The sand grains must be within certain diameters, contain
silica, and be a particular humidity. These conditions exist in
about 35 locations around the world, including Kelso Dunes and
Eureka Dunes in California’s Mojave Desert. The sound is usually
triggered by wind passing over the crest of a dune or by walking
on the sand. Scientists have not been able to definitively
determine how the sand produces the sound, but the face of the
dune apparently acts like a huge loudspeaker, amplifying the
volume of the grains of sand as they collide. Sound of singing
dunes (recorded by Dr. Franco Nori and Dr. Nick Lancaster at
Sand Mountain, near Reno, Nevada} Another unusual phenomenon is
the system of blowholes at Wupatki National Monument in the lava
fields of northern Arizona. Water seeping into fractures in the
limestone layers of the Colorado plateau dissolved limestone and
created fissures and cavities. Small openings in the earth —
blowholes and wells — tap into the cavities. When the atmosphere
above the blowhole