Jorge Yepes

Güímar and La Orotava Mega-Landslides (Tenerife) and Tsunamis Deposits in Canary Islands

More than 20 mega-landslides have been described in the Canary Islands affecting the flanks of the volcanic edifices. Guimar and La Orotava landslides, in Tenerife, are two exceptional cases due to their huge dimensions and outstanding geomorphological features. The estimated volume of these landslides exceed tens of cubic km. Tsunami deposits have been also identified in some of the islands of the archipelago probably associated to the large landslides of the islands flanks.

Ultrasound data for laboratory calibration of an analytical model to calculate crack depth on asphalt pavements

This article outlines the ultrasound data employed to calibrate in the laboratory an analytical model that permits the calculation of the depth of partial-depth surface-initiated cracks on bituminous pavements using this non-destructive technique. This initial calibration is required so that the model provides sufficient precision during practical application. The ultrasonic pulse transit times were measured on beam samples of different asphalt mixtures (semi-dense asphalt concrete AC-S; asphalt concrete for very thin layers BBTM; and porous asphalt PA). The cracks on the laboratory samples were simulated by means of notches of variable depths. With the data of ultrasound transmission time ratios, curve-fittings were carried out on the analytical model, thus determining the regression parameters and their statistical dispersion. The calibrated models obtained from laboratory datasets were subsequently applied to auscultate the evolution of the crack depth after microwaves exposure in the research article entitled “Top-down cracking self-healing of asphalt pavements with steel filler from industrial waste applying microwaves” (Franesqui et al., 2017) [1].

Evolution of Pajonales Landslide (Tirajana Depression, Gran Canaria): A Case of Advancing Landslide

We studied the evolution of different stages of Pajonales landslide (Tirajana Depression, Gran Canaria), based on the geotechnical investigations of both in situ and mobilized volcanic materials. The deposit extends over 560 ha and it has undergone successive reactivations, some during the 20th century. The landslide comprises four large bodies that have successively broken away from a single initial rock mass. The main scarp affects the lava flows with intercalations of pyroclastic materials of the Roque Nublo Group and later volcanic activity (5.5 Ma to present-day). The basal surface of the landslide developed in old rocks of the Mogan Group (14.0–13.3 Ma), which are rhyolitic and trachytic ignimbrites with hydrothermal alteration related to the infilling of the Tejeda caldera. This alteration caused silty-clay layers presenting a low friction angle, high plasticity and expansive behavior. Representative samples of pyroclasts and soils from landslides were collected and laboratory tests were performed to identify them, determine unit weight, grain-size, plasticity, and shear strength. The morphology of slope prior to sliding was reconstructed considering the location of the failure surfaces and scarps of first and second generation. Failure surfaces for each stage of sliding were identified using software of limit equilibrium analysis. These surfaces have been developed through clayey-silt levels that result from the alteration of pyroclastic materials, showing the most unfavorable geotechnical parameters (minimal or residual values). Moreover, the presence of water is a triggering factor, since total or partial saturation of the materials is required. Finally, the landslide is an advancing type: as successive reactivations occur, the sliding masses are broken down into smaller ones moving towards the Tirajana ravine.

Onshore Record of Ancient Landslides in Taganana (Tenerife, Canary Islands)

This study presents a geomorphologic review of the northern sector of Anaga Massif in order to establish a relative sequence of geomorphic processes. The present-day relief shows a polygenic nature, combining fluvial erosion with other prior erosive processes. The analysis of slopes and watersheds suggests the existence of an active instability process during the Quaternary. However, the anomalies of the drainage system are related with the differential strength which shows basic dykes against erosion. Some geomorphologic features suggest the occurrence of an old great landslide affecting the slopes of Taganana village. This instability will be a stage of the retreatment of the slopes which occurs in a volcanic island along time, in both emerged and submerged flanks.

Analysis of Rockfall Stop-Distance Factors with CRSP-3D in Volcanic Talus

Open image in new window The costs associated with rockfall risk are high. Many resources are invested in rock slope maintenance and stabilization, and protection measures to reduce rockfall hazards on transport infrastructures. However, few studies aim to evaluate the relative influence of the different factors (geometrical and material properties) affecting falling rock trajectories and the efficiency (retention capacity) of catchment areas. Numerous factors influence both the characteristics of rockfall motion, and their impact and stop-distance. Ritchie’s empirical research (1963) was the first to identify these characteristics and determine the expected impact distance of rockfalls depending on slope geometry. Later studies showed that Ritchie’s results were not as conservative as previously thought, and also that it was hard to apply his ditches on roadways due to their excessive depth (dangerous for vehicles) and width (expensive construction and maintenance). The Ritchie ditch has therefore been improved by computer simulation programs, and the proposed use of concrete walls or fences at the edge of the road. Optimization of the catchment area geometry requires systematic and quantitative analysis of the effect of each factor on rock stop-distance through application of a simulation model. With this aim, this study applies a CRSP 3D computer simulation model (Colorado DoT, USA) considering 75 different configurations of slope-ditch geometries, 4 types of materials and 9 size and shape combinations of falling rocks. In all we examined 270 different cases for hard rock and 180 for soft rock. A statistical analysis was performed with the simulated rock stop-distances to assess the different variables affecting rockfall motion.

Rockfall Hazard Mitigation Using Ditch Charts Modeled with CRSP-3D

Open image in new window Rockfalls on roadways are a serious hazard to users. Many resources are invested in rock slope maintenance and measures of stabilization and protection to mitigate the risk. Catchment areas (ditches) are one of the least expensive and most effective protective measures to contain and restrict rockfall onto roadways. While their effectiveness depends directly on their design criteria, previous studies have mainly been limited and based on empirical studies. Ritchie (Evaluation of rockfall and its control., pp. 13–28, 1963) drew up the first design charts and tables, establishing the impact distance of a rockfall as a function of the slope height and steepness. Though his work is still accepted, it has some significant limitations: his design relies on such a deep, steeply sloped ditch that it reduces road safety, restricts the slope geometry and complicates the maintenance of these catchment areas. Pierson et al. (Rockfall Catchment area design guide. Final Report SPR-3(032), 2001) created new graphic charts based on real rockfall tests carried out on different slope-ditch arrangements, but their research presents certain drawbacks: the examined situations are limited to a specific type of material, shape and possible rock size, the dimensions proposed to obtain certain percentages of rockfall retention are very large and, in most cases, the costs are unreasonably high. This present research complements previous studies by using a CRSP 3D computer simulation model (Colorado DoT, USA) and analyzing a wider number of slope-ditch arrangements and input parameters: (A) 5 talus heights, 5 slope gradients and V-ditches with 3 foreslopes. The highest slopes (≥18 m) have an intermediate 1 m bench at 12 m height. (B) Different kinds of materials are handled: 4 bedrock lithologies, two of them for the slope (hard rock and soft rock), one for the ditch (concrete) and the other for the road pavement (asphalt). The properties of these materials (density, elasticity, roughness) have been established according to the CRSP 3D methodology and adapted to previous empirical knowledge of each material

Stability Analysis of Potential Rock Slides in El Rincón Cliff (GC-2 Highway, Gran Canaria, Spain)

In this work we have found landslides that may be developed in El Rincon cliff (Gran Canaria) and its impact on the GC-2 highway, at the base of the cliff. The stability analysis performed for the current conditions indicates that the slope is stable. The long-term analysis considers the water-saturated rock mass and defines the presence of two rocky blocks that are most likely to experience sliding, one along the mid-slope and another in the head. The mid-slope landslide would be favored by failure through the Formacion Detritica de Las Palmas, while the landslide located on the head of slope would have a more superficial character and would be favored by the failure through the pyroclasts of the Post-Roque Nublo Group. The landslide of the block of the top seems more likely since it only requires the saturation of the pyroclasts and is favored by the reduction of strength related to the progressive opening of the sub-vertical cracks.