How far inland could a tsunami theoretically reach?

[chorpler]

The Discovery Channel here in Las Vegas had a “tsunami day” yesterday, running several programs about the science of tsunamis and mega-tsunamis over and over during the day. One of them, the BBC’s Horizon program Mega-Tsunami: Wave of Destruction, discussed the tremendous tsunamis that can be generated by landslides, and at one point there was mention of the incredible tsunamis that could be generated by large meteorite or comet impacts.

Watching these programs got me thinking about a scene that I remember reading – I think it was from the book Lucifer’s Hammer, by Larry Niven and Jerry Pournelle, which involves a comet hitting the earth – where a fragment of comet hits the Gulf of California and sends a megatsunami washing up northward, funneled through the narrow gulf like a bullet out of a gun, or something like that. (Note that I’m not sure that’s the book involved, and now I can’t find any reference to it as I look through the book, but I don’t know what other book it could have been. Hmmm. OH, here it is. It just doesn’t call it the “Gulf of California.”)

@Niven/Pournelle in *Lucifer's Hammer*

Between Baja California and the west coast of Mexico is a narrow body of water whose shoreline is like the two prongs of a tuning fork. The Sea of Cortez is as warm as bathwater and as calm as a lake, a playground for swimmers and sailors.

But now the pieces of Hamner-Brown’s nucleus sink through Earth’s atmosphere like tiny blue-white stars. One drops toward the mouth of the Sea of Cortez until it touches water between the prongs. Then water explodes away from a raw orange-white crater. The tsunami moves south in an expanding crescent; but, confined between two shorelines, the wave moves north like the wave front down a shotgun barrel. Some water spills east into Mexico; some west across Baja to the Pacific. Most of the water leaves the northern end of the Sea of Cortez as a moving white-peaked mountain range.

The Imperial Valley, California’s second largest agricultural region, might as well have been located in the mouth of a shotgun.

Similarly, in some movies or books or whatever, I’ve heard it claimed that a large enough impact could send waves washing up to 600 miles inland.

So, does anybody know how far, in general, a wave could possibly wash inland?

More specifically, I’m wondering if I’m absolutely safe here in southern Nevada. At about 2,000 feet above sea level, something like 250-300 miles from the nearest coast, and a big mountain range between me and the Pacific, it feels like I should be safe … but that whole “shotgun blast” tsunami scene from Lucifer’s Hammer is unnerving. I know that we get a lot of storms from that direction; according to my Geology 101 professor, that is because there aren’t any high mountains in between us and the Gulf of California, so the moist sea air isn’t forced up to a high altitude where it sheds its water as rain before reaching us, as happens with the air coming over California when it reaches the Sierra Nevadas.

So, is there anywhere a meteorite or comet could impact that would create a tsunami big enough to reach Las Vegas? How about Hoover Dam – I know the Colorado River and Lake Mead around here, and thus the dam, is only at about 1100 feet above sea level, as opposed to the 2000-2500 feet that the surrounding cities are at. And it would still be bad for me if the dam or its surrounding electrical facilities got damaged, because then we’d be without power.

I guess I should clarify that I’m not actually worried about this happening, realistically; I understand that there are a huge number of dangers that are much more likely to occur, like a fatal car accident or whatever. But what with the recent Indian Ocean tsunami and the whole “The minor planet 2004MN4 might impact the earth on Friday, April 13th, 2029!” furor that was going on at the same time, I’ve been wondering about this more exotic danger recently.

Thanks for any replies.

[David_Simmons]

On an onobstructed beach with a slope of 10’/mile a 30’ wave would go somewhat less than 3 miles depending on the friction losses. For some low-lying islands it could wash clear over the whole island.

[David_Simmons]

On thinking it over, the example wave might even go further friction or no. That much water moving at high speed has an awful lot of inertia which tends to keep it going.

[chorpler]

What about a wave that is, say, a kilometer high when it reaches the shore?

[Ale]

@chorpler

…More specifically, I’m wondering if I’m absolutely safe here in southern Nevada. At about 2,000 feet above sea level, something like 250-300 miles from the nearest coast, and a big mountain range between me and the Pacific…

I am the only one picturing Chorpler being chased by a tsunami wave as Leslie Nielsen in Wrongfully Accused was chased by a locomotive??

Anyway, if an event can make that big a wave, water is the least of your concerns.

[David_Simmons]

@chorpler

What about a wave that is, say, a kilometer high when it reaches the shore?

Were you just watching the Discovery Channel? There was a program on megatsunamis caused by landslides into the ocean. One in a bay in Alaska, I think it was Alaska, resulted in a wave 1500’ high that washed right over a peninsula. A man and his young son were in a boat that was carried on the front of the wave a long way inland and luckily survived. Two other boats were taken across the peninsula and out to sea and disappeared.

As I recall, if that hunk of rock on Palmas (or maybe Las Palmas) in the Canary islands falls off and is as big as they think, the estimate is the wave will reach inland on the US eastern shore as far as 30 miles in places.

[chorpler]

@David Simmons

Were you just watching the Discovery Channel? There was a program on megatsunamis caused by landslides into the ocean. One in a bay in Alaska, I think it was Alaska, resulted in a wave 1500’ high that washed right over a peninsula. A man and his young son were in a boat that was carried on the front of the wave a long way inland and luckily survived. Two other boats were taken across the peninsula and out to sea and disappeared.

As I recall, if that hunk of rock on Palmas (or maybe Las Palmas) in the Canary islands falls off and is as big as they think, the estimate is the wave will reach inland on the US eastern shore as far as 30 miles in places.

Heh heh … I linked to the BBC’s Horizon site for the Mega-Tsunami: Waves of Destruction program in the first paragraph of the OP; there’s even a transcript available. Very interesting program.

I was desperately hoping they’d show the Mega-Tsunami: Waves of Destruction episode again, because last Monday I was telling my dad about that 1958 megatsunami in Lituya Bay, Alaska, the one that reached 520 meters, and about how the island of La Palma could create a similar wave that would wipe out the Atlantic coasts. He demanded to know if any eyewitnesses were present for the Lituya Bay incident, because he just couldn’t believe a wave could be that high. So I recorded all three of the tsunami specials that Discovery had on yesterday.

But anyway …

@Ale

I am the only one picturing Chorpler being chased by a tsunami wave as Leslie Nielsen in Wrongfully Accused was chased by a locomotive??

Hey, come on! A megatsunami is WAY scarier than a locomotive. I should get a LOT more credit than him!

You know, come to think of it, there is a scene in Lucifer’s Hammer where a guy manages to surf the megatsunami as it inundates the California coast … I think I’ll picture that instead.

@Ale

Anyway, if an event can make that big a wave, water is the least of your concerns.

Well, obviously there would be further concerns if a sufficiently large meteorite hit the ocean – Lucifer’s Hammer and Footfall detail those further concerns quite nicely. Like the earth being swathed in heavy cloud cover, crops dying en masse, global temperatures plunging, an ice age returning in all of its glory, civilization collapsing … all that good stuff. But I would think the immediate concern, aside from any seismic tremors or shock waves or blasts of hot air or whatever from the impact, would be the megatsunami created. And if the strike was far enough away, people on the surrounding continents could avoid being killed by those but still be vulnerable to the resulting megatsunami. Which is why I ask – how far away would you have to go to be safe? And is my area, and power source, safe?

[Ale]

@chorpler

Well, obviously there would be further concerns if a sufficiently large meteorite hit the ocean – Lucifer’s Hammer and Footfall detail those further concerns quite nicely. Like the earth being swathed in heavy cloud cover, crops dying en masse, global temperatures plunging, an ice age returning in all of its glory, civilization collapsing … all that good stuff. But I would think the immediate concern, aside from any seismic tremors or shock waves or blasts of hot air or whatever from the impact, would be the megatsunami created. And if the strike was far enough away, people on the surrounding continents could avoid being killed by those but still be vulnerable to the resulting megatsunami. Which is why I ask – how far away would you have to go to be safe? And is my area, and power source, safe?

I´d be more concerned about the brimstone and hellfire raining from the sky, the meteorite that slammed on Yucatan 65 million years ago created a tsunami that washed Mexico and Texas, it didn´t make it all the way to Nevada, AFAIK. So you´d need an even larger rock for that. Now, if
this cite is correct you´d be roasted well before the water came.

[silenus]

@chorpler

You know, come to think of it, there is a scene in Lucifer’s Hammer where a guy manages to surf the megatsunami as it inundates the California coast … I think I’ll picture that instead.

No place is safe if a big enough body impacts us. A big enough hit in the Sea of Cortez will get Vegas wet.

As for feeling safer picturing the surfer…finish the paragraph.
“Sometimes you’re the windshield, sometimes you’re the bug.”

[Triskadecamus]

South Florida, Louisiana and southeast Texas are the parts of the United States that offer the most glaring examples of where a Richter 9 or greater spawned Tsunami could head farthest inland. And it is not outside of the realm of geologic possibility that such an event could happen.

The crustal rock on which the Gulf of Mexico sits is subsiding, and has been for a billion years or so. It is very old crustal rock, and very brittle as such things go. If it has built up a tension, and failed catastrophically, the nearest Gulf Coast areas would have a very large Tsunami travelling over a very gradual slope.

Keep in mind that most of southern Florida is less than a 150 feet above sea level, and a good portion is already covered with water. Parts of Louisiana are below sea level, and the entire region is flat as a pancake. And the real estate values are . . . pricey in spots.

Tris

“It was a woman drove me to drink and I didn’t even have the decency to thank her.” ~ W.C. Fields ~

[chorpler]

@silenus

No place is safe if a big enough body impacts us. A big enough hit in the Sea of Cortez will get Vegas wet.

Is there any way of figuring out what size impact that would require, short of modeling the whole terrain and simulating the impact in a very detailed way with a supercomputer or something?

As for feeling safer picturing the surfer…finish the paragraph.
“Sometimes you’re the windshield, sometimes you’re the bug.”

Hey, I never said it was safer – those pesky thirty-story apartment buildings are hard to avoid. But it’s a lot more fun than just being chased.

(You know, incidentally, at the time I first read Lucifer’s Hammer, that scene was one of the ones that made me the saddest. I was really hoping Gil was going to make it. You can’t help but love a guy who sees the world’s biggest wave rushing toward him and thinks “If death was inevitable, what was left? Style, only style.”)

[Polycarp]

@chorpler

(You know, incidentally, at the time I first read Lucifer’s Hammer, that scene was one of the ones that made me the saddest. I was really hoping Gil was going to make it. You can’t help but love a guy who sees the world’s biggest wave rushing toward him and thinks “If death was inevitable, what was left? Style, only style.”)

In either N-Space or Playgrounds of the Mind, together the two-volume retrospective with samples of his work from throughout his career that he published a few years ago, he mentioned in an afterword to the excerpts from Lucifer’s Hammer that Gil’s ride was the one thing about the book that had engendered the most letters – virtually all of which wanted to see Gil live. He did point out in that essay that he and Jerry didn’t write the actual impact – which means he might have avoided the building at the last minute.

[KGS]

@David Simmons

Were you just watching the Discovery Channel? There was a program on megatsunamis caused by landslides into the ocean. One in a bay in Alaska, I think it was Alaska, resulted in a wave 1500’ high that washed right over a peninsula. A man and his young son were in a boat that was carried on the front of the wave a long way inland and luckily survived. Two other boats were taken across the peninsula and out to sea and disappeared.

As I recall, if that hunk of rock on Palmas (or maybe Las Palmas) in the Canary islands falls off and is as big as they think, the estimate is the wave will reach inland on the US eastern shore as far as 30 miles in places.

I’m skeptical about that theory. A wave 3,000 miles wide and half a kilometer high seems like an awful lot of water to be pushed inland by a tiny landslip barely a cubic mile in size. The landslips in Alaska didn’t destroy California or Hawaii, for instance. (The scientists did say that they were kinda blurry on just how fast these giant waves dissipate over distance.)

I also wonder if Discovery had this “tsunami weekend” on their schedule two weeks ago.

[David_Simmons]

@KGS

I’m skeptical about that theory. A wave 3,000 miles wide and half a kilometer high seems like an awful lot of water to be pushed inland by a tiny landslip barely a cubic mile in size. The landslips in Alaska didn’t destroy California or Hawaii, for instance. (The scientists did say that they were kinda blurry on just how fast these giant waves dissipate over distance.)

I also wonder if Discovery had this “tsunami weekend” on their schedule two weeks ago.

Actually the wave was in a bay so it wasn’t 3000 miles wide. The bay appeared to be long and relatively narrow, a sort of a fjord, although there was no scale given as to it’s actual width.

The story was skimpy on details as to what happened after the wave got out into the open ocean. Based on how light behaves I would assume it diffracted at the edges of the bay exit and diminished as something like the the square of the distance. In addition to that effect, as the water deepened I would think the wave would rapidly diminish in height. As you say, investigation and studies of this phenomenon are pretty new.

[David_Simmons]

If you are speaking of La Palma I think they are talking about a wave quite a bit more than half a kilometer in height, depending upon the slope and configuration of the approach to the shore. I gathered from the program that a lot depends upon the speed with which the rock falls. If it slides in slowly, no problem If the fall is rapid and delivers an impulse of energy there is the distinct possibility of large waves on shorelines a long way away.

[Polycarp]

@KGS

I’m skeptical about that theory. A wave 3,000 miles wide and half a kilometer high seems like an awful lot of water to be pushed inland by a tiny landslip barely a cubic mile in size. The landslips in Alaska didn’t destroy California or Hawaii, for instance. (The scientists did say that they were kinda blurry on just how fast these giant waves dissipate over distance.)

@David Simmons

Actually the wave was in a bay so it wasn’t 3000 miles wide. The bay appeared to be long and relatively narrow, a sort of a fjord, although there was no scale given as to it’s actual width.

The story was skimpy on details as to what happened after the wave got out into the open ocean. Based on how light behaves I would assume it diffracted at the edges of the bay exit and diminished as something like the the square of the distance. In addition to that effect, as the water deepened I would think the wave would rapidly diminish in height. As you say, investigation and studies of this phenomenon are pretty new.

I believe we’re mixing two wave-forming phenomena here. The quarter-mile-high Lituya wave was the result of a seiche produced by a landslide in a narrow fjordlike drowned valley. The wave of the same order of magnitude expected to be created by the predicted Canary Islands landslide may or may not meet the catastrophic expectations of the worst-case scenario predictions. But it would result from a wave generated by the collapse of a rather enormous landmass into the oceans. To what extent it would be reinforced or dissipate requires a knowledge of physics I don’t have. But it would be quite different from the Lituya seiche wave, which reached that height for much the same reason that changing position in a nearly-full bathtub creates significantly more intense wave motion than doing likewise while swimming in the ocean, or why the Bay of Fundy has such comparatively enormous tides.

[aahala]

Based upon internet estimates of the land mass of the earth and volume of water of all oceans and seas, in the somewhat(?) unlikely event all the water suddenly moved to land, it would have a uniform depth of roughly 1.8 miles.

So if you’re living 10,000 feet above ground in your area and can within stand the original force of such an event, things look A-OK for you.

[ITR_champion]

I recall reading in a book in high school (I believe the book was The Atlas of Natural Disasters) that there’s evidence of a 3,000 foot tidal wave in the north Pacific about forty million years back. If it happened, it was presumably caused by either a truly massive seismic event or a meteor crash.

[KP]

in the somewhat(?) unlikely event all the water suddenly moved to land, it would have a uniform depth of roughly 1.8 miles.

I have the image of a kid screaming “Shark!” and the terrified ocean leaping onto the land like a 1950s cartoon housewife leaping onto a table after seeing a mouse.

Okay, maybe it’s more like a cartoon elephant. Who could blame it for being afraid? Sharks are, well… the sharks of the ocean.

[Carnac_the_Magnificent]

@ITR champion

I recall reading in a book in high school (I believe the book was The Atlas of Natural Disasters) that there’s evidence of a 3,000 foot tidal wave in the north Pacific about forty million years back. If it happened, it was presumably caused by either a truly massive seismic event or a meteor crash.

On the Discovery program, IIRC, at least two experts said there is an upper limit for seismic-generated waves, or tsunami. I think they cited something in the 30-meter range.

Technically, I don’t think a 3,000-foot wave can have a “tidal” origin. We’re talking a splash of some sort, either asteroid, landslip/slide, or something involving Bruce Willis or Morgan Freeman.