Laura J. Connor

Inversion Is the Key to Dispersion: Understanding Eruption Dynamics by Inverting Tephra Fallout

Volcanologists increasingly rely on numerical simulations to better understand the dynamics of erupting volcanoes. Mathematical models are often used to explain the geologic processes responsible for eruption deposits found in the geologic record, and to better characterize possible hazards from future volcanic activity. Examples of models include the finite element flow and transport codes used to simulate pyroclastic flows, lahars, and volcanic debris avalanches (Iverson, 1997; Patra et al., 2005), analytical solutions or finite difference approximations to the advection-diffusion equation that are used to model tephra dispersion (see Bonadonna, this volume) and gas emissions from quiescent volcanoes (Delmelle et al., 2001), and cellular automata algorithms that model the advance of lava (Barca et al., 1994). Commonality among these examples involves the fact that we wish to estimate parameters related to the dynamics of volcanic activity directly from field observations. For instance, how well can we estimate the magnitude of an eruption from measurements of tephra deposits?

Probabilistic approach to modeling lava flow inundation: a lava flow hazard assessment for a nuclear facility in Armenia

Probabilistic modeling of lava flow hazard is a two-stage process. The first step is an estimation of the possible locations of future eruptive vents followed by an estimation of probable areas of inundation by lava flows issuing from these vents. We present a methodology using this two-stage approach to estimate lava flow hazard at a nuclear power plant site near Aragats, a Quaternary volcano in Armenia.

Relationship between dike and volcanic conduit distribution in a highly eroded monogenetic volcanic field: San Rafael, Utah, USA

We mapped 63 conduits, ∼2000 dike segments, and 12 sills in the San Rafael subvolcanic field, Utah (United States), where this Pliocene magmatic system is eroded to a depth of ∼0.8 km and is exceptionally well exposed. Although the number of mapped conduits, dikes, and sills might represent minimums, depending on the level of erosion and exposure, mapped dikes are more numerous around the areally extensive sills and interact with sills and conduits in complex ways. We analyze conduit distribution using kernel density methods and compare results with dike and sill distribution. We find that the distribution of conduits matches the major features of dike distribution, including development of clusters and distribution of outliers. These statistical models are then applied to the distributions of volcanoes in several recently active volcanic fields, where intrusion distributions must be inferred from very sparse data, and compared with San Rafael conduit distribution. This comparison supports the use of statistical models in probabilistic hazard assessment for distributed volcanism. Specifically, renewed dike intrusion and potential eruptions in active basaltic systems can be assessed probabilistically from the distribution of older volcanoes in distributed volcanic systems.

Volcanic and Tectonic Hazard Assessment for Nuclear Facilities

Preface 1. Tectonic events and nuclear facilities N. A. Chapman, H. Tsuchi and K. Kitayama 2. The nature of tectonic hazards M. Cloos 3. The nature of volcanism C. B. Connor, R. S. J. Sparks, M. Diez, A. C. M. Volentik and S. C. P. Pearson 4. Tectonic uplift and subsidence N. Litchfield, Y. Ota and D. Merritts 5. Glacial isostatic adjustment: implications for glacially induced faulting and nuclear waste repositories B. Lund and J. O. Naslund 6. Using global positioning system data to assess tectonic hazards L. M. Wallace, J. Beavan, S. Miura and R. McCaffrey 7. Tectonic setting of volcanic centers in subduction zones: 3D structure of mantle wedge and arc crust Y. Tamura, J. Nakajima, S. Kodaira and A. Hasegawa 8. Conceptual model for small-volume alkali basalt petrogenesis: implications for volcanic hazards at the proposed Yucca Mountain nuclear waste repository F. J. Spera and S. J. Fowler 9. Aspects of volcanic hazard assessment for the Bataan nuclear power plant, Luzon Peninsula, Philippines A. C. M. Volentik, C. B. Connor, L. J. Connor and C. Bonadonna 10. Multidisciplinary probabilistic tectonic hazard analysis M. Stirling, K. Berryman, L. Wallace, N. Litchfield, J. Beavan and W. Smith 11. Tsunami hazard assessment W. Power and G. Downes 12. Regional-scale volcanology in support of site-specific investigations H. Kondo 13. Exploring long-term hazards using a Quaternary volcano database S. H. Mahoney, R. S. J. Sparks, L. J. Connor and C. B. Connor 14. Estimating spatial density with kernel methods C. B. Connor and L. J. Connor 15. Cox process models for the estimation of long-term volcanic hazards O. Jaquet and C. Lantuejoul 16. Spatial distribution of eruptive centers about the Idaho National Laboratory P. H. Wetmore, S. S. Hughes, L. J. Connor and M. L. Caplinger 17. Modeling the flow of basaltic magma into subsurface nuclear facilities T. Menand, J. C. Phillips, R. S. J. Sparks and A. W. Woods 18. Intrusion dynamics for volatile-poor basaltic magma into subsurface nuclear installations A.-M. Lejeune, B. E. Hill, A. W. Woods, R. S. J. Sparks and C. B. Connor 19. Volcanic risk assessment at Yucca Mountain, NV, USA: integration of geophysics, geology and modeling G. A. Valentine and F. V. Perry 20. Geological issues in practice: experience in siting US nuclear facilities L. Reiter 21. Characterizing active tectonic structures for nuclear facilities in Japan D. Inoue 22. Issues for coastal sites I. G. McKinley and W. R. Alexander 23. Stable tectonic settings: designing site investigations to establish the tectonic basis for design and safety evaluation of geological repositories in Scandanavia T. McEwen and J. Anderson 24. The impact of subsidence, uplift and erosion of geological repositories for radioactive wastes I. G. McKinley and N. A. Chapman 25. Recommendations for assessing volcanic hazards at sites of nuclear installations B. E. Hill, W. P. Aspinall, C. B. Connor, J.-C. Komorowski and S. Nakada 26. Formal expert assessment in probabilistic seismic and volcanic hazard assessment K. J. Coppersmith, K. E. Jenni, R. C. Perman and R. R. Youngs Index.

Probabilistic Methodology for Long-Term Assessment of Volcanic Hazards

Abstract Because of the difficulty of describing the complex spatial and temporal patterns inherent to volcanism, the use of solely deterministic models is not sufficient for long-term estimation of volcanic hazards. In order to account for the intrinsic uncertainty of volcanism that occurs in space and time and with respect to event types and their intensity, the use of probabilistic models becomes quite natural for long-term hazard assessment. Here, we discuss a range of probabilistic approaches to forecast the future spatial distribution of volcanism, including kernel, adaptive kernel, and Cox process methods. An application to the volcanic arc of Tohoku illustrates the proposed methodology.

Role of sills in the development of volcanic fields: Insights from lidar mapping surveys of the San Rafael Swell, Utah

Analysis of airborne and terrestrial lidar data demonstrates that >0.4 km 3 of magma cooled in sills at shallow (<1 km) depth in the now-eroded Pliocene San Rafael Swell distributed volcanic field, Utah (USA). The volumes of each of seven sills are estimated from three-dimensional (3-D) models of the lidar data and range from 10 –4 to 10 –1 km 3 . Directions of magma flow during emplacement are interpreted from precise sill thickness measurements and measurements of linear vertical offsets within the sills, helping to identify feeder conduits and dikes; 3-D map relationships derived from lidar data demonstrate that magma flowed into and out of sills from these active dikes and eruptive conduits. Mapped sill volumes account for >92% of intrusive material within the 50 km 2 study area. We conclude that sills played a significant role in modifying eruption dynamics during activity in San Rafael, and suggest that monitoring of sill inflation and deflation in active distributed volcanic fields may provide key information about unrest and potential eruption dynamics.

Evidence of small-volume igneous diapirism in the shallow crust of the Colorado Plateau, San Rafael Desert, Utah

Magma is transported through Earth9s solid crust by two different processes, diking and diapirism, although other mechanisms, such as porous and channeled flow, can transport melt through partially molten crustal areas. Dikes are ubiquitous indicators of the transport of magma in the shallow crust by brittle fracture, and there is ample geological and geophysical evidence supporting diking as a magma-ascent mechanism through the crust. On the other hand, igneous diapirism, involving magma ascent by gravitational instability and requiring viscous or plastic flow of country rock (“hot Stokes” diapirs), is often invoked as a magma-transport mechanism restricted to the ductile upper mantle or lower crust. However, unequivocal geological field evidence for igneous diapirism has proven elusive and has been a matter of considerable debate. We report geological and geophysical evidence showing that Pliocene sills emplaced in the upper levels of brittle continental crust of the Colorado Plateau in the San Rafael subvolcanic field (Utah) became gravitationally unstable by mechanically altering the overlying sedimentary rocks. These sills grew into structures that we recognize as domes and plugs at the current level of exposure. Some of these plugs continued to transport magma to shallower levels of the continental crust and eventually acted as conduits feeding volcanic eruptions. Our geological and geophysical findings indicate that gravitational instability is a viable mechanism for the initiation of magma ascent in the upper continental crust for small volumes of basaltic magma under specific conditions.

Introducing Geoscience Students to Numerical Modeling of Volcanic Hazards: The example of Tephra2 on VHub.org

The Tephra2 numerical model for tephra fallout from explosive volcanic eruptions is specifically designed to enable students to probe ideas in model literacy, including code validation and verification, the role of simplifying assumptions, and the concepts of uncertainty and forecasting. This numerical model is implemented on the VHub.org website, a venture in cyberinfrastructure that brings together volcanological models and educational materials. The VHub.org resource provides students with the ability to explore and execute sophisticated numerical models like Tephra2. We present a strategy for using this model to introduce university students to key concepts in the use and evaluation of Tephra2 for probabilistic forecasting of volcanic hazards. Through this critical examination students are encouraged to develop a deeper understanding of the applicability and limitations of hazard models. Although the model and applications are intended for use in both introductory and advanced geoscience courses, they could easily be adapted to work in other disciplines, such as astronomy, physics, computational methods, data analysis, or computer science.

TephraProb: a Matlab package for probabilistic hazard assessments of tephra fallout

TephraProb is a toolbox of Matlab functions designed to produce scenario–based probabilistic hazard assessments for ground tephra accumulation based on the Tephra2 model. The toolbox includes a series of graphical user interfaces that collect, analyze and pre–process input data, create distributions of eruption source parameters based on a wide range of probabilistic eruption scenarios, run Tephra2 using the generated input scenarios and provide results as exceedence probability maps, probabilistic isomass maps and hazard curves. We illustrate the functionality of TephraProb using the 2011 eruption of Cordón Caulle volcano (Chile) and selected eruptions of La Fossa volcano (Vulcano Island, Italy). The range of eruption styles captured by these two events highlights the potential of TephraProb as an operative tool when rapid hazard assessments are required during volcanic crises.

High-Resolution Ground-Based Magnetic Survey of a Buried Volcano: Anomaly B, Amargosa Desert, NV

Aeromagnetic surveys over the Amargosa Desert, Nevada, have revealed the presence of several magnetic anomalies that have been interpreted to be caused by buried volcanoes; many of these anomalies have been confirmed by drilling. We present data collected from a high-resolution, ground-based magnetic survey over Anomaly B, the largest of these anomalies, that reveal details about a buried crater and its associated lava flow, not observed in the aeromagnetic surveys. These details provide insight into the nature of the eruption and volume of this buried volcano. Results from non-linear inversion demarcate a crater with a diameter of approximately 700 m and a base approximately 150 m below the ground surface. Coupled with well log data, the inversion results suggest a total volume for the Anomaly B crater area and associated lava flows of approximately 1.0 ± 0.4 km3, based on an estimated lava flow field area of 24 km2 and a lava thickness of 42 ± 15 m. A workflow is presented for processing such large ground-based magnetic data sets with attendant GPS data, filtering these data and constructing maps and models using the provided PERL scripts.