How exactly did the glaciers flatten the Midwestern United States, and was the entire continent mountainous prior to this?

Question

When exactly was this? I have always pictured a giant block of ice slowly sliding diagonally down the middle of the country 🤣

In: 1

Answer 1

> I have always pictured a giant block of ice slowly sliding diagonally down the middle of the country 🤣

That is essentially accurate. The ice sheets involved were absolutely enormous – they were [a kilometer or more thick](https://xkcd.com/1225/) in those areas – and thus extremely heavy. They more or less steamrolled the area.

But it wasn’t that mountainous even before that. Everything between the Appalachians and the Rockies, aside from a few highlands in Arkansas, Kansas, Oklahoma, and Missouri (the Ozarks and Ouachita mountains) has always been lowland; much of it was even covered by shallow seas during times of high sea level (which is part of why it has rich soil today).