Earlier this week a video (above) recorded by a guy named Phil McNamara went viral because it caught the active Tavurvur volcano in Papua New Guinea erupting with a massive explosion. The shock wave visibly approaches and a voice off camera says, "Watch out for the shock. It's coming." Then a sonic boom blasts and the boat McNamara's on rocks wildly.
Ash shot so high into the air from this eruption that Australia had to reroute flights around the island. McNamara caught the volcano erupting for the first time in almost 10 years. And no wonder his stunning video's accumulated millions of views... I don't know about you, but I had no idea a volcano eruption could be so powerful that it could break the sound barrier.
How did Tavurvur's volcano generate such speed? Well, as magma is formed it contains a lot of dissolved gases that have been suspended in a dissolved state. When the pressure around the magma becomes less than that of the gas inside, it expands and forms bubbles. These bubbles have a lower density than the magma itself and are pushed out like the foam from a shaken bottle of soda. This is what causes the eruption.
But if all volcanoes erupt this way, why did Tavurvur create a sonic boom when others do not? The magma was probably thicker than most, with a high viscosity that gave the gas bubbles difficulty flowing upward. This results in a more violent eruption, with more material spewed into the air. Also, the composition of the magma might have had more gas bubbles than other volcanoes, depending on what natural materials were melted inside. So high viscosity and high gas levels means more KABOOM.
We usually associate a sonic boom with an aircraft traveling faster than the speed of sound (which varies, but is typically 700 mph). In this case, the volcano's eruption hurtled objects outward so fast that their wake broke the sound barrier. Tavurvur was able to do this because it has a "Vulcanian" volcano, known for impressive eruptions with high-velocity projectiles. The pyroclastic "bomb" fragments that come out usually aren't aerodynamic either, both due to the viscosity of the magma and the crystalline rock material that plugs up the throat of the volcano. Sakurajima, Japan also has a volcano like this, capable of brief but loud eruptions.
Want to see the aftermath of the Tavurvur eruption for evidence? NASA has before-and-after satellite imagery available.
So I've learned my lesson. Volcanoes are capable of firing objects from their spouts faster than the speed of sound. The world's an even stranger, scarier place than I previously imagined.
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