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¿Was the volcanic eruption triggered by the earthquake?¿ The answer to this question usually is ¿maybe¿ or ¿a coincidence¿. A region like Central America, is an adequate area to find hints to answer this question because have the necessary ingredients: the frequent occurrence of large earthquakes (M5+) and dozens of active volcanoes. This research focuses on whether the uncommon occurrence of three large earthquakes in the subduction zone of Central America, within a time span of ten weeks in 2012, promoted enhanced volcanic activity. The time window analyzed is from 2000 to 2019, which includes a total of 50 volcanic eruptions with a VEI¿2. Before the 2012 earthquakes, 22 eruptions occurred. The Monte Carlo statistical simulation method allowed to demonstrate that this increase in the number of volcanic eruptions after the three large earthquakes of 2012 it is not a temporal coincidence. We analyzed the characteristics of each earthquake and described how they could disturb the volcanic systems. Although Central America hosts 24 volcanoes with historical eruptions, only 11 of them erupted after the 2012 earthquakes. Why did only these volcanoes erupt? To answer this question, we calculated the dynamic and static stress in each volcano and the level of volcanic unrest (the change in volcanic activity beyond background behavior to worrisome levels) prior to the earthquakes. We found that volcanoes in a unrest stage before the earthquakes but, without experiencing explosive eruptions before, erupted after receiving the seismic shocks. This fact suggests that the earthquakes by themselves did not transfer enough energy to generate the volcanic eruptions when volcanoes were not ready to erupt. However, earthquakes could promote volcanic eruptions when volcanoes were already at unrest. This research offers a tool for forecasting volcanic activity when a large earthquake hits a region, if the volcanic activity is previously monitored.

The complex geodynamic evolution of Aeolian Arc in the southern Tyrrhenian Sea resulted in melts with some of the most pronounced along the arc geochemical variation in incompatible trace elements and radiogenic isotopes worldwide, likely reflecting variations in arc magma source components. Here we elucidate the effects of subducted components on magma sources along different sections of the Aeolian Arc by evaluating systematics of elements depleted in the upper mantle but enriched in the subducting slab, focusing on a new set of B, Be, As, and Li measurements. Based on our new results, we suggest that both hydrous fluids and silicate melts were involved in element transport from the subducting slab to the mantle wedge. Hydrous fluids strongly influence the chemical composition of lavas in the central arc (Salina) while a melt component from subducted sediments probably plays a key role in metasomatic reactions in the mantle wedge below the peripheral islands (Stromboli). We also noted similarities in subducting components between the Aeolian Archipelago, the Phlegrean Fields, and other volcanic arcs/arc segments around the world (e.g., Sunda, Cascades, Mexican Volcanic Belt). We suggest that the presence of melt components in all these locations resulted from an increase in the mantle wedge temperature by inflow of hot asthenospheric material from tears/windows in the slab or from around the edges of the sinking slab.

In 1864-1866, Turrialba volcano had a strombolian eruption with some phases of phreatic and phreatomagmatic activity, that covered the Central Valley of Costa Rica with a variable thickness of ash. During this eruption, the ash fell up to the province of Puntarenas, 110 km west of Turrialba. After more than 100 years of hydrothermal activity, in 2005 the gas emission showed an increase of (HCl+HF)/CO2 and (SO2+H2S)/CO2 ratios (Vaselli et al. 2009), which indicates a change from a hydrothermal to a magmatic fluids source. Conforming with data from Hilton et al. (2010), we obtained increased values of R/Rair (4He/3He) from 6.85 to 8.2 and CO2 /3He from 9.4 to 19.6 x109. The highest values were measured in the SW crater. These geochemical changes were accompanied by an increase in seismicity and temperatures of the newly appeared fumaroles. After that, on January 2010, a new phreatic eruption occurred from a 100 m large, new vent in the inner wall of the SW crater. Small amounts of ash fell in the Capital San José. On 12 January 2012, a second phreatic eruption occurred along the rim between the SW and Central craters, near the Arbol Quemado gas fracture (which has been active since 2001). The day before this eruption molten sulphur flows were originated from Arbol Quemado. A third phreatic eruption on 21 May 2013 involved both the new vents simultaneously. All the erupted material was lithic. The volcanic unrest continued with tremor episodes and LP seismic signals accompanied by a further increase in the temperature of fumaroles, reaching 700 °C, as measured by FLIR thermal camera. During the night of 29-30 October 2014, a first strombolian eruption occurred as demonstrated by direct observation, temperatures near 900°C measured by FLIR thermal camera and the release of ballistic scoriaceous bombs and abundant magmatic gases (type 0; Leduc et al. 2015). This was the first magmatic eruption of Turrialba volcano since the major 1864-66 eruptive period. The eruption produced the collapse of a large portion of the eastern inner wall of the SW crater. Some scoriaceous bombs were collected during the following days, together with ash samples in different sectors of the summit area. Petrochemical analyses of the bombs were compared to those of the bombs of the 1864-66 eruption, in order to evaluate variations in the eruptive dynamics and feeding system. Early results revealed a basaltic andesitic composition with a similar petrography (plagioclase, pyroxene and olivine) and porphyricity compared to the 1864-66 iuvenile products. Morphoscopic SEM analyses of ash revealed the dominant occurrence of lithic fragments consisting of sulfate and hydrothermalized aggregates. This means that ash is almost entirely related to the phreatic explosions, as result of the wall collapse. Other eruptions occurred in December 2014, and, more recently, in March and April 2015. Ash fell in different provinces, including San José, and caused the closure of the international airport of Costa Rica for one day. UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias Geológicas (CICG) UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela Centroamericana de Geología

A new geological map of Stromboli (southern Italy) at 1:10,000 scale is performed by adopting a modern stratigraphic approach based on lithostratigraphic units (rock types), lithosomes (landforms eruptive centres) and unconformity-bounded units (correlations). The eruptive, structural and magmatic history of Stromboli is described as a result of six major constructional stages (eruptive epochs) separated by periods of quiescence, erosion and volcano-tectonic collapses (calderas and lateral collapses). The epochs of activity are characterized by distinctive compositional features of the erupted products, ranging from the calc-alkaline to potassic, through high-K calcalkaline and shoshonitic series. Insights on hazard assessment are provided by stressing the role played by recurrent lateral collapses in controlling the location of eruptive vents and activity through time. A number of eccentric eruptive fissures are recognized along the NE and W flanks of Stromboli during the Holocene, together with a detailed mapping of the most recent lava flows from summit vents and fissures along Sciara del Fuoco and the distribution of the major paroxysmal spatter deposits. Moreover, a (chrono)stratigraphy of the Recent Stromboli units and information on the onset of the Present-day activity of Stromboli are provided.

New stratigraphic data allowed the reconstruction of the activity responsible of the construction of the Monte dei Porri cone. Alternating explosive and effusive activity, which emplaced fall and pyroclastic density current deposits, and lava flows, form the volcanic cone. The magma composition that fed the different phases of the Monte dei Porri eruptive cycle is poorly evolved to intermediate (basaltic, basaltic andesite and andesite), with the exception of that of the initial phase (dacitic). Hydromagmatic fragmentation cannot be claimed for explaining large variations in explosivity deduced from the stratigraphic succession, being excluded by SEM image analysis on coarse ash from the different pyroclastic units. This suggests that mechanisms responsible of eruption style transitions have to be searched in timing of magma rising, including variations in the local tectonic stress in combination with variable magma chamber overpressure.

Vulcano geological history displays several changes of eruption magnitude, eruption styles and composition of magmas through time. Various volcanic edifices and two intersecting multi-stage calderas resulted from such evolution. The collection for many years of detailed geological data on this island (as well as on those nearby) have made it possible to carry out a detailed lithostratigraphy together with the identification of lithosomes and unconformity-bounded units (UBU) based on the main volcano-tectonic events and/or shifting of volcanic centres. Together with the critical use of available radiometric ages and compositional data as well as the knowledge of regional tephrochronology, this has finally provided the ability to synthesize in a map - at 1:10,000 scale - a large number of information, ranging from the duration of the volcanic activity to the hazard(s) assessment on the island. In particular, this geological map includes a thematic map on volcanic hazard derived from an even more detailed stratigraphy and geological survey performed on La Fossa Cone, where the most recent volcanic activity occurred. The historical activity of this tuff cone is characterized by several eruptions, with the latest eruption occurred during 1888–1890 AD and representing the tail of a two millennia long period of activity. As it is deduced from its stratigraphic record, most of the eruptions were characterized by pulsatory explosive events mainly driven by phreatomagmatic processes, with a minor role for magmatic fragmentation. Both the fragmentation mechanisms involved compositionally distinct magmas (from shoshonites to rhyolites), often mutually interacting (mingling, mixing). They led to the formation of hundreds of meters thick, dilute and turbulent pyroclastic density currents (PDCs), of base surges type, formed in rapid succession and moving down the volcano slope at velocities exceeding 50 m/s. The dispersion of these PDCs affected the whole Vulcano Porto and Vulcanello areas and for one eruption (Grotta dei Palizzi 2 Formation, 1.6 ka) also overrode the La Fossa Caldera rims, spreading radially over further Vulcano areas. Fallout of ballistic blocks and bread-crust bombs on intermediate-distal area was limited. With the aim to provide for a possible reactivation of La Fossa cone, a short-term eruptive scenario (tens to hundreds of years) has been drawn. Going into detail, the PDCs related to the Grotta dei Palizzi 2 activity are expected to be the most hazardous events in future eruptions and the corresponding deposits are used as the best reference for this hazard scenario. In order to quantitatively express the expected impact of these density currents, the dynamic pressure and particle volumetric concentration were calculated. It’s important to stress that these parameters and the impact energy of ballistic blocks are derived through the physical stratigraphic study of volcanic products (definition of individual depositional units and their thickness, sedimentary structures, granulometry and clast morphology of the Grotta dei Palizzi 2 pyroclastics). In order to depict even a long-term eruptive scenario with similar physical parameters, also older deposits (the Upper Brown Tuffs) produced by recurrent hydromagmatic eruptions from the multiphase La Fossa Caldera were studied in detail.

Stromboli (southern Italy) is a 924 m-high active composite volcano made up of thick successions of scoriaceous products and lava flows subdivided by erosional discontinuities related to five calderas and seven large-scale lateral collapses (Francalanci et al. 2013). Volcanic hazards generated by the present-days intermittent and moderately explosive strombolian activity mostly consist of fallout of scoriae and ballistic blocks affecting the area around the summit craters, together with lava flows flowing down the Sciara del Fuoco collapse. These processes produce a limited hazard for the settled areas, which are only occasionally affected by the fallout of bombs and blocks during higher-energy explosions or paroxysms (at a decade-scale). Moreover, events of gravitational instability at various scales (both in time and volume) have occurred throughout the Stromboli history mostly along the north-western flank of Stromboli in the frame of the Sciara del Fuoco collapse, although minor SE-dipping collapse events are recognized to truncate the Pizzo cone on the summit of Stromboli in late Medieval times. The steep Sciara del Fuoco scar is the place where the historic to Present-day activities have mostly taken place, and is the result of recurrent NW-dipping collapses, at times associated with the development of landslides or debris avalanches giving rise to tsunamis events. A low-probability but remarkable hazard scenario is that a flank collapse triggers a large-scale hydromagmatic explosion (as a consequence of a sudden decompression of the magmatic-hydrothermal system) resulting in the generation of pyroclastic density currents (PDC) that flow down the slopes of the volcano (Bertagnini and Landi 1996; Giordano et al. 2008). Based on new geological and geochemical data, we provide the evidence for three distinct hydromagmatic eruptions occurred during the Holocene evolution of Stromboli at ~12.5 ka (Semaforo Nuovo), ~7 ka (Secche di Lazzaro) and ~4 ka (Semaforo Labronzo). As discussed in the literature, they are more likely related to successive collapse events of the Stromboli volcano. These eruptions have produced dilute PDCs able to reach the lower slopes of the volcano and deposit meters-thick pyroclastic accumulations in the surroundings of the settled areas of San Vincenzo-Stromboli (Semaforo Nuovo), Ginostra (Secche di Lazzaro) and Piscità (Semaforo Labronzo). According to these data, the occurrence of collapse-driven hydromagmatic eruptions and PDCs is an eruptive scenario more frequent than previously thought, thus introducing further (previously undervalued) source of volcanic hazard on Stromboli.

The Panarea volcanic group is made up of dome-fields that are the subaerial culminations of a largely dissected volcanic complex mostly located below sea level. The correlation of marine isotope stage (MIS) 5 marine terrace deposits and numerous tephra layers, combined with the available radiometric ages, shows that the Panarea dome-fields mostly developed between c. 155– 149 and 124–118 ka through the emplacement of successive lava domes, lava flows and minor pyroclastic products, interrupted by dormant periods and episodes of faulting in a context of regional uplift, plus volcano-related deformation. Recurrent explosive phases subsequently occurred in the area of minor islets at c. 100 ka (Punta Falcone), 67–56 ka (p1) and 24–8.7 ka (Drauto), together with the emission of the c. 54 ka Basiluzzo dome. The Panarea volcanic group is presently in a quiescent state with fumarolic activity and episodic gas outbursts. Panarea rocks show basaltic andesite and high-K basaltic andesite to high-K dacite and rhyolite compositions, with minor shoshonites. Radiogenic isotope signatures range between those typical of the western Aeolian islands and Stromboli. This reveals a heterogeneous mantle source, which resulted from migration of more primitive asthenospheric mantle from the west during slab rollback, and its admixture with more strongly contaminated Stromboli-type resident mantle

Stratigraphic, structural, volcanological and geochemical data allow a detailed reconstruction of the geological history of the island of Salina (central Aeolian sector). Its subaerial volcanism (~244 ka to 15.6 ka) developed through six successive Eruptive Epochs interrupted by major quiescence periods, volcano-tectonic collapses and recurrent episodes of marine terrace formation during MIS 7 and MIS 5. Several stratovolcanoes were constructed by strombolian and effusive (Pizzo Capo, Mt. Rivi, Mt. Fossa delle Felci, Mt. dei Porri) to hydromagmatic and subplinian (Mt. dei Porri, Pollara) activity, with a general east-to-west shift of active vents, controlled primarily by the dominant NNW-SSE and minor NE-SW regional tectonic trends, and a progressive chemical differentiation of the erupted products from calc-alkaline basalts to rhyolites. The magma compositions and variations through time are the result of contamination of primary magmas derived from a subduction-modified mantle source with the Calabro-Peloritano lower crust and subsequent differentiation dominated by polybaric fractional crystallisation. Magma mixing and mingling processes occurred during individual eruptions. The early basalts were fed from deep reservoirs located near the crust-mantle boundary, whereas the later andesitic to dacitic and, ultimately, rhyolitic magmas originated through combined assimilation and fractional crystallisation processes in magma reservoirs at mid- to upper-crustal levels.

A regional framework for stratigraphic correlations in the Aeolian archipelago is provided by widespread tephra layers and Late Quaternary marine terrace deposits combined with the available radiometric ages. Several tephra layers of Campanian and Aeolian provenance extending back to c. 110 ka are reported. The most important key-beds are the Ischia Tephra (56 ka), the Grey Porri Tuffs (70–67 ka) and Lower Pollara products (27.5 ka) from Salina, the M. Guardia pyroclastics from Lipari (27–24 ka) and the Brown Tuffs from Vulcano (c.70–8 ka). Late Quaternary marine terrace deposits are recognized along the coastal slopes of most of the Aeolian archipelago. They record distinct interglacial sea-level peaks during marine isotope stages (MIS) 5 and 7 in a context of prevalent long-term crustal uplift. Key erosional unconformities bounding the terrace deposits are the F1, UI, L3 and UII (in stratigraphic order). They are the ravinement surfaces formed at the onset of MIS 7.3 (F1), MIS 5e (UI) and MIS 5c interglacial peaks (L3), and the subaerial unconformity formed during the MIS 5a sea-level fall up to the emplacement of Brown Tuffs (UII). These unconformities are important regional-scale markers for chronostratigraphic classification and correlation between distant islands of the Aeolian archipelago.

Vulcano is an active NW–SE-elongated composite volcano located in the central Aeolian archipelago. Based on available radiometric ages and tephrochronology, the exposed volcanism started at c. 127 ka and spread through eight Eruptive Epochs separated by volcano-tectonic events and major quiescent stages. Various eruptive centres and two intersecting multi-stage calderas resulted from such evolution. Vulcano geological history displays several changes of eruption magnitude, eruption styles and composition of magmas through time. Vulcano rocks range from basalt to rhyolite and show variable alkali contents, roughly increasing during time. Magmas with low to intermediate SiO2 contents and high-K to shoshonite affinity prevail in the early Epochs 1–5 (c. 127–28 ka), whereas intermediate to high-SiO2 shoshonite and potassic alkaline products dominate the last three Epochs (,30 ka). This sharp increase in silicic products is related to the shallowing of the plumbing system and resulting major role of the differentiation processes in shallowlevel reservoirs. Radiogenic isotope compositions are variable (87Sr/86Sr ¼ 0.70424–0.70587, 143Nd/144Nd ¼ 0.51254–0.51276, 206Pb/204Pb ¼ 19.305–19.759, 207Pb/204Pb ¼ 15.659–15.752, 208Pb/204Pb ¼ 39.208–39.559) as a result of both source heterogeneities and shallow-level interaction of magmas with continental crust. The compositional variations of mafic magmatism with time suggest that the source zone changed from a metasomatized, fertile, ocean island basalt- (OIB-) like mantle to a metasomatized depleted lithospheric mantle.

The geological history of Filicudi in the Middle–Late Pleistocene (246–29 ka) is described by four successive Epochs of activity separated by quiescence stages, erosional episodes during marine isotope stage (MIS) 7 and MIS 5 and the Vallechiesa sector collapse. The partially overlapping Casa Ficarisi, Fossa Felci and Chiumento stratocones and the Monte Guardia scoria cone are built up under control of the WNW–ESE regional tectonic trend, with a subsequent progressive south-eastwards shift and chemical differentiation towards the Monte Terrione and Capo Graziano domes. The Monte Montagnola dome (64 ka) and Case dello Zucco Grande pyroclastics (,56 ka) are the youngest products, together with the Canna neck (29 ka) of an independent volcanic centre offshore of Filicudi. Filicudi rocks are calc-alkaline basalts, basaltic andesites and high-K andesites with minor dacites. Incompatible elements increase from basalts to dacites, with much scatter. Sr, Nd and Pb isotopes show moderate variations. d18O‰of clinopyroxene phenocrysts ranges from þ5.37 to þ6.20, and shows the highest values in the mafic rocks. Geochemical data suggest a complex interplay of different evolution processes (fractional crystallization, crustal assimilation and mixing) for the various eruptive centres of Filicudi. Variable incompatible element ratios of mafic rocks are suggested to reflect source heterogeneity.

The Alicudi composite volcano (western Aeolian archipelago) was constructed between c. 106 and 28 ka by lava flows, domes and strombolian scoriae erupted during six Eruptive Epochs, interrupted by periods of dormancy and three caldera-type collapses in the summit area. Marine Isotope Stage (MIS) 5a (81 ka) terrace deposits and widespread Brown Tuffs of external origin are recognized and provide important marker beds for regional stratigraphic correlations. Volcanism was of central type, under control of the summit caldera collapses with negligible influence of regional tectonic trends. Alicudi rocks are basaltic to high-K andesitic and have the most primitive petrological compositions (high MgO, Ni, Cr contents), the lowest Sr–O and the highest Nd–He isotope ratios (87Sr/86Sr ¼ 0.70352 to 0.70410; 143Nd/144Nd ¼ 0.51289 to 0.51279; d18O ¼ þ5.0 to 5.6; 3He/4He–R/Ra ¼ c. 6.5 to 7.1) over the entire Aeolian archipelago. Their composition and variation through time are the result of polybaric crystal–liquid fractionation of parental calc-alkaline basalts to give basaltic andesitic and andesitic derivative melts. These underwent crustal assimilation during ascent, with basalts being contaminated more strongly than andesitic magmas. Sr–Nd–Pb isotopes suggest source metasomatic modification by fluids from an oceanic-type slab, with a minor role for subducted sediments.

Introduction to the Memoir no 37 of the Geological Society of London dedicated to the geology, eruptive history and magmatology of the Aeolian Islands (including a CD-ROM with 1:10000 scale maps and three mathy-morphological maps of the submarine portions)

A stratigraphic approach to geological fieldwork and mapping of the Aeolian archipelago is performed by primarily using unconformity-bounded units (UBUs) in addition to lithosomes and classical lithostratigraphic units, which are the basic mappable units. Lithosomes are largely used to identify the localization of eruptive vents or non-volcanic source areas through time. The UBUs display an encompassing framework of correlation on a scale from local (single islands) to regional (Aeolian archipelago), by placing particular emphasis on the stratigraphic role played by Late Quaternary marine terrace deposits and widespread tephra layers (e.g. Brown Tuffs). By establishing a direct relationship between UBUs and time-stratigraphic units, the volcanic successions are readable in terms of different and successive Eruptive Epochs (separated by prolonged non-volcanic periods), which are characterized by distinctive eruptive vents and eruption types. As such, the UBUs allow the reconstruction of the main steps of geological evolution of a volcano as the result of the interplay between volcanic activity of local and external provenance, sea-level fluctuations and volcano-tectonic or regional fault lineaments.