The research presented in this thesis concerns the granular collapse problem, where a mass of a granular material is allowed to collapse under its own weight and spread out across a base surface. Whilst this collapse process has been studied in the past, there are a number of potentially important aspects of this problem that have not been fully considered. We start this thesis by repeating previous experiments with the simplest case of a cylindrical mass of a monodisperse material of approximately spherical grains flowing over a horizontal base. By applying new measurement techniques we find differences with previously reported results. We then extend the problem to the bidisperse case by using layers of two types of particles that differ only in their size. We find that, contrary to expectation, there is little segregation of the two species during the collapse. We then return to the monodisperse problem and consider the effects of increasing the initial column aspect ratio beyond the values previously considered. We first use an asymptotic analysis of the possible shapes of the final deposit to find restrictions on the large aspect ratio behaviour of the deposit's maximum height and radius. Finally, we perform monodisperse collapses of a range of materials with aspect ratios of up to 80. We find that the dynamics of the flow and the shape of the final deposit are significantly different in this regime.