Volcanic subsidence, caused by partial emptying of magma in the subsurface reservoir has long been observed by spaceborne radar interferometry. Monitoring long-term crustal deformation at the most notable type of volcanic subsidence, caldera, gives us insights of the spatial and hazard-related information of subsurface reservoir. Several subsiding calderas, such as volcanoes on the Galapagos islands have shown a complex ground deformation pattern, which is often composed of a broad deflation signal affecting the entire edifice and a localized subsidence signal focused within the caldera floor. Although numerical or analytical models with multiple reservoirs are proposed as the interpretation, geologically and geophysically evidenced ring structures in the subsurface are often ignored. Therefore, it is still debatable how deep mechanisms relate to the observed deformation patterns near the surface. We aim to understand what kind of activities can lead to the complex deformation. Using two complementary approaches, we study the three-dimensional geometry and kinematics of deflation processes evolving from initial subsidence to later collapse of calderas. Firstly, the analog experiments analyzed by structure-from-motion photogrammetry (SfM) and particle image velocimetry (PIV) helps us to relate the surface deformation to the in-depth structures. Secondly, the numerical modeling using boundary element method (BEM) simulates the characteristic deformation patterns caused by a sill-like source and a ring-fault. Our results show that the volcano-wide broad deflation is primarily caused by the emptying of the deep magma reservoir, whereas the localized deformation on the caldera floor is related to ring-faulting at a shallower depth. The architecture of the ring-fault to a large extent determines the deformation localization on the surface. Since series evidence for ring-faulting at several volcanoes are provided, we highlight that it is vital to include ring-fault activity in numerical or analytical deformation source formulation. Ignoring the process of ring-faulting in models by using multiple point sources for various magma reservoirs will result in erroneous, thus meaningless estimates of depth and volume change of the magmatic reservoir(s).

Uncertainty surrounding volcanic activity can lead to socio-economic crises with or without an eruption as demonstrated by the post-1978 response to unrest of Long Valley Caldera (LVC), CA. Extensive research in physical sciences provides a foundation on which to assess direct impacts of hazards, but fewer resources have been dedicated towards understanding human responses to volcanic risk. To evaluate natural hazard risk issues at LVC, a multi-hazard, mail-based, household survey was conducted to compare perceptions of volcanic, seismic, and wildfire hazards. Impacts of volcanic activity on housing prices and businesses were examined at the county-level for three volcanoes with a “very high” threat designation from the U.S. Geological Survey (USGS); LVC, (caldera system), Mount St. Helens, WA (stratovolcano), and Kīlauea, HI (shield volcano). A negative relationship was found between volcanic risk perception and preparedness. Additionally, the perception that housing prices declined after volcano alerts was confirmed by econometric modeling.

Cone-sheet swarms are magmatic sheet intrusions and part of volcanic plumbing systems and are pathways for magma to the Earth’s surface, where they feed volcanic eruptions. The analysis of cone-sheets provides information on the geometry of the magmatic plumbing system of a volcano and allows to understand processes and dynamics of magma transport. This is important to interpret information during a volcanic crisis and to help reduce risks to humans and infrastructure. In order to create a realistic model, the structure and shape of cone-sheet complexes can be reconstructed in three-dimensional space. Most cone-sheet swarms are not sufficiently exposed to allow such a reconstruction. The Tejeda cone-sheet swarm on Gran Canaria (Canary Islands, Spain), however, is an excellent location to study a cone-sheet complex in great detail, as it is exposed over 15 kmhorizontally and 1000 m vertically. This allows to determine its geometry in 3D space. The felsic deposits of the Miocene Tejeda caldera were intruded by cone-sheets between 11.7 and 7.3 Ma. Schirnick et al. (1999) assumed straight cone-sheets, based on 2D projections, and suggested that the Tejeda cone-sheet swarm is formed by a stack of uniformly dipping, parallel intrusive sheets that converge towards a common, static, laccolith-like source, forming a concentric structure around acentral axis that has the geometry of a truncated cone. This hypothesis was tested in this study, using structural data from Schirnick (1996) as well as additional data collected in the field. Using the software Move™, the extensive data set was visualized and projected in three dimensional space. The underlying magmatic source of the cone-sheets was reconstructed using two different approaches, with the first one based on sets of cross-sections to select intersection points, following an approach prognosed by Burchardt et al. (2013a). To improve the quality of the reconstruction of the magma chamber, a second method was developed using geometric calculations in MATLAB. The results indicate that individual cone-sheets are straight with parallel to slightly fanning dips, which can be steeper in the central part of the cone-sheet complex. They converge towards a common centre, creating a sub-spherical geometry of the source of the cone-sheet complex. Comparison of the two approaches used for the magma chamber reconstruction indicate that the second approach (geometric calculations) produces less uncertainties in data interpretation. The modelling results lead to the proposition of a dynamic model for the emplacement of the Tejeda cone-sheet complex. Cone-sheets would start to intrude from a reservoir situated at about 4500m below sea level that became successively shallower with time. / Inverterade koniska intrusionssvärmar är en del av det underjordiska vulkaniska systemet som möjliggör vägar för magma till jordens yta, där de livnär vulkaniska utbrott. Genom analys av inverterade koniska intrusioner kan information om geometrin hos magmatiska system erhållas vilket gör det möjligt att förstå magmans processer och transportdynamik. Detta är viktigt då det hjälper att tolka information under vulkaniska kriser och kan bidra till att minska risker för människor och infrastruktur. För att skapa en realistisk modell, kan strukturer och former av komplexa inverterade koniska intrusionssvärmar rekonstrueras i ett tredimensionellt utrymme. De flesta inverterade koniska intrusionssvärmar är inte tillräckligt blottade på jordens yta för att möjliggöra en sådan rekonstruktion.Tejedas inverterade koniska intrusionssvärm på Gran Canaria (Kanarieöarna, Spanien) är dock utmärktbelägen för att studera ett inverterat koniskt intrusionskomplex i detalj, detta då den är blottad i över 15 km horisontell och 1000 m i vertikal utsträckning. Detta gör det möjligt att bestämma dess geometrii tre dimensioner. De felsiska avlagringarna av den Miocena Tejeda kalderan blev intruderade av inverterade koniskaintrusioner mellan 11,7 och 7,3 Ma. Schirnick et al. (1999) antog att dessa intrusioner var raka, baseratpå 2D-projektioner, och föreslog att Tejedas inverterade koniska intrusionssvärm bildades som enlikformigt stupande stapel av parallella intruderande plan som konvergerar mot en gemensam, statiskoch lakkolitisk källa, vilken i sin tur bildar en koncentrisk struktur runt en central axel med samma geometri som en inverterad stympad kon. Denna hypotes undersöktes i detta arbete, med hjälp avstrukturell data från Schirnick (1996) samt ytterligare data insamlat från fält. Den omfattande datamängden visualiserades och projicerades i tre dimensioner med hjälp av mjukvaran Move™. Denunderliggande magmatiska källan till det inverterade koniska intrusionskomplexet rekonstruerades medhjälp av två olika metoder, den första är baserad på tvärsnitt där planens skärningspunkter kan studeras, följt av ett tillvägagångssätt framställt av Burchardt et al. (2013a). För att förbättra kvalitén pårekonstruktionen av magmakammaren utvecklades en andra metod med hjälp av geometriskaberäkningar i MATLAB. Resultaten tyder på att enskilda inverterade koniska intrusioner är raka med parallellt till svagt flacktstupning, vilka kan vara brantare mot den centrala delen av komplexet. De konvergerar mot ettgemensamt centrum, vilket skapar en sub-sfärisk geometri hos källan till det inverterade koniskaintrusionskomplexet. Jämförelse av de två metoderna som används för magmakammarens rekonstruktion tyder på att denandra metoden (geometriska beräkningar) ger färre osäkerheter i tolkningen. Modelleringsresultatettyder på en dynamisk modell för bildningen av Tejedas inverterade koniska intrusionskomplex. Enligtdessa resultat skulle de inverterade koniska intrusionerna till en början ha utgått från en reservoarungefär 4500 m under havsytan som med tiden förflyttade sig mot grundare nivåer.

Four multicyclic complex calderas and smaller ignimbrite shields located within the Altiplano Puna Volcanic Complex of the Central Andes (APVC) erupted 13000 km�� of magma within the last 11 Ma. One of the largest and most complex of these is the Cerro Guacha Caldera. Ar-Ar age determinations and paleomagnetic directions suggest that the Cerro Guacha Caldera was formed by two major eruptions, caldera collapse, resurgence cycles and several smaller eruptions. Two major ignimbrites (> 600 km��) are found with ������Ar-�����Ar from biotites and sanidines of 5.65 �� 0.01Ma for the 1300 km�� (magma volume) Guacha ignimbrite and 3.49 �� 0.01Ma for the 800 km�� Tara Ignimbrite. The last major eruption occurred on the western flank producing the 1.72 �� 0.02 Ma Puripica Chico Ignimbrite with a volume of approximately 10 km��. Characteristic remanent magnetization data (ChRM) for these ignimbrites show that the Guacha has reverse polarity, while the Tara is normally polarized and the magnetic fingerprints have allowed their current full extents to be identified. A conspicuous lineament of volcanic structures in the eastern part of the caldera, bordering a caldera moat, filled out welded ignimbrites and sedimentary lacustrine sequences suggest an earlier 60x40 km outer collapse associated with the Guacha explosive episode. A central graben formed on the Guacha welded ignimbrite is related to a first episode of resurgence. Evidence of a second 30 x15 km inner collapse includes offset of welded Guacha ignimbrites and alignment of lava domes associated with the Tara ignimbrite. A second resurgence episode is suggested by the presence of an uplifted central block consisting primarily of welded Tara ignimbrite. As a whole the three ignimbrites (Guacha, Tara and Puripica Chico) share the same petrological and geochemical characteristics: high-K series, compositional ranges from dacite to rhyolite, with andesitic members present as lavas (for the Guacha and Puripica Chico Ignimbrites) and as pumices (for the Tara Ignimbrite). Highest silica content is found in the Chajnantor dome. Rayleigh modeling for Ba, Rb and Sr suggests at least 60% of crystal fractionation to account for the compositional variation between the Guacha andesite and the Chajnantor dome. Dy/Hb ratio increases with time from the Guacha andesite to the Negreal andesite suggesting stabilization of garnet owing to crustal thickening. Fe-Ti exchange geothermometry for the Tara Ignimbrite yielded log fO��� values ranging from -13.06 to -13.38 and temperatures of 714�� to 801��C. Amphibole geobarometry yielded pressures ranging from 150 to 180 MPa equivalent to 5.3 and 6.4 km depth respectively for the Tara Ignimbrite; the pressures range between 133 to 242 MPa, equivalent to 5.0 to 9.2 km depth for the Guacha Ignimbrite. The zircon saturation method yielded saturation temperatures of 716�� and 705��C for the Guacha and Chajnantor dome respectively and 784��C for the Tara Ignimbrite. The zircon crystallization range for the magmas of the Cerro Guacha Caldera is 1.25 Ma for the Guacha Ignimbrite; 1.09 Ma for the Puripica Chico Ignimbrite and 0.95 Ma for the Tara Ignimbrite. Recycling of antecrystic zircons within the caldera magmas is continuos through time. / Graduation date: 2012

Στη διδακτορική αυτή διατριβή διερευνάται κατά πόσον η τηλεσκόπηση μπορεί να χρησιμεύει ως αρωγός για την κοιτασματολογική έρευνα και ειδικότερα για την εύρεση "στόχων" επιθερμικής μεταλλοφορίας πολύτιμων μετάλλων μέσω της αναγνωρίσεως ηφαιστειακών και τεκτονικών δομών και ζωνών υδροθερμικών εξαλλοιώσεων από αέρος. Το πεδίο έρευνας είναι το μειοκαινικό ηφαιστειακό-γεωθερμικό πεδίο της νήσου Λέσβου. Ερευνάται η ορυκτολογία των μεταλλικών ορυκτών και συνοδευόντων ορυκτών εξαλλοίωσης. Γίνονται πάραυτα μικροθερμομετρικοί προσδιορισμοί, προσδιορισμοί χρυσού-αργύρου, ιχνοστοιχείων- ιχνηλατών και άλλων ιχνοστοιχείων στις περιοχές-στόχους και τα γεωχημικά δεδομένα τίθενται σε περιβάλλον GIS (θεματικοί χάρτες). / In this phd dissertation it is investigated if remote sensing techniques can be used successfully as an aid in the ore deposits research and specifically for the localization by air "target" areas of epithermal mineralization of precious metals through the recognition of volcanic and tectonic structures and detection of hydrothermal alteration zones. The research area is the miocene volcanic-geothermal field of the island of Lesvos. The research includes also identification of ore and alteration minerals microthermometric measurements, measurement of the Au-Ag parts, of pathfinder and other trace elements in the target areas. The geochemical data are subsequently placed in a GIS environment for future research and/or mineral exploration purposes.

Better understanding of pyroclastic density current (PDC) dynamics is one of the key volcanological focuses, as PDCs represent one of the most life-threatening volcanic hazards. PDCs associated with explosive collapse calderas are difficult to observe and examine directly, and thus research of internal architecture of calderas and their PDC deposits is focused on extinct and partly eroded volcano-plutonic systems. Such a case is the Late-Carboniferous Altenberg-Teplice caldera in NW Bohemian Massif, which exposes a large body of ignimbrites (deposits of the PDC) called Teplice rhyolite (an intra-caldera fill). This body is well exposed on the southern flank of the Krušné hory/Erzgebirge Mts., mainly its members: Teichweg, Lugstein-Pramenáč, Vlčí kámen-Medvědí vrch and Přední Cínovec. As these ignimbrites appear macroscopically isotropic, I employed the Anisotropy of magnetic susceptibility (AMS) in order to quantify their internal structure. A total of 1232 specimens from 63 sampling stations were analyzed for the AMS, complemented by susceptibility vs. temperature variations and petrographic observations. Obtained AMS data, carried by a mixture of paramagnetic ferrosilicates and low-Ti titanomagnetite, indicate various processes recorded in ignimbrites. The relatively oldest and moderately welded Teichweg...

Better understanding of pyroclastic density current (PDC) dynamics is one of the key volcanological focuses, as PDCs represent one of the most life-threatening volcanic hazards. PDCs associated with explosive collapse calderas are difficult to observe and examine directly, and thus research of internal architecture of calderas and their PDC deposits is focused on extinct and partly eroded volcano-plutonic systems. Such a case is the Late-Carboniferous Altenberg-Teplice caldera in NW Bohemian Massif, which exposes a large body of ignimbrites (deposits of the PDC) called Teplice rhyolite (an intra-caldera fill). This body is well exposed on the southern flank of the Krušné hory/Erzgebirge Mts., mainly its members: Teichweg, Lugstein-Pramenáč, Vlčí kámen-Medvědí vrch and Přední Cínovec. As these ignimbrites appear macroscopically isotropic, I employed the Anisotropy of magnetic susceptibility (AMS) in order to quantify their internal structure. A total of 1232 specimens from 63 sampling stations were analyzed for the AMS, complemented by susceptibility vs. temperature variations and petrographic observations. Obtained AMS data, carried by a mixture of paramagnetic ferrosilicates and low-Ti titanomagnetite, indicate various processes recorded in ignimbrites. The relatively oldest and moderately welded Teichweg...

Malea Planum is a volcanic plain on the southern rim of Hellas Planitia, the largest impact basin on Mars. Four large circular structures on Malea Planum have traditionally been identified as paterae, or low relief, central vent volcanoes (Plescia and Saunders, 1979). A geologic map was constructed and new crater counts made to explore the ages and origins of the paterae. Amphitrites and Peneus Paterae have radial patterns of wrinkle ridges on their flanks and distinct summit calderas (95 km and 130 km across) with arcuate bounding scarps. In contrast, Malea and Pityusa Paterae are broad depressions with diameters greater than 400 km. In some ways Pityusa and Malea Paterae resemble old, filled impact craters (Plescia, 2003) but they also have characteristics of volcanic subsidence features (Roche et al., 2000). A very strong positive gravity anomaly is centered over Amphitrites and smaller positive anomalies are associated with Peneus and Malea Paterae. A slight annular positive anomaly is associated with Pityusa. The geology of the Malea Planum Region has been influenced by impact cratering, volcanic, tectonic, fluvial, and most recently, eolian processes. The Noachian was dominated by impact cratering, the formation of Hellas Basin, and the eruption of flood lavas. Malea Planum formed during the mid- to late-Noachian, likely the result of sills liquefying the volatile-rich crust. Malea and Pityusa Paterae formed during the late Noachian. The Hesperian was marked by the formation of Peneus and Amphitrites and complex valley networks. During the mid-Hesperian, southern Malea Planum may have been covered by a very thick polar mantle deposit that melted and sublimated during the late Hesperian. Smaller episodes of polar mantle deposition continued through the Amazonian to the present. The Amazonian is also characterized by eolian activity creating dune fields, etched surfaces, and dust devil tracks. Based on the topographic and geophysical evidence, Amphitrites and Peneus are typical highland paterae. We conclude that a mid-crustal sill complex similar to that thought to exist beneath the eastern Snake River Plain in Idaho may be the best explanation for the formation of Malea and Pityusa Paterae. A lack of associated flow features on the surface suggests that the loads are the result of an accumulation of dense intrusions. A surficial load (e.g., lava flows) is insufficient to cause the amount of subsidence observed. A mid-crustal mafic or ultra-mafic sill or a dense network of sills and dikes may have contributed to the subsidence.

Dans le Jbel Saghro (Anti-Atlas oriental, Maroc), deux évènements tectono-magmatiques ont été reconnus et mis en relation avec les processus hydrothermaux. Le socle sédimentaire Néoprotérozoïque moyen a été affecté par une déformation ductile faible, sous le contrôle d'une direction de raccourcissement orientée ca. NW-SE, responsable de la formation de grands plis et d'une schistosité plan axial, d'accidents décrochants dextres N070-090°E, de chevauchements localisés et de la mise en place de plutons granodioritiques syntectoniques. Le deuxième évènement se caractérise par l'instauration d'un important volcano-plutonisme acide Néoprotérozoïque supérieur associé au dépôt des principales minéralisations à Au-Ag du secteur. A Kelâa M'Gouna, cet épisode a été rattaché à la formation d'une caldera ignimbritique. Bien que chacun des dépôts hydrothermaux présente des spécificités particulières, toutes les structures minéralisées se sont formées en réponse à une direction de raccourcissement orientée ca. WNW-ESE, la même qui contrôle la mise en place du volcanisme ignimbritique.

Au Cambrien (Tommotien à cambro-trémadocien), l'extrémité orièntale du, Massif armoricain est le siège d'une intense activité volcanique localisée dans le graben du Maine, important fossé d'effondrement comblé de plus de 3 000 mètres de sédiments marins peu profonds. Les centres éruptifs se situent à l'intérieur de trois grandes calderas (calderas d'Ecouves, de Perseigne et d'Assé-Ie-Boisne - Pail), bordées d'un vaste domaine externe méridional où se placent les Coëvrons et la Charnie. L'activité volcanique s'exerce au cours de plusieurs cyc l~s (6 au total, dénommés Vo à VS, dont les éruptions, aériennes ou sous-aquatiques, se caractérisent surtout par leur très fort degré d'explosivité. Lors des crises paroxysmales correspondant au stade de formation des calderas, sont libérées de très volumineuses nappes ignimbritiques 'chaudes à texture soudée, empilées sur plusieurs centaines de mètres à l'intérieur de la structure. Dans la caldera d'Assé-Ie-Boisne - Pail, la plus engagée dans le domaine marin, de très violents phénomènes hydroclastiques se déclenchent, parmi lesquels des éruptions phréatopliniennes délivrant d'énormes quantités de cÊmdres humides à pisolithes volcaniques, accompagnées de l'émission de nappes ignimbritiques ponceuses qui se propagent dans le domaine externe jusqu'à plus de 30 km de leur source. Ces coulées pyroclastiques distales non soudées ("out-flow") sont piégées dans un réseau de chenaux fluvio-marins par où transitent des décharges bréchiques et conglomératiques, ainsi que d'épaisses coulées lahariques. L'accumulation de ces matériaux en domaine externe contribue à la création de puissants complexes volcano-sédimentaires reconnus dans les Coëvrons et la Charnie. Conformément au dynamisme des éruptions, les produits de l'activité volcanique sont su rtout représentés par des ignimbrites et des pyroclastites acides (>90 % du volume tota,1 des volcanites) ainsi que par quelques laves andésitiques, dacitiques et rhyolitiques. La totalité de ces volcanites a subi d'importanles transformations minéralogiques (paragenèses de basse température) apparues soit au cours de phénomènes hydrothermaux, soit lors d'un métamorphisme régional varisque de degré anchizonal (T =300 à 400°C; P<2 kb) . Les laves appartiennent à une suite de termes d'affinité calco-alcaline, dont les concentrations en éléments hygromagmaphiles, éléments réfractaires aux processus d'altération ~t de métamorphisme, possèdent des valeu rs de rapports comparables à celles des laves des domaines ' orogéniques actuels (LafTh=2 à 7; Thrra=8 à 10). L'évolution de cette lignée andésitique obéit à des mécanismes de cristallisation fractionnée impliquant tout d'abord l'assemblage plagioclase + pyroxène + oxydes ferro-titanés (andésite à dacite), puis plagioclase + FK + amphibole + minéraux accessoires (dacite à rhyolite). L'origine présumée des andésites basaltiques, termes les plus primitifs de cette lignée, est rechmchée dans la fusion partielle d'une souche mantellique dépourvue de grenat, fusion vraisemblablement déclenchée par un processus de décompression adiabatique lors de la distension cambrienne. Les ignimbrites dérivent de la fus ion crustale des séries volcano-sédi mentaires briovériennes, sous l'action probable de l'injection répétée des magmas andésitiques en base de croûte. Le cadre géodynamique dans lequel s'exerce l'activité volcanique cambrienne du Maine est celui d'un fossé d'effondrement soumis à une forte extension et qui jalonne une discontinuité crustale majeure, héritée de l'histoire cadomienne (limite entrE:) le bassin marginal mancellien et sa marge continentale méridionale). Cette activité marque la fin des manifestations magmatiques cadomiennes, caractérisées en domaine mancellien par d'intenses fusions crustales contribuant à la cratonisation : du dispositif d'arcs et de bassins de la chaîne fini-précambrienne.