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abstract: Lava flow emplacement in the laboratory and on the surface of Mars was investigated. In the laboratory, the effects of unsteady effusion rates at the vent on four modes of emplacement common to lava flow propagation: resurfacing, marginal breakouts, inflation, and lava tubes was addressed. A total of 222 experiments were conducted using a programmable pump to inject dyed PEG wax into a chilled bath (~ 0° C) in tanks with a roughened base at slopes of 0, 7, 16, and 29°. The experiments were divided into four conditions, which featured increasing or decreasing eruption rates for either 10 or 50 s. The primary controls on modes of emplacement were crust formation, variability in the eruption rate, and duration of the pulsatory flow rate. Resurfacing – although a relatively minor process – is inhibited by an extensive, coherent crust. Inflation requires a competent, flexible crust. Tube formation requires a crust and intermediate to low effusion rates. On Mars, laboratory analogue experiments combined with models that use flow dimensions to estimate emplacement conditions and using high resolution image data and digital terrain models (e.g. THEMIS IR, CTX, HRSC), the eruption rates, viscosities, and yield strengths of 40 lava flows in the Tharsis Volcanic Province have been quantified. These lava flows have lengths, mean widths, and mean thicknesses of 15 – 314 km, 0.5 – 29 km, and 11 – 91 m, respectively. Flow volumes range from ~1 – 430 km3. Based on laboratory experiments, the 40 observed lava flows were erupted at 0.2 – 6.5x103 m3/s, while the Graetz number and Jeffrey’s equation when applied to 34 of 40 lava flows indicates eruption rates and viscosities of 300 – ~3.5 x 104 m3/s and ~105 – 108 Pa s, respectively. Another model which accounts for mass loss to levee formation was applied to a subset of flows, n = 13, and suggests eruption rates and viscosities of ~30 – ~1.2 x 103 m3/s and 4.5 x 106 – ~3 x 107 Pa s, respectively. Emplacement times range from days to centuries indicating the necessity for long-term subsurface conduits capable of delivering enormous volumes of lava to the surface. / Dissertation/Thesis / Chapter 4 - Mars Lava Flow Data and Calculations / Chapter 2 - Experimental Data / Chapter 3 - Experimental Data / Doctoral Dissertation Geological Sciences 2020

Lava flow hazards are one of the few constant themes across the wide spectrum of volcanic research in the solar system. These dynamic hazards are controlled by the location of the eruption, the topography and material properties of the land upon which the flow spreads, and the properties of the lava (e.g., volume, temperature, and rheology). Understanding the influences on eruption location and how lava flows modify the landscape are important steps to accurately forecast volcanic hazards. Three studies are presented in this dissertation that address di˙erent aspects of modeling and assessing vent opening and lava flow hazards. The first study uses hierarchical clustering to explore the distribution of activity at Craters of the Moon (COM) lava field on the eastern Snake River Plain (ESRP). Volcanism at COM is characterized by 53 mapped eruptive vents and 60+ lava flows over the last 15 ka. Temporal, spatial, and spatio-temporal clustering methods that examine different aspects of the distribution of volcanic vents are introduced. The sensitivity of temporal clustering to different criteria that capture the age range of magma generation and ascent is examined Spatial clustering is dictated by structures on the ESRP that attempt to capture the footprint of an emplacing dike. A combined spatio-temporal is the best approach to understanding the distribution of linked eruptive centers and can also provide insight into the evolution of volcanism for the region. Spatial density estimation is used to visualize the differences between these models. The goal of this work is to improve vent opening forecasting tools for use in assessing lava flow hazards. The second study presents a new probabilistic lava flow hazard assessment for the U.S. Department of Energy’s Idaho National Laboratory (INL) nuclear facility that (1) explores the way eruptions are defined and modeled, (2) stochastically samples lava flow parameters from observed values for use in MOLASSES, a lava flow simulator, (3) calculates the likelihood of a new vent opening within the boundaries of INL, (4) determines probabilities of lava flow inundation for INL through Monte Carlo simulation, and (5) couples inundation probabilities with recurrence rates to determine the annual likelihood of lava flow inundation for INL. Results show a 30% probability of partial inundation of the INL given an e˙usive eruption on the ESRP, with an annual inundation probability of 8.4×10^−5 to 1.8×10^−4. An annual probability of 6.2×10^−5 to 1.2×10^−4 is estimated for the opening of a new eruptive center within INL boundaries. The third study models thermo-mechanical erosion of a pyroclastic substrate by flow-ing lava on Volcán Momotombo, Nicaragua. It describes the unique morphology of a lava flow channel using TanDEM-X/TerraSAR-X and terrestrial radar digital elevation models. New methods for modeling paleotopography on steep-sided cones are introduced to mea-sure incision depths and document cross-channel profiles. The channel is incised ~35 m into the edifice at the summit and transitions into a constructional feature halfway down the ~1,300 m high cone. An eroded volume of ~4×10^5 m3 was calculated. It is likely that a lava flow eroded into the cone as it emplaced during an eruption in 1905. There is not suÿcient energy to thermally erode this volume, given the observed morphology of the flow. Models are tested that explore the relationship of shearing and material properties of the lava and substrate against measured erosion depths and find that thermo-mechanical erosion is the most likely mode of channel formation. Additionally, it is likely that all forms of erosion via lava flow are impacted by thermal conditions due to the relationship between temperature and substrate hardness. The evolution of these structures (their creation and subsequent infilling) plays an important role in the growth of young volcanoes and also controls future lava flows hazards, as seen by the routing of the 2015 flow into the 1905 channel.

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The volume of lava flows provide important information on the magnitude of volcanic eruptions, and accurate volumes are necessary to produce reliable models of lava flow emplacement or constrain the internal structure of volcanoes. The most accurate lava flow volumes are obtainable when the topography before and after an eruption are both known, but information for the topography before lava flow emplacement is absent in non-historic lava flows. To calculate the volume of non-historic lava flows, this pre-emplacement topography needs to be reconstructed. Common methods for this include using inverse distance-weighted averages or global polynomial interpolation methods, but these can still underestimate the volume of the flow, and the surface of the flow itself is not considered in these interpolations. A new calculation method seems necessary to better constrain the volume of lava flows, and including the lava flow surface in the volume calculation, given that it is generally excluded during interpolation of pre-emplacement topography, may be the solution to improving lava flow volume calculation for flows where the base surface is unknown. The 2012-2013 Tolbachik lava flow is used to look at potential relationships due to the availability of elevation data before and after the eruption. A quantitative analysis on the relationships between the slope of topography before and after lava flow emplacement and on the relationship between the slope and thickness of lava flows is performed. In addition to this, the slope of the topography calculated over local and regional scales is used as a new interpolation method, and the calculated thickness from the interpolated surface is compared to the known thickness for the lava flow.

Magmatism is a dominant process on Earth and Mars that has significantly modified and evolved the lithospheres of each planet by delivering magma to shallow depths and to the surface. Two common modes of volcanism are present on both Earth and Mars: central-vent dominated volcanism that creates large edifices from concentrating magma in chambers before eruptions and distributed volcanism that creates many smaller edifices on the surface through the independent ascent of individual magmatic dikes. In regions of distributed volcanism, clusters of volcanoes develop over thousands to millions of years. This dissertation explores the geology of distributed volcanism on Earth and Mars from shallow depths (~1 km) to the surface. On long time scales, distributed volcanism emplaces magmatic sills below the surface and feeds volcanoes at the surface. The change in spatial distribution and formation rate of volcanoes over time is used to infer the evolution of the source region of magma generation. At short time scales, the emplacement of lava flows in these fields present an urgent hazard for nearby people and infrastructure. I present software that can be used to simulate lava flow inundation and show that individual computer codes can be validated using real-world flows. On Mars, distributed volcanism occurs in the Tharsis Volcanic Province, sometimes associated with larger, central-vent shield volcanoes. Two volcanic fields in this province are mapped here. The Syria Planum field is composed three major volcanic units, two of which are clusters of 10s to >100 shield volcanoes. This area had volcanic activity that spanned 900 million years, from 3.5-2.6 Ga. The Arsia Mons Caldera field is associated with a large shield volcano. Using crater age-dating and mapping stratigraphy between lava flows, activity in this field peaked at ~150 Ma and monotonically waned until 10-90 Ma, when volcanism likely ceased.

The 2014-15 lava flow crisis at Kīlauea volcano, Hawai‘i and post-September 2015 elevated unrest at adjacent Mauna Loa volcano provided opportunities to assess households’ psychological and behavioral responses to different levels of volcanic activity. Weused the Protective Action Decision Model to examine stakeholder perceptions and confidence in warnings, in addition toattitudes toward lava flow mitigation strategies, such as diversion by berms and bombing, and people’s acceptance of additional risk to personal property in exchange for protecting important elements of their community, such as schools, major roads, electrical substation, and shopping centers. Respondents’ confidence in events important in decision-making during emergencies and evacuations were significantly correlated with their past experience with lava forecasts. Consistent with previous studies, overall support for the two different mitigation measures was higher for earthen berms/trenches than it was for bombing/blasting. Finally, diversion acceptance was strongly correlated with residents’ perceptions of lava flow diversion strategies.

Des structures prismées sont fréquemment observées dans les coulées de lave comme la Chaussée des Géants (Irlande). Plusieurs théories existent pour expliquer ces formations, dont la plus répandue est celle de la contraction thermique. Or cette théorie permet difficilement de comprendre certaines observations de terrain comme la séparation fréquente des coulées en plusieurs niveaux. Afin de mieux comprendre la structuration au sein des coulées basaltiques, nous avons procédé à une étude pluridisciplinaire basée sur les propriétés magnétiques, les variations structurales et géochimiques de deux coulées prismées du Massif Central (La Palisse, Ardèche et Saint-Arcons-d’Allier, Haute-Loire). Notre approche permet de montrer que les fabriques cristallographiques et magnétiques sont gouvernées par l’écoulement de la lave. L’orientation du plagioclase contrôle la distribution des titanomagnétites à l’origine des fabriques magnétiques. Notre étude montre également que l’utilisation de l’ASM est un outil fiable pour déterminer l’orientation de l’écoulement à condition d’être contrôlée par des mesures de fabriques cristallographiques. Les mesures de la quantité d’eau et les analyses isotopiques (H et O) montrent que l’effet de l’altération météorique est faible et que l’eau contenue dans la roche est essentiellement de l'eau de constitution. De plus, à l’échelle du prisme, des variations de deuxième ordre sont observées comme celle des paramètres d’hystérésis qui indique des tailles de grains de titanomagnétites plus importantes vers le centre. Ces variations au sein du prisme semblent difficilement compatibles avec une structuration des coulées par la simple contraction thermique. / Columnar jointing is frequently observed in lava flows, as in the Giant Causeway (Ireland). The most common theory explaining the formation of prisms is by the thermal contraction. However, this theory hardly explains some field observations such as the frequent existence of three parts within the lavas flows, from the base to the top. To complete our understanding of the structuring lava flows, we carried out a multidisciplinary study based on the magnetic properties, structural and geochemical characterization of two basaltic flows from the French Massif Central (La Palisse, Ardèche and Saint-Arcons-d'Allier, Haute-Loire). Our approach shows that crystallographic and magnetic fabrics are governed by the flow. The distribution of titanomagnetite grains carrying the magnetic fabrics is mainly controlled by the plagioclase orientation. Our study also shows that the use of the AMS to determine the flow direction is a reliable tool, provided punctual control by measurements of crystallographic fabrics are performed. Measurements of the water content and isotopic analyses (H and O) show a limited weathering effect in the studied areas: rock water is mostly primary water in equilibrium with the magma. Moreover, second order changes are noted across the prism section such as hysteresis parameters associated to grain size variation of titanomagnetite (larger grains in the center). The variations of magnetic properties across the prism section suggest a gradient of the crystallization rate from the center to the edge of the prism, which seems difficult to reconcile with the structuring of the flow by thermal contraction only.

Nous présentons une contribution autour de la modélisation des écoulements viscoplastiques. En vue d'applications réalistes telle que la simulation numérique des coulées de lave volcanique, le travail se concentre particulièrement sur les fluides complexes dont la rhéologie dépend fortement de grandeurs physiques telle que la température ou la concentration en particule. Nous développons un nouvel algorithme de résolution numérique des équations de Herschel-Bulkley combinant une méthode de Lagrangien augmenté à paramètre d'augmentation variable, une méthode des caractéristiques d'ordre 2 et une adaptation de maillage automatique. Sur des problèmes stationnaires ou en évolution tel que le problème test de la cavité entraînée, il apporte une solution efficace pour garantir à la fois une précision numérique élevée et un temps de calcul raisonnable. Cet algorithme est ensuite étendue et adapté au cas des rhéologies non-isothermes et aux suspensions. Concernant la simulation numérique des coulées de lave volcanique, nous détaillons une méthode de réduction par analyse asymptotique des équations de Herschel-Bulkley pour des écoulements de faible épaisseur sur une topographie arbitraire. Elle permet alors de décrire ces écoulements tridimensionnels de fluides viscoplastiques à surface libre par des équations bidimensionnelles surfaciques. Cette approche est ensuite étendue au cas non-isotherme en y ajoutant l'équation de la chaleur et des dépendances thermiques sur la rhéologie. Par intégration verticale de l'équation de la chaleur, on retrouve un modèle bidimensionnel. Le modèle non-isotherme est validé sur une expérience de dôme réalisée en laboratoire et une simulation numérique est réalisée autour d'une coulée qui a eu lieu sur le volcan du Piton de la Fournaise à la Réunion, en décembre 2010. La comparaison donne des résultats qui sont de notre point de vue satisfaisants et encourageants. / We present a contribution about modeling of viscoplastic flows. For realistic applications such as numerical simulation of volcanic lava flows, the work focuses particularly on complex fluids whose rheology strongly depends on physical quantities such as temperature or the particle concentration. We develop a new numerical resolution algorithm of Herschel-Bulkley's equations combining an augmented Lagrangian method with variable augmentation parameter, a second order characteristic method and an auto-adaptive mesh procedure. On stationary or evolving problems as the lid-driven cavity flow benchmark, it provides an effective solution to ensure both a high numerical accuracy within a reasonable computing time. This algorithm is then extended and adapted to the case of non-isothermal rheological and suspensions. On the numerical simulation of volcanic lava flows, we describe a method of reducing by asymptotic analysis of the Herschel-Bulkley's equations for thin flows on arbitrary topography. It allows to describe the three-dimensional flows of viscoplastic fluid with free surface by bidimensional surface equations. This approach is then extended to the non-isothermal case by adding the heat equation and thermal dependencies on rheology. By vertical integration of the heat equation, a two-dimensional model is maintained . The non-isothermal model is validated on a laboratory experiment of dome and a numerical simulation is performed on a December 2010 Piton de la Fournaise lava flow from La Réunion island. In our view, the comparison gives satisfactory and encouraging results.