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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.

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

The geological map at 1:50.000 scale of the El Tatio volcanic area (central Andes, northern Chile) is presented. The map is performed on the basis of i) geological field survey, ii) satellite-aerial imagery analysis, iii) petrochemical investigation and iiii) literature radiometric ages. Using reconstructed unconformity-bounded stratigraphy, together with more descriptive lithostratigraphic units and lithosomes, the Miocene Quaternary geological history of the study area is described in terms of the interaction between volcanic activity of local and external provenance, and regional fault systems. Local andesitic to dacitic lava cones, stratovolcanoes and monogenic lava domes are emplaced mostly during the Pleistocene (and subordinately during the Miocene) under control of NE-SW to N-S alignments. Local volcanic products are interbedded with regional ignimbrite sheets originated in the Altiplano Puna Volcanic Complex from Miocene to Pleistocene. Periods of volcanic inactivity during the Pleistocene are characterized by extensional tectonic phases developing along NW-SE-aligned normal faults. The youngest tectonic event during middle-late Pleistocene is demonstrated by a series of roughly NNE-SSW trending, west-verging thrust faults, which, in addition to a local NW-SE-oriented strike-slip lineament, indicate contractional deformation processes in a NW-SE direction. The easternmost thrust fault is proposed to have driven magma ascent leading to the emplacement of the 34-ka-old Co. La Torta rhyolitic lava dome, which is the youngest recorded phase of activity in the study area. Field evidence of glacial advance during the Last Glacial Maximum (and, subordinately, during middle-late Pleistocene major glaciations) is recorded in the entire study area providing a relative age assignment of most of volcanic products and tectonic features. At present, the study area is characterized by intense fluid discharge in the El Tatio geothermal field, which is apparently conditioned by the westermost portion of the demonstrated thrust fault system.

Understanding the relationship cause/effect between tectonic earthquakes and volcanic eruptions is a striking topic in Earth Sciences. Volcanoes erupt with variable reaction times as a consequence of the impact of seismic waves (i.e. dynamic stress) and changes in the stress field (i.e. static stress).In2012, three large(Mw≥7.3)subductionearthquakes struck Central Americawithin a period of 10 weeks;subsequently, some volcanoesin the regionerupted a few days after, whileotherstook months or even years to erupt. Here, we show thatthese threeearthquakes contributed to the increase in the number of volcanic eruptionsduring the 7 years that followed these seismic events. We found that onlythosevolcanoes that were already in a critical state ofunrest eventually erupted, which indicates that the earthquakes only prompted the eruptions. Therefore, we recommend the permanent monitoring of active volcanoes toreveal which are more susceptible to culminate into eruption in the aftermath of the next large-magnitude earthquake hits a region., Funding was provided by Japan International Cooperation Agency (JICA) and Istitute Nazionale di Geofisica e Vulcanologia (INGV).

Southern Italy is a most active tectonic and volcanic setting comprising active (Stromboli, Vulcano) or dormant (Lipari) volcanic islands in the Aeolian Arc, and the majestic Etna volcano (together with the Campanian volcanoes). They have attracted the attention of a great number of volcanologists and can be rightfully considered the cradle of the scientific discipline of Volcanology. In the Aeolian Arc, the main features are the incessant and rhythmic Strombolian exlosive activity of Stromboli and the Sciara del Fuoco collapse, together with the deposits of historical Vulcanian eruptions of Vulcano and its present-day intense fumarolic activity. The well-known Rocche Rosse obsidian lava flow and Mt. Pilato pumice are the traces of the Middle Ages activity of Lipari. On Etna, the geology of the valle del Bove depression and the summit craters and NE-Rift, and the 2001, 2002-03 and the 2011-2017 eruptive fissures and lava flow fields give an idea of the variability of its eruptive scenarios. The spectacular geology of these volcanoes and the INGV real-time monitoring network are the bases to discuss the main aspects of volcanic hazard and risk mitigation in case of future eruptions in a highly-urbanized territory characterized by intense tourism exploitation during the summer.

The Neostromboli volcanic succession is characterized by packages of lava flow units and scoria beds erupted from the summit of the Stromboli volcano, and by scoria cones and lava flows poured out from lateral vents and fissures. Available radiometric ages constrain Neostromboli activity in the 14–4 ka BP age window, but the chronological relations of central vs. peripheral activity are still poorly understood. Furthermore, radiometric and palaeomagnetic ages for some of the peripheral eruptions are strikingly inconsistent. Here we report on the palaeomagnetic dating of thirty-four sites from Neostromboli products. Seventeen are new palaeomagnetic directions, while additional seventeen ages are recalculated - using published directions by Speranza et al. (2008) - with the recent SHA.DIF.14K palaeo-secular variation (PSV) field model. We show that the beginning of Neostromboli succession could be much younger than the commonly accepted ≈14 ka onset, providing our oldest data an age of ≈9 ka. The improved geochronological resolution allowed by palaeomagnetic dating suggests that the early stages of the Neostromboli activity occurred at 9–8 ka BP and were characterized by summit lava flow units blanketing both the SW and northern volcano flanks; after ≈7.5 ka lateral eruptions from peripheral cones and fissures became dominant. We suggest that the intense flank activity enabled magma-water interaction thus yielding explosive activity and repeated collapse events, leading to the Sciara del Fuoco formation. Our work confirms that PSV analysis of Holocene volcanics may yield eruption chronology definition with an accuracy unlikely to be achieved with other radiometric techniques.

Katla is a threatening volcano in Iceland, partly covered by the M\'yrdalsj\"okull ice cap. The volcano has a large caldera with several active geothermal areas. A peculiar cluster of long-period seismic events started on Katla's south flank in July 2011, during an unrest episode in the caldera that culminated in a glacier outburst. The seismic events were tightly clustered at shallow depth in the Gvendarfell area, 4 km south of the caldera, under a small glacier stream on the southern margin of M\'yrdalsj\"okull. No seismic events were known to have occurred in this area before. The most striking feature of this seismic cluster is its temporal pattern, characterized by regular intervals between repeating seismic events, modulated by a seasonal variation. Remarkable is also the stability of both the time and waveform features over a long time period, around 3.5 years. No comparable examples have been found in the literature. Both volcanic and glacial processes can produce similar waveforms and therefore have to be considered as potential seismic sources. Discerning between these two causes is critical for monitoring glacier-clad volcanoes and has been controversial at Katla. For this new seismic cluster on the south flank we regard volcano-related processes as more likely than glacial ones for the following reasons: 1) the seismic activity started during an unrest episode involving sudden melting of the glacier and a j\"okulhlaup; 2) the glacier stream is small and stagnant; 3) the seismicity remains regular and stable for years; 4) there is no apparent correlation with short-term weather changes, such as rain storms. We suggest that a small, shallow hydrothermal system was activated on Katla's south flank in 2011, either by a minor magmatic injection or by changes of permeability in a local crack system.

The Aeolian arc (Italy) is characterized by some of the strongest along-the-arc geochemical variations in the planet, making it an ideal location to study the effect of subducting components in modifying the mantle source of island arc melts. Here, we use high-precision element concentrations in primitive phenocrystic olivine from basalts along the arc to elucidate the effects of mantle source modification by the subduction process. Olivines from this arc have Ni concentrations and Fe/Mn ratios that show similarity to peridotite sources that melted to produce mid-ocean ridge basalts. Nevertheless, they also have systematically lower Ca concentrations and Fe/Mn ratios that broadly overlap with olivines from the available global arc array. These phenocrysts also do not show significant variations in Ca as a function of olivine forsterite content. The global data suggest that all olivines crystallizing from island-arc melts have suppressed Ca concentrations and Fe/Mn ratios, relative to olivines derived from melts at intraplate and mid-ocean ridge settings suggesting elevated H 2 O concentrations and higher oxidation state of the equilibrium melts. Based on olivine chemistry, we interpret a predominantly peridotite source (fluxed by subduction fluids) beneath the Aeolian Arc and also for other examples of arc-related lavas.

Over the last ~267 ky, the island of Lipari has erupted magmas ranging in compositions from basaltic andesites to rhyolites, with a notable compositional gap in the dacite field. Bulk geochemical and isotopic compositions of the volcanic succession, in conjunction with major and trace elemental compositions of minerals, indicate that the rhyolites were dominantly generated via crystal fractionation processes, with subordinate assimilation. Radiogenic (Sr, Nd, and Pb) and stable (O) isotopes independently suggest ≤30 % of crustal contamination with the majority of it occurring in mafic compositions, likely relatively deep in the system. Within the rhyolites, crystal-rich, K2O-rich enclaves are common. In contrast to previous interpretations, we suggest that these enclaves represent partial melting, remobilization and eruption of cumulate fragments left-over from rhyolite melt extraction. Cumulate melting and remobilization is supported by the presence of (1) resorbed, low-temperature minerals (biotite and sanidine), providing the potassic signature to these clasts, (2) reacted Fo-rich olivine, marking the presence of mafic recharge, (3) An38–21 plagioclase, filling the gap in feldspar composition between the andesites and the rhyolites and (4) strong enrichment in Sr and Ba in plagioclase and sanidine, suggesting crystallization from a locally enriched melt. Based on Sr-melt partitioning, the high-Sr plagioclase would require ~2300 ppm Sr in the melt, a value far in excess of Sr contents in Lipari and Vulcano magmas (50–1532 ppm) but consistent with melting of a feldspar-rich cumulate. Due to the presence of similar crystal-rich enclaves within the rhyolites from Vulcano, we propose that the eruption of remobilized cumulates associated with high-SiO2 rhyolites may be a common process at the Aeolian volcanoes, as already attested for a variety of volcanic systems around the world., Contributions to Mineralogy and Petrology, 170 (5-6), ISSN:0010-7999, ISSN:1432-0967