Extinction event in my story, is it believable?

[DeliriousEncore]

I am writing a saga of multiple stories set at different time periods in a fictional version of our real world. At a certain point in the worlds timeline, in the next thousand or so years of the current real world time, an extinction level event wipes out all civilization and most life on earth, only for human civilization to return to the world in the far future.

My idea for this extinction level event is that of a worldwide Tidal Wave that knocks over and drowns out almost all civilization at the time.
I was brainstorming a couple interesting explanations for how this event occurs, however, I have a series of questions regarding if any of my possible explanations for this event, or combinations of thereof, are plausible or believable.

The first cause that I thought of was the possibility of the Moon becoming closer to the Earth by becoming caught in a slightly more exaggerated elliptical orbit, causing much greater high tides at the Moons Perigee which may cause great tidal waves when the moon begins to move further away from the earth in its orbit. However, I am unsure if this change in orbit would be great enough to cause such a Tidal Wave while also not being so extreme as to cause a different extinction event or to ruin the inhabitable conditions of Earth. If it is believable that the moon could grow closer to earth in a way to impact the tides while leaving the earth inhabitable over a long period of time, what other affects would this alteration to the moons orbit cause?
The other question with this first idea is what could be the potential cause of the change in the moons orbit, which to this question, I don't have a solid idea of what could cause it. And while I considered the idea of a large asteroid impact to the moon causing it to be pushed closer to the earth in its orbit, or possibly breaking the moon into multiple large fragments that would begin to orbit the earth, I understand that such an impact would likely completely destroy the moon before altering its orbit in the desired way for this story.

The other idea that I considered was simply the concept of humanity being so advanced that we had developed some magical science of Gravity Manipulation which may even be used over a planetary scale and which may have accidentally caused or added to this extinction incident. For context, this extinction event happens in a time where human civilization is much more advanced.

So the idea that I have been left with is this. In a hyper advanced future human society, where humans play god with the ability to manipulate Gravitational Forces among other things, the development and testing of this gravitational manipulation has caused the Moon to move closer to the Earth and into an more exaggerated elliptical orbit. This change in orbit has caused many disastrous effects on the world, such as extremely high tides, violet tidal waves and earthquakes as the tides reside, a possible an increase in Earth rotational speed which may cause shorter days and shorter nights, etc. To negate some of these disastrous effects and fight these tidal waves as they have increased in severity over the years, humanity now must utilize their Gravitational manipulation science to counteract the high tides during the perigee by pulling the water away from from the closest point of the earth to the moon. At the time of this extinction event, the worldwide gravity array which has been set up to counteract the high tides at the perigee falls to activate, and a great tide rises and falls, causing worldwide Tidal waves and earthquakes that wipe out the existing civilization. Then after a great amount of time, the fraction of remaining life in the world begins to repopulate the world after adapting to the harsher conditions of the world.
Does this sound at all believable, and what problems are there with this premise?

Regarding a completely separate possibility, is it possible for a galaxy wide Syzygy to occur that may cause such a tidal wave?

 

[Hornbein]

Tsunami would be too easily avoided and affect only the coasts. It would be catastrophic but they can't cause an extinction. But I see the basic idea as OK. I'd recommend earthquakes though as the trigger. You can't predict an earthquake. You can hide from earthquakes by going to sea but that's just a stopgap. Such severe earthquakes would not only cause cataclysmic destruction of infrastructure they could also unleash widespread volcanism. The copious spewed atmospheric ash would drastically decrease global temperatures and wreck any harvest. This is solid science, as significant global drops in temperature followed the big Krakatoa and Mount Agung eruptions. The closer the Moon gets the worse it would be, so you can make it as bad as you like. For extra drama you can have the ellipticity increasing without bound, so that unless something is done the Moon will actually collide with the Earth multiple times. That would truly be an extinction event.

You are correct that instead of having the Moon get closer overall you conserve energy (that's important) by having the orbit get more and more elliptical instead. That means the Moon gets both farther and closer during its orbit.

 

[Nik_2213]

If you want a plausible global mega tsunami, something that will douse all low-lying land unto mountains' foot-hills, then a cometary bolide is the simplest.

Have it split to swarm of big pieces: Land cruelly hammered, sea impacts spawn mile-high waves.
Plus run-up, of course, of course...

( Stuff that stooopid movie-- Yes, that one: No 'ark' would survive, but moon-base may... )

Back-story: About 70,000 years ago, Scholz' Star, a tiny 'M9+T5' binary made a 'close' pass to our solar system.
https://en.wikipedia.org/wiki/Scholz's_Star
As there are no apparent terrestrial mega-craters of that age, looks like its Oort objects missed us.
( How old is Jupiter's 'Great Red Spot' ?? )
But, pass will have stirred our Oort Cloud.
IIRC, in-fall time for such nudged 'iceteroids' to become inner-system 'comets' is around half a million years.
What if one came early ??

 

[pinball1970]

And while I considered the idea of a large asteroid impact to the moon causing it to be pushed closer to the earth in its orbit, or possibly breaking the moon into multiple large fragments that would begin to orbit the earth, I understand that such an impact would likely completely destroy the moon before altering its orbit in the desired way for this story.

The D.A.R.T. mission did something like that. https://science.nasa.gov/mission/dart/

An asteroid could hit the moon knocking a lot of debris in space but the main body, what is left could get closer to earth by changing its orbit.

The film Oblivion had a broken moon too if you remember. The parts would still exert a gravitational pull on the sea.

 

[DrJohn]

I was going to suggest asteroid or comet impact, mentioned above, for all the reasons given above.

I like NIK_2213's idea of it breaking up to hit more places, something I hadn't considered. That is believable.

But do you need ALL life to go extinct or just humans or almost all human life, as a few small isolated groups surviving in some way is easier to explain, rather then jumping forward 4 billion years to wait from them to appear. You can have near to total destruction, then just jump forward as many years as you want, to have enough people to talk about - small groups of a 100 or less, jump a thousand years, groups of 1000 or more (rival groups?), and eventually rival groups in the 10,000s who discover each other on exploring the world - how will they interact. That gives you a set of books with freedom to change how they live due to the time gaps. New humans have to take millions of years to appear, and what would they be descendants of, if all live went extinct???

And if you don't go of total extinction, you could have a small group in an area that the comet missed somehow surviving. Many stories have small isolate groups fighting each other to survive as they are close together and use whatever they find that's a 100 years old. So you want to avoid that unless you are really good at creating a new version of that sort of survival story. Remember, you are up against many similar books, so avoid copying them too much.

 

[pinball1970]

Tsunami would be too easily avoided and affect only the coasts. It would be catastrophic but they can't cause an extinction. But I see the basic idea as OK. I'd recommend earthquakes though as the trigger. You can't predict an earthquake. You can hide from earthquakes by going to sea but that's just a stopgap. Such severe earthquakes would not only cause cataclysmic destruction of infrastructure they could also unleash widespread volcanism. The copious spewed atmospheric ash would drastically decrease global temperatures and wreck any harvest. This is solid science, as significant global drops in temperature followed the big Krakatoa and Mount Agung eruptions. The closer the Moon gets the worse it would be, so you can make it as bad as you like. For extra drama you can have the ellipticity increasing without bound, so that unless something is done the Moon will actually collide with the Earth multiple times. That would truly be an extinction event.

You are correct that instead of having the Moon get closer overall you conserve energy (that's important) by having the orbit get more and more elliptical instead. That means the Moon gets both farther and closer during its orbit.

A prolonged gamma ray burst from a cosmic event is plausible. Researches say this has already happened.

https://www.independent.co.uk/news/...in-eighth-century-say-scientists-8460351.html

Just make it more intense and for longer.

 

[Vanadium 50]

Stephane Mallarmé said "To suggest is to create. To define is to kill."

Why do you need the details to tell your story? Besides, the "giant flood" has been done before. Over 4000 years before.

 

[pbuk]

The phenomenon you are talking about is a tsunami. Whilst these are often called "tidal waves" this is a misnomer because they have nothing to do with tides.

So no, moving the Moon into an elliptical orbit would not create a tsunami. It could however have significant, unpredictable, long-term effects on climate which could do anything you wanted to fit your story.

 

[Drakkith]

Regarding a completely separate possibility, is it possible for a galaxy wide Syzygy to occur that may cause such a tidal wave?

No. Galactic tidal forces are immeasurably weak owing to the huge distances between objects in space. By far the largest source of tidal forces on Earth is from the Moon, with the Sun exerting 46% of the tidal force the Moon does despite being about 27 million times more massive than the Moon.

 

[Drakkith]

For reference, a solar mass object placed 4 light years away from Earth has a tidal force of only 3.1x10^-23 N. Compare this with the Moon's tidal force of 1.08x10^-6 N, a difference of 17 orders of magnitude. To get the same tidal force from a mass placed 4 light years away you would need 6.95x10⁴⁶ kg of mass, which is more than 10,000x the mass of the Milky Way galaxy (5x10⁴² kg).

 

[FactChecker]

If I wanted to kill all life on Earth, I would start with a moderate earthquake in California. Then when everyone thinks it's over and safe, steam starts rising in the Pacific. They realize that a continental plate has snapped in half and lava is spewing up in the Pacific floor. Super-heated steam cooks everyone in a day.
BWAHAHAHAHA!
There, I'm glad I got that off my chest. I'll discuss this with my shrink at the next meeting. ;-)

 

[Hornbein]

Suppose the distance from Earth to Moon were reduced from 384,000 km to 38,400 km. Then by Newton's law of gravitation the force that the Moon exerts on the water's of the ocean would be increased by a factor of 100. Now tides are complicated but the crudest thing to do would to be multiply a ten foot tide by 100. That gets a thousand feet high tide. That would be quite a force.

The closest the centers of the two orbs can be without colliding is about 10,000 km. So we could get an increase of a factor 1600 in force. Could that mean a tide 16 thousand foot tide? Three miles. That's higher than the tallest mountain in the continental United States. That would be pretty apocalyptic. And the moon approaching so closely would be a mightily dramatic sight.

 

[Bystander]

The closest the centers of the two orbs can be without colliding is about 10,000 km. So we could get an increase of a factor 1600 in force.

https://en.wikipedia.org/wiki/Roche... the Roche,the second body's self-gravitation.

 

[DeliriousEncore]

The phenomenon you are talking about is a tsunami. Whilst these are often called "tidal waves" this is a misnomer because they have nothing to do with tides.

So no, moving the Moon into an elliptical orbit would not create a tsunami. It could however have significant, unpredictable, long-term effects on climate which could do anything you wanted to fit your story.

I do understand the difference between a Tsunami and normal Tidal Waves, though I was more so asking if it was believable that the moon being much closer could result in tidal waves large enough to become tsunamis, particularly as the tides recede, though I had figured it wouldn't.

On another note, if the moon had become much closer to the earth, more than just our oceans would feel the gravitational pull from the moon. What other affects would their be, and particularly, would earthquakes become more frequent during the moons perigee due to the moons gravity pulling on the earths plates more than normal? If so, is it possible for more destructive earthquakes in this case? And as most tsunamis are caused by earthquakes, could both earthquakes and tsunamis become more frequent?

 

[DeliriousEncore]

Stephane Mallarmé said "To suggest is to create. To define is to kill."

Why do you need the details to tell your story? Besides, the "giant flood" has been done before. Over 4000 years before.

Just because something has been done before doesn't mean that it shouldn't be done again. Yes, floods have been done before, and while you can say that makes them overused, I can also say that their establishment in existing stories and their familiarity gives excellent opportunity for certain themes to be explored. Besides, most apocalyptic events that many could think of have already been utilized many times, but what matters more is how that idea is used, not the basic idea itself.
For my story, water is very important symbolically, so water taking part in the extinction is something I am attempting to explore, though explaining all the reasons why I am interested in flooding or tsunamis could take a while and I don't want to give away too many details of my story.

And regarding defining the details rather than just suggesting what happens, I want an explanation that is somewhat believable and that doesn't feel like a gaping plot hole or contrivance to a substantial portion of its audience. Some people, like me, enjoy stories having more concrete answers to things, including magic systems, while others are fine without defined answers. So I want the details precisely because I like knowing them and I like being able to believe my own fiction rather than constantly questioning the validity of it.

That being said, I do agree with many of the criticisms of the validity of my initial ideas I posted, which is why I wanted other opinions on it.

 

[Hornbein]

https://en.wikipedia.org/wiki/Roche_limit#:~:text=In celestial mechanics, the Roche,the second body's self-gravitation.

I get that the Roche limit is about 8500 km. That's less than the collision distance, so the Earth/Moon can't exceed it.

 

[DrJohn]

I do understand the difference between a Tsunami and normal Tidal Waves, though I was more so asking if it was believable that the moon being much closer could result in tidal waves large enough to become tsunamis, particularly as the tides recede, though I had figured it wouldn't.

I don't think you do understand the difference between a tidal wave and a tsunami.
Because they are the same thing. A tidal wave does not turn into a tsunami if it becomes big enough. The terms are just different words for the same thing. Tsunami is used because the term tidal wave implies it is something to do with the tide - it isn't. And of course we want people to use a name that doesn't imply something has its origin in tides - ie we want to educate people.

What is probably confusing you with respect to these two terms is that in the movies they always feature huge tsunamis and use the word tsunami. Probably because a) they want the wave to be huge and b) they get fed up being told the term tidal wave is misleading.

Also, on tv reports, they try to avoid using the term tidal wave when referring to disasters, so you assume they are different things.

 

[pbuk]

I don't think you do understand the difference between a tidal wave and a tsunami.
Because they are the same thing.

No they are not.

Although both are sea waves, a tsunami and a tidal wave are two different and unrelated phenomena. A tidal wave is a shallow water wave caused by the gravitational interactions between the Sun, Moon, and Earth ("tidal wave" was used in earlier times to describe what we now call a tsunami.) A tsunami is an ocean wave triggered by large earthquakes that occur near or under the ocean, volcanic eruptions, submarine landslides, or by onshore landslides in which large volumes of debris fall into the water.​

https://www.usgs.gov/faqs/what-difference-between-a-tsunami-and-a-tidal-wave​

A tidal wave is a shallow water wave caused by the gravitational interactions between the Sun, Moon, and Earth​

https://oceanservice.noaa.gov/facts/tidalwave.html​

etc.

 

[pbuk]

I do understand the difference between a Tsunami and normal Tidal Waves,

Are you sure? Because...

I was more so asking if it was believable that the moon being much closer could result in tidal waves large enough to become tsunamis, particularly as the tides recede

...no matter how large a tidal wave becomes it cannot become a tsunami.

Anyway let's stop bothering about terminology, to address your original question the only plausible cause of a megatsunami leading to a global extinction event following which the planet returns to habitability is a meteor strike. Again.

 

[Nik_2213]

IIRC, part of the confusion stems from mistranslation of tsunami as 'tidal wave'. Admittedly, like the more common 'Storm Surge', they're even worse should they strike when tide is in...

As I understand it, 'tsunami' better translates as 'Harbour Wave', literally one that mugs you when you thought you were safely docked...

Um, IIRC, following Moon's formation via 'Big Splat', would have orbited close enough to raise massive earth-tides and sea-tides, causing heroic erosion. Frictional dissipation would have been 'considerable', prompting rapid regression. But, part-way out to current orbit, Moon got 'locked' by a resonance with Earth's orbit around sun. Regression effectively halted until Earth's orbital parameters shifted. Think Milankovitch Cycles, writ larger. Apparently, had this hiatus not occurred, the Moon would now be too distant for Total solar eclipses...

https://www.nature.com/articles/s41561-023-01202-6
https://www.nature.com/articles/s41467-024-46171-5

 

[FactChecker]

Anyway let's stop bothering about terminology, to address your original question the only plausible cause of a megatsunami leading to a global extinction event following which the planet returns to habitability is a meteor strike. Again.

Good point. And even then, a meteor impact large enough to send a tsunami to both oceans and end human life on Earth would have many other consequences (heat, poisonous air, even splitting the Earth's crust?, etc.). They would be more deadly. The dinosaurs were killed off by a meteor that was not nearly large enough to send a tsunami over the entire Earth.

 

[Hornbein]

If the Moon were radically closer to the Earth then tidal waves could be enormous. A crude estimate is a maximum of 1600 times larger that what we see now. That seems apocalyptic to me. Though I'd also expect a lot of volcanism and huge earthquakes due to intense tidal forces, these in turn producing tsunami. I'd expect these to be even more apocalyptic. But this is fiction so tidal waves may be used. It appears they alone could do the job.

 

[DeliriousEncore]

Are you sure? Because...


...no matter how large a tidal wave becomes it cannot become a tsunami.

Anyway let's stop bothering about terminology, to address your original question the only plausible cause of a megatsunami leading to a global extinction event following which the planet returns to habitability is a meteor strike. Again.

Yeah, I don't understand why this thread has become a debate over the difference between a Tsunami and Tidal Waves. There is really no reason to be talking about the difference between the terms as it seems most of the replies completely ignored my actual questions from my last post and instead decided to pick apart my understanding of terminology or the explanation for why I originally wanted feedback.

I already stated that I understand the difference, but I was simply asking if in this purely fictional, not at all real scenario, could super waves that could level the world (Mega Tsunami's) result from Tidal Waves from the moons gravitational pull. I understood that in no normal circumstance could Tsunamis result from tidal pull (Tidal Waves) though I was asking since this was a abnormal scenario. I did realize after thinking about it a bit that it couldn't happen, as even in this scenario, the shifting of the tides would still be gradual as the moon moves further away from the earth in this hypothetical elliptical orbit, and there is no way that would cause a tsunami. I did make my initial post late at night so I realize that I kind of overlooked that even though it was obvious.

Also, regarding the meteor strike, that was already explained to me prior in this thread and I understand that's the only explanation for a mega tsunami, though, a meteor large enough to cause near total worldwide destructive would cause that destruction by shockwave, earthquakes, heat, or other means rather than result in a worldwide tsunami, so that explanation doesn't really work for my initial story idea. Though that has made it clear to me that their is really no good explanation for an apocalyptic worldwide tsunami, so I'll need to shift my way of thinking to other possibilities for my apocalyptic event.

I am still considering some ideas for the fictional future world in my story. If there is any further posts here, I would appreciate feedback or answers on the other questions I had asked in my last post regarding what affects the earth would experience if the moon was orbiting more closely to earth. I did create a new thread with these questions as the focus, so if there are people willing or gracious enough to take the time to answer questions regarding my silly hypothetical story ideas, I would appreciate that feedback and I would appreciate if people went over to my new thread to answer those questions.
Here is the link to the new thread: https://www.physicsforums.com/threa...ser-could-that-result-in-earthquakes.1062266/

 

[FactChecker]

The big problem that I see is your goal of an extinction level event caused by ocean water. Humans live all around the Earth and at altitudes of a mile above sea level, so that is an ambitious goal. It's easier to imagine a huge asteroid killing everything in other ways, or complete destruction by tsunami in one area, or the Moon causing tides that flood all coastal areas daily. Would one of those work for you?