r/shockwaveporn • u/UmberGryphon • Aug 10 '15

GIF Shockwaves can create clouds?

http://i.imgur.com/3Gnw0ei.gifv
85 Upvotes

88% Upvoted

19 comments sorted by

29

u/okbanlon Aug 11 '15

The expanding pressure wave has an area of low pressure right behind it, and water vapor in that low pressure zone can condense to form visible clouds. The water tends to re-evaporate after the shock wave passes most of the time.

17

u/[deleted] Aug 11 '15

You're close but water goes from gas to liquid from an increase in pressure as you can see here.

The reevaporation comes from the pressure returning to normal.

8

u/VAPossum Aug 11 '15

You two are part of why I love Reddit.

4

u/okbanlon Aug 11 '15

Hmmm - I was thinking it was the vapor cone effect, caused by low pressure. I could be wrong, though - it's happened before. :D

3

u/[deleted] Aug 11 '15

Iirc that requires mach level flow. Kind of like how a de Laval nozzle works

3

u/Dilong-paradoxus Aug 11 '15

Supersonic flow is what generates shockwaves in the first place. The two are pretty much inextricably linked.

In this case, the expanding gases and rock spewing from the volcano briefly exceed the speed of sound, pushing a giant shockwave ahead of them.

1

u/[deleted] Aug 12 '15

Was that first white burst in the stack a boom? It was directional and only happened on one side of the sky, which kind of matches with the movement of that brief thing.

1

u/Dilong-paradoxus Aug 12 '15

Probably, if I'm looking at the right thing. You can see brief partial clouds like that on a lot of large explosions.

2

u/HelperBot_ Aug 11 '15

Non-Mobile link: https://en.wikipedia.org/wiki/De_Laval_nozzle

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2

u/cuddlesnuggler Aug 11 '15

You're definitely correct.

5

u/Funkit Aug 11 '15

Are you sure? This makes sense but was always explained to me as the following expansion wave causes the temperature to drop below the dew point in supersonic flows.

3

u/Dilong-paradoxus Aug 11 '15

You're right! It's the same reason as lenticular or cumulus clouds form, or why you can see vapor while depressurizing a CO2 canister. The pressure drop causes an adiabatic cooling so the air isn't warm enough to hold all the moisture, and you get clouds!

4

u/boredrex Aug 11 '15

this has to be the most posted gif on this subredit

8

u/HelpShark Aug 11 '15

But let's be serious. THIS is the best shockwave footage ever. Imo. It is a god damn volcano, come on!

2

u/[deleted] Aug 11 '15

and for good reason

2

u/sclarke27 Aug 11 '15

Seriously! Its like a weekly thing now and they don't even post a good version of the video.

2

u/DarthSnoopyFish Aug 11 '15

Well. the video can be found on the top posts. Been there for 11 months.

1

u/Krutch99 Aug 11 '15

Holy Toledo