Most beaches are quiet underfoot, apart from the waves. But on a handful of shores around the world, the sand itself makes noise. Scuff your feet and it squeaks, whistles, or even barks. In some deserts, whole dunes give off a deep, rumbling hum. So how can sand possibly sing?
The short answer is that the sand grains have to be just right: rounded, similar in size, clean, made with silica, and at the right level of dryness. When layers of those grains slide over one another, they can move together in a way that produces sound. Scientists still aren't completely sure about the exact mechanism, and several theories are in play.
America's Own Singing Beach
About a mile from the center of Manchester-by-the-Sea, Massachusetts, sits Singing Beach. It got its name because the sand squeaks when you walk on it. It's easy to reach from Boston by train, and it's popular in the summer months.
It's far from the only one. Singing sand has been reported on 33 beaches in the British Isles, including Porth Oer in Wales, better known as Whistling Sands. Hawaii has Barking Sands Beach. Singing sands also turn up on Prince Edward Island in Canada and along the shores of Lake Michigan and Lake Superior.
Why Only Some Sand Sings
Beach sand that sings tends to be quartz with very round grains. Many researchers believe the grains need to be similar in size and well sorted by wind and waves, with surfaces free of dust and pollution. One idea is that each layer of grains slides over the layer beneath it, and because the grains are so uniform, they move up and down together, creating a tone.
That's also why singing sand is so delicate. Even small amounts of pollution on the grains can silence it. Other theories suggest the sound comes from grains coated in dried salt rubbing together, a bit like rosin on a violin bow, or from thin layers of trapped air acting as tiny cushions that vibrate.
Water matters too. Wet sand is usually silent because the grains stick together, though a tiny bit of moisture can raise the pitch. The best place to listen is usually the dry upper beach, above the normal high tide line.
Dunes That Boom
In the desert, the effect can be far more dramatic. Singing dunes can produce a loud, low rumble of up to 105 decibels, lasting as long as several minutes. The sound has been reported at about 35 desert locations around the world.
The booming happens when sand slumps or avalanches down the face of a dune, often triggered by wind or by someone walking near the top. In California's Mojave Desert, visitors to the Kelso Dunes sometimes climb to the top and slide down slowly to set off a low rumble they can both hear and feel. The effect is much stronger when the dunes are very dry.
The sound even inspired music of the regular kind. Bing Crosby's 1947 album Drifting and Dreaming includes a song called "The Singing Sands of Alamosa," inspired by the dunes near Alamosa, Colorado, now Great Sand Dunes National Park.
Go Have a Listen
So the next time you're at the shore on a dry, sunny day, try shuffling your feet across the upper beach. If the sand is clean and the grains are just right, you might hear it squeak back. It's one of the few concerts in nature where you get to play along.
