Remote Sensing Of Volcanoes And Volcanic Processes

Author : Judit Gonzalez Santana
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (14 download)

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Download or read book Remote Sensing Observations and Modeling of Volcano Flank Instability written by Judit Gonzalez Santana and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Volcano instability refers to the condition where a volcanic edifice has reached a state of destabilization that increases the likelihood that all or part of the edifice will undergo structural failure. Flank instability can arise from complex interactions between gravity forces, magmatic activity, and local or regional tectonics, and develop over a variety of timescales and lengthscales. Despite debris avalanches resulting from the catastrophic failure of volcanic flanks taking place at a frequency of 5 every 100 years, and causing over 20,000 fatalities in the past 400 years, flank motion only attained recognition as an important process in the mid-20th century, so its expression and drivers are poorly understood relative to those of other volcanic processes. The purpose of this dissertation is to investigate the occurrence of long-term flank instability at volcanoes, including the processes, precursory signals and conditions required to develop and sustain volcanic flank creep. This is motivated by the need to better understand the conditions under which catastrophic flank collapse will take place and to identify precursory activity that could enable suitable hazard assessment and early warning for risk mitigation purposes. Specifically, I present research on volcanic flank instability and its interaction with magmatic activity. The emphasis is on improving observations of flank instability through satellite remote sensing and leveraging models to better understand the relative contributions of different processes to flank instability. This dissertation is composed of four main chapters: the first three focus on an active volcano in Guatemala, Pacaya, where previous studies have shown evidence for flank instability, whereas the fourth is a parametric study applicable to the range of volcano geometries in nature. The first chapter focuses on the detection and modeling of low magnitude flank creep at Pacaya. The second presents a conceptual model for the links between flank creep behaviour and volcanic unrest at Pacaya. The third focuses on validating the conceptual model and testing the performance of different radar satellite platforms to detect ground motion as well as the applicability of single-station seismic analyses to monitor eruption evolution. The final chapter addresses the impact of volcano and fault geometry on the likelihood of developing magma driven flank instability. Despite the prevalence of debris avalanches across volcanic settings, flank instability has mostly been considered at ocean island volcanoes. In Guatemala, all but one volcano with elevation >2000 m have undergone edifice failure. Pacaya is one of these Guatemalan volcanoes, which experienced at least one past episode of flank collapse and where recent transient flank motion was identified during two large eruptions in 2010 and 2014. I investigate the existence of long-term slip at Pacaya through a time-series analysis method that enables retrieval of long-term signals by combining information from multiple shorter interval radar satellite image pairs and reveal, for the first time, long-term displacement of the southwest flank of Pacaya between 2010 and 2014. Through inverse geodetic modeling and analysis of stress changes, I find that that the observed flank motion could be accommodated by slip on a southwest-dipping detachment fault, with an observed increase in slip rate attributed to magma intrusion during a major eruption in 2014. The identification of long-term flank creep and its modulation by magmatic activity at Pacaya between 2012 and 2014 raised the question of whether creep was ongoing and how other instances of lava flow effusion and explosive activity relate to flank motion. Thus, I investigated the links between flank creep rates and eruptive behavior at Pacaya, to better constrain the conditions under which flank creep can be initiated, sustained, or halted at active volcanoes. I computed time-series of surface displacements from 2007 to 2020 using seven radar satellite datasets to quantify flank creep rates and compiled volcanic activity reports, ash advisories, thermal anomalies, and lava flow maps to describe the concurrent eruptive activity. The observations were combined into a conceptual model showing how during periods of elevated volcanic unrest attributed to open-vent volcanic activity, magma migrates in an open conduit with little associated deformation or flank motion, whereas during activity involving the opening of new vents outside the summit area, transient flank creep can be initiated. Pacaya underwent another heightened period of volcanic activity in early 2021, as the culmination of effusive and explosive activity starting in mid-2015. Given the association of past vigorous eruptive activity from vents beyond the summit area with initiation or acceleration of flank creep, I assessed whether this process repeated itself in 2021. I also leveraged the availability of radar data availability from 5 different satellite platforms with different spatial and temporal resolutions to assess the relative performance of different platforms for monitoring volcanic eruptions. Ground displacement time-series results revealed subsidence and westward displacements on the southwest flank that are compatible with down-dip motion, but might include contributions from lava flow compaction and seasonal tropospheric water vapor variations. Overall, results highlight the advantage of high resolution SAR amplitude imagery for mapping surface changes, the vulnerability to geometric distortions of low incidence angle platforms, and the obstacle of reliance on tasking to obtain imagery over volcanoes, as well as the need for advanced techniques to unravel sources of ground motion signals. An additional seismic dataset revealed that real-time seismic amplitude measurement peaks reflect the vigor of magma effusion and single-station correlations capture the effects of rainfall, but gaps and noise in the datasets impeded identifying any characteristic signals coincident with changes in eruptive activity or flank displacement trends. To further the understanding of the complex interplay between magmatic intrusion and volcanic flank creep observed at Pacaya, but also at other volcanoes, I carried out a parametric study using numerical models. Specifically, I assessed how edifice slope, the geometry of faults, and intrusion depth affect the potential for the development of magma-driven flank instability at volcanoes. I quantified whether each modeled condition would be conducive or detrimental to slip through calculation of stress changes on example receiver faults for endmember scenarios in nature. Additionally, the surface displacements for each case were extracted, to highlight deviations from the displacements that would be obtained through more commonly used analytical models that neglect relief. Development of instability is most likely when receiver faults have shallow dips and the dike intrusion spans the edifice, regardless of edifice steepness, or in steep edifices when receiver faults have steep dips and the dike is beneath the edifice. Neglecting topography yields different magnitudes and extents of surface deformation and stress changes.