  We present a directed unloading sand box type avalanche model, driven by
slowly lowering the retaining wall at the bottom of the slope. The avalanche
propagation in the two dimensional surface is related to the space-time
configurations of one dimensional Kardar-Parisi-Zhang (KPZ) type interface
growth dynamics. We express the scaling exponents for the avalanche cluster
distributions into that framework. The numerical results agree closely with KPZ
scaling, but not perfectly.
