The process of dewetting of a thin film from a solid substrate is important for its scientific and technological relevance, but can be difficult to observe experimentally. We report on an experimental method that may be used to investigate morphological changes, including dewetting, during laser heat treatment of alloys used for phase change memory devices. We have used nanosecond-scale time-resolved imaging to differentiate between competing thin film instabilities in GeTe, a chalcogenide-based phase change material. It is shown that in the absence of nucleated dewetting, thin films of phase change alloys may be unstable, but that nucleated dewetting can lead to a more disrupted final state of the thin film. (C) 2014 Elsevier B.V. All rights reserved.