Atomic force microscopy (AFM) has been used to examine the morphological evolution of the Bi2MO3O12(010) surface at 400-600 degreesC in dry air and air-2.3% H2O. The (010) cleavage surface is characterized by atomically flat terraces separated by straight steps that are integer multiples of b/2 (5.75 Angstrom) in height. During treatments at or above 500 degreesC, the surface is etched due to the volatilization of Mo. In dry air, etching affects both steps and flat terraces and results in step recession, the development of half-unit-cell (b/2) step loops (pits and islands), and the accumulation of Bi-rich surface deposits. In air-2.3% H2O, steps are etched with preference to terraces, and this leads to step recession as well as the formation of Bi-rich deposits. Mo volatilization proceeds at an enhanced rate in air-2.3% H2O and culminates in the nucleation and growth of Bi2MoO6 and Bi2Mo2O9 precipitates at 500 and 600 degreesC, respectively.