Analysis of the Geological Controls and Kinematics of the Chgega Landslide (Mateur, Tunisia) Exploiting Photogrammetry and InSAR Technologies

Exploration of territories not previously analyzed by landslide experts provides interesting findings. The Chgega landslide, in northern Tunisia, represents a paradigmatic mass movement. It can be classified as a complex landslide, or more specifically as vast rock spreading that evolved into a block slide. It involves a great block of limestone—about 900 m long and 400 m wide—sliding over ductile clays and marls. The viscoplastic creep of the clays drives the landslide and creates, in its crown, a graben ~800 m long and ~120 m wide that breaks the summit of Chgega Mountain. Using Interferometric Synthetic Aperture Radar (InSAR) technologies, we demonstrate that this complex landslide is currently active and moreover shows progressive movement without clear episodic accelerations. The velocity of the limestone block is just above 2 mm/yr. The occurrence of gravity-induced joints indicates that the movement has an orientation towards 333° of azimuth on average, conditioned by the landscape around Chgega. These results were obtained through the analysis of a 3D model and a high-resolution orthoimage created from photographs acquired by an Uncrewed Aerial Vehicle (UAV). We may conclude that the landslide movement is determined by normal faults with directions N060°E and N140–150°E. This characterization of the Chgega landslide can serve as the basis for future studies about the origin of this slope movement. Furthermore, the data provided here may support the recognition of Chgega as a singular geological point that deserves to be declared a geosite.

Practical Estimation of Landslide Kinematics Using PSI Data

Kinematics is a key component of a landslide hazard because landslides moving at similar rates can affect structures or collapse differently depending on their mechanisms. While a complete definition of landslide kinematics requires integrating surface and subsurface site investigation data, its practical estimate is usually based on 2D profiles of surface slope displacements. These can be now measured accurately using Persistent Scatterer InSAR (PSI), which exploits open access satellite imagery. Although 2D profiles of kinematic quantities are easy to retrieve, the efficacy of possible descriptors and extraction strategies has not been systematically compared, especially for complex landslides. Large, slow rock slope deformations, characterized by low displacement rates (<50 mm/year) and spatial and temporal heterogeneities, are an excellent testing ground to explore the best approaches to exploit PSI data from Sentinel-1 for kinematic characterization. For three case studies, we extract profiles of different kinematic quantities using different strategies and evaluate them against field data and simplified numerical modelling. We suggest that C-band PSI data allow for an effective appraisal of complex landslide kinematics, provided that the interpretation is (a) based on decomposed velocity vector descriptors, (b) extracted along critical profiles using interpolation techniques respectful of landslide heterogeneity, and (c) constrained by suitable model-based templates and field data.

The need for protecting, promoting, and managing a Quaternary geoheritage site: Bahluiet Valley at Costești village (Moldavian Plateau, North-Eastern Romania

The Bahluieț Valley at Costești village geosite has been recently studied and proposed as a geoheritage site. Previously this area was investigated due to the presence of the Costești-Cier archaeological site, which is currently integrated into the National Archaeological Repertoire. In this archaeological site, different levels of populations have been studied (Eneolithic Cucuteni A, Cucuteni AB, and Horodiștea-Erbiceni Culture populations) as well as an earth wall from La Tene (8th‒10th/11th century BC), and a 15th‒17th century AD necropolis. In the area of the present-day Costești village, Bahluieț River leaves the Suceava Plateau area (with altitudes of 350‒550 m a.s.l.) and enters the Jijia Hills (with altitudes of 50 to 200 m a.s.l.), flowing between Ulmiș Hill (306 m a.s.l., at north) and Ruginii Hill (326 m a.s.l., at the south). The valley, which is incised more than 100 m below the plateau level, suddenly becomes broader because of massive Late Pleistocene landslides that covered the former Bahluieț river floodplain and are now fossilized by fluvial deposits. During the Holocene, the river incision detached paleochannels and fluvial terraces while the landslides reactivated through retrogressive mechanisms, creating a complex landslide. A cut-off meander island hosts the Costești-Cier archaeological site, being currently actively eroded by the river. In the riverbank of this island, a multi-layered stratigraphy can be seen, consisting of landslide and fluvial deposits, paleosoils, and archaeological remains. The layered deposits, the complex landslide, and the fluvial processes have the potential to become one of the most representative Quaternary sites of the Moldavian Plateau and Romania. By using geomorphosite assessment, geomorphological mapping optically stimulated luminescence dating, and geoconservation ideas, I show (i) the importance of the geosite due to the presence of the oldest dated fossil landslide from Romania and the landslide-fluvial-archaeological relations, (ii) the needs for protection at local, regional and national level considering the active processes that affect the site, and propose (iii) management and (iv) promotion of the geoheritage site using a geoconservation strategy.

Pre-Event Deformation and Failure Mechanism Analysis of the Pusa Landslide, China with Multi-Sensor SAR Imagery

The Pusa landslide, in Guizhou, China, occurred on 28 August 2017, caused 26 deaths with 9 missing. However, few studies about the pre-event surface deformation are provided because of the complex landslide formation and failure mechanism. To retrieve the precursory signal of this landslide, we recovered pre-event deformation with multi-sensor synthetic aperture radar (SAR) imagery. First, we delineated the boundary and source area of the Pusa landslide based on the coherence and SAR intensity maps. Second, we detected the line-of-sight (LOS) deformation rate and time series before the Pusa landslide with ALOS/PALSAR-2 and Sentinel-1A/B SAR imagery data, where we found that the onset of the deformation is four months before landslide event. Finally, we conceptualized the failure mechanism of the Pusa landslide as the joint effects of rainfall and mining activity. This research provides new insights into the failure mechanism and early warning of rock avalanches.