Jorge Pedro Galve

Investigating gravitational grabens related to lateral spreading and evaporite dissolution subsidence by means of detailed mapping, trenching, and electrical resistivity tomography (Spanish Pyrenees)

The active lateral spread of the Peracalc Range (Spanish Pyrenees) has developed on a Cretaceous limestone sequence around 250 m thick, underlain by tectonically thickened (∼2.5 km) Triassic halite-bearing evaporites and clays. Outward expansion of the Triassic sequence by ductile deformation and probably halokinesis toward the debuttressed and unloaded front of the range has been accommodated in the overlying cap rock through the development of a striking horst and graben morphostructure. Fault scarps show anomalously high height to length ratios (aspect ratio; H max / L ) compared to the values reported for tectonic faults. This retrogressive gravitational deformation has aborted a paleodrainage, expressed as wind gaps, hanging valleys, and defeated streams. The significant vertical displacement component in this rock spread is attributed to subsidence caused by interstratal evaporite dissolution, as supported by the dissolution-induced collapse and graben structures mapped at the foot of the range. To our knowledge, the rock spread of Peracalc, covering around 4.5 km 2 and with a minimum volume of 0.9 km 3 , is the largest documented landslide of the Pyrenees. The excavation of trenches and the acquisition of electrical resistivity tomography profiles provided information on the thickness and subsurface structure of the graben fills, the age of the lateral spread (older than 45 ka), an unexpected episodic kinematic behavior of the gravitational faults, and the timing of deformation events, including slumping of lake deposits.

Assessment of shallow landslide risk mitigation measures based on land use planning through probabilistic modelling

On October 25, 2011, an extreme rainfall event affected a wide area along the coasts of Cinque Terre (eastern Liguria, northern Italy). Particularly, in the Vernazza catchment, the event triggered hundreds of shallow landslides and a debris flood that caused three casualties. Investigation of the slope stability after the event was carried out aiming at defining the most effective mitigation measures which may be adopted in future land use planning. To this objective, a susceptibility model was produced and a series of scenarios were simulated using probabilistic methods. The susceptibility model has provided information about landslide conditioning factors on which to act for reducing landslide occurrence and therefore the associated risk. The simulations have taken into consideration the following alternative types of mitigation measures: (1) restoration of abandoned terraces, (2) reforestation of abandoned terraces, (3) use of local structural measures over stretches of potentially unstable hillsides and (4) avoidance of any intervention. The advantages and the disadvantages of the proposed mitigation measures for shallow landslide risk are discussed considering the results of the simulations and taking into account their complex interaction with environmental, historical, cultural and socio-economic aspects. The results show that the most effective mitigation strategy for reducing landslide risk at short term consists of applying structural measures over potentially unstable slopes. However, a long-term programme promoting the development of agricultural or forestry practices on terraced slopes is necessary. In fact, the simulations indicate that if no measures are applied to avoid the degradation of the terraced areas, landslide areal frequency would inevitably increase.

Recognition and assessment of sinkholes as geosites: lessons from the Island of Gozo (Malta)

Recognition and assessment of sinkholes as geosites: lessons from the Island of Gozo (Malta) There is a wide literature on sinkhole or doline classification, formation and evolution. However, despite the fact that they are often characterised by spectacular morphological features, sinkholes are not normally described as geological resources which might be valuable for the society and worth of being promoted for their geomorphological importance. A series of sinkholes have been investigated in the Island of Gozo (Malta), some of which of notable size and high aesthetic interest. These sinkholes have been assessed applying a methodology which has been specifically set up with the aim of verifying whether any of them could be considered as geosites according to their scientific, additional (ecological, aesthetic, cultural) and use values. The paper shows the geosite assessment procedure and discusses its outputs, according to which 6 out of the 17 investigated sinkholes can be considered as geosites of geomorphological interest (geomorphosites). Finally, issues related to their enhancement and fruition are taken into account in the frame of potential geotourism strategies.

Shallow landslides susceptibility assessment in different environments

ABSTRACT The spatial distribution of shallow landslides is strongly influenced by different climatic conditions and environmental settings. This makes difficult the implementation of an exhaustive monitoring technique for correctly assessing the landslide susceptibility in different environmental contexts. In this work, a unique methodological strategy, based on the statistical implementation of the generalized additive model (GAM), was performed. This method was used to investigate the shallow landslide predisposition of four sites with different geological, geomorphological and land-use characteristics: the Rio Frate and the Versa catchments (Southern Lombardy) and the Vernazza and the Pogliaschina catchments (Eastern Liguria). A good predictive overall accuracy was evaluated computing by the area under the ROC curve (AUROC), with values ranging from 0.76 to 0.82 and estimating the mean accuracy of the model (0.70–0.75). The method showed a high flexibility, which led to a good identification of the most significant predisposing factors for shallow landslide occurrence in the different investigated areas. In particular, detailed susceptibility maps were obtained, allowing to identify the shallow landslide prone areas. This methodology combined with the use of the rainfall thresholds for triggering shallow landslides may provide an innovative tool useful for the improvement of spatial planning and early warning systems.

1:5000 Landslide map of the upper Gállego Valley (central Spanish Pyrenees)

A 1:5000 scale geomorphological landslide inventory map of the glaciated headwaters of the Gállego River in the Spanish Pyrenees is presented. This map, covering an area of 57.6 km2 and mainly produced by direct mapping in the field, provides a more comprehensive and accurate picture of the distribution of slope movements than previous maps. Around 20% of the area is affected by large flow-dominated slope movements developed on Paleozoic slates. Our map shows that some of these post-glacial landslides have blocked the main drainage at several sites creating landslide-dammed lakes. The damage caused by landslides in the mapped area, with an estimated cost of greater 10 million euros, is mostly related to the activity of pre-existing slope movements, some of which have been reactivated or accelerated by adverse human alterations (e.g., excavation at the toe, overloading, higher water infiltration). This study illustrates that the incorporation of detailed cartographic landslide inventories in the planning and development process of alpine areas may contribute to reduce significant landslide-related damage in a cost-effective manner.

New insights into the genesis of the Miocene collapse structures of the island of Gozo (Malta, central Mediterranean Sea)

The large palaeosinkholes located in the NW of Gozo (central Mediterranean Sea, Malta) offer excellent exposures that provide information on the geometry and kinematics of large karst-related collapse structures. Detailed geological analysis of these peculiar palaeosinkholes indicates that deep-seated evaporite dissolution is the most feasible hypothesis to explain their formation, according to the following evidence. (1) Several structures have been formed by progressive foundering of cylindrical blocks with limited internal deformation as revealed by the synsedimentary subsidence recorded by their Miocene sedimentary fill. This subsidence mechanism is more compatible with interstratal dissolution of evaporites than karstification and cave development in limestone formations. (2) The dimensions and deformation style of the palaeosinkholes are similar to those of other collapse structures related to deep-seated dissolution of salt-bearing evaporites. (3) The arcuate monocline associated with some of these collapse structures is also a characteristic feature of subsidence related to dissolution of evaporites. However, no major evaporite formations have been documented so far in the subsurface of the Malta Platform. Supplementary material: Detailed descriptions of the collapse structures of the island of Gozo (Malta, central Mediterranean Sea) are available at www.geolsoc.org.uk/SUP18808.

Research paperSwathProfiler and NProfiler: Two new ArcGIS Add-ins for the automatic extraction of swath and normalized river profiles

The present-day great availability of high-resolution Digital Elevation Models has improved tectonic geomorphology analyses in their methodological aspects and geological meaning. Analyses based on topographic profiles are valuable to explore the short and long-term landscape response to tectonic activity and climate changes. Swath and river longitudinal profiles are two of the most used analysis to explore the long and short-term landscape responses. Most of these morphometric analyses are conducted in GIS software, which have become standard tools for analyzing drainage network metrics. In this work we present two ArcGIS Add-Ins to automatically delineate swath and normalized river profiles. Both tools are programmed in Visual Basic . NET and use ArcObjects library-architecture to access directly to vector and raster data. The SwathProfiler Add-In allows analyzing the topography within a swath or band by representing maximum-minimum-mean elevations, first and third quartile, local relief and hypsometry. We have defined a new transverse hypsometric integral index (THi) that analyzes hypsometry along the swath and offer valuable information in these kind of graphics. The NProfiler Add-In allows representing longitudinal normalized river profiles and their related morphometric indexes as normalized concavity (CT), maximum concavity (Cmax) and length of maximum concavity (Lmax). Both tools facilitate the spatial analysis of topography and drainage networks directly in a GIS environment as ArcMap and provide graphical outputs. To illustrate how these tools work, we analyzed two study areas, the Sierra Alhamilla mountain range (Betic Cordillera, SE Spain) and the Eastern margin of the Dead Sea (Jordan). The first study area has been recently studied from a morphotectonic perspective and these new tools can show an added value to the previous studies. The second study area has not been analyzed by quantitative tectonic geomorphology and the results suggest a landscape in transient state due to a continuous base-level fall produced by the formation of the Dead Sea basin.

SwathProfiler and NProfiler

The present-day great availability of high-resolution Digital Elevation Models has improved tectonic geomorphology analyses in their methodological aspects and geological meaning. Analyses based on topographic profiles are valuable to explore the short and long-term landscape response to tectonic activity and climate changes. Swath and river longitudinal profiles are two of the most used analysis to explore the long and short-term landscape responses. Most of these morphometric analyses are conducted in GIS software, which have become standard tools for analyzing drainage network metrics. In this work we present two ArcGIS Add-Ins to automatically delineate swath and normalized river profiles. Both tools are programmed in Visual Basic . NET and use ArcObjects library-architecture to access directly to vector and raster data. The SwathProfiler Add-In allows analyzing the topography within a swath or band by representing maximum-minimum-mean elevations, first and third quartile, local relief and hypsometry. We have defined a new transverse hypsometric integral index (THi) that analyzes hypsometry along the swath and offer valuable information in these kind of graphics. The NProfiler Add-In allows representing longitudinal normalized river profiles and their related morphometric indexes as normalized concavity (CT), maximum concavity (Cmax) and length of maximum concavity (Lmax). Both tools facilitate the spatial analysis of topography and drainage networks directly in a GIS environment as ArcMap and provide graphical outputs. To illustrate how these tools work, we analyzed two study areas, the Sierra Alhamilla mountain range (Betic Cordillera, SE Spain) and the Eastern margin of the Dead Sea (Jordan). The first study area has been recently studied from a morphotectonic perspective and these new tools can show an added value to the previous studies. The second study area has not been analyzed by quantitative tectonic geomorphology and the results suggest a landscape in transient state due to a continuous base-level fall produced by the formation of the Dead Sea basin.

Stream Length-Gradient Index Mapping as a Tool for Landslides Identification

The Stream Length-Gradient (SL) index is used to detect knickpoints potentially related to surface and sub-surface deformation processes. In this work, the SL index has been calculated along streams draining the southern sector of the Emilia-Romagna Region within the Northern Apennines (Italy), to detect knickpoints associated with active landslides. The methodology allowed the rapid analysis of an area of ca. 2300 km\(^{2}\). Approximately thirty hillslopes potentially affected by landslides were identified studying the SL index outlier values. Field survey confirmed the presence of large deep-seated landslides associated with 90 % of the observed anomalies. This study illustrates that stream profiles metrics may have a high potential in different geological studies covering wide areas in a short time and investing limited resources.

Evaluation of the SBAS InSAR Service of the European Space Agency’s Geohazard Exploitation Platform (GEP)

The analysis of remote sensing data to assess geohazards is being improved by web-based platforms and collaborative projects, such as the Geohazard Exploitation Platform (GEP) of the European Space Agency (ESA). This paper presents the evaluation of a surface velocity map that is generated by this platform. The map was produced through an unsupervised Multi-temporal InSAR (MTI) analysis applying the Parallel-SBAS (P-SBAS) algorithm to 25 ENVISAT satellite images from the South of Spain that were acquired between 2003 and 2008. This analysis was carried out using a service implemented in the GEP called “SBAS InSAR”. Thanks to the map that was generated by the SBAS InSAR service, we identified processes not documented so far; provided new monitoring data in places affected by known ground instabilities; defined the area affected by these instabilities; and, studied a case where GEP could have been able to help in the forecast of a slope movement reactivation. This amply demonstrates the reliability and usefulness of the GEP, and shows how web-based platforms may enhance the capacity to identify, monitor, and assess hazards that are associated to geological processes.