How Young is the Grand Canyon?

To answer that question briefly, it is really really old if you mean "how old are the oldest rocks that are exposed by the Grand Canyon," and it is probably just a few million years old (5 or 6 by some estimates) if you mean "how long did the canyon itself take to form."

A repost

But Creationists, of course, have a different story, especially young earth creationists. I'm not going to recount it here. If you want to hear their story, I'll bet dollars to donuts (GoogleDollars that is) that if you look in the sidebars of my site, you'll find a Google Adsense ad pointing to a creationist site that will tell you the answer to that.I am not violating Google Adsense policy by saying that, just making an entirety apropos observation and enjoying my first amendment rights.

Since creationists, especially Young Earth Creationists (YECs) require a very short chronology, part of their Grand Canyon story is that it formed in a very short amount of time, like, just a few years.

What actually happened, of course, was this: In the total absence of tectonic uplift or volcanic effluence, all continents will eventually reach virtual equilibrium with the sea. That makes sense, right? The process of erosion will eventually flatten everything above the ocean. Water erosion (from rivers) will do most of the work, and wind erosion (and rainfall, surface water, and bio-erosion) will follow behind working on parts left high and dry when bypassed by the rivers. So in a few hundred million years or so, a medium sized continent will be roughly at sea level except a few tenacious, or simply "lucky," high spots which may be rounded hills of hard granite, or mesas and buttes.

Now, imagine that happening. Then, after it has happened, there is some kind of tectonic uplift, so that a large part of the continent actually rises up, maybe 800 meters or so on average, above sea level. Maybe there is a tilt to this event, so one side of the continent is a few tens of meters higher than the other. Now, the erosive process starts again.

In real life, of course, tectonic uplift and erosion are often both going on at the same time on a given continent, though not equally and not necessarily in the same locations. Even without any kind of active thermally-induced uplift and without plates crashing into each other causing uplift, the erosion itself will often cause uplift. This happens because continents are sometimes relatively buoyant objects, and if you erode off a few meters from the top, they tend to "bob" upwards by about that amount.

The grand canyon sits on a piece of landscape called a "raised peneplain." A peneplain is one of those flattened out regions of a continent after a long period of erosion. A raised peneplain is a peneplain that has undergone uplift. Often, the uplift involves doming or otherwise uneven increase in elevation. There are a lot of places where you can look out over the landscape and see the tops of a bunch of "mountains" or hills, and you see that the tops are a bit flattened, then you realize that you can imagine a very smoothly curving dotted line connecting all of these flattish tops. That dotted line is the old peneplain. Go look for this in your own neighborhood, maybe you've been living on or near an ancient raised peneplain all your life and never noticed it. Now you can go find it and bore all your friends with this interesting fact.

"Look, look at the raised peneplain! Can you see the slightly curved dotted line in the sky???"

One peneplain that is visible from a distance, raised up for all to see, that is really cool, is the Catskill Mountains. It is not really a landscape flattened from ancient mountains and valleys that is raised up there. It's more like an enormous inland sea/delta complex that was very flat and is now raised up. But it is the product of erosion-related flattening, so I will count it. You can probably see peneplains all up and down the Allegheny. The rift valleys of East Africa and Central Africa have uplifted a peneplain where doming has occurred, so if you happen to be reading this from the slopes of Mount Kenya or from Ishango, Congo, just look out the window and see ... ah, clouds most likely, but on a clear day ...

Anyway, the Grand Canyon represents the beginning of intense erosion that occurs when there is an uplifted peneplain. South of the Grand Canyon, in Northern Arizona, the erosion is much more advanced, and you get a badlands landscape with mesas and buttes everywhere. North of the Grand Canyon you get more of that, plus some other complex stuff happening to the west with folding and thrust faulting and such. That's a whole other story.

Now, let's get back to the creationists and the age of the grand canyon for a moment. Here and there, there are canyons that are buried by subsequent sediments. I'm sitting on one right now. I'm looking out northward across a lake, and to the west in my view is a peninsula sticking out into the lake, pointing roughly at an island. This peninsula and the island form the exposed "west bank" of a buried canyon. On the right side of my view is another ridge forming the east side of the lake. Again, this is the exposed "east bank" of the same canyon. Below me is sediment that has a well drilled into it that reaches nearly 400 feet without hitting bedrock, yet I can find bedrock on the two "banks" I described above. So the canyon is easily 400 or 450 feet deep at this location. Northwards, beyond my view, is another lake and beyond that a wide shallow valley, then another long lake (called, as it happens "Long Lake") and so on. These lakes and valleys contitute an elongaged depression that is the imprint of the upper parts of this now-filled in canyon. And it is a canyon, not a valley. It has steep sides and a flattish bottom (though the bottom may be a bit U-shaped) and caused by the erosion of a river.

As a matter of fact, immediately in front of me is a coffee table with a USGS topo map embedded in it under glass (all coffee tables should have maps in them), and I can see all these features this way as well. In fact, I can trace this canyon north-northeast to where it joins the present day course of the Mississippi River, and I can trace it south (but I need more maps to do that, but trust me, it works) to join, again, the Mississippi River way downstream. Indeed, I am sitting on a sediment-filled canyon that was at one time in the past the channel of an earlier incarnation of the Mississippi River. When glacial sediment filled this canyon at the end of the last glacial period, it also deposited huge chunks of ice in with the sediment. This ice has melted away exposing the groundwater that naturally settles in the canyon. Those exposures of groundwater are lakes, including the lake I'm looking at right now.

Now, if downstream in this canyon, an erosional event happened that cut into a lake, that lake would empty out downstream. That would probably enhance upstream erosion where the lake used to be, and eventually, the sediment damming up the next lake in the chain up-canyon would also be exposed and wash out, and so on. In this way, this canyon could become re-exposed over time. As it happens, I suspect that these northerly lands are still too depressed in elevation from having suffered the weight of a mile-thick glacier, so that the canyons up here which would flow roughly south are tilted down to the north, so don't expect this erosion to happen soon. But it will, unless this landscape is overrun by glaciers first. It's a race. A very long-term, slow moving race...

Just recently, a previously buried canyon was exposed in Texas:

CANYON LAKE, Texas (AP) - ...A torrent of water from an overflowing lake sliced open the earth in 2002, exposing rock formations, fossils and even dinosaur footprints in just three days. Since then, the canyon has been accessible only to researchers to protect it from vandals, but on Saturday it opens to its first public tour.

"It exposed these rocks so quickly and it dug so deeply, there wasn't a blade of grass or a layer of algae," said Bill Ward, a retired geology professor from the University of New Orleans who started cataloging the gorge almost immediately after the flood.

The mile-and-a-half-long gorge, up to 80 feet deep, was dug out from what had been a nondescript valley covered in mesquite and oak trees. It sits behind a spillway built as a safety valve for Canyon Lake, a popular recreation spot in the Texas Hill Country between San Antonio and Austin.

The reservoir was built in the 1960s to prevent flash flooding along the Guadalupe River and to assure the water supply for central Texas. The spillway had never been overrun until July 4, 2002, when 70,000 cubic feet of water gushed downhill toward the Guadalupe River for three days, scraping off vegetation and topsoil and leaving only limestone walls.

...

The sudden exposure of such canyons is rare but not unprecedented. Flooding in Iowa in 1993 opened a limestone gorge behind a spillway at Corvalville Lake north of Iowa City,...

source

...

Now, I'll bet you dollars to donuts that this event will make its way into the creationist-talk pretty soon. Here we have a canyon that is 80 feet deep that formed in 5 years. The grand canyon is about 5,000 feet deep. That means that the grand canyon can form in 310 years, approximately.

But, this Texas canyon was already there before. While some of it certainly has formed since its exposure, this really is a case of a canyon that formed some time ago, but then active erosion slowed down or stopped, and it got filled in with sediments and somewhat flattened out, then more recently, re-excavated.

This does not mean, of course, that canyons can't form quickly. The grand canyon is cut into some pretty soft rock, at least in the upper layers. Most of it is sandstone or similar sediments, very easily eroded. Roughly speaking, just one tenth of a foot per year of erosion would make a grand canyon size feature far bigger than the actual grand canyon in five million years. But to get the grand canyon to happen if it started on the day God created the Universe you'd have to get nearly a foot of erosion per year (which we do not see happening right now). And to get the Grand Canyon to have formed only since the Noachian Flood, but before the Cliff Dwellings that we find built into the side of the canyons by Native Americans (indicating that the canyon was already there) then you'd have to calculate the time of Noah's flood and the time of the Lost Tribes of Israel coming over from the holey land, subtract one from the other, add in a fudge factor to account for the differential hardness of the sediments through which the canyon cut ... let me see, where did I put my Christian Calculus Calculating Machine ...

In any event, look for this latest Revision of Reality to come from the Creationist Camp. Intent, they are, on eroding the concept of rational thought in our society. How annoying.