**1. Introduction**

Volcanic deposits are present since the very beginning of the geological record, thus confirming that volcanism has been a main component of Earth's evolution. Active volcanism has important implications for our society. There is of course the constant threat that volcanic activity represents for the immediate areas around active volcanoes, but there are also risks at greater distances, even globally, depending on the intensity of this activity. On the other hand, volcanic systems represent an important source of natural resources (e.g., geothermal energy, mineral deposits) (**Figure 1a**). In addition, volcanism provides relevant information to understand the dynamics of the Earth's mantle and crust, which is essential to understand the evolution our planet, in addition to other planetary bodies with similar characteristics. For these reasons, characterizing past volcanic events in the same way that we characterize active volcanism is essential to decipher the meaning of these past volcanic episodes

#### **Figure 1.**

*Sketch illustrating the main concepts of modern and paleovolcanism and their main observational differences. a) Current state of an active central volcano and sedimentation in and adjacent basin. Primary volcanic deposits (lava flows, pyroclastic (air fall, PDC, lahars, etc.)) deposits contribute to the infill of the basin together with deposits resulting from their erosion and redeposition (reworking) by external (epiclastic) processes. Black arrows indicate the sense of movement of magma inside the volcanic edifice, lava flows, eruption column, and PDC. b) State of the same depositional environment after volcanic activity has ceased and the volcanic edifice has been partially dismantled, producing volcanic epiclastic deposits that will mostly contain fragments from the primary volcanic deposits. c) Same scenario after hypothetical compressional tectonics and further erosion (white line).*

## *Volcano Geology Applications to Ancient Volcanism-Influenced Terrains: Paleovolcanism DOI: http://dx.doi.org/10.5772/intechopen.108770*

in a local, regional, or even global context. Unfortunately, the degree of preservation of ancient volcanic deposits, which may have suffered important transformations due to erosion, diagenesis, hydrothermal alteration, tectonic deformation, etc., may not always be conclusive to recognizing their nature and significance, hence complicating their comparison with modern deposits (**Figure 1b**). However, the study of ancient volcanic successions, even if this represents an additional handicap, should employ the same concepts and methods (e.g., stratigraphic correlations, facies analysis, textural characterization, componentry analysis) that are used in the characterization and interpretation of historical eruption products (e.g., [1]).

The same transformation that volcanology has undergone regarding the study of active or recent volcanic areas—from a basically descriptive to a more interpretative and quantitative science—should also affect the study of ancient volcanic terrains. The presence of volcanic episodes in the geological record should not be regarded as an isolated or sporadic event that does not necessarily need to be relevant to interpret the remainder of rocks found at a particular site [2]. On the contrary, we should try to deduce the tectonic controls that conditioned the rise and accumulation of magmas and their geodynamic significance, the mechanisms responsible for their eruptions, or to determine the influence that volcanic activity had had on sedimentation in the basin. In this sense, the invariance over time of the physical parameters that control the ascent and eruption of magmas allows ancient and modern volcanic products to be compared and interpreted in the same terms.

In this chapter, I will revise the main concepts that should be considered in the study of ancient volcanic succession to achieve the same degree of accuracy and information as in the study of recent volcanism.
