Massive asteroid impact in 2036?

[Whiplash]

Just like how that 30ft high Tsunami from the 2004 Boxing Day Earthquake drowned millions when it ran through the Indian Ocean?

Oh wait...

I've got an idea. Why don't you just admit you don't know what you're talking about?

Thunder does like to preach authoritatively on subjects that he is clearly rather ignorant on. I've noticed it many times.

 

[lionking]

Thunder does like to preach authoritatively on subjects that he is clearly rather ignorant on. I've noticed it many times.

But, but, it works with a rock in a pond!

 

[gumboot]

Just too make sure I am on the same page here:

Do you mean the asteroid is 200 yards across prior to entering the earths atmosphere, or 200 yards when it actually impacts the ocean.

I don't know. It's not my scenario. I was basing it on comparing with the energy release from other examples cited in the same document. For whatever reason they declined to provide sufficient detail to do much more.

I suppose the speed the asteroid is travelling is important in determining the energy release. Would the relationship between speed and energy release be linear?

KE=mv², does it not?

But as mythbusters has so kindly demonstrated, faster objects actually have less chance of penetrating deep into water.

The article I linked to refers to estimated damage calculated by software written by http://www.lpl.arizona.edu/Support/faculty/faculty.php?nom=Lewis

I wouldn't dismiss his scenario as not remotely plausible without a very good reason.

My issue relates specifically to the tsunami event. Even seismologists, who specialise in these matters, don't claim to be able to predict with any sort of certainty which quakes will and won't generate a tsunami, and again, tsunamis are caused by massive shifts in the sea floor which displace the entire water column from floor to surface. Earthquakes demonstratively release vastly more energy that the impact events we're discussing (as cited by the simulation), and release this energy immediately in the ocean floor itself rather than spread across the entire atmosphere and the entire ocean. A surface-originated event just isn't going to be able to transfer that same level of energy to the sea floor - it's going to be dissipated massively as the object passes through the water. And if it did somehow hit with enough force to slam right into the bottom of the ocean it would probably vapourise vast amounts of water, resulting in a localised water collapse and a drop in local sea level.

It just seems to me, from listening to this scenario, that the people know a lot more about impact events than they do tsunamis, and in particular the difference between a megatsunami and a normal tsunami. A megatsunami is so-called because of the extraordinary size of the wave front, but they're actually magnitudes weaker, more localised, and less damaging than a regular tsunami.

There's other factors too that I really just can't see any sort of computer simulation, no matter how sophisticated, being able to predict in any way remotely useful. Like, to begin with the basics, the status of human civilisation. This simulation is talking about the next one million years. A million years ago humans were apes wandering the grasslands of Africa, and our rate of development over the last few thousand years has been insanely exponential. I don't see how anyone can even begin to speculate on the status of human civilisation on the time scales that simulation is talking about.

It all starts to sound a bit like an exercise in pointless scaremongering with about as much scientific usefulness as a post-apocalyptic film starring Kevin Costner.

 

[gumboot]

Was that the height of the wave on the ocean itself or the height of the wave after it reached shallow water? My understanding is that on the ocean the wave was quite small; it was only upon entering shallower areas that the wave height grew due to the wave 'piling up.'

Tsunamis actually have a lower amplitude than regular waves generated by wind. A typical Tsunami will only be 1m high out in the deep ocean, compared with 2m for a typical "regular" wave. The difference is that a Tsunami is a column of water moving from sea floor to surface, where as a regular wave is a tension difference on the surface alone. A Tsunami, also, will have a wave length hundreds of kilometers long (compared with a few meters for a regular wave) and can travel at speeds in excess of 800km/h.

If you were out at sea, and a Tsunami passed, you wouldn't even notice (which is why the best thing to do if you're on a boat and a Tsunami is approaching is to get as far out to sea as possible).

Actually, it does, but it's an extremely thin one, composed mostly of helium and argon. For all practical purposes, however, it has no atmosphere.

Correction noted.

 

[gumboot]

Have you ever heated a glass bottle in a campfire and then tossed it into a stream? It explodes if you do that, due to the rapid change in temperature and related thermal stresses.

With an asteroid impacting Earth's atmosphere, it would undergo something similar because the vacuum of space, in general, is COLD. And slamming into the atmosphere at ~30 km/sec would heat it up pretty damn quick from the friction.

Not to mention, hitting the top of our atmosphere at such high speeds would be kind of like smacking a near-solid object. If the asteroid in question weren't a really solid lump of metallic material (such as iron), that alone could cause good-sized chunks of it to split off from the main body.

It's quite common for asteroids to bounce off our atmosphere all together. They'll only get through onto the planet if they hit at a fairly square angle.

 

[gumboot]

But, but, it works with a rock in a pond!

The rock in the pond is a valid example, he just hasn't scaled up accordingly. A 200 yard asteroid hitting the sea is like dropping a pebble in a pond. Dropping a big rock in a pond is more like the moon hitting the pacific ocean. I'd happily conceded that if the moon landed in the pacific ocean we would experience tsunamis.

However as I pointed out earlier, tsunamis would be the least of our troubles.

 

[Skwinty]

It all starts to sound a bit like an exercise in pointless scaremongering with about as much scientific usefulness as a post-apocalyptic film starring Kevin Costner.

The article I linked to had this disclaimer in the beginning:

"The results, described below, are not official predictions, but they do lay out some frightening possibilities that put the threat of rocks from space into tangible terms, while at the same time pointing to the need to search for the uncharted asteroids and comets (known as Near Earth Objects or NEOs) that threaten our civilization."

I think this exercise was probably more effective in highlighting the need to track NEO's than any Kevin Costner movie.

The article dates back to 2000.

 

[gumboot]

The article I linked to had this disclaimer in the beginning:

"The results, described below, are not official predictions, but they do lay out some frightening possibilities that put the threat of rocks from space into tangible terms, while at the same time pointing to the need to search for the uncharted asteroids and comets (known as Near Earth Objects or NEOs) that threaten our civilization."

I think this exercise was probably more effective in highlighting the need to track NEO's than any Kevin Costner movie.

The article dates back to 2000.

To be honest I don't think the average person needs any sort of scientific simulation to know that massive rocks slamming into the earth at vast speeds are a bad thing.

My sole issue really, and it comes back to Thunder's claim, not that study, is that I think the size of an impact event necessary to cause devastating tsunamis is so vast, the other consequences of such an impact would vastly outweigh the damage from the tsunami.

I am not sure a computer simulation (whose parameters are completely unknown) really trumps that as we already have plenty of data on the force release involved in actual impact events and actual earthquakes and the sort of energy that caused actual tsunamis.

The Boxing Day Earthquake released 5,600PJ of energy, and most of that went into generating a Tsunami.

Now, obviously there's a lot of issues with calculating a probable energy release from an asteroid, because of variation in mass and shape, but for this exercise I'm going to allow for maximum energy by assuming a perfect sphere 200m in diameter, and using the density of the most dense asteroid known in the solar system which is Vesta at 3.42 g/cm³
So our theoretical asteroid has a total volume of 33,510,321.63829 m³ which is 33,510,321,638,290cm³ giving a total mass of 114,605,300,002.9518kg.

We can calculate the velocity it would need to be traveling to generate the equivalent energy as that earthquake (5,600,000,000,000,000,000J).

We get a necessary speed of 9,885.682548127574m/s or 35,000km/h. Now that's considerably slower than the "unusually fast" comet the same study mentions, in fact it's only 1/4 of the speed, and the average speed for asteroids entering out atmosphere is 10 - 70km/s which puts this theoretical object at the lower end, but this is the entry speed. The 50m wide object that made the Barringer Crater is thought to have burned up half its mass on its journey through our atmosphere, slowing considerably as it did so. Further, for our scenario we've used the densest asteroid known in the entire solar system.

You're then left with the problem of how this asteroid, assuming it's the most dense asteroid we've ever encountered, and assuming it loses none of its mass nor any of its velocity passing through the atmosphere, somehow manages to then plunge through the ocean (still without losing any velocity or mass) and then transfer its entire KE load into displacing the sea floor in such a way that it causes a Tsunami.

Then, only then, would it maybe cause a 10m high Tsunami (still 1/4 the size Thunder claimed) that, based on our recent example, might kill a quarter of a million people (again, far less than the millions Thunder claimed).

So as you can see, even allowing for the ideal (worst case?) scenario, the odds of a 200 yard asteroid causing a 40m Tsunami that drowned "millions" is virtually nil.

 

[Skwinty]

My sole issue really, and it comes back to Thunder's claim, not that study, is that I think the size of an impact event necessary to cause devastating tsunamis is so vast, the other consequences of such an impact would vastly outweigh the damage from the tsunami.

I understand the issue with Thunders claim. He has reality on ignore.

The reason I questioned the impact of asteroids and tsunamis is due to the opposite opinion of Thunders.

That is, that asteroids crashing into the sea will probably not be noticed.

I understand that size, proximity to land, features of the ocean floor and a host of other parameters would be important factors in determining the effect.

On further investigation, there appear to be many other studies suggesting that the fall of meteorites or asteroids in the earth's oceans has the potential of generating tsunamis of cataclysmic proportions.
I subscribe to "Discretion is the better part of valour" philosophy.

Lets hope we don't have to experience one to believe it.

Thanks for your opinion on the matter.

 

[Cuddles]

You're then left with the problem of how this asteroid, assuming it's the most dense asteroid we've ever encountered, and assuming it loses none of its mass nor any of its velocity passing through the atmosphere, somehow manages to then plunge through the ocean (still without losing any velocity or mass) and then transfer its entire KE load into displacing the sea floor in such a way that it causes a Tsunami.

Not sure I agree with this part. As noted earlier, an impact in the ocean will vapourise a significant amount of water, with the surrounding ocean consequently pouring back in. I don't think you need the impactor to drop right to the bottom of the ocean in order to cause a tsunami, you just need it to vapourise enough water that an equivalent volume will move anyway. In fact, your hypothetical impactor would have to do exactly that before ever reaching the sea floor, so obviously actually displacing the floor itself is unnecessary. It may well still require an impactor larger than those being discussed, but it's the volume of water displaced that matters, not the exact method of doing so.

My sole issue really, and it comes back to Thunder's claim, not that study, is that I think the size of an impact event necessary to cause devastating tsunamis is so vast, the other consequences of such an impact would vastly outweigh the damage from the tsunami.

Totally agree with this though. No matter what the exact mechanism for creating a tsunami, the impact is going to have to be large enough that the tsunami is likely to be the least of your problems. In fact, I've seen it argued that an oceanic impact would be a lot worse than a continental one, due to the effects of dumping that much water vapour into the atmosphere compared to a similar amount of dust.

 

[dudalb]

From everything I have read, some of the other effects from a large object from space hiting the earth would be much more destructive ,though not as spectucular, then a tsunumi.

 

[dudalb]

Not sure I agree with this part. As noted earlier, an impact in the ocean will vapourise a significant amount of water, with the surrounding ocean consequently pouring back in. I don't think you need the impactor to drop right to the bottom of the ocean in order to cause a tsunami, you just need it to vapourise enough water that an equivalent volume will move anyway. In fact, your hypothetical impactor would have to do exactly that before ever reaching the sea floor, so obviously actually displacing the floor itself is unnecessary. It may well still require an impactor larger than those being discussed, but it's the volume of water displaced that matters, not the exact method of doing so.



Totally agree with this though. No matter what the exact mechanism for creating a tsunami, the impact is going to have to be large enough that the tsunami is likely to be the least of your problems. In fact, I've seen it argued that an oceanic impact would be a lot worse than a continental one, due to the effects of dumping that much water vapour into the atmosphere compared to a similar amount of dust.

Although some of the science in wonky in "Deep Impact" (what the surface of a comet would look like, the way the world is saved in the end of the film) it's description of what kind of damage would be caused is pretty accurate, and the Tsumani is a minor event compared to the other stuff.

 

[gumboot]

I understand the issue with Thunders claim. He has reality on ignore.

The reason I questioned the impact of asteroids and tsunamis is due to the opposite opinion of Thunders.

That is, that asteroids crashing into the sea will probably not be noticed.

I understand that size, proximity to land, features of the ocean floor and a host of other parameters would be important factors in determining the effect.

On further investigation, there appear to be many other studies suggesting that the fall of meteorites or asteroids in the earth's oceans has the potential of generating tsunamis of cataclysmic proportions.
I subscribe to "Discretion is the better part of valour" philosophy.

Lets hope we don't have to experience one to believe it.

Thanks for your opinion on the matter.

Sure. I should clarify, as it was me who made the "wouldn't be noticed" comment. I was referencing an impact comparable with the Tunguska impact event, which scientists have said would probably have gone unnoticed if it landed in an ocean. That was of the scale Thunder was referring to. Even an event like that would cause a localised megatsunami. Were it to land in water near the coast, said megatsunami would certainly cause severe localised damage.

Substantially larger impact events could without a doubt cause much larger megatsunami events with wider scope of damage, and if large enough, an impact event could cause a tsunami proper. I do not dispute that.

 

[Pugilist]

Then there is always the slim chance it could slam into the moon as well.

 

[gumboot]

Not sure I agree with this part. As noted earlier, an impact in the ocean will vapourise a significant amount of water, with the surrounding ocean consequently pouring back in. I don't think you need the impactor to drop right to the bottom of the ocean in order to cause a tsunami, you just need it to vapourise enough water that an equivalent volume will move anyway. In fact, your hypothetical impactor would have to do exactly that before ever reaching the sea floor, so obviously actually displacing the floor itself is unnecessary. It may well still require an impactor larger than those being discussed, but it's the volume of water displaced that matters, not the exact method of doing so.

Not entirely. A Tsunami is caused by a displacement that forces existing sea water to move away from the event point, with momentum carrying it to coastlines where it causes damage. An event that vapourised water would have the opposite effect, removing an amount of water and thus displacing sea water into the event point. It would, if anything, result in a drop in sea levels, which would be unlikely to drown millions, but rather open up large swathes of beachfront property. Only people in the immediate vicinity of the impact would be in danger, and the impact would have already vapourised them anyway.

There is one way I can think of an impactor generating a tsunami (as opposed to a megatsunami) without causing sea floor displacement, and that is the impactor itself displacing its own volume in water. Again, however, you're talking about an object so enormous a tsunami would be the least of your worries.

Totally agree with this though. No matter what the exact mechanism for creating a tsunami, the impact is going to have to be large enough that the tsunami is likely to be the least of your problems. In fact, I've seen it argued that an oceanic impact would be a lot worse than a continental one, due to the effects of dumping that much water vapour into the atmosphere compared to a similar amount of dust.

This is really my point. I'm not really arguing about whether it's possible for an impactor to create a tsunami at all but rather
1) rejecting Thunder's specifics of a relatively small impactor
2) arguing that the size of impactor which might generate significant tsunamis (comparable with those generated from large earthquakes) would be sufficiently large that it would cause other problems that would render tsunamis irrelevant.

 

[Cuddles]

Not entirely. A Tsunami is caused by a displacement that forces existing sea water to move away from the event point, with momentum carrying it to coastlines where it causes damage. An event that vapourised water would have the opposite effect, removing an amount of water and thus displacing sea water into the event point. It would, if anything, result in a drop in sea levels, which would be unlikely to drown millions, but rather open up large swathes of beachfront property. Only people in the immediate vicinity of the impact would be in danger, and the impact would have already vapourised them anyway.

I'm far from an expert in fluid dynamics, but I was thinking of the bounce back as the water pours into the opening and collides with all the other water doing the same. Throwing a rock into a pond produces waves, but so does lifting it back out.

This is really my point. I'm not really arguing about whether it's possible for an impactor to create a tsunami at all but rather
1) rejecting Thunder's specifics of a relatively small impactor
2) arguing that the size of impactor which might generate significant tsunamis (comparable with those generated from large earthquakes) would be sufficiently large that it would cause other problems that would render tsunamis irrelevant.

Yeah, I don't think there are any arguments about that (except possibly from Thunder). It's just a fairly minor side-debate over exactly how big an impactor is needed to create a tsunami, and what mechanism might be the best for doing so.

 

[MattusMaximus]

It's quite common for asteroids to bounce off our atmosphere all together. They'll only get through onto the planet if they hit at a fairly square angle.

Oh yes, I know. I've personally observed meteors hitting our atmosphere and then skipping off it (just like a rock skipping along a pond) - it's quite beautiful to see

 

[MattusMaximus]

KE=0.5mv², does it not?

FTFY - just a nitpick

 

[gumboot]

FTFY - just a nitpick

Oops. How embarrassing. Okay ignore my calculations earlier. The impactor would need to be even bigger/travelling faster to bring the same amount of KE to the table.