Tunguska explosion

[wasteofo2]

Any thoughts on what this could have been?

Bassically in 1908 there was this massive explosion in the Tunguska region of Russia. the blast had approx a 20 mile radius, happened in the woods and the trees are all knocked over away from a central point. When investigated, there wasn't any impact crater nor any debris reminiscant of a meteorite, there were unusal debris found when people dug around, but unlike anything which usually accompanies a meteorite. Even stranger, where the crater should have been, there's an area of trees which weren't knocked over. Local wildalife and people began developing genetic mutations following the blast very simmilar to those developed post the nuclear bomb blasts in japan. It's estimated that the blast had approx 1,000 times the force of the bomb dropped on hiroshima.

The theories I'm aware of are:

-Alien ship with a nuclear reactor exploded.

-Aliens nuked a forest as a kind of way to alert us that there are other beings out there.

-Giant meteorite exploded approx 3 miles above ground, thus no crater.

-Some sort of super seceret human weapon.

None of these offer reasons for there being trees standing and alive left at the epicenter.

http://www.tmeg.com/artifacts/tunguska/epicenter_1927.gif
epicenter - 1927

http://www.tmeg.com/artifacts/tunguska/forest_1927.gif

[Jonathan]

I don't know, I heard a theory that it was Tesla's fault. They gave pretty convincing meathod and oppurtunity, the question is if and how, so I'm not convinced of that one.
I think the meteor one is the best, because it makes sense that if something explodes overhead, it will put pressure straight down on you. If you are a tree, you might be able to take this vertical pressure, and it is only when you are hit at enough of an angle that there is enough horizontal pressure to knock you over.

[wasteofo2]

Originally posted by Jonathan
I don't know, I heard a theory that it was Tesla's fault. They gave pretty convincing meathod and oppurtunity, the question is if and how, so I'm not convinced of that one.
I think the meteor one is the best, because it makes sense that if something explodes overhead, it will put pressure straight down on you. If you are a tree, you might be able to take this vertical pressure, and it is only when you are hit at enough of an angle that there is enough horizontal pressure to knock you over.

1,000 times the force of the hiroshima bomb would knock over the tree at any kind of angle, and if not knock it over, destroy it to the point of total incineration, especially at "ground zero"

Tesla was crazy, in a very awesome way, it'd be cool if that was his infamous "Tesla beam" or something like that.

[Jonathan]

You're right, I have no idea why there were trees standing up.

[Ivan Seeking]

The working explanation is that this was a comet or a soft meteor [I'm not sure of the proper language here]. If the object entering is not too hard and dense, it can vaporize before hitting the ground. This can yield results like those found in Tunguska. In the this particular event, the pattern of destruction was a dinstinctive butterfly shape. One scientists has been able to physically model this - using small scale dynamic models. A comet-like object entering at the proper trajectory produces results entirely consistent with those observed in Siberia. It was big, fast, mean[massive],the approach angle was very low, and if it had hit NY city we really would have noticed for about a 100 mile radius, but it was most likely a comet.

[Jonathan]

Yes, I understood the theory, but I don't understand why the vaporization of a comet wouldn't knock down trees. Or is that not as an explosive of an event as I think? Then why were people miles away knock on their butts when the shockwave came by (why was there a shockwave?)?

[Guybrush Threepwood]

Originally posted by wasteofo2
-Aliens nuked a forest as a kind of way to alert us that there are other beings out there.


[:D] [:D]

[Ivan Seeking]

Originally posted by Jonathan
Yes, I understood the theory, but I don't understand why the vaporization of a comet wouldn't knock down trees. Or is that not as an explosive of an event as I think? Then why were people miles away knock on their butts when the shockwave came by (why was there a shockwave?)?

Basically that's what happens in cases like this. You get nothing but a tremendously powerful shockwave; as opposed to a solid object and an obvious impact site. This shockwave is what produces the butterfly shape mentioned earlier.

In other words, as I understand this stuff which ain't much, when it vaporizes it acts like a directed explosion - a nuclear bomb sized explosion in this case.

[Ivan Seeking]

Oh yes, his actual [high energy] tests left trees standing at the epicenter.

[Phobos]

Good explanation Ivan. Yep, the going explanation is an air burst of a small comet or asteroid. ("small" meaning like 50-75 meters or so) Impacts of this size happen every few hundred years, statistically speaking. Good thing it was an uninhabited area.

Offhand, it makes sense that it would be easier for a shockwave to knock over a tree if it hits it from the side rather than straight down. I imagine that the standing trees at the "epicenter" were stripped of their branches though.

The sky is falling.

[;)]

[radagast]

Originally posted by Jonathan
Yes, I understood the theory, but I don't understand why the vaporization of a comet wouldn't knock down trees. Or is that not as an explosive of an event as I think? Then why were people miles away knock on their butts when the shockwave came by (why was there a shockwave?)?

A comet would have had a large amount of kinetic energy. The comet that hit Jupiter, just a few years back, was thought to hit hard enough to have induced fusion in a little of the hydrogen in Jupiter's atmosphere. That much energy has to go somewhere.

The amount of energy needed to knock down a tree, which is pointing directly at the epicenter of the blast, would have to have greatly exceeded the energy released at Tunguska. It would have almost had to be enough to disintegrate the wood. Vertical structures (telephone poles, walls, etc.) under the epicenter of Hiroshima and Nagasaki blasts were also left standing.

[wasteofo2]

ok ivan, your explanation makes sense except for the aftereffects of genetic mutations simmilar to those of radiation poisoning.

History channel had a special on this just recently, and someone who was explaining how a meteorite could have done thins explained how the particles moving so fast could have cause some sort of radiation like effect, but I didn't really follow him at all, do you have any idea what I'm talking about?

[Ivan Seeking]

Originally posted by Phobos
("small" meaning like 50-75 meters or so)

I assume that this means 50-75 meters at the time of the air burst? If so, then can we estimate the size of the object before it hit the atmosphere? If the otherway around, how big was the object when it exploded?

[Jonathan]

My bet would be: smaller.
As to wasteofo2's question, if there was an asteroid, there might have been some radioactive stuff in it. And who knows what radiation it emitted as it streaked throught the atmosphere, and then exploded. It seems to me that everything in the area would be fried, and so mutation would be the least of the problems.

[Phobos]

Originally posted by Ivan Seeking
I assume that this means 50-75 meters at the time of the air burst? If so, then can we estimate the size of the object before it hit the atmosphere? If the otherway around, how big was the object when it exploded?

Pretty sure that means the size of the object before hitting the atmosphere. 'Fraid I don't know how much would be left at the time of explosion after some had ablated away in the upper atmosphere. If I get some free time, I'll try to look into it.

p.s. Just found a source (UK report on Near Earth Object Hazards) saying Tugunska was likely a 50 to 60 m object that exploded at an altitude of 8 km which flattened 2000 sq. km of forest below. Scary thing is, this kind of impact (statistically) happens about every 250 years. Tunguska was in 1908 so I guess we're ok for a while. [:D]

[Ivan Seeking]

Originally posted by wasteofo2
ok ivan, your explanation makes sense except for the aftereffects of genetic mutations simmilar to those of radiation poisoning.

History channel had a special on this just recently, and someone who was explaining how a meteorite could have done thins explained how the particles moving so fast could have cause some sort of radiation like effect, but I didn't really follow him at all, do you have any idea what I'm talking about?

Yes I have heard this explanation for reports of biological mutations in the area. Perhaps radagast's comments apply here also? That's about all I can say.

[Ivan Seeking]

Originally posted by Phobos
Scary thing is, this kind of impact (statistically) happens about every 250 years. Tunguska was in 1908 so I guess we're ok for a while. [:D]

In Oregon, we have had two 500 year floods in the last 14 years. [8)]

[Phobos]

I'm sure the Oregonian actuaries are thrilled.

[LURCH]

Originally posted by wasteofo2
ok ivan, your explanation makes sense except for the aftereffects of genetic mutations simmilar to those of radiation poisoning.

History channel had a special on this just recently, and someone who was explaining how a meteorite could have done thins explained how the particles moving so fast could have cause some sort of radiation like effect, but I didn't really follow him at all, do you have any idea what I'm talking about?

A blast like that releases a tremendous amount of energy. That much energy would not be confined to a few frequencies of the EM spectrum, but would put out over the full range (in verying degrees of course). Included in this would be some X-rays, which are the main source of radiation poisoning in an atomic blast. Also Gamma, which I think is the cause of genetic mutations after a nuke attack.

[Nereid]

OK, so our input data are:
-> an object 50 to 75 m (in diameter?)
-> relative speed at top of the atmosphere 12 km/sec (a tad over escape velocity)
-> terminal speed 0 km/sec
-> density 1,000 kg/m3

Some assumptions:
-> all the kinetic energy of the impactor goes into heating the impactor
-> realistic figures for the average specific heat of the impactor
-> resulting ball of gas radiates as a blackbody

Some questions:
-> how deadly would the resulting X-ray and gamma radiation be? (assume no absorption between the ball of gas and the ground, 8 km below; assume isotropic radiation)
-> what nuclear reactions could we expect to happen in or near the gas ball? (assume just ordinary matter is out and about, nothing exotic)
-> if we make our assumptions more realistic (e.g. some of the impactor's kinetic energy goes into an atmospheric shock wave), how does that affect our answers?

[Jonathan]

I don't know, except for the last question, that scenario would make the radiation less harmful; less intensity and/or lower frequency.

[Nereid]

OK, I'll do the first step:

Energy to be converted to heating the impactor = kinetic energy of impactor

= ½mv2

Mass of impactor = density x volume

Volume = 4/3πr3

So, mass ~= 6.5 x 107 kg

v = 12 km/sec = 12,000 m/s

So, energy (in SI units) ~= 4.7 x 1015 J

Comments?

Next, who wants to calculate the temperature of the ball of hot gas, which used to be the impactor? You can make simplifying assumptions; this is only an OOM/back-of-the-envelope estimate.

[GRQC]

Originally posted by Jonathan
Yes, I understood the theory, but I don't understand why the vaporization of a comet wouldn't knock down trees. Or is that not as an explosive of an event as I think? Then why were people miles away knock on their butts when the shockwave came by (why was there a shockwave?)?

Getting into this discussion a bit late, but a comment on this question: explosions are generally spherically-symmetric, so the shockwave travels out in such a fashion. If the explosion is above ground, then the shock front will eventually hit the ground and reflect. When it does reflect, it will travel along with the original front, superposing and reinforcing the wave. This is called the Mach Stem, or Mach effect, or variants thereof. Generally it's only observable for suitably large explosions (e.g. nuclear). The effect has been well-studied in nuclear tests.

Hence, the shock wave becomes stronger at some point further from ground zero, which could help explain why trees at the epicenter survived but those further afield did not.

[Jonathan]

That doesn't entirly make sense to me, so I'm not sure I understood, the shockwave will go out, reflect off the ground, and reinforce the original shockwave. It seems to me that in fact there will be varying degrees of reinforcement. It seems like the first blow striaght down on the trees at the epicenter would try to crush them and then the reflection of it would try to stretch them, and in that direction trees are very strong. But at some number of degrees away(from the point of explosion's veiw), a considerable portion of the blow has a horizontal component, as would it's reflection, and trees are not very strong against horizontal blows.
This seems to reinforce what I said in my first post.

[Evo]

Here is a link that gives some interesting facts about the incident.

http://www.usm.maine.edu/~planet/tung.html