Review article: Retrogressive thaw slump theory and terminology

Abstract. Retrogressive thaw slumps (RTSs in plural and RTS in singular) are spectacular landforms that occur due to the thawing of ice-rich permafrost or melting of massive ground ice often in hillslope terrain. RTSs occur in the Arctic, Subarctic as well as high mountain (Tibetan Plateau) permafrost regions and are observed to expand in size and number due to climate warming. As the observation of RTS is receiving more and more attention due to their important role in permafrost thaw, impacts on topography, mobilization of sediment, carbon, nutrients, and contaminants, and their effects on downstream hydrology and water quality, the thematic breadth of studies increases and scientists from different scientific backgrounds and perspectives contribute to new RTS research. At this point, a wide range of terminologies originating from different scientific schools is being used and we identified the need to provide an overview of theoretical approaches, terms, and variable characteristics of RTS to clarify terminologies and create common ground for understanding RTS processes, dynamics, and feedbacks. We here review the theoretical geomorphological background of RTS formation and landform characteristics to provide an up-to-date understanding of the current views on terminology and underlying processes. The presented overview can be used not only by the international permafrost community but also by scientists working on ecological, hydrological, and biogeochemical consequences of RTS occurrence as well as remote sensing specialists developing automated methods for mapping RTS dynamics. The framework will foster a better understanding of the nature and diversity of RTS phenomena and provide a useful base for experts in the field but also ease the introduction to the topic of RTSs for scientists who are new to it.