The results of the experimental study of the dynamics of a shallow fluidize
d bed are reported. The behavior of granular material is controlled by the
interplay of two factors-levitation due to the upward airflow, and sliding
back due to gravity. Near the threshold of instability, the system shows cr
itical behavior with remarkably long transient dynamics. The experimental o
bservations are compared with a simple cellular automata model. [S1063-651X
(99)03812-X].