Temporal behavior of deep-seated gravitational slope deformations: A review

Deep-seated gravitational slope deformations (DSGSDs) are slow moving, hillslope-scale mass movements featuring characteristic landforms such as double-crested ridges and upslope-facing scarps that occur in diverse landscapes throughout the world. Although these deformations have been studied since the 1960s, significant insights to the rates of DSGSDs have only been gained within the last two decades owing to progress in geochronology, remote sensing and instrumental monitoring. Absolute age and monitoring data indicate that DSGSD movements are observable over long-term (>= 10(2) years) and short-term (<10(2) years) intervals. Apart from creep, an episodic deformation also plays a crucial role, especially in regions with earthquakes and heavy rainfall. Our review also supports the notion of DSGSDs as precursors of catastrophic rock slope failures, given that many of the world's largest rock avalanches have occurred in areas with diagnostic DSGSD features, indicating that sudden collapse was preceded by a prolonged stage of slope sagging. Detailed studies on DSGSDs have therefore the potential for better prediction of catastrophic rock slides and rock avalanches. Future research directions include constraining the lifespan of DSGSDs with absolute age dating and precise high resolution monitoring of spatio-temporal displacement across DSGSD bodies. It is of great importance to include absolute time scales in the numerical models of DSGSDs. Furthermore, combining remote sensing techniques such as Synthetic Aperture Radar Interferometry with high-resolution LiDAR scanning and near-surface geophysics offers a promising toolkit for collecting very detailed and accurate data on the short-term deformation rates of DSGSDs. (C) 2016 Elsevier B.V. All rights reserved.