We investigate the effects of shock pressure and pore morphology on the formation and growth of hot spots in HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine). Both non-reactive and reactive ALE3D simulations are used in these studies. Our non-reactive simulations show a viscous-dominated pore collapse mode at lower shock pressures (2-10GPa) with shear band formation and a hydrodynamic-dominated mode at higher shock pressures (20-40GPa) due to bulk melting. When normalized by bulk shock heating, viscous-dominated pore collapse modes are more efficient at generating hot spots. Pore morphology influences the post-collapse temperature distributions and reaction rate for a fixed pore area and shock pressure. We find that multiple surface pores at the binder-grain interface tend to react the fastest. Due to their upstream location in the HMX grain, the surface pores collapse sooner than interior pores; thus, the extent of reaction will generally favor these morphologies because they have more time to grow. In general, multiple smaller hot spots tend to react faster than a single larger hot spot because they accelerate one another's burning. The rank order of morphology effects, however, is not the same for non-reactive and reactive simulations. For example, while multiple surface pores produce the highest reaction rates they do not produce the highest (non-reactive) hot spot temperatures. Our numerical studies provide insights on hot spot mechanisms in lieu of direct measurements and can be used to develop advanced shock initiation models.