Evidence For Gas And Magmatic Sources Beneath The Yellowstone Volcanic Field From Seismic Tomographic Imaging

The 3-D P-wave velocity and P- to S-wave velocity ratio structure of the Yellowstone volcanic field, Wyoming, has been determined from local earthquake tomography using new data from the permanent Yellowstone seismic network. We selected 3374 local earthquakes between 1995 and 2001 to invert for the 3-D P-wave velocity (Vp) and Pwave to S-wave velocity ratio (Vp/Vs) structure. Vp anomalies of small size (15U15 km) are reliably imaged in the northwestern part of the model outside the Yellowstone caldera; inside the caldera only Vp anomalies of large size extending over several grid nodes are reliably imaged. The Vp/Vs solution is generally poorer due to the low number of S^Parrival times. Only the northwestern part of the model is resolved with confidence; the Vp/Vs solution also suffers from strong vertical and horizontal velocity smearing. The tomographic images confirm the existence of a low Vp-body beneath the Yellowstone caldera at depths greater than 8 km, possibly representing hot, crystallizing magma. The most striking result of our study is a volume of anomalously low Vp and Vp/Vs in the northwestern part of the Yellowstone volcanic field at shallow depths of 62.0 km. Theoretical calculations of changes in P- to S-wave velocity ratios indicate that these anomalies can be interpreted as porous, gas-filled rock. The close spatial correlation of the observed anomalies and the occurrence of the largest earthquake swarm in historic time in Yellowstone, 1985, suggest that the gas may have originated as part of magmatic fluids released by crystallization of magma beneath the Yellowstone caldera.

Quantifying the timescales of current geological processes is critical for constraining the physical mechanisms operating on the Earth today. Since the Earth’s origin 4.55 billion years ago magmatic processes have continued to shape the Earth, producing the major reservoirs that exist today (core, mantle, crust, oceans and atmosphere) and promoting their continued evolution. But key questions remain. When did the core form and how quickly? How are magmas produced in the mantle, and how rapidly do they travel towards the surface? How long do magmas reside in the crust, differentiating and interacting with the host rocks to yield the diverse set of igneous rocks we see today? How fast are volcanic gases such as carbon dioxide released into the atmosphere? This book addresses these and other questions by reviewing the latest advances in a wide range of Earth Science disciplines: from the measurement of short-lived radionuclides to the study of element diffusion in crystals and numerical modelling of magma behaviour. It will be invaluable reading for advanced undergraduate and graduate students, as well as igneous petrologists, mineralogists and geochemists involved in the study of igneous rocks and processes.

Volcanoes and eruptions are dramatic surface man telemetry and processing, and volcano-deformation ifestations of dynamic processes within the Earth, source models over the past three decades. There has mostly but not exclusively localized along the been a virtual explosion of volcano-geodesy studies boundaries of Earth's relentlessly shifting tectonic and in the modeling and interpretation of ground plates. Anyone who has witnessed volcanic activity deformation data. Nonetheless, other than selective, has to be impressed by the variety and complexity of brief summaries in journal articles and general visible eruptive phenomena. Equally complex, works on volcano-monitoring and hazards mitiga however, if not even more so, are the geophysical, tion (e. g. , UNESCO, 1972; Agnew, 1986; Scarpa geochemical, and hydrothermal processes that occur and Tilling, 1996), a modern, comprehensive treat underground - commonly undetectable by the ment of volcano geodesy and its applications was human senses - before, during, and after eruptions. non-existent, until now. Experience at volcanoes worldwide has shown that, In the mid-1990s, when Daniel Dzurisin (DZ to at volcanoes with adequate instrumental monitor friends and colleagues) was serving as the Scientist ing, nearly all eruptions are preceded and accom in-Charge of the USGS Cascades Volcano Observa panied by measurable changes in the physical and tory (CVO), I first learned of his dream to write a (or) chemical state of the volcanic system. While book on volcano geodesy.

Millions of years ago, the North American continent was dragged over the world's largest continental hotspot, a huge column of hot and molten rock rising from the Earth's interior that traced a 50-mile wide, 500-mile-long path northeastward across Idaho. Generating cataclysmic volcanic eruptions and large earthquakes, the hotspot helped lift the Yellowstone Plateau to more than 7,000 feet and pushed the northern Rockies to new heights, forming unusually large glaciers to carve the landscape. It also created the jewel of the U.S. national park system: Yellowstone. Meanwhile, forces stretching apart the western U.S. created the mountainous glory of Grand Teton National Park. These two parks, with their majestic mountains, dazzling geysers, and picturesque hot springs, are windows into the Earth's interior, revealing the violent power of the dynamic processes within. Smith and Siegel offer expert guidance through this awe-inspiring terrain, bringing to life the grandeur of these geologic phenomena as they reveal the forces that have shaped--and continue to shape--the greater Yellowstone-Teton region. Over seventy illustrations--including fifty-two in full color--illuminate the breathtaking beauty of the landscape, while two final chapters provide driving tours of the parks to help visitors enjoy and understand the regions wonders. Fascinating and informative, this book affords us a striking new perspective on Earth's creative forces.

"Home to more than 10,000 thermal features, Yellowstone has experienced over 20 large hydrothermal explosions producing craters from 100 to over 2500 meters in diameter during the past 16,000 years. Using new mapping, sampling, and analysis techniques, this volume documents a broad spectrum of ages and geologic settings for these events and considers additional processes and alternative triggering mechanisms that have not been explored in previous studies. Although large hydrothermal explosions are rare on the human time scale, the potential for future explosions in Yellowstone is not insignificant, and events large enough to create a 100-m-wide crater might be expected every 200 years. This work presents information useful for determining the timing, distribution, and possible causes of these events in Yellowstone, which will aid in the planning of monitoring strategies and the anticipation of hydrothermal explosions."--Publisher's description.

This book contains 12 chapters dealing with the studies on volcanoes, their geological and geophysical setting, the theoretical aspects and the numerical modeling on volcanoes, the applications of volcanoes to the industry, and the impact of volcanoes on the human health, in different geological settings and using several techniques and methods, including the volcanology, the seismology, the statistical methods to assess the correlation between seismic and volcanic activity (modified Ripley's K-function to regional seismicity), the field geological survey of volcanic successions, the analytical methods of petrologic analysis, the petrography of the volcanic rocks with the individuation of the modal compositions of volcanic rocks and their comparison with major elements and trace elements in variation diagrams, and the argon isotopic measurements performed through the peak height comparison (unspiked) method. The oceanographic methods have also been applied to case studies of submarine volcanic edifices located in the Canary Islands (Atlantic Ocean), including the sampling of the water column with a conductivity-temperature-depth (CTD) sensor rosette with 24 Niskin bottles, in order to determinate key physical and chemical parameters, such as the total-scale pH, the total dissolved inorganic carbon (C), the total alkalinity (A), the temperature, the salinity, and the dissolved oxygen. Problems of volcanic risk mitigation have also been treated, regarding the eruption disasters in Indonesia, a country where a high number of people live next to the volcanoes, and characterized by the lack of public awareness of the eruption disasters. Petrographic methods have been successfully applied to the study of the Cretaceous magmatism of the layered gabbroids of the Chukotka region (Pekulney Ridge, Russia), and geodynamic implications have been successfully established through geological and petrographic studies. The relationships among the mantle wedge, the convective heat and mass transfer, the infiltration metasomatism, the zoning, and the mathematical models have been applied to the comprehension of complex volcanic areas through the theoretical aspects of volcanic studies on magmatic chambers coupled with numerical modeling, including finite element models (FEMs) in the individuation of volcanic deformations.

The interaction of the lithosphere and hydrosphere sets the boundary conditions for life, as water and the nutrients extracted from rocks are essential to all known life-forms. Water-rock interaction also affects the fate and transport of pollutants, mediates the long-term cycling of fluids and metals in the earth's crust, impacts the migration and

[1] The movement of the lithosphere over a stationary mantle magmatic source, often thought to be a mantle plume, explains key features of the 16 Ma Yellowstone?Snake River Plain volcanic system. However, the seismic signature of a Yellowstone plume has remained elusive because of the lack of adequate data. We employ new teleseismic P and S wave traveltime data to develop tomographic images of the Yellowstone hot spot upper mantle. The teleseismic data were recorded with two temporary seismograph arrays deployed in a 500 km by 600 km area centered on Yellowstone. Additional data from nearby regional seismic networks were incorporated into the data set. The VP and VS models reveal a strong low-velocity anomaly from ~50 to 200 km directly beneath the Yellowstone caldera and eastern Snake River Plain, as has been imaged in previous studies. Peak anomalies are -2.3% for VP and -5.5% for VS. A weaker, anomaly with a velocity perturbation of up to -1.0% VP and -2.5% VS continues to at least 400 km depth. This anomaly dips 30° from vertical, west-northwest to a location beneath the northern Rocky Mountains. We interpret the low-velocity body as a plume of upwelling hot, and possibly wet rock, from the mantle transition zone that promotes small-scale convection in the upper ~200 km of the mantle and long-lived volcanism. A high-velocity anomaly, 1.2% VP and 1.9% VS, is located at ~100 to 250 km depth southeast of Yellowstone and may represent a downwelling of colder, denser mantle material.