Nice. I hadn't thought of there being a limit (due to vacuum) to sound intensity.<p>Reminds me of this recent comment on reddit: <a href="http://np.reddit.com/r/space/comments/2h9y9g/the_first_launch_from_cape_canaveral_1950/ckr6mev" rel="nofollow">http://np.reddit.com/r/space/comments/2h9y9g/the_first_launc...</a><p>"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,"
Hey, 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.)
Interestingly, 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.<p>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.<p>For longer distances, the curvature of the earth will play a role. Come to think of it, it must have been <i>really</i> loud somewhere diametrically opposite to Krakatoa, 17 hours after the eruption...
To 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.<p>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!
Another 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.
For anyone interested, I'd recommend Simon Winchester's book "Krakatoa": <a href="http://www.amazon.com/Krakatoa-World-Exploded-August-1883/dp/0060838590" rel="nofollow">http://www.amazon.com/Krakatoa-World-Exploded-August-1883/dp...</a><p>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.
I'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.
One 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?
It 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)