Formation
of the Great LakesThe Great Lakes
Features
Formation
of the Great Lakes
The Great Lakes’ basin was set about 3 billion years ago during
the Precambrian Era. During this era, volcanic activity and tremendous stresses
occurred to form great mountain systems. The sedimentary and volcanic rocks
that were already there were folded and heated by these stresses. Later, these
were eroded away leaving what you see today as rolling hills.
At the end of the Precambrian Era and the beginning of the Paleozoic Era, much of North America was flooded by oceans and inhabited by many different life forms. Some of these included: corals, crinoids, brachiopods, and mollusks. The seas left behind sands which eroded away to form layers of limestone, sandstone, and shales.
Then came the glaciers. The first glacier that began to cover the Great Lakes basin changed the terrain over a million years ago. As the glacier scraped the land, it changed the landforms beneath it. Thousands of years later, the climate began to warm up melting the glacier. Wildlife and vegetation soon returned following the melting. The cycle continued to happen many times over.
The melting glacier left large volumes of water. The water filled the lower land caused by the weight of the glacier forming gigantic lakes larger than our Great Lakes today! The land began to rise as the enormous weight of the glacier was lifted changing the depth, size, and shape of the lakes and causing what we see today.
Climate
of the Region
Climate in the Great Lakes region, or the average condition
of the weather over a period of years, is affected by three different factors:
air masses from other regions, the location of the basin, and the effects that
the lakes themselves make on the weather conditions. Most of the air masses
that affect the weather here come from the west. Because of this, we see our
weather changing very rapidly from warm, humid air (from the Gulf of Mexico)
to cold, dry air (from the Arctic).
During the summer, the northern regions of the Great Lakes receive cool, dry air masses from the Canadian northwest. To the south, the region experiences the tropical air masses coming from the Gulf of Mexico. When the Gulf air crosses the lakes, the bottom layers of water stay cool while the top layers are warmed by this humid air. This very process causes humid days and even smog!
During the winter, the region is affected by two major air masses. The Arctic from the northwest is very cold and dry when it first enters the basin, but it is warmed up and also picks up moisture as it travels over the warmer lakes. As this air reaches the land, the moisture condenses to form snow, accounting for out heavy snow falls and the area that we call the snowbelt. A Pacific air mass also affects the region for a part of the winter. As this air mass crosses the western mountains in its path to the Great Lakes region, it loses a lot of its moisture. Our winters bring lake temperatures that continually drop causing many of the lakes to form ice. Frequently, ice will cover the entire surface of Lake Erie but the other Great Lakes seldom freeze completely over.
As spring comes to the Great Lakes region, it brings weather that change all the time. Different air masses that run across the region cause cloud cover and thunderstorms. The sun will begin to melt the snow and lake ice. The lakes take longer to warm up than the land does causing cooler temperatures and a delay in plant blossoming for the areas that are close to the lakes!
Human Impact
and Future of the Great Lakes
In the 20th century the fish populations have changed due to
over fishing and the introduction of exotic species. As a ship sails through
water from one place to another, they may carry animals and life forms that
are stuck on the boat. These new organisms then grow and live in this new environment
and can cause some big problems. One species that was brought to the Great Lakes
was the sea lamprey, which entered the lakes through the Erie Canal. The sea
lamprey wiped out almost the entire lake trout populations of Lakes Huron and
Michigan. As the lamprey killed the lake trout, the alewife began to multiply
because it no longer hunted by the lake trout. Another species that was introduced
from Europe was the zebra mussel. This species grew very quickly. Zebra mussels
eat water-eating algae and this hurts the other species that feed on algae.
The mussels also have a hard shell that becomes cemented to boats and clogs
water intakes at power plants.You can see that foreign invaders can seriously
change the ecosystem.
The habitats within the region have also suffered from the impacts that humans have on the environment. Almost every forest has been cut at least one time and the soils in the prairie suitable for agriculture have been plowed or over-grazed. Also, as humans built dams and cities they vastly changed the populations of plants and animals in the region. The wetlands are a category of habitat that is very important because of the effect they have on the aquatic plant and animal community.Many wetland regions have been filled in for building houses and cities. Others have been drained to be used for agricultural purposes. The southern parts of the region have seen the most damage. It has been estimated that between 70 and 80 percent of the original wetlands have been lost due to human impact. Some species of animals and plants have even become extinct due the changes that humans have made. Others remain in danger.
As pollution is controlled and reduced, the importance of protecting the natural
habitat has become a main concern. There are many organizations that focus on
the ways that humans can help protect this natural wonder. For students, there
are camps that study and inform children on what they can do to help. The internet
provides thousands of resources on the Great Lakes for
students, teachers, and parents so that everyone can learn about The Great Lakes.
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Questions? Contact Kristen Bogyo at
bogyokm@uwec.edu
Page Last Updated March
30, 2003