*Introduction to the Sedimentary Geology, Genesis, and Evolution of the Pontine Plain in Relation… DOI: http://dx.doi.org/10.5772/intechopen.111683*

consists of coalescing, peri-caldera, fissure-related scoria cones interbedded with lava flows; the fissure system forms two segments controlled by regional faults. The second is the steep-sided Faete stratovolcano (949 m a.s.l.), which filled the caldera. The TA and Faete lithosomes, which partly interfinger, were emplaced at ∼350–260 ka. Their products indicate reduced eruption rates relative to the VL period and a change to effusive and mildly explosive eruptions. The most recent and still active phase of phreatomagmatic activity formed overlapping maars and tuff cones along the western and northern slopes of the volcano, collectively named the *via* dei Laghi composite lithosome [19]. The Alban Hills caldera is a polyphase caldera: (1) A piecemeal caldera is associated with large-volume ignimbrites of the VL edifice, and the present shape of the caldera is related to the Villa Senni eruption. (2) The TA composite edifice, erupted from peripheral caldera fissures, is unrelated to explosive phases of caldera collapse. The TA final products cover a morphologically stable caldera wall. The peripheral fractures feeding the TA composite edifice are interpreted as volcano-tectonic structures activated during the late-stage downsagging of the caldera. Reduced eruption rates during the TA and the Faete stages (1–10 km3 /ka compared to >100 km3 /ka for the VL edifice) suggest that diminished recharge of the magma chamber may have induced prolonged deflation and downsagging of the caldera floor and the opening

#### **Figure 15.**

*Simple sketch of the geology of Aprilia village. Simply qualitatively taken from the web: Pedological sketch compiled by the Chemical-Agricultural Station of Rome, offers a summary view of the main types of soil that occur in the area.*

of outward-dipping peripheral fractures [19]. Based on this interpretation, the TA edifice represents the surface expression of ring dikes at depth. The absence of similar fissure structures along the western caldera rim may be related to the deep geometry of the inward-dipping ring faults in those areas, which therefore were not favorably oriented for magma intrusion during a period of general subsidence. "In contrast, the subsequent and still active phreatomagmatic phase, which emplaced the *via* dei Laghi composite edifice and is active on the western side of the caldera, may produce resurgent conditions that could affect Aprilia village and other areas near the volcano" (**Figure 13**) [16]. A volcano model of Alban Hills [12] suggests that such a volcano could potentially affect all of the territory around it, a densely inhabited area, in addition to Aprilia village (Latium Province) (**Figures 13**–**15**).
