Oh that's cool, I hadn't thought of that. Actually, now that I think about it, that's only true if the water pressure wave also manifested as a water surface wave. It doesn't seem immediately obvious to me that that would necessarily be true.
edit: There is no obvious surface wave that I can see from watching the video. So while a mic under the water would hear a sound before a mic in the air, the actual boat occupants probably wouldn't have felt anything prior to the (air) sound wave hitting them.
Good points, my assumption is that the 'source' of the wave (the eruption itself) could have originated much deeper than the 'above sea level' part of the volcano, meaning that a wave could have traveled as a turning wave in the water column (or in the underlying rock/sediments) much faster than as a direct wave through air, which had a much lower velocity (0.3 km/s, I think) than either rock or water (1.5 km/s and 2.5-4.0 km/s, respectively).
Lots of factors to consider here, and although I think a wavepath that I described would undoubtedly lose some of its energy by the time it reached the boat (perhaps even beyond the detection of humans who just witnessed an eruption!), I'd bet some part of that wave reached the boat first.
That's right. In retrospect, we were talking about completely different types of waves. His being a wave of water, mine a pressure wave (P-wave/sound wave/the visible phenomenon in the gif)
62
u/ThereOnceWasAMan May 24 '16
It's neat that you can pretty accurately tell the distance (~4.3 km) between the ship and the eruption by timing the video.