Video Of Volcanic Eruption Produceing A Terrifying Sonic Boom

We’ve all heard a sonic boom before. It’s kind of like an explosion, a sudden shattering of the eardrums as a supersonic plane flies directly above us. However, if you’re a particularly lucky person, you may have encountered a volcanic eruption that, as part of the pyrotechnics, also included a sonic boom or two as well.

Evacuated Matapit Islanders (foreground) watch Tavurvur volcano erupt on New Britain Island in Papua New Guinea, 07 October 2006. (Photo: BRUCE ALEXANDER/AFP/Getty Images)

Although there are plenty of videos online that wonderfully depict the awesome power of a volcanically-generated shockwave, my absolute favorite clip has to be that of a recent eruption of Tavurvur, a volcano in Papua New Guinea. This is an active stratovolcano, one that feeds off the same magmatic source as the nearby Rabaul caldera, an enormous, cauldron-like volcano.

Back in August 2014, Tavurvur erupted rather explosively, sending ash 18,300 meters (60,000 feet) into the sky, and causing lava bombs to rain down into the Pacific Ocean. At one point, an explosion at the vent caused the clouds to part. Shortly afterwards, what appears to be a sonic boom rocked the boat containing both Linda and Phil McNamara, who beautifully captured the moment on film.

Credit: Linda McNamara via Facebook/Video Newser via YouTube

“Holy smoking toledos!” the latter exclaimed, before telling the Brisbane Times that the two onlookers “absolutely crapped themselves” as the wall of sound smacked into their vessel. So what’s actually happening in the video here – is this a true sonic boom? Did the blast involve objects that were propagating through the air faster than the speed of sound?

During this volcanic eruption, a large slug of gas clearly got stuck in Tavurvur’s conduit, the hollow-ish path leading from the bowels of the volcano up to the vent. Perhaps a rock fall, or a particularly viscous chunk of magma, prevented many individual gas bubbles from escaping up to the surface as per normal.

Consequently, these bubbles coalesced, forming one giant slug of gas – mostly water vapor, sulfur compounds and perhaps some traces of carbon dioxide. Upon reaching the surface, this slug of highly-pressurized gas expanded upwards and outwards at an incredible speed, shooting plenty of lava and ash into the air with it.

The outward rush of gas dramatically compressed the air in the atmosphere around it, creating a shockwave. This obliterated the pre-existing clouds above the volcano, but it also managed to create new, temporary ones – the blast forcefully compressed additional water vapor in front of it, turning them into temporary clouds.

Smoke and ash fills the air as Mount Tavurvur erupts in Rabaul in eastern Papua New Guinea on August 30, 2014. (Photo: Ness Kerton/AFP/Getty Images)

After about 13 seconds or so, the shockwave impacts the McNamaras, much in the same way one from a supersonic jet or missile would. Indeed, these shockwaves resemble the ones that you would experience if you stood near the source of a sonic boom.

Nevertheless, it must be noted that it’s difficult to tell whether or not this was a true sonic boom. Technically, this only refers to shockwaves generated by an object travelling faster than the speed of sound.

However, if you look closely, you can see that the volcanic debris ejected by the eruption was moving at speeds in excess of the speed of sound. Around the tip of the debris cloud at around 00:13, you can spot a vapor cone, much the same as the one that forms around a plane travelling at supersonic speeds. This is a cloud of rapidly condensed water vapor, one that forms due to the sudden localized changes in air pressure.

Although it only lasts for a brief moment, it is clear that the debris ejection caused a sonic boom, which in turn was most likely to have generated the shockwaves that subsequently hit the boat.

 

Sound: http://www.forbes.com/sites/robinandrews/2017/01/18/watch-this-volcanic-eruption-produce-a-terrifying-sonic-boom/#6927234fdc30

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