@phdthesis{Mueller2024,
  author    = {M{\"u}ller, Daniel},
  title     = {Identification and monitoring of structures, controls, and evolution dynamics of hydrothermal systems and associated alteration through high-resolution remote sensing and in situ analysis},
  doi       = {10.25932/publishup-62668},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-626683},
  school      = {Universit{\"a}t Potsdam},
  pages     = {205},
  year      = {2024},
  abstract  = {Volcanic hydrothermal systems are an integral part of most volcanoes and typically involve a heat source, adequate fluid supply, and fracture or pore systems through which the fluids can circulate within the volcanic edifice. Associated with this are subtle but powerful processes that can significantly influence the evolution of volcanic activity or the stability of the near-surface volcanic system through mechanical weakening, permeability reduction, and sealing of the affected volcanic rock. These processes are well constrained for rock samples by laboratory analyses but are still difficult to extrapolate and evaluate at the scale of an entire volcano. Advances in unmanned aircraft systems (UAS), sensor technology, and photogrammetric processing routines now allow us to image volcanic surfaces at the centimeter scale and thus study volcanic hydrothermal systems in great detail. This thesis aims to explore the potential of UAS approaches for studying the structures, processes, and dynamics of volcanic hydrothermal systems but also to develop methodological approaches to uncover secondary information hidden in the data, capable of indicating spatiotemporal dynamics or potentially critical developments associated with hydrothermal alteration. To accomplish this, the thesis describes the investigation of two near-surface volcanic hydrothermal systems, the El Tatio geyser field in Chile and the fumarole field of La Fossa di Vulcano (Italy), both of which are among the best-studied sites of their kind. Through image analysis, statistical, and spatial analyses we have been able to provide the most detailed structural images of both study sites to date, with new insights into the driving forces of such systems but also revealing new potential controls, which are summarized in conceptual site-specific models. Furthermore, the thesis explores methodological remote sensing approaches to detect, classify and constrain hydrothermal alteration and surface degassing from UAS-derived data, evaluated them by mineralogical and chemical ground-truthing, and compares the alteration pattern with the present-day degassing activity. A significant contribution of the often neglected diffuse degassing activity to the total amount of degassing is revealed and constrains secondary processes and dynamics associated with hydrothermal alteration that lead to potentially critical developments like surface sealing. The results and methods used provide new approaches for alteration research, for the monitoring of degassing and alteration effects, and for thermal monitoring of fumarole fields, with the potential to be incorporated into volcano monitoring routines.},
  language  = {en}
}
@phdthesis{GaeteRojas2020,
  author    = {Gaete Rojas, Ayleen Barbara},
  title     = {Monitoring and modeling observations of plumbing systems at caldera-like topography},
  doi       = {10.25932/publishup-44613},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-446135},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 96},
  year      = {2020},
  abstract  = {In this dissertation, I describe the mechanisms involved in magmatic plumbing system establishment and evolution. Magmatic plumbing systems play a key role in determining volcanic activity style and recognizing its complexities can help in forecasting eruptions, especially within hazardous volcanic systems such as calderas. I explore the mechanisms of dike emplacement and intrusion geometry that shape magmatic plumbing systems beneath caldera-like topographies and how their characteristics relate to precursory activity of a volcanic eruption. For this purpose, I use scaled laboratory models to study the effect of stress field reorientation on a propagating dike induced by caldera topography. I construct these models by using solid gelatin to mimic the elastic properties of the earth's crust with a caldera on the surface. I inject water as the magma analog and track the evolution of the experiments through qualitative (geometry and stress evolution) and quantitative (displacement and strain computation) descriptions. The results show that a vertical dike deviates towards and outside of the caldera-like margin due to stress field reorientation beneath the caldera-like topography. The propagating intrusion forms a circumferential-eruptive dike when the caldera-like size is small, whereas a cone sheet develops beneath the large caldera-like topography. To corroborate the results obtained from the experimental models, this thesis also describes the results of a case study utilizing seismic monitoring data associated with the unrest period of the 2015 phreatic eruption of Lascar volcano. Lascar has a crater with a small-scale caldera-like topography and exhibited long-lasting anomalous evolution of the number of long-period (LP) events preceding the 2015 eruption. I apply seismic techniques to constrain the hypocentral locations of LP events and characterize their spatial distribution, obtaining an image of Lascar's plumbing system. I observe an agreement in shallow hypocentral locations obtained through four different seismic techniques; nevertheless, the cross-correlation technique provides the best results. These results depict a plumbing system with a narrow sub-vertical deep conduit and a shallow hydrothermal system, where most LP events are located. These two regions are connected through an intermediate region of path divergence, whose geometry and orientation likely is influenced by stress reorientation due to topographic effects of the caldera-like crater. Finally, in order to further enhance the interpretations of the previous case study, the seismic data was analyzed in tandem with a complementary multiparametric monitoring dataset. This complementary study confirms that the anomalous LP activity occurred as a sign of unrest in the preparatory phase of the phreatic eruption. In addition, I show how changes observed in other monitored parameters enabled to detect further signs of unrest in the shallow hydrothermal system. Overall, this study demonstrates that detecting complex geometric regions within plumbing systems beneath volcanoes is fundamental to produce an effective forecast of eruptions that from a first view seem to occur without any precursory activity. Furthermore, through the development of this research I show that combining methods that include both observations and models allows one to obtain a more precise interpretation of the volcanic processes.},
  language  = {en}
}
@phdthesis{Nikkhoo2019,
  author    = {Nikkhoo, Mehdi},
  title     = {Analytical and numerical elastic dislocation models of volcano deformation processes},
  doi       = {10.25932/publishup-42972},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-429720},
  school      = {Universit{\"a}t Potsdam},
  pages     = {x, 175},
  year      = {2019},
  abstract  = {The advances in modern geodetic techniques such as the global navigation satellite system (GNSS) and synthetic aperture radar (SAR) provide surface deformation measurements with an unprecedented accuracy and temporal and spatial resolutions even at most remote volcanoes on Earth. Modelling of the high-quality geodetic data is crucial for understanding the underlying physics of volcano deformation processes. Among various approaches, mathematical models are the most effective for establishing a quantitative link between the surface displacements and the shape and strength of deformation sources. Advancing the geodetic data analyses and hence, the knowledge on the Earth's interior processes, demands sophisticated and efficient deformation modelling approaches. Yet the majority of these models rely on simplistic assumptions for deformation source geometries and ignore complexities such as the Earth's surface topography and interactions between multiple sources. This thesis addresses this problem in the context of analytical and numerical volcano deformation modelling. In the first part, new analytical solutions for triangular dislocations (TDs) in uniform infinite and semi-infinite elastic media have been developed. Through a comprehensive investigation, the locations and causes of artefact singularities and numerical instabilities associated with TDs have been determined and these long-standing drawbacks have been addressed thoroughly. This approach has then been extended to rectangular dislocations (RDs) with full rotational degrees of freedom. Using this solution in a configuration of three orthogonal RDs a compound dislocation model (CDM) has been developed. The CDM can represent generalized volumetric and planar deformation sources efficiently. Thus, the CDM is relevant for rapid inversions in early warning systems and can also be used for detailed deformation analyses. In order to account for complex source geometries and realistic topography in the deformation models, in this thesis the boundary element method (BEM) has been applied to the new solutions for TDs. In this scheme, complex surfaces are simulated as a continuous mesh of TDs that may possess any displacement or stress boundary conditions in the BEM calculations. In the second part of this thesis, the developed modelling techniques have been applied to five different real-world deformation scenarios. As the first and second case studies the deformation sources associated with the 2015 Calbuco eruption and 2013-2016 Copahue inflation period have been constrained by using the CDM. The highly anisotropic source geometries in these two cases highlight the importance of using generalized deformation models such as the CDM, for geodetic data inversions. The other three case studies in this thesis involve high-resolution dislocation models and BEM calculations. As the third case, the 2013 pre-explosive inflation of Volc{\´a}n de Colima has been simulated by using two ellipsoidal cavities, which locate zones of pressurization in the volcano's lava dome. The fourth case study, which serves as an example for volcanotectonics interactions, the 3-D kinematics of an active ring-fault at Tend{\"u}rek volcano has been investigated through modelling displacement time series over the 2003-2010 time period. As the fifth example, the deformation sources associated with North Korea's underground nuclear test in September 2017 have been constrained. These examples demonstrate the advancement and increasing level of complexity and the general applicability of the developed dislocation modelling techniques. This thesis establishes a unified framework for rapid and high-resolution dislocation modelling, which in addition to volcano deformations can also be applied to tectonic and humanmade deformations.},
  language  = {en}
}