Remember that infrasound is something that humans cannot hear unaided because the sound has a very long wavelength and travels over a large distance. If you think that the straw you would use would need to be really, really, really l-o-n-g and really, really, really w-i-d-e, you are correct. Do you think just the length of the straw would matter? How about the width of the straw? Think about the dimensions of the straw.How long do you think your straw would need to be in order to make a sound that you couldn’t actually hear, an infrasound?.Remember that the scientists are focused on volcano sounds that are subaudible.
Listen again to the infrasound from the Villarrica volcano chamber. Inferring is what scientists do when explaining phenomenon. Inferring is when you use prior knowledge, past experience, and observations to explain what is happening. Once scientists have used computers to process the volcano’s infrasound, they identify what this indirect observation is “telling” them by making an inference. Credit: The Official CTBTO Photostream, CC BY 2.0, via Wikimedia Commons Infrasound arrays at infrasound station IS18, Qaanaaq, Greenland. In fact, because infrasound waves are often very long, scientists have to stretch out their sensor arrays over large areas and collect the infrasound over a long time such as days or weeks. Since humans are generally less perceptive of the low-frequency sounds produced by volcanoes, scientists have to process volcano infrasounds with computers and speed up the infrasound to be able to identify the wave features. Many animals use infrasound to communicate, so cool examples to check out are alligators and baleen whales. Some natural producers of infrasound are calving icebergs and avalanches. Infrasounds occur below the 20Hz frequency threshold of human hearing and have long sound waves. If a sound has a low frequency and travels over a very long distance, it will be below the range that humans can hear, this is referred to as sub-audible or infrasound. However, there are some sounds that humans cannot hear. Some sounds are audible, meaning you can hear the sound without any assistance, like when your friend calls your name.
Let’s check in with volcanologist Jeffrey Johnson again as he describes what he hears in that volcano recording. After listening to Johnson’s explanation, can you describe how changing the pitch of your straw kazoo models the change in the sound you heard in the Villarrica volcano?.Shorter straws can be expected to make a higher sound. Why do you think that happens? Longer straws produce a deeper sound, so you can expect to make a deeper sound. You might have noticed that as you make your straw shorter, the sound becomes higher-pitched than the sound you made when you first created your kazoo. How might your straw kazoo help you understand the volcano sounds that Jeffery Johnson studies?.How does the sound from your kazoo change as you shorten the straw?.The sound will be more like a buzz.Īfter you master using your kazoo to make a sound, try cutting off length of the straw to change the sound or pitch. Place the “V” shape end in your mouth and blow.Open the flattened end – just a little bit.Cut the flattened end to make a “V” shape (like a point to a pencil).Place one end of the drinking straw in your mouth and bite down on it to flatten it.Please be careful to not cut yourself and don’t share used straws/kazoos with friends. You can model the up and down pattern of the sound that the volcano makes in the audible range by playing a kazoo made from a straw. Can you identify where the sound changes? Listen to the Villarrica volcano’s sound. This difference in the sound can tell us how soon the volcano might erupt or even whether a volcano is more active. The higher up in the volcano’s chamber the magma is, the higher-pitched the sound is, and the lower the magma in the chamber, the lower the sound. Instead, scientists are interested in the sound that comes from deep underground as the magma changes position before an eruption. But scientists don’t listen to the sounds you hear as a volcano is erupting. Infrasound is one type of data that can indicate that the volcano is becoming more active. It can be a useful tool to help gather information about when or if a volcano might erupt. Sound is important to the work of many volcanologists-scientists who study volcanoes, lava, magma, and related geological phenomena.
Note: As you move through this activity, there are different clips from Johnson’s interview with Science Friday. Let’s check in with Johnson for more information about the sounds of volcanos. Science Friday sat down with Jeffrey Johnson, an associate professor of geophysics at Boise State University to talk about what we can learn by listening to volcanos.
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