We propose a thermal-fluid system model for hollow formation. A subsurface heat source (typically impact-related) produces volatiles from LRM and drives them to the surface. Volatiles generated through heating of LRM are likely S and S-bearing gases produced by thermal decomposition of sulfides heated by the impact process. C-bearing volatiles, such as CH4 and other simple organics, and potentially fullerenes within LRM, may also be involved in proposed thermal-fluid systems responsible for hollow formation.