Misti volcano in southern Peru has a record of explosive eruptions and a nearby population of over 810,000, making it a hazardous volcano. The city center of Arequipa, Peru's second most populous city, is 15 km from the summit of Misti, and many neighborhoods are closer. As the population increases yearly, the urban boundary continues to move up the south side of the volcano. Many parts of the city are built upon the deposits from Misti's most recent Plinian eruption at ca. 2 ka. The 2 ka Plinian eruption (Volcanic Explosivity Index [VEI] 5) produced a 1.4 km 3 tephra-fall deposit and 0.01 km 3 of pyroclastic-flow deposits in ~2–5 h. Column height varied during the eruption but ascended up to 29 km. Pyroclastic flows descended only the south side of the volcano. The tephra fall spread southwest, resulting in ~20 cm of tephra accumulation in the area now occupied by the city center. The flowage deposits were previously identified as pyroclastic-flow deposits, but new sedimentologic and textural evidence suggests that ~80% (by volume) of the deposits were emplaced wet and relatively cold. As such, they are lahar deposits. A Neoglacial advance concurrent with the eruption supports evidence for voluminous snow and ice on the edifice. Pyroclastic flows melted between 0.01 km 3 and 0.04 km 3 of ice and snow on the volcano, triggering lahars that descended the volcano and inundated channels and some interfluves on the south flank. The lahars evolved downstream from proximal debris flows to distal hyperconcentrated flows, emplacing ~0.04 km 3 of deposits. Four facies of lahar deposits are present in the channels and another facies occurs on the interfluves. Such a comprehensive understanding of the 2 ka eruption will help to inform future volcanic hazards assessments. Pyroclastic-flow and tephra-fall deposits of the same magnitude could occur again and are useful in hazards assessment. The 2 ka lahars required voluminous water, which is no longer available on the volcano, and, within modern climate conditions, these deposits are not representative of possible future events. Estimations of water available from modern rain and snow suggest that lahars with volumes between 1 × 10 5 m 3 and 3 × 10 6 m 3 are possible. Lahars are more likely if an eruption occurs during a period of high snow accumulation or during subsequent heavy rainfall. Lahars up to 1 × 10 7 m 3 are possible if the Río Chili is dammed during an eruption. Lahar hazard zones generated using these volumes suggest the largest lahars could enter Arequipa.

In this work, unconformity-bounded stratigraphic (UBS) units are applied to a complex volcanic terrain. UBS units allow us to summarize the spatial-temporal relationships between the cartographic units of a volcanic district or complex, and identify individual successions of volcanic deposits and their probable connection with morphogenetic and/or tectonic phases. The UBS unit approach for the interpretation of significant preserved unconformity surfaces is supported by data from geomorphology, sedimentology, petrology, tectonics, and volcano-tectonics. The result is a stratigraphic scheme that combines the recognized lithostratigraphic units into a series of synthems, in which several phases of geological evolution of Ustica Island are recognized. The emplacement in the early Pleistocene of the basaltic Monte Guardia dei Turchi lithosome, which represents the emerged part of the volcanic seamount, was followed by hydromagmatic activity and construction of a tuff cone that is part of the Monte Costa del Fallo synthem. Following a period of quiescence, volcanism on the island resumed with a Plinian eruption that deposited a thick sequence of trachytic pumice breccias and was accompanied by a caldera collapse. Subsequently, marine terracing occurred in the southwest, while extrusive volcanics filled the caldera in the northern part of the island. Lava flows associated with this volcanism are present on the western flank of the volcano, whereas along the sublittoral zones, dike swarms provide evidence of phreatomagmatic activity. This volcanic activity was followed by repeated alluvial deposition and marine erosion. Finally, recent subaerial monogenetic centers produced shallow subvolcanic bodies, scoria and tuff cones, and lava flows.

Campi Flegrei is a densely populated active volcanic field. Two major explosive volcanic events have led to the formation of nested calderas. Detailed stratigraphy of the volcanic rocks outcropping in part of this area contributes toward a better understanding and definition of the volcanic hazard. Our research activity focuses on the southwestern sector of Campi Flegrei including Procida Island. This area is particularly suitable for stratigraphic reconstruction due to the thick pyroclastic sequences exposed on the coastal cliffs. These sequences include several paleosol horizons and substantially represent the products of all the volcanic activity of Campi Flegrei. The onset of volcanic activity in this area is represented by products related to the activity of scattered vents of unconstrained age. From 74 to 55 ka, they were mantled by products erupted in the nearby island of Ischia. Circa 39 ka, the Campanian Ignim-brite eruption occurred in the Campi Flegrei area, producing a large caldera. A thick succession of welded pyroclasts, lithic breccias, and associated ash- and pumice-flow deposits was emplaced in the proximal area. The local activity resumed at 19–17 ka with the formation of monogenetic volcanoes. A phreatoplinian eruption (Neapolitan Yellow Tuff) occurred at 15 ka, which produced a second, nested caldera. Stratified yellow tuff volcanoes, ranging in age between 9 and 5 ka, developed along the Neapolitan Yellow Tuff caldera boundary. Minor tephra layers testify to the final explosive activity vented in this area.