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SUMMARY:Booming Sand Dunes: An Example of Wave Propagation Through a Granu
 lar Material - Nathalie Vriend\, DAMTP
DTSTART:20100423T150000Z
DTEND:20100423T160000Z
UID:TALK24560@talks.cam.ac.uk
CONTACT:Raymond E. Goldstein
DESCRIPTION:Booming sand dunes are known for the persistent\, low-frequenc
 y sound they emit during avalanches on the leeward face of the dune. The s
 ound can last for several minutes and be audible from miles away. A domina
 nt audible frequency (70 - 105 Hz) and several higher harmonics characteri
 ze the acoustic emission. Travel literature has described the phenomenon f
 or centuries\, but to date no scientific explanation covers all field obse
 rvations. \n\nQuantitative field research at the booming dunes of the Moja
 ve Desert and Death Valley National Park has been combined with modeling t
 o unravel the booming phenomenon. The waveguide model explains the selecti
 on of the booming frequency and the amplification of the sound in terms of
  constructive interference in a confined geometry. Microphone and geophone
  recordings of the acoustic and seismic emissions show a variation of boom
 ing frequency in space and time. Geophysical techniques image the subsurfa
 ce structure of the dune and reveal a natural internal layering. This laye
 ring is crucial for the existence of a natural waveguide that guides and a
 mplifies the waves to a magnificent sound. The variation in booming with l
 ocation and season indicate that the waveguide theory successfully unravel
 s the phenomenon of booming sand dunes.\n\n
LOCATION:MR2\, Centre for Mathematical Sciences\, Wilberforce Road\, Cambr
 idge
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