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Kokichi Iizasa - One of the best experts on this subject based on the ideXlab platform.
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submarine silicic Caldera at the front of the izu bonin arc japan voluminous seafloor eruptions of rhyolite pumice
Geological Society of America Bulletin, 2001Co-Authors: Richard S. Fiske, Jiro Naka, Kokichi Iizasa, Makoto Yuasa, Adam KlausAbstract:Myojin Knoll Caldera, a submarine rhyolitic center 400 km south of Tokyo, is one of nine silicic Calderas along the northern 600 km of the Izu-Bonin(-Ogasawara) arc and the first anywhere to receive detailed, submersible-based study. The Caldera, slightly smaller than the Crater Lake structure in Oregon, is 6 × 7 km in diameter; its inner walls are 500–900 m high, and it has a remarkably flat floor at 1400 m below sea level (mbsl). The Caldera collapse volume is ∼18 km 3 , suggesting that more than 40 km 3 of pumiceous tephra may have been erupted at the time the Caldera formed. PreCaldera seafloor eruptions built a broad volcanic edifice consisting of overlapping composite volcanoes made of rhyolitic lavas, shallow intrusions, and a variety of volcaniclastic deposits—including thick accumulations of rhyolitic pumice erupted at 900– 500 mbsl. The Caldera-forming eruption produced a 150–200 m deposit of nonwelded, fines-depleted pumice that resembles a colossal layer of popcorn at the top of the Caldera wall. Freshly erupted pumice behaved as “sinkers” or “floaters,” depending on the environment in which it cooled. The pumice clasts deposited proximally and exposed in the Caldera wall were likely quenched in eruption columns that remained below sea level. This pumice ingested seawater and sank as gases filling its vesicles cooled, particularly as steam in its vesicles condensed to liquid water. Some eruption columns may have broken through the sea surface and entered the air, especially during vigorous phases of the Caldera-forming eruption. These pumices had the opportunity to ingest air as they cooled, becoming floaters as they fell back to the sea; these could have been carried distally on the sea surface by the combined effects of ocean currents and wind. The age of the Caldera is unknown, but it may be as young as several thousand years. Its magmatic system at depth retains sufficient heat to sustain an actively growing intraCaldera Kuroko- type polymetallic sulfide deposit, rich in gold and silver and topped by chimneys emitting fluids as hot as 278 °C. Sufficient time has elapsed, however, for a 250-m-high postCaldera dome to grow on the Caldera floor and for the Caldera rim to be deeply scalloped by slumping.
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a kuroko type polymetallic sulfide deposit in a submarine silicic Caldera
Science, 1999Co-Authors: Kokichi Iizasa, Richard S. Fiske, Jiro Naka, Makoto Yuasa, Osamu Ishizuka, Jun Hashimoto, Junichiro Ishibashi, Y Horii, Y Fujiwara, Akira ImaiAbstract:Manned submersible studies have delineated a large and actively growing Kuroko-type volcanogenic massive sulfide deposit 400 kilometers south of Tokyo in Myojin Knoll submarine Caldera. The sulfide body is located on the Caldera floor at a depth of 1210 to 1360 meters, has an area of 400 by 400 by 30 meters, and is notably rich in gold and silver. The discovery of a large Kuroko-type polymetallic sulfide deposit in this arc-front Caldera raises the possibility that the numerous unexplored submarine silicic Calderas elsewhere might have similar deposits.
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assessment of the hydrothermal contribution to seafloor sediments in the myojinsho submarine Caldera shichito iwojima ridge izu ogasawara arc japan
Marine Geology, 1993Co-Authors: Kokichi IizasaAbstract:Abstract To assess the hydrothermal contribution to sediments of submarine Calderas on a volcanic front, seafloor sediments from the Myojinsho submarine Caldera, Shichito-Iwojima ridge, Izu-Ogasawara arc, northwestern Pacific were chemically and mineralogically analysed. The Caldera (ca. 5 · 6 km wide and 1114 m water depth) has a flat-topped central cone (ca. 330 m deep) and is covered with muddy to sandy sediments dominated by fragments of volcanic ash with lesser amounts of foraminifera, radiolaria and diatoms. Microscopic observations of the heavy mineral fraction indicate that the sediments include sulfides, barite, fahlore and epidote associated with chlorite, suggesting the presence of hydrothermal activity. Ag is present in fahlore in polished sections according to SEM supplemented with EDX. The sediments are relatively enriched in Au, Zn, Pb, Cu, Co, As, Sr, Ca, Mg, Fe, Mn and Ba compared to fresh dacitic rocks sampled from the Caldera. Factor analysis of the compositional data produces three major factors—detrital, hydrogenous and hydrothermal. One site nearest to a probable hydrothermal source was evaluated by the characteristic assemblage and abundance of hydrothermal minerals, and factor analysis of the sediment samples.
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petrographic investigations of seafloor sediments from the kita bayonnaise submarine Caldera shichito iwojima ridge izu ogasawara arc northwestern pacific
Marine Geology, 1993Co-Authors: Kokichi IizasaAbstract:Abstract Seafloor sediment samples were recovered by box and gravity corers from the Kita-Bayonnaise submarine Caldera, Shichito-Iwojima Ridge, Izu-Ogasawara Arc, northwestern Pacific. The samples were separated into heavy, light, and claysized fractions for assessment of the hydrothermal contribution to the sediments of the submarine Caldera, and have been determined by microscopy, SEM-EDX, and XRD. Heavy fractions are composed of predominant magnetic minerals, dominant silicates and common sulfides and sulfate, minor sulfosalt, rutile, phosphates, carbonates and Mn-oxyhydroxides. Primary hydrothermal phases are composed of barite, pyrite, sphalerite, chalcopyrite, galena, fahlore, marcasite and rutile. Secondary mineral associations are usually present around galena and chalcopyrite grains. The assemblages of barite-pellet type pyrite-chalcopyrite-sphalerite and sphalerite-chalcopyrite-pyrite with galena or fahlore suggest that hydrothermal mineralization took place in the Caldera. The assemblages of epidote-carbonate or chlorite in heavy transparent fractions and of sericite-quartz-feldspar in light fractions are indicative of hydrothermal alteration origin because of only dacite sampled from the Caldera. Some of the smectite, chlorite, sericite and kutnahorite in clay-sized fractions could also support the existence of hydrothermal activity. Other minerals consisting of hypersthene, augite, hornblende, quartz, feldspar and biotite are observed in heavy and light fractions as detritus of dacite in the Caldera. Significant amounts of sulfides and barite mixtures (ranging from about 1.0 to 3.5 wt.% in treated fractions, 0.063–0.25 mm) in gravity core samples suggest that hydrothermal mineralization took place several times in the Caldera. Many lines of evidence indicate the presence of hydrothermal mineralizations associated with Ag and Th in the Kita-Bayonnaise submarine Caldera. The mineralogical analyses are powerful for exploring signs of past or present hydrothermal mineralization in submarine Calderas.
Stefano Carlino - One of the best experts on this subject based on the ideXlab platform.
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progressive approach to eruption at campi flegrei Caldera in southern italy
Nature Communications, 2017Co-Authors: Christopher R J Kilburn, Giuseppe De Natale, Stefano CarlinoAbstract:Unrest at large Calderas rarely ends in eruption, encouraging vulnerable communities to perceive emergency warnings of volcanic activity as false alarms. A classic example is the Campi Flegrei Caldera in southern Italy, where three episodes of major uplift since 1950 have raised its central district by about 3 m without an eruption. Individual episodes have conventionally been treated as independent events, so that only data from an ongoing episode are considered pertinent to evaluating eruptive potential. An implicit assumption is that the crust relaxes accumulated stress after each episode. Here we apply a new model of elastic-brittle failure to test the alternative view that successive episodes promote a long-term accumulation of stress in the crust. The results provide the first quantitative evidence that Campi Flegrei is evolving towards conditions more favourable to eruption and identify field tests for predictions on how the Caldera will behave during future unrest.
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the campi flegrei deep drilling project cfddp new insight on Caldera structure evolution and hazard implications for the naples area southern italy
Geochemistry Geophysics Geosystems, 2016Co-Authors: Giuseppe De Natale, Stefano Carlino, Mauro A Di Vito, Diana Barra, Claudia Troise, D F Mark, Angela Mormone, M Piochi, Roberto Isaia, Renato SommaAbstract:The 501 m deep hole of the Campi Flegrei Deep Drilling Project, located west of the Naples metropolitan area and inside the Campi Flegrei Caldera, gives new insight to reconstruct the volcano-tectonic evolution of this highly populated volcano. It is one of the highest risk volcanic areas in the world, but its tectonic structure, eruptive history, and size of the largest eruptions are intensely debated in the literature. New stratigraphic and 40Ar/39Ar geochronological dating allow us to determine, for the first time, the age of intraCaldera deposits belonging to the two highest magnitude Caldera-forming eruptions (i.e., Campanian Ignimbrite, CI, 39 ka, and Neapolitan Yellow Tuff, NYT, 14.9 ka) and to estimate the amount of collapse. Tuffs from 439 m of depth yield the first 40Ar/39Ar age of ca. 39 ka within the Caldera, consistent with the CI. Volcanic rocks from the NYT were, moreover, detected between 250 and 160 m. Our findings highlight: (i) a reduction of the area affected by Caldera collapse, which appears to not include the city of Naples; (ii) a small volume of the infilling Caldera deposits, particularly for the CI, and (iii) the need for reassessment of the collapse amounts and mechanisms related to larger eruptions. Our results also imply a revaluation of volcanic risk for the eastern Caldera area, including the city of Naples. The results of this study point out that large Calderas are characterized by complex collapse mechanisms and dynamics, whose understanding needs more robust constraints, which can be obtained from scientific drilling.
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Eruptive versus non-eruptive behaviour of large Calderas: the example of Campi Flegrei Caldera (southern Italy)
Bulletin of Volcanology, 2010Co-Authors: Stefano Carlino, Renato SommaAbstract:Caldera eruptions are among the most hazardous of natural phenomena. Many Calderas around the world are active and are characterised by recurrent uplift and subsidence periods due to the dynamics of their magma reservoirs. These periods of unrest are, in some cases, accompanied by eruptions. At Campi Flegrei Caldera (CFc), which is an area characterised by very high volcanic risk, the recurrence of this behaviour has stimulated the study of the rock rheology around the magma chamber, in order to estimate the likelihood of an eruption. This study considers different scenarios of shallow crustal behaviour, taking into account the earlier models of CFc ground deformation and Caldera eruptions, and including recent geophysical investigations of the area. A semi-quantitative evaluation of the different factors that lead to magma storage or to its eruption (such as magma chamber size, wall-rock viscosity, temperature, and regional tectonic strain rate) is reported here for elastic and viscoelastic conditions. Considering the large magmatic sources of the CFc ignimbrite eruptions (400–2,000 km^3) and a wall-rock viscosity between 10^18 and 10^20 Pa s, the conditions for eruptive failure are difficult to attain. Smaller source dimensions (a few cubic kilometres) promote the condition for fracture (eruption) rather than for the flow of wall rock. We also analyse the influence of the regional extensional stress regime on magma storage and eruptions, and the thermal stress as a possible source of Caldera uplift. The present study also emphasises the difficulty of distinguishing eruption and non-eruption scenarios at CFc, since an unambiguous model that accounts for the rock rheology, magma-source dimensions and locations and regional stress field influences is still lacking.
Renato Somma - One of the best experts on this subject based on the ideXlab platform.
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the campi flegrei deep drilling project cfddp new insight on Caldera structure evolution and hazard implications for the naples area southern italy
Geochemistry Geophysics Geosystems, 2016Co-Authors: Giuseppe De Natale, Stefano Carlino, Mauro A Di Vito, Diana Barra, Claudia Troise, D F Mark, Angela Mormone, M Piochi, Roberto Isaia, Renato SommaAbstract:The 501 m deep hole of the Campi Flegrei Deep Drilling Project, located west of the Naples metropolitan area and inside the Campi Flegrei Caldera, gives new insight to reconstruct the volcano-tectonic evolution of this highly populated volcano. It is one of the highest risk volcanic areas in the world, but its tectonic structure, eruptive history, and size of the largest eruptions are intensely debated in the literature. New stratigraphic and 40Ar/39Ar geochronological dating allow us to determine, for the first time, the age of intraCaldera deposits belonging to the two highest magnitude Caldera-forming eruptions (i.e., Campanian Ignimbrite, CI, 39 ka, and Neapolitan Yellow Tuff, NYT, 14.9 ka) and to estimate the amount of collapse. Tuffs from 439 m of depth yield the first 40Ar/39Ar age of ca. 39 ka within the Caldera, consistent with the CI. Volcanic rocks from the NYT were, moreover, detected between 250 and 160 m. Our findings highlight: (i) a reduction of the area affected by Caldera collapse, which appears to not include the city of Naples; (ii) a small volume of the infilling Caldera deposits, particularly for the CI, and (iii) the need for reassessment of the collapse amounts and mechanisms related to larger eruptions. Our results also imply a revaluation of volcanic risk for the eastern Caldera area, including the city of Naples. The results of this study point out that large Calderas are characterized by complex collapse mechanisms and dynamics, whose understanding needs more robust constraints, which can be obtained from scientific drilling.
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Eruptive versus non-eruptive behaviour of large Calderas: the example of Campi Flegrei Caldera (southern Italy)
Bulletin of Volcanology, 2010Co-Authors: Stefano Carlino, Renato SommaAbstract:Caldera eruptions are among the most hazardous of natural phenomena. Many Calderas around the world are active and are characterised by recurrent uplift and subsidence periods due to the dynamics of their magma reservoirs. These periods of unrest are, in some cases, accompanied by eruptions. At Campi Flegrei Caldera (CFc), which is an area characterised by very high volcanic risk, the recurrence of this behaviour has stimulated the study of the rock rheology around the magma chamber, in order to estimate the likelihood of an eruption. This study considers different scenarios of shallow crustal behaviour, taking into account the earlier models of CFc ground deformation and Caldera eruptions, and including recent geophysical investigations of the area. A semi-quantitative evaluation of the different factors that lead to magma storage or to its eruption (such as magma chamber size, wall-rock viscosity, temperature, and regional tectonic strain rate) is reported here for elastic and viscoelastic conditions. Considering the large magmatic sources of the CFc ignimbrite eruptions (400–2,000 km^3) and a wall-rock viscosity between 10^18 and 10^20 Pa s, the conditions for eruptive failure are difficult to attain. Smaller source dimensions (a few cubic kilometres) promote the condition for fracture (eruption) rather than for the flow of wall rock. We also analyse the influence of the regional extensional stress regime on magma storage and eruptions, and the thermal stress as a possible source of Caldera uplift. The present study also emphasises the difficulty of distinguishing eruption and non-eruption scenarios at CFc, since an unambiguous model that accounts for the rock rheology, magma-source dimensions and locations and regional stress field influences is still lacking.
Motohiro Shimanaga - One of the best experts on this subject based on the ideXlab platform.
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meiofaunal communities in hydrothermal vent and proximate non vent habitats around neighboring seamounts on the izu ogasawara arc western north pacific ocean
Marine Biology, 2017Co-Authors: Yuki Uejima, Yuka Setoguchi, Hidetaka Nomaki, Tomo Kitahashi, Hiromi Watanabe, Reina Senokuchi, Motohiro ShimanagaAbstract:The present study investigated spatiotemporal variations in meiofaunal abundance and composition at high taxonomic levels, and their associations with certain measures of food availability around hydrothermal vents on chimney structures and in adjacent non-vent fields in the Calderas of three neighboring seamounts (Bayonnaise Knoll, Myojin Knoll, and Myojin-sho Caldera), in the Izu-Ogasawara Arc, western North Pacific Ocean. Total meiofaunal abundance in seafloor sediment at the bases of vent chimneys appeared to be greater than that in other non-vent habitats outside or inside the Calderas of all seamounts, which was partly explained by temporal variations at the bases of the chimneys. There was no significant difference in the mean meiofaunal abundances among those habitats. A typical deep-sea meiofaunal composition (nematodes as the most abundant taxon, harpacticoid copepods as the second) was observed in the seafloor sediments in the non-vent fields, and even in the sediments at chimney bases. This was significantly different from the meiofaunal composition observed on the surfaces of vent chimneys, where copepods and their nauplii were most abundant. This spatial difference was significantly correlated with a difference in stable carbon isotope ratios (δ13C) of organic matter in sediment, suggesting that the availability of chemosynthetic food controls the spatial differences in meiofaunal composition around these hydrothermal vents, even at a high taxonomic level.
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nematode community composition in hydrothermal vent and adjacent non vent fields around myojin knoll a seamount on the izu ogasawara arc in the western north pacific ocean
Marine Biology, 2014Co-Authors: Yuka Setoguchi, Hidetaka Nomaki, Tomo Kitahashi, Hiromi Watanabe, Koji Inoue, Nanako O Ogawa, Motohiro ShimanagaAbstract:In contrast to specific large benthic invertebrates in chemosynthetic ecosystems such as hydrothermal vents, meiofaunal communities in such habitats have been reported to have strong taxonomic overlap with meiofauna in the adjacent “normal” environments. However, meiofauna have only recently been included in studies of those environments and detailed information on these communities is still rare. This is especially true in the Northwest Pacific Ocean, even though there are many seamounts with active vents in the Calderas of the region. Nematode community composition at the genus level in sediments from a hydrothermal vent field in the Caldera of Myojin Knoll (32°06′N, 139°52′E, depth 1,300 m), a seamount on the Izu-Ogasawara Arc, Japan, was investigated for the first time and was compared with adjacent non-vent areas inside and outside the Caldera. Multivariate analyses showed that the composition of nematodes in the hydrothermal field was significantly different from that in the non-hydrothermal fields around the Caldera. However, the common genera, such as Oxystomina, Pareudesmoscolex, Desmoscolex, and Microlaimus were found in two, or all three vent fields while their rank contributions differed among the three fields. When the data from Myojin Knoll were compared with those from other deep-sea vent environments in different regions (e.g., North Fiji Basin, East Pacific Rise, Mid-Atlantic Ridge), the nematode composition in the vent field of the Myojin Caldera was more similar to that of the non-vent fields around the Caldera than the composition in vent fields of other regions. These data from the Northwest Pacific Ocean also suggest the absence of long-range transport systems and local adaptations for meiofauna in hydrothermal vent fields.
Joan Martí - One of the best experts on this subject based on the ideXlab platform.
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statistical data analysis of the ccdb collapse Caldera database insights on the formation of Caldera systems
Journal of Volcanology and Geothermal Research, 2010Co-Authors: Adelina Geyer, Rosa Sobradelo, Joan MartíAbstract:Collapse Calderas are one of the most important volcanic structures because of their hazard implications, but also because of their high energy potential and their association with mineral deposits of high economic interest. The worldwide Collapse Caldera Database (CCDB) [22], (http://www.GVB-csic.es/CCDB.htm), currently formed by 473 Calderas and 28 variables, updates the current field based knowledge on Calderas, merging together the existing databases, complementing them with new examples found in the bibliography and leaving it open for the incorporation of new data from future studies. The area of the Caldera is a relevant indicator of the dynamics of the Caldera system, as it is directly related to the size of the magma chamber and other variables of the volcanic systems such as crustal type, magma composition, and tectonic setting. Despite this being a generally assumed geological belief, it has never been numerically studied. In this paper we have conducted a statistical analysis using ANOVA (Analysis of Variance) on a selected sample from the CCDB containing the relevant variables, in order to determine if the area of the collapse Caldera depends on a group of geological characteristics or is it due to random variability alone, and if so, what is the relationship. The results identify three groups of collapse Calderas in different geodynamic environments according to Crustal Type, Rock Suite and Plate Tectonic Setting, which we name GE1, GE2 and GE3. These groups have significantly different Caldera Area, suggesting how the dynamics of the volcanic system hosting the collapse Caldera are intrinsically related to the geodynamic environment where it develops.
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April 2007 collapse of Piton de la Fournaise: A new example of Caldera formation
Geophysical Research Letters, 2007Co-Authors: Laurent Michon, Patrick Bachèlery, Thomas Staudacher, Valérie Ferrazzini, Joan MartíAbstract:Collapse Calderas are frequent in the evolution of volcanic systems, but very few have formed during historical times. Piton de la Fournaise is one of the world's most active basaltic shield volcanoes. The Caldera collapse, which occurred during the April 2007 lateral eruption is one of the few large documented collapse events on this volcano. It helps to understand the mode and origin of Caldera collapses in basaltic volcanoes. Field observations, GPS and seismic data show that the collapse occurred at an early stage of the eruption. The cyclic seismic signal suggests a step by step collapse that directly influenced the lateral eruption rate. Likely, the Caldera results from the combined effect of (i) the progressive collapse of the plumbing system above the magma chamber since 2000, and (ii) the large amount of magma withdrawal during the early stage of the eruption by both a significant intrusion within the edifice and an important emission rate.
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relationship between Caldera collapse and magma chamber withdrawal an experimental approach
Journal of Volcanology and Geothermal Research, 2006Co-Authors: Adelina Geyer, Arnau Folch, Joan MartíAbstract:Collapse Calderas have received considerable attention due to their link to Earth's ore deposits and geothermal energy resources, but also because of their tremendous destructive potential. Although Calderas have been investigated through fieldwork, numerical models and experimental studies, some important aspects on their formation still remain poorly understood. One key issue concerns the volume of magmas involved in Caldera-forming eruptions. We perform analogue experiments to correlate the structural evolution of a collapse with the erupted magma chamber volume fraction. The experimental device consists of a transparent box (60 × 60 × 40 cm) filled with dry quartz sand and a water-filled latex balloon as a magma chamber analogue. Evacuation of water through a pipe causes a progressive deflation of the balloon that leads to a collapse of the overlying structure. The experimental design allows to record the temporal evolution of the collapse and to track the evolution of fractures and faults. We study the appearance and development of specific brittle structures, such as surface fractures or internal reverse faults, and correlate each different structure with the corresponding removed magma chamber volume fraction. We also determine the critical conditions for Caldera onset. Experimental results show that, at any stage of Caldera developments, the experimental relationship between volume fraction and chamber roof aspect ratio fits a logarithmic curve. It implies that volume fractions required to trigger Caldera collapse are lower for chambers with low aspect ratios (shallow and wide) than for chambers with high aspect ratios (deep and small). These results are in agreement with natural examples and previous theoretical studies.
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The Las Cañadas Caldera (Tenerife, Canary Islands): an overlapping collapse Caldera generated by magma-chamber migration
Journal of Volcanology and Geothermal Research, 2000Co-Authors: Joan Martí, Agust GudmundssonAbstract:Abstract The Las Canadas Caldera is one of the most important geological structures of Tenerife. Stratigraphic, structural, volcanological, petrological, geochronological, and geophysical data suggest that the Las Canadas Caldera resulted from multiple vertical collapse episodes that occurred during the construction of the Las Canadas edifice Upper Group. Three long-term (≥200 ka) cycles of phonolitic explosive activity, each culminating with a Caldera collapse, have been identified in the Upper Group. During the construction of the Upper Group, the focus of felsic volcanism migrated from west to east. Using the results of field observations, experimental analogue models and numerical studies, we propose that the formation of the overlapping Las Canadas collapse Caldera is related to the migration of the associated magma chamber. Our model implies that each collapse of this overlapping Caldera partly, or completely, destroyed the feeding magma chamber. This destruction led to changes in the local stress field that favoured the formation of a new chamber at one side of the previous one, resulting in magma-chamber migration. The proposed model accounts for the formation of the Las Canadas Caldera. In particular, it explains the geometrical relationships, stratigraphy and chronology of the Caldera wall deposits. Comparison with other overlapping collapse Calderas suggests that our model may apply to other overlapping Calderas.
