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The eruptive power and often long intervals of quiet dormancy of volcanoes make them both difficult to study, and difficult to live near. The threat of eruption is always there, but because eruptions are temporally episodic and occur distributed around the globe, we must rely on methods that give us observations of volcanic activity globally. Primary to our increased understanding of eruptive systems is building an inventory of active volcanoes. With remote terrestrial volcanoes and undersea volcanic activity, there are thousands of volcanoes whose level of activity is completely unknown. Indicators of activity include surface deformation, seismicity, change in gravity, fluxing of gasses, and actual eruptions. We know little, however, of how these phenomena are interrelated. The physical mechanisms that cause surface deformation and those that control the rate and styles of eruptions are similarly poorly understood. The ability to predict the timing, magnitude, and style of volcanic eruptions is a laudable but still generally unmet goal.[1]

Existing and foreseeable advances in technology allow us to now consider a variety of questions critical to advancing our understanding of volcanic systems. Critical observables, such as surface deformation, magma composition and volatiles, and thermal emissions already allow limited volcanic eruption forecasting. For example, under simplifying assumptions of an elastic crust and a simple range of possible magma chamber shapes, available measurements of surface deformation are routinely used to quantify the location and geometry of active magmatic bodies. Recent observations (geodetically-derived) are also beginning to image a wide variety of complex sources of deformation such as flank instabilities, rift systems, and crater floor dynamics. Besides deformation processes, recent experiments have demonstrated the ability to measure thermal anomalies associated with volcanic plumes, degassing of SO2 and CO2.

The most fundamental issue we face is the lack of a global inventory of the number of active volcanoes and the style of their activity. Different characteristics we must assess include geometry of the volcanic plumbing system, physical properties of the magma (composition, volatile content), magma ascent rates, and location and mechanism of volatile exsolution. A key question is how we actually determine a volcano's level of activity, whether by surface deformation, variations in gravity, heat flux, mass transfer, seismicity, or gas emissions. At any given time, only one of these manifestations of activity may be present.

The societal benefits of a continuously updated global inventory are obvious and potentially include a warning system for volcanoes temporarily quiescent, to a monitoring system for ongoing eruptions. At this time, the extent to which we can predict eruptions is largely undetermined due to lack of observations.

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[1] Solid Earth Science Working Group Report

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