The following article is from the book Uncle John's Bathroom Reader Plunges into California.
Kelso Dunes (Image credit: Binksternet)
If we told you that there are sand dunes in California that can actually play music all by themselves, would you believe us?
WHEN IN DOUBT, BLAME EVIL SPIRITS
In the 13th century, while traveling through the Gobi Desert, explorer Marco Polo heard eerie sounds coming from the sand dunes around him. He described the noise as “all kinds of musical instruments, and also of drums and the clash of arms.” After hearing the mysterious noises, Polo came to the “logical” conclusion that he must be in the presence of evil spirits. These days, we know that all that music was nature, not spirits. Of all the sand dunes in the world, only a few have the ability to “sing” in the ways that so startled Marco Polo. Beach sand sometimes makes brief squeaking noises, but it’s rare to find dunes that produce the magnificent instrumentals Polo described. There are actually only about 30 singing sand dunes on earth, and California has four noisy sets of them.
• The Kelso Dunes are the loudest of California’s singing sands. Located in the Devil’s Playground area of the Mojave National Preserve, the Kelso Dunes rise as high as 650 feet.
• The sounds of the Dumont Dunes, also located in the preserve, were filmed for the PBS Nova episode “Booming Sands.” According to researchers, the Dumont Dunes “sing” the note of G.
• The Eureka Dunes in Death Valley National Park are the highest group of dunes in California. Rising 680 feet from the valley floor, the dunes are also thought to be the tallest in North America.
• Also found in the park, the Panamint Dunes have been known to produce noises, but are the least tuneful of all of California’s singing sands.
Eureka Dunes (Image credit: Peretz Partensky)
Why is it that some dunes sing while others are silent? Scientists are still trying to figure that out, but they know some things for sure. Singing dunes need a special recipe of sand, moisture, wind, and movement. In particular, the dunes must be created out of grains of sand that have been windblown over long distances, making them unusually smooth and round. All the grains must be similar in size, and the dunes free of foreign particles. Humidity and moisture also affect the sound—too much moisture and the sand goes silent because the grains can’t move. But the dune must have some rainfall so that its inner grains stay a little damp.
When a dune creates sound, its outer layer (a few feet thick) of sand grains are dry from the sun, but its inner core can be wet and hard as cement from previous rainstorms. Wind then pushes sand grains to the top of the dune and they accumulate there until the angle of the slope reaches a tipping point of about 35 degrees. That causes an avalanche of sand grains to fall, moving against one another, creating friction and producing the loud bass rumble of dune music.
At least, that’s how it’s done in nature. In the name of science, researchers usually produce their own avalanches and sandy symphonies by hiking to the highest spot on the dune and then sliding down on their derrieres.
SCIENCE FROM THE BOTTOM UP
Dumont Dunes (Image credit: Stan Shebs)
California Institute of Technology professor Melany L. Hunt and many of her graduate students have been among those sliding down California’s dunes to research the secrets of sand noise. By sitting on the dunes when they sing, researchers have learned that vibrations throughout the entire dune are part of the music. Often, even after the sand has stopped moving, the dunes continue to vibrate and boom for a few minutes. And by using radar, computers, and geophones (microphones that can be buried in sand), Caltech researchers have measured the frequencies and rates of vibration of the dune songs. They’ve discovered that older, higher dunes with steep slopes are most likely to produce music, which is louder in the fall than in the spring. Most importantly, though, they’ve found that dunes produce a tone similar to one produced by a stringed instrument, and they think they know how that happens.
Singing dunes have their outer layer of dry sand (about five feet thick) that conducts sound much better than the moist inner sand. The differences in conduction between the dry and hard sand causes the noise to bounce around in the dry layer, magnifying the vibrations and amplifying the sound. Hunt has compared the singing sand dunes to cellos: “In a cello, the musician bows the strings, and the sound is amplified through vibrations of the cello [body] and the enclosed air. In the dune, we excite the system by avalanching the sand on the upper surface, and the sound is amplified in the dry, loose upper layer of sand.”
Scientific research has also shown that the windblown sands in California’s singing dunes do have special, noisemaking properties. Put ordinary beach sand in a jar and shake it up, and you won’t hear a peep. Put dry singing dune sand in a clean jar, shake it up, and you’ll probably hear a sound. Next time you’re in the Mojave Desert, give it a try.
The article above was reprinted with permission from Uncle John's Bathroom Reader Plunges into California. This volume brings you stories of the Golden State you've never heard before. You’ll meet child prodigies, spies, traitors, celebrities (and sidekicks), gossips, hermits, humanitarians, and zealots.
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