Instruments of Unusual Size

Volcanic craters could be the largest musical instrument on Earth, producing unique sounds that tell scientists what is going on deep in a volcano’s belly. Chile’s Villarica volcano acted much like a gigantic horn when it erupted in 2015, created reverberating sounds that changed pitch as its lava lake rose to the crater rim. On the other hand, Ecuador’s Cotopaxi volcano has a deep, cylindrical crater that acts much like a massive organ pipe. The crater produced strange sounds scientists dubbed tornillos, the Spanish word for screw, when Cotopaxi began rumbling in 2015. Jeffrey Johnson, a geophysicist at Boise State University, studies the unusual low-frequency sounds made by volcanic eruptions, earthquakes and avalanches. Understanding each volcano’s unique voiceprint could alert scientists to changes going on inside the crater that may signal an impending eruption, according to Jeff. In this episode, Jeff describes how volcanoes and earthquakes produce infrasound – sound waves below the frequency of human hearing – and how the size and shape of a volcano’s crater defines the range of vibrations it can produce. Listen to Jeff recount the strange sounds geophysicists noticed during the eruption of Mt. St. Helens in 1980 and hear how earthquakes can make mountains ring like giant bells. This episode was produced and mixed by Lauren Lipuma.