Shinmoedake volcano started eruptng about January 26, and it now joins a few other volcanoes in the world as one capable of producing atmospheric shock waves. Turn up your speakers (well, not too far), play the video on this site, and listen to the shock just a couple of seconds into the video! Assuming that the camera is in the town of Miyazaki, it took the shock about 25 seconds to cover the 8 km (5 mi) from the volcano to the town. So, the process that created the shock occurred well before the eyewitness turned on the recording device. The shock broke hundreds of windows. After I wrote this, I discovered another video that starts earlier and captures the whole eruption sequence; fortunately, my calculation of the shock travel time above seems to be right on!
Added on Feb. 7. In this video, you can see the air shock sweeping rapidly down the flank of the volcano in the first few seconds, and you can hear the shock at about 33 seconds.
This volcano, in a quieter time in 1967, was the location of the notorious villan, Blofield, and his SPECTRE organization in the movie "You only live Twice", and thus the name that is now appearing in the press, the James Bond volcano.
The shock wave that produced the boom you heard in the video did not have a visible presence, only audible. However, visible shock waves at volcanoes were first described at Mount Vesuvius by F.A. Perret who called them "flashing arcs." In his article in the American Journal of Science (volumes 183-184, Article XXXII, pp. 329-333, 1912). From that article: "The frequency of the explosions varied from approximately one every three or four seconds to at least three per second. Although powerful, they were verysharp and sudden in their nature, and at the instant of each--but before it could be sensed by the eye or ear--a thin, luminous arc flashed upward and outward from the crater and disappeared in space. Then came the sound of the explosion and the projection of gas and detritus above the lip of the crater. The motion of translation of the arcs, while very rapid in comparison with that of the detritus, was not above the limits of easy observation and there could be no doubt as to the reality of the phenomenon, which was repeated some hundreds of times. ...of the actual phenomenon, the beauty of which lies in the delicate luminosity, the elegance and perfection of form, and the grace and vivacty of the arcs amid the contrasting color and relatively sluggish movement of their surroundings."
Ah, wouldn't it be nice if some of our peer reviewed journals today allowed us to regain some of this style of writing!
Perret travelled to volcanoes around the world, but it was not until four years later that he saw them again, this time at Vesuvius. After proposing that the arcs were related to sound waves, he concluded "...the flashing arcs may be considered one of the most beautiful of all volcanic phenomena."
This posting got me to a wonderful blog by David Bressen on the history of geology, and I'll refer you there "for the rest of the story". The discussion of Perret that accompanies the picture above is on the January 18, 2011, blog.
Other volcanoes that have shocks are Ngauruhoe (New Zealand), Sakurajima (Japan), Matua (Siberia), and, just last summer, Eyjafjallajokull.
Added on Feb. 7. In this video, you can see the air shock sweeping rapidly down the flank of the volcano in the first few seconds, and you can hear the shock at about 33 seconds.
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| Set from the "You Only Live Twice" |
The shock wave that produced the boom you heard in the video did not have a visible presence, only audible. However, visible shock waves at volcanoes were first described at Mount Vesuvius by F.A. Perret who called them "flashing arcs." In his article in the American Journal of Science (volumes 183-184, Article XXXII, pp. 329-333, 1912). From that article: "The frequency of the explosions varied from approximately one every three or four seconds to at least three per second. Although powerful, they were verysharp and sudden in their nature, and at the instant of each--but before it could be sensed by the eye or ear--a thin, luminous arc flashed upward and outward from the crater and disappeared in space. Then came the sound of the explosion and the projection of gas and detritus above the lip of the crater. The motion of translation of the arcs, while very rapid in comparison with that of the detritus, was not above the limits of easy observation and there could be no doubt as to the reality of the phenomenon, which was repeated some hundreds of times. ...of the actual phenomenon, the beauty of which lies in the delicate luminosity, the elegance and perfection of form, and the grace and vivacty of the arcs amid the contrasting color and relatively sluggish movement of their surroundings."
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| F.A. Perret at Campi Flagrei, Italy, possibly 1906-1907 photo is from http://historyofgeology.blogspot.com/p/about_02.html |
Ah, wouldn't it be nice if some of our peer reviewed journals today allowed us to regain some of this style of writing!
Perret travelled to volcanoes around the world, but it was not until four years later that he saw them again, this time at Vesuvius. After proposing that the arcs were related to sound waves, he concluded "...the flashing arcs may be considered one of the most beautiful of all volcanic phenomena."
This posting got me to a wonderful blog by David Bressen on the history of geology, and I'll refer you there "for the rest of the story". The discussion of Perret that accompanies the picture above is on the January 18, 2011, blog.
Other volcanoes that have shocks are Ngauruhoe (New Zealand), Sakurajima (Japan), Matua (Siberia), and, just last summer, Eyjafjallajokull.
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