Replies

I suppose WHEN the maximum occurred is an academic exercise in any case. It's my understanding during the last ice age the ice sheets sortof ebbed and flowed, so to speak.

I don't know it you've ever looked closely at a shaded relief map of America del Norte or not, but in particular around the southern edges of the Great Lakes you'll find what appear to be numerous "terminal" moraines. That would indicate to me that most likely the ice sheets' "flows" became smaller and smaller as they gradually retreated in fits and spurts overall. Maybe not but that's the way it looks to me...

The Great Lakes ended up having very high levels, and then a moraine dam somewhere would break and that'd drain the lake down several dozen feet, and then that would happen again, and again.

Each time the lake dropped you got a new beach, and additional indentations in the very large terminal moraines at the margins.

BTW, Lake Erie's last big drop was only 4,000 years ago. Virtually NO American Indian settlements were built in the muck area left behind that extended from Ohio through North Central Indiana. That area is still drying out!

Most of the big changes we can see today are a consequence of the movement of water, not ice. The Ice was mostly gone 14,000 years ago but came back in the Younger Dryas ~ which is a totally separate topic ~ but that happened AFTER humans had started moving to America, and may well have wiped almost all of them out ~