Volcanic Eruptions and Their Repose, Unrest, Precursors, and Timing (2017) / Chapter Skim
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1 Introduction
1 Introduction
Pages 9-26
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Eruptions K asatochi volcano, Alaska, distributed volcanic gases are influenced by the tectonic setting, the properties over most of the continental United States within a of Earth's crust, and the history of the volcano. Yet, week (Figure 1.1)
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. Moreover, not all signals of volcanic unrest Volcanic eruptions evolve over very different tem- are immediate precursors to surface eruptions (e.g., poral and spatial scales than most other natural hazards currently Long Valley, California, and Campi Flegrei, (Figure 1.3)
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Geochemical undertake the following tasks: and geophysical techniques are used to study volcano processes at scales ranging from crystals to plumes of • Summarize current understanding of how volcanic ash. Models reveal essential processes that magma is stored, ascends, and erupts.
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The U.S. Geological Survey Volcano Hazards Program monitors and studies active and potentially active volcanoes, assesses their hazards, and conducts research on volcano processes to issue forecasts, warnings, and information about volcano hazards to emergency management professionals and the public.
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volcanoes, domes, and lava flows. These various land The Aleutian arc extends 2,500 km across the forms reflect the plate tectonic setting, the ways in North Pacific and comprises more than 130 active which those volcanoes erupt, and the number of erup and potentially active volcanoes.
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does not increase at a constant rate. Compared to a model of steady volcanic activity (dashed line)
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, which, in turn, can influence the deeper magmatic system; and (3) hydrothermal Volcano monitoring is critical for hazard forecasts, systems are energy resources and create ore deposits.
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changes. Thermal monitoring tools, such as infrared cameras, Deformation monitoring tools, including tiltmeters, are used to detect dome growth and lava breakouts.
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NOTE: DOAS, differential optical absorption spectrometer; FTIR, Fourier Transform Infrared Spectroscopy; GPS, Global Positioning System. Background image is the concentration of SO2 measured with an ultraviolet camera.
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. Thermal infrared data are and recycling of other volatile species, and tracking used to detect eruption onset and cessation, calculate volcanic clouds that may be hazardous to aviation in lava effusion rates, map lava flows, and estimate ash col- near real time.
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measurements of the Sierra Negra volcano, Galapagos.
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The VEI classifica- sity currents, lava flows, and lahars. Pyroclastic density tion is still in use, despite its many limitations, such currents are hot volcanic flows containing mixtures of as its reliance on only a few types of measurements gas and micron- to meter-sized volcanic particles.
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often generating clastogenic, gas-charged lava flows from single vents or from fissures Strombolian Short-duration, low-vigor, episodic, small (<100s of meters) explosions driven by escape of pockets of gas and ejecting some bombs and spatter Vulcanian Short-duration, moderately vigorous, magma-fragmenting explosions producing ash-rich columns that may reach heights >1,000 m Surtseyan Short duration, weak phreatomagmatic explosive eruptions where fluid magma interacts with standing water Phreatoplinian Prolonged powerful phreatomagmatic explosions where viscous magma interacts with surface water or groundwater Dome collapse Dome collapse pyroclastic flows occur at unstable gas-charged domes either with an explosive central column eruption (e.g., Mount Pelee)
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Distal hazards include flooding and sedimentation over extended areas, airborne ash, and fallout of tephra downwind of the volcano.
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pyroclastic density currents and lava flows travel, and Observed impacts of basaltic eruptions in Hawaii and the atmosphere through which eruption columns rise. Iceland include regional volcanic haze ("vog")
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, but at the expense of increased complexity and computational demands. They also require additional components, such as a model for FIGURE 1.10 Multiphase simulation of a pyroclastic density how magma in magma chambers and conduits deforms current from the 2006 eruption of Tungurahua, Ecuador, show- when stressed; a model for turbulence in pyroclasing the interaction of the current with topography and the formation of dilute, turbulent eddies.
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. Such experiments provide insights on fundamental processes, such as crystal dynamics in flowing magmas, entrainment in eruption columns, propagation of dikes, and sedimentation from pyroclastic density currents (Figure 1.11)
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