Colombian Andes Research Articles

An updated synopsis of Neurolaena (Neurolaeneae, Asteraceae) with a new species from the Colombian Andes

Neurolaena is a genus native to the Americas and occurring from Mexico to Bolivia, including the Caribbean Islands. It includes shrubs or small trees with alternate leaves, paniculiform capitulescence, discoid or radiate capitula, 3–7-seriate involucre, and pappus with 25–70 bristles. Based on recent taxonomic studies in Neurolaeneae, we provide updates for the infrageneric classification of Neurolaena and recognize the occurrence of disc florets not associated with paleae for the first time in the genus. Furthermore, we describe a new species, N. curtipalea, which is the second species of the genus found in South America and the only species endemic to the Colombian Andes. It can be distinguished from the widespread N. lobata, occurring from Mexico to Bolivia and across the Caribbean Islands, by eucamptodromous (vs. penninervous) venation, radiate (vs. discoid) capitula, 5-seriate (vs. 6-seriate) involucre, paleae shorter (vs. longer) than corolla disc, and disc florets with white (vs. yellow) corollas. The new species is described, illustrated, and mapped, its taxonomic affinities are discussed, and a key to the infrageneric taxa and species belonging to Neurolaena is provided.

Landslide susceptibility assessment in scarce-data regions using remote sensing data

Landslides triggered by rainfall are among the most frequent causes of natural disasters in mountainous terrains. However, landslide susceptibility assessments are often limited due to the scarcity of reliable observations. Due to this lack of data, especially in developing countries, remote sensing is used for landslide susceptibility analysis. This study presents the application of remote sensing data and a logistic regression model to assess landslide susceptibility in a basin on a remote terrain in the northern Colombian Andes, where a rainstorm on May 18th, 2015, triggered more than 40 landslides and an associated debris flow afterwards. The methodology applied is based on free access remote sensing tools, since the study area is considered a scarce-data zone. The results show that free remote sensing tools provide enough information to run a model as logistic regression and achieve a successful first approach to the landslide susceptibility map of complex terrains as the study area. This suggests that the proposed methodology could be implemented in several regions with similar characteristics based only on free access information.

Nesting Behavior, Phenology, and Bionomics of the High Andean Leaf-Cutter Bee Megachile (Cressoniella) amparo.

Megachile amparo (González, Revista Colombiana De Entomología 32(1):93-96,2006)is the only high Andean leaf-cutter bee reported in Colombia and is possibly endemic to the Colombian Andes. Although it is frequently observed, even in urban areas, its biology and ecology remain unknown. The present study aimed to describe detailed aspects of its bionomy. Trap-nests were installed on the Campus of the Nueva Granada University (Cajicá, Colombia) from June/2018 to March/2020. The trap-nests were wooden blocks (25 × 15 × 14cm) with 30 cavities of Ø = 1cm and different lengths (50mm, 75mm, and 100mm) lined with waxed paper straws. During the observations, an increasing number of trap-nests were installed, increasing from 250 to 720 cavities. The trap-nests were monitored three times a week, recording both the date the start and end building by female. Most of the nest were maintained in the field to estimate the sex ratio, cell survival, and total development time under natural conditions. Thirty-two nests were removed at different times of the observation period to establish number of cells per nest, and cells built per female per day. We incubated 20 cells from different nests at 18°C, 22°C, 26°C, and 32°C to estimate the base temperature, thermal constant k (developmental time in degree days), and cell survival. Young cells of different positions were dissected and weighed to characterize food provision and brood cells. Computerized tomography-CT scans were performed in 30 brood cells to determine if diapause occurred during prepupal stage. Females nested 7- and 10-cm-long cavities and the number of cells per nest varied with cavity length. The brood cells had a length of 1.23 ± 0.12cm and a diameter of 0.92 ± 0.05cm. The female spends 1.17 ± 0.29days to build a brood cell. Food provision varied according to the position of the brood cell in the nest. The adults of M. amparo present a marked seasonality being more active during dry months. Base temperature and thermal constant k were different for males and females. The sex ratio is female biased (1.9:1), and cell survival in the field was 89% with no cleptoparasites or predators recorded.

Mesocarnivores activity patterns in the Northern Colombian Andes

Temporal segregation plays an important role as a coexistence mechanism between potentially competing and closely related species, especially in species with similar morphology and ecological requirements, such as mesocarnivores. This study investigates the temporal niche ecology of mesocarnivores coexisting in the southeastern Aburrá Valley, northern Colombian Andes. Specifically, this study i) evaluated the daily activity patterns of six mesocarnivore species, ii) analyzed the influence of the lunar cycle on the activity patterns of nocturnal species, iii) estimated the temporal overlap between pairs of mesocarnivores, and iv) estimated the functional similarities of these species. We hypothesized that mesocarnivores with similar functional traits exhibit greater temporal niche segregation, thus showing low overlap in their activity patterns to reduce competition. We used data from tracking cameras (10,744 camera-days) and estimated daily activity patterns using Kernel density analysis, non-negative trigonometric summation, and overlap analysis with the Overlap package in R. Also, lunar influence was evaluated using circular statistics in the software Oriana 4.02. Functional similarity was analyzed by similarity clustering using Jaccard's index in PAST. Nine species were recorded; six were included in the analyses of daily activity patterns. Activity patterns were not uniform throughout the circadian cycle. Cerdocyon thous, Leopardus tigrinus, and Nasuella olivacea showed mainly nocturnal activity, while Eira barbara, Nasua nasua, and Neogale frenata displayed a diurnal activity pattern. Only Leopardus tigrinus showed significant activity related to the lunar cycle. The activity overlap between pairs of species was variable, with a tendency to a low overlap, showing a high ecological similarity between species. This study represents the first estimate of the activity patterns of mesocarnivore species in the southeastern Aburrá Valley. The observed activity patterns are similar to those reported in other works. Species with high overlap showed ecological differences, especially in size and diet. The low number of records for some species may be associated with poor detectability but also with low abundance as a result of urban development and anthropogenic disturbance (e. g., roadkills). Our results suggest that temporal segregation contributes to mediating intra-gremial interactions and coexistence between sympatric and potentially competing species. These results will hopefully contribute to the knowledge of the ecology of mesocarnivores, mainly in ecosystems surrounding large cities in the northern Andes.

Diversity and distribution of macrofungi (Ascomycota and Basidiomycota) in Tolima, a Department of the Colombian Andes: an annotated checklist.

Macrofungi are classified in the phylum Ascomycota and Basidiomycota and they are very important from an ecological and economic point of view. Most studies of fungi in Colombia have been carried out mainly in the Andean Region, especially in the Departments of Antioquia, Valle del Cauca and Cundinamarca. However, other Departments in the Andean Region, like Tolima, located in the Cordillera Central, are well documented for plants (4,797 species) and animals (2,983 species), but very poorly documented in terms of knowledge of fungal diversity. This study provides a compiled and annotated checklist of all known macrofungi in the Department of Tolima, based on published literature and on the identification of new specimens collected from five localities of the Department. All records were updated taxonomically and we include detailed information on the localities in which they are distributed in the Department. The list includes 164 taxa distributed in 15 orders (Agaricales, Polyporales, Russulales, Boletales, Hymenochaetales, Xylariales, Auriculariales, Thelephorales, Cantharellales, Hypocreales, Pezizales, Gloeophyllales, Phallales, Tremellales, Dacrymycetales) and eighteen records in a doubtful taxa section. We present 26 new reports, 19 for Tolima and nine for Colombia. We also provide genetic and phylogenetic evidence of the occurrence of Gloeoporustelephoroides and Podoscyphavenustula in Colombia. This checklist provides the basis for future studies on species diversity and taxonomy in Tolima, by identifying the least studied taxa and ecosystems and conservation priorities.

Quantifying the distribution and morphological variation of the beetles Homocopris achamas and Uroxys coarctatus in Andean ecosystems of Colombia

AbstractInsects that inhabit high‐altitude ecosystems are an ecologically specialized group whose distribution is restricted by the presence of biogeographical barriers. These biogeographical constraints are thought to mould the shape of some insect structures because of environmental pressures that may produce better adaptations in extreme environments. We evaluated the potential distribution of Homocopris achamas and Uroxys coarctatus in two life regions (the Andean region and the Páramo region) found in the Andes of Colombia, and we determined if there were differences in their morphology along an elevational gradient. To determine the potential distribution of the species, we obtained geographical data through the systematic search of databases and entomological collections that we modelled under the maximum entropy model. We then evaluated the morphological variations by measuring geometric structures such as the clypeus (MC), the eye (ME) and the area of the anterior tibia (TA). We found that both species along the entire gradient exhibited the following characteristics: H. achamas was dominant in the Páramo region and showed two population nuclei separated by a wide biogeographic barrier, while U. coarctatus was more dominant in the Andean region and was distributed only in the northern Andes. Both were always linked to ecosystems with open vegetation that was both natural or intervened. H. achamas did not show changes in the shape of the structures while U. coarctatus showed differences in MC and ME. We suggested that livestock activity could act as an engine for breaking down biogeographical barriers allowing the distribution of a species to expand, and with this distributional expansion changes in the morphological structures of some species linked to their phenotypic plasticity could be promoted.

Harmonization Approach to Spatial and Social Techniques to Define Landscape Restoration Areas in a Colombian Andes Complex Landscape

Landscape restoration activities must be conducted through a transdisciplinary process, integrating social, economic, environmental, and governance aspects. Combining visions from the natural and social sciences is a challenge in highly complex territories, where unique ecosystem characteristics, economic processes, stakeholders of diverse nature, and different normativity converge. The harmonization of multiple techniques, such as multicriteria spatial analysis, expert knowledge elicitation, and social mapping, allows for an approach to defining landscape restoration areas in complex regions. This paper employs multiple techniques to define ecosystem restoration areas in a complex Colombian Andes landscape, integrating ecological and social components for sustainable development. We observed that areas of high and very high feasibility for ecological restoration, encompassing 179.5 hectares (4.84% of the study area), are predominantly located near primary forests. Although some areas have a low feasibility for conservation processes, they should not be disregarded as they still require protection. Landowners prioritize watershed and soil restoration as the most important landscape restoration activity due to their interest in improving water-related ecosystem services. This proposal enables the identification of areas with a higher restoration potential at the property level, facilitating prioritization and investment allocation for future implementation.

A new species of Iochroma Benth. (Solanaceae) from the eastern Andes of Colombia.

Iochromaorozcoae A.Orejuela & S.D.Sm., sp. nov. (Solanaceae) is described from the Andean forests of Cundinamarca in the eastern cordillera of Colombia. Iochromaorozcoae was first collected by the eminent Spanish priest and botanist José Celestino Mutis in the late part of the 18th century, but the specimens have lain unrecognised in herbaria for over 200 years. The species shares many features with its closest relative, Iochromabaumii S.D.Sm. & S.Leiva, but it differs from it in having small flowers with five corolla lobes and few inflorescences per branch, located near the shoot apex with 1 to 4 (-8) flowers, fruits that are greenish-yellow when ripe and its restricted geographic distribution. A description of I.orozcoae is provided, along with a detailed illustration, photographs of live plants, a comparison with closely-related species and a key to all Colombian species of Iochroma Benth. In closing, we emphasise the value of historical collections for the knowledge of biodiversity.

Taxonomic inflation and a reconsideration of speciation in the Andes: the case of the high-elevation tree frog Dendropsophus molitor (Anura: Hylidae)

Abstract Dendropsophus molitor is a hylid frog endemic to the Eastern Cordillera of the Colombian Andes, where it exhibits extensive geographic variation in size and colour pattern. Previous multivariate analyses of acoustic and genetic data suggested that northern and southern populations of D. molitor were distinct lineages, and consequently, the northern populations were described as Dendropsophus luddeckei. In this study, we conducted morphometric and genetic analyses of populations of D. molitor and D. luddeckei to test the validity of this recent taxonomic split. We sequenced the mitochondrial genes 12S, 16S, and COI, and the nuclear marker POMC, and also tested whether variation in the MC1R gene was associated with colour polymorphism in these frogs. Phylogenetic analyses recovered D. molitor and D. luddeckei as polyphyletic and species delimitation tests failed to recover them as separate lineages. Genetic differentiation between populations was mostly explained by high intra- and interpopulation variation in the absence of a north-south split, and we found no differences in morphometry between northern and southern populations. In addition, the coding region of MC1R is not associated with colour polymorphism. Thus, multiple lines of evidence suggest that D. luddeckei is not a valid species and D. molitor should be considered a single species. Our study highlights the danger of taxonomic inflation in the face of limited geographic sampling and a lack of clear diagnostic characters.

Erosion rate maps highlight spatio-temporal patterns of uplift and quantify sediment export of the Northern Andes

Erosion rates are widely used to assess tectonic uplift and sediment export from mountain ranges. However, the scarcity of erosion rate measurements often hinders detailed tectonic interpretations. Here, we present 25 new cosmogenic nuclide-derived erosion rates from the Northern Andes of Colombia to study spatio-temporal patterns of uplift along the Central and Eastern Cordillera. Specifically, we combine new and published erosion rate data with precipitation-corrected normalized channel steepness measurements to construct high-resolution erosion rate maps. We find that erosion rates in the southern Central Cordillera are relatively uniform and average ∼0.3 mm/a. In the northern Central Cordillera rapidly eroding canyons dissect slowly eroding, low-relief surfaces uplifting since 8.3−2.6+3.7 Ma, based on a block uplift model. We interpret that persistent steep slab subduction has led to an erosional steady-state in the southern Central Cordillera, whereas in the northern Central Cordillera, Late Miocene slab flattening caused an acceleration in uplift, to which the landscape has not yet equilibrated. The Eastern Cordillera also displays pronounced erosional disequilibrium, with a slowly eroding central plateau rimmed by faster eroding western and eastern flanks. Our maps suggest Late Miocene topographic growth of the Eastern Cordillera, with deformation focused along the eastern flank, which is also supported by balanced cross-sections and thermochronologic data. Spatial gradients in predicted erosion rates along the eastern flank of the Eastern Cordillera suggest transient basin-ward migration of thrusts. Finally, sediment fluxes based on our erosion maps, suggest that the Eastern Cordillera exports nearly four times more sediment than the Central Cordillera. Our analysis shows that accounting for spatial variations in erosion parameters and climate reveals important variations in tectonic forcing that would otherwise be obscured in traditional river profile analyses. Moreover, given relationships between tectonic and topographic evolution, we hypothesize that spatio-temporal variations in slab dip are the primary driver of the dynamic landscape evolution of the Northern Andes, with potentially superposed effects from inherited Mesozoic rift structures.

Digital image processing for atmospheric monitoring at Colombian Andes

ABSTRACT As an alternative to the current technologies, we explored the feasibility of using low cost and massive use of digital cameras as photometric sensors to retrieve the atmospheric total optical depth (τ) in the urban area of a city in the Colombian Andes. This study proposes a simple way to estimate τ from digital processing of images of the Sun based on the Beer-Bouguer-Lambert law Langley’s linear fitting for the colour levels in channels red, green, and blue registered by the pixels of cameras’ sensors. From February to March 2022, the τ values retrieved from the images were correlated to the retrieved values from a solar spectral radiometer (SSR). We found that τ is sensible to the featured changes in the local atmosphere and to the cameras’ exposure parameters setup. Under conditions of partly clear sky, around 80% (r > 0.8) of the τ values from cameras showed a linear correspondence to those retrieved from SSR system. Its spectral dependency (τ _red < τ _green < τ _blue) is in accordance with the physical phenomena in light-atmosphere interaction. The results suggest that the methodology applied can be used for monitoring the atmosphere at any geographical location in the world.

Snow Albedo Reduction in the Colombian Andes Mountains Due to 2000 to 2020 Saharan Dust Intrusions Events

This article investigates the snow albedo changes in Colombian tropical glaciers, namely, Sierra Nevada de Santa Marta (SNSM), Sierra Nevada del Cocuy (NSC), Nevado del Ruíz (NDR), Nevado Santa Isabel (NDS), Nevado del Tolima (NDT), and Nevado del Huila (NDH). They are associated with the possible mineral dust deposition from the Sahara Desert during the June and July months using snow albedo (SA), snow cover (SC), and land surface temperature (LST) from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra and Aqua satellites. And mineral dust (MD) from The Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), both of them during 2000–2020. Results show the largest snow albedo reductions were observed at 39.39%, 32.1%, and 30.58% in SNC, SNSM, and NDR, respectively. Meanwhile, a multiple correlation showed that the glaciers where MD contributed the most to SA behavior were 35.4%, 24%, and 21.4% in NDS, NDC, and NDR. Results also display an increasing trend of dust deposition on Colombian tropical glaciers between 2.81 × 10−3 µg·m−2·year−1 and 6.58 × 10−3 µg·m−2·year−1. The results may help recognize the influence of Saharan dust on reducing snow albedo in tropical glaciers in Colombia. The findings from this study also have the potential to be utilized as input for both regional and global climate models. This could enhance our comprehension of how tropical glaciers are impacted by climate change.

How erosional efficiency modulates landscape response to drainage reorganization: New empirical evidence from the Andes

The fluvial network in active mountain ranges is considered to evolve from longitudinal to transverse-dominated drainage systems. This hypothesis links to the forelandward migration of the orogen, while crustal thickening modifies the range's flank slopes, enhancing erosional efficiency. We probe such a proposition with new empirical observations from the Colombian Andes by studying the recent capture of the longitudinal Suárez and Chicamocha Rivers by the transverse Sogamoso River. Firstly, by integrating published low-temperature thermochronology and quantitative topographic metrics like χ, we found that rejuvenated rock uplift in the Cocuy and Yariguies ranges delays the transition from longitudinal to transverse-dominated drainage systems by compensating the across-divide contrasts in erosion. To further constrain the spatiotemporal response of the Suárez and Chicamocha Rivers after the discrete capture, we computed sediment-gauge erosion rates in conjunction with rainfall-normalized channel steepness and Gilbert metrics. We observe stark contrasts in erosion rates between the Chicamocha (maximum of 148.22 ± 44.86 m/Myr) and Suárez Rivers (maximum of 71.9 ± 21.5 m/Myr). Higher erosion rates in the former are expressed with widely distributed slope-break knickpoints that migrated further upstream with catchment expansion at the expense of the less efficiently erosive Suárez River basin. We interpret these erosional differences as a lithological control on the pace of topographic response to an external perturbation (discrete capture), given low-lying sedimentary rocks delay the erosional response of the Suárez River basin. Our research therefore emphasizes the role that lithology poses in keeping the landscape in an unsteady topographic condition.

Decoupling in governance: the land governance network in a region of the Colombian Andes

Land governance requires coherence not only in terms of policies but also between its governance functions to achieve the desired goals. In this study, we focus on the functions that direct influence land use (boundary setting and resource appropriation; project formulation and financing; and monitoring, evaluation, and learning), which are expected to form a feedback loop necessary for adaptive co-management. We evaluated the degree of coherence of these three functions (as an approach to efficient management) via geo-located multilayer social network analysis and using an area of the Rio Grande and Chico basin in the Colombian Andes as the case study. According to the results, there is a conflict between production and conservation goals, necessitating collaboration among actors and institutions from various levels. The social network analysis revealed that the three functions are not articulated; instead, there exist two feedback loops (one per goal) in the boundary setting and resource appropriation function, leading to such conflict. The imposition of a governance system on the community by a few actors is recognized as the root of this conflict; hence, the need to move toward a governance with the community by promoting active participation in the various functions and interactions within them. We recommend future studies to assess the impact of governance networks on land-use actions to identify the reasons for land-use change and propose new strategies.

Comparison study of a landslide-event hazard mapping using a multi-approach of fuzzy logic, TRIGRS model, and support vector machine in a data-scarce Andes Mountain region

Landslides are a significant global hazard, especially prevalent in regions with high rainfall, active tectonic processes, and rugged topography, such as the Colombian Andean region. Therefore, it is crucial to identify areas prone to landslides in order to protect human lives and mitigate the adverse impacts on national economies, especially in developing countries situated in tropical and mountainous regions. Assessing landslide hazard and susceptibility is a fundamental step in comprehending the fundamental characteristics of slopes susceptible to failure, particularly under extreme rainfall conditions. Various researchers have devised methods and techniques to assess and map landslides, employing heuristic, statistical, and deterministic approaches. This study carried out a geographic information system-based approach for shallow landslides, with the objective to compare different methods for a landslide-event hazard mapping using the landslide records on May 18, 2015, triggered by a rainstorm in the La Liboriana basin (Colombia). In the first place, a fuzzy logic gamma model was applied using landslide conditioning factors. Then, the deterministic model TRIGRS was applied to assess shallow landslides. Finally, a support vector machine (SVM) model was used to obtain an intermediate scale solution. All models consider the rainfall that triggered the aforementioned landslide event. The results indicated that the SVM (radial basis function) model permits to obtain a better performance (AUC = 0.95) in landslide hazard zonation rather than quantitative heuristic fuzzy gamma model (AUC = 0.86) and the deterministic TRIGRS model (AUC = 0.60), obtaining best accurate at predicting the landslide hazard in the study area.

Ecology and Diversity of Weed Communities in the Northern Andes under Different Anthropogenic Pressures

Weeds can have both positive and negative effects on agricultural environments. However, despite the growing interest in the ecology of weed communities in agricultural areas, a few studies have been carried out in the northern region of the Andes of Colombia, where urban and agricultural expansion have generated highly disturbed scenarios. The aim of this study was to analyze the diversity of vegetation and weed seed banks in three agricultural production systems and a forest ecosystem in the northern Andes of Colombia. Hill numbers were used to compare diversity, Beta diversity to assess changes in composition, and range—abundance–dominance curves at different sites. Likewise, indicator species were analyzed to find species associations to each system. The results revealed differences in the composition of weeds between the forest ecosystem and the agricultural production systems, with higher equitability in the forest ecosystem and higher dominance in agricultural systems. Significant differentiation was observed among the dominant species within each agricultural system, particularly highlighting those species considered pests due to their unique life history traits. These traits confer them with a greater advantage in the face of various anthropogenic selection pressures. These findings highlight the impact of anthropogenic disturbances on the ecological dynamics of weed communities in different ecosystems, which should be considered when planning integrated weed management techniques.

Fossil leaves, woods, gastropods, and a crocodile tooth: Is the Amagá Formation worth exploring?

We have generated a spatial framework for macrofossil searching based on the current knowledge of fossil localities and fossil beds reported for the Amagá Formation in the northwestern Andes in Colombia. Our results show that twenty-three fossil localities and ninety-five fossil beds are distributed along this sedimentary succession. Preservation potential is higher in the Lower Member, given the high accommodation space and the dominance of a meandering fluvial system, compared with the Upper Member, where there was less accommodation space with a braided fluvial system controlling it. Our findings show that even though paleontological studies are null in this area, there are several options to find terrestrial macrofossil assemblages that will allow us to investigate the possible biological role of global climatic changes and regional tectonics in the Neotropical biomes based on the Amagá Formation.

Urban and peri-urban bats (Mammalia: Chiroptera) in Manizales, Colombia: exploring a conservation area in sub-Andean and Andean ecosystems

Abstract In Colombia, 217 bat species have been recorded of which at least 22 species occur in Andean and sub-Andean ecosystems. To evaluate the richness of bats in an Andean elevational range at the Municipality of Manizales, Central Andes of Colombia, we performed surveys supplemented with incidental captures from 2018 to 2022 at different urban and peri-urban areas, and reviewed specimens in biological collections. We evaluated the perception and knowledge that local people have about bats using an online survey. We reported 33 species in the study area. Phyllostomidae showed the highest richness (20 species), followed by Vespertilionidae (11 species), and Molossidae (2 species). For the survey, we obtained responses from 219 people who showed a good knowledge about bats and their ecological importance. We did not find significant differences between ages and levels of schooling in the perception about bats. Our results highlight the relevance of conserving the green areas of Manizales and the need for environmental education programs to reduce possible bat-human conflicts and negative perceptions. Manizales has the potential as an Area of Importance for the Conservation of Bats, due to its high bat richness and that reproduction is occurring within the study area.

Landslide Susceptibility Analysis on the Vicinity of Bogotá-Villavicencio Road (Eastern Cordillera of the Colombian Andes)

Landslide occurrence in Colombia is very frequent due to its geographical location in the Andean mountain range, with a very pronounced orography, a significant geological complexity and an outstanding climatic variability. More specifically, the study area around the Bogotá-Villavicencio road in the central sector of the Eastern Cordillera is one of the regions with the highest concentration of phenomena, which makes its study a priority. An inventory and detailed analysis of 2506 landslides has been carried out, in which five basic typologies have been differentiated: avalanches, debris flows, slides, earth flows and creeping areas. Debris avalanches and debris flows occur mainly in metamorphic materials (phyllites, schists and quartz-sandstones), areas with sparse vegetation, steep slopes and lower sections of hillslopes; meanwhile, slides, earth flows and creep occur in Cretaceous lutites, crop/grass lands, medium and low slopes and lower-middle sections of the hillslopes. Based on this analysis, landslide susceptibility models have been made for the different typologies and with different methods (matrix, discriminant analysis, random forest and neural networks) and input factors. The results are generally quite good, with average AUC-ROC values above 0.7–0.8, and the machine learning methods are the most appropriate, especially random forest, with a selected number of factors (between 6 and 8). The degree of fit (DF) usually shows relative errors lower than 5% and success higher than 90%. Finally, an integrated landslide susceptibility map (LSM) has been made for shallower and deeper types of movements. All the LSM show a clear zonation as a consequence of the geological control of the susceptibility.

Miocene Paleogeography of NW Colombia: A review of the sedimentary and magmatic evolution of the Amagá Basin a century after Grosse’s work

In 1918, the geologist Emile Grosse was commissioned to conduct geological studies in the Amagá Basin, Antioquia, Colombia. In 1923, Grosse finished a comprehensive cartographic work that became the cornerstone for the geology of the northwest (NW) Colombian Andes. Today, 100 years later, the volcanoclastic strata preserved in the Amagá Basin are crucial for understanding major Oligocene to Pliocene tectonic events that occurred in the NW South-American margin, including the fragmentation of the Nazca Plate, the collision of the Panamá-Chocó Block, and the shallowing of the subducted slab. Our contribution includes new mineral chemistry and zircon petrochronological data from the Combia Volcanic Complex and published data to provide a review of the Oligocene to Pliocene deformation, sedimentation, and magmatic patterns in the Amagá Basin and their implications for the tectonic evolution of NW South America. The Amagá Basin was the result of the Eocene to Oligocene uplift of the Western Cordillera followed by the Middle Miocene to Pliocene uplift of both the Central and Western cordilleras, events that modified the Miocene drainage network in the Northern Andes. Coeval with the final Miocene deformation phases in the Amagá basin, the magmatism of the Combia Complex was the result of subduction magmas emplaced in a continental crust affected by strike-slip tectonics.