Message 526 of 533 (730658) 06-29-2014 3:20 PM

Reply to: Message 525 by Dr Adequate 06-29-2014 2:51 PM

That's about 5000 feet in ten million years for the sandstone. Pretty much takes care of that, shouldn't be any left standing without even multiplying the "tens" of millions. And 1660 feet in ten million years for the siltstone. Kinda does it there too wouldn't you say? So which part do you disagree with, the tens of millions of years since they started eroding or the rate or what?

ABE: Of course the truth of the matter is that layers were deposited in the Flood to a depth of some three miles or more, then when the water receded it eroded away a lot of the upper strata all over the Southwest leaving all those interesting formations. After the water was gone the formations were subject to yearly erosion. That's how it really happened.

Edited by Faith, : No reason given.

Edited by Faith, : No reason given.

Edited by Faith, : add URL

Message 530 of 533 (730669) 06-29-2014 4:12 PM

Reply to: Message 487 by Faith 06-29-2014 9:16 AM

Scree is exposed to weathering, which means things like wind, rain, temperature variations and freeze/thaw cycles. Even buried scree is vulnerable, though to a lesser degree, to weathering. Particles flake off the scree, water erodes and carry some away, grinding against other pieces of scree creates flakes, and over time each piece becoming smaller and smaller. The tiers upon which the scree rests are also subject to erosion, and buried scree eventually loses its supporting platform and falls to the next tier, eventually reaching the valley floor. The tiny particles that flake off the scree become the soil of the valley floor.

Yes, of course. In time the West Mitten Butte will erode down to nothing.

The top of the butte represents former valley floor. The current valley floor was once a thousand feet higher than it is now. But when the region was uplifted it became an area of net erosion. Riverbeds crisscrossed the valley and gradually eroded it down, creating canyons that gradually widened and joined, leaving a valley of buttes behind. Almost all the material that once filled the current valley is now gone, only a few buttes remaining.

Yes, clearly the layers form tiers upon which the scree rests.

If you wanted to know whether the current amount of scree represents the accumulations of a hundred thousand years or a million years or ten million years, then yes, we need to know precisely how much scree is present, precisely how fast it erodes off the sides of the butte, and precisely how fast it weathers away. But if you just want to know if that much scree could accumulate in a mere 4300 years then the answer is no, there's far too much scree to have accumulated in so brief a period of time. The entire valley floor is scree and the particles weathered from scree.

That's true, you didn't provide an estimate, but I did provide a lower bound for you. Niagara Falls used to erode back about 5 feet per year before the diversion of water for electric power generation. The floor of Monument Valley used to be at least a thousand feet higher than it is today, and it is miles across. How do you imagine your flood eroded away an entire valley a thousand feet deep and at least 50,000 feet across in just a year when Niagara Falls can only manage 5 feet?

Yes, someone did happen to mention that there actually are some types of rock that can form by drying, but they aren't the types of rock that make up most sedimentary layers, which are limestone, siltstone, sandstone and shale in this region and in most regions throughout the world. These types of layers form by deep burial, compaction, and cementation.

I've read ahead in this thread, and so I won't reply to your Message 488 because it looks like you figured out that the White Cliffs of Dover are eroding off their face, not off their top (at least not significantly). The English Channel widens every year.

--Percy

Message 531 of 533 (730670) 06-29-2014 4:41 PM

Reply to: Message 526 by Faith 06-29-2014 3:20 PM

Ringo already addressed this, but it doesn't hurt to say it another way. The region didn't begin eroding until it was uplifted some tens of millions of years ago. At the time the surface that would eventually become Monument Valley was a thousand feet higher, and what would eventually become the buttes were just buried sedimentary layers miles and miles in extent. Rivers crisscrossed the valley cutting it into canyons whose sides eroded away, eventually joining and continuing to erode and finally leaving behind only the buttes we see today.

That's not a bad estimate. Another way of looking at it is that these buttes were once as wide as all of Monument Valley. It did take millions and millions of years to erode them away to their current breadth of only thousands of feet. There must have been many more buttes millions of years ago, but they've eroded away to dust.

--Percy

Edited by Percy, : Improve phrasing.

Message 532 of 533 (730674) 06-29-2014 5:48 PM

Summary mode - One last message per member, hopefully something about depositional models.

Adminnemooseus

Message 533 of 533 (730682) 06-29-2014 6:37 PM

Edited by Faith, : No reason given.