Pictures and Movies... 

Phys. Rev. Letters . Ripples in Tapped and Blown Powders . 84, 5126, (2000) J. Duran
 

Controlled pressure experiments to test the gas influence on the pattern forming :
No gas : No pattern !

  Cylindric part balloon center

 Pushing gas through a dry fine powder cake deposited on a micropore filter
 Bird-eye view (overall pattern size ~5cm)
 

A myriad of small erupting volcanoes
 
Instantaneous snapshot of erupting volcanoes spewing out powder particles

 
20microns dry powder, blown from below
with a gentle continuous dry nitrogen flux

Tapping at two different points under a metallic box, half filled with dry silica powder
 

A surprisingly realistic mountain-like landscape showing relief branching, bifurcations and river-like tributaries...
Just using air and powder, WITHOUT a single drop of LIQUID !
A careful scrutiny allows to see that a few particles are ejected from the numerous apices of the pattern which mimics the box instantaneous deformation at each tap.

Analogy with wetting instabilities : ( Phys Rev Letters, 87, 254301, (2001)) Rayleigh-Taylor Instabilities in Thin Films of Tapped Powder. J. Duran

Syrup on a wire and powder dropplets behave similarly.

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Upper part : 1 and 2 : The big bubble sucks the small one.
Lower part : 1, 2 and 3 : The larger powder heap sucks the small one.

A few movies ...
(click on the first image to start the movies)
Ripples forming
Using nitrogen pulses from below
Dropplets forming
Tapping from below aplate covered with a thin slice of powder
Birdeye view of micro volcanoes
Steady gas flow from under a thin powder cake
Lateral view of micro volcanoes
Steady gas flow from under a thin powder cake
A handmade cartoon
Showing the basic mechanism of gas pattern forming : The heap sucks particles from around itself as it spews out the same amount of particles.

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