Spall, the result of tensional failure of material, has been observed in compressive, explosive surface tests. The configuration of these tests requires the spall mechanism to be different from the classical theory of tensional reflection of a compressive wave from a free surface. The data show that following the initial compression and partial rebound, acceleation wave forms have -1 g dwells followed by an impulsive rejoin which has been identified as spall. The spall appears to be caused by shear waves initiating from the finite edges of the explosive falls array, upward until the soil fails and fails with a -1 g acceleration. This is a new mechanism for the generation of spall due to explosions and is completely different from the classical theory. The new mechanism applies to the case of surface sources.