Localised heating and intensive magmatic conditions prior to the 22–23 April 2015 Calbuco volcano eruption (Southern Chile)

Calbuco volcano is a Late Pleistocene composite stratovolcano and member of the Southern Volcanic Zone of the Chilean Andes (41°19′S, 72°36′W). It lies ~ 20 km west of the Liquiñe–Ofqui Fault Zone, but is not located directly upon any major regional structures. During April 2015, a sub-Plinian eruption occurred, with a bulk erupted volume of ~ 0.3–0.6 km3 (~ 0.1–0.2 km3 DRE). The eruption was a rapid-onset event that produced highly crystalline products (from 40 to 60 vol.%) including the mineral phases: plagioclase, clinopyroxene, orthopyroxene, amphibole, olivine, apatite, ilmenite, titanomagnetite and chalcopyrite. An upper-crustal reservoir is inferred using available geophysical data combined with amphibole geobarometry. Consideration of textural features, including high crystallinity, complex mineral zonation, crystal clots and interstitial glass between crystals from clots, suggests the presence of a mush zone within this reservoir. From the nine collected samples, whole-rock chemistry and an array of geothermometers (amphibole, amphibole-plagioclase, two-pyroxenes and Fe–Ti oxides) gave similar results for all samples possessing ~ 40 vol.% of crystals, with the exception of the sample Cal-160 (~ 60 vol.% crystallinity), which is slightly more evolved and yields lower temperatures for all geothermometers. By comparing temperatures calculated in sample Cal-160 using pairs of ilmenite-titanomagnetite core compositions with those calculated using rim compositions, we observe a late-stage temperature increase of between 70 and 200 °C. We suggest that this local-scale heating event was at least partly responsible for triggering the eruption. Our data suggest that the bulk of the erupted magma was derived from a relatively uniform (970–1000 °C), crystal-rich magma mass. Sample Cal-160 was derived from a cooler environment (910–970 °C), where it was subjected to pre-eruptive heating to temperatures considerably higher than those observed in associated, erupted magmas (up to 1070 °C). This requires the involvement of a hot, presumably mafic magma injection at the base of a shallow, crystal-rich reservoir, though the mafic magma was not itself erupted. The localised nature of interaction and rapidity of eruption onset have implications for potential future hazards at Calbuco volcano

Liraglutide increases serum levels of microRNA-27b, -130a and -210 in patients with type 2 diabetes mellitus. a novel epigenetic effect

Liraglutide has shown favourable effects on several cardiometabolic risk factors, beyond glucose control. MicroRNAs (miRNAs) regulate gene expression, resulting in post-transcriptional modifications of cell response and function. Specific miRNAs, including miRNA-27b, miRNA-130a, and miRNA-210, play a role in cardiometabolic disease. We aimed to determine the effect of liraglutide on the serum levels of miRNA-27b, miRNA-130a and miRNA-210. Twenty-five subjects with type-2 diabetes mellitus (T2DM), naïve to incretin-based therapy, were treated with liraglutide (1.2 mg/day as an add-on to metformin) for 4 months. miRNAs were quantified using real-time polymerase chain reaction. After liraglutide treatment, we found significant reductions in fasting glucose (from 9.8 ± 5.3 to 6.7 ± 1.6 mmol/L, p = 0.0042), glycosylated haemoglobin (HbA1c) (from 8.1 ± 0.8 to 6.6 ± 1.0%, p = 0.0008), total cholesterol (from 5.0 ± 1.0 to 4.0 ± 0.7 mmol/L, p = 0.0011), triglycerides (from 1.9 ± 1.0 to 1.5 ± 0.8 mmol/L, p = 0.0104) and low-density lipoprotein cholesterol (from 2.9 ± 1.2 to 2.2 ± 0.6 mmol/L, p = 0.0125), while the serum levels of miRNA-27b, miRNA-130a and miRNA-210a were significantly increased (median (interquartile range, IQR) changes: 1.73 (7.12) (p = 0.0401), 1.91 (3.64) (p = 0.0401) and 2.09 (11.0) (p = 0.0486), respectively). Since the changes in miRNAs were independent of changes in all the metabolic parameters investigated, liraglutide seems to exert a direct epigenetic effect in T2DM patients, regulating microRNAs involved in the maintenance of endothelial cell homeostasis. These changes might be implicated in liraglutide’s benefits and may represent useful targets for cardiometabolic management

Rheology and dynamics of lava flows

This thesis presents the results of laboratory experiments, theoretical analysis, field work and petrological analysis conducted to study the rheology and dynamics of lava flows. The rheology of suspensions of cubic crystals in viscous liquids was investigated with a series of experiments, consisting of the release of a fixed volume of fluid inside a horizontal channel. A Herschel-Bulkley rheology was assumed and the consistency K and the shear rate exponent n of this constitutive equation were calculated using the evolution of the flow front; the yield strength was calculated using the final shape of the flow. Results show an increase in K when crystal content increases. The mixtures start to show a shear thinning behaviour at 4>-0.3 with n values going from approximately 1 (Newtonian behaviour) to 0.5 at 4>=0.6. Yield strength was detected at the same 4> as the beginning of shear thinning behaviour and increases with a power-law relationship with crystal content. Suspensions with bimodal crystal sizes show a dramatic decrease of the apparent viscosity compared to unimodal suspensions, especially at the higher total crystal concentrations. Further experiments, with the same types of fluids (with approximately Herschel- Bulkley rheology) in a sloping channel with a constant flux rate were approximated with a simplified 2-D model. The results show an excellent agreement between the theory and the experiments. Additionally, experiments with two fluids, where a low viscosity fluid (syrup) is injected in a fixed volume of more viscous material (syrup plus crystals) suggest that the front advance and height is controlled mainly by the rheology of the fixed volume fluid. The simplified 2-D theory was applied to real lava flows. Three dynamical regimes were considered: A Newtonian viscous regime, a yield strength-dominated regime, and a crust-dominated regime. The resulting equations were applied to published data from eruptions of 10 lava flows with a range of compositions and conditions. Comparisons of the fits of the models to the data reveal that short-lived, high effusion rate eruptions typical of Hawaiian lava flows, are dominated by the internal viscosity of the lava, whereas low effusion rate or long lived eruptions are dominated by the yield strength in the growing crust. Finally, eruptions with very high initial crystal contents are dominated by the internal yield strength. The developed rheological model and 2-D theory were applied to the 2002 lava flow deposits at the NE flank of Etna volcano to reconstruct the variations in flow rate and advance of the flow front. Analyses of samples were used to estimate crystal content and liquid viscosity variations with distance. Yield strength variations were estimated from levee width measurements. The modelled flow rate and advance of the flow front compare well with the measured data, with a mean flow rate of 19.5 m3/s. The method developed in this thesis provides the prospect of using measurements of flow dimensions together with analysis of samples from the deposits to estimate the rheology of the flow and reconstruct variations of eruption parameters.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The Influence of Plumbing System Structure on Volcano Dimensions and Topography

Volcano morphology has been traditionally studied from a descriptive point of view, but inthis work we took a different more quantitative perspective. Here we used volcano dimensions such asheight and basal radius, together with the topographic profile as indicators of key plumbing systemproperties. We started by coupling models for the ascent of magma and extrusion of lavaflows withthose for volcano edifice construction. We modeled volcanic edifices as a pile of lavas that are emittedfrom a single vent and reduce in volume with time. We then selected a number of arc-volcano examplesto test our physical relationships and estimate parameters, which were compared with independentmethods. Our results indicate that large volcanoes (>2,000 m height and base radius>10 km) usually arebasaltic systems with overpressured sources located at more than 15 km depth. On the other hand,smaller volcanoes (<2,000 m height and basal radius<10 km) are associated with more evolved systemswhere the chambers feeding eruptions are located at shallower levels in the crust (<10 km). Wefind thatsurface observations on height and basal radius of a volcano and its lavas can give estimates offundamental properties of the plumbing system, specifically the depth and size of the magma chamberfeeding eruptions, as the structure of the magmatic system determines the morphology of thevolcanic edifice

The interaction between active crustal faults and volcanism: A case study of the Liquiñe-Ofqui Fault Zone and Osorno volcano, Southern Andes, using magnetotellurics

Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT) CONICYT FONDECYT 1170195 Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT) CONICYT PIA/ANILLOS ACT-172002 Centro de Excelencia en Geotermia de Los Andes FONDAP 1509001

Evolution of crust- and core-dominated lava flows using scaling analysis

Artículo de publicación ISIWe present a simple tool to evaluate the dominant dynamical regime of a lava flow and to estimate the order of magnitude of the main rheological parameter (viscosity or yield strength) controlling the length of the lava flow with time. We consider three dynamical regimes: a Newtonian viscous regime, a yield strength-dominated regime and a crust-dominated regime. For each of these regimes,we present a scaling analysis to derive relationships between front position and time, emitted volume, slope, width of the flow and rheological properties. We apply the resulting equations to published data from eruptions of 10 lava flows with a range of compositions and conditions. Comparisons of the fits of the models to the data reveal that short-lived, high effusion rate eruptions are dominated by the internal viscosity of the lava, whereas low effusion rate or long-lived eruptions are dominated by the yield strength in the growing crust. Finally, blocky lavas with very high initial crystal contents are dominated by the internal yield strength. The evolution of some flows can be approximated with only two viscosity values: an early low lava viscosity stage and a later higher viscosity stage. The increase in viscosity is attributed to the initial disequilibrium conditions of the magma at the vent with further degassing and cooling triggering crystallisation of the lava flow. For yield strength-dominated flows yield strength is always within an order of magnitude of 105 Pa. This study provides a practical framework for predicting the evolution of the length of lava flows from estimates of the crystal content of the erupting lava and its effusion rate.AC thanks the financial support given by CONICYT Chile through the Presidente de la Republica scholarship and FONDAP project 15090013

Comparison of lake and land tephra records from the 2015 eruption of Calbuco volcano, Chile

Tephra layers in lake sediment cores are regularly used for tephrostratigraphy as isochronous features for dating and recording eruption frequencies. However, their value for determining volcanic eruption size and style may be complicated by processes occurring in the lake that modify the thickness and grain size distributions of the deposit. To assess the reliability of data from lake cores, we compare tephra deposited on land during the 2015 eruption of Calbuco volcano in Chile to records in sediment cores from three lakes of different sizes that are known to have received primary fall deposits. In general, the thickness and granulometry of the deposit in lake cores and nearby terrestrial sections are very similar. As anticipated, however, cores sampled close to (here, within 300 m of) fluvial inflows were affected by sediment deposition from the lake’s catchment; they differed from primary deposits not only in their greater thickness and organic content but a

Eruptive parameters and dynamics of the April 2015 sub-Plinian eruptions of Calbuco volcano (southern Chile)

International audienceWe conducted geological and petrological analyses of the tephra fallout and pyroclastic density current (PDC) products of the 22-23 April 2015 Calbuco eruptions. The eruptive cycle consisted of two sub-Plinian phases that generated > 15 km height columns and PDCs that travelled up to 6 km from the vent. The erupted volume is estimated at 0.38 km3 (non-DRE), with approximately 90% corresponding to tephra fall deposits and the other 10% to PDC deposits. The erupted products are basaltic-andesite, 54-55 wt.% SiO2, with minor amounts of andesite (58 wt.% SiO2). Despite the uniform composition of the products, there are at least four types of textures in juvenile clasts, with different degrees of vesicularity and types and content of crystals. We propose that the eruption triggering mechanism was either exsolution of volatiles due to crystallization, or a small intrusion into the base of the magma chamber, without significant magma mixing or with a magma compositionally similar to that of the residing magma. In either case the triggering mechanism generated convection and sufficient overpressure to promote the first eruptive phase. The start of the eruption decompressed the chamber, promoting intense vesiculation of the remaining magma and an increase in eruption rate towards the end of the eruption