Abstract An updated and complete landslide inventory is the starting point for an appropriate hazard assessment. This paper presents an improvement for landslide mapping by integrating data from two well-consolidated techniques: Differential Synthetic Aperture Radar (DInSAR) and Landscape Analysis through the normalised channel steepness index ( k sn ). The southwestern sector of the Sierra Nevada mountain range (Southern Spain) was selected as the case study. We first propose the double normalised steepness ( k snn ) index, derived from the k sn index, to remove the active tectonics signal. The obtained k snn anomalies (or knickzones) along rivers and the unstable ground areas from the DInSAR analysis rapidly highlighted the slopes of interest. Thus, we provided a new inventory of 28 landslides that implies an increase in the area affected by landslides compared with the previous mapping: 33.5% in the present study vs. 14.5% in the Spanish Land Movements Database. The two main typologies of identified landslides are Deep-Seated Gravitational Slope Deformations (DGSDs) and rockslides, with the prevalence of large DGSDs in Sierra Nevada being first revealed in this work. We also demonstrate that the combination of DInSAR and Landscape Analysis could overcome the limitations of each method for landslide detection. They also supported us in dealing with difficulties in recognising this type of landslides due to their poorly defined boundaries, a homogeneous lithology and the imprint of glacial and periglacial processes. Finally, a preliminary hazard perspective of these landslides was outlined. 

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Improving landslide inventories by combining satellite interferometry and landscape analysis: the case of Sierra Nevada (Southern Spain)

Structural control on drainage patterns has long been suggested to play an important role in the development of fluvial systems, including their map pattern. Along the western Taiwan orogenic wedge, a prominent drainage pattern change is present, from predominantly orogen parallel drainages in the south to river systems that flow perpendicular to the long axis of the mountain belt in the north. Such change likely reflects the temporal evolutionary process as the Taiwan orogen propagates southward. We propose that the flow direction change of river systems is produced by the development of the fold‐and‐thrust belt on the pro‐wedge side of the mountain belt and is facilitated by drainage reorganization that includes abrupt drainage captures and more gradual divide movements, permitting drainage basins to attain a geometrically stable configuration with time. Our observations in Taiwan demonstrate not only how tectonic uplift is effective at modifying river patterns in the early stages of orogenic development but also how time and increased stream power encourage river networks to adjust to more effective patterns in mature mountain belts.

Structural control on drainage pattern development of the western Taiwan orogenic wedge

Geomorphic indices (e.g., the normalized channel steepness index (Ksn) and the stream length-gradient index (SL)) highlight changes in fluvial shapes and gradients. However, the application of these indices was seldom used to identify potential landslide zones. In this study, we used the Ksn and SL indices to detect the significant variations in the stream power along river reaches, which are anomalies associated with landslides, in the Zengqu River watershed, the upper reaches of the Jinsha River. Most of the landslide anomalies originate along the trunk and surrounding tributaries below the knickpoint of the mainstream. This suggests an erosional wave is migrating upstream throughout the drainage area. The fluvial incision may generate over-steepened hillslopes, which could fail in the future. In addition, the divide asymmetry index (DAI) predicts the direction of the divide as the headwaters migrate toward lower relief, higher elevation surfaces. Landslides are expected to occur as the unstable divide migrates. The proposed methodology can benefit the detection and characterization of potential landslide zones. It should improve hazard and risk analysis and the identification of drainage network areas associated with landslides.

Xin Yao

Papers

Applicability of Geomorphic Index for the Potential Slope Instability in the Three River Region, Eastern Tibetan Plateau.