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Ólafur Gudmundsson - One of the best experts on this subject based on the ideXlab platform.

Peter Gudmundson - One of the best experts on this subject based on the ideXlab platform.

Per Fredriksson - One of the best experts on this subject based on the ideXlab platform.

Agust Gudmundsson - One of the best experts on this subject based on the ideXlab platform.

  • Forecasting the propagation paths of fluid-driven fractures, particularly dikes and inclined sheets
    2020
    Co-Authors: Agust Gudmundsson, Kyriaki Drymoni, Mohsen Bazargan, Kayode Adeoye-akinde
    Abstract:

    <p>It is of great importance in many fields to be able to forecast the likely propagation paths of fluid-driven factures. These include mineral veins, human-made hydraulic fractures, and dikes/inclined sheets. The physical principles that control the propagation of all fluid-driven fractures are the same. Here the focus is on dikes and inclined sheets where the selected path determines whether, where, and when a particular dike/sheet reaches the surface to erupt. Here we provide analytical and numerical models on dike/sheet paths in crustal segments (including volcanoes) that include layers of various types (lava flows, pyroclastic flows, tuff layers, soil layers, etc) as well as mechanically weak contacts and faults. The modelling results are then compared with, and tested on, actual data of two types. (a) Seismic data on the paths of dikes/sheets as well as human-made hydraulic fractures, and (b) field data on the actual propagation paths of dikes/sheets in layered and faulted rocks</p><p>The numerical results show that, particularly in stratovolcanoes, the paths are likely to be complex with common deflections along layer contacts, in agreement with field observations.  Also, some dikes/sheets may use existing faults as parts of their paths, primarily steeply dipping and recently active normal faults. The propagation path is thus not entirely in pure mode I but rather partly in a mixed mode. The energy required to propagate the dike/sheet is mainly the surface energy needed to rupture the rock, to form two new surfaces and move them apart as the fracture propagates. The energy available to drive the fracture is the stored elastic energy in the hosting crustal segment.</p><p>From its point of initiation in the magma-chamber roof, a dike/sheet can, theoretically, select any one of an infinite number of paths to follow to its point of arrest or eruption. It is shown that the eventual path selected is the one of least action, that is, the path along which the time integral of the difference between the kinetic and potential energies is an extremum (normally a minimum) relative to all other possible paths with the same endpoints. If the kinetic energy is omitted, and there are no constraints, then least action becomes the minimum potential energy, which was postulated as a basis for understanding dike propagation by Gudmundsson (1986). Here it is shown how this theoretical framework can help us make reliable forecasts of dike/sheet paths and associated volcanic eruptions.</p><p>Gudmundsson, A., 1986. Formation of dykes, feeder-dykes, and the intrusion of dykes from magma chambers. Bulletin of Volcanology, 47, 537-550.</p><p>Gudmundsson, A., 2020. Volcanotectonics: Understanding the Structure, Deformation, and Dynamics of Volcanoes. Cambridge University Press, Cambridge.</p><p>Drymoni, K., Browning, J. Gudmundsson, A., 2020. Dyke-arrest scenarios in extensional regimes: insights from field observations and numerical models, Santorini, Greece. Journal of Volcanology and Geothermal Research (in press).</p><p> </p>

  • Understanding stress and deformation in active volcanoes
    Tectonophysics, 2009
    Co-Authors: Agust Gudmundsson, Valerio Acocella, Sergio Vinciguerra
    Abstract:

    No eruption, no caldera collapse, and no large landslide can takeplaceinavolcanounlessitsstateofstressissuitablefortheassociatedtype of rock failure. The state of stress, in turn, results in deformation,andbothstressanddeformationdependonthemechanicalpropertiesof the rocks that constitute the volcano. Understanding stress anddeformation in volcanoes is thus of fundamental importance forunderstanding unrest periods and for accurate forecasting volcanofailure, such as may result in large-scale lateral and vertical collapsesand eruptions.Deformation studies in volcanic areas have significantly improved,both in quality and quantity, during the past decade. While theinterest of the scientific community, and the volcanological commu-nity in particular, has primarily been in the description andinterpretation of the deformation, especially at active volcanoes,new and powerful techniques have recently become available toimprove our understanding of the local stresses and mechanicalproperties of volcanoes and how they relate to surface deformation.Volcano deformation studies in the last years have of courseincluded standard field and analytical techniques, but in additionthere has been increasing use of advanced analogue and numericalmodels, as well as modern geophysical monitoring techniques such asGPS and InSAR. All these techniques have contributed to an improvedunderstanding of various aspects of both regional and local volcanodeformation. At the regional scale, the relationship between tectonicsand magmatism at divergent plate boundaries is now better under-stood (e.g. Kendall et al., 2005; Wright et al., 2006) and so is thegeneral relationship between arc volcanism and seismicity (e.g.Walter and Amelung, 2007). At a more local scale, significantimprovements have been made in understanding the mechanics ofmagma-chamber rupture (e.g. Gudmundsson, 2006), dyke propaga-tion(e.g.Polandetal.,2004;Gudmundssonetal.,2008),thestructureof calderas (e.g. Acocella, 2007; Gottsmann and Marti, 2008; Geshi,2009), the collapse of volcanoes (e.g. Cervelli et al., 2002; Amelunget al., 2007), the relationships between volcanic activity and edificedeformation (e.g. Neri et al., 2009), the seismicity associated withvolcanism (Benson et al., 2008) and the interactions betweenvolcanoes (e.g. Miklius and Cervelli, 2003; Andrew and Gudmunds-son, 2008). These and other studies confirm the crucial importance ofunderstandingdeformationandstressinvolcanicareas,asisgenerallyrecognised by the volcanological and tectonic communities.Oneimportanttopicrelatedtovolcanodeformationandstressthatis still not well understood is how active deformation can be used toforecast eruptions and their behaviour. This applies particularly to themechanics of dike emplacement. The vast majority of volcaniceruptions are fed by dikes, and understanding dike propagation andarrest is necessary so as to mitigate various hazards associated withvolcanic eruptions, caldera collapses, and landslides. In particular,major eruptions, seismicity, and sector collapses pose threats out togreat distances from volcanoes. Understanding these processes,however, depends on knowing the more general relationshipsbetween deformation, stress, and volcanic activity.The structure and contents of this special issue are motivatedprimarily by our belief that understanding deformation and stress inactive volcanoes is a necessary condition for reliable forecast ofvolcanic eruptions, caldera collapses, and large landslides. Thesetopics all belong to the field of volcanotectonics. Also, we think thatcorrect interpretation of volcano deformation, in terms of localstresses and mechanical properties, is fundamental for understandingvolcano behaviour and, thereby, assessing volcanic hazards.This special issue derives from a session on volcanotectonics at the2007EGUAssemblyinVienna,Austria.Thefocusisonfivemaintopicswithin the field of volcanotectonics. The first topic concerns generalaspects of volcano deformation, stress, and failure (Bonafede andFerrari, 2009-this volume; Eggert and Walter, 2009-this volume;Gudmundsson, 2009-this volume). The second topic is collapsecalderas (Battaglia and Hill, 2009-this volume; Jonsson, 2009-thisvolume; Kusumoto and Gudmundsson, 2009-this volume), followedby dike propagation and arrest (Acocella and Neri, 2009-this volume;Contents lists available at ScienceDirect

  • Reply to Comment on ‘Dykes, faults and paleostresses in the Teno and Anaga massifs of Tenerife (Canary Islands)’ by J.A. Rodrı́guez-Losada and A. Hernández-Pacheco
    Journal of Volcanology and Geothermal Research, 2002
    Co-Authors: Laura Marinoni, Agust Gudmundsson
    Abstract:

    Abstract We welcome the comment by Rodriguez-Losada and Hernandez-Pacheco (hereafter LP) and we are pleased that they have ‘no objections to the conclusions’ of Marinoni and Gudmundsson (2000 ; hereafter MG). The LP comment deals only with the Anaga massif and mostly with (1) dykes supposed to be folded by post-emplacement ductile deformation, (2) tilting of the oldest part of the Anaga succession, (3) selection of profiles, (4) the horizontal extension due to dykes, and (5) the paleostress field of Anaga. We reply briefly to these points below.

A Hernandezpacheco - One of the best experts on this subject based on the ideXlab platform.