Are the Great Lakes in America caused by internal forces? What is the specific effect?

The Great Lakes are the final product of glacial activities that began about 654.38 million years ago. Today's Great Lakes are located in a valley that is constantly being expanded by glacial activities. A large amount of ice on the ground also depressed the valley. The Great Lakes are the last stage of the formation of many lakes in this area in the late Pleistocene.

The Great Lakes of North America were formed 7000 ~ 32000 years ago, which was gradually formed by the retreat of Pleistocene glaciers. Before the Pleistocene Ice Age, the Great Lakes region was an east-west water system. During the ice age, glaciation widened and deepened the valley. During the last glacial retreat in Pleistocene, the southern bank of this area left the last moraine ridge, and the lower reaches of the St. Lawrence River were still covered by glaciers, during which a large area of water was blocked, and the wide and shallow valleys became lake basins, forming the embryonic form of the Great Lakes. It is generally believed that Lake Erie reached its present scale about 1 10,000 years ago, Lake Ontario was formed 7,000 years ago, and the other three lakes were formed 3,000 years ago.

The elevation of the lake drops gradually from west to east: the water level difference between Lake Superior and Lake Huron is 7 meters, forming the St. Mary River with many rapids; Lake Michigan and Lake Huron are horizontal and connected by the Mackinac Waterway. The water level difference between Lake Huron and Lake Erie is 2m, which forms the saint clair river rapids. The water level of Lake Erie is 99 meters higher than that of Lake Ontario, during which the niagara river Rapids formed, and Niagara Falls, a world-famous waterfall with a drop of 50.9 meters, formed in half. Finally, the lake enters the St. Lawrence River through the mouth of Lake Ontario and flows into the St. Lawrence Bay in the Atlantic Ocean. The deepest is Lake Superior, with a maximum depth of 406 meters; The shallowest is Lake Erie, with a maximum depth of only 64 meters; The other three lakes have a maximum depth of more than 200 meters.

Lake water is mainly supplied by precipitation and receives many small rivers, which is rich in water. The average annual flow of Lake Ontario into the St. Lawrence River is 6640 cubic meters per second. The water level is higher in summer and lower in late winter and early spring. In summer, the lake temperature is 16 ~ 2 1℃, in winter it is lower than 0℃, and the ice age is more than 4 months. The Great Lakes can obviously regulate the climate of the surrounding lakes, making them mild and humid, with a long frost-free period, which is beneficial to agriculture. Agriculture, forestry, fruit and fishery are developed, which is the main concentration area of inland fishery in North America, mainly producing lake trout, white fish and lake herring.