Studying Volcanic Plumbing Systems – Multidisciplinary Approaches to a Multifaceted Problem

Magma transport and storage beneath active volcanoes occurs in the so-called volcanic plumbing system (VPS), a network of different magmatic sheet intrusions and magma reservoirs. The complex physical and chemical processes, which occur in the volcanic plumbing system, are key parameters that control the occurrence of an eruption, as well as type and size of the eruption. It is therefore imperative to assess plumbing system processes and their dynamics. Traditionally, plumbing system research is done as a part of various scientific disciplines, each with its own research questions, methods, and terms. As a consequence, there is often little overlap and communication between the disciplines. In this chapter, we give an overview of the history of plumbing system research and outline the state of the art of the main scientific disciplines involved. We summarise the potential and limitations of each discipline and then discuss three key components to foster multidisciplinary research—namely communication, information, and education—which are essential to promote a better understanding of the complexity of volcanic plumbing systems

Regional fold structure analysis in the Eastern Alpi Apuane, Northern Apennine

The Alpi Apuane represent a large tectonic window within the Northern Apennine in Italy. In this area, not only a complete succession of the tectonic units of the Northern Apennine can be studied, but also the structures that result from at least two Alpine deformational events. The rocks of the Alpi Apuane have been deposited from Triassic to Tertiary times on the Hercynian basement of the passive continental margin of the Apulian plate. The sedimentary succession included meta-dolostones, marbles, metacherts, schists, and turbiditic arenites. During late Oligocene more internal units (the Tuscan Nappe together with the overlying Ligurides and Sub- Ligurides) were thrusted over the External Tuscan Domain (Alpi Apuane). The Alpi Apuane stratigraphic sequence was subject to greenschist facies metamorphosis and severe deformation within a crustal scale shear zone. Kilometrescale tight recumbent folds developed during a first deformation event (D1). The successive crustal shortening resulted in a further tightening of folds and the formation of an antiformal stack geometry with a central culmination. This late phase of D1 produced a curving of N–S (Apenninic) trending folds towards an E–W (anti-Apenninic) trend. During Miocene the overthickened antiform underwent gravitational collapse resulting in the refolding of D1 structures producing D2 open and back folds. The studied field area is located in the Eastern Alpi Apuane between Arni and Isola Santa in an area of anti-Apenninic trending D1 folds. The purpose of this study is to contribute to an understanding of 1. how the anti-Apenninic fold trend is developed in the Eastern Alpi Apuane, 2. how the D2 deformational event influenced the D1 folds in the area, and 3. how the anti-Apenninic fold trend developed.conferenc

Host-rock deformation during the emplacement of the Mourne Mountains granite pluton : insights from the regional fracture pattern

The Mourne Mountains magmatic center in Northern Ireland consists of five successively intruded granites emplaced in the upper crust. The Mourne granite pluton has classically been viewed as a type locality of a magma body emplaced by cauldron subsidence. Cauldron subsidence makes space for magma through the emplacement of ring dikes and floor subsidence. However, the Mourne granites were more recently re-interpreted as laccoliths and bysmaliths. Laccolith intrusions form by inflation and dome their host rock. Here we perform a detailed study of the deformation in the host rock to the Mourne granite pluton in order to test its emplacement mechanism. We use the host-rock fracture pattern as a passive marker and microstructures in the contact-metamorphic aureole to constrain large-scale magma emplacement-related deformation. The dip and azimuth of the fractures are very consistent on the roof of the intrusion and can be separated into four steeply inclined sets dominantly striking SE, S, NE, and E, which rules out pluton-wide doming. In contrast, fracture orientations in the northeastern wall to the granites suggest shear parallel to the contact. Additionally, contact-metamorphic segregations along the northeastern contact are brecciated. Based on the host-rock fracture pattern, the contact aureole deformation, and the north-eastward-inclined granite-granite contacts, we propose that mechanisms involving either asymmetric "trap-door" floor subsidence or laccolith and bysmalith intrusion along an inclined or curved floor accommodated the emplacement of the granites and led to deflection of the northeastern wall of the intrusion.Publisher PDFPeer reviewe

Syn-emplacement fracturing in the sandfell laccolith, eastern iceland—implications for rhyolite intrusion growth and volcanic hazards

Field work was funded by Uddeholms travel stipend (Värmlands nation, Uppsala, Sweden), Otterborgs travel stipend and the Swedish Royal Academy of Science (KVA). The research was funded by the Swedish Research Council (VR) grant 2015-03931_VR. ER is funded by the Center of Natural Hazards and Disaster Science (CNDS).Felsic magma commonly pools within shallow mushroom-shaped magmatic intrusions, so-called laccoliths or cryptodomes, which can cause both explosive eruptions and collapse of the volcanic edifice. Deformation during laccolith emplacement is primarily considered to occur in the host rock. However, shallowly emplaced laccoliths (cryptodomes) show extensive internal deformation. While deformation of magma in volcanic conduits is an important process for regulating eruptive behavior, the effects of magma deformation on intrusion emplacement remain largely unexplored. In this study, we investigate the emplacement of the 0.57km3 rhyolitic Sandfell laccolith, Iceland, which formed at a depth of 500m in a single intrusive event. By combining field measurements, 3D modeling, anisotropy of magnetic susceptibility (AMS), microstructural analysis, and FEM modeling we examine deformation in the magma to constrain its influence on intrusion emplacement. Concentric flow bands and S-C fabrics reveal contact-parallel magma flow during the initial stages of laccolith inflation. The magma flow fabric is overprinted by strain-localization bands (SLBs) and more than one third of the volume of the Sandfell laccolith displays concentric intensely fractured layers. A dominantly oblate magmatic fabric in the fractured areas and conjugate geometry of SLBs, and fractures in the fracture layers demonstrate that the magma was deformed by intrusive stresses. This implies that a large volume of magma became viscously stalled and was unable to flow during intrusion. Fine-grained groundmass and vesicle-poor rock adjacent to the fracture layers point to that the interaction between the SLBs and the flow bands at sub-solidus state caused the brittle-failure and triggered decompression degassing and crystallization, which led to rapid viscosity increase in the magma. The extent of syn-emplacement fracturing in the Sandfell laccolith further shows that strain-induced degassing limited the amount of eruptible magma by essentially solidifying the rim of the magma body. Our observations indicate that syn-emplacement changes in rheology, and the associated fracturing of intruding magma not only occur in volcanic conduits, but also play a major role in the emplacement of viscous magma intrusions in the upper kilometer of the crust.Publisher PDFPeer reviewe

Dynamics of dikes versus cone sheets in volcanic systems

International audienceIgneous sheet intrusions of various shapes, such as dikes and cone sheets, coexist as parts of complex volcanic plumbing systems likely fed by common sources. How they form is fundamental regarding volcanic hazards, yet no dynamic model simulates and predicts satisfactorily their diversity. Here we present scaled laboratory experiments that reproduced dikes and cone sheets under controlled conditions. Our models show that their formation is governed by a dimensionless ratio (Π1), which describes the geometry of the magma source, and a dynamic dimensionless ratio (Π2), which compares the viscous stresses in the flowing magma to the host rock strength. Plotting our experiments against these two numbers results in a phase diagram evidencing a dike and a cone sheet field, separated by a sharp transition that fits a power law. This result shows that dikes and cone sheets correspond to distinct physical regimes of magma emplacement in the crust. For a given host rock strength, cone sheets preferentially form when the source is shallow, relative to its lateral extent, orwhen the magma influx velocity (or viscosity) is high. Conversely, dikes form when the source is deep compared to its size, or when magma influx rate (or viscosity) is low. Both dikes and cone sheets may form fromthe same source, the shift fromone regime to the other being then controlled by magma dynamics, i.e., different values of Π2. The extrapolated empirical dike-to-cone sheet transition is in good agreement with the occurrence of dikes and cone sheets in various natural volcanic settings

Strukturgeologische Analysen des Thingvellir Spaltenschwarms, Südwest Island

Der Holozäne Thingvellir Spaltenschwarm ist Teil des 60 km langen Hengill Vulkansystems, das sich in der Westvulkanischen Zone in Island befindet und ein etwa 9000 Jahre altes basaltisches Lavafeld nördlich des Sees Thingvallavatn durchquert. Dieser Spaltenschwarm enthält einige der größten postglazialen Verwerfungen und Brüche, die in der Riftzone Islands anzutreffen sind. Das Zentrum des Hengill Vulkansystems bildet der 0.8 Ma alte gleichnamige Vulkan. Der Gipfel des Vulkans ist durchzogen von NE-SW streichenden Abschiebungen, von denen einige bis zum See Thingvallavatn verfolgt werden können. Der Thingvellir Spaltenschwarm wird von nahezu vertikalen Zugbrüchen und geöffneten Abschiebungen dominiert...conferenc

Tektonische Entwicklung des Geitafell-Vulkans, Südost-Island

Der Geitafell-Vulkan ist ein erloschener tertiärer Zentralvulkan (Stratovulkan) in Südost-Island. Aufgrund tiefer glazialer Erosion ist das Innere des Vulkans bis hinab zur erloschenen krustalen Magmakammer aufgeschlossen. Das bietet die einmalige Möglichkeit, die Infrastruktur und die tektonische Entwicklung eines typischen isländischen Zentralvulkans zu untersuchen. Der Geitafell-Vulkan besteht aus einer Abfolge von eruptiven Materialien unterschiedlicher mechanischer Eigenschaften wie zum Beispiel basaltische Laven, Hyaloklastite und saure Extrusiva. Im Kern des Vulkans ist der obere Teil einer erloschenen krustalen Magmakammer in Form mehrerer Gabbrokörper aufgeschlossen. Im direkten Kontakt mit der Magmakammer befindet sich ein sehr dichter Schwarm von Kegelgängen, die von der Magmakammer injiziert wurden, als der Geitafell-Vulkan von etwa 5 bis 6Ma aktiv war (Fridleifsson, 1983). Um unser Verständnis über die vulkanotektonische Entwicklung des Zentralvulkans zu verbessern, wurden im Geitafell-Gebiet mehr als 500 Gänge und Kegelgänge, 400 Mineralgänge und etwa 1100 Klüfte gemessen...conferenc

Emplacement and segment geometry of large, high-viscosity magmatic sheets

This project and Tobias Schmiedel are funded by the Knut and Alice Wallenberg Foundation through a Wallenberg Academy Fellow grant to Steffi Burchardt (grant No. KAW 2017.0153).Understanding magma transport in sheet intrusions is crucial to interpreting volcanic unrest. Studies of dyke emplacement and geometry focus predominantly on low-viscosity, mafic dykes. Here, we present an in-depth study of two high-viscosity dykes (106 Pa·s) in the Chachahuén volcano, Argentina, the Great Dyke and the Sosa Dyke. To quantify dyke geometries, magma flow indicators, and magma viscosity, we combine photogrammetry, microstructural analysis, igneous petrology, Fourier-Transform-Infrared-Spectroscopy, and Anisotropy of Magnetic Susceptibility (AMS). Our results show that the dykes consist of 3 to 8 mappable segments up to 2 km long. Segments often end in a bifurcation, and segment tips are predominantly oval, but elliptical tips occur in the outermost segments of the Great Dyke. Furthermore, variations in host rocks have no observable impact on dyke geometry. AMS fabrics and other flow indicators in the Sosa Dyke show lateral magma flow in contrast to the vertical flow suggested by the segment geometries. A comparison with segment geometries of low-viscosity dykes shows that our high-viscosity dykes follow the same geometrical trend. In fact, the data compilation supports that dyke segment and tip geometries reflect different stages in dyke emplacement, questioning the current usage for final sheet geometries as proxies for emplacement mechanism.Publisher PDFPeer reviewe

Dyke emplacement in Tenerife (Canary Islands): Field studies and numerical models

Dykes are magma-driven extension fractures and the main conduits for magma in volcanic eruptions. To understand the mechanics of dyke emplacement is thus essential to assess volcanic hazards. To improve the understanding of the processes of dyke initiation from shallow magma chambers and dyke propagation through a mechanicallylayered crust, field measurements and observations from Tenerife (Canary Islands) are used and compared with the results from numerical models. Careful studies of 550 dykes in three profiles in the Anaga massif (Tenerife) include measurements of dyke geometry and orientation. The results of these measurements show that dykes have been injected from a deep-seated reservoir during the shield-building phase. Furthermore, the dyke attitudes agree with the main axial trends of Tenerife that are preserved in the old massifs of Teno, Anaga, and Roque del Conde...conferenc

Fluidtransport entlang von Störungen und Klüften im Gebiet des Hengill-Vulkans, SW-Island

Das Holozäne Hengill-Vulkansystem liegt in der aktiven Westvulkanischen Zone in Südwestisland. Es beinhaltet den Hengill-Zentralvulkan, der sich südlich des Sees Thingvallavatn befindet, und ist eines der aktivsten geothermischen Systeme Islands (Abb. 1). Die aktuelle Spreizungsrate in der Westvulkanischen Zone liegt zwischen 3 und 7mma−1 bei einer Subsidenzrate von 1mma−1 (Tryggvason 1982; La Femina et al. 2005). Das Hengill-Vulkansystem ist 60–70km lang und zwischen 5 und 10km breit. Strukturgeologisch wird das Gebiet von großen NNE-streichenden Abschiebungen dominiert. Das Hauptziel dieser Untersuchung ist, das Verständnis für die Bruchentwicklung und die Fluidtransportmechanismen im Hengill-Gebiet zu verbessern. Dieses Verständnis ist notwendig, um realistischere Modelle über den Fluidtransport in den geothermischen Feldern erstellen zu können und um bessere Prognosen über ihre Lebensdauer zu ermöglichen. Weiterhin soll der Kenntnisstand über den Einfluss von Wässern auf Erdbebenentstehung untersucht werden, da in diesem Gebiet die meisten Erdbeben durch Fluidüberdruck ausgelöst werden.conferenc