Nevado De Research Articles

Occurrence and effect of dwarf mistletoe (Arceuthobium globosum and A. vaginatum) in high-elevation forests in México

Climate change has very important effects on high mountain forests (>3500 masl), which face various ecological problems associated with global change including the proliferation of pests and parasitic plants. These sensitive ecological systems cover approximately 39,000 ha of Mexican territory and occur around some of the highest volcanoes in the country. The objective of this research was to determine the spatial distribution and infestation levels of dwarf mistletoe (Arceuthobium spp.) in the main populations of Pinus hartwegii in five mountains of the Trans-Mexican Volcanic System (Pico de Orizaba, Nevado de Toluca, Cofre de Perote, Nevado de Colima and Monte Tláloc) and identify infestation patterns in relation to the structure of the forest. In the study, 2658 sampling sites (1000 m² each) were installed using the contour lines as access transects to the forest, distributed at every 100 of altitude, between 3500 and 4000 masl. Approximately 32 % of the sampled area had some level of attack by dwarf mistletoe, distributed across all diameter categories of the trees. The infestations affected the establishment of natural regeneration and rates of tree mortality.

Establishing monarch butterfly overwintering sites for future climates: Abies religiosa upper altitudinal limit expansion by assisted migration

Climate change projections suggest a precarious future for the Monarch butterfly (Danaus plexippus) as the suitable climatic habitat of its exclusive overwintering host Abies religiosa (oyamel, Sacred fir, a conifer endemic to Mexico) inside the Monarch Butterfly Biosphere Reserve (MBBR) is expected to disappear by 2090. Since the upper elevation limit of A. religiosa is approximately 3,500 m and the summits of mountains within the MBBR are ca. 3,550 m, we tested the feasibility of establishing A. religiosa at four locations outside its current geographic range in the MBBR, on a geographically close volcano, Nevado de Toluca at 4000 (timberline, an extreme site), 3,800, and 3,600 m (to test species range expansion upward in elevation), and at 3400 m (a reference site, slightly lower than the upper elevation limit of A. religiosa). Using existing shrubs as nurse plants to protect the seedlings from extreme temperatures, at each site we planted five to eight populations, originating between 3,100 and 3,500 m within the MBBR. After three growing seasons in the field (6 years after sowing), we found that: (a) survival and height increment declined steeply with test site elevation; (b) even at the highest sites (3,800 and 4,000 m), survival was acceptable, at 68 and 44%, respectively, although the growth was very poor at 4000 m; (c) populations responded similarly to transfer; (d) transfer effects were best accounted for by annual dryness index; (e) to compensate for the expected 2.3°C increase in mean annual temperature or 0.009 √°Cmm−1 increase of annual dryness index from the reference period (1961–1990) to the decade centered in 2060, it would be necessary to shift populations approximately 500 m to higher elevations; and (f) upward transfers to compensate for the 2.3°C increase in mean annual temperature are expected to result in height increment and survival that are approximately 47 and 21% lower, respectively, than values expected at zero transfer distance. We conclude that the establishment of A. religiosa at 3600 and 3,800 m is feasible and that planted stands could eventually serve as overwintering sites for the Monarch butterfly under projected future climates.

Geodetic monitoring of the recent activity and the dome forming eruption at Nevado del Ruiz (Colombia), 2010–2023

Nevado del Ruiz (Colombia) is infamous for the catastrophic eruption of 1985 that destroyed the villages of Armero and Chinchiná. However, this was not the volcano’s first destructive event; similar eruptions also occurred in 1595 and 1845. In 1985, the limited geodetic data available failed to provide a clear warning of the impending eruption. Since then, advancement in geodetic monitoring, now incorporating tilt and satellite geodesy, along with improvements in seismic, geochemical, geological and remote sensing monitoring, have enhanced hazards assessment and mitigated the risk during subsequent eruptions in 1989, 2012, and 2015–2019, as well as during periods of unrest over the last 13 years. Modeling of deformation data over the past 13 years reveals complex interactions between the local, shallow magmatic system beneath Nevado del Ruiz and a deep, regional magmatic system beneath Nevado de Santa Isabel, 9 km southwest of Nevado del Ruiz. Before February 2012, the volcano deflated because of the depressurization of the local shallow reservoir. This same reservoir later fueled ash emissions and gas release (2012–2023), and a dome-forming eruption (2015–2019). In contrast, the inflation observed from 2012 to 2023 is linked to the pressurization of the deep reservoir beneath the Nevado de Santa Isabel.

Reconstruction of Hualca Hualca volcano (southern Peru) based on geomorphological and geological evidence and 40Ar/39Ar dating

The volcanic history of many of the western Central Andes volcanoes, including Hualca Hualca in the northern Ampato Volcanic Complex, remains poorly constrained. Based on an updated 1:50,000-scale geological map, new cross-sections of the Ampato Complex, a compilation of published dates, new geochemical data and 40Ar/39Ar ages, we present new insights into its volcanic evolution. Our study identifies 7 principal geological units (4 were not reported on the previous geologic map) and 8, mostly constructive, volcanic phases. The 40Ar/39Ar dating supports that Hualca Hualca began its formation during the Early Pleistocene (>1.6 Ma) with the establishment of an ancient stratovolcano. This volcano underwent a massive sector collapse to the north that created a U-shaped large amphitheater. This collapse likely resulted in the temporary damming of the Colca River, though no dates or associated deposits have been identified. Subsequent eruptions led to the formation of a smaller volcano along the amphitheater's scar that emplaced andesitic and dacitic lavas. This volcano dubbed modern Hualca Hualca holds the main summit. One of the longest lavas of this edifice reach the Colca valley and was previously dated at 610 ka. Sometime around 550 ka, volcanic activity migrated to the interior of the amphitheater forming the Nevado de Puye, Cruz del Condor, and Ahuashune domes that produced lavas of andesitic and dacitic composition. Around 164 ka a dacitic lava flow was emitted between Nevado del Puye and the base of the modern Hualca Hualca inside the horseshoe crater. The youngest known collapse of the Hualca Hualca complex involved parts of Nevado de Puye dome and the modern Hualca Hualca volcano, emplacing a debris avalanche that again dammed the Colca River and formed an upstream temporary lake that emplaced lacustrine and volcaniclastic deposits. After this collapse, no other volcanic deposit of the Hualca Hualca complex has been identified. Subsequently, glacial erosion during the local Last Glacial Maximum (17–16 ka) modified the volcanic landscape. Geochemical characteristics of Hualca Hualca suggest that their magmas were produced in a metasomatized mantle wedge and likely underwent crustal contamination during their ascent through the thick continental crust.

Nutrient contents and microbial communities as mediators of the effects of land-use in ecosystem functioning in alpine ecosystems from Central Mexico

PurposeThe interplay between microbial taxonomy, functional diversity, and land-use changes across diverse ecosystems must be better understood. This study explores, through a statistical modeling approach, the intricate relationships between microbial communities, soil properties (nutrient contents and physicochemical parameters), and land-use changes, using stable isotopes ratio (δ13C/δ15N) as ecosystem function indicator.MethodsUsing Structural Equation Modeling (SEM) this study aims to investigate how soil microbial communities, soil properties and ecosystem function are interconnected in three ecosystems undergoing land-use change in Nevado de Toluca, Mexico.ResultsMultivariate analyses of microbial communities and soil parameters for the different land-uses reveal significant variation in both microbial composition and soil properties (i.e. nutrient contents) mainly explained by the land-use history of the studied ecosystems. Through the SEM approach, it was possible to disentangle the relative contribution of land-use change, microbial community composition and nutrient contents to the ecosystem function defined as the δ13C/δ15N ratio.ConclusionsMicrobial communities are the main drivers of soil ecosystem functioning. However, through SEM approach it is possible to formally test direct and indirect relationships impacting microbial communities and the resulting functional consequences, contributing to a mechanistic understanding of the ecological implications of land-use change, aiding in sustainable land-use decision-making.

The House Is Burning: Assessment of Habitat Loss Due to Wildfires in Central Mexico

Fire suppression and climate change have increased the frequency and severity of wildfires, but the responses of many organisms to wildfire are still largely unknown. In this study, we assessed the risk of habitat loss for amphibians, mammals, and reptiles caused by wildfires in central Mexico. We accomplished this by: (1) determining the likelihood of wildfire occurrence over a 12-year period using historical records and the Poisson probability mass function to pinpoint the most susceptible areas to wildfire; (2) evaluating species exposure by identifying natural land use that aligns with the potential distribution areas of biodiversity; (3) assessing species vulnerability based on the classifications established by the IUCN and CONABIO. Our findings have unveiled three regions exhibiting a concentration of high-risk values. Among these, two are positioned near major urban centers, while the third lies in the southeastern sector of the Nevado de Toluca protection area. Amphibians emerged as the taxonomic group most severely impacted, with a substantial number of species falling within the Critically Endangered and Endangered categories, closely followed by mammals and reptiles. Furthermore, we have identified a correlation between the location of risk zones and agricultural areas. This study revealed hotspots that can offer valuable guidance for strategic initiatives in fire-prone regions associated to the potential distribution of amphibians, mammals, and reptiles. Moreover, future studies should contemplate integrating field data to enhance our comprehension of the actual effects of wildfires on the spatial distribution of these animal groups.

Formas de vida de la vegetación en el límite superior de un bosque de alta montaña en México

The objective of the present study was to characterize the diversity of life forms and the plant community structure along an altitudinal gradient of the treeline ecotone of Pinus hartwegii Lindl. at Nevado de Toluca, Mexico. Plant species in the treeline ecotone were sampled, identified, and quantified according with the life forms. Diversity of life forms of the ecotone was calculated according to the Shannon diversity Index, and the structure was evaluated based on the density and abundance of plant species. A total of 43 plant species belonging to 30 genera and 18 botanical families were identified. Chamaephytes were the most abundant life form (>50 %), with increasing altitude, the diversity of life forms increased, while the abundance of life forms decreased. Species diversity was proportionally and significantly related accordingly to one-way ANOVA, with increasing altitude along the treeline ecotone. Pinus hartwegii treeline ecotone was diffuse in form and characterized by greater abiotic stress conditions at higher altitudes which was not observed in this case, due to the altitudinal range sampled, and to the fact that this ecotone represents the forest species distribution limit and the beginning of grassland distribution. At high altitudes life forms experiment greater selective pressures and must be adapt to extreme environmental conditions, which increase with the altitude. Also, distinct life forms present at the treeline ecotone of P. hartwegii may modify environmental conditions or processes and therefore regulate the response of other associated species to climate change.

A socio-ecological evaluation of the conservation efforts in the Nevado de Toluca protected area, Mexico: Governmental performance and local community perception from a rural context

Abstract Protected Areas (PA) are the main conservation instrument in Latin America, but rural communities are rarely integrated into the decision-making. In Mexico, many conflicts related to PAs stem from guaranteeing equitable access to resources for local communities against private economic interests. The aim of this manuscript is to present a strategy to evaluate the functioning of the PA from a socio-ecological perspective, including: diagnosis, evaluation of the conservation instrument, and intervention proposal. The results show that the Nevado de Toluca PA was recategorized without adequate characterization of the problems facing its conservation. The impact has been biased towards the development of large-scale activities while local communities have been excluded. This scenario has resulted in a migration of local men to cities in search of work, while women and children face unequal management of natural resources. In terms of aquatic ecological quality, indicators show signs of degradation that have not been improved through the management plan. The activities proposed in the annual operational plans are unrealistic since they include no support and training. We propose participatory monitoring as a strategy for community empowerment in the use of water resources, as well as a cohesive element that reconciles government policies and local needs.

Livestock in the sustainability of changing livelihoods in high mountain communities in a Natural Protected Area in Central Mexico

Objective: Livelihoods of communities within the high mountain Natural Protected Area for Flora and Fauna ‘Nevado de Toluca’ (NPAFFNT) in the central highlands of Mexico have changed due to statuary limitations established in management program respect to agro-silvopastoral activities. In these communities, the small scale farmers who still rely on livestock, mainly sheep production. There is no knowledge on the sustainability, strengths and weaknesses of these systems and the influence of seasons in this area of marked bioclimatic seasonality. Methodology: The IDEA method to assess sustainability was applied in a small village within NPAFFNT in the dry as in the rainy season. Results: Sustainability is limited by the economic scale while their main strengths were in the agroecological scale in both seasons. Indicators show deficiencies in farmer education, lack of technical assistance, poor local infrastructures, lack of access to institutional support programmes, and the revision of norms for the natural protected area. Conclusions and implications: Results are useful for improving the sustainability of these systems that may improve que quality of life of high-mountain communities and provide ecosystemic services relevant for society. Diversification of income sources are of needed given the limitations that the new statute create on livestock and agricultural activities. It is advisable to increase the educational level of the inhabitants and farmers receive specialized technical training in agricultural and sustainable livestock production.

Phenotypic plasticity of growth ring traits in Pinus hartwegii at the ends of its elevational gradient.

Phenotypic plasticity (PP) could be an important short-term mechanism to modify physiological and morphological traits in response to climate change and global warming, particularly for high-mountain tree species. The objective was to evaluate PP response of growth ring traits to temperature and precipitation in Pinus hartwegii Lindl. populations located at the ends of its elevational gradient on two volcanic mountains in central Mexico (La Malinche and Nevado de Toluca). Increment cores collected from 274 P. hartwegii trees were used to estimate their PP through reaction norms (RN), which relate the ring width and density traits with climate variables (temperature and precipitation). We estimated the trees' sensitivity (significant RN) to climatic variables, as well as the relative proportion of RN with positive and negative slope. We also estimated the relationship between the PP of ring width and density traits using correlation and Principal Component (PC) analyses. Over 70% of all trees showed significant RN to growing season and winter temperatures for at least one growth ring trait, with a similar proportion of significant RN at both ends of the gradient on both mountains. Ring width traits had mostly negative RN, while ring density traits tended to have positive RN. Frequency of negative RN decreased from lower to higher elevation for most traits. Average PP was higher at the lower end of the gradient, especially on LM, both for ring width and ring density traits, although high intrapopulation variation in PP was found on both mountains. Results indicate that P. hartwegii presents spatially differentiated plastic responses in width and density components of radial growth. PP was particularly strong at the lower elevation, which has higher temperature and water stress conditions, putting these populations at risk from the continuing global warming driven by climate change.

Food web differences between two neighboring tropical high mountain lakes and the influence of introducing a new top predator.

High mountain lakes (HMLs) are considered unique and comparable ecosystems for monitoring global climate change. The food web structure can indicate the response of these ecosystems to ecological threats, such as fish introduction, by analyzing the trophic dynamics. Nonetheless, the food webs of tropical HMLs are less well-studied than temperate HMLs. The present study assessed the food webs of two neighboring (600 m apart) tropical HMLs, El Sol and La Luna, inside the crater of the Nevado de Toluca volcano, Mexico. It used stable isotopes (δ13C and δ15N) and Bayesian mixing models with different trophic discrimination factors and priors to assess the impacts of introduced rainbow trout, persisting only in the larger lake, El Sol. The food web in Lake El Sol was more complex than in Lake La Luna, mainly due to its larger size, extensive vegetated littoral zone, and being fueled by autochthonous primary production. In contrast, the smaller and fishless Lake La Luna has a reduced and bare littoral zone that harbored a simple food web substantially sustained by allochthonous carbon inputs. The persistence of introduced rainbow trout in Lake El Sol but not in Lake La Luna accentuated the differences between the lakes. The models suggested that rainbow trout fed on key consumers of littoral macroinvertebrates (70-80%) and pelagic zooplankton (20-30%), increasing the linkage between sub-networks. In both tropical HMLs, the species richness and herbivorous fraction were elevated compared with temperate HMLs, while the linkage density and omnivorous fraction were lower. Basal nodes dominated these tropical HMLs, and the vegetated littoral zone of Lake El Sol had more intermediate (omnivore) nodes. Our results showed the convenience of food web analysis to compare the effects of introduced fish in originally fishless lakes in different latitudes.

Analysis of the Vigor of Pinus hartwegii Lindl. along an Altitudinal Gradient Using UAV Multispectral Images: Evidence of Forest Decline Possibly Associated with Climatic Change

Future climate forecasts predict major changes that will have negative impacts on the distribution, abundance, and dynamics of forest ecosystems. In Mexico, there is evidence of symptoms of massive forest decline; however, there is no consensus in terms of attributing these symptoms to climate change. This study aimed to provide evidence of forest decline possibly associated with climatic change in the highland pine (Pinus hartwegii Lindl.) populations of the Nevado de Toluca Flora and Fauna Protection Area. Using unmanned aerial vehicles (UAV) equipped with multispectral sensors, the study applied digital photogrammetry techniques, automated tree crown detection algorithms, and calculation of the normalized difference vegetation index (NDVI) and leaf chlorophyll index (LCI) to assess forest health across an altitudinal transect (from 3300 m to the timberline at 4040 m elevation). Climate analysis was conducted with TerraClimate data using mean annual temperature (MAT), April temperature, and Palmer Drought Severity Index (PDSI) from the studied altitudinal transect and its xeric limit. We found that lower altitude populations had significantly higher stress levels, indicating forest decline phenomena, while intermediate altitude populations showed greater vigor of the detected trees. Statistically significant differences in the NDVI and LCI values along the altitudinal gradient provided evidence of forest decline in terms of forest vigor and productivity, with the greatest disturbance found at the lower altitude of the examined forest species. The analysis of the climatic data revealed an increase in April temperature +1.4 °C of the xeric limit of the transect (low altitude) when comparing the reference period, 1961–1990 (mean: 12.17 °C), with the decade prior to our study (2011–2020; mean: 13.57 °C). This would be equivalent to an upward shift in elevation of 280 m of the xeric limit. In addition, the PDSI analysis revealed that droughts are becoming increasingly intense at a rate of 0.06 PDSI units per decade, with greater intensity in the last five years. These findings highlight the negative impacts of climate change on forest ecosystems and the urgent need for alternative forest management and conservation practices to increase resilience and adaptation in the temperate forests of Mexico. This study sets a precedent for further research to improve our understanding of the impacts of climate change on forest ecosystems and the development of sustainable management practices.

Contexto ambiental dos processos de mudança de uso e cobertura da terra em Calimaya, Altiplano Mexicano

The convergence of conventional agriculture, real estate investments and sand and gravel mining characterize Calimaya as one of the most negatively impacted municipalities of the Mexican altiplano by anthropic activities. The objective of this work was to analyse the geographical and environmental context of land use and land cover change (LULCC) processes in this Municipality. For this, the following indicators were estimated: the cover change rate proposed by Food and Agriculture Organization of the United Nations by using the land cover classes proposed by the Intergovernmental Panel on Climate Change. LULCC in the last decade (2010-2019) were: deforestation and advancement of potato crop in the Nevado de Toluca Flora and Fauna Protection Area; decrease in the process of occupation of cropland areas by settlements; and, soil degradation in abandoned mines.

Insights into the plumbing system of Colima Volcanic Complex from geophysical evidence

The Colima Volcanic Complex (CVC) consists of three stratovolcanoes: El Cántaro, Nevado de Colima and Volcán de Colima, aligned from north to south, with the same chronological order. It has been assumed that the magmatic system also has migrated in the same direction, with the surface trend of the volcanic edifices following the same pattern at depth. However, 3D inversion of gravimetric and aeromagnetic data, combined with spectral analysis (Werner deconvolution) give a detailed analysis of the CVC magmatic system, resulting in a new model of its geometry and migration, which takes into account the rifting process of the Colima Graben, and the separation of the Jalisco and Michoacán Blocks. The resulting fractures favor magma ascent through the western Michoacán Block boundary, which follows a NE-SW direction and gradually changing its angle, becoming more vertical close to Volcán de Colima. This research shows that the CVC magmatic system is best described as a Trans-crustal mush system, characterized by a zone of crystal rich magma storage located within the structural system. The direction of the magmatic migration at depth does not correspond to vertical ascent, illustrated by the lack of correlation with the volcanic edifices on the surface. Additionally, in the results it is possible to identify the separation between distinct phases of the magma, whereby the lower viscosity mobile phase is located in distinct zones within the upper crust, feeding the activity of Volcán de Colima.

Warming effects on tree-ring variables in P. hartwegii Lindl. at the extremes of its natural elevational distribution in central Mexico

In alpine forests, the impact of warming differs at the upper and lower extremes of the elevation gradient causing trees to compensate through different adaptive mechanisms. The objective was to retrospectively evaluate the radial growth response to recent interannual climate variation in Pinus hartwegii trees growing at the extremes of their elevational gradient on two volcanic mountains in central Mexico (La Malinche and Nevado de Toluca). Increment cores collected from 174 P. hartwegii trees were used to estimate time-series of growth ring including ring width and density variables, as well as basal area increment (BAI) and ring biomass (BIO) for 1964–2016. Differences in average radial growth and time-trends of ring variables in response to climate variables were estimated based on correlations of ring variables, BAI, and BIO with inter-annual variation in temperature, rainfall, and length of the frost-free period (FFP). Results showed higher average values of ring width and density variables, as well as BAI and BIO (i.e., higher productivity) at low elevation on both mountains. Time-trends for BAI and BIO were positive at both ends of the elevation gradient, but ring width and density variables followed opposite trends. Inter-annual variation of ring variables was explained more by temperature than by rainfall or FFP; however, temperature was negatively correlated with RW and positively with RD, even though BAI and BIO were positively correlated with temperature (All them with P < 0.001) at both elevational end on both mountains. For most of the ring variables, the total variation explained by the ANOVA model was more related to the linear warming trend (greater than 67%). Warming is affecting radial growth of P. hartwegii trees differently at high versus low elevation on both mountains, showing warning signs from the perspective of functional traits, but not in terms of productivity.

The shallow three-dimensional structure of Volcán de Colima revealed by ambient seismic noise tomography

Volcán de Colima is one of the most active volcanoes in North America. Even so, it has a poorly constrained upper crustal structure. Here, we present the highest-resolution three-dimensional shear-wave velocity tomography to date of the volcano.We measured group velocity dispersion curves of Rayleigh and Love waves extracted from ambient seismic noise recorded on the Colima Volcanic Complex and regionalised them into 2-D velocity maps. Those were then locally inverted using a neighborhood algorithm to obtain accurate shear-velocity models down to 4 km below sea level. The resulting three-dimensional shear wave velocity model gives us a new insight into the internal structure of the volcano to specifically better understand the shallow magma storage and magmatic plumbing system and, in turn, how it can be placed in a wider geotectonic context.Our results highlight a network of deeply rooted NE-SW low velocity zones oriented along a local fault system. The southward orientation of this low-velocity anomaly also roughly aligns with the north-south trend of the volcanoes that compose the quaternary Colima Volcanic Complex and could be associated with the gradual trenchward shift of the magmatic front of the volcanic complex dating from the formation of the Cántaro Volcano. The low-velocity anomaly overlaps a negative radial anisotropy indicating that magma follows vertically oriented structures, such as interfingered dikes or faults and cracks with a substantial vertical component.The low velocity anomaly under Volcán de Colima contrasts with a distinct high-velocity anomaly under Nevado de Colima that highlights the difference between the former active system, filled with solidified dikes and sills, and the current one, associated with a network of fluid-filled dikes.

Thermal Regime and Water Balance of Two Tropical High-Mountain Lakes in the Nevado de Toluca Volcano, Mexico

High-mountain lakes are unique ecosystems with very few examples at tropical latitudes for experimentation. A two-year, high-frequency meteorological and water-column dataset from the crater of the Nevado de Toluca volcano, in Mexico, at an altitude of about 4200 m above sea level, allowed for the study of temporal changes in the thermal structure, water level, and water balance in the Lakes El Sol and La Luna, separated by about 500 m by a lava dome. Annual fluctuations in the water level of the lakes and calculations of the annual variability of the water balance showed that the lakes accumulated almost four times less water from rainfall than expected. Furthermore, the temperature measured at a depth of 15 cm in the bottom sediments of Lake El Sol revealed an unexpected warming during the cold season. Estimated heat fluxes through the lake bottom were less than 0.3 W m−2 during the winter and less than 0.1 W m−2 during the rest of the year. Although the variability of the hydrometeorological regime of high-mountain lakes remains relatively poorly understood, our results significantly improve the understanding of these complex processes of stratification and mixing in these unique lake ecosystems.

Modeling spatial landslide susceptibility in volcanic terrains through continuous neighborhood spatial analysis and multiple logistic regression in La Ciénega watershed, Nevado de Toluca, Mexico

Modeling spatial landslide susceptibility in volcanic terrains through continuous neighborhood spatial analysis and multiple logistic regression in La Ciénega watershed, Nevado de Toluca, Mexico

Magma and Mineral Composition Response to Increasing Slab-Derived Fluid Flux: Nevado de Longaví Volcano, Southern Chilean Andes

Nevado de Longaví volcano (NLV), in the Southern-Central Chilean Andes, has erupted during the Holocene magmas with compositions that are in several ways atypical for the region. These characteristics include elevated La/Yb ratios in evolved magmas, in an area of only moderately thick crust, coupled with low concentrations of K, Th, and other incompatible elements and elevated ratios of fluid-mobile (B, Cs, Li, Sb) to fluid-immobile elements. Samples have an unusual mafic mineralogy dominated by amphibole. The petrology of the Holocene products of NLV have been related to the influence of an oceanic transform fault (Mocha Fracture Zone; MFZ) that supplies the mantle wedge with unusually high amounts of fluids via dehydration of serpentinite bodies hosted by the subducted oceanic lithosphere. Because the trace of this transform fault is oblique to the convergence vector, its position along the arc has varied through time, as has the magnitude of its influence on the nature of the magmas erupted at NLV. The whole-rock and mineral chemistry of volcanic products from NLV, tied to a simplified stratigraphy, documents the secular changes in the magmatic system as the oceanic fault approached its current position. Magmas erupted ∼1–0.6 Ma are relatively low in water (as inferred from mineralogy and chemical proxies) and reduced (NNO-1 to NNO+0.5), and are similar to compositions found in neighboring volcanoes. From 0.25 Ma to the present, magmas are water-rich and oxidized (NNO-0.5 to NNO+1.7). In the intervening 0.6–0.25 Ma, mafic magmatism acquired a transient crustal component, which we identify as subducted sediment melts, on the basis of radiogenic isotopes and Pb, Th, and U abundances. Fluids released from serpentinite in the fracture zone were rich in Li, B, Sb, Cs and Ba, but not in K, Th, U and Sr. The fluid addition led to enhanced melting, particularly hydrous magmas that stabilized amphibole early during fractionation, higher oxygen fugacities, and distinctive chemical compositions.

Organochlorine pesticides and polychlorinated biphenyls in high mountain lakes, Mexico.

Pollution levels of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) were investigated in the El Sol and the La Luna alpine lakes. The lakes are located in central Mexico, in the crater of the Nevado de Toluca volcano. The El Sol and the La Luna lakes are extremely relevant in Mexico and in the world because they are recognized as pristine regions and environmental reservoirs. Samples of atmospheric aerosol, sediment, plankton, and Tubifex tubifex (sludge worm) were collected at three different sample locations for three years (2017, 2018, and 2019) at three different times of year, meaning that the weather conditions at the time of sampling were different. Pollutants were analysed by gas chromatography-mass spectrometry with negative chemical ionisation (GC-MS/NCI). Endosulfan was the most frequent and abundant pollutant, showing the highest peaks of all. Atmospheric aerosol revealed Σ2 = 45pg/m3, including α and β, while sediment lakes displayed α, β and endosulfan sulfate as Σ3 = 1963pg/g, whereas plankton and Tubifex tubifex showed Σ2 = 576pg/g and 540pg/g for α and β respectively. Results of endosulfan ratios (α/β) and (α-β/endosulfan sulfate) suggest that both fresh and old discharges continue to arrive at the lakes. This study shows for the first time the pollution levels of OCP and PCB in high mountain lakes in Mexico. These results that must be considered by policy makers to mitigate their use in the various productive activities of the region.