What is the geologic history of the Great Lakes?

After a long period of erosion beginning about 500 million years ago ancient seas covered the Great Lakes basin off and on and Phanerozoic sedimentary rocks began to be deposited. They consist largely of shale, limestone, and sandstone on top of the Precambrian bedrock.

What is the oldest rock in the Great Lakes?

In our area, the oldest rocks are about 2.7 billion years old. Found mostly along Lake Superior’s Ontario shores and located in the area called the Superior Province of the Canadian Shield, these ancient rocks date from the Archean Eon.

What is the formation history of the Great Lakes?

The Wisconsin glaciation occurred about 200,000 years ago and, in its final retreat, some 35,000 years ago, the Great Lakes began to be established. Niagara Falls was born about 20,000 years ago and the Lakes, as we know them today, are roughly only 3,000 years old.

What were the Great Lakes before the ice age?

before present, during the last glacial period called the “Wisconsian”. The lakes which we now call Superior, Michigan and Huron were part of two vast inland lakes called “Lake Duluth” and “Lake Algonquin”. These lakes were later joined as the glaciers retreated to form one vast lake.

Is there a volcano under Lake Superior?

A north-south cross section compiled from seismograms shows a deep depression under Lake Superior filled by layers of volcanic rocks and overlying sediments to a depth of 18 miles (30 km), which is much deeper than Lake Superior’s average depth of about 500 feet (150 m).

Did glaciers form the Great Lakes?

The massive weight and movement of this glacier gouged out the earth to form the lake basins. About 20,000 years ago, the climate warmed and the ice sheet retreated. Water from the melting glacier filled the basins , forming the Great Lakes.

What was there before the Great Lakes?

Before the Ice Age there were no great lakes, only shallow basins, except for Lake Superior which had originated aeons earlier as a rift valley lake in the Central North American Rift System. The river that drained this area, the Laurentian River, flowed through the Toronto area.