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The Sound So Loud That It Circled the Earth Four Times
- kevinskii 12y agoFor anyone interested, I'd recommend Simon Winchester's book "Krakatoa": http://www.amazon.com/Krakatoa-World-Exploded-August-1883/dp/0060838590 http://www.amazon.com/Krakatoa-World-Exploded-August-1883/dp... Also interesting are how quickly the volcano has risen out of the sea again after being totally obliterated, and how much life now thrives on it.
- jgalt212 12y agoI second that opinion. Great book.
- aatish 12y agoHey, I'm the author of the post (on twitter @aatishb). Thanks for voting it up. Would love to hear your thoughts and constructive feedback. Cheers. (PS the references linked to at the bottom of the post are packed with fascinating information about Krakatoa, for anyone who wants to dig deeper.)
- aatish 12y agoI was also captivated by this vivid first person account of a Dutch pilot in the coastal town of Anjer who survived the ensuing Tsunami http://www.vansandick.com/familie/links/vulcaan2.php#h1 http://www.vansandick.com/familie/links/vulcaan2.php#h1
- double0jimb0 12y agoHow does something like the Tzar bomb compare in terms of sound pressure? Would the immense volume of ejected material from the volcanic explosion move more air than a nuclear explosion? I'd guess lots of mass (air molecules) is just vaporized in a nuclear explosion, leaving much less mass to create pressure deltas.
- MrBuddyCasino 12y agoThat was my first thought, too. Fun facts [1]: - its ignition was the most powerful artificial explosion in human history - The seismic shock created by the detonation was measurable even on its third passage around the Earth [1] http://en.wikipedia.org/wiki/Tsar_Bomba http://en.wikipedia.org/wiki/Tsar_Bomba
- kordless 12y agoWikipedia says it was four times as powerful as Tzar Bomba, which would put it in the neighborhood of 200Mt. Technically Tzar Bomba was suppose to yield about 100Mt, but the scientists dialed it down a bit because they were worried about it.
- qq66 12y agoKind of crazy to think that humans made a bomb 1/4 as powerful as the Krakatoa eruption.
- SerpentJoe 12y agoMy understanding is that the yield was halved by the use of a lead tamper, rather than a uranium one. The tamper is a shield around the core that slows down the explosion in order to consume the reactants more fully. In production they commonly make the tamper out of waste uranium, which undergoes fission during the blast and contributes a significant amount of energy, but if you don't need the boost then lead works fine, or anything else heavy. The other thing about uranium is it greatly multiplies the radioactive fallout (fusion bombs are actually pretty clean when lead is used), which may have contributed to the decision not to use it.
- aatish 12y agoThe Tsar bomb was in the ballpark of a 50 megaton explosion, whereas estimates that I've seen for Krakatoa put it at up to 200 megatons. That said, there would be differences due to the fact that h-bombs are exploded at a height to maximize the damage from the blast wave, and that a significant fraction of Krakatoa's energy would have been spent on throwing earth around. It's always hard to compare different explosions because it's difficult to know what fraction of the energy output goes into acoustic energy, but I think it's reasonable to assume that Krakatoa was louder (at least in that the sound was heard further).
- vanderZwan 12y agoIt's a great article - makes me wonder how long the shockwave of the impact that killed the dinosaurs must have been echoing across the globe, or the one that created the moon (well, that one was before earth had an atmosphere, but it probably was strong enough to make the entire planet vibrate for quite a while).
- b_emery 12y ago> impact that killed the dinosaurs I once saw a talk about this at a scientific meeting, so the papers are out there. All I can remember from it is that they estimated the ejecta at "about the mass of the Sierra Nevada". This was quite a while ago so I'm sure they've got a better estimate by now.
- SEJeff 12y agoOne thing I'm surprised you didn't mention is infrasound[1], which is sound so low that it can potentially damage the human body. Some of the newer non-lethal weapons the US military use for crowd control include a directional infrasound "gun" that basically vibrates your inner organs fast enough to make everyone super nauseous. [1] http://en.wikipedia.org/wiki/Infrasound http://en.wikipedia.org/wiki/Infrasound
- fl0wenol 12y agoInfrasound is about a specific frequency range of sound which isn't audible but still carries energy (which is why it can be dangerous). This article was about a wideband sound that was so loud that it defies comparison. Loudness is related to the amplitude, or "height" of the wave, not frequency.
- SEJeff 12y agoOh agreed, the article just goes into so much detail about sound. Seemed relevant (in my head).
- Anechoic 12y agoSome of the newer non-lethal weapons the US military use for crowd control include a directional infrasound "gun" that basically vibrates your inner organs fast enough to make everyone super nauseous. Do you have a cite for this? A "directional" outdoor infrasound weapon would be huge (10s of feet) and quick web search seems to indicate these types of weapon are at best "not mature" and at worst fiction.
- 001sky 12y agohttp://www.globalsecurity.org/military/systems/munitions/accoustic.htm http://www.globalsecurity.org/military/systems/munitions/acc...
- Anechoic 12y agoThat article describes a theoretical infrasound weapon, not something that is being used today: But this [infrasound weapon] has seemed to be not a very practical weapon, since large banks of speakers were required to provide directionality, and power demands were deemed excessive. The article goes on to describe LRAD which does exist and has been deployed, but is a high-frequency weapon, not an infrasound weapon (and can be defended against with a good pair of earplugs).
- randall 12y agoThis is one of my favorite things i've read on the internet in recent memory.
- NIL8 12y agoYes! There's a lot of fluff on HN nowadays, but every once in a while we strike gold.
- jbert 12y agoNice. I hadn't thought of there being a limit (due to vacuum) to sound intensity. Reminds me of this recent comment on reddit: http://np.reddit.com/r/space/comments/2h9y9g/the_first_launch_from_cape_canaveral_1950/ckr6mev http://np.reddit.com/r/space/comments/2h9y9g/the_first_launc... "the Saturn V rocket produced a SWL (Sound Power Level) of about 220 decibels, which is sufficient to melt concrete nearby and set grass aflame a mile away,"
- BrandonMarc 12y agoWait, the sound caused the grass to catch fire?!
- alex_duf 12y agoI guess that at this level "shockwave" is more correct than "sound"
- ars 12y agoDon't forget that compression causes gas to heat up.
- marcosdumay 12y agoA 220 dB sound is quite strong. As an example, its intensity (in W/solid angle) is 14 orders of magnitude (AKA 100 billion times) highter than the 80 dB people usualy use as a safety limit.
- aruggirello 12y agoAre you sure? Shouldn't a 140 dB difference in intensity equate to just about 2^14, hence 16384 times stronger?
- jrkatz 12y agoThe decibel scale uses a log_10, not log_2.
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- ChristianGeek 12y agoNot only is this article fascinating, even more so is the 600-page report it links to! Thanks.
- danielweber 12y agoSo the sound got harder to hear as you were farther away, but what if you were at the exact antipode on Earth? Would it have been audible at all?
- aatish 12y agoThe sound was only audible up to 3000 miles in radius, or about 1/13th the globe. It wasn't audible in the other side of the Earth (although it was detectable.)
- stromgo 12y agoHe mentioned the "exact antipode on Earth", so he's probably thinking of an effect similar to antipodal chaotic terrain [1]. The fact that sound was only audible up to 3000 miles in radius is not enough to rule it out, you need other arguments. [1] http://en.wikipedia.org/wiki/Caloris_Basin#Antipodal_chaotic_terrain_and_global_effects http://en.wikipedia.org/wiki/Caloris_Basin#Antipodal_chaotic... ("It is thought by some to have been created as seismic waves from the impact converged on the opposite side of the planet.")
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- ars 12y agoAssuming it was powerful enough to get there, you would hear it. At the antipode you would feel an identical pressure wave from both side. This would manifest as compression which you would feel since you are compressible. A flag would not move in either direction (i.e. the wave is canceled out), but there would still be a compression wave in it. Like imagine hitting a piece of wood with two hammers simultaneously.
- rspeer 12y agoSomething that makes this extra intriguing: the exact antipode of Krakatoa seems to be in an inhabited area on the banks of the Rio Magdalena in Colombia. I wonder if anyone was there at the time to notice a pressure wave coming from all directions.
- beloch 12y agoTo put this in context, the Krakatoa eruption released energy roughly equivalent to a 200 megaton bomb, which is roughly four times larger than the "Tsar Bomba", an H-Bomb which is the largest nuclear weapon detonated to date. The globe's average temperature fell 1.2 C after the eruption due to SO2 increasing the Earth's albedo. The Volcanic Explosivity Index (VEI) of the Krakatoa eruption was 6, and it's estimated to be a roughly once in a century eruption. When you think about it, we're living on a extremely thin crust that's formed on the surface of a molten, roiling ball of rock and metal. People are strangely obsessed with the threat of asteroid impacts when what's beneath our feet presents a perhaps even greater danger, one which we know next to nothing about!
- Balgair 12y agoMy wife is a geo-chemist. She says that plastic is a better term to get an idea on the mantel. Yeah, it is a liquid, but the pressures and temperatures are just so crazy to us that calling it 'roiling' is a little bit of a misnomer. Also, because of these pressures and temperatures, it's hard to ever know anything about the interior of the planet. Turns out, dense things that are very deep and hot are very hard to study.
- pavel_lishin 12y ago> People are strangely obsessed with the threat of asteroid impacts when what's beneath our feet presents a perhaps even greater danger, one which we know next to nothing about! I'd wager we're much closer, technologically, to do something about asteroids, though. Not quite so much about eruptions.
- D-Coder 12y agoEruptions are limited in size by the (lack of) strength and weight of the material keeping it suppressed. Asteroids have no size limit. Disclaimer: I am a software engineer, not any kind of geologist.
- SeanDav 12y agoAnother amazing/frightening statistic is that pyroclastic flows killed people living 30 miles away over open ocean. If I was living that far away across an ocean, I would have felt perfectly safe. It just boggles my mind that even at this distance Krakatoa was deadly.
- MattWard 12y agointeresting article
- th0ma5 12y agoOne thing I only see a little bit about is the negative pressure pole created on the opposite side of the earth? I guess I need to spend some time at the library, but I've only seen this stated as a trivia item, but no further details, like was the effect as pronounced at that point given this is when the reflections outward all met up again?
- jychang 12y agoSound doesn't travel at the same speed given different air pressures and temps. I think the waves wouldn't meet up at certain point.
- ivan_ah 12y agoInterestingly, the sound intensity will decay as a 1/r law, where r is the distance from the source. (I'm assuming conservation of sound energy as it travels horizontally, i.e., no loss to interactions with atmosphere and terrain). Compare with the 1/r² laws like the strength of an electric field at a distance r from charge Q: E(r)=kQ/r². In both cases there is a total of something (sound energy or electric field lines) and that total must be split over all possible directions. The total electric field must be split over the surface area of increasingly larger and larger spheres hence the 1/r² behaviour (1/4πr² to be precise). The sound energy is spread uniformly over a circle with circumference C=2πr, hence giving a 1/r decay, over short distances. For longer distances, the curvature of the earth will play a role. Come to think of it, it must have been really loud somewhere diametrically opposite to Krakatoa, 17 hours after the eruption...
- abduhl 12y agoI don't think this is correct. A sound wave propagates in three dimensions the same as an electrical field (spherically) and so should also obey the inverse square law.
- femto 12y agoIn this case, the atmosphere is essentially a thin (compared to the radius of the Earth) two dimensional sheet wrapping the Earth, so it's probably valid to think of the sound as propagating on a surface. There wouldn't be much loss of energy to space. Would the atmospheric interface with the ground reflect or absorb? The divergence is probably even less that 1/r because the Earth is roughly sperical, and the sound will focus at the antipode of its source. There might even be a region, approaching the focus, where as the sound propagates its sound level is actually increasing, not decreasing! It would be interesting to know what history has to say about Medellin, in Colombia, in 1883. Being at coordinates 6N 75E, it is roughly at the antipode of Krakatoa and could well have had an awful lot of energy dumped in it general direction a few hours after the eruption.
- sillysaurus3 12y ago
- skosuri 12y agoI've been really impressed with Nautilus. Awesome to have a new magazine that seriously covers scientific topics, and do it quite well and with style.
- robjekt 12y agoFantastic article. Thanks for sharing
- hypertexthero 12y ago"Holy smokin' toledos"
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- Shivetya 12y agoIt would be so amazing to capture such an event from satellite. I wonder how much deformation would be evident, sure some material was pushed into space (not speaking earth - but gases)