San Gabriel Vy Trib, Discovery, etc: Why the sliding dune sings
Booming sands — dunes that rumble with remarkably clear, low notes when portions of them cascade — have long charmed poets and bedeviled physicists and other more practical-minded researchers. Now a group of the latter, engineers and their students at Caltech, has a new conclusion and a model to explain it. They’ve been talking it up for awhile but recently it was in Geophysical Research Letters. That triggered a small news cascade of its own. The gist is that the noise seems to arise within a lens of loosely packed sand descending the steep, lee side of the dune. It acts as a wave guide. The denser sand below it reflects audio waves so that they resonate within the looser portion on the move. This stimulates the whole dune face to sing. One mechanical engineer says it reminds her of a cello. It runs counter to some theories of colleagues in France who felt the sand’s grain size determined the timbre of the tumble. Another thing: the sand must be bone dry.
-CP
Stories:
Discovery.com Larry O’Hanlon with excellent background (and a tip of the hat to Sarah Goforth at Discovery for nudging The Tracker to this story), plus links to the team’s audio and videos – in Grist below; San Gabriel Valley Trib Sept. 13 Elise Kleeman tells readers this is nothing like the chirping of some dry sand as one walks through it; New Scientist David Cohen (Aug 24) blogged on his visit to the tuneful dunes where he slid, filled his shorts with sand, and as payoff got a “thousand yogis chanting” from beneath his backside.
Grist for the Mill:
Jan. 12 Caltech Press Release; AGU/GRL Paper (via Caltech website); Caltech Booming Sand Dunes project; Audio/video links (a particularly good one is here , which also ran on YouTube, and it helps to have decent bass speakers hooked up;
