Lithostratigraphic analysis and geochemistry of a vitric spatter-bearing ignimbrite: the Quaternary Adeje Formation, Cañadas volcano, Tenerife

"The 1.5-Ma Adeje Formation in SW Tenerife contains an ignimbrite sheet with remarkable textural and chemical complexity. A basal Plinian pumice-fall layer is overlain by a partly welded compound ignimbrite in which phonolitic pumice lapilli and dense obsidian spatter rags with irregular, fluidal-shaped margins are supported in a poorly sorted tuff matrix. The lower ignimbrite flow-unit contains accretionary lapilli in its upper part, overlain by an ash-pellet-bearing fallout layer from a co-ignimbrite plume. The upper ignimbrite flow-unit comprises a locally welded massive lapilli-tuff that grades up into lithic breccia containing juvenile obsidian blocks and both cognate and vent-derived lithic blocks. Geochemically, the Adeje Formation shows two distinct juvenile populations that relate to crystal-poor and crystal-rich magma types. Crystal-rich juvenile clasts contain multiple compositions of ilmenite and magnetite, and crystal aggregates of bytownite (An79-86). The varied assemblage of juvenile clasts reflects an eruptive style that may have involved rapid changes in magma chamber pressure associated with caldera collapse, and possibly the disruption of a lava lake. The Adeje eruption started with a Plinian explosive phase that rained ash and pumice lapilli across SW Tenerife; followed by pyroclastic fountaining feeding density currents with explosive ejecta of juvenile glassy material producing the coarse, spatter-bearing ignimbrite facies. A short pause between pyroclastic density currents is recorded by the co-ignimbrite ash and pellet-fall bed. The climactic phase of the eruption probably involved caldera subsidence as recorded by a widespread massive heterolithic breccia.

Alternating Subplinian and phreatomagmatic phases during the construction of a phonolitic maar-diatreme volcano (Caldera del Rey, Tenerife, Canary Islands)

The Early Pleistocene, well exposed, Caldera del Rey maar-diatreme volcano, Tenerife, Canary Islands was constructed during a ∼ VEI 4 phonolitic eruption that involved two cycles of magmatic-to-phreatomagmatic activity and resulted in two overlapping craters aligned NE-SW. Magmatic phases fed unsteady Subplinian eruption columns that reached 8–12 km altitude and dispersed tephra to the west and southwest of the volcano and shed pyroclastic density currents. Phreatomagmatic phases, driven by explosive interactions between magma and groundwater, constructed an extensive tephra ring via deposition from ballistic curtains, pyroclastic density currents, and tephra fall. Near-optimal-scaled depth phreatomagmatic explosions (strong and/or shallow) excavated a substantial diatreme beneath the north crater and constructed a substantial tephra ring. This abruptly transitioned to deeper-than-optimal scaled depth explosions (weak and/or deep) that erupted mostly fine ash which was dispersed by dilute pyroclastic density currents and fallout and filled the south crater. At distances of >4 km from the volcano, over a metre of ash and pumice accumulated during the phreatomagmatic phases. The Caldera del Rey volcano provides an instructive study on how interaction between ascending felsic magma and groundwater can modify Subplinian eruptions

Deep-seated gravitational slope deformations triggered by extreme rainfall and agricultural practices (eastern Michoacan, Mexico)

"The study of deep-seated gravitational slope deformations (DSGSD) in Mexico is scarce; therefore, their localization and causes are highly overlooked. The present paper examines the characterization of the DSGSD of Jungapeo and Las Pilas in eastern Michoacan state, currently active and endangering their inhabitants. An integrated study, including detailed lithology, morpho-structural inventories, analysis of land use, and pluviometric regime, was performed and complemented with differential global positioning system monitoring networks. Both landslides developed over highly weathered volcano-sedimentary rocks. On the one hand, the Jungapeo landslide has an estimated volume of 990,455 m3 with steady decreasing velocity rates from 41 to 15 cm/month in the first monitoring period to 13–3 cm/month in the last one. On the other hand, the Las Pilas landslide estimated volume is about 1,082,467 m3 with a stable velocity rate of 1.3 to 0.1 cm/month. Despite the multi-storeyed style of activity, two behaviors of instability were distinguished: slow deformation and secondary landslide stages. The conditioning factors for slow deformation in both DSGSD are the combination of weathered lithology with clay- and sand-rich content, and the shift toward intensive monoculture. The triggering factor is related to excess water produced by an inefficient flood-irrigation system that also generates an atypical acceleration behavior in both landslides during the dry season. The DSGSD activity thus predisposes the generation of tension cracks and secondary scarps from which the collateral landslides are triggered by atypical rainfall, such as that of 2010.

Nonlocal anisotropic dispersal with monostable nonlinearity

We study the travelling wave problem J\astu - u - cu' + f (u) = 0 in R, u(-\infty) = 0, u(+\infty) = 1 with an asymmetric kernel J and a monostable nonlinearity. We prove the existence of a minimal speed, and under certain hypothesis the uniqueness of the profile for c = 0. For c = 0 we show examples of nonuniqueness

Eruption of Shallow Crystal Cumulates during Explosive Phonolitic Eruptions on Tenerife, Canary Islands

The recent eruptive history on the island of Tenerife is characterized in part by the presence of zoned phonolitic ignimbrites, some of which prominently display two types of juvenile clasts (i.e. light-colored, aphyric pumices alongside darker, more crystal-rich pumices, here dubbed ‘crystal-poor' and ‘crystal-rich', respectively). Petrographic observation of the crystal-rich pumices reveals intensely resorbed and intergrown mineral textures, consistent with the system reaching a high crystallinity, followed by perturbation and remobilization prior to eruption. Some trace elements show anomalous concentrations in such crystal-rich pumices (e.g. bulk Ba > 2000 ppm alongside low Zr and a positive Eu anomaly) indicative of crystal accumulation (of feldspar ± biotite). Many biotite and feldspar crystals are reversely zoned, with rim concentrations that are high in Ba but low in Sr, implying crystallization from an ‘enriched' melt, potentially derived from remobilization by partial melting of the aforementioned cumulate zones. Given (1) the presence of cumulates in the eruptive record on Tenerife and a bimodality of pumice textures, (2) the presence of three dominant compositions (basanite, phonotephrite, phonolite, separated by compositional gaps) in the volcanic record, and (3) abundant support for crystal fractionation as the dominant drive for magmatic evolution in Tenerife, it is hypothesized that crystal-poor magmas are extracted from mushy reservoirs in both the lower and upper crust. The thermodynamic software MELTS is used to test a polybaric differentiation model whereby phonolites (sensu lato) are generated by extraction of residual liquids from an intermediate-crystallinity phonotephritic mush in the upper crust, which is in turn generated from the residual liquids of an intermediate-crystallinity basanitic mush at deeper levels. Latent heat spikes following crystallization of successive phases in the upper crustal reservoir provide a thermal buffering mechanism to slow down cooling and crystallization, permitting enhanced melt extraction at a particular crystallinity interval (mostly ∼40-60 vol. % crystals). MELTS modeling typically fits the observed chemical data adequately, although some major elements (mostly Al2O3) also indicate partial ‘cannibalization' of feldspar along with some magma mixing (and potentially minor crustal contamination

Evolución volcánica del maar Joya de Los Contreras, San Luis Potosí México, a partir de estratigrafía y análisis de facies

La Joya de Los Contreras es una de cuatro estructuras freatomagmáticas que forman parte del Campo Volcánico Santo Domingo, un campo volcánico monogenético asociado a magmatismo intraplaca del Pleistoceno al norte del estado de San Luis Potosí (México), relacionado a fallamiento extensional y adelgazamiento cortical. Estudios previos incluyen geoquímica de lavas y xenolitos, pero no abundan en la evolución volcánica de la secuencia piroclástica. La Joya de los Contreras es un cráter volcánico excavado en calizas (Formación El Abra, Cretácico superior), de forma elíptica y dimensiones de 1,160 m de diámetro por 210 m de profundidad. Expone lavas máficas en la base (basanitas), un anillo de tobas muy bien preservado y expuesto, y también lavas máficas en la cima de la secuencia. Con el objeto de conocer los procesos magmáticos y freatomagmáticos que le dieron origen, se desarrolló un levantamiento estratigráfico y análisis de facies, petrografía, granulometría, componentes y geoquímica. La secuencia se compone de 1) Unidades pre-maar, lavas máficas, basanitas y aglomerados; 2) Unidades formadoras del maar, tobas conformando el anillo; y 3) Unidades post-maar, lavas coronando la secuencia. Se fechó una de estas últimas en 447 ± 11 ka (edad 40Ar/39Ar en roca total). La historia volcano-estratigráfica resulto en la reconstrucción de 5 fases eruptivas que van de efusiva-estromboliana pre-maar a freatomagmática explosiva, con variaciones en proporciones de interacción agua-magma y cerrando estromboliana-efusiva post-maar. Aunque no hay evidencia directa de una diatrema a profundidad, se infiere su existencia en base a diversos criterios geomorfológicos, tales como el alto volumen de material calcáreo lítico en el anillo de tobas (excavación y relleno – reciclaje), la relación de aspecto del cráter y su relleno

Distributed stress fluidisation: Insights into the propagation mechanisms of the Abona volcanic debris avalanche (Tenerife) through a novel method for indurated deposit sedimentological analysis

Introduction: Volcanic debris avalanches mobilise large volumes and achieve long runouts with high destructive potential. However, the propagation processes that generate them are not currently explained by theoretical or numerical models, which are unable to represent deposit observations. Evaluation of the dynamics represented in deposits is therefore vital for constraining su ch models. The Abona volcanic debris avalanche deposit is located on the southern flank of the island of Tenerife, Spain. The deposit exhibits universal microfracturing and cataclasis. Fluidal features such as fluidal mixing of lithological units and diffuse boundaries, and mixed matrix are observed throughout the deposit.Methods: Field description including sedimentology and facies identification and the evaluation of their distribution have allowed the generation of a new conceptual model for the propagation dynamics of this volcanic debris avalanche, and potentially others with similar properties. The deposit is indurated making the detailed study of its sedimentology difficult, especially clast-size analysis. A novel method utilising structure from motion photogrammetry and photographic sampling was employed.Results: The universal cataclasis of the material and fluidal features suggest that the lack of a major competent material component allowed the mass to fragment and enabled fluidised granular flow behaviour. It is proposed that shear was periodically distributed throughout the body of the avalanche in chaotic temporary shear networks rearranging according to the instantaneous distribution of the mass. Stress and agitation were not temporally or spatially homogenous during propagation. This is also reflected in the unsystematic erosion of the substrate according to the variable basal shear accommodation.Discussion: It is proposed that lithological properties are potentially a determining factor for the propagation mechanisms, stress distribution, and consequently the evolution of a volcanic debris avalanche from the initial collapse to its emplacement. This study highlights the importance of dedicated field examinations of sedimentological, morphological, and structural features for providing constraints for models of volcanic debris avalanche dynamics and the factors dictating them. The novel methodology proposed has the potential of broadening the number of events that can be studied and enhancing the understanding of these complex and hazardous phenomena

Disruption of long-term effusive-explosive activity at Santiaguito, Guatemala

Rapid transitions in eruptive activity during lava dome eruptions pose significant challenges for monitoring and hazard assessment. A comprehensive understanding of the dynamic evolution of active lava dome systems requires extensive sets of multi-parametric datasets to fully constrain and understand shifts in eruptive behavior, but few such datasets have been compiled. The Santiaguito lava dome complex, Guatemala, is a remarkable example of an open-vent volcanic system where continuous eruptive activity has typically been characterized by cycles of effusion and frequent, small to moderate, gas-and-ash explosions. During 2015–2016 the volcano experienced a rapid intensification of activity including large vulcanian explosions, frequently accompanied by pyroclastic density currents. Here we present a chronology of the eruptive activity at Santiaguito from November 2014–May 2017, compiled from field observations (visual and thermal) and activity reports. We also present seismic and acoustic infrasound data collected during the same period, the longest and largest dataset collected at Santiaguito to date. Three major phases of eruptive activity took place during the study period. The first phase was consistent with the long-term eruptive behavior reported at Santiaguito by previous studies: lava effusion simultaneous with small (<1 km plume height), regular (25–200 min intervals), gas-and-ash explosions. The second phase from July 2015 to September 2016 was defined by large (<5–7 km plume height) vulcanian explosions at irregular intervals and often accompanied by pyroclastic density currents. The third phase was marked by a return to effusive activity in October 2016 interspersed by small, gas-rich explosions. Over 6,000 explosive events were recorded by seismic and infrasound during the study period and clearly delineate the three phases of activity at the volcano. Furthermore, we present the first documented geophysical evidence of explosion blast waves and volcano-tectonic earthquake swarms at Santiaguito. An important implication of our observations is that negative trends in explosion rates at silicic lava dome eruptions cannot be used alone as an indicator of future weaker activity and reduced hazard. This case study of Santiaguito will serve as a useful foundation for future studies of long-lived lava dome eruptions featuring rapid transitions between effusive and explosive activity

Vegetation optical depth at L-band and above ground biomass in the tropical range: Evaluating their relationships at continental and regional scales

Abstract The relationship between vegetation optical depth (VOD) retrieved by L-band SMOS radiometer and forest above ground biomass (AGB) was investigated in tropical areas of Africa and South America. VOD was retrieved from the latest version of level 2 SMOS algorithm, while reference AGB was obtained from a pantropical database, encompassing a large number of ground plot data derived from field surveys conducted on both continents. In Africa and South-America, VOD increased with AGB, reaching saturation at about 350 Mg ha−1. The strength of the relation was improved selecting VOD data in appropriate seasons, characterized by a higher dynamic range of values. The capability of VOD data to estimate AGB was further investigated using Random Forest decision trees, adding to VOD selected climate variables from the Climatic Research Unit (temperature, potential evapotranspiration, and precipitation) and water deficit data, and validating regression tests with ground data from the reference AGB database. The results for the five analyzed years indicate that the best estimates of AGB are obtained by the joined use of VOD and potential evapotranspiration input data, but all climate variables brought an improvement in AGB estimates. AGB estimates were relatively stable for the considered period, with limited variations possibly due to changes in biomass and to data quality of VOD and of climate variables. The VOD signal and estimated AGB were also analyzed according to ecological homogeneous units (ecoregions), evidencing data clusters, partially overlapped to each other, in the VOD - AGB plane