If your phone is like mine, it loves to send you back in time by reminding you of photos you took one, two, or five years ago. These days it’s been showing me vacation photos from summers past, and though it’s pleasant to remember enjoying time with family at museums or walking along a crowded boardwalk, it’s also a reminder of how different things are now. Recently, however, my phone surfaced a vacation video that I had completely forgotten about, one that sent me down a little acoustics rabbit hole.
A couple of years ago, I traveled to Barbados with my partner and her family. We spent most of our time on the west coast of the island where the Caribbean Sea is typically calm and quiet, picture-perfect for a lazy beach holiday. But in exploring the rest of the island on afternoon drives and morning hikes with the National Trust, I learned that this 170 square mile island is far more diverse geologically and ecologically than a postcard could ever communicate.
One of these excursions took us to the east coast which meets the Atlantic Ocean and stands a stark contrast to the west coast beaches just 15 miles away. Instead of placid breezes, here the wind is so strong and regular that the trees have grown bowed to brace themselves against it. The surf is much bigger and the wind picks up a salty spray off the water that leaves your skin feeling sticky after just a few minutes, but it does give your hair nice body.
Walking around the beach, I noticed that our sandals were all squeaking, but then when we took our sandals off, the squeaking continued beneath our feet. It was the sand itself making this noise under our every step, a phenomenon referred to as singing sand. Though not fully understood, the sound is believed to be the result of shear forces as one layer of very similarly sized sand particles slides over another. In sand dunes, the singing sound can carry on for minutes at a time. Activity or wind causes a large layer of sand to slide down the slope of the dune, imparting shear and emitting a sound that can range in frequency from a squeak to a rumble until the sand comes to a rest.
One of the things I love about working in the acoustics field and with science, in general, is that the process of discovery and education never stops. Even on vacation, out in the natural world, there are phenomena to discover that can teach us something new about the behavior of sound.