How often does a Tunguska event happen?

By Phil Plait | December 19, 2007 7:00 am

Please read the update at the bottom of this post; I correct a couple of errors I made.

In summer 1908, an explosion over a remote area in Siberia near the Podkamennaya Tunguska river devastated hundreds of square kilometers of land. Trees were flattened, the area scorched, and the pressure wave from the blast was felt around the world.

Decades later, it was determined that a small chunk of asteroid or comet came in at an angle and exploded high over the ground, and the fireball is what did the damage. It was assumed the rock was 50-100 meters in size, and the explosion yield was 10-20 megatons.

However, a new study just released by the folks at Sandia Lab indicates that the rock may have been smaller, and the yield smaller as well. The ever-increasing speed of computers has allowed them to make extremely detailed three-dimensional models of the explosion — models that are incredibly difficult to make due to the fiendishly complex nature of how air moves under extremely high-pressure and temperature conditions.


Their results show that the blast created a tongue or finger of pressure which blasted downward from the explosion itself, as opposed to the explosion making a big spherical blast wave. Scientists have always assumed the blast wave expanded spherically, which means it takes a lot of energy to do the damage seen. However, a finger of destruction is more concentrated than a sphere, and can do more damage with less energy. So the rock and explosion were smaller than previously thought.

In my mind, that makes Tunguska even scarier than it was before: smaller rocks are more common in space. This means events like what occurred in 1908 may happen more frequently than we thought.

Unfortunately, the press release from Sandia is very scant with details. How big is their revised size for the meteoroid? What was the yield of the explosion? How does this change the frequency of impact?

They have some cool videos on the site too, but they are not labeled and have no supporting info. The first couple seem to contradict each other as to how the rock came in, too. Maddening. If I get a chance, I’ll try to call some of the people behind the study and get more info. Chapter 1 of my book is all about asteroid impacts, and I still have time to make some edits if needed!

UPDATE: I called Neil Singer at Sandia Labs about the press release and he cleared up some issues. First, I misread the release: the yield of the explosion was listed; it was something like 3 – 5 megatons (down from the earlier estimates of 10 – 20). That makes the focusing of the fireball very efficient! That’s interesting. Second, the size of the meteoroid itself isn’t given because it depends on too many other factors like speed, composition, and the like. This is actually in the press release itself and I somehow stupidly missed it. Now, the energy released by an incoming chunk of material depends pretty much linearly on the mass, so if the explosion itself was a factor of, say, 1/4 as big as previous estimates, then the mass of the object was 1/4 of the older estimate as well. That means its diameter was very roughly 60% of what was previously thought.

Also, as I said the videos aren’t labeled (Mr. Singer said he was going to fix that), but I think I understand the first two now. The second one shows the blast from the side, with the bolide coming in at an angle of 35 degrees from horizontal and exploding well above the ground. The first one is most likely the same thing, but seen from a different angle, along the path of the incoming rock. That makes it look like it’s headed straight down, but it’s just a perspective effect. The explosion of the rock itself is dwarfed by the focused blast wave, so you don’t see it clearly. The two videos are compatible, and don’t contradict each other.

As far as changing the statistical frequency of such impacts, that’s tough to nail down as well, because there is still too much fuzziness in the size estimate. The next time I talk to some of my asteroid expert friends I’ll see what they think of this. No doubt David Morrison will be sending an email out about this result soon!

So my apologies to Sandia and Mr. Singer for what were essentially my own mistakes.

CATEGORIZED UNDER: Astronomy, DeathfromtheSkies!, Science

Comments (42)

  1. Sergeant Zim

    You mentioned a “finger of pressure”. I can just see the (oxymoron alert) ‘religious right’ calling this effect the “Finger of God”, and claiming some sort of judgement, since this happened in ‘godless’ Siberia.

    It reminded me more of this:

    The Moving Finger writes; and, having writ,
    Moves on; nor all your Piety nor Wit
    Shall lure it back to cancel half a Line,
    Nor all your Tears wash out a Word of it.
    – The Rubaiyat of Omar Khayyam

  2. I think their server barfed because they got Slashdotted, so there’s a mirror, as linked in one of the comments.

    Anyway, the videos are fascinating.

  3. cope

    The article over at Space.com states the revised energy yield at about 3.5 megatons and the revised asteroid size at about 20 meters.

    Scary stuff when you consider how many objects that size there must be.

  4. Just Al

    Hey, cool! I want a Shroud of Tunguska like the one shown!

    The Tunguska Event has been quite a collection of stories through the years. If it wasn’t for the acres of physical evidence, it would resemble some of the questionable legends (like the Bermuda Triangle) that on close examination turn out to be more the imagination of the researchers. It’s a meteor, no, a comet, no, antimatter, no, a spaceship, no, a Transformer…

    Personally, I think it was a time machine that blew the orbital position. You know, that whole English/Metric/Bratophy translation thing.

  5. So do you have to go rewrite a chapter of the new book. Speaking of which, when do we get the new book?

  6. Hmmm. Problem with the finger of pressure is it makes the chances of the pressure wave being felt as far away as it was unlikely. Other than that, though, it would still account for the observed results of the explosion. I’m just not sure what would physically cause a finger of pressure other than high velocity ‘shaping’ the explosion, so I’m undecided.

    On the other hand, these guys know what they’re talking about. I’ll have to wait and see.

  7. This makes me think of a cosmic SMITE button, but Sgt Zim beat me to the punch.

  8. Michelle

    The image looks more like psychedelic art than science content! :P It’s all graffiti ish.

  9. Sergeant Zim writes:

    [[You mentioned a “finger of pressure”. I can just see the (oxymoron alert) ‘religious right’ calling this effect the “Finger of God”, and claiming some sort of judgement, since this happened in ‘godless’ Siberia.]]

    Yeah, I can imagine you imagining that. Except, of course, that even the religious right knows the Russian Revolution was in 1917.

  10. I can see Jesus in that image!

    Wait…not Jesus…more like a face-on image of an Easter Island statue…breathing fire. Damn, the theological implications are staggering.

  11. Unfortunately, the press release from Sandia is very scant with details.

    Well, here’s their poster from an open house a few months ago.

  12. (No embedded URLs, eh?)

    Unfortunately, the press release from Sandia is very scant with details.

    Well, here’s their poster from an open house a few months ago: http://www.sandia.gov/LDRD/images/Posters/Boslough_Poster.pdf

  13. Michael Lonergan

    Does anyone else see the uncanny resemblance to the Shroud of Turin in that image?

    Okay, now the BA is contributing to my nightmares. Not only do I have to worry about Bigfoot grabbing me as I walk down the street (I live in Bigfoot country in BC), aliens abducting me from my bed at night, GW Bush being elected for a third term, the planet being burned to a crisp because my neighbor drives a Hummer, and Richard Hoagland being accepted as a mainstream scientist, I now have the added worry of being vaporized by a hunk o’, hunk ‘o burning rock from space. Someone please pass me my meds….

  14. Sergeant Zim

    @ Barton:
    “even the religious right knows the Russian Revolution was in 1917.”

    If there’s one thing I’ve learned from dealing with the RR, it’s to NEVER assume they accept anything remotely connected to reality.

    e.g.: Hovind, in one of his lecture tapes, placed the blame for the Cherokee “Trail of Tears” on Darwin – The irony that the Trail of Tears occured ~ 20 years BEFORE Origin of Species completley escaped him.

  15. Charles

    The focusing mechanism is probably of great interest to weapons designers. After all, there are literally several thousand 3.5 megaton explosive devices laying in storage across this world, and most of them are only a few meters in size as well.

    To me that is far scarier than any pedantic prattle from the religious right.

  16. BaldApe

    “If it wasn’t for the acres of physical evidence, it would resemble some of the questionable legends ”

    And that’s the thing, isn’t it?

    BTW, I think it looks like Joseph. Jesus had his mother’s eyes, and it just doesn’t look like a water streak on a window to me.

    As to worrying about it, I’m not a fatalist, but if I were, what could I do about it?

  17. Will. M.

    Yes, it would be helpful if the Quicktime movies had captions; also, why
    are the distances in centimeters instead of meters? It sure seems as though the shock waves from the initial blast did the damage in a radiating fashion, also – especially if the thing exploded in the air above the damaged area. I get the main point that the object was smaller but packed a larger punch, though. I guess I need a course on how to read computer-generated images…

  18. Kent Hovind

    It may have been 20 years before Origin of the Species, but Darwin was THINKING of his godless theory!

  19. Michael Lonergan

    This reminds me of something: “How Often Does a Tunguska Event Happen?”

    How often could a woodchuck chuck wood if a woodchuck could chuck wood?

  20. Quiet_Desperation

    the “Finger of God”,

    Actually, that’s a wicked cool name for an orbital space weapon. :)

  21. Cory Meyer

    I see pareidolia in that diagram! Anybody else? (It’s a cool diagram, nonetheless)

  22. Stephen

    I’m really not worried about Tunguska events and these new figures don’t make them any likelier, at least not significantly.

    Consider this. Small bodies are commoner in the solar system than large ones. The Tunguska event devastated something like 4000 sq. km. of forest. Now, how many events in the last couple of centuries have devastated 400 sq. km. of forest? Answer: none (apart from Tunguska itself).

    How about 40 sq. km? None.

    4 sq km? Er … none.

    If events 1000 times less devastating than Tunguska are very rare, Tunguska-sized events must be *extremely* rare; far too rare to be worth worrying about. The actual mass involved doesn’t really matter.

    If we’re talking about destructive events that we should be worrying about, I’m far more concerned about the propensity of the US to attack other countries.

  23. Sergeant Zim

    One thing that occured to me a little while ago:

    If this was from a meteroid that small, but a focused blast wave, what would the people living in a largley agricultrural society think of a similar occurance – especially if it happened to ‘smite’ a couple of minor towns that were known to be…. well, let’s just say they were somewhat less than paragons of virtue (similar to Vegas)?

    Can you say Sodom and Gommorrah?

    After all, wasn’t Sodom supposed to be close to the Dead Sea, which is rather brackish…. A fiery blast would pick up superheated steam, laden with salt… anybody who happened to be within the blast zone might have essentially been turned into a ‘pillar of salt’.

  24. Mike Torr

    Stephen’s post was good, but one line bothers me…

    “If events 1000 times less devastating than Tunguska are very rare, Tunguska-sized events must be *extremely* rare”

    Is that actually something we can assume? Is it possible that low-devastation events might be LESS common than, say, medium-devastation events, for some reason? Perhaps because the bodies are more prone to burning up in the atmosphere or something. I don’t know, just wondered about the premise, that’s all.

  25. Mick

    Colour me a little skeptic on THIS account.

    If it should be so common. Then why aren’t there way more examples then the Tunguska one?

    I’m not buying luck… If it really was so common then wouldn’t there be at least some ten Tunguska events known from human history? (I know there’s plenty in geological history, but thats a long scale of time. I mean the last few centuries.)

    Sure, eventually an asteroid will come heading for the Earth again. However for all we know it might take five million years.

    These small rocks may be common, but yet they don’t seem to hit us that often if the only one we can really verify is from 1908.

    (The only thing that springs to mind as a possible other example is something I once read about some vision of a ‘flaming mountain coming down from the sky.’ I think it was Revelations, but might have been the Qu’ran. I don’t remember exactly I was reading some religious writings at the time. Still flaming mountains coming from the sky does sound like an asteroid impact (Although if any ancient people saw those and wrote about it I assume they where not close to where it fell.)

    Or could maybe that big Tsunami in Asia have been caused by an asteroid instead of a seaquake?

  26. CR

    @ Sergeant Zim, regarding Sodom & Gommorrah being smited by an asteroid… that’s… that’s really brilliant! That’s one of the most original things I’ve heard in a long time.
    Since we often get people who try to ‘disprove’ science on this site by citing Christian explanations for things, why not turn the tables and try to explain the Bible scientifically? Might be an impossible task, but it might be a fun exercise.

  27. tussock

    Mick: The christmas tsunami resulted from the sudden geological shift of a large island and the collapse of an nearby sea cliff, and asteroids don’t do either of those things.

    But still, I do recall reading something about a fiery land strike in the middle east in the first millennium, and it’d be easy to lose one in the Amazon, the Sahara, Australia, Antarctica, inland deserts, large mountain ranges, and so on up until 1800 or so. One every couple centuries on land isn’t impossible, as they don’t scar for long like a solid impactor, or about one per millennium over land covered by written history, which we’ve got.
    Increase it for any more falling stars, fiery columns, or flattened forests that people can find in the records, or notice in the near future.

  28. CR

    Correction to my last post: I meant blast wave, not asteroid.

  29. Charles says: “The focusing mechanism is probably of great interest to weapons designers. After all, there are literally several thousand 3.5 megaton explosive devices laying in storage across this world, and most of them are only a few meters in size as well.”

    Nothing very new here. That’s exactly how the propulsion devices of Project Orion worked. The biggest advance that came from that project was the design of the nuclear shape charge, a nuclear device that focuses most of it’s energy in one direction, in this case towards the “pusher plate” of the vehicle.

    - Jack

  30. One of the most fascinating Greek myths to me is the story of Phaeton, the son of Helios, the god who daily drove the chariot carrying the sun across the sky. One day Phaeton convinced his dad to let him take the chariot out for a drive. He screwed up royally, as described in the online Encyclopedia Mythica (http://www.pantheon.org/articles/p/phaeton.html):

    The horses, feeling their reins held by a weaker hand, ran wildly out of their course and came close to the earth, threatening to burn it. Zeus noticed the danger and with a thunderbolt he destroyed Phaeton. He fell down into the legendary river Eridanus where he was found by the river nymphs who mourned him and buried him.

    I’ve always wondered if this could be an ancient memory of a really, really big bolide. Maybe something Tunguska-level that happened 2600+ years ago?

  31. StevoR

    Vaguely recall seeing a doco on a historically quite recent major asteroid strike in the Amazon ..

    An answer for the person asking what they could do about being a fatalist : Stop being one & think proactive!

    I too am alot more worried about the USA’s propensity to bomb the living daylights out of all the nations it dislikes – yet scream blue murder when its enemies do anything even remotely of the kind to it. Two skyscrapers going down with about 3000 people does NOT justify totally destoryuing invading and occupying two whole nations and killing millions of innocnet people.

    Here’s a simple idea America needs to adopt – Leave other nations the heck alone & stop funding Israeli aggression in a region where its never wanted & will never fit. Evacuate Israel & let the Jewish lobby purchase New York and surrounds at crippling cost. Give Palestine back to the Palestineans, leave the rest of the planet in peace -and we’ll all be incomparably better off!

    Otherwise a very, very, ve-ery will keep on hoping the next Tunguska occurs somewhere close to Washington …

    (It might be blunt, you may disagree with me – but thats the stark truth as I see it.)

  32. StevoR

    Correction for above :

    Otherwise a very, very, ve-ery large percentage of the global populace will keep on hoping the next Tunguska occurs somewhere close to Washington …

    If America wants honesty & free speeech. It should accept others doing so.

    If Amercia wants peace as itclaims -itneeds toset tehexamople and stop invading otherplaces leftrightand scentre and shift itscultural awayu from guns and more towards thoughtful behaviour.

    Believe it or not, I do like the United States and wish ‘em the best … & to be the best rather than worst they can be. Apollo was awesome, Iraq & Vietnam & Isreali neo-con-run foreign policy- just awful.

  33. StevoR

    & correcting again coz I can’t edit … Sigh :

    If America wants peace as it claims – it needs to set the example and stop invading other lands left right and centre and shift its culture away from guns and cowboy politics & more towards thoughtful, co-operative behaviour.

    Believe it or not, I do like the United States and wish ‘em the best … & to be the best rather than worst they can be. Apollo was awesome, Iraq & Vietnam & Isreali neo-con-run foreign policy- just awful.

  34. TomR

    Glad to see they were able to use all those warhead re-entry simulations for something. Gotta admit, the simulations are beautiful. Any idea how much CPU time it takes to run something like that?

    Charles–there actually aren’t that many 3.5 megaton devices around anymore. The multi-megaton monsters were part cold-war pissing match, part designed to distroy hardened silos when ICBM accuracy was measured in miles. Once ICBMs actually got able to hit things, weapon sizes dropped dramatically. Most of the U.S. arsenal is in the 100KT range, and only the highest yield weapon in the inventory is 1.2Mt.

    Not that that makes them any more pleasant…

    Source: http://www.nrdc.org/nuclear/nudb/datainx.asp?gclid=CPuA8sPOt5ACFQHgPAodhRh0KQ

  35. StevoR posts:

    [[Here’s a simple idea America needs to adopt - Leave other nations the heck alone & stop funding Israeli aggression in a region where its never wanted & will never fit. Evacuate Israel & let the Jewish lobby purchase New York and surrounds at crippling cost.]]

    Yeah, that’ll show those dirty Jews! Good plan, Stevo.

    Um, wait, it’s a ridiculous, racist plan better suited to the fantasies of William Turner and David Duke than to a science blog. My bad.

    [[ Give Palestine back to the Palestineans, leave the rest of the planet in peace -and we’ll all be incomparably better off! ]]

    Like we were when we took that attitude in the ’20s and ’30s. Just leave other countries alone, and things will be fine! It’s the US that causes all the problems! People in other countries are sinless!

    Oh, wait, that’s stupid.

  36. The absence of strikes by smaller objects may be due to their being more prone to be deflected by the atmosphere, or to burn up in it. The impact cross-section at Earth’s surface won’t resemble that at the Moon’s surface.

  37. Michael Lonergan

    Barton, not everyone has to have the opinion that Israel is a favored nation above all others. Why are you so quick to judge Steve because he happened to state, what quite frankly, many people are thinking. No we are not all racists. I happen to think the Jews have a right to a homeland. But, so do the Palestinians. I also believe, that America, or any other nation should not have to do the dirty work of any other nation. Let her fight her own wars. If Israel is concerned about Iran, let Israel take care of Iran. Why should thousands more US soldiers be slaughtered fighting someone else’s battle. No, the Jews should not have to evacuate Israel, but they should have to find a way of co-existing with her neighbours, and like it or not, that includes the Palestinians. Rabid fundamentalists and Christian Zionists like John Hagee, quite frankly scare the crap out of me far more than a Tunguska event. These people are driven by a fanaticism that borders on insanity. The attitude seems to be, “If Israel cries ‘Foul’, we will come running.” They view it as their divine mandate to protect this nation at all costs, yet thousands are dying in Darfur. They are determined to bring about nuclear annihilation to fulfill some type of biblical end time prophecy (lie).

    I apologize if this offends anyone, especially any Jewish people that may be here, I reiterate, I am not opposed to the Jews having a homeland. Personally I think many Jews agree that it is time to find a solution to this never ending quagmire.

    Anyway, back to the topic at hand. Mick stated that these events should be more common. Let’s not forget that 75% of the Earth’s surface is covered by water. It is only in the last 50 or so years that we would have been able to detect airbursts over our vast oceans. So, that being said, these events could very well be more prevalent than we think. We were just unable to see them. Such a possible event took place over the Indian Ocean in the late ’70′s, where the Vela satellite observed a flash over the Southern Indian Ocean. This is widely believed to have been either a South African, or Israeli nuclear test, but has never been confirmed.

  38. Mike Lonergan writes:

    [[Barton, not everyone has to have the opinion that Israel is a favored nation above all others.]]

    Neither do I.

    [[ Why are you so quick to judge Steve because he happened to state, what quite frankly, many people are thinking.]]

    Because he wants Israel forcibly evacuated to New York and all American Jews moved there and presumably the border sealed off. Did you not read his post? Go back and read it again. It’s essentually identical to David Duke’s plan for settling blacks in “Minoria,” Hispanics in Bantustans in the west, Jews in the northeast, etc. — leaving 98% for the Aryans, of course.

    [[ No we are not all racists. I happen to think the Jews have a right to a homeland. But, so do the Palestinians. ]]

    I agree.

  39. Michael Lonergan

    Barton, I stated in my post that I believe in the right of the Jews to have a homeland, and for the record, I do not agree with Steve’s comment about evacuating all Jews out of Israel and moving to them to New York. That idea makes no sense whatsoever. I also make it clear that I believe the Palestinians have a right to a homeland.

    I live in Canada, a much smaller country, population-wise than the US. I wouldn’t like it very much if the US came into my country, expanded her borders, and threw me out of my home, forcing me to live somewhere I have no desire to live. I would most likely, take up arms, and fight back for what I believe is mine.

    Neither would the people of Montana like it if Canada, with it’s much superior military technology, (we supply our troops with Mukluks – I can’t tell you what they are, it’s a closely guarded government secret) invaded their state. (We love their open roads and lack of speed limits.) Then the much superior Canadian invasion force displaced it’s citizens. The reaction would be much the same.

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