find presentations from leading research scientists, downloadable educational materials and much more.

This article was adapted from Great Lakes Literacy: Essential Principles and Fundamental Concepts for Great Lakes Learning (Ohio Sea Grant, 2010).

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