Why You Can't Hear Volcanoes Erupt

Even if a volcano is just a few miles away, you might not hear it erupt. How is that possible? It has to do with a phenomenon known as sound shadows! Hank will tell you all about it in this new episode of SciShow! Join us!

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[mrbarth]

When Mt. St. Helens erupted I was living about 250 miles away. Our house was jolted by about 6 very loud explosive noises that had some physical pressure to them. Then a few moments later we had a repeat in the pattern but in reverse order. We found out that it was the sound wave bouncing off the "roof" of the atmosphere layer and back down. Sort of an echo it was reported. It was so loud at that distance that we found it hard to believe that people living near the mountain didn't hear a thing.

[bobspringer]

You might also have mentioned that, during World War II, submarine commanders knew that, if they got below the thermocline, they were not detectable by sonar.

[tekuaniaakab]

For a second I thought the title read “...could protect our cities FROM manatees” as they are truly formidable beings

[DiscoChixify]

Omg the manatee in a dress and wig in the ocean was so adorable 🥰 😅😂 thank you for that visual. I literally had to pause just to get the giggles out so I could get back to focusing and finish absorbing the content. ❤ you guys made my day.

[iriandia]

Where I live in San Diego, there are often fighter jets overhead, and they take off from the runways along the coast. There are a bunch of hills inland, and the sound bounces off of them in weird ways. So people miles from the runways often get confused by how loud the jets are when they’re miles away. I assumed this was entirely due to the hills, but this video makes it clear that there’s more going on. I would love to know how strong onshore winds or Santa Ana winds affect these extremely loud sounds.

[muxpux]

I work at Mt St Helens, so I cringed when you said it blew in 1983 (it was 1980), but this phenomena is noticeable where I live. On a clear night, I hear no road noise, as the freeway is about 1.5 miles from me as the crow flies. But if the cloud deck comes in at just the right level, I can hear the freeway noise loud and clear. It’s less noticeable under a clear air inversion.

[Lemanic]

Ornamentation on houses works as sound shadows. It disperses the sounds. Plain outer walls don’t. That’s why modernist/brutalist architecture works as an excellent amplifiers of sound. The Johanneberg neighborhood of Gothenburg is literally planned and built like the inside of early tube amplifiers, for example.

[narnigrin]

Over here giggling at the manatee lady showing up at the opera house, thanks Scishow 😅

[timogul]

This sort of thing happens in my neighborhood. It's about a mile or two from a busy highway, and normally I can't hear it from my house, but sometimes, generally when the weather is misty or something, the traffic noise carries all the way over and seems only a few hundred feet away. It's like a ghost highway.

[terramater]

It's fascinating to see different solutions to save marine animals. The sound shadows have potential! Our crew filmed another project that aims to avoid whales being hit and killed by ships. The project is about creating a corridor to separate vessels and whales; we even found a success story!

[hopolo]

i'm very excited you decided to focus on the health consequences of chronic noise.

[mozismobile]

Amused that most of the examples of city noise is motor vehicles. "the problem is cars and roads" in so many different ways. I've lived in a house facing 8 tracks of commuter rail and that was noisy, but I've never dared live next to a road that carries 200, 000 people a day. I wouldn't want to live within a couple of kilometres of a road like that.

[tiacho]

It's weird. Scishow probably used a stock footage service for that highway. But I recognise it because I drive under that highway sign in Toronto Canada to get to work almost every day.

[levihowell]

When I was at a friends apartment once there was a college football game at the stadium nearby. The sound coming from the stadium was bouncing off the apartment building behind his and it sounded like the stadium was right behind that apartment building. In reality the stadium was in the exact opposite direction. It was a very bizarre and interesting experience

[yourbuddyunit]

As a former sound guy, I love this. Sound shadows are can be a powerfully useful tool (drum shields, soundproof foam panels/walls).
It can also be your WORST ENEMY, as depicted in the video. It gets even worse in outdoor shows.

[just_kos]

Granted, Mt St Helens did the big boom in May 1980, but it DID erupt in 1983 as well: "Between February 1983 and February 1984, the dome grew continuously both by the intrusion of magma into it and by the extrusion of lava onto its surface. As of May 1984, it appeared that Mount St. Helens had returned to the episodic style of dome growth."

BTW, on the morning of May 18, 1980, I was up reading the Sunday funnies and when the volcano blew, all it sounded like to me was a POP! like a jet going supersonic (I used to live next to a SAC airbase, so I knew that sound). I was just south of Seattle, in Burien, WA.

[Rubrickety]

I really want a deeper dive into the poignant story of Opera Guy and his tragic love triangle with Polly Puffyshoulders and her manatee twin.

[robinhahnsopran]

Opera singer here! I see y'all with your Pavarotti animations 😂👏

[mersilvaureus]

It seems a bit surprising at first that sounds travels faster through warmer air. Sound traveling faster through solids than liquids, and faster through liquids than gasses makes me think it's related to density. And with warm air being less dense than cold air, my first thought would be it would be faster in cold air. Obviously I don't have the full story, so to speak, but it's still interesting.

[EchoeOne]

This made me think of the Tom Scott video about the hills near Amsterdam Schiphol Airport which deliberately cause destructive interference so the noise from the airport does not reach the city, but I don’t know whether this counts as a sound shadow