I need help answering the following three questions:

1. What geological event explains the formation of the great lakes, the st. lawrence river system, the columbia-snake river system, and great slat lake?

2. How did this same geological event isolate the human population of the Americas from that of Asia?

3. Given the original geographical origins of the indian populations, in which direction did their earliest migrations across North America occur: from southeast to north and west, from southwest to north and east, or from northwest to south and east?

Thanks in advance for helping me.

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1) the Rockies and the Appalachians.
2) The Last Ice Age. The Melting ice helped.
3) Allowed for lower sea level and provided a land bridge to America. At the tend of the ice age the water covered the land bridge

1) the Rockies and the Appalachians.
2) The Last Ice Age. The Melting ice helped.
3) Allowed for lower sea level and provided a land bridge to America. At the tend of the ice age the water covered the land bridge