Classification of volcanoes by activity Dormant volcanoes are classified due to their historic eruptions as well as their potential to erupt again in the future. Any volcano which has erupted within recordable history, and is expected to erupt again, is considered to be dormant. Extinct volcanoes are classified based on the likely probability that they will never erupt again. In the entire classification scheme of volcanoes however, it is worth noting that man-made systems of classifying natural features are always open to the potential for error, as such there have been recorded eruptions from what were previously considered extinct volcanoes.
Classification of volcanoes by structure
Structurally volcanoes are categorized based on their shape and internal characteristics. These classification go alongside those given on the basis of activity, and can be used to help predict eruption or seismic trends to aid in forecasting. Volcanoes are separated into three structural categories: cinder cones, composite volcanoes, and shield volcanoes. Cinder cone volcanoes are considered to be one of the more structurally simplistic volcano types, as they consist of nothing more than cinders and other vent ejected particles centered around a single vent. Cinder cone volcanoes typically have a crater at their summits, and grow through the process of erupted lava fragments from the vent breaking up and solidifying into the cinders which eventually fall and cement themselves together to form the slopes of the volcano. Composite volcanoes exist as large,steep-sided cones which form from alternating layers of lava flows and other volcanic material thrown up during eruptions, and in many cases have reached the size of mountains during their development. Unlike cinder cones, composite volcanoes grow due to the lava which flows down their flanks, as well as other erupted material, and eventually solidifies to form a higher and more steeper side than that made from prior eruptions.
Structurally composite volcanoes operate through a conduite which allows magma from deep within the earth to reach its peak to produce an eruption, these conduites unlike the vents present in cinder cone volcanoes are not directly above the magma source which eventually erupts, and as a result are capable of reaching much taller heights. Shield volcanoes similar to composite volcanoes grow from the solidification of magma, however these structures are almost completely composed of liquid flows rather than other ejected material. The structure of shield volcanoes is much more gentle sloping than the other forms of volcanoes, as well as much wider in diameter also. Within shield volcanoes a central vent is present much like that within cinder cones, however due to the large diameter typically created by shield volcanoes, it is possible for this vent to branch to other areas of the structure as well.
Seismically volcanic eruptions can be forecasted in some cases by the presence of preceding earthquakes and other subsurface activity. The presence of data collection stations allows for constant monitoring of seismic activity, and utilization of observation equipment enables forecasting to be done with great accuracy in comparison to older monitoring systems and methods. Seismic activity is a relevant indicator of volcanic eruptions or active volcanic processes in the subsurface, due to the fact that the injection (or removal) of magma to/from solid rock creates stress which in turn produces earthquakes known as volcano tectonic earthquakes. Volcano tectonic earthquakes can be used for forecasting because they reflect a volcanic area of interest is capable of still erupting, however, they are not used to determine anything else about prospective volcanic behavior. Volcanic tremors produce seismic activity from the interaction of magma and subsurface rocks, however unlike volcano tectonic earthquakes, volcanic tremors are caused by the injection of magma into solid rock which results in a pressure change during its unsteady transport which generates seismic activity. The nature of volcanic tremors allows for them to be used to predict when a volcano is about to erupt, and this is because they are only caused by the movement of magma towards the surface of the earth. The collection of recently erupted magma temperatures is also linked to seismic correlations, as the most accurate instruments require hands on operation by field scientist, only seismic patterns of interest are used to determine which eruptions warrant in-situ data collection of magma properties, this is done in order to help better correlate magma sources within the subsurface with trends in mantle behavior and crustal interactions.
Monitoring via remote sensing
Through the usage of satellite data it is possible to use infrared bands to monitor and detect changes in thermal activity of volcanic areas; this method allows for not only increasingly active thermal anomalies to be captured, but also decreasingly active ones as well which may provide information in terms of a subsidence in volcanic activity. Remote sensing applications can also detect the presence of airborne volcanic material such as ash or gases, and utilize the data to generate predictive maps in terms of coverage and direction due to wind directions. 
During active eruptions ultra violet remote sensing is utilized to track atmospheric reflectance as a way of denoting various gases upthrown during eruptions, and even long term ozone effects from prior eruptions. Data obtained from various remote sensing applications (Infrared, ultraviolet, thermal, etc.) can also be used to make predictive models for eruptions, the accuracy of these models is further increased due to the inclusion of historical seismic data collected from data stations and observation networks which allow for both remote sensing and seismic trends to be used in the prediction of future volcanic behavior. In terms of detection, geostationary satellites can be used to generate automatic eruption detection notices based on parameters such as thermal activity increases, surface deformation, and even increases in specific gases within the atmosphere near the desired volcanic area.
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- The volcanology Nature page