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The International Symposium on Andean Geodynamics (ISAG) is an international conference that was held, on average, every 3–4 years in different European cities between 1990 (Grenoble) and 2008 (Nice). These symposia usually offer an opportunity for researchers from Latin American countries and Europe as well as other countries to review the state of knowledge in geosciences on the Andes. After a long period without an edition, the 8th ISAG was organized for the first time in a Latin American country, Ecuador, from 24th to 26th September 2019. The organizing committee led by Pablo Samaniego relied heavily on the Instituto Geofísico of the Escuela Politécnica Nacional (IG-EPN) and the Institut de Recherche pour le Développement (IRD), in particular through its office in Quito, and through the Laboratoire Mixte International in France and Ecuador: "Seismes et Volcans dans les Andes du Nord" (LMI-SVAN); and the French Embassy in Ecuador. Field trips in tectonics, seismotectonics and volcanology at emblematic sites in Ecuador were organized by researchers from the IRD (Isterre and LMV), the Institut de Radio Protection Nucléaire (IRSN), IG-EPN and the University of Geneva. Four invited speakers gave presentations: Peter Molnar (University of Boulder) on the mechanisms of the Andes uplift, Suzanne Kay (Cornell University) on its magmatism, Victor Ramos (University of Buenos Aires) on the scientific approaches developed through time for the Andean orogeny and Eric Calais (Ecole Normale Supérieure de Paris) on the difficulty of dialog between seismic risk specialists and the authorities in Haiti. The symposium also provided an opportunity for more than 250 participants to meet, with more than 80 oral presentations and over 150 posters. As a result of this conference, the Editor of the Journal of South American Earth Sciences proposed to the organizing committee to publish a special issue on the contours of these presentations. Following the peer review process, 19 papers are published in this special issue. These manuscripts reflect the various disciplinary fields, geophysics and deep imaging, tectonics, volcanism, geomorphology and seismic hazard, from the local scale to the Andes as a whole. Not surprisingly, a higher density of works is found in Ecuador and the northern Andes (Figure 1). As this collection of articles reflects the outlines of a symposium and not a specific scientific question, our aim here is not to develop a synthesis of current knowledge on the Andes. We therefore present these articles in sequence, by discipline, although this categorization may appear subjective since some articles are multidisciplinary. [ABSTRACT FROM AUTHOR]

The shadow-height method has been extensively used to extract the heights of buildings from the shadows they cast in non-stereo (single view) aerial and satellite imagery. However, the use of this method in Earth sciences has been limited, partially due to the relatively low accuracy reported, the fuzziness of shadow edges, the complexities of the scanning sensors, and a lack of software tools. In this paper, we present an enhanced shadow-height methodology offering significant accuracy improvement. These improvements are mainly the result of using a physical approach to model the illumination gradient through the edge of shadows and by leveraging meteorological data to precisely estimate atmospheric refraction. We validated 91 shadow-derived height estimations from images obtained by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) at three sites with latitudes between 33 and 78°S: The Andes Mountains, Sentinel Range, and Abbot ice shelf. Reference measurements were obtained from Global Navigation Satellite System (GNSS) surveys and the Ice, Cloud, and land Elevation Satellite (ICESat). The observed errors fell below 6% for small height differences (∼20 m) and below 2% for larger height differences (≳300 m). Our validation data cover solar elevations ranging from 3.7 to 42.2°, and we observed smaller absolute errors at lower solar elevations. This novel information can be valuable for studying surface elevation changes in present and old imagery and extending glacier volume variation time-series. [ABSTRACT FROM AUTHOR]

Background: Climate change is arguably a major threat to biodiversity conservation and there are several methods to assess its impacts on species potential distribution. Yet the extent to which different approaches on species distribution modeling affect species richness patterns at biogeographical scale is however unaddressed in literature. In this paper, we verified if the expected responses to climate change in biogeographical scale—patterns of species richness and species vulnerability to climate change—are affected by the inputs used to model and project species distribution. Methods: We modeled the distribution of 288 vertebrate species (amphibians, birds and mammals), all endemic to the Amazon basin, using different combinations of the following inputs known to affect the outcome of species distribution models (SDMs): 1) biological data type, 2) modeling methods, 3) greenhouse gas emission scenarios and 4) climate forecasts. We calculated uncertainty with a hierarchical ANOVA in which those different inputs were considered factors. Results: The greatest source of variation was the modeling method. Model performance interacted with data type and modeling method. Absolute values of variation on suitable climate area were not equal among predictions, but some biological patterns were still consistent. All models predicted losses on the area that is climatically suitable for species, especially for amphibians and primates. All models also indicated a current East-western gradient on endemic species richness, from the Andes foot downstream the Amazon river. Again, all models predicted future movements of species upwards the Andes mountains and overall species richness losses. Conclusions: From a methodological perspective, our work highlights that SDMs are a useful tool for assessing impacts of climate change on biodiversity. Uncertainty exists but biological patterns are still evident at large spatial scales. As modeling methods are the greatest source of variation, choosing the appropriate statistics according to the study objective is also essential for estimating the impacts of climate change on species distribution. Yet from a conservation perspective, we show that Amazon endemic fauna is potentially vulnerable to climate change, due to expected reductions on suitable climate area. Climate-driven faunal movements are predicted towards the Andes mountains, which might work as climate refugia for migrating species. [ABSTRACT FROM AUTHOR]

Precipitation estimate is important for earth science studies and applications, and it is one of the most difficult meteorological quantities to estimate accurately. For regions such as Peru, reliable gridded precipitation products are lacking due to complex terrains and large portions of remote lands that limit the accuracy of satellite precipitation estimation and in situ measurement density. This study evaluates and cross-examines two high-resolution satellite-based precipitation products, a global rain-gauge interpolated precipitation product, and a Weather Research and Forecast (WRF) model that simulated precipitation for a ten-year period from 2010 to 2019 in the Peruvian Andes region across the Pacific coast, Andes, and in the Amazon. The precipitation estimates examined in this study are the Integrated Multi-SatellitE Retrievals for GPM (IMERG), Multi-Source Weighted-Ensemble Precipitation (MSWEP), Global Precipitation Climatology Center product (GPCC), and a 3 km grid spacing WRF-based regional climate model (RCM) simulation. The evaluation and cross-examination were performed at sub-daily (6 h), daily, and monthly time scales, and at various spatial resolutions. The results show that the WRF simulation performs as well as, if not better than, GPM IMERG in the low precipitation and dry regions but becomes inaccurate in wet regions. GPM IMERG is more suitable for higher precipitation and wet regions, and MSWEP shows a systematic overestimation over the study area. It is therefore important to choose the most suitable precipitation product based on research needs and climate condition of the study for the challenging Peruvian Andes region. [ABSTRACT FROM AUTHOR]

A new FAO Penman-Monteith reference evapotranspiration gridded dataset is introduced, called PISCOeo_pm. PISCOeo_pm has been developed for the 1981–2016 period at ~1 km (0.01°) spatial resolution for the entire continental Peruvian territory. The framework for the development of PISCOeo_pm is based on previously generated gridded data of meteorological subvariables such as air temperature (maximum and minimum), sunshine duration, dew point temperature, and wind speed. Different steps, i.e., (i) quality control, (ii) gap-filling, (iii) homogenization, and (iv) spatial interpolation, were applied to the subvariables. Based on the results of an independent validation, on average, PISCOeo_pm exhibits better precision than three existing gridded products (CRU_TS, TerraClimate, and ERA5-Land) because it presents a predictive capacity above the average observed using daily and monthly data and has a higher spatial resolution. Therefore, PISCOeo_pm is useful for better understanding the terrestrial water and energy balances in Peru as well as for its application in fields such as climatology, hydrology, and agronomy, among others. Measurement(s) reference evapotranspiration • air temperature • sunshine duration • dew point temperature • wind speed Technology Type(s) weather station Factor Type(s) reference evapotranspiration Sample Characteristic - Environment Climatology • Hydrology • Meteorology • Ecology • Earth Science Sample Characteristic - Location Peru • Andes [ABSTRACT FROM AUTHOR]

Quartz segregations in paragneisses from the Paleozoic basement of the North Patagonian Andes contain highly saline multiphase fluid inclusions with the rare daughter mineral ferropyrosmalite detected by Raman analysis, besides halite, sylvite, hematite, and/or magnetite. During heating experiments, L-V homogenization occurs (256-515 °C), followed by halite dissolution (287-556 °C) and the dissolution of ferropyrosmalite at 550-581 °C. The latter phase transition triggers the growth of clinoamphibole crystals according to the following idealized reactions, written for potential end-members: 4Fe8Si6O15 [(OH)6Cl4] + 6Ca2+ (aq) ↔ 3Ca2Fe5Si8O22 (OH)2 + 17Fe2+ (aq) + 16 Cl- (aq) + 12OH- + 3H2 Ferropyrosmalite ↔ Ferro-actinolite Fe8Si6O15 [(OH)6Cl4] + 2Ca2+ (aq) + Fe3+ (aq) + 2Al3+ + (aq) + Na+ (aq) + H2O ↔ NaCa2(Fe42+ Fe3+)(Al2Si6) O22Cl2 + 4Fe2+ (aq) + 2Cl- (aq) + 4H2 Ferropyrosmalite ↔ Chloro-hastingsite The amphibole resembles the composition of ferro-actinolite but also has striking similarities with chloro-hastingsite, as indicated by Raman spectroscopy. During the heating experiment, hematite (when present) transforms to magnetite by the uptake of H2, whereas inclusions without Fe-oxides contain traces of H2 after the reaction. This mineral transformation shows that ferropyrosmalite might result from the retrograde re-equilibration of amphibole with the brine, implying the uptake of Fe2+, Cl-, and H2O and the enrichment of Ca2+ in the brine. Pervasive fluid flow and fluid-assisted diffusion are recorded by channel way microstructures, healed microfractures, and dissolution-reprecipitation phenomena, as demonstrated by cathodoluminescence microscopy. These alkali- and FeCl2-rich brines, derived from magmatic sources and of possible Mesozoic age, were related to regional metasomatism, coeval with widespread granitoid activity. [ABSTRACT FROM AUTHOR]

We evaluated if two sigmodontine rodent taxa (Abrothrix olivacea and Phyllotis darwini) from the Andes and Coastal mountaintops of central Chile, experienced distributional shifts due to altitudinal movements of habitat and climate change during and after the Last Glacial Maximum (LGM). We tested the hypothesis that during LGM populations of both species experienced altitudinal shifts from the Andes to the lowlands and the coastal Cordillera, and then range retractions during interglacial towards higher elevations in the Andes. These distributional shifts may have left remnants populations on the mountaintops. We evaluated the occurrence of intraspecific lineages for each species, to construct distribution models at LGM and at present, as extreme climatic conditions for each lineage. Differences in distribution between extreme climatic conditions were interpreted as post-glacial distributional shifts. Abrothrix olivacea displayed a lineage with shared sequences between both mountain systems, whereas a second lineage was restricted to the Andes. A similar scenario of panmictic unit in the past was recovered for A. olivacea in the Andes, along with an additional unit that included localities from the rest of its distribution. For P. darwini, both lineages recovered were distributed in coastal and Andean mountain ranges at present as well, and structuring analyses for this species recovered coastal and Andean localities as panmictic units in the past. Niche modeling depicted differential postglacial expansions in the recovered lineages. Results suggest that historical events such as LGM triggered the descending of populations to Andean refuge areas (one of the A. olivacea’s lineages), to the lowlands, and to the coastal Cordillera. Backward movements of populations after glacial retreats may have left isolates on mountaintops of the coastal Cordillera, suggesting that current species distribution would be the outcome of climate change and habitat reconfiguration after LGM. [ABSTRACT FROM AUTHOR]

Socio-economic and environmental changes are well known causes of demographic collapse of agrarian cultures. The collapse of human societies is a complex phenomenon where historical and cultural dimensions play a key role, and they may interact with the environmental context. However, the importance of the interaction between socio-economic and climatic factors in explaining possible breakdowns in Native American societies has been poorly explored. The aim of this study is to test the role of socio-economic causes and rainfall variability in the collapse suffered by the Aymara people of the semiarid Andean region of Tarapacá during the period 1820–1970. Our motivation is to demonstrate that simple population dynamic models can be helpful in understanding the causes and relative importance of population changes in Andean agro-pastoral societies in responses to socio-environmental variability. Simple logistic models that combine the effects of external socio-economic causes and past rainfall variability (inferred from Gross Domestic Product [GDP] and tree-rings, respectively) were quite accurate in predicting the sustained population decline of the Aymara people. Our results suggest that the depopulation in the semiarid Tarapacá province was caused by the interaction among external socio-economic pressures given by the economic growth of the lowlands and demands for labor coupled with a persistent decline in rainfall. This study constitutes an example of how applied ecological knowledge, in particular the application of the logistic equation and theories pertaining to nonlinear population dynamics and exogenous perturbations, can be used to better understand major demographic changes in human societies. [ABSTRACT FROM AUTHOR]

The stream profiles of rivers of northern Chile reveal two graded segments separated by 20-km-long knickzones. Their formation was initiated in the Late Miocene in response to surface uplift of the western flank of the Altiplano. This phase of uplift that was coeval with the shift of deformation from the Altiplano to the sub-Andean zone caused relief to grow at the scale of the whole drainage basin. Above and beneath these knickzones, the presence of braided channels and the absence of erosion on adjacent pediplains suggest no substantial modification in the local relief. The knickzones, however, show bedrock channels, and fluvial dissection rates have exceeded erosion rates on adjacent pediplains by two orders of magnitudes. Hence, the data imply that the only geomorphic recorders of relief growth are the knickzones that currently transpose the effects of the Late Miocene phase of surface uplift from the coast to the Altiplano. [ABSTRACT FROM AUTHOR]