Booming or Singing Dunes - Dune Worlds: How Windblown Sand Shapes Planetary Landscapes - page 110

Fig. 10.1 Power spectrum recorded by Lorenz of a short 'burp' made
by jumping into sand on Sand Mountain, Nevada in October 2012—
on that occasion sustained avalanching/booming was not obtained.

The peak here is at about 50 Hz, rather lower than the 70 and 85 Hz
peaks noted by Dagois-Bohy et al. (2012)

The emphasis on existing layers in the dune prompted a
rebuttal from Andreotti (2008), who argued that the seismic
interpretation of discrete layers was flawed, that gradients of
porosity in the dune would refract, rather than reflect,
seismic energy. To the dismay of those of us attempting to
follow the literature, Andreotti shows a plot, purportedly of
the same data, with a very strong dependence of emission
frequency versus grain size. What to make of all this? A
counter-rebuttal by Vriend shows more data, with more
error bars (Fig. 10.2 ).
In the meantime, the Douady group has followed up with
some useful laboratory work exploring the change in
emission frequency during the progress of a laboratory
avalanche (Dagois et al. 2010; interestingly, in an Ultra-
sonics journal: perhaps an effort to circumvent the grid-
locked trenches of the geomorphology and physics
journals). This chapter also points out some work on what
sands sing and which don't. For example, glass beads do
not, but after tumbling them with materials to enhance their
friction, they will. Similarly, the beach sands from Morocco
near their dune site do not sing, but the sand in the barchans
downwind of a sebka (where the beach sands have been
wetted with salt water and dust and then dried out) do.

Clearly the sand texture is important. Additional laboratory
experiments and analysis has been pursued by Patsistas
in Canada (e.g., Patitsas 2008) and most recently by

Dagois-Bohy et al. (2012).
Two recent review chapters summarize the situation well
and are the suggested starting points for serious scholars;
despite the acrimony in the subject, some impressive pro-
gress has been made in the last decade. Hunt and Vriend
(2010) focus on geophysical investigations of the dunes
they have studied (including GPR data showing layers at
Dumont—see Radar chapter) and present a nice list of some
40 or so booming dunes worldwide. Andreotti (2012) pre-
sents a thoughtful overview with a stronger physics slant,
and outlines the challenges any theory must address.
It seems to us that there are elements of truth in all these
works, but a key point has apparently been missed. It seems
to us that the avalanche is the key thing, and the layer of
sliding sand is both the energy source and the resonator. But
avalanching sand does not have the same properties as
stationary sand: essentially, grains behave as a gas of
individually massive grains bouncing against each other and
thereby inhibiting friction. These agitated properties, on the
large scale, are important in allowing large landslides