Experimental studies show that the density of a vibrated granular material evolves from a low density initial state into a higher density final steady state. The relaxation towards the final density value follows an inverse logarithmic law. We propose a simple stochastic adsorption-desorption process which captures the essential mechanism underlying this remarkably slow relaxation. As the system approaches its final state, a growing number of beads have to be rearranged to enable a local density increase. In one dimension, this number grows as N = ρ/(1 − ρ), and the density increase rate is drastically reduced by a factor e −N . Consequently, a logarithmically slow approach to the final state is found ρ∞ − ρ(t) ∼ = 1/ ln t.