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Author Topic:   Continuation of Flood Discussion
Percy
Member
Posts: 22392
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.3


Message 530 of 535 (731254)
06-29-2014 4:12 PM


Faith writes:
Scree once positioned on the pile has no reason to keep disintegrating like that, it's just going to get covered over by more scree.
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.
Anyway, the more likely scenario is that in all that time the butte should have been eroded down to nothing but a pile of scree in itself. IMHO of course.
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.
But of course we don't know the actual amount there do we? And if you look closely at the scree area it appears that it isn't all scree but that the scree has collected on top of a tier of layers that were already there which would of course take up quite a bit of the total volume of that talus or skirt. Unless those tiers were built to hold the scree? Hard to tell from the picture.
Yes, clearly the layers form tiers upon which the scree rests.
Seems to me we need to know just exactly how much scree there is in that pile.
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.
I don't recall estimating the speed of the water running off around the monuments.
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?
Somewhere back in those discussions about all that it was proved by some official link or other that drying does indeed form rock in some cases,...
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

Percy
Member
Posts: 22392
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.3


Message 531 of 535 (731255)
06-29-2014 4:41 PM


Faith writes:
In Message 480 Percy says the monuments have been exposed to erosion for tens of millions of years and that the sandstone erodes at a rate of around 15 cm per thousand years, and siltstone at a rate of about 5 cm per thousand years.
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 about 5000 feet in ten million years for the sandstone.
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.

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