Volcan De Colima Research Articles

Absence of Detectable Precursory Deformation and Velocity Variation Before the Large Dome Collapse of July 2015 at Volcán de Colima, Mexico

Improving the ability to foresee volcanic eruption is one of the main objectives of volcanologists. For this purpose, it is essential to better detect eruption forerunners and to understand their relationship with eruptive processes. The evaluation of the performance of the forecasting methods partly relies on the estimation of the frequency of occurrence of the various precursory phenomena. Possible lack of precursor before some events must also be carefully documented and analyzed. In this study, we check for the existence of detectable precursors before the large dome collapse event of Volcan de Colima, which occurred in July 2015, leading to the emplacement of more than 10 km long Pyroclastics Density Currents and the opening of a large breach in the crater. Based on volumes of emitted magma, the 2015 eruption is the largest event recorded at Volcan de Colima since the 1913 Plinian eruption. Surface displacements in the summit cone area are quantified over the period November 2014-June 2015 based on Synthetic Aperture Radar (SAR) images acquired by Sentinel-1 satellite. Velocity variations are investigated by coda wave interferometry. Daily cross-correlation functions of seismic noise recorded at 5 broadband stations are calculated for the period January 2013 – April 2017 and apparent velocity variations are obtained by applying the stretching method. We show that no significant surface deformation can be measured by the SAR images over an area reaching 5 km from the summit, such that the volume of emitted magma cannot have been accommodated elastically in the 6 months preceding the eruption at a depth shallower than 5 km. The time series of apparent velocity variations display fluctuations of the order of 0.05 % with characteristic time shorter than one month. Sharp velocity decreases of up to 0.2 % are associated with strong regional tectonic earthquakes. However, no velocity change with amplitude larger than the noise level is observed before the July 2015 eruption. The behavior of the surface deformation and the velocity variation is consistent with the relative quiescence of the volcano-tectonic and low-frequency seismic activities observed before this large eruptive event, a situation that could be frequent in

Understanding eruptive style variations at calc-alkaline volcanoes: the 1913 eruption of Fuego de Colima volcano (Mexico)

The 1913 sub-Plinian eruption of Fuego de Colima volcano (Mexico) occurred after almost 100 years of effusive and (minor) Vulcanian explosive activity, which modulated dome growth and destruction. Dome extrusion persisted from 1869 to 1913. The transition to explosive eruption started on 17 January 1913, and it progressed in three phases: (1) opening, with the generation of block-and-ash flows, (2) vent clearing, with strong explosions that destroyed the summit dome and decompressed the magmatic system, and (3) sustained column (sub-Plinian fallout) with final collapse producing pyroclastic density currents. Because of this succession of events, the 1913 activity represents an excellent case-study for investigating the eruptive style changes at calc-alkaline volcanoes. We investigated the conditions that led to eruptive style transition from effusive (dome growth) to explosive (the final sub-Plinian fallout) through steady-state numerical simulations, using subsurface data and independently inferred (from volcanological data) mass discharge rates as constraints. Results show good matches for hybrid geometrical settings of the shallow conduit-feeding system (i.e., dyke developing into a shallower cylindrical conduit), and the magma chamber top at 6 km of depth. The fragmentation level was shallower than 2 km, as inferred from the lithics contained in the sub-Plinian fall deposits of Phase (3). The most likely solution is represented by a dyke having major axis between 200 and 2000 m and the minor axis of 40 m. The dyke-cylinder transition was set at a depth of 500 m, with a cylinder diameter of 40 m. It emerges that at least two main mechanisms may be responsible for the effusive to explosive transition that led to the Phase (3) of the 1913 eruption: (i) an increase in magma chamber overpressure (magmatic triggering) or (ii) decrease of lithostatic stress acting on the volcano (non-magmatic triggering). The former implies arrival into the magma chamber of a batch of fresh magma, which can have volume between 10 and 200 × 106 m3, depending on the values of magma and host rock compressibility. The latter requires decompression-induced emptying of at least the equivalent of 1000 m of the magma column to produce the necessary unloading of the conduit-feeding system. A sudden jerk in the lateral spreading of the Fuego de Colima cone would be a reliable mechanism for decompressing the upper conduit and driving fragmentation processes over a time period of few hours. The results are not conclusive on an internal (magma chamber overpressure), external (lowering of lithostatic load), or mixed (internal and external) trigger of the observed eruptive style transition. This work highlights how different processes can have non-linear cascade effects on close-to-equilibrium volcanic systems like Fuego de Colima volcano.

An Overview of the Dynamics of the Volcanic Paroxysmal Explosive Activity, and Related Seismicity, at Andesitic and Dacitic Volcanoes (1960–2010)

Understanding volcanic paroxysmal explosive activity requires the knowledge of many associated processes. An overview of the dynamics of paroxysmal explosive eruptions (PEEs) at andesitic and dacitic volcanoes occurring between 1960 and 2010 is presented here. This overview is based mainly on a description of the pre-eruptive and eruptive events, as well as on the related seismic measurements. The selected eruptions are grouped according to their Volcanic Explosivity Index (VEI). A first group includes three eruptions of VEI 5-6 (Mount St. Helens, 1980; El Chichon, 1982, and Pinatubo, 1991) and a second group includes three eruptions of VEI 3 (Usu volcano, 1977; Soufriere Hills Volcano (SHV), 1996, and Volcan de Colima, 2005). The PEEs of the first group have similarity in their developments that allows to propose a 5-stage scheme of their dynamics process. Between these stages are: long (more than 120 years) period of quiescence (stage 1), preliminary volcano-tectonic (VT) earthquake swarm (stage 2), period of phreatic explosions (stage 3) and then, PEE appearance (stage 4). It was shown also that the PEEs of this group during their Plinian stage “triggered” the earthquake sequences beneath the volcanic structures with the maximum magnitude of earthquakes proportional to the volume of ejecta of PEEs (stage 5). Three discussed PEEs of the second group with lower VEI developed in more individual styles, not keeping within any general scheme. Among these, one PEE (SHV) may be considered as partly following in development to the PEEs of the first group, having stages 1, 3 and 4. The PEEs of Usu volcano and of Volcan de Colima had no preliminary long-term stages of quiescence. The PEE at Usu volcano came just at the end of the preceding short swarm of VT earthquakes. At Volcan de Colima, no preceding swarm of VT occurred. This absence of any regularity in development of lower VEI eruptions may refer, among other reasons, to different conditions of opening of the magmatic conduit during these eruptions.

The anatomy of a pyroclastic density current: the 10 July 2015 event at Volcán de Colima (Mexico)

Pyroclastic density currents (PDCs) represent one of the most dangerous phenomena occurring in explosive volcanic eruptions, and any advance in the physical understanding of their transport and sedimentation processes can contribute to improving their hazard assessment. The 10–11 July 2015 eruption at Volcan de Colima provided a unique opportunity to better understand the internal behaviour of PDCs based on seismic monitoring data. On 10 July 2015, the summit dome collapsed, producing concentrated PDCs that filled the main channel of the Montegrande ravine. A lahar monitoring station installed 6 km from the volcano summit recorded a PDC before being completely destroyed. Real-time data acquisition from a camcorder and a geophone that were part of the station, along with field observations and grain-size data of the pyroclastic deposits, are used here to interpret the internal flow structure and time-variant transport dynamics of low-volume, valley-confined concentrated PDCs. The PDC that reached the monitoring station moved at a velocity of ~ 7 m/s and filled a 12-m-deep channel. The outcrops show massive, block-and-ash flow deposits with trains of coarse clasts in the middle and towards the top of the depositional units. The seismic record gathered with the geophone was analysed for the time window when the flow travelled past the sensor. The geophone record was also compared with the recordings of a broadband seismic station located nearby. Two main frequency ranges were recognised which could be correlated with the basal frictional forces exerted by the flow on the channel bed (10–20 Hz) and a collisional regime (20–40 Hz) interpreted to be associated with a clast segregation process (i.e. kinematic squeezing). This latter regime promoted the upward migration of large blocks, which subsequently deviated towards the margin of the flow where they interacted with the sidewall of the main channel. The energy calculated for both seismic components shows that the collisional regime represents 30% of the total energy including an important sidewall-stress component. These results, gathered directly from a moving flow, contribute to unravelling the internal behaviour of concentrated PDCs providing information on energy partitioning and particle-particle interactions. This confirms previous assumptions inferred from field observations, and tested by analogue or numerical modelling. The nature of the contact between grains is still poorly documented in natural PDCs, and there is still much uncertainty and discussion about dominant forces in such currents. Data reported here may thus be useful to better constrain the physics of low-volume, valley-confined concentrated PDCs and our findings need to be considered in theoretical models. In parallel, this study shows how geophones can provide a cheap alternative for PDC detection.

Efecto de Arceuthobium vaginatum (Willd.) Presl. subsp. vaginatum en Pinus hartwegii Lindl. en Colima


 
 
 A pesar de que los muérdagos son abundantes en México, se sabe muy poco acerca de su comportamiento en los diferentes hospederos. Existen algunos trabajos que documentan evaluaciones de daños y son más escasos los que integran información de árboles infestados con diferentes grados de ataque. El objetivo de este estudio fue determinar el efecto de Arceuthobium vaginatum subsp. vaginatum en la altura, diámetro y volumen de Pinus hartwegii, en el parque nacional Volcán Nevado de Colima. Se eligieron 18 árboles en un rodal natural con presencia de muérdago enano: nueve sanos y nueve enfermos; con edades entre 30 y 40 años a los cuales se les realizaron análisis troncales para reconstruir su historial de crecimiento. Se consideró el grado de infección 6, con base en el sistema de clasificación de Hawksworth. Se probaron las ecuaciones de Shumacher y Chapman-Richards a fin de seleccionar el modelo más adecuado para la descripción del fenómeno. El modelo de Shumacher presentó mejores ajustes en la predicción del crecimiento. La infestación por muérdago enano lo redujo 22 % en altura, 9 % en diámetro y 50 % en volumen; además afectó en porcentajes similares al incremento corriente anual e incremento medio anual, lo cual disminuye el volumen de madera producido y aumenta el turno técnico maderable del arbolado, en un promedio de 10 años. Los resultados sugieren la aplicación de prácticas de prevención y combate del parásito, así como el establecimiento de sitios de monitoreo continuo para la generación de conocimiento sobre la relación parásito-hospedero.
 
 

Spatio-temporal land-use changes in the Colima-Villa de Álvarez metropolitan area, and their relationship to floodings

El crecimiento demográfico, y por consiguiente los cambios de uso de suelo, se consideran entre los principales factores que pueden provocar el incremento de inundaciones en ciudades de países en desarrollo. Durante las últimas décadas en la Ciudad de Colima se ha incrementado la frecuencia con la que suceden inundaciones. Estos fenómenos ocurren mayormente durante tormentas tropicales asociadas a huracanes, como es el caso de Jova en 2011, Manuel en el 2013 y Patricia en el 2015, todas con lluvias acumuladas promedio de 200 mm en 24 h. También suceden con tormentas intensas y de corta duración a comienzos de la temporada de lluvia. Para definir los mecanismos que aumentan la ocurrencia de este fenómeno, se presenta un análisis espacio-temporal del cambio de uso de suelo, junto con la caracterización de suelos naturales y urbanos para el área metropolitana de Colima.Se definieron tres categorías principales de uso de suelo: Nativo (N1), Urbano (N4) y Agrícola (N5). Cada categoría tiene subcategorías dependiendo de la cobertura vegetal y/o nivel de urbanización. Imágenes SPOT adquiridas en 2005, 2009 y 2015 fueron clasificadas para analizar espacial y temporalmente los cambios de uso de suelo. Se analizaron treinta y dos muestras de suelo representativas de diferentes usos de suelo para obtener sus propiedades físicas y químicas, como granulometría, densidad aparente y de partícula, porosidad y contenido de materia orgánica. Pruebas de conductividad hidráulica in situ se hicieron usando un infiltrómetro por goteo.Con base en el análisis temporal y espacial de las imágenes SPOT, se pudo detectar que la mayoría de los cambios de uso de suelo corresponden al área urbana y agrícola; la primera mostrando un incremento y la segunda una drástica disminución, especialmente hacia el norte donde el crecimiento urbano es evidente durante el periodo 2005-2009. Los suelos en las áreas agrícolas resultaron ser los más permeables, mientras que los suelos constituido por material compactado para construcción corresponden a los menos permeables en el área; por lo tanto, el reemplazo de las zonas agrícolas por zonas habitacionales tiene un impacto significativo en el proceso de lluvia-escurrimiento. Estos resultados indican que mientras más zonas permeables sean substituidas por suelos perturbados, la capacidad de infiltración será reducida, incrementando la frecuencia de inundaciones en el área metropolitana Colima-Villa de Álvarez.Para prevenir y reducir el impacto destructivo de las inundaciones en el área metropolitana de Colima, se recomienda tener un manejo adecuado del cambio de uso de suelo y conservar las superficies permeables alrededor de la ciudad. Adicionalmente, es necesario revisarla infraestructura hidráulica existente de las zonas urbanas y definir los sitios adecuados para las futuras. Evitar desarrollos urbanos en zonas susceptibles a inundación a través de la buena planificación y la reglamentación, podría reducir las pérdidas de vidas y daños materiales producto de estos eventos.

Seismic signals of rockfalls as indicators of the origin of lava fragments emplaced during the 2010 endogenous and exogenous growth in the crater of Volcán de Colima, México

The 2010–2011 exogenous emplacement of a lava lobe during the 2007–2011 lava dome growth at andesitic Volcan de Colima, Mexico, interrupted the previous endogenous regime and allowed us to obtain seismic signals associated with rockfalls triggered by both exogenous and endogenous growth. We analyzed a total of 410 seismic signals of rockfalls with durations from 50 to 150 s recorded during January–April 2010. Two characteristic populations of seismic signal peak frequencies were identified: a low frequency (LF) group (mean = 1.76 ± 0.44 Hz) and a high frequency (HF) group (mean = 3.13 ± 0.63 Hz), associated respectively with rockfalls caused by endogenous and exogenous growth in the crater. Application of the Kolmogorov-Smirnov test showed at the 0.01 significance level that the databases of LF and HF seismic signals of rockfalls belong to different groups of signals and may be considered as having different origins. The results show that the spectral properties of the seismic signals produced by rockfalls may serve as indicators of the origin of falling lava fragments and thus can be used to monitor effusive volcanic activity.

Ambient seismic noise tomography of the Colima Volcano Complex

The Colima Volcanic Complex (CVC) located in the western sector of the Trans-Mexican Volcanic Belt contains the most active Mexican volcano, Volcan Colima. The CVC is located within the Colima Rift, a regional north south striking extensional structure. We used ambient seismic noise recorded by stations deployed in western Mexico during the Mapping the Rivera Subduction Zone (MARS) and the Colima Volcano Deep Seismic Experiment (CODEX). We computed the cross-correlations of the vertical component of continuous records of ambient noise data to extract empirical Greens functions. These functions provide detailed images of Rayleigh wave group velocity for different periods. Using the arrival travel time of these waves for a given period, estimates can be obtained of the lateral variations in velocity for a given period using 2D tomography. The study aims to better understand the geometry and the seismic surface wave velocity structure of the CVC and relate it to the volcanoes' structure and the geologic setting of the region. Source of low velocity anomaly over CVC is distributed fairly continuously with depth in the subsurface, which indicates magma rising along fractures. The progressive increasing toward the south in the size of low velocity anomalies indicates migration towards the south of the melting that correlates with the trend of the stratovolcanoes that form the CVC. The zone of magma generation presently fully developed under Volcan de Fuego might be starting to shift towards south to the area NW of Armeria where a new void in the tear zone may be starting to form.

Full vector magnetic dating of some pyroclastic rocks associated to the Colima volcano, western Mexico

Full vector magnetic dating of some pyroclastic rocks associated to the Colima volcano, western Mexico

Anatomy of the Colima volcano magmatic system, Mexico

Colima volcano is one of the most active volcanoes in continental north America. It is located within the Colima graben on the western part of the Colima rift zone. Although extensively studied, the internal structure and deep magmatic system remains unknown. This research gives new clues to understand how and where magmas are produced and stored at depth. Using ambient seismic noise, we jointly invert for Rayleigh and Love wave dispersion curves for both phase and group velocity, which is applied for the first time in a volcanic environment. We invert for both the shear wave velocity and radial anisotropy. The 3D high resolution shear wave velocity model shows a deep, large and well-delineated elliptic-shape magmatic reservoir below the Colima volcano complex at a depth of about 15 km. On the other hand, the radial anisotropy model shows a significant negative feature (i.e., VSV>VSH) revealed from ≥35 km depth until the top of the magma reservoir at about 12 km depth. The latter suggests the presence of numerous vertical fractures where fluids, rooting from a well-known mantle window, can easily migrate upward and then accumulate in the magma reservoir. Furthermore, the convergence of both a low velocity zone and a negative anisotropy suggests that the magma is mainly stored in conduits or inter-fingered dykes as opposed to horizontally stratified magma reservoir.

Notes on the genus Entoloma (Basidiomycota, Agaricales) in two volcanic areas of Jalisco, Mexico

Fifteen species of the genus Entoloma, found in high elevations of Nevado de Colima and the Tequila volcanos, both in the state of Jalisco, Mexico, are presented. Their macromorphological and micromorphological structures are described and general characteristics of their habitat; furthermore, comments about their distinctive features and similar species in the literature are given. Of these 15 species, three are described as new, 11 represent the first records for Mexico, and the remaining one is the second record for the country. The species generally show much resemblance to Entoloma taxa described from the Southern United States of America and to a lesser extent, those of Europe.

Blowing Off Steam: Tuffisite Formation As a Regulator for Lava Dome Eruptions

Tuffisites are veins of variably sintered, pyroclastic particles that form in conduits and lava domes as a result of localized fragmentation events during gas-and-ash explosions. Those observed in-situ on the active 2012 lava dome of Volcan de Colima range from voids with intra-clasts showing little movement and interpreted to be failure-nuclei, to sub-parallel lenses of sintered granular aggregate interpreted as fragmentation horizons, through to infilled fractures with evidence of viscous remobilization. All tuffisites show evidence of sintering. Further examination of the complex fracture-and-channel patterns reveals viscous backfill by surrounding magma, suggesting that lava fragmentation was followed by stress relaxation and continued viscous deformation as the tuffisites formed. The natural tuffisites are more permeable than the host andesite, and have a wide range of porosity and permeability compared to a narrower window for the host rock, and gauging from their significant distribution across the dome, we posit that the tuffisite veins may act as important outgassing pathways. To investigate tuffisite formation we crushed and sieved andesite from the lava dome and sintered it at magmatic temperatures for different times. We then assessed the healing and sealing ability by measuring porosity and permeability, showing that sintering reduces both over time. During sintering the porosity-permeability reduction occurs due to the formation of viscous necks between adjacent grains, a process described by the neck-formation model of Frenkel (1945). This process leads the granular starting material to a porosity-permeability regime anticipated for effusive lavas, and which describes the natural host lava as well as the most impervious of natural tuffisites. This suggests that tuffisite formation at Volcan de Colima constructed a permeable network that enabled gas to bleed passively from the magma. We postulate that this progressively reduced the lava dome’s ability to seal and build pressure that drives explosions. Indeed, the time interval between explosions during 2007 to 2011 gradually increased before the onset of a period of quiescence starting in June 2011. We suggest that the permeability evolution during tuffisite formation has important consequences for modeling of gas-and-ash explosions, common at dome-forming volcanoes.

Vanadium, V – a new native element mineral from the Colima volcano, State of Colima, Mexico, and implications for fumarole gas composition

AbstractVanadium, V, is a new mineral found in sublimates of high-temperature fumaroles of the Colima volcano, Mexico. The mineral precipitates over a narrow temperature range of 550–680°C, and occurs in association with colimaite (K3VS4) and shcherbinaite (V2O5). Native vanadium was been found on the inner wall of an inserted silica tube and subsequently in the adjacent rock of the Z3 fumarole. Vanadium forms smooth, irregular to flattened crystals, 5–20 μm in diameter. Smaller irregular crystals have also been observed in silica tubes. Due to its small crystal size, its physical properties (hardness, cleavage and density) could not be determined. An EDS spectrum indicated the presence of V, Fe, Al and Ti with an empirical formula calculated on the basis of EPMA analyses of V0.86Fe0.09Al0.04Ti0.01. Gandolfi and glancing-angle X-ray diffraction data showed that the microcrystals were body-centred cubic, space group Im3̄m, a = 3.022(3) Å, V = 27.60 (5) Å3, Z = 2. The five strongest calculated diffraction lines are [ d spacings in Å, (I) (hkl)]: 2.1411 (100)(110), 1.5126 (12)(200), 1.2301 (19)(211), 0.9565 (8)(310) and 8.8090 (11)(321). The calculated density is 6.033 g cm–3. Thermochemical modelling was used to explain why very oxidized gas at Colima precipitates V-bearing minerals and some native elements (vanadium and gold). Vanadium, is the second newly recognized mineral species (after colimaite) collected from an active fumarole in this volcanic crater. The mineral and its name have been approved by the CNMNC (IMA 2012-021a).

Field and seismic evaluation of the block-and-ash flows emplaced from eruption columns of the 2005 Vulcanian explosions at Volcán de Colima, Mexico

The May–September 2005 Vulcanian explosion sequence was the most intense of all the activity during the recent 1998–2015 unrest at Volcan de Colima, Mexico. This study presents field measurements of volume and runout distances of block-and-ash flows emplaced from eruption columns that punctuated the six largest explosions of this sequence. The energy of these explosions and the emplacement duration of the pyroclastic flows were obtained from broadband seismic signals associated with these events. The field and seismic characteristics of the 2005 explosions at Volcan de Colima and associated block-and-ash flows showed that six explosions with energy ranging between 3.0 × 1011 and 1.5 × 1013 J emplaced the block-and-ash flows with volumes ranging between 1.8 × 105 and 3.1 × 105 m3 DRE (dense rock equivalent). Analysis of durations of seismic signals associated with the movement of the 2005 block-and-ash flows emplaced from the eruption columns allowed us to quantify them as M3-magnitude events using the techniques proposed by Zobin et al. (Bull Volcanol 67: 679–688, 2005) to quantify the block-and-ash flows emplaced from the partial collapse of the lava dome at Volcan de Colima.

Heuristic and Eulerian interface capturing approaches for shallow water type flow and application to granular flows

Determining the wet–dry boundary and avoiding the related spurious thin-layer problem when solving the depth-averaged shallow-water (SW) equations (or similar granular flow models) remains an outstanding challenge, though it has been the focus of much research effort. In this paper, we introduce the use of level set and phase field based methods to address this issue and related problems. We also propose new heuristic methods to address this problem. We implemented all of these methods in TITAN2D, which is a parallel adaptive mesh refinement toolkit designed for numerical simulation of granular flows. Results of the methods for flow over a simple inclined plane and Colima volcano are used to illustrate the methods. For the inclined plane, we compared the results with experimental data and for Colima volcano they are compared to field data. Our approaches successfully captured the interface of the flow and solved the accuracy and stability problems related to the thin layer problem in SW numerical solution. The comparison of results shows that although all of the methods can be used to address this problem, each of them has its own advantages/disadvantages and methods have to be chosen carefully for each problem.

Seismic characterisation of lahars at Volcán de Colima, Mexico

Volcan de Colima is one of the most active volcanoes in Mexico, not only for its eruptive history, but also for its annual occurrence of lahars. This makes the volcano a natural laboratory for monitoring and studying lahar processes. Since 2011, monitoring instruments have been deployed along the highly active Montegrande ravine, with at least three lahar events per year. Here, we report the datasets of three events collected during the 2012 and 2013 seasons, then interpret the acquired data. An event classification scheme based on lahar magnitude, duration and seismic characteristics is presented to distinguish “single-pulse” events (SPEs) from “multi-pulse” events (MPE). SPEs lasted approximately 60 min, had average velocities of ~2 m/s and mean peak discharges of ~24 m3/s. MPEs endured for more than 3 h, reached mean velocities of ~4.5 m/s and peak discharges of ~60 m3/s (for block-rich surges). The seismic signal-analysis also allowed us to discriminate physical flow fluctuations within single lahars, i.e. between the arrival of block-rich fronts and subsequent variations in flow discharge. The exponential regression analysis showed a best fit, with correlation coefficients around 0.92 and exponential coefficients of ~0.01 s, for the block-rich fronts, with seismic amplitudes increasing from 4.8 × 10−4 to 2.3 × 10−3 m/s and frequency ranges from 10 to 20 Hz. The variations in flow discharge were distinguished by lower amplitudes of ~5.7 × 10−4 m/s than those of the block-rich fronts and with frequency ranges of 10–40 Hz. The results presented in this paper demonstrate that the seismic data of events allowed us to describe and discriminate among different flow types; these records are thus a useful investigation tool for lahar events that have a seismic record but are not observed directly. We propose that a seismic early warning system can be developed to help civil protection authorities in designing risk mitigation strategies.

Pore pressure embrittlement in a volcanic edifice

The failure mode of porous rock in compression—dilatant or compactant—is largely governed by the overlying lithostatic pressure and the pressure of pore fluids within the rock (Wong, Solid Earth 102:3009–3025, 1997), both of which are subject to change in space and time within a volcanic edifice. While lithostatic pressure will tend to increase monotonously with depth due to the progressive accumulation of erupted products, pore pressures are prone to fluctuations (during periods of volcanic unrest, for example). An increase in pore fluid pressure can result in rock fracture, even at depths where the lithostatic pressure would otherwise preclude such dilatant behaviour—a process termed pore fluid-induced embrittlement. We explore this phenomenon through a series of targeted triaxial experiments on typical edifice-forming andesites (from Volcan de Colima, Mexico). We first show that increasing pore pressure over a range of timescales (on the order of 1 min to 1 day) can culminate in brittle failure of otherwise intact rock. Irrespective of the pore pressure increase rate, we record comparable accelerations in acoustic emission and strain prior to macroscopic failure. We further show that oscillating pore fluid pressures can cause iterative and cumulative damage, ultimately resulting in brittle failure under relatively low effective mean stress conditions. We find that macroscopic failure occurs once a critical threshold of damage is surpassed, suggesting that only small increases in pore pressure may be necessary to trigger failure in previously damaged rocks. Finally, we observe that inelastic compaction of volcanic rock (as we may expect in much of the deep edifice) can be overprinted by shear fractures due to this mechanism of embrittlement. Pore fluid-induced embrittlement of edifice rock during volcanic unrest is anticipated to be highest closer to the conduit and, as a result, may assist in the development of a fractured halo zone surrounding the conduit, potentially explaining commonly observed near-conduit outgassing at many active volcanoes. Further, rock embrittlement at depth may create transient outgassing pathways by linking fracture networks near the edifice to larger-scale regional fault systems. Our experimental results affirm that pore pressure fluctuations associated with volcanic unrest may play a crucial role in dictating the evolution of a volcanic system.

Preliminary report on the July 10–11, 2015 eruption at Volcán de Colima: Pyroclastic density currents with exceptional runouts and volume

On July 10–11, 2015 an eruption occurred at Colima volcano produced 10.5km long pyroclastic density currents (PDCs) along the Montegrande, and 6.5km long along the San Antonio ravines. The summit dome was destroyed and a new crater excavated and breached to the south. This new breach connects to a narrow channel that descends along Colima's southern flank and was used by a subsequent lava flow. The Montegrande PDCs represent the longest and hottest flow of this type recorded during the past 30years but are still smaller in comparison to the 15-km long PDCs produced during the 1913 Plinian eruption. Data obtained from field reconnaissance, lahar monitoring stations, and satellite imagery suggest that at least six PDCs occurred. The two largest PDCs (H/L 0.2) were able to surmount topographic barriers or bends. Based on field reconnaissance and digital elevation models extracted from SPOT satellite imageries we estimate a minimum volume for the valley-pond and distal fan deposits of 4.5×106m3. After one week, the deposits were still hot with burning trees on the surface and millimeter-sized holes from which fumes were emanating. The juvenile components of the deposits consist of gray dense blocks and vesicular dark-gray blocks and bombs with bread-crust textures and cooling joints. The mineral association of these rocks consists of plagioclase+clinopyroxene+orthopyroxene+FeTi-oxides±olivine and resorbed hornblende in a dark glassy matrix that corresponds to an andesitic composition.

Pulsed Vulcanian explosions: A characterization of eruption dynamics using Doppler radar

Understanding the dynamics of ongoing volcanic eruptions is essential for predicting the input and transport of volcanic ash in the atmosphere. To constrain near-vent dynamic processes of explosive Vulcanian events, we used Doppler radar measurements, providing tephra velocities and a proxy of the mass flux, in two field experiments at Volcan de Colima (Mexico) and Santiaguito (Guatemala). We find that explosive eruptions at both volcanoes consist of individual degassing pulses. The analysis of the timing of such pulses shows that both volcanoes have preferred interpulse times of 3 s (Santiaguito) and 2–5 s (Volcan de Colima). The interpulse time during one event may change, but it often returns to the preferred interpulse time. This behavior is similar at both volcanoes and the interpulse time roughly follows a log-logistic distribution indicating the interplay of two competing processes. These could be short-duration degassing of the uppermost conduit versus decreasing permeability due to progressive gas loss and compaction during an eruption.

Seismic Characteristics of the Vulcanian Explosions from the 2003–2005 Eruption at Colima Volcano, Mexico

Colima Volcano (19.512°N, 103.617°W, 4000 m.a.s.l.), located on the border between the states of Jalisco and Colima in western Mexico, is the most active volcano in the country. Its activity has taken place through diverse styles of eruption, from very explosive to effusive. In the last decades it has presented frequent vulcanian eruptions with episodes of dome construction–destruction. Four of these cycles occurred from 1990 to 2005, the last one from July 2003 to September 2005. We focus on this last period, for which we analyzed seismic phases and coupled pressure airwaves from high dynamic range seismograms, both in the time and frequency domains, to determine characteristic features, propagation velocities, and origin times for both deep seismic sources and the associated explosions. The results show that the sources of the P-waves associated with the explosions are not located at the summit, but instead at different shallow locations for the different explosions, suggesting the presence of various magmatic pathways within the volcano.