Real Science Friday: New Island, Old Look

[aharvey]

My claim is similar to Bob's. If canyons on Mars could be formed quickly by a water source that is no longer existent then why not canyons on Earth.

Now there are two important elements in your statement: 1) quick formation, and 2) water that is no longer present. With respect to the latter, it's my understanding that there are some good reasons why Mars might not be able to hold onto its surface water as well as Earth. The atmosphere, or lack thereof, for example. And is there any evidence that Earth is losing water? Or are you hinting at some physical process that is no longer in operation, even with the vast surface area of Earth that is exposed water? See, with Mars there is evidence of lots of water in the past, there is evidence of little water today, and there are at least rational hypotheses to explain the discrepancy. With Earth, there is evidence of lots of water in the past, there is evidence of lots of water in the present, and to my knowledge no evidence of a discrepancy between the two. So what do you want again?

With respect to the former, no one has said canyons on Earth couldn't, or haven't, formed quickly, have they? That's why I provided those images. Quickly moving water would carve out a very different path than leisurely moving water, wouldn't it? Can't you predict what those differences would be?

If Mars once had water enough to carve those canyons then that is evidence for a lot of water on Mars. I won't claim it was entirely under water, but it seems unlikely that any water layer was confined only to the places where it would form canyons.

Okay...

How would a physicist define pressure? I'm perfectly willing to discuss situations in which the pressure changes, but I would see those changes simply as a result of more water and/or more rock. It'd be easier on me if I were speaking in conventional terms though

Fine. Compare lots of water in a rock basin with a narrow crack with the same amount of water in the same rock basin with a much wider gap. Any differences worth noting in your mind, regarding the issues you are dwelling on here?

 

[aharvey]

Now there are two important elements in your statement: 1) quick formation, and 2) water that is no longer present. etc. ...

Gee, stipe, as of now you've made 25 posts since I made this reply to you. Suddenly lost interest in the dynamics of canyon formation?

 

[Stripe]

Now there are two important elements in your statement: 1) quick formation, and 2) water that is no longer present. With respect to the latter, it's my understanding that there are some good reasons why Mars might not be able to hold onto its surface water as well as Earth. The atmosphere, or lack thereof, for example.

Sure thing. Or the water could well be still there somewhere, right?

And is there any evidence that Earth is losing water? Or are you hinting at some physical process that is no longer in operation, even with the vast surface area of Earth that is exposed water? See, with Mars there is evidence of lots of water in the past, there is evidence of little water today, and there are at least rational hypotheses to explain the discrepancy. With Earth, there is evidence of lots of water in the past, there is evidence of lots of water in the present, and to my knowledge no evidence of a discrepancy between the two. So what do you want again?

I simply want to say that every canyon we see here was formed by a water source that is no longer acting in the way it did when the canyon was formed. The water hasn't left Earth (or Mars) necessarily. It's just in a different place now. Gravity and all that.

With respect to the former, no one has said canyons on Earth couldn't, or haven't, formed quickly, have they? That's why I provided those images. Quickly moving water would carve out a very different path than leisurely moving water, wouldn't it? Can't you predict what those differences would be?

Sure! A fast moving bunch of water will make straighter streams than a slow moving one.

Fine. Compare lots of water in a rock basin with a narrow crack with the same amount of water in the same rock basin with a much wider gap. Any differences worth noting in your mind, regarding the issues you are dwelling on here?

The speed of the water escaping.

Gee, stipe, as of now you've made 25 posts since I made this reply to you. Suddenly lost interest in the dynamics of canyon formation?

Sorry, mate. Must have missed this morning's update.

 

[aharvey]

Sure thing. Or the water could well be still there somewhere, right?

Yup.

I simply want to say that every canyon we see here was formed by a water source that is no longer acting in the way it did when the canyon was formed. The water hasn't left Earth (or Mars) necessarily. It's just in a different place now. Gravity and all that.

And, what, you don't think geologists are aware of this?

Sure! A fast moving bunch of water will make straighter streams than a slow moving one.

...and it would take longer for slow moving water to carve out a given amount of rock than a fast moving one, right?

The speed of the water escaping.

So far still so good (!?).

Sorry, mate. Must have missed this morning's update.

No worries. I'm just missing the punch line, I guess. I thought you were arguing that it was silly to claim on the one hand that the Martian canyon resulted from a large amount of water blasting through over a short period of time and on the other hand that the Grand Canyon resulted from a large amount of water moving slowly over much longer periods. But I must have misunderstood you. Sorry!

 

[Stripe]

And, what, you don't think geologists are aware of this?

I don't know. I usually don't hear things put the way I view them... :chuckle:

...and it would take longer for slow moving water to carve out a given amount of rock than a fast moving one, right?

Too slow and it wouldn't do any carving.

No worries. I'm just missing the punch line, I guess. I thought you were arguing that it was silly to claim on the one hand that the Martian canyon resulted from a large amount of water blasting through over a short period of time and on the other hand that the Grand Canyon resulted from a large amount of water moving slowly over much longer periods. But I must have misunderstood you. Sorry!

That would be fairly silly unless there was clear evidence that such happened. The default idea should be that they formed in the same way.

 

[aharvey]

I don't know. I usually don't hear things put the way I view them... :chuckle:

Yeah, I'll bet! But really, you can't think geologists are unaware that water can change locations!

Too slow and it wouldn't do any carving.

I guess that's bound to be true!

Originally Posted by aharvey
No worries. I'm just missing the punch line, I guess. I thought you were arguing that it was silly to claim on the one hand that the Martian canyon resulted from a large amount of water blasting through over a short period of time and on the other hand that the Grand Canyon resulted from a large amount of water moving slowly over much longer periods. But I must have misunderstood you. Sorry!
That would be fairly silly unless there was clear evidence that such happened. The default idea should be that they formed in the same way.

But you yourself identified the necessary evidence! Fast moving water would quickly carve out a straight channel (e.g., the Martian canyon), whereas slow moving water would take longer to carve out a more meandering channel (e.g., the Grand Canyon). Or do you think these pictures show equally straight cuts?

 

[Stripe]

Yeah, I'll bet! But really, you can't think geologists are unaware that water can change locations!

I would guess not.

But you yourself identified the necessary evidence! Fast moving water would quickly carve out a straight channel (e.g., the Martian canyon), whereas slow moving water would take longer to carve out a more meandering channel (e.g., the Grand Canyon). Or do you think these pictures show equally straight cuts?

Which channel? The Grand Canyon has two. There's the one which the river runs in today and there's the really big one.

 

[Stripe]

Which channel? The Grand Canyon has two. There's the one which the river runs in today and there's the really big one.

map
One marked in blue, the other in red.

 

[aharvey]

map
One marked in blue, the other in red.

Yes, the blue lines mark a relatively short, wide stretch that then fans out at 90 degree angles. The red lines mark a relatively longer, narrower stretch that eventually takes, at least to the west, a sharp 90 degree angle turn. The red lines, incidentally, also highlight a relatively short stretch smack dab in the middle of the meandering Colorado River system (and if you look at the margins, you can see that rivers that seem to flow in a straight line on one scale may still be meandering).

But anyways, you've shown the pictures, now please explain them in the context of the point you've been trying to make.

 

[Stripe]

The channel indicated by the blue lines is the result of a water source that is no longer operating.

 

[aharvey]

The channel indicated by the blue lines is the result of a water source that is no longer operating.

A water source that is different from, and preceded, the water source that carved out the Colorado River Basin that occurs upstream, through the middle of, and downstream your little blue area? A water source that thus couldn't have had anything to do with the Grand Canyon proper (you know, that huge meandering "side canyon" you started to mark in red)?

 

[Stripe]

A water source that is different from, and preceded, the water source that carved out the Colorado River Basin that occurs upstream, through the middle of, and downstream your little blue area? A water source that thus couldn't have had anything to do with the Grand Canyon proper (you know, that huge meandering "side canyon" you started to mark in red)?

Umm ... yes. I think so. Not entirely sure what you're saying.

The water that carved out the large blue channel is not the same or of the same source as the one we currently see flowing in the Grand Canyon.

 

[Stripe]

What is a 'river basin'?

EDIT: Forget that. I got it.

A River basin is the portion of land drained by a river and its tributaries. It encompasses all of the land surface dissected and drained by many streams and creeks that flow downhill into one another, and eventually into one river. The final destination is an estuary or an ocean. As a bathtub catches all the water that falls within its sides, a river basin sends all the water falling on the surrounding land into a central river and out to the sea.

I think we called them drainage systems or something when I was in University. Or perhaps it was river basin and I'm just getting old :chuckle:


:noid:

 

[aharvey]

Umm ... yes. I think so. Not entirely sure what you're saying.

The water that carved out the large blue channel is not the same or of the same source as the one we currently see flowing in the Grand Canyon.

Well, er, if the short broad bit marked in blue had nothing to do with the carving of the Grand Canyon or the canyon system upstream of it, why are we talking about it? My whole point has been that the meandering configuration of the Grand Canyon fits the criteria you acknowledged as being evidence for a longer bout of slower moving water, whereas the straight shot configuration of the Martian canyon fits the bill for a shorter blast of faster moving water. Even if the short broad bit in blue does represent an earlier episode of fast moving water (and I don't know if it does or not), if it didn't also carve out the Grand Canyon then it has nothing to do with whether geologists are silly for thinking the GC was carved out from slow processes and the Martian canyon from fast ones.

 

[Stripe]

Well, er, if the short broad bit marked in blue had nothing to do with the carving of the Grand Canyon or the canyon system upstream of it, why are we talking about it? My whole point has been that the meandering configuration of the Grand Canyon fits the criteria you acknowledged as being evidence for a longer bout of slower moving water, whereas the straight shot configuration of the Martian canyon fits the bill for a shorter blast of faster moving water. Even if the short broad bit in blue does represent an earlier episode of fast moving water (and I don't know if it does or not), if it didn't also carve out the Grand Canyon then it has nothing to do with whether geologists are silly for thinking the GC was carved out from slow processes and the Martian canyon from fast ones.

And I would say that much larger features are usually a key to understanding the whole situation.

 

[aharvey]

And I would say that much larger features are usually a key to understanding the whole situation.

Perhaps you should just cut to the chase and explain the whole situation using those much larger features, because so far everything you've been agreeing to suggests a slow Grand Canyon origin and a fast Martian canyon (sorry, can't recall its name) origin, but you seem to be rejecting this interpretation!

 

[Stripe]

Perhaps you should just cut to the chase and explain the whole situation using those much larger features, because so far everything you've been agreeing to suggests a slow Grand Canyon origin and a fast Martian canyon (sorry, can't recall its name) origin, but you seem to be rejecting this interpretation!

Of course I reject that! Nothing I've said has lent support to that silly idea. Why would you believe that a lot of water on Mars could form a large canyon but reject the same process being able to operate on Earth?!

 

[Jukia]

Of course I reject that! Nothing I've said has lent support to that silly idea. Why would you believe that a lot of water on Mars could form a large canyon but reject the same process being able to operate on Earth?!

If I have been following this discussion, perhaps because of the shape of the canyons?

 

[aharvey]

Of course I reject that! Nothing I've said has lent support to that silly idea. Why would you believe that a lot of water on Mars could form a large canyon but reject the same process being able to operate on Earth?!

Not only did I not "reject the same process being able to operate on Earth," I gave you an example of it. Stop playing games. Surely you're sharp enough to realize that just because something can happen a certain way doesn't mean it had to happen that way every time. And you yourself acknowledged that the shape of the canyon will depend on the rate of the water flow; perhaps it's no accident that you have stubbornly refused to comment on the meandering nature of not only the Grand Canyon, but also the much larger system of which it is part. Instead, you've focused on one small stretch in the middle, presumably because it is the straightest bit you could find, even though you then admitted that whatever water might have been responsible for that short wide bit could not have been responsible for the Grand Canyon itself! And though you won't say why you acknowledge that, isn't it because the Grand Canyon is just too meandering to have been formed by a single short blast of fast-moving water?

 

[fool]

Don't forget ice ages.
They pen up alot of water.