Were merely storm-landslides driven by the 2015-2016 Niño in the Mendoza River valley?

Since Holocene time, above-mean precipitations recorded during the El Niño warm ENSO phase have been linked to the occurrence of severe debris flows in the arid Central Andes. The 2015–2016 El Niño, for its unusual strength, began driving huge and dangerous landslides in the Central Andes (32°) in the recent South Hemisphere summer. The resulting damages negatively impacted the regional economy. Despite this, causes of these dangerous events were ambiguously reported. For this reason, a multidisciplinary study was carried out in the Mendoza River valley. Firstly, a geomorphological analysis of affected basins was conducted, estimating morphometric parameters of recorded events such as velocity, stream flow, and volume. Atmospheric conditions during such events were analyzed, considering precipitations, snow cover, temperature range, and the elevation of the zero isotherm. Based on our findings, the role of El Niño on the slope instability in the Central Andes is more complex in the climate change scenario. Even though some events were effectively triggered by intense summer rainstorm following expectations, the most dangerous events were caused by the progressive uplifting of the zero isotherm in smaller basins where headwaters are occupied by debris rock glaciers. Our research findings give light to the dynamic coupled system ENSO–climate change–landslides (ECCL) at least in this particular case study of the Mendoza River valley. Landslide activity in this Andean region is driven by wetter conditions linked to the ENSO warm phase, but also to progressive warming since the twentieth century in the region. This fact emphasizes the future impact of the natural hazards on Andean mountain communities.     

The Rio Narcea gold belt intrusions: geology, petrology, geochemistry and timing

This paper discusses the petrographical, mineralogical and geochemical characteristics of the intrusive rocks located along the Rio Narcea Gold Belt, and the timing of formation of the El Valle-Boinás deposit. Rocks in the belt range from quartz-monzodiorites through quartz-monzogranites to monzogranites. The former are made up of pyroxene (clino and ortho), amphibole (magnesiohornblende), biotite, zoned plagioclase (An35-70), and to a lesser degree quartz and K-feldspar. The monzogranites consist of biotite, zoned plagioclase (An30-60), quartz and K-feldspar. All igneous rocks are characterized by the presence of ilmenite and the lack or scarce presence of magnetite indicating their formation under reducing conditions. The granitoids are calc-alkaline I type, potassium-rich and highly reducent with more ferrous than ferric iron. Their characteristics are like the plutons associated with gold and copper (zinc) skarns, but their characteristics reflect more reducent formation conditions, increasing their capacity to form gold skarns.The Boinas granitoid emplacement occurred at about 303±6 Ma and generated calcic and magnesic skarns at the contact with limestone and dolostones of the Láncara Formation. Skarns and granitoids were first altered to amphibole and sericite, respectively, and mineralized at 302±9 Ma. The intrusion of subvolcanic porphyritic dikes produced a second period of alteration at 285±4 Ma, characterized by carbonatization and sericitization of the monzogranites and chloritization and serpentinization of the skarns. The later intrusion of diabasic dikes at 255±6 Ma produced limited carbonatization, silicification and sericitization and hypogene oxidation of the previous stages. Supergene oxidation then occurred at the top of the ore and along fractures and breccias.     

Landslide incidence zonation in the Rio Mendoza valley,Mendoza Province,Argentina

This paper presents a landslide incidence zonation map showing the percentage of underlying material involved in mass‐movement processes in the Rio Mendoza valley, Argentina. The landslide incidence zonation map was derived from an inventory map of landslides and reveals that many areas of the Rio Mendoza valley are implicated in this kind of process. A correlation has been found between the occurrence of landslides, earthquakes, and rainfall. The relation between lithology and landslides is clear: areas covered by friable sedimentary and volcanic rocks of the Choiyoi Group are prone to debris ?ows and complex landslides. The slope map has been ranked and a general relation between slope and type of event is shown. Falls commonly develop in high‐angle slopes. Copyright © 2004 John Wiley & Sons, Ltd.     

The role of snow melting upon landslides in the central Argentinean Andes

This paper focuses on the historical range of variability of landslide activity and its relation to climate in the Aconcagua Park, Argentina. Landslide frequency data are obtained through historic compilation, including the review of more than 85 data sources and personal interviews with members of the local community. Based on these records, the study analyzes major landslide triggering mechanisms and evaluates the role of climate. Slope instability in Aconcagua Park appears to be mainly forced by the melting of snow accumulated during the winter season, which in turn promotes soil saturation and landslide occurrence the following spring–summer (December–February). This finding is supported by a strong correlation between landslides and stream flows of Andean rivers. These peaks occur during warmer seasons, fed by snow and ice‐glacier melting. In contrast, the correlation between landslide frequency and precipitation (diary/accumulative/monthly/annual) is less certain; and the relationship of landslide to temperature records (mean annual temperature/mean temperature during November–February period) is weak. Copyright © 2012 John Wiley & Sons, Ltd.     

Summer rainstorm associated with a debris flow in the Amarilla gully affecting the international Agua Negra Pass (30°20′S), Argentina

The Central-West region of Argentina was seriously affected by a series of convective summer storms on January–February of 2013 generating many debris flows and rockfall in the Central Andes mountain regions. In particular, the unreported 8th February event caused the sad death of a 10-year-old child being completely ignored by society and local authorities. Despite this, meteorological conditions associated with this event and further episodes were rarely measured and determined mainly due to scarce meteorological stations in Andean mountain areas. In this paper, meteorological data from CMORPH algorithm and measurements of surrounding gauges were analyzed for estimating the triggering precipitation value of this event. As well, the particular debris flow channeled into the main branch of the Amarilla gully in the Agua Negra valley was geomorphologically described. The amount of precipitation associated with this debris flow was 5.5 and 13.2 mm accumulated previous to the event. This violent debris flow was generated in a talus zone in a periglacial environment located just below a covered rock glacier. However, the influence of the permafrost thawing in this process is not feasible. The altitude of the 0 °C isotherm was lower during the previous days of the event, and no monitoring on permafrost is available for this area. The volume of removed mass was estimated in 5 × 10⁴ m³, and the mean velocity was 35 km/h. Boulders of 4 m diameter were found in the source area, while the deposit is up to 75% sandy with clasts that hardly exceed 10 cm in the alluvial fan distal part. Herein the main objective is to advice about the probable catastrophic impact of similar events in the future. These findings could be useful for hazard remediation, mitigation, and prevention plans for the Agua Negra international pass under construction.     

Simulation of debris flows in the Central Andes based on Open Source GIS: possibilities,limitations, and parameter sensitivity

A GIS-based model framework, designed as a raster module for the Open Source software GRASS, was developed for simulating the mobilization and motion of debris flows triggered by rainfall. Designed for study areas up to few square kilometres, the tool combines deterministic and empirical model components for infiltration and surface runoff, detachment and sediment transport, slope stability, debris flow mobilization, and travel distance and deposition. The model framework was applied to selected study areas along the international road from Mendoza (Argentina) to Central Chile. The input parameters were investigated at the local scale. The model was run for a number of rainfall scenarios and evaluated using field observations and historical archives in combination with meteorological data. The sensitivity of the model to a set of key parameters was tested. The major scope of the paper is to highlight the capabilities of the model—and of this type of models in general—as well as its limitations and possible solutions.     

Climatic effect of ENSO associated with landslide occurrence in the Central Andes, Mendoza Province, Argentina

Temporal distribution of landslides can be verified by means of climatic anomalies linked to the ENSO phenomenon. An increasing number of landslides triggered by rainfall have been recorded during warm episodes (El Niño) in the Cordillera Frontal, and a decreasing number during cold episodes (La Niña), concluding that this geological province is mainly influenced by the Pacific Anticyclone. However, slope instability in the Precordillera, located east of the Cordillera Frontal, seems to be mainly influenced by the Atlantic Anticyclone. Analysis of variance shows that there is no significant difference between landslide records and cold-warm episodes, and a higher number of landslides were recorded in years linked to wet periods than during dry periods. Furthermore, the precipitation threshold value associated with landslide occurrence and antecedent precipitation are analysed.     

Linking earthquake-triggered paleolandslides to their seismic source and to the possible seismic event that originated them in a portion of the Argentine Precordillera (31°–33°S)

Natural Hazards - A total of 36 rock slides were selected for analysing a probable seismic source in the active Andean Precordillera (31°–33°S), the most seismic region of...     

Reconstruction of the environmental history of a coastal insular system using shallow marine records: the last three millennia of the Cíes Islands (Ría de Vigo,NW Iberia)

The coastal lagoon‐beach complex at the Cíes Islands located at the opening of the Ría de Vigo (NW Iberia) is an important ecosystem currently threatened by anthropogenic impacts and climate variations. We used multiproxy marine sediment analyses to reconstruct the millennial environmental dynamics of this insular system and, in particular, the recent history of its coastal lagoon. Geophysical surveys were used to obtain bathymetry and identify the major sedimentary units of its closest submarine basin as well as their sediment sources. Core samples were taken in the middle and distal parts of the sedimentary body, where several prograding sedimentary units are thinner, allowing continuous sampling of the facies. Lithological, textural, elemental and chronological analyses were carried out on two cores. The detailed palynological studies on one of the cores included the analyses of the pollen, non‐pollen palynomorphs and dinocysts dating back three millennia. Our results revealed noticeable environmental changes affecting this area during the last 3000 years, due mainly to changing climate and oceanic conditions but also to the impact of historic human occupation of the islands. Several cold events (the 2.8 ka BP event and the Little Ice Age) characterized by enhanced upwelling alternated with warmer stormy periods of prevailing downwelling conditions in the ria. These circumstances altered the balance amongst the lacustrine, marsh, dune and lagoon systems, opening ephemeral inlets and modifying the trophic stage of the shallow waters surrounding the archipelago. Here we provide a background of the human and climatic impacts affecting these highly sensitive habitats, which may serve to improve their future management strategies.