Tilting of Earth's crust, Ancient Megafloods, e.g., Missoula Floods

[Astronuc]

Tilting of Earth's crust governed the flow of ancient megafloods​

https://phys.org/news/2022-02-tilting-earth-crust-ancient-megafloods.html

As ice sheets began melting at the end of the last ice age, a series of cataclysmic floods called the Missoula megafloods scoured the landscape of eastern Washington, carving long, deep channels and towering cliffs through an area now known as the Channeled Scablands. They were among the largest known floods in Earth's history, and geologists struggling to reconstruct them have now identified a crucial factor governing their flows.

In a study published February 14 in Proceedings of the National Academy of Sciences, researchers showed how the changing weight of the ice sheets would have caused the entire landscape to tilt, changing the course of the megafloods.

Upthrust of Earth's surface is also documented around the Great Lakes of US/Canada.

With the lack of ice sheet, which weighed down the land, the area around the Great Lakes is rising, so eventually, it is expected the lakes to rise and in some cases, the water will stop flowing to the lake region. There would still be precipitation. At the same time, the erosion of Niagara Falls will reach lake Erie at some point, and Lake Erie and the others will drain very quickly.

 

[Mark44]

Re the recurring Lake Missoula floods, what we know now about them is due mostly to the work of J. Harlen Bretz, a high school teacher of history and physiography (who also held a PhD in geology). He spent many summers in Eastern Washington looking at the topography there and speculating that it was shaped by massive floods.

Between 1922 and 1931 he published 15 papers, but the prevailing view of uniformitarianism amongst academic geologists caused his work to be discredited. It wasn't until the 1950s that his work was finally vindicated.

It should have been clear to anyone venturing near Missoula, Montana, and viewing the contour lines on the nearby hills, that these possibly were the result of varying levels of a very large body of water. The contour lines can still be seen.

There is a visitor center at Sun Lakes State Park in Washington, that commemorates the work the Bretz did, and describes the massive waterfall that once roared over the ground here -- a waterfall 400 feet high and 3.5 miles wide, four times the size of Niagara Falls.

 

[Oldman too]

This is a local (Missoula) site, not technical, but not bad either.
https://www.glaciallakemissoula.org/the-big-picture.html

Left an "Ice Rafted" Erratic or two.
https://en.wikipedia.org/wiki/Erratic_Rock_State_Natural_Site

And at least one "Gem".
https://en.wikipedia.org/wiki/Willamette_Meteorite

It's also worth noting that the actual Ice damn site has some of the best Huckleberries on Earth.

 

[Mark44]

It's also worth noting that the actual Ice damn site has some of the best Huckleberries on Earth.

That would be "ice dam" and I assume you're referring to the area around Sandpoint, Idaho and Lake Pend Oreille, which is fed by the Clark Fork.

 

[Oldman too]

That would be "ice dam" and I assume you're referring to the area around Sandpoint, Idaho and Lake Pend Oreille, which is fed by the Clark Fork.

Hi Mark,
Sorry about the Faux Pax, You are correct on all points. (Situation Nominal)

I believe the Dam site must have been around the Hope Id. area on the average, there would have been at least 40 events repeated and it appears the damming went on at various points between Hope and Noxon. Just across the Mt. state line, the Bull River would reverse course and flow towards Troy Mt. until the Dam burst, then as the Lake drained it switched back to it's current direction.

A point not often mentioned in this Process is Lake Pend Oreille and how the leading edge of the Ice sheet dredged it out. It's current depth is 1,158' (4th deepest in the US) with an estimated 400' of loose Glacial Till covering the bedrock so assuming an original depth of approximately 1500'. The Cordilleran Ice Sheet was huge.

The lake also shares some unique Acoustic properties that make it a test site for USN Sub Research, been the source of more than a few conspiracy theories but I like to keep those things in the file shredder for "safe keeping".
https://spokanehistorical.org/items/show/589

I should mention, getting back to the original title of this thread, The "Tilting of the crust" is is a new dynamic that I've never heard before, very interesting.

Cheers, Scott

 

[Mark44]

I should mention, getting back to the original title of this thread, The "Tilting of the crust" is is a new dynamic that I've never heard before, very interesting.

The eastern flank of the Sierra Nevada Range in California is the upturned edge of a large fault block that is at least 100 miles wide be several hundred miles long. As you go from west to east, the tilted block rises gently, but at its eastern flank, the escarpment is about 10,000' in elevation.

Not only can large blocks tilt, but they can rotate. An example of that, in current geologic thinking, is much of central and western Washington and Oregon, thought by many geologists to have rotated clockwise about 15 degrees in the past 16 million years (https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016TC004223) and an overall rotation of about 75 degrees in the past 50 million years. A possible cause of this rotation was the docking of the Siletzia terrane off the coasts of these states.

What usually happens is that relatively heavy ocean crust subducts under lighter continental crust, but the Siletzia terrane was too large to slip under the continental crust, so it got stuck. The ocean crust kept coming, causing a large chunk of Washington and Oregon to rotate clockwise. More info: https://en.wikipedia.org/wiki/Siletzia.
BTW, I imagine Siletzia was named after the town of Siletz, Oregon, not far from Newport, Oregon.

 

[Oldman too]

I've wondered about the dynamics your describing, thanks, this explains so much. My search skills being at best, so so, I hadn't seen the links and info.

Thanks again, Scott