The surface termination, structure, and morphology of the LaAlO3{100} surface has been studied as a function of temperature by means of time-of-flight scattering and recoiling spectrometry (TOF-SARS), atomic force microscopy (AFM), low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and x-ray photoelectron spectroscopy (XPS). The results show that the surface is terminated in a Al-O layer from room temperature up to similar to 150 degrees C and a La-O layer at temperatures above similar to 250 degrees C. The surfaces are terminated exclusively in either Al-O or La-O layers, with mixed terminations observed only in the intermediate region of 150-250 degrees C. These surfaces exhibit ordered (1 X 1) LEED patterns and stepped AFM images with step heights of 3.9 +/-0.5 Angstrom and terrace widths of similar to 1000 Angstrom. A mechanism is proposed for this low-temperature surface stoichiometry change which is linked to the observation of the creation of surface oxygen deficiencies upon heating. The oxygen deficient Al-O terminating layer transforms to a La-O terminating layer, creating a near-surface vacancy in the twelve coordinate site of the perovskite structure.