纳米比亚沙丘为何会发出轰鸣声？科学家解释奇特声学现象
Deep in the Namib Desert, one of the oldest and driest on Earth, certain towering dunes occasionally produce a deep, mysterious hum. When a cascade of sand slips down a steep slope, the air fills with a resonant boom that can last for several minutes, sounding like a distant bassoon or a low-flying propeller plane. Locals have long been aware of these eerie songs, but only in recent decades have scientists begun to unravel their cause.
The phenomenon, known as "booming dunes," arises from a delicate interplay of granular physics. For the sound to occur, the sand grains must be almost perfectly spherical, uniform in size—mostly between 0.1 and 0.5 millimeters—and coated with a thin layer of silica gel. As an avalanche triggers a shearing motion down the dune face, the grains slide in synchronized layers, creating a stick-slip vibration that synchronizes across the entire sliding mass. This acts much like the membrane of a loudspeaker, exciting a resonant air cavity inside the dune below the dry surface crust.
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