- #1
fayaazhussain
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Lava fountain is also a form of jet. When other jets produce noise, why do lava fountains not produce any noise?
Why Are Lava Fountains Silent?
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Discussion Overview
The discussion centers around the phenomenon of lava fountains and their relative silence compared to other types of jets, such as those produced by jet engines. Participants explore the reasons for this difference in noise production, considering factors related to the physics of gas expansion and the characteristics of volcanic eruptions.
Discussion Character
- Exploratory
- Debate/contested
- Technical explanation
Main Points Raised
- Some participants note that lava fountains are a form of jet but question why they do not produce noise like other jets, such as those from jet engines.
- One participant asserts that there is indeed a substantial amount of noise from lava fountains due to hot gases expanding and escaping.
- Another participant emphasizes that the aerodynamic noise from jet engine exhaust is different from the noise produced by lava fountains, which may not be as high-pitched or loud.
- Concerns are raised about the kinetic energy of lava fountains reaching significant heights, suggesting that this should produce noticeable noise similar to jet engines.
- Participants discuss historical context, referencing the eruption of Mount Vesuvius and clarifying that the deaths were primarily due to pyroclastic flows rather than lava fountains.
- One participant describes their experience with lava fountains, noting that the noise is primarily mid to low frequency, contrasting with the small orifice of jet exhausts.
Areas of Agreement / Disagreement
Participants express differing views on the noise produced by lava fountains compared to jet engines. While some assert that lava fountains are noisy, others maintain that they are relatively silent, leading to an unresolved discussion regarding the nature of the sounds produced by these geological phenomena.
Contextual Notes
Participants reference specific characteristics of lava fountains and jet engines, including the size of the orifices and the types of frequencies produced. There is also mention of historical events and their implications, which may influence the understanding of noise production in volcanic eruptions.
- #2
davenn
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fayaazhussain said:
have you not experienced a lava fountain up close?
there is a substantial amount of noise of all the hot gasses expanding and escaping as they push the lava into the air.
what "other jets" were you referring to in particular ?
cheers
Dave
- #3
fayaazhussain
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By other jets i am referring to jets issued from a nozzle for ex. jet engine jets. Considerable amount of noise is produced from the exhaust of jet engines. Why do lava fountains don't create that much noise when compared to the exhaust jets of jet engines?
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davenn
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fayaazhussain said:
thats what i suspected you meant... well its not a jet engine spinning at 20,000 +- a bit RPM, so its not going to produce a hi pitched scream :) But as i said in my other post, they are quite noisey
Dave
- #5
fayaazhussain
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I am talking about the aerodynamic noise from the exhaust jets of an engine and not the mechanical noise. Any air flow causes noise take the example of wind. Likewise when a lava fountain comes out of the volcano mouth shouldn't it cause noise which can be heard from quite a distance like in the case of jet engine? Lava fountains are known to rise to heights of even 450m. If the lava is able to reach that much height naturally it's kinetic energy can be compared to that of a jet engine.
This question was actually raised by my teacher. The famous pompeii volcano eruption caused millions of deaths because people couldn't hear the lava fountain and so he asked me why don't they create much noise.
This question was actually raised by my teacher. The famous pompeii volcano eruption caused millions of deaths because people couldn't hear the lava fountain and so he asked me why don't they create much noise.
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tiny-tim
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fayaazhussain said:
no, the deaths (less than 50,000 i think) were caused mostly because people couldn't hear or see the very fast (up to 450 mph) completely silent and invisible pyroclastic surges that asphyxiated them, see http://en.wikipedia.org/wiki/Pyroclastic_flow
they knew Vesuvius was erupting, but a lot of people didn't think there was any need to flee (although a lot of people did), since it was 5 miles away, and lava doesn't flow very fast (unlike pyroclastic surges)
- #7
davenn
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its still a very different situation and my previous response still applies
in my geology activities over the years I have been fortunate to be around lava fountains, much of the noise is mid to low freq ranging, particularly lower freq booms
with lava fountains you also generally don't have the very small orifice of a jet exhaust, which is ~ 1 to 2 metres. The throat of a volcano tends to be much larger ... many metres to in some cases a kilometre or more...
like this one during 1984 in Hawaii...
cheers
Dave
in my geology activities over the years I have been fortunate to be around lava fountains, much of the noise is mid to low freq ranging, particularly lower freq booms
with lava fountains you also generally don't have the very small orifice of a jet exhaust, which is ~ 1 to 2 metres. The throat of a volcano tends to be much larger ... many metres to in some cases a kilometre or more...
like this one during 1984 in Hawaii...
cheers
Dave
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- #8
davenn
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fayaazhussain said:
tiny-tim said:no, the deaths (less than 50,000 i think) were caused mostly because people couldn't hear or see the very fast (up to 450 mph) completely silent and invisible pyroclastic surges that asphyxiated them, see http://en.wikipedia.org/wiki/Pyroclastic_flow
they knew Vesuvius was erupting, but a lot of people didn't think there was any need to flee (although a lot of people did), since it was 5 miles away, and lava doesn't flow very fast (unlike pyroclastic surges)
Thanks tiny tim
I was going to respond to that as well but was busy with the other response as you posted...
and I agree... Yes it wasnt lava or lava fountains that killed the residents of Pompeii
it was the huge pyroclastic flows
cheers
Dave
- #9
fayaazhussain
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Thanks to both of you for your replies! :)
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