  Internal avalanches of grain displacements can be created inside a granular
material kept in a bin in two ways: (i) By removing a radomly selected grain at
the bottom of the bin (ii) By breaking a stable arch of grains clogging a hole
at the bottom of the bin. Repeated generations of such avalanches lead the
system to a steady state. The question asked, is this state a critical state as
that in Self-Organized Criticality? We review here some of the recent studies
on this problem using cellular automata as well as hard disc models.
