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Looking past the old Milwaukee RR tracks up the Shonkin Sag. If you'd like to read more about the Sag: http://home.onemain.com/~gplains/lake_g ... m#STANDARD
He says:
I have suggested that the formation of the Shonkin Sag must be much more complex than the simple picture of catastrophic overflows from a single vast lake. With the knowledge that the Missouri River may have continued flowing throughout most of the Ice Ages, we can infer the sequence of events from the topography of the land and rivers.
A more complete explanation for the Shonkin Sag is that it was formed over immensely long periods, probably during at least several Ice Ages. It was formed not by a single violent event, but in a much more complex sequence of events, including diversion of the flow of the Missouri river for most of the duration of the Ice Ages. For the past million years the Earth has spent most of the time locked in ice; so there has been sufficient time for a river to gradually cut a channel around the ice—a channel that could have been scoured and enlarged by several violent overflow events.
Rather than a temporary, short-lived channel, the lower part of the Shonkin Sag may have been the preferred channel for the Missouri River for immensely long times. That it looks so fresh today, unlike the other valleys of the Missouri, is because it was never eroded by glaciers, and because there has been little erosion since the river returned to its present course.
He says:
I have suggested that the formation of the Shonkin Sag must be much more complex than the simple picture of catastrophic overflows from a single vast lake. With the knowledge that the Missouri River may have continued flowing throughout most of the Ice Ages, we can infer the sequence of events from the topography of the land and rivers.
A more complete explanation for the Shonkin Sag is that it was formed over immensely long periods, probably during at least several Ice Ages. It was formed not by a single violent event, but in a much more complex sequence of events, including diversion of the flow of the Missouri river for most of the duration of the Ice Ages. For the past million years the Earth has spent most of the time locked in ice; so there has been sufficient time for a river to gradually cut a channel around the ice—a channel that could have been scoured and enlarged by several violent overflow events.
Rather than a temporary, short-lived channel, the lower part of the Shonkin Sag may have been the preferred channel for the Missouri River for immensely long times. That it looks so fresh today, unlike the other valleys of the Missouri, is because it was never eroded by glaciers, and because there has been little erosion since the river returned to its present course.