Introduction to the Great Lakes

1. Introduction to the Great Lakes The Great Lakes are located in North America, separating the United States from Canada. Earning the name “great” from their size, the Great Lakes are also fresh water. As a result they become the largest fresh bodies of water in the world. The origin of the Great Lakes dates back to the late Cenozoic.

2. Lake Michigan Lake Michigan, the Southernmost of the Great Lakes, is the only lake entirely within the United States. Erosion paved the way for glaciers to climb over a valley. Glaciers sat over a basement of Precambrian rocks. As the basin became to flood from the melting glacier, the unique shape of Lake Michigan was formed. Lake Michigan began to take its current shape in the late Cenozoic. Being the most North to South shaped lake, there is a noticeable change in water temperature as you move along the lake. A sunset over Lake Michigan at Grand Haven, Michigan.

3. Lake Ontario • Formation began during Wisconsin glaciation, 70,000 yrs. Ago •2-3 km thick glacier formed deep depressions– when glacier melted formed large “Lake Iroquois” •St. Lawrence Valley blocked by glacier, so little water flowed out, through Hudson River •As glacier shrunk northward, much of the lake flowed out to Atlantic through St. Lawrence River; water levels dropped • Land underlying lake began to rebound; crustal uplift caused water levels to rise, forming present-day lake Lake Ontario is the fifth largest of the Great Lakes and ranks as the 17th largest lake in the world.

4. Lake Erie • In its recent form, Lake Erie is only about 4,000 yrs. old • Over last 14,000 years, lake has gone through many different stages of elevation– up to 230 feet higher than current elevation • Fertile clay deposited during high-level periods affect life in region today; shorelines of these different stages now appear as ridges • Comprised of 3 basins— possibly separate lakes until barriers between were eroded by currents • Eastern basin comprised of a long, deep trench that might correspond with a fault line; characters of basins and shorelines suggest catastrophic events •With Lake Michigan, was the first of the lakes to be formed/uncovered by glacier

5. Lake Superior • About 1 billion years ago N. American continent began to split, forming rift valley into which lava welled • Air bubbles trapped in cooled lava filled with iron, quartz, and other minerals, forming agates. • Before the glacier period, the Lake Superior area was covered in rivers and wide valleys • As the glacier moved over these valleys it scoured away the “softer” rock, leaving basins that filled with water when the glacier melted

6. Lake Huron • As with other lakes, area experienced post-glacial uplift; this caused water to drain southward, affecting the shape of the lake • Evidence of extreme erosion in Precambrian rock is attributed to catastrophic flooding due to glacial melting • Rock formations around Georgian Bay suggest area may have been eroded not by moving ice, but by fast currents • For a brief period of time, Lakes Huron, Michigan, and Superior combined to form one large lake, then separated as water drained • Huron continued to drain eastward into the Ottawa-St. Lawrence Rivers until about 5,500 years ago, when it reached its present form.

7. Evolution of the Great Lakes • The lakes’ form today is similar to that of 4000 years ago • However, these, like all lakes, are expected to be geologically short lived. Shorelines are constantly being eroded and the lakes are constantly changing and experiencing outflow of water.

8. Environment Plant life is another important aspect of the Great Lakes Basin. Along each of the lakes, different plants thrive. These plants also are directly affected by the Great Lakes, and in return affect the Great Lakes. Having ample forestry and water, the Great Lakes Basin calls itself home to a variety of animal life. Moose and deer are examples of the animals that can be found. The animal life originally drew people the Great Lakes area, and as a result affected the current state of the Great Lakes.

9. Commerce The Great Lakes Basin harbors many factories and industries. Hosting cities like Chicago and Milwaukee, urban areas along the lakes have not only become industry giants, but tourist attractions. A harbor in Chicago Although current affairs have no baring on the origin of the Great Lakes, they do alter how the lakes evolve. The lake water rises. Pollutants enter the water, not only affecting the lake, but the animal and plant life around it. DC Cook Nuclear Power Plant

10. Conclusion The Great Lakes have an affect on the area around it, as the area has an affect on the Great Lakes. Yet there wouldn’t be the animals or cities, if not for the creation of the Great Lakes. Eroded valleys toppled by glaciers caused fresh water to fill these basins. As time passed from Paleozoic to Mesozoic and to Cenozoic, the lakes changed and evolved. Each time period took its toll on the Great Lakes, and helped formed not only the lakes, but the basin around them. As a result of the lakes being formed, life flourished on every stage.