The Great Lakes A Presentation made by Benjamin Ashraf IB 447 - Spring 2006
Areas of Focus • The Great Lake Region During the Ice Age. • The Formation of the Great Lakes • The Drainage of the Lakes • The Modern Lakes
The Pleistocene Epoch • Occurred on earth from about 1.6 million to 10,000 years ago. • During this time the majority of the northern hemisphere was covered in ice with average temperatures around 15 degrees colder than the average today.
The Pleistocene Epoch Cont. • This epoch was also marked by at least 4 separate incidences in which glaciers advanced and retreated from Canada to as far down as Chicago. • Of these 4 glaciers the one we will be most concerned with is the final one known as the Laurentide Glacier.
Laurentide Glacier • Began to form around 100,000 years ago. • At its peak around 18,000 years ago the Laurentide covered almost all of Canada and extended as far down as Chicago. • The Glacier was also estimated around 4km thick.
Laurentide cont. • As the glacier advanced across N. America, several mountains and hills that it came across was subsequently destroyed. • This process known as glacial erosion is responsible for the majority of the modern day valleys across the United States and Canada.
End of the Laurentide Yet around 14,000 years ago the Laurentide glacier began to recede due the rising temperature of the earth. This meltdown is responsible for the formation of what would become the Great Lakes.
Early Lakes - Formation • As mentioned before as the Laurentide Glacier advanced across North America several mountains and hills were subsequently destroyed by the process of glacial erosion. • Some of these destroyed land bodies left massive craters within the crust of the earth.
Early Lake Formation cont. • And as the Laurentide receded and began to melt, these craters were subsequently filled with what is known as “meltwater” from the glacier.
Early Lakes - Characteristics of • These early Lakes were by all accounts far larger than there modern day counterparts. • As well these lakes also had different drainage routes than they had today.
Early Lakes Characteristics Cont. • Yet around 7,000 years ago the recession of the Laurentide Glacier revealed what became known as the St. Lawrence River Valley which emptied into the Atlantic Ocean. • Eventually the Lakes’ water levels dropped to levels similar to the lakes of today.
Great Lakes - Drainage of • As previously mentioned there were several different avenues for drainage for the early lakes before the emergence of the St. Lawrence River valley around 7,000 years ago.
Drainage Cont. • For instance, the two ancestral Great Lakes known as Lake Maumee and Lake Chicago had multiple outlets depending upon how far the ice had receded at that time. • For instance Lake Maumee, which became Lake Erie, initially emptied into the Mississippi River but around the time of 7,000 years ago was emptying in Lake Ontario and then to the Atlantic Ocean.
Drainage Cont. • For the upper lakes one is able to see a similar instance of different drainage outlets depending upon the location of the Laurentide ice sheet. • Around 13,000 years ago the upper lakes emptied chiefly into Lake Chicago much like Lake Maumee did.
Drainage Cont. • Yet with the final recession of the ice around 11,000 years ago the formation of Lake Algonquin both Huron and Michigan became connected and started to drain into the newly formed Lake Ontario. • Eventually through various stages of Crustal Rebound the main area of drainage also became the St Lawrence for the upper Lakes as well.
The Modern Lakes • After the St. Lawrence became the main avenue of drainage for the lakes they have pretty much remained the same with minor changes in both water levels and the shifting of shore lines. • Thus concludes my presentation.
Resources Used 1) Formation of the Great Lakes www.emporia.edu/earthsci/ student/damery1/gl_form.html. 2) Great Lakes Formation techalive.mtu.edu/meec/module/ GreatLakesPastandPresent.htm