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1.
R. Sulpizio R. Cioni M. A. Di Vito D. Mele R. Bonasia P. Dellino 《Bulletin of Volcanology》2010,72(5):539-558
The stratigraphic succession of the Pomici di Avellino Plinian eruption from Somma-Vesuvius has been studied through field
and laboratory data in order to reconstruct the eruption dynamics. This eruption is particularly important in the Somma-Vesuvius
eruptive history because (1) its vent was offset with respect to the present day Vesuvius cone; (2) it was characterised by
a distinct opening phase; (3) breccia-like very proximal fall deposits are preserved close to the vent and (4) the pyroclastic
density currents generated during the final phreatomagmatic phase are among the most widespread and voluminous in the entire
history of the volcano. The stratigraphic succession is, here, divided into deposits of three main eruptive phases (opening,
magmatic Plinian and phreatomagmatic), which contain five eruption units. Short-lived sustained columns occurred twice during
the opening phase (Ht of 13 and 21.5 km, respectively) and dispersed thin fall deposits and small pyroclastic density currents onto the volcano
slopes. The magmatic Plinian phase produced the main volume of erupted deposits, emplacing white and grey fall deposits which
were dispersed to the northeast. Peak column heights reached 23 and 31 km during the withdrawal of the white and the grey
magmas, respectively. Only one small pyroclastic density current was emplaced during the main Plinian phase. In contrast,
the final phreatomagmatic phase was characterised by extensive generation of pyroclastic density currents, with fallout deposits
very subordinate and limited to the volcano slopes. Assessed bulk erupted volumes are 21 × 106 m3 for the opening phase, 1.3–1.5 km3 for the main Plinian phase and about 1 km3 for the final phreatomagmatic phase, yielding a total volume of about 2.5 km3. Pumice fragments are porphyritic with sanidine and clinopyroxene as the main mineral phases but also contain peculiar mineral
phases like scapolite, nepheline and garnet. Bulk composition varies from phonolite (white magma) to tephri-phonolite (grey
magma). 相似文献
2.
The caldera-forming eruption of Volcán Ceboruco, Mexico 总被引:1,自引:1,他引:0
3 of magma erupted, ∼95% of which was deposited as fall layers. During most of the deposition of P1, eruptive intensity (mass
flux) was almost constant at 4–8×107 kg s−1, producing a Plinian column 25–30 km in height. Size grading at the top of P1 indicates, however, that mass flux waned dramatically,
and possibly that there was a brief pause in the eruption. During the post-P1 phase of the eruption, a much smaller volume
of magma erupted, although mass flux varied by more than an order of magnitude. We suggest that caldera collapse began at
the end of the P1 phase of the eruption, because along with the large differences in mass flux behavior between P1 and post-P1
layers, there were also dramatic changes in lithic content (P1 contains ∼8% lithics; post-P1 layers contain 30–60%) and magma
composition (P1 is 98% rhyodacite; post-P1 layers are 60–90% rhyodacite). However, the total volume of magma erupted during
the Jala pumice event is close to that estimated for the caldera. These observations appear to conflict with models which
envision that, after an eruption is initiated by overpressure in the magma chamber, caldera collapse begins when the reservoir
becomes underpressurized as a result of the removal of magma. The conflict arises because firstly, the P1 layer makes up too
large a proportion (∼75%) of the total volume erupted to correspond to an overpressurized phase, and secondly, the caldera
volume exceeds the post-P1 volume of magma by at least a factor of three. The mismatches between model and observations could
be reconciled if collapse began near the beginning of the eruption, but no record of such early collapse is evident in the
tephra sequence. The apparent inability to place the Jala pumice eruptive sequence into existing models of caldera collapse,
which were constructed to explain the formation of calderas much greater in volume than that at Ceboruco, may indicate that
differences in caldera mechanics exist that depend on size or that a more general model for caldera formation is needed.
Received: 18 November 1998 / Accepted: 23 October 1999 相似文献
3.
New physical characterization of the Fontana Lapilli basaltic Plinian eruption,Nicaragua 总被引:1,自引:1,他引:0
The Fontana Lapilli deposit was erupted in the late Pleistocene from a vent, or multiple vents, located near Masaya volcano
(Nicaragua) and is the product of one of the largest basaltic Plinian eruptions studied so far. This eruption evolved from
an initial sequence of fluctuating fountain-like events and moderately explosive pulses to a sustained Plinian episode depositing
fall beds of highly vesicular basaltic-andesite scoria (SiO2 > 53 wt%). Samples show unimodal grain size distribution and a moderate sorting that are uniform in time. The juvenile component
predominates (> 96 wt%) and consists of vesicular clasts with both sub-angular and fluidal, elongated shapes. We obtain a
maximum plume height of 32 km and an associated mass eruption rate of 1.4 × 108 kg s−1 for the Plinian phase. Estimates of erupted volume are strongly sensitive to the technique used for the calculation and to
the distribution of field data. Our best estimate for the erupted volume of the majority of the climactic Plinian phase is
between 2.9 and 3.8 km3 and was obtained by applying a power-law fitting technique with different integration limits. The estimated eruption duration
varies between 4 and 6 h. Marine-core data confirm that the tephra thinning is better fitted by a power-law than by an exponential
trend. 相似文献
4.
The small- to moderate-volume, Quaternary, Siwi pyroclastic sequence was erupted during formation of a 4 km-wide caldera on the eastern margin of Tanna, an island arc volcano in southern Vanuatu. This high-potassium, andesitic eruption followed a period of effusive basaltic andesite volcanism and represents the most felsic magma erupted from the volcano. The sequence is up to 13 m thick and can be traced in near-continuous outcrop over 11 km. Facies grade laterally from lithic-rich, partly welded spatter agglomerate along the caldera rim to two medial, pumiceous, non-welded ignimbrites that are separated by a layer of lithic-rich, spatter agglomerate. Juvenile clasts comprise a wide range of densities and grain sizes. They vary between black, incipiently vesicular, highly elongate spatter clasts that have breadcrusted pumiceous rinds and reach several metres across to silky, grey pumice lapilli. The pumice lapilli range from highly vesicular clasts with tube or coalesced spherical vesicles to denser finely vesicular clasts that include lithic fragments.Textural and lithofacies characteristics of the Siwi pyroclastic sequence suggest that the first phase of the eruption produced a base surge deposit and spatter-poor pumiceous ignimbrite. A voluminous eruption of spatter and lithic pyroclasts coincided with a relatively deep withdrawal of magma presumably driven by a catastrophic collapse of the magma chamber roof. During this phase, spatter clasts rapidly accumulated in the proximal zone largely as fallout, creating a variably welded and lithic-rich agglomerate. This phase was followed by the eruption of moderately to highly vesiculated magma that generated the most widespread, upper pumiceous ignimbrite. The combination of spatter and pumice in pyroclastic deposits from a single eruption appears to be related to highly explosive, magmatic eruptions involving low-viscosity magmas. The combination also indicates the coexistence of a spatter fountain and explosive eruption plume for much of the eruption.Editorial responsibility: R. Cioni 相似文献
5.
Although the oldest volcanic rocks exposed at Pantelleria (Strait of Sicily) are older than 300 ka, most of the island is
covered by the 45–50 ka Green Tuff ignimbrite, thought to be related to the Cinque Denti caldera, and younger lavas and scoria
cones. Pre-50 ka rocks (predominantly rheomorphic ignimbrites) are exposed at isolated sea cliffs, and their stratigraphy
and chronology are not completely resolved. Based on volcanic stratigraphy and K/Ar dating, it has been proposed that the
older La Vecchia caldera is related to ignimbrite Q (114 ka), and that ignimbrites F, D, and Z (106, 94, and 79 ka, respectively)
were erupted after caldera formation. We report here the paleomagnetic directions obtained from 23 sites in ignimbrite P (133 ka)
and four younger ignimbrites, and from an uncorrelated (and loosely dated) welded lithic breccia thought to record a caldera-forming
eruption. The paleosecular variation of the geomagnetic field recorded by ignimbrites is used as correlative tool, with an
estimated time resolution in the order of 100 years. We find that ignimbrites D and Z correspond, in good agreement with recent
Ar/Ar ages constraining the D/Z eruption to 87 ka. The welded lithic breccia correlates with a thinner breccia lying just
below ignimbrite P at another locality, implying that collapse of the La Vecchia caldera took place at ~130–160 ka. This caldera
was subsequently buried by ignimbrites P, Q, F, and D/Z. Paleomagnetic data also show that the northern caldera margin underwent
a ~10° west–northwest (outwards) tilting after emplacement of ignimbrite P, possibly recording magma resurgence in the crust. 相似文献
6.
O.A. Braitseva I.V. Melekestsev V.V. Ponomareva V.Yu. Kirianov 《Journal of Volcanology and Geothermal Research》1996,70(1-2)
The largest Plinian eruption of our era and the latest caldera-forming eruption in the Kuril-Kamchatka region occurred about cal. A.D. 240 from the Ksudach volcano. This catastrophic explosive eruption was similar in type and characteristics to the 1883 Krakatau event. The volume of material ejected was 18–19 km3 (8 km3 DRE), including 15 km3 of tephra fall and 3–4 km3 of pyroclastic flows. The estimated height of eruptive column is 22–30 km. A collapse caldera resulting from this eruption was 4 × 6.5 km in size with a cavity volume of 6.5–7 km3. Tephra fall was deposited to the north of the volcano and reached more than 1000 km. Pyroclastic flows accompanied by ash-cloud pyroclastic surges extended out to 20 km. The eruption was initially phreatomagmatic and then became rhythmic, with each pulse evolving from pumice falls to pyroclastic flows. Erupted products were dominantly rhyodacite throughout the eruption. During the post-caldera stage, when the Shtyubel cone started to form within the caldera, basaltic-andesite and andesite magma began to effuse. The trigger for the eruption may have been an intrusion of mafic magma into the rhyodacite reservoir. The eruption had substantial environmental impact and may have produced a large acidity peak in the Greenland ice sheet. 相似文献
7.
David J. Kratzmann Steven Carey Roberto Scasso Jose-Antonio Naranjo 《Bulletin of Volcanology》2009,71(4):477-439
The August 1991 eruptions of Hudson volcano produced ~2.7 km3 (dense rock equivalent, DRE) of basaltic to trachyandesitic pyroclastic deposits, making it one of the largest historical
eruptions in South America. Phase 1 of the eruption (P1, April 8) involved both lava flows and a phreatomagmatic eruption
from a fissure located in the NW corner of the caldera. The paroxysmal phase (P2) began several days later (April 12) with
a Plinian-style eruption from a different vent 4 km to the south-southeast. Tephra from the 1991 eruption ranges in composition
from basalt (phase 1) to trachyandesite (phase 2), with a distinct gap between the two erupted phases from 54–60 wt% SiO2. A trend of decreasing SiO2 is evident from the earliest part of the phase 2 eruption (unit A, 63–65 wt% SiO2) to the end (unit D, 60–63 wt% SiO2). Melt inclusion data and textures suggest that mixing occurred in magmas from both eruptive phases. The basaltic and trachyandesitic
magmas can be genetically related through both magma mixing and fractional crystallization processes. A combination of observed
phase assemblages, inferred water content, crystallinity, and geothermometry estimates suggest pre-eruptive storage of the
phase 2 trachyandesite at pressures between ~50–100 megapascal (MPa) at 972 ± 26°C under water-saturated conditions (log fO2 –10.33 (±0.2)). It is proposed that rising P1 basaltic magma intersected the lower part of the P2 magma storage region between
2 and 3 km depth. Subsequent mixing between the two magmas preferentially hybridized the lower part of the chamber. Basaltic
magma continued advancing towards the surface as a dyke to eventually be erupted in the northwestern part of the Hudson caldera.
The presence of tachylite in the P1 products suggests that some of the magma was stalled close to the surface (<0.5 km) prior
to eruption. Seismicity related to magma movement and the P1 eruption, combined with chamber overpressure associated with
basalt injection, may have created a pathway to the surface for the trachyandesite magma and subsequent P2 eruption at a different
vent 4 km to the south-southeast.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
8.
C. Silva Parejas T. H. Druitt C. Robin H. Moreno J.-A. Naranjo 《Bulletin of Volcanology》2010,72(6):677-692
The Pucón eruption was the largest Holocene explosive outburst of Volcán Villarrica, Chile. It discharged >1.0 km3 of basaltic-andesite magma and >0.8 km3 of pre-existing rock, forming a thin scoria-fall deposit overlain by voluminous ignimbrite intercalated with pyroclastic
surge beds. The deposits are up to 70 m thick and are preserved up to 21 km from the present-day summit, post-eruptive lahar
deposits extending farther. Two ignimbrite units are distinguished: a lower one (P1) in which all accidental lithic clasts
are of volcanic origin and an upper unit (P2) in which basement granitoids also occur, both as free clasts and as xenoliths
in scoria. P2 accounts for ∼80% of the erupted products. Following the initial scoria fallout phase, P1 pyroclastic flows
swept down the northern and western flanks of the volcano, magma fragmentation during this phase being confined to within
the volcanic edifice. Following a pause of at least a couple of days sufficient for wood devolatilization, eruption recommenced,
the fragmentation level dropped to within the granitoid basement, and the pyroclastic flows of P2 were erupted. The first
P2 flow had a highly turbulent front, laid down ignimbrite with large-scale cross-stratification and regressive bedforms,
and sheared the ground; flow then waned and became confined to the southeastern flank. Following emplacement of pyroclastic
surge deposits all across the volcano, the eruption terminated with pyroclastic flows down the northern flank. Multiple lahars
were generated prior to the onset of a new eruptive cycle. Charcoal samples yield a probable eruption age of 3,510 ± 60 14C years BP. 相似文献
9.
Daniela Mele Roberto Sulpizio Pierfrancesco Dellino Luigi La Volpe 《Bulletin of Volcanology》2011,73(3):257-278
New volcanological studies allow reconstruction of the eruption dynamics of the Pomici di Mercato eruption (ca 8,900 cal.
yr B.P.) of Somma-Vesuvius. Three main Eruptive Phases are distinguished based on two distinct erosion surfaces that interrupt
stratigraphic continuity of the deposits, indicating that time breaks occurred during the eruption. Absence of reworked volcaniclastic
deposits on top of the erosion surfaces suggests that quiescent periods between eruptive phases were short perhaps lasting
only days to weeks. Each of the Eruptive Phases was characterised by deposition of alternating fall and pyroclastic density
current (PDC) deposits. The fallout deposits blanketed a wide area toward the east, while the more restricted PDC deposits
inundated the volcano slopes. Eruptive dynamics were driven by brittle magmatic fragmentation of a phonolitic magma, which,
because of its mechanical fragility, produced a significant amount of fine ash. External water did not significantly contribute
either to fragmentation dynamics or to mechanical energy release during the eruption. Column heights were between 18 and 22 km,
corresponding to mass discharge rates between 1.4 and 6 × 107 kg s−1. The estimated on land volume of fall deposits ranges from a minimum of 2.3 km3 to a maximum of 7.4 km3. Calculation of physical parameters of the dilute pyroclastic density currents indicates speeds of a few tens of m s−1 and densities of a few kg m−3 (average of the lowermost 10 m of the currents), resulting in dynamic pressures lower than 3 kPa. These data suggest that
the potential impact of pyroclastic density currents of the Pomici di Mercato eruption was smaller than those of other Plinian
and sub-Plinian eruptions of Somma-Vesuvius, especially those of 1631 AD and 472 AD (4–14 kPa), which represent reference
values for the Vesuvian emergency plan. The pulsating and long-lasting behaviour of the Pomici di Mercato eruption is unique
in the history of large explosive eruptions of Somma-Vesuvius. We suggest an eruptive scheme in which discrete magma batches
rose from the magma chamber through a network of fractures. The injection and rise of the different magma batches was controlled
by the interplay between magma chamber overpressure and local stress. The intermittent discharge of magma during a large explosive
eruption is unusual for Somma-Vesuvius, as well as for other volcanoes worldwide, and yields new insights for improving our
knowledge of the dynamics of explosive eruptions. 相似文献
10.
Eruptive history and magmatic evolution of the 1.9 kyr Plinian dacitic Chiltepe Tephra from Apoyeque volcano in west-central Nicaragua 总被引:1,自引:1,他引:0
The youngest dacitic Plinian eruption in west-central Nicaragua, forming the 18 km3 Chiltepe Tephra (CT), occurred about nineteen hundred years ago at Apoyeque stratovolcano, which dominates the Chiltepe volcanic
complex 15 km north of the capital Managua, where the CT is 2 m thick. We have traced the CT from its proximal facies at the
crater rim, through the medial facies in the lowlands around Apoyeque, and to the distal facies up to 550 km offshore in the
Pacific. While medial and distal facies consist of widespread Plinian fall deposits, the proximal facies reveals the complexity
of this eruption, which we divide into four phases (I–IV). Interaction of rising magma with a pre-existing crater lake generated
the phreatomagmatic opening phase I of the eruption, which produced ash fall with accretionary lapilli. Phase II marked a
rapid change to persistent magmatic activity that yielded several large Plinian eruptions, declining through a period of unstable
eruption conditions, followed by a short hiatus. Phase III began with unstable conditions, probably as a result of eastward
migration and widening of the vent, leading to a second period of Plinian eruptions with three major events reaching magma
discharge rates five times larger than those of phase II. Phase III again declined through unstable eruption conditions before
magmatic activity terminated. Numerous explosions in the shallow hydrothermal system during the final phase IV resulted in
the formation of a phreatic tuff ring on the rim of Apoyeque crater. The white, highly-vesicular, dacitic CT pumice contains
plagioclase (An45–68), orthopyroxene, clinopyroxene, and minor hornblende, apatite and titanomagnetite phenocrysts. A very subordinate fraction
of gray pumice has the highest crystal content, the least evolved bulk-rock, but the most evolved matrix-glass composition.
The CT dacite has two unusual compositional features: (1) all white dacite has the same melt (matrix-glass) composition such
that variations in bulk-rock compositions (64–68 wt% SiO2) simply reflect different phenocryst contents of 10–35%, interpreted as the result of gradual phenocryst settling in the
magma chamber. (2) Abundant olivine crystals with a bimodal distribution in Mg# (modes at Mg# = 0.75 and Mg# = 0.8) are dispersed
throughout the erupted dacite. These are clearly out of equilibrium with the dacitic melt and are interpreted as xenocrysts
derived from the basaltic Nejapa-Miraflores volcanic lineament that intersects the Chiltepe volcanic complex and was contemporaneously
active. Thermobarometric estimates place the dacitic CT magma reservoir in the upper crust (<250 MPa), with a temperature
of about 890°C and about 5 wt% water dissolved in the melt. Comparing water and chlorine contents with respective solubility
models suggests that volatile degassing began in the magma reservoir and triggered the CT eruption. From the vertical compositional
variation pattern of the CT we deduce that the conduit tapped the magma chamber not at the top but from the side, at some
deeper level, and that subsequent magma withdrawal was governed by both variations in discharge rate and possible upward migration
and/or widening of the conduit entrance. 相似文献
11.
12.
Event-stratigraphy of a caldera-forming ignimbrite eruption on Tenerife: the 273 ka Poris Formation 总被引:1,自引:1,他引:0
The 273 ka Poris Formation in the Bandas del Sur Group records a complex, compositionally zoned explosive eruption at Las Cañadas caldera on Tenerife, Canary Islands. The eruption produced widespread pyroclastic density currents that devastated much of the SE of Tenerife, and deposited one of the most extensive ignimbrite sheets on the island. The sheet reaches ~ 40-m thick, and includes Plinian pumice fall layers, massive and diffuse-stratified pumiceous ignimbrite, widespread lithic breccias, and co-ignimbrite ashfall deposits. Several facies are fines-rich, and contain ash pellets and accretionary lapilli. Eight brief eruptive phases are represented within its lithostratigraphy. Phase 1 comprised a fluctuating Plinian eruption, in which column height increased and then stabilized with time and dispersed tephra over much of the southeastern part of the island. Phase 2 emplaced three geographically restricted ignimbrite flow-units and associated extensive thin co-ignimbrite ashfall layers, which contain abundant accretionary lapilli from moist co-ignimbrite ash plumes. A brief Plinian phase (Phase 3), again dispersing pumice lapilli over southeastern Tenerife, marked the onset of a large sustained pyroclastic density current (Phase 4), which then waxed (Phase 5), covering increasingly larger areas of the island, as vents widened and/or migrated along opening caldera faults. The climax of the Poris eruption (Phase 6) was marked by widespread emplacement of coarse lithic breccias, thought to record caldera subsidence. This is inferred to have disturbed the magma chamber, causing mingling and eruption of tephriphonolite magma, and it changed the proximal topography diverting the pyroclastic density current(s) down the Güimar valley (Phase 7). Phase 8 involved post-eruption erosion and sedimentary reworking, accompanied by minor down-slope sliding of ignimbrite. This was followed by slope stabilization and pedogenesis. The fines-rich lithofacies with abundant ash pellets and accretionary lapilli record agglomeration of ash in moist ash plumes. They resemble phreatomagmatic deposits, but a phreatomagmatic origin is difficult to establish because shards are of bubble-wall type, and the moisture may have arisen by condensation within ascending thermal co-ignimbrite ash plumes that contained atmospheric moisture enhanced by that derived from the evaporation of seawater where the hot pyroclastic currents crossed the coast. Ash pellets formed in co-ignimbrite ash-clouds and then fell through turbulent pyroclastic density currents where they accreted rims and evolved into accretionary lapilli.Editorial Responsibility: J. Stix 相似文献
13.
Gerardo J. Aguirre-Díaz Margarita López-Martínez 《Journal of Volcanology and Geothermal Research》2009,179(1-2):133-148
The Donguinyó-Huichapan caldera complex is located 110 km to the NNW of Mexico City, in the central sector of the Mexican Volcanic Belt. It is a 10 km in diameter complex apparently with two overlapping calderas, each one related to an ignimbrite sequence that contrasts in composition, mineralogy, welding, distribution, and physical aspect. The geologic evolution of this complex includes the following phases, 1) A first caldera formed at 5.0 ± 0.3 Ma, with the eruption of several discrete pulses of andesitic to trachydacitic pyroclastic flows that produced a series of densely welded ignimbrites; 2) At 4.6 ± 0.3 Ma, several small shield volcanoes and cinder cones built the rim of this caldera and erupted basaltic-andesite and andesitic lava flows; 3) At 4.2 ± 0.2 Ma, a second caldera was formed associated to the eruption of the Huichapan Tuff, which is a rhyolitic pyroclastic sequence consisting of minor unwelded ignimbrites, pumice fall and surge deposits, and a voluminous welded ignimbrite; 4) Also yielding an age of 4.2 ± 0.2 Ma, several trachydacitic lava domes were extruded along the new ring fracture and formed the rim of the Huichapan caldera, as well as five intra-caldera domes of dacitic and trachydacitic composition. Peripheral volcanism includes a large 2.5 ± 0.1 Ma shield volcano that was emplaced on the Huichapan caldera rim.The two calderas that form the Donguinyó-Huichapan complex have contrasting differences in volcanic styles that were apparently due to their differences in composition. Products erupted by the Donguinyó caldera are basaltic-andesite to trachydacitic in composition, whereas Huichapan caldera products are all high-silica rhyolites. 相似文献
14.
New insights into Late Pleistocene explosive volcanic activity and caldera formation on Ischia (southern Italy) 总被引:2,自引:1,他引:1
A new pyroclastic stratigraphy is presented for the island of Ischia, Italy, for the period ∼75–50 ka BP. The data indicate
that this period bore witness to the largest eruptions recorded on the island and that it was considerably more volcanically
active than previously thought. Numerous vents were probably active during this period. The deposits of at least 10 explosive
phonolite to basaltic-trachyandesite eruptions are described and interpreted. They record a diverse range of explosive volcanic
activity including voluminous fountain-fed ignimbrite eruptions, fallout from sustained eruption columns, block-and-ash flows,
and phreatomagmatic eruptions. Previously unknown eruptions have been recognised for the first time on the island. Several
of the eruptions produced pyroclastic density currents that covered the whole island as well as the neighbouring island of
Procida and parts of the mainland. The morphology of Ischia was significantly different to that seen today, with edifices
to the south and west and a submerged depression in the centre. The largest volcanic event, the Monte Epomeo Green Tuff (MEGT)
resulted in caldera collapse across all or part of the island. It is shown to comprise at least two thick intracaldera ignimbrite
flow-units, separated by volcaniclastic sediments that were deposited during a pause in the eruption. Extracaldera deposits
of the MEGT include a pumice fall deposit emplaced during the opening phases of the eruption, a widespread lithic lag breccia
outcropping across much of Ischia and Procida, and a distal ignimbrite in south-west Campi Flegrei. During this period the
style and magnitude of volcanism was dictated by the dynamics of a large differentiated magma chamber, which was partially
destroyed during the MEGT eruption. This contrasts with the small-volume Holocene and historical effusive and explosive activity
on Ischia, the timing and distribution of which has been controlled by the resurgence of the Monte Epomeo block. The new data
contribute to a clearer understanding of the long-term volcanic and magmatic evolution of Ischia. 相似文献
15.
Batur is an active stratovolcano on the island of Bali, Indonesia, with a large, well-formed caldera whose formation is correlated with the eruption about 23,700 years ago of a thick ignimbrite sheet. Our study of the volcanic stratigraphy and geochemistry of Batur shows the formation of the caldera was signalled by a change in the composition of the erupting material from basaltic and andesitic to dacitic. The dacitic rocks are glassy, possess equilibrium phenocryst assemblages, and display compositional characteristics consistent with an origin by crystal-liquid fractionation from more mafic parent magmas in a shallow chamber, possibly at 1.5 km depth and 1000–1070°C.However, although separated by a gap of 6 wt.% SiO2, the dacitic rocks are clearly related in their minor- and trace-element geochemistry to those basalts and basaltic andesites erupted after the caldera was formed rather than to the andesites erupted immediately before the dacites first appeared. We infer from this and published experimental modelling of the possible crystallization behaviour of basaltic magma chambers that a magmatic cycle involving caldera formation began independently of the previous activity of Batur by formation of a new, closed-system magma chamber beneath the volcano. Fractional crystallization, possibly at the walls of the chamber, led to the early production of derivative siliceous magmas and, consequently, to caldera formation, while most of the magma retained its original composition. The postcaldera Batur basalts represent the largely undifferentiated core liquids of this chamber.This model contrasts with the traditional evolutionary model for stratovolcano calderas but may be applicable to the origins of calderas similar to that of Batur, particularly those in volcanic island arcs. 相似文献
16.
Alexander Rybin Marina Chibisova Peter Webley Torge Steensen Pavel Izbekov Christina Neal Vince Realmuto 《Bulletin of Volcanology》2011,73(9):1377-1392
After 33 years of repose, one of the most active volcanoes of the Kurile island arc—Sarychev Peak on Matua Island in the Central
Kuriles—erupted violently on June 11, 2009. The eruption lasted 9 days and stands among the largest of recent historical eruptions
in the Kurile Island chain. Satellite monitoring of the eruption, using Moderate Resolution Imaging Spectroradiometer, Meteorological
Agency Multifunctional Transport Satellite, and Advanced Very High Resolution Radiometer data, indicated at least 23 separate
explosions between 11 and 16 June 2009. Eruptive clouds reached altitudes of generally 8–16 km above sea level (ASL) and in
some cases up to 21 km asl. Clouds of volcanic ash and gas stretched to the north and northwest up to 1,500 km and to the
southeast for more than 3,000 km. For the first time in recorded history, ash fall occurred on Sakhalin Island and in the
northeast sector of the Khabarovsky Region, Russia. Based on satellite image analysis and reconnaissance field studies in
the summer of 2009, the eruption produced explosive tephra deposits with an estimated bulk volume of 0.4 km3. The eruption is considered to have a Volcanic Explosivity Index of 4. Because the volcano is remote, there was minimal risk
to people or infrastructure on the ground. Aviation transport, however, was significantly disrupted because of the proximity
of air routes to the volcano. 相似文献
17.
B N Turbeville 《Bulletin of Volcanology》1992,55(1-2):110-118
The Latera caldera is a well-exposed volcano where more than 8 km3 of mafic silica-undersaturated potassic lavas, scoria and felsic ignimbrites were emplaced between 380 and 150 ka. Isotopic ages obtained by 40Ar/39Ar analysis of single sanidine crystals indicate at least four periods of explosive eruptions from the caldera. The initial period of caldera eruptions began at 232 ka with emplacement of trachytic pumice fallout and ignimbrite. They were closely followed by eruption of evolved phonolitic magma. After roughly 25 ky, several phonolitic ignimbrites were deposited, and they were followed by phreatomagmatic eruptions that produced trachytic ignimbrites and several smaller ash-flow units at 191 ka. Compositionally zoned magma then erupted from the northern caldera rim to produce widespread phonolitic tuffs, tephriphonolitic spatter, and scoria-bearing ignimbrites. After 40 ky of mafic surge deposit and scoria cone development around the caldera rim, a compositionally zoned pumice sequence was emplaced around a vent immediately northwest of the Latera caldera. This activity marks the end of large-scale explosive eruptions from the Latera volcano at 156 ka. 相似文献
18.
The Averno 2 fissure eruption: a recent small-size explosive event at the Campi Flegrei Caldera (Italy) 总被引:1,自引:0,他引:1
Mauro Antonio Di Vito Ilenia Arienzo Giuseppe Braia Lucia Civetta Massimo D’Antonio Valeria Di Renzo Giovanni Orsi 《Bulletin of Volcanology》2011,73(3):295-320
The Averno 2 eruption (3,700 ± 50 a B.P.) was an explosive low-magnitude event characterized by magmatic and phreatomagmatic
explosions, generating mainly fall and surge beds, respectively. It occurred in the Western sector of the Campi Flegrei caldera
(Campanian Region, South Italy) at the intersection of two active fault systems, oriented NE and NW. The morphologically complex
crater area, largely filled by the Averno lake, resulted from vent activation and migration along the NE-trending fault system.
The eruption generated a complex sequence of pyroclastic deposits, including pumice fall deposits in the lower portion, and
prevailing surge beds in the intermediate-upper portion. The pyroclastic sequence has been studied through stratigraphical,
morphostructural and petrological investigations, and subdivided into three members named A through C. Member A was emplaced
during the first phase of the eruption mainly by magmatic explosions which generated columns reaching a maximum height of
10 km. During this phase the eruption reached its climax with a mass discharge rate of 3.2 106 kg/s. Intense fracturing and fault activation favored entry of a significant amount of water into the system, which produced
explosions driven by variably efficient water-magma interaction. These explosions generated wet to dry surge deposits that
emplaced Member B and C, respectively. Isopachs and isopleths maps, as well as areal distribution of ballistic fragments and
facies variation of surge deposits allow definition of four vents that opened along a NE oriented, 2 km long fissure. The
total volume of magma extruded during the eruption has been estimated at about 0.07 km3 (DRE). The erupted products range in composition from initial, weakly peralkaline alkali-trachyte, to last-emplaced alkali-trachyte.
Isotopic data and modeling suggest that mixing occurred during the Averno 2 eruption between a more evolved, less radiogenic
stored magma, and a less evolved, more radiogenic magma that entered the shallow reservoir to trigger the eruption. The early
phases of the eruption, during which the vent migrated from SW to the center of the present lake, were fed by the more evolved,
uppermost magma, while the following phases extruded the less evolved, lowermost magma. Integration of the geological and
petrological results suggests that the Averno 2 complex eruption was fed from a dyke-shaped shallow reservoir intruded into
the NE-SW fault system bordering to the west the La Starza resurgent block, within the caldera floor. 相似文献
19.
R.S.J. Sparks P.W. Francis R.D. Hamer R.J. Pankhurst L.O. O'Callaghan R.S. Thorpe R. Page 《Journal of Volcanology and Geothermal Research》1985,24(3-4)
The 35 × 20 km Cerro Galán resurgent caldera is the largest post-Miocene caldera so far identified in the Andes. The Cerro Galán complex developed on a late pre-Cambrian to late Palaeozoic basement of gneisses, amphibolites, mica schists and deformed phyllites and quartzites. The basement was uplifted in the early Miocene along large north-south reverse faults, producing a horst-and-graben topography. Volcanism began in the area prior to 15 Ma with the formation of several andesite to dacite composite volcanoes. The Cerro Galán complex developed along two prominent north-south regional faults about 20 km apart. Dacitic to rhyodacitic magma ascended along these faults and caused at least nine ignimbrite eruptions in the period 7-4 Ma (K-Ar determinations). These ignimbrites are named the Toconquis Ignimbrite Formation. They are characterised by the presence of basal plinian deposits, many individual flow units and proximal co-ignimbrite lag breccias. The ignimbrites also have moderate to high macroscopic pumice and lithic contents and moderate to low crystal contents. Compositionally banded pumice occurs near the top of some units. Many of the Toconquis eruptions occurred from vents along a north-south line on the western rim of the young caldera. However, two of the ignimbrites erupted from vents on the eastern margin. Lava extrusions occurred contemporaneously along these north-south lines. The total D.R.E. volume of Toconquis ignimbrite exceeds 500 km3.Following a 2-Ma dormant period a single major eruption of rhyodacitic magma formed the 1000-km3 Cerro Galán ignimbrite and the caldera. The ignimbrite (age 2.1 Ma on Rb-Sr determination) forms a 30–200-m-thick outflow sheet extending up to 100 km in all directions from the caldera rim. At least 1.4 km of welded intracaldera ignimbrite also accumulated. The ignimbrite is a pumice-poor, crystal-rich deposit which contains few lithic clasts. No basal plinian deposit has been identified and proximal lag breccias are absent. The composition of pumice clasts is a very uniform rhyodacite which has a higher SiO2 content but a lower K2O content than the Toconquis ignimbrites. Preliminary data indicate no evidence for compositional zonation in the magma chamber. The eruption is considered to have been caused by the catastrophic foundering of a cauldron block into the magma chamber.Post-caldera extrusions occurred shortly after eruption along both the northern extension of the eastern boundary fault and the western caldera margin. Resurgence also occurred, doming up the intracaldera ignimbrite and sedimentary fill to form the central mountain range. Resurgent doming was centred along the eastern fault and resulted in radial tilting of the ignimbrite and overlying lake sediments. 相似文献
20.
Eruptive style of the young high-Mg basaltic-andesite Pelagatos scoria cone,southeast of México City 总被引:1,自引:1,他引:0
The eruption of the Pelagatos scoria cone in the Sierra Chichinautzin monogenetic field near the southern suburbs of Mexico
City occurred less than 14,000 years ago. The eruption initiated at a fissure with an effusive phase that formed a 7-km-long
lava flow, and continued with a phase of alternating and/or simultaneous explosive and effusive activity that built a 50-m-high
scoria cone on the western end of the fissure and formed a compound lava flow-field near the vent. The eruption ended with
the emplacement of a short lava flow that breached the cone and was accompanied by weak explosions at the crater. Products
consist of a microlite-rich high-Mg basaltic andesite. Samples were analyzed to determine the magma’s initial properties as
well as the effects of degassing-induced crystallization on eruptive style. Although distal ash fallout deposits from this
eruption are not preserved, a recent quarry exposes a large section of the scoria cone. Detailed study of exposed layers allows
us to elucidate the mode of cone-building activity. Petrological and textural data, combined with models calibrated by experimental
work and melt-inclusion analyses of similar magmas elsewhere, indicate that the magma was initially hot (>1,200°C), gas-rich
(up to 5 wt.% H2O), crystal-poor (~10 vol.% Fo90 olivine phenocrysts) and thus poorly viscous (40–80 Pa s). During the early phase, low magma ascent velocity at the fissure
vent allowed low-viscosity magma to degas and crystallize during ascent, producing lava flows with elevated crystal contents
at T < 1,100°C, and blocky surfaces. Later, the closure of the fissure by cooling dikes focused the magma flow at a narrow section
of the fissure. This led to an increased magma ascent velocity. Rapid and shallow degassing (<3 km deep) triggered ~40 vol.%
microlite crystallization. Limited times for gas-escape and higher magma viscosity (6 × 105–4 × 106 Pa s) drove strong explosions of highly (60–80 vol.%) and finely vesicular magma. Coarse clasts broke on landing, which implies
brittle behavior due to complete solidification. This requires sufficient time to cool and in turn implies ejection heights
of over 1 km, which is much higher than “normal” Strombolian activity. Hence, magma viscosity significantly impacts eruption style at monogenetic volcanoes because it affects the kinetics
of shallow degassing. The long-lasting eruptions of Jorullo and Paricutin, which produced similar magmas in western México,
were more explosive. This can be related to higher magma fluxes and total erupted volumes. Implications of this study are
important because basaltic andesites are commonly erupted to form monogenetic scoria cones of the Trans-Mexican Volcanic Belt. 相似文献