Solving The Riddle Of The Grand Canyon's Formation The Grand Canyon may seem to be a simple case of "river carves rock," but to geologists, its formation is still puzzling. Ira Flatow and guests discuss the canyon's mysteries, and the scientific sleuthing being done to solve them--millions of years after the Colorado River carried off the evidence.

#### Solving The Riddle Of The Grand Canyon's Formation

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Solving The Riddle Of The Grand Canyon's Formation

# < Solving The Riddle Of The Grand Canyon's Formation

#### Solving The Riddle Of The Grand Canyon's Formation

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IRA FLATOW, host: This is SCIENCE FRIDAY. I'm Ira Flatow. We're broadcasting live today from Flagstaff, Arizona. And just north of here is, of course, the Grand Canyon, one of the most beautiful and awesome gashes on the face of the planet.

(SOUNDBITE OF LAUGHTER)

FLATOW: And if you're like me, you probably assume that the canyon was carved out by a river running through it, just like the Colorado does today. Well, that's sort of true, but the story's a bit more complicated. But like most things in life, the devil is in the details. And for over a century, geologists have been puzzling over how and when the canyon formed.

The earliest American to lead a river expedition through the Grand Canyon was Major John Wesley Powell, who set out in August 1869 with several wooden boats and a month's supply of flour, bacon, dried apples and coffee. He went on to describe in detail the rock formations he found, what the cliff walls were made of, and, of course, the lively rapids.

We've learned a lot since Powell's trip, but there are still some points of debate. For example, some geologists dispute the age of the canyon, others the reason it even began forming in the first place. Will we ever be able to answer these questions definitively? Are some of these mysteries of the canyon lost in the rocks, carried away long ago by the river?

That's what we'll be talking about this hour. You can tweet us @scifri, @-S-C-I-F-R-I. And if you're in the audience here, don't be shy. Step up to the microphone. And you get to ask that question you've always wondered about the Grand Canyon, but no one was here to answer.

They're here to answer today, and let me introduce them to you. Karl Karlstrom is a professor of structural geology and tectonics at the University of New Mexico in Albuquerque. Welcome to SCIENCE FRIDAY, Dr. Karlstrom.

KARL KARLSTROM: Thank you very much.

FLATOW: You're welcome. Ivo Lucchitta is emeritus scientist at the U.S. Geological Survey. He's also a research associate at the Museum of Northern Arizona here in Flagstaff. Welcome back to SCIENCE FRIDAY, Dr. Lucchitta.

IVO LUCCHITTA: Thank you.

FLATOW: Richard Young is a professor of geological sciences at the State University of New York in Geneseo. He joins us from WXXI in Rochester. Welcome to SCIENCE FRIDAY, Dr. Young.

RICHARD YOUNG: Thank you, Ira.

FLATOW: Karl, let me begin with you first, and talk about why is the canyon so mysterious to geologists? It seems - it's there. There's a river running through it. It seems simple.

(SOUNDBITE OF LAUGHTER)

KARLSTROM: Yes, well, I suppose an even deeper question is: Why is it to fascinating to the world's public? But to answer the question of why it's mysterious, I don't think it really is that mysterious. I think that, as you said earlier, the basic ideas of how a river carves through rock to carve a canyon are well-understood.

The timing of how it happened, I think, is reasonably well-understood. Maybe the age of the canyon, in my opinion, is very well-understood. But the events that led to the carving of the canyon, I think, are challenging because, as you said, it's an erosional landscape, and the record is being carried away.

So as you go farther back into the history of this iconic landscape, I think the evidence becomes more fragmentary, and there's much more room for discussion and debate about how we got to where we are now.

FLATOW: Richard Young, your work on the Grand Canyon began at the same time as Ivo's, 50 years ago, when you discovered that rivers around there used to flow east and not west, as they do today. How is that possible? How'd you find that out?

YOUNG: Well, I was sent out to work on a different problem altogether, but eventually, over a period of years, it became obvious that there was another canyon right next to the existing canyon, which is kind of amazing since all the erosion that has occurred. So it just kind of gradually emerged that there was a much older story, but we had a hard time getting the actual age confirmations until, in fact, only about a couple years ago.

FLATOW: Mm-hmm. Ivo, your research on the Grand Canyon was sort of a plug at the western edge of the canyon, correct, where the Colorado couldn't have flowed before a certain time?

LUCCHITTA: It's an immovable object.

(SOUNDBITE OF LAUGHTER)

FLATOW: So how certain can we be of the age of the Grand Canyon, based on that immovable object?

LUCCHITTA: Well, I think one has to start by defining a few terms. The history is very complicated, and we should be talking about the Grand Canyon that we see today and the Colorado River that we see today.

But in reality, these are just the last episode of a long chain of events stretching back millions, if not tens of millions, of years. So it is - one really has to say: How much departure for what we see today will we accept and still view it within the same framework?

Now, the river that we see today, because of the immovable object at the mouth - and let me explain to the audience what that would be. It is a sequence of deposits that were laid down in the conditions of interior drainage. You can get the mental picture of that by going to any basin in Nevada, (unintelligible) at the bottom, no river flowing through it.

Those are the kinds of deposits that you see at the mouth of the Grand Canyon. And they have a date and age that has been debated, but we're zeroing in on it, for sure around six million years - it could be less. It could be less.

And so that, in a sense, are - no, not in a sense, rather conclusively, I think - gives you an upper boundary for the age of the carving of the present canyon. So we're looking at six, for sure, perhaps as little as between five and six.

FLATOW: So this was not just - as most people, and everybody, I think, the general public thinks a gradual decay of the river down through, you know, a period of millions of years. It's a lot more complicated. Things were going up. There was thrusting of tectonics happening, things like that, Ivo, at the same time.

LUCCHITTA: Sure, sure. But really what - fundamentally one has to think of river systems - and this has been one of the great lessons, I think. One has to think of them as competing entities which respond to external circumstances - uplift, glaciers, you name it.

Each of these entities is trying to increase its kingdom by a variety of means, like a headwater, erosion or what have you. And ultimately, some of these entities, some of these drainages become advantaged by what happens, external causes, and some become disadvantaged. So they're all duking it all, and some of them win out.

And what we see today is the result of a long process of such responses to external conditions - the physical equivalent of biological evolution, I might add.

FLATOW: I see. There is a - there was a theory that there was a giant lake - and Richard, you can jump in on this, too. There's a giant lake that was around here that spilled over and carried away all kinds of stuff and maybe some of the secrets of the Grand Canyon. Can you tell us about that, Richard?

YOUNG: Well, basically, that was a theory that went back to the 1960s, but we didn't have good age control at that time. But basically, when Ivo and I started working together, he started at the top of a section, kind of with the younger rocks, and I really started at the bottom and worked my way up.

So the lake story is really - it really belongs in the younger part of the history, rather than where I started at the bottom.

FLATOW: Mm-hmm. And are we ever going to be able to solve the mystery, do you all think, of how old the Grand Canyon is and how it finally - Karl, you're shaking your head. Yeah, you think we're going to get that?

KARLSTROM: Well, we've had a number of decadal conferences, collaborative get-togethers of scientists. I think the first one was, what, in the...

LUCCHITTA: Sixty-four.

KARLSTROM: Sixty-four, and then in 2000 and then in 2010. And each of these - is that right, Dick, 2000 for the - yes. So each one of these brought together people with very different points of view and different data sets, and I think each decadal meeting has resulted in a giant leap forward.

This present one that was just last year, I think there were several really important data sets. So I think, yes, we're honing in on it, and the ability to measure age is better, and to look deeply into the earth better and understand river systems better. I think we're close.

FLATOW: Well, then, Richard, can you tell us, then, why the Grand Canyon is even here and not some other place along the Colorado River?

YOUNG: Well, I think part of the story that you just finished discussing is the fact that there are hardly any rocks that are between approximately 20 and six million years old. So there's a big gap, because the rocks are missing. But from my point of view, the country to the west of the plateau and the rocks that I study was much higher, so that the rivers were actually flowing from California, Nevada, toward Flagstaff and toward the east.

So the system I saw was totally the reverse of what we see today, and gradually that went on for tens of millions of years, until approximately maybe 50 million years ago, somewhere in that range. And then we begin to lose track of the details for a period of time, and there's very little evidence.

FLATOW: So 10 to 20 million years ago, that's the fuzzy period?

(SOUNDBITE OF LAUGHTER)

YOUNG: Well, from, say, six to 20 million years ago.

FLATOW: Six to 20 - how did the river - why did the river stop moving from - going from west to east, and then start going another direction and formation of the river and all that kind of stuff.

YOUNG: Can I jump in? We know that...

KARLSTROM: (unintelligible) Oh, sorry.

KARLSTROM: We know that the country that used to be mountainous off to the east in the past suddenly dropped precipitously due to Karl's area of expertise, the tectonics of North America. And that's called the Basin and Range orogeny, roughly 20 million years ago. And that lowered the area to the west. So it made it possible for a river to reverse direction. It's just the question of knowing exactly what the details were.

FLATOW: Karl, do you want to jump in?

(SOUNDBITE OF LAUGHTER)

KARLSTROM: Well, the - yeah. I think most - one of the exciting new datasets is coming along through the National Science Foundation telescope. We call it Earth Scope, and it's our Hubble telescope, except we don't look up, we look down. And this experiment is imaging the continent of North America at unprecedented resolution. It's going to take us another 10 years to finish it.

But the images that are coming out from the Earth Scope experiment are showing an interior, an Earth's interior that's quite dynamic. And there's upwelling portions of the mantle, and there's down-welling portions of the mantle. And although they're 100 kilometers beneath us, they're exerting forces on the surface, causing the plate to tilt one way and the other, to extend.

And it's those dynamic forcings - to me, this is the exciting part about the Grand Canyon, is that it's providing a very sensitive record of young and ongoing uplift of the Western U.S.

FLATOW: So while it looks to us like it's standing still, it's not standing still.

KARLSTROM: It's slow, but we have to get the time factor in here. The canyon's getting deeper by about a thickness of that piece of paper every year.

FLATOW: I thought I noticed a difference.

KARLSTROM: Yeah, yeah.

(SOUNDBITE OF LAUGHTER)

FLATOW: We're going to take a short break and come back and talk lots more about the canyon. Please, step up to the mic if you've got a question, talking with Karl Karlstrom, Ivo Lucchitta and Dick Young. Stay with us. We'll be right back after this break.

(SOUNDBITE OF MUSIC)

FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY, from NPR.

(SOUNDBITE OF MUSIC)

FLATOW: This is SCIENCE FRIDAY. I'm Ira Flatow. We're talking this hour about the origins of the Grand Canyon with my guests, Karl Karlstrom of the University of New Mexico in Albuquerque; Ivo Lucchitta, who is from the Museum of Northern Arizona here in Flagstaff; Dick Young of the State University of New York in Geneseo.

Our number, 1-800-989-8255. And when we left talking about this mystery, we were talking about, this is a dynamically tectonic, active place. In other words, the Earth goes up, moves around, changes direction, tilts up. And you can see that in the Grand Canyon. And it makes it hard to decide the exact nature of how things happen here.

I heard it described, and it may have been by you in a research paper, as maybe having a - it's like having a cake knife standing still while the cake moves up, right?

KARLSTROM: That's right. That's the way you cut your cake, isn't it, hold the knife there and lift the cake up?

(SOUNDBITE OF LAUGHTER)

FLATOW: Sort of, but I mean that's what's going on here with the river. The river is standing - is etching out just enough now as the surrounding area is rising.

KARLSTROM: Well, and the river is cutting down too. So it's the balance of - you know, the river would like to reduce the landscape to sea level with enough time. But in this case, the land level, I think, is moving up as well. So how to quantify those two interacting forces, the erosion that's moving things down and the tectonics that may be moving things up.

FLATOW: Is the tectonics evident around here? Are there, you know, earthquakes and volcanoes and things like that, Ivo, that...

LUCCHITTA: Well, there are certainly plenty of volcanoes. We are living in the middle of a very active volcanic field. But to go back to what Karl was talking about a little bit, the geomorphic evidence that we see, in other words the reason why we have canyons as opposed to big, wide, broad mature valleys, is probably because there has been a recent uplift which has caused the river to cut down at a very rapid rate.

So it hasn't had time to expand the valley side. It's just cut down. So all of those things work together rather nicely to tell us, yes, there has been young uplift.

FLATOW: The two big dams on the Colorado, the Glen Canyon Dam and the Hoover Dam, how have they changed the evolution of the river?

LUCCHITTA: Oh, my goodness. Rivers are living things, and they've taught us a great deal about a great many things, including the processes by which they react. Now, a river likes to erode and likes to carry sediment. If you are - and it likes to carry a certain amount of sediment so it is in equilibrium.

If you cut off the supply of sediment, the river is hungry, it's angry. It wants to do something with all this energy that it has, and it starts cutting down and transporting some new material down to the sea.

Well, when, for example, Glen Canyon Dam was built, people were very much aware of what would happen to the reservoir upstream. But as far as one can tell, they didn't really think enough about what would happen downstream in the Grand Canyon National Park. And national parks are pretty touchy. I mean, you don't mess around with them.

So there's been a big to-do about the fact that the beaches are being eroded away. The ecosystem is being changed, and so the big thing has been what to do about that. And a couple of us, Luna Leopold(ph), a famous hydrologist, and I, discovered that by utilizing floods on the Little Colorado River, which happen every seven years or so, and by adding to that flood some input from the dam to give you enough discharge so that the sand would be parked high, one can actually remedy that to a considerable extent.

You can never bring it back to the way it was, but you can help.

FLATOW: Is it possible, if you don't do anything, the dam is just going to fill up with silt, and it'll look like a wall is there?

LUCCHITTA: It will, absolutely.

KARLSTROM: But, you know, nature has performed this experiment many times in the past with the lava dams that poured over the walls of the Grand Canyon and blocked the river. And the river makes pretty short order. We have to get the time scales right. And so tens and hundreds of thousands of years see these dams long gone.

So - but at the scale of the - our human time scales, we have to worry about the silt filling up and dredging the dam, for sure.

FLATOW: Dick Young, did the engineers not know this would happen when they built it?

YOUNG: They did know, and they got the timing pretty right. For example, Lake Mead today, at the other end, is seriously filling with sediment, and it was projected to have a lifetime of about 100 years, which is kind of approaching us now from the 1930s.

FLATOW: Wow, they got it right. Let's go to the audience here, yes.

NIKKI: Hello, my name's Nikki(ph). I'm from the Navajo Nation. And I've always wanted to ask this question on your show, Ira: How do you scientists - and I'm hoping, Ira, you can answer this too - incorporate Native American indigenous knowledge and science into your work down in the Grand Canyon? Because Powell was not the first one to go through.

(SOUNDBITE OF APPLAUSE)

NIKKI: It was (unintelligible) - there was a Hopi and a Navajo boy that actually went through there first, so...

FLATOW: Okay, let's set the record straight. Karl, Ivo?

LUCCHITTA: Well, yeah, thanks.

(SOUNDBITE OF LAUGHTER)

LUCCHITTA: Actually, I didn't know that, but it wouldn't surprise me that there had been a lot of people before Powell who had gone down at least parts of the river. And the best I can tell you is that in the current studies, the people who are studying the Grand Canyon, monitoring it and so on and so forth, which I'm not doing anymore, but they do include Navajo and Hopi as stakeholders, as it is said, to make sure that the cultural issues are preserved and the ideas are also incorporated.

So the best I can tell you is that yes, it's a process that's happening.

FLATOW: Karl?

KARLSTROM: And also, we just finished - in October we opened an exhibit at Grand Canyon Trail of Time Exhibit to try and communicate to the public a sense of the magnitude of geologic time. Into that exhibit we incorporated - we were told very early on by some Native Americans that time is not linear. And yet we're doing a timeline. So how to incorporate the concept of cycles and repetition and the interplay between the upper - the atmospheric forcings and the Mother Earth forcings, these are all things that are embedded in the exhibit and very powerful concepts that have come, I think, from indigenous science.

FLATOW: All right, thank you. Let's go to this side, yes.

UNIDENTIFIED MAN: Well, I'm wondering about the Mexican equivalent of the Grand Canyon. And is that a similar laboratory to the Grand Canyon, or is it just completely different, that it perhaps can't apply?

YOUNG: Copper Canyon?

UNIDENTIFIED MAN: Yes.

YOUNG: It's wider, and it's deeper, but it's not as grand, we say.

(SOUNDBITE OF LAUGHTER)

YOUNG: It's not as spectacular in terms of different rock layers that preserve the history of the rock. It's mostly volcanic. It's a spectacular canyon but carved by a spectacular drainage system as well. So there's lots of lessons from it.

I think the Grand Canyon preserves a longer and richer record of the geologic history. And just a comment, that at the Grand Canyon we're trying to make clear to people is that it's a relatively young canyon carved into very old rocks. So in the case of Copper Canyon, it's a relatively young canyon carved into relatively young rocks.

FLATOW: When you go to the Grand Canyon, you see layers, wonderful layers upon layers of different colored rocks, which the river has cut into. What is the age of those rocks up there?

YOUNG: The top ones are 270 million, and then as you go down, they get older, and the oldest rocks that we've dated in the inner gorge of Grand Canyon is almost two billion, 1.84 billion years.

FLATOW: And so give us - jump in our time machine and take us ahead to a couple of million years.

YOUNG: Well, but that's only half the age of the Earth, of course, two billion. Okay, now jump ahead - as I say, it's getting deeper, about a thickness of a piece of paper every year. And the river is carving down, and the landscape is moving up. So I would hazard a guess that we're going to - the Grand Canyon is getting grander.

LUCCHITTA: Probably, for sure. But, you know, this is a good time to introduce an idea that a lot of people don't really understand. What is a million years? How many people have really a physical understanding of what a million years is? A good way of doing that is I think to bring in human life.

Assume that the human generation is 20 years, good enough, easy number to work with. So how many generations between us and Christ? A hundred. How many generations between us and the time when Bronze Age Troy was sacked and burned as described by Homer? A hundred and sixty.

How many years between us and the time when people in Mesopotamia, between the Tigris and Euphrates, started, invented agriculture and invented urban living and gave rise to the civilization we have today? Well, that's about 300.

How many generations in a million years? Fifty thousand.

FLATOW: That's a long time.

LUCCHITTA: And that's - you see?

FLATOW: But not in Earth time.

LUCCHITTA: No, one million years for us geologists is chump change.

(SOUNDBITE OF LAUGHTER)

LUCCHITTA: But it's 50,000 generations, and that explains why you can carve Grand Canyons in five million years.

FLATOW: You know, creationists have jumped on some of these problems that still need to be solved, and they say this proves creationism. I mean, how do you react to that, Karl? When you go out to the Grand Canyon and go on a raft, and you go to a spot, and you describe it, and then someone else comes along and says, oh, this is carved out by Noah's flood.

KARLSTROM: Yeah, the next river trip behind us could be creationists talking about the same rocks with a different set of stories. They view the horizontal layers in the Grand Canyon as Noah's flood rocks, and the ones in the basement as the ones that God created in the first days. The - it's a difficult one to address. I think the Grand Canyon gets visitors from all over the world with all different creation stories about how humans originated. And scientists operate a little differently.

Scientists operate with data, with testing of evidence, with refinement. The arguments that go on between scientists are to refine the ages, not to presume any particular answer from the beginning. So it's just a different way of approaching your belief system. And we think science is the one to - the park agrees they're presenting the scientific interpretation of Grand Canyon as the one which the public deserves to hear.

FLATOW: Dick Young, any comment?

YOUNG: Well, I don't - fortunately, being out in the Western Canyon with the Hualapai Indians, I have not encountered too many creationists. It's too hot and dry out there.

(SOUNDBITE OF LAUGHTER)

FLATOW: Now, let's go to the audience. Yes, Beth.

BETH: I was wondering if - do you know if the Grand Canyon would ever completely erode?

FLATOW: When you say completely erode, what do you mean by that?

BETH: Like, not exist anymore.

FLATOW: OK. Dick Young, you want to take a shot at that first?

YOUNG: Good question. Well, I guess only if we build enough dams to fill it up, as we started to do. But I think that's not an issue anymore, since they defeated the last dam that was in my field area.

FLATOW: Ivo, no?

LUCCHITTA: Well, what happens is with time, the river will carve - well, erosion will carve the - the sides of the canyon of the valley back and back and back and back. And the river will transport the debris that's produced by this down to the sea. How fast this happens is very variable, depends on the rock that you're dealing with, depends on the energy of the stream, and so on and so forth. But one thing is for sure, and that is in time, the Grand Canyon will not be a canyon anymore. Maybe it'll be a wide-open valley.

FLATOW: Huh. Will it find, on its own, a way around these dams before that?

LUCCHITTA: Oh, absolutely. In fact, this is an interesting thing. If you look at Glen Canyon Dam from below, from below, you'll notice - and many of us have noticed that there are some big springs developing on the right abutment of the dam that didn't use to be there, and big blocks of rock are falling down. Now, the abutment is in a sandstorm, which is cemented with calcite, calcium carbonate. Calcium carbonate is soluble in acid. The water of the lake is weak acid. So guess what happens? It's a self-reinforcing mechanism. The more solution happens, the more water goes through, the more solutions - so it is possible that at some time, perhaps not too far from today, there will be a big plug of concrete sitting there, with the river going around it, maybe on both sides.

FLATOW: Good tourist attraction.

LUCCHITTA: Because (unintelligible) wonderful.

(SOUNDBITE OF LAUGHTER)

FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY, from NPR. You sort of revel in nature's triumphing over humans, don't you? You like that (unintelligible).

(SOUNDBITE OF LAUGHTER)

LUCCHITTA: No. We humans do stupid things all the time.

(SOUNDBITE OF LAUGHTER)

KARLSTROM: Yeah. We have to keep in mind the time frames. And this whole discussion is great. To think about the things that geologists can help society with that are at human time scales, for my lifetime, for my children's lifetime, versus the processes that we need to think of over longer periods of time. That's what geosciences have to offer, I think.

FLATOW: Let's go to the - yes, this man in the audience.

UNIDENTIFIED CHILD: Well, so there's lots of caves in the Grand Canyon, like, around it. So how might they have formed?

FLATOW: How did the caves form in the Grand Canyon? Good question.

KARLSTROM: The cave systems are, for the most part, in the limestone layers. And just as Ivo was describing, these weakly acid waters will move down through the crack and expand the crack into a room, and then eventually the rooms can be linked together into vast cave systems. And once that happens, then our groundwater finds its way through the caves. So if you want to find a lot of water out in the plateau, you have to somehow figure out where the water is flowing through these cave systems. And it's a great challenge, but it's one of the main aquifers for the Colorado Plateau, which is the place where the water can be found, if you could find the crack systems.

FLATOW: You're not suggesting he go out and find those.

KARLSTROM: Well, he may want to. He may want to.

(SOUNDBITE OF LAUGHTER)

FLATOW: It'll be fun.

KARLSTROM: He sounds like he's interested. OK.

FLATOW: One more question, here. Yes.

UNIDENTIFIED MAN: Hi. I was wondering if you could explain what the effect has been of past polar shifts on the geology of this area, and also globally, and also, what the anticipated effect of the current polar shift will have with the polar north being over Siberia.

KARLSTROM: So there's a couple of, I guess, a question back to you. Are you talking about magnetic reversals, where the North Pole becomes the South Pole? It happens intermittently in Earth history?

UNIDENTIFIED MAN: Correct.

KARLSTROM: There's also another thing where the - called secular variation, where the North Magnetic Pole moves around a little bit, relative to the - where Santa Claus lives, the rotational pole.

(SOUNDBITE OF LAUGHTER)

FLATOW: Very scientific terms we're using.

(SOUNDBITE OF LAUGHTER)

KARLSTROM: To my knowledge, no one has demonstrated a direct effect between the reversals in the magnetic fields and, say, extinctions or events in terms of geomorphic features. So the Earth's core is churning away with a convective system that generates the magnetic field. It doesn't seem to have a direct effect, to my knowledge, of the surface system.

LUCCHITTA: Well, I'm just saying, nor do we know of any correlation, which, for example, tectonics, which would be something you could conceivably see.

FLATOW: Could a big tectonic event just plug up the Grand Canyon somewhere?

LUCCHITTA: Oh, well...

KARLSTROM: Yeah.

LUCCHITTA: ...yeah. I suppose so. A great, big fault or something. Yeah.

KARLSTROM: There are major faults in the western Grand Canyon that - the river's actually very powerful and able to carry away the debris over short periods of time.

LUCCHITTA: It takes...

KARLSTROM: Excuse me. There have also been huge landslides in the Grand Canyon.

LUCCHITTA: But they get cleaned out.

KARLSTROM: They get cleaned out. Yeah.

FLATOW: All right. I want to thank you both - all three of you gentlemen for taking time to join us. It's fascinating. I learned everything about the Grand Canyon. Karl Kalstrom, professor of structural geology and tectonics at the University of New Mexico in Albuquerque. Ivo Lucchitta, who is emeritus scientist at the U.S. Geological Survey. He's also a research associate at the Museum of Northern Arizona here in Flagstaff. Ivo, thanks for joining us today. And Richard "Dick" Young is a professor of geological sciences at the State University of New York in Geneseo. Karl, Ivo, Richard, thank you all for taking time to be with us today.

LUCCHITTA: Thank you.

(SOUNDBITE OF APPLAUSE)

FLATOW: We're going to take a short break. And after we come back, we're going to talk about the Lowell Observatory, which is just a piece of the road, here, where scientists first spied Pluto. No wonder they love Pluto here so much. And we'll talk about the exoplanets they've discovered since then, and a visit to the observatory is always welcome. So stay with us. We'll be right back after this break.