Geotechnical Data and Numerical Analysis of Edifice Collapse and Related Hazards at Pacaya Volcano, Guatemala

The continual eruptive activity, occurrence of an ancestral catastrophic collapse, and inherent geologic features of Pacaya volcano (Guatemala) demands an evaluation of potential collapse hazards. This thesis merges techniques in the field and laboratory for a better rock mass characterization of volcanic slopes and slope stability evaluation. New field geological, structural, rock mechanical and geotechnical data on Pacaya is reported and is integrated with laboratory tests to better define the physical-mechanical rock mass properties. Additionally, this data is used in numerical models for the quantitative evaluation of lateral instability of large sector collapses and shallow landslides. Regional tectonics and local structures indicate that the local stress regime is transtensional, with an ENE-WSW sigma 3 stress component. Aligned features trending NNW-SSE can be considered as an expression of this weakness zone that favors magma upwelling to the surface. Numerical modeling suggests that a large-scale collapse could be triggered by reasonable ranges of magma pressure (greater than or equal to 7.7 MPa if constant along a central dyke) and seismic acceleration (greater than or equal to 460 cm/s2), and that a layer of pyroclastic deposits beneath the edifice could have been a factor which controlled the ancestral collapse. Finally, the formation of shear cracks within zones of maximum shear strain could provide conduits for lateral flow, which would account for long lava flows erupted at lower elevations.

VALIDATION OF A 'DISPLACEMENT TOMOGRAPHY' INVERSION METHOD FOR MODELING SHEET INTRUSIONS

The study of volcano deformation data can provide information on magma processes and help assess the potential for future eruptions. In employing inverse deformation modeling on these data, we attempt to characterize the geometry, location and volume/pressure change of a deformation source. Techniques currently used to model sheet intrusions (e.g., dikes and sills) often require significant a priori assumptions about source geometry and can require testing a large number of parameters. Moreover, surface deformations are a non-linear function of the source geometry and location. This requires the use of Monte Carlo inversion techniques which leads to long computation times. Recently, ‘displacement tomography’ models have been used to characterize magma reservoirs by inverting source deformation data for volume changes using a grid of point sources in the subsurface. The computations involved in these models are less intensive as no assumptions are made on the source geometry and location, and the relationship between the point sources and the surface deformation is linear. In this project, seeking a less computationally intensive technique for fracture sources, we tested if this displacement tomography method for reservoirs could be used for sheet intrusions. We began by simulating the opening of three synthetic dikes of known geometry and location using an established deformation model for fracture sources. We then sought to reproduce the displacements and volume changes undergone by the fractures using the sources employed in the tomography methodology. Results of this validation indicate the volumetric point sources are not appropriate for locating fracture sources, however they may provide useful qualitative information on volume changes occurring in the surrounding rock, and therefore indirectly indicate the source location.

Determining magmatic processes from analysis of phenocrysts and gabbroic xenoliths contained in Calbuco andesites

Calbuco Volcano, in Southern Chile, has eruptive products of predominantly andesitic hornblende-bearing lava. A purpose of this work is to understand magmatic processes and how Calbuco magma chemistry is related to the explosive volcanic character. Calbuco lava has a mineral assemblage of plagioclase, hornblende, orthopyroxene, clinopyroxene, olivine, and magnetite and entrained gabbroic xenoliths with the same mineral assemblage. The presence of hornblende is evidence for dissolved water in the magma. Detailed petrographic/textural analysis has been done using petrographic microscopy and back-scattered electron imaging (BSE); geochemical analysis by electron microprobe (EPMA). Major findings include 1) that hornblende and hornblende-bearing gabbroic cumulates crystallize from Calbuco magma, 2) that plagioclase grains are compositionally zoned, recording evidence of temperature, chemical, and water content fluctuations in the magma, and 3) that hornblende is unstable under upper magma chamber conditions at Calbuco, and is breaking down into plagioclase, olivine, orthopyroxene, clinopyroxene, and magnetite in the magma.

Los proverbios de animales en árabe clásico: análisis, estudio comparativo y equivalencias en español

This study entitled «Classical Arabic proverbs: analysis, comparative study and equivalence in Spanish», aims on one hand, to display the multiple problems we face when translating proverbs between Arabic and Spanish, and on the other hand, offers an updated check up of the proverbs uses as well as an analysis of the equivalence between proverbs. It was an arduous task looking for reference works which were of interest to our research both in Arabic and Spanish. We consulted many references but if we were to cite the most important ones, we would talk about works such as Magma alamtal by al-Maydani, which constituted the base we relied on in the analytical part of our work. Also of interest was Hayatu Al-Hayauani l-al-Kubra, from ad-Dummayri and his other work Mungid al-lugati w al-a'lam; as well as Ğamharat al-amtal by Abū Hilāl Al-‘Askarī and Ğamharat al-amtal al-baġdadiyya by‘Abd ar-Rahman Tikritī. As for the references in Spanish, we relied on Martinez Kleiseŕs Ideological General Spanish Proverbs; as well as 1001 Spanish sayings and their correspondence in eight languages from Julia Seville Muñoz and Ortiz de Urbina; also, Introduction to the study of fixed expressions by Julio Casares; Vocabulary of proverbs and proverbial phrases (1627-2000) by G. Correas; Dictionnary of sayings by Campos and Barella; the famous The Ingenious Gentleman Don Quixote of La Mancha by Miguel de Cervantes; the work of Sebastián Orozco de Covarrubias Treasure of Castilian Spanish; as well as Sayings and Proverbs in Romance from Hernán Núñez; or Over 21,000 Castilian Sayings not contained in the Large Collection of the Master Gonzalo Correas by Rodriguez Marín. Our work covered two main levels: a descriptive empirical area that included a historical approach with a definition of the different terms related to the proverbs used in our study. The other level is analytical which, besides holding our personal stamp, has been executed through a rigorous study of the three major aspects of our research: analysis, translation and equivalence of the proverb. We started by making a brief description of the empirical part we have divided into several sections, each devoted to the study of one particular aspect...

Cartografía de dominios litosféricos y estilo de deformación en el margen continental de Galicia (margen noroeste de la Península Ibérica)

El margen continental de Galicia presenta una estructura muy compleja, debido a dos efectos principales. Por un lado, se trata de un margen de rift pobre en magma, generado en las proximidades del punto triple R-R-R que dio lugar a la apertura simultánea del Océano Atlántico y el golfo de Vizcaya durante el Cretácico. Por otra parte, el régimen de esfuerzos compresivo Cenozoico generó la inversión parcial del margen continental hacia el norte y el noroeste, aportando una mayor complejidad estructural. En este trabajo hemos realizado un análisis detallado de la nueva información gravimétrica y batimétrica obtenida durante las campañas del Proyecto ZEE, así como de nuevos perfiles de sísmica de reflexión multicanal procedentes del Proyecto ERGAP. Presentamos aquí parte de los resultados de este análisis conjunto de toda la información geofísica y geológica disponible, consistentes en una cartografía continua de los diferentes dominios litosféricos y del tipo de deformación que los afectan, desde el margen oeste de la Península Ibérica hasta el margen norte.

A practical MEMS gravimeter

The ability to measure tiny variations in the local gravitational acceleration allows – amongst other applications – the detection of hidden hydrocarbon reserves, magma build-up before volcanic eruptions, and subterranean tunnels. Several technologies are available that achieve the sensitivities required (tens of μGal/√Hz), and stabilities required (periods of days to weeks) for such applications: free-fall gravimeters, spring-based gravimeters, superconducting gravimeters, and atom interferometers. All of these devices can observe the Earth tides; the elastic deformation of the Earth’s crust as a result of tidal forces. This is a universally predictable gravitational signal that requires both high sensitivity and high stability over timescales of several days to measure. All present gravimeters, however, have limitations of excessive cost (£70 k) and high mass (<8 kg). In this thesis, the building of a microelectromechanical system (MEMS) gravimeter with a sensitivity of 40 μGal/√Hz in a package size of only a few cubic centimetres is discussed. MEMS accelerometers – found in most smart phones – can be mass-produced remarkably cheaply, but most are not sensitive enough, and none have been stable enough to be called a ‘gravimeter’. The remarkable stability and sensitivity of the device is demonstrated with a measurement of the Earth tides. Such a measurement has never been undertaken with a MEMS device, and proves the long term stability of the instrument compared to any other MEMS device, making it the first MEMS accelerometer that can be classed as a gravimeter. This heralds a transformative step in MEMS accelerometer technology. Due to their small size and low cost, MEMS gravimeters could create a new paradigm in gravity mapping: exploration surveys could be carried out with drones instead of low-flying aircraft; they could be used for distributed land surveys in exploration settings, for the monitoring of volcanoes; or built into multi-pixel density contrast imaging arrays.

The 1998-2001 submarine lava balloon eruption at the Serreta Ridge (Azores archipelago): constraints from volcanic facies architecture, isotope geochemistry and magnetic data

The most recent submarine eruption observed offshore the Azores archipelago occurred between 1998-2001 along the submarine Serreta ridge (SSR), ~4-5 nautical miles WNW of Terceira Island. This submarine eruption delivered abundant basaltic lava balloons floating at the sea surface and significantly changed the bathymetry around the eruption area. Our work combines bathymetry, volcanic facies cartography, petrography, rock magnetism and geochemistry in order to (1) track the possible vent source at seabed, (2) better constrain the Azores magma source(s) sampled through the Serreta submarine volcanic event, and (3) interpret the data within the small-scale mantle source heterogeneity framework that has been demonstrated for the Azores archipelago. Lava balloons sampled at sea surface display a radiogenic signature, which is also correlated with relatively primitive (low) 4He/3He isotopic ratios. Conversely, SSR lavas are characterized by significantly lower radiogenic 87Sr/86Sr, 206Pb/204Pb and 208Pb/204Pb ratios than the lava balloons and the onshore lavas from the Terceira Island. SSR lavas are primitive, but incompatible trace-enriched. Apparent decoupling between the enriched incompatible trace element abundances and depleted radiogenic isotope ratios is best explained by binary mixing of a depleted MORB source and a HIMU­type component into magma batches that evolved by similar shallower processes in their travel to the surface. The collected data suggest that the freshest samples collected in the SSR may correspond to volcanic products of an unnoticed and more recent eruption than the 1998-2001 episode.

Extensional orogenic collapse captured by strike-slip tectonics:

The late Paleozoic collision between Gondwana and Laurussia resulted in the polyphase deformation and magmatism that characterizes the Iberian Massif of the Variscan orogen. In the Central Iberian Zone, initial con- tinental thickening (D1; folding and thrusting) was followed by extensional orogenic collapse (D2) responsible for the exhumation of high-grade rocks coeval to the emplacement of granitoids. This study presents a tectonometamorphic analysis of the Trancoso-Pinhel region (Central Iberian Zone) to ex- plain the processes in place during the transition froman extension-dominated state (D2) to a compression-dom- inated one (D3).Wereveal the existence of low-dipping D2 extensional structures later affected by several pulses of subhorizontal shortening, each of them typified by upright folds and strike-slip shearing (D3, D4 and D5, as identified by superimposition of structures). The D2 Pinhel extensional shear zone separates a low-grade domain from an underlying high-grade domain, and it contributed to the thermal reequilibration of the orogen by facil- itating heat advection from lower parts of the crust, crustal thinning, decompression melting, and magma intru- sion. Progressive lessening of the gravitational disequilibrium carried out by this D2 shear zone led to a switch from subhorizontal extension to compression and the eventual cessation and capture of the Pinhel shear zone by strike-slip tectonics during renewed crustal shortening. High-grade domains of the Pinhel shear zone were folded together with low-grade domains to define the current upright folded structure of the Trancoso-Pinhel re- gion, the D3 Tamames-Marofa-Sátão synform. Newdating of syn-orogenic granitoids (SHRIMP U\\Pb zircon dat- ing) intruding the Pinhel shear zone, together with the already published ages of early extensional fabrics constrain the functioning of this shear zone to ca. 331–311 Ma, with maximum tectonomagmatic activity at ca. 321–317 Ma. The capture and apparent cessation of movement of the Pinhel shear zone occurred at ca. 317– 311 Ma.

ERUPCIÓN DEL VOLCAN ARENAL EN EL AÑO 1968

En este informe personal sobre la actividad del volcán Arenal en 1968 el autor señala que es posible distinguir dos grandes ciclos de actividad: uno que corresponde a la constitucios de la base sobre la cual se levanta este volcan y su vecino inmediato,  el Cherro Chato, y que alcanza a unos 900m. s.n.m; y el otro de actividad intensa, con emisión de lavas y piroclastos que restituyeron la altura perdida por una activa erosión. La actividad, en todo caso, fue mas intensa en el Arenal que en el Chato y, por tanto, aquel es mas alto. Por observación de las fotos aéreas, el autor considera que ambos volcanes presentan restos de una soma; pero, mientras en el Chato toda actividad parece haber terminado, a juzgar por la ausencia de fumarolas, el Arenal ha seguido con períodos paroxismales, manifestados por la emision de las Nuées ardentes, Cenizas y otros piroclastos. La erupcion que comenzo en julio de 1968 se produjo despues de un periodo de reposo estimado en 700 a 400 años, causando ingentes daños materiales y la muerte de varias personas. Se han medido bloques lanzados por el volcan de 10 x 6m de diametro X 4.0 de profundidad. Bombas y piroclatos finos son de andesita hipersteno-hornbléndica y andesia hipersténica. La erupción fue acompañada de cientos de templores  y microsismos. Como conclusiones, pueden sañalarse: la erupción del tipo peleano, la lava extruida no ha cambiado respcto a la emitida 700 a 1000 años atrás la actividad paroxismal ha estado acompañada de numerosos sismos; el total de materiales piroclásticos se calcula en 26.5 millones de metros cúbicos; puede suponerse que el magma era muy viscoso si se toma en cuenta el tamaño de los “Piroclastic Flows” y las “nuées Ardientes”  no dieron lugar, en ningún caso, a ignimbritas (togas soldadas).

Consideraciones sobre la viscosidad de lavas y la estructura de las coladas de Volcán Arenal. Costa Rica

La aplicación estadística del método propuesto por Shaw (1972) permite calcular, conocidas las temperaturas de extrusión y las características de las lavas, el coeficiente de viscosidad teórica. La comparación de los datos teóricos con las medidas de campo, permite evaluar el comportamiento físico del magma y, en consecuencia, la influencia del mismo sobre la estructura de las coladas. La alta viscosidad de las lavas del Volcán Arenal se debe a microdiferenciación entre los fenocristales y la matriz, y a la estructura dinámica de las coladas. En particular, la parte superior de la colada y las paredes del canal de flujo se comportarían como aislador térmico y estructura  de confinamiento dinámico inhibiendo la distribución areal de las coladas. La continúa efusión de magma esta directamente ligada a la alta temperatura de las lavas; lo que parece estar en relación con particulares condiciones físico-estructurales en el contacto manto placa, en subducción, en correspondencia del Volcán Arenal.