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1.
Roberto Scandone Giovanni Arganese Flavio Galdi 《Journal of Volcanology and Geothermal Research》1993,58(1-4)
Volcanic Risk has been defined as the product: R = Value × Vulnerability × Hazard, where value is the total amount of lives or properties at risk for a volcani eruption, the vulnerability is the percentage of value at risk for a given volcanic event, and the hazard is the probability that a given area may be affected by a certain volcanic phenomenon.We used this definition to evaluate the Risk of loss of human lives for volcanic eruptions of Vesuvius. Value has been determined based on the total number of inhabitants living in areas that could be affected by an eruption. Vulnerability is based on the relative probability of deaths as a result of different volcanic phenomena (tephra fall, pyroclastic flows, etc.). Hazard is evaluated based on the absolute probability of a given phenomenon in a certain area. This last parameter is the most difficult to evaluate.We subdivided the activity of Vesuvius, that produces risk of loss of human lives, into three classes of eruptions, based on the Volcanic Explosivity Index. We assume that the events of each class are distributed according to a poissonian distribution (this is demonstrated for VEI = 3, and inferred for the other classes), so that we can evaluate the absolute probability of an eruption for each class within a given time span. We use a time window of 10 years and evaluate the probabilities of occurrence of at least one eruption for VEI = 3, 4, 5; the probability is respectively: P3 = 0.09896, P4 = 0.01748, P5 = 0.00298We have made a hazard evaluation for the entire Vesuvian area as well as an evaluation of Volcanic Risk.The obtained map shows that the areas with higher risk are on the southern side of Vesuvius, in the coastal region where each town is characterized by an average Risk of 1000 inhabitants/10 years. The risk regularly decreases with increasing distance from the volcano. The risk is mostly due to the events with VEI = 3 and 4, as the most destructive effects of VEI = 5 are counterbalanced by the lower probability of such events.The map of volcanic risk is not intended to predict the loss of human lives of an eruption, but to give a methodology that permits to identify those areas where it is necessary to operate in order to reduce the risk of an eruption before it occurs. 相似文献
2.
Hwong-wen Ma 《Stochastic Environmental Research and Risk Assessment (SERRA)》2000,14(3):195-206
The selection of optimal management strategies for environmental contaminants requires detailed information on the risks
imposed on populations. These risks are characterized by both inter-subject variability (different individuals having different
levels of risk) and by uncertainty (there is uncertainty about the risk associated with the Yth percentile of the variability distribution). In addition, there is uncertainty introduced by the inability to agree fully
on the appropriate decision criteria. This paper presents a methodology for incorporating uncertainty and variability into
a multi-medium, multi-pathway, multi-contaminant risk assessment, and for placing this assessment into an optimization framework
to identify optimal management strategies. The framework is applied to a case study of a sludge management system proposed
for North Carolina and the impact of stochasticity on selection of an optimal strategy considered. Different sets of decision
criteria reflecting different ways of treating stochasticity are shown to lead to different selections of optimal management
strategies. 相似文献
3.
4.
The role of carbon dioxide in the dynamics of magma ascent in explosive eruptions is investigated by means of numerical modeling.
The model is steady, one-dimensional, and isothermal; it calculates the separated flow of gas and a homogeneous mixture of
liquid magma and crystals. The magma properties are calculated on the basis of magma composition and crystal content and are
allowed to change along the conduit due to pressure decrease and gas exsolution. The effect of the presence of a two-component
(water + carbon dioxide) exsolving gas phase is investigated by performing a parametric study on the CO2/(H2O+CO2) ratio, which is allowed to vary from 0 to 0.5 at either constant total volatile or constant water content. The relatively
insoluble carbon dioxide component plays an important role in the location of the volatile-saturation and magma-fragmentation
levels and in the distribution of the flow variables in the volcanic conduit. In detail, the results show that an increase
of the proportion of carbon dioxide produces a decrease of the mass flow rate, pressure, and exit mixture density, and an
increase of the exit gas volume fraction and depth of the fragmentation level. A relevant result is the different role played
by water and carbon dioxide in the eruption dynamics; an increasing amount of water produces an increase of the mass flow
rate, and an increasing amount of carbon dioxide produces a decrease. Even small amounts of carbon dioxide have major consequences
on the eruption dynamics, implying that the multicomponent nature of the volcanic gas must be taken into account in the prediction
of the eruption scenario and the forecasting of volcanic hazard.
Received: 6 March 1998 / Accepted: 28 October 1998 相似文献
5.
Michael O. Garcia J. M. Rhodes Frank A. Trusdell Aaron J. Pietruszka 《Bulletin of Volcanology》1996,58(5):359-379
The Puu Oo eruption has been remarkable in the historical record of Kilauea Volcano for its duration (over 13 years), volume
(>1 km3) and compositional variation (5.7–10 wt.% MgO). During the summer of 1986, the main vent for lava production moved 3 km down
the east rift zone and the eruption style changed from episodic geyser-like fountaining at Puu Oo to virtually continuous,
relatively quiescent effusion at the Kupaianaha vent. This paper examines this next chapter in the Puu Oo eruption, episodes
48 and 49, and presents new ICP-MS trace element and Pb-, Sr-, and Nd-isotope data for the entire eruption (1983–1994). Nearly
aphyric to weakly olivine-phyric lavas were erupted during episodes 48 and 49. The variation in MgO content of Kupaianaha
lavas erupted before 1990 correlates with changes in tilt at the summit of Kilauea, both of which probably were controlled
by variations in Kilauea's magma supply rate. These lavas contain euhedral olivines which generally are in equilibrium with
whole-rock compositions, although some of the more mafic lavas which erupted during 1990, a period of frequent pauses in the
eruption, accumulated 2–4 vol.% olivine. The highest forsterite content of olivines (∼85%) in Kupaianaha lavas indicates that
the parental magmas for these lavas had MgO contents of ∼10 wt.%, which equals the highest observed value for lavas during
this eruption. The composition of the Puu Oo lavas has progressively changed during the eruption. Since early 1985 (episode
30), when mixing between an evolved rift zone magma and a more mafic summit reservoir-derived magma ended, the normalized
(to 10 wt.% MgO) abundances of highly incompatible elements and CaO have systematically decreased with time, whereas ratios
of these trace elements and Pb, Sr, and Nd isotopes, and the abundances of Y and Yb, have remained relatively unchanged. These
results indicate that the Hawaiian plume source for Puu Oo magmas must be relatively homogeneous on a scale of 10–20 km3 (assuming 5–10% partial melting), and that localized melting within the plume has apparently progressively depleted its incompatible
elements and clinopyroxene component as the eruption continued. The rate of variation of highly incompatible elements in Puu
Oo lavas is much greater than that observed for Kilauea historical summit lavas (e.g., Ba/Y 0.09 a–1 vs ∼0.03 a–1). This rapid change indicates that Puu Oo magmas did not mix thoroughly with magma in the summit reservoir. Thus, except
for variable amounts of olivine fractionation, the geochemical variation in these lavas is predominantly controlled by mantle
processes.
Received: 8 March 1996 / Accepted: 30 April 1996 相似文献
6.
Kazuhiko Kano 《Bulletin of Volcanology》1996,58(2-3):131-143
A subaqueous volcaniclastic mass-flow deposit in the Miocene Josoji Formation, Shimane Peninsula, is 15–16 m thick, and comprises
mainly blocks and lapilli of rhyolite and andesite pumices and non- to poorly vesiculated rhyolite. It can be divided into
four layers in ascending order. Layer 1 is an inversely to normally graded and poorly sorted lithic breccia 0.3–6 m thick.
Layer 2 is an inversely to normally graded tuff breccia to lapilli tuff 6–11 m thick. This layer bifurcates laterally into
minor depositional units individually composed of a massive, lithic-rich lower part and a diffusely stratified, pumice-rich
upper part with inverse to normal grading of both lithic and pumice clasts. Layer 3 is 2.5–3 m thick, and consists of interbedded
fines-depleted pumice-rich and pumice-poor layers a few centimeters thick. Layer 4 is a well-stratified and well-sorted coarse
ash bed 1.5–2 m thick. The volcaniclastic deposit shows internal features of high-density turbidites and contains no evidence
for emplacement at a high temperature. The mass-flow deposit is extremely coarse-grained, dominated by traction structures,
and is interpreted as the product of a deep submarine, explosive eruption of vesicular magma or explosive collapse of lava.
Received: 10 January 1996 / Accepted: 23 February 1996 相似文献
7.
During the 1944 eruption of Vesuvius a sudden change occurred in the dynamics of the eruptive events, linked to variations
in magma composition. K-phonotephritic magmas were erupted during the effusive phase and the first lava fountain, whereas
the emission of strongly porphyritic K-tephrites took place during the more intense fountain. Melt inclusion compositions
(major and volatile elements) highlight that the magmas feeding the eruption underwent differentiation at different pressures.
The K-tephritic volatile-rich melts (up to 3 wt.% H2O, 3000 ppm CO2, and 0.55 wt.% Cl) evolved to reach K-phonotephritic compositions by crystallization of diopside and forsteritic olivine
at total fluid pressure higher than 300 MPa. These magmas fed a very shallow reservoir. The low-pressure differentiation of
the volatile-poor K-phonotephritic magmas (H2O<1 wt.%) involved mixing, open-system degassing, and crystallization of leucite, salite, and plagioclase. The eruption was
triggered by intrusion of a volatile-rich magma batch that rose from a depth of 11–22 km into the shallow magma chamber. The
first phase of the eruption represents the partial emptying of the shallow reservoir, the top of which is within the volcanic
edifice. The newly arrived magma mixed with that resident in the shallow reservoir and forced the transition from the effusive
to the lava fountain phase of the eruption.
Received: 14 September 1998 / Accepted: 10 January 1999 相似文献
8.
The ascent of magma during the A.D. 79 eruption of Vesuvius was studied by a steady-state, one-dimensional, and nonequilibrium two-phase flow model. The gas exsolution process was modeled by assuming a chemical equilibrium between the exsolved and dissolved gas, whereas the magma density and viscosity were modeled by accounting for the crystal content in magma. The exsolution, density, and viscosity models consider the effect of different compositions of the white and gray magmas. By specifying the conduit geometry and magma composition, and employing the model to search for the maximum discharge rate of magma which is consistent with the specified geometry and magma composition, the model was then used to establish the two-phase flow parameters along the conduit. It was found that for all considered conditions the magma pressure in the conduit decreases below the lithostatic pressure near the magma fragmentation level, and that in the deep regions of the conduit the white magma pressure is larger and the gray magma pressure is lower than the lithostatic one. The exsolution and fragmentation levels were found to be deeper for the white than for the gray magma, and the changing composition during the eruption causes an increase of the exit pressure and decrease of the exit gas volumetric fraction. The model also predicted a minimum conduit diameter which is consistent with the white and gray magma compositions and mass flow-rates. The predictions of the model were shown to be consistent with column collapses during the gray eruption phase, large presence of carbonate lithics in the gray pumice fall deposit, and magma-water interaction during a late stage of the eruption. 相似文献
9.
In situ measurement of volcanic eruption velocities is one of the great challenges left in geophysical volcanology. In this
paper we report on a new radar Doppler technique for monitoring volcanic eruption velocities. In comparison with techniques
employed previously (e.g., photographic methods or acoustic Doppler measurements), this method allows continuous recordings
of volcanic eruptions even during poor visibility. Also, radar Doppler instruments are usually light weight and energy efficient,
which makes them superior to other Doppler techniques based on laser light or sound. The proposed new technique was successfully
tested at Stromboli Volcano in late 1996 during a period of low activity. The recorded data allow a clear distinction between
particles rising from the vent and particles falling back towards the vent. The mean eruption velocity was approximately 10 m/s.
Most of the eruptions recorded by radar were correlated to seismic recordings. The correlation between the magnitude of the
volcanic shocks and the eruption force index defined in the paper may provide new insights into magma transport in the conduit.
Received: 15 May 1998 / Accepted: 15 December 1998 相似文献
10.
A discontinuous pumiceous sand, a few centimeters to tens of centimeters thick, is located up to 15 m above mean high tide
within Holocene peat along the northern Bristol Bay coastline of Alaska. The bed consists of fine-to-coarse, poorly to moderately
well-sorted, pumice-bearing sand near the top of a 2-m-thick peat sequence. The sand bed contains rip-up clasts of peat and
tephra and is unique in the peat sequence. Major element compositions of juvenile glass from the deposit and radiocarbon dating
of enclosing peat support correlation of the pumiceous sand with the caldera-forming eruption of Aniakchak Volcano. The distribution
of the sand and its sedimentary characteristics are consistent with emplacement by tsunami. The pumiceous sand most likely
represents redeposition by tsunami of climactic fallout tephra and beach sand during the approximately 3.5 ka Aniakchak caldera-forming
eruption on the Alaska Peninsula. We propose that a tsunami was generated by the sudden entrance of a rapidly moving, voluminous
pyroclastic flow from Aniakchak into Bristol Bay. A seismic trigger for the tsunami is unlikely, because tectonic structures
suitable for tsunami generation are present only south of the Alaska Peninsula. The pumiceous sand in coastal peat of northern
Bristol Bay is the first documented geologic evidence of a tsunami initiated by a volcanic eruption in Alaska.
Received: 3 December 1997 / Accepted: 11 April 1998 相似文献
11.
Stephen J. Matthews Moyra C. Gardeweg R. Stephen J. Sparks 《Bulletin of Volcanology》1997,59(1):72-82
Lascar Volcano (5592 m; 23°22'S, 67°44'W) entered a new period of vigorous activity in 1984, culminating in a major explosive
eruption in April 1993. Activity since 1984 has been characterised by cyclic behaviour with recognition of four cycles up
to the end of 1993. In each cycle a lava dome is extruded in the active crater, accompanied by vigorous degassing through
high-temperature, high-velocity fumaroles distributed on and around the dome. The fumaroles are the source of a sustained
steam plume above the volcano. The dome then subsides back into the conduit. During the subsidence phase the velocity and
gas output of the fumaroles decrease, and the cycle is completed by violent explosive activity. Subsidence of both the dome
and the crater floor is accommodated by movement on concentric, cylindrical or inward-dipping conical fractures. The observations
are consistent with a model in which gas loss from the dome is progressively inhibited during a cycle and gas pressure increases
within and below the lava dome, triggering a large explosive eruption. Factors that can lead to a decrease in gas loss include
a decrease in magma permeability by foam collapse, reduction in permeability due to precipitation of hydrothermal minerals
in the pores and fractures within the dome and in country rock surrounding the conduit, and closure of open fractures during
subsidence of the dome and crater floor. Dome subsidence may be a consequence of reduction in magma porosity (foam collapse)
as degassing occurs and pressurisation develops as the permeability of the dome and conduit system decreases. Superimposed
upon this activity are small explosive events of shallow origin. These we interpret as subsidence events on the concentric
fractures leading to short-term pressure increases just below the crater floor.
Received: 12 December 1996 / Accepted: 6 May 1997 相似文献
12.
Dacite tephras produced by the 1991 pre-climactic eruptive sequence at Mt. Pinatubo display extreme heterogeneity in vesicularity,
ranging in clast density from 700 to 2580 kg m–3. Observations of the 13 surge-producing blasts that preceded the climactic plinian event include radar-defined estimates
of column heights and seismically defined eruptive and intra-eruptive durations. A comparison of the characteristics of erupted
material, including microlite textures, chemical compositions, and H2O contents, with eruptive parameters suggests that devolatilization-induced crystallization of the magma occurred to a varying
extent prior to at least nine of the explosive events. Although volatile loss progressed to the same approximate level in
all of the clasts analyzed (weight percent H2O=1.26-1.73), microlite crystallization was extremely variable (0–22%). We infer that syn-eruptive volatile exsolution from
magma in the conduit and intra-eruptive separation of the gas phase was facilitated by the development of permeability within
magma residing in the conduit. Correlation of maximum microlite crystallinity with repose interval duration (28–262 min) suggests
that crystallization occurred primarily intra-eruptively, in response to the reduction in dissolved H2O content that occurred during the preceding event. Detailed textural characterization, including determination of three-dimensional
shapes and crystal size distributions (CSD), was conducted on a subset of clasts in order to determine rates of crystal nucleation
and growth using repose interval as the time available for crystallization. Shape and size analysis suggests that crystallization
proceeded in response to lessening degrees of feldspar supersaturation as repose interval durations increased. We thus propose
that during repose intervals, a plug of highly viscous magma formed due to the collapse of vesicular magma that had exsolved
volatiles during the previous explosive event. If plug thickness grew proportionally to the square root of time, and if magma
pressurization increased during the eruptive sequence, the frequency of eruptive pulses may have been modulated by degassing
of magma within the conduit. Dense clasts in surge deposits probably represent plug material entrained by each subsequent
explosive event.
Received: 4 December 1997 / Accepted: 13 September 1998 相似文献
13.
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
14.
Analysis of the petrochemical characters of the 1669 Etnean lavas shows that they can be grouped into two sets: SET1 lavas
were erupted from 11 to 20 March and are more primitive in composition than SET2, erupted later until the end of activity.
Both sets may be interpreted as the result of crystallization under different conditions of two primary magmas which are compositionally
slightly distinct and which fractionate different volumetric proportions of minerals. To explain why more mafic lavas (SET1)
were erupted earlier than more acid ones (SET2), we argue that new deeper magma rose up into a reservoir where residing magma
was fractionating. Density calculations demonstrate that new magma is less dense and may originate a plume, rapidly rising
through the residing magma which is cooler and more volatile-depleted than the new magma. Calculations of uprise velocity
assuming laminar flow are consistent with this hypothesis.
Received: 20 November 1995 / Accepted: 2 August 1996 相似文献
15.
水氡动态图强震危险区预测的新方法 总被引:4,自引:0,他引:4
水氡动态图强震危险区预测法是一种地下流体的地震分析预报新方法。 对该方法做了系统的介绍,其内容有: 水氡基值变化率动态图像的生成方法,水氡变化率高值异常区图形演化与地震震中位置的关系,强震危险区预测的标志与方法。检验性预测结果表明,该方法具有预测效能,可在实际地震预报中使用。 相似文献
16.
We investigated the existence of a fractal law (power law) distribution of size pyroclastic fragments erupted during the fallout phase of the 79 A.D. Plinian eruption at Mt. Vesuvius. In particular, we performed a particle size distribution analysis on 18 white and grey pumice samples collected in six sites distributed in the SW sector of Mt. Vesuvius. Our measurements show that the fragmentation of samples in the investigated range (from 32 mm to 850 μm) follows a power law, guaranteeing the scale invariance of the process. The relationship frequency-size distribution of the fragments is verified independently from the nature (i.e., pumices and lithics) and stratigraphic height of the considered samples in the pyroclastic deposit. Therefore, the fractal fragmentation theory can be indicated for evaluating the relationship between the intensity of fragmentation (fractal dimension D) and eruption energy. In this way the apparent chaotic distribution of the particles in the fallout deposits hides a self-organized complexity revealed by the retrieved power law distribution. We further remark that a key aspect of our analysis is the founded evidence that the fractal dimension of the lithics is systematically greater than that of the pumices. 相似文献
17.
Cynthia A. Gardner Katharine V. Cashman Christina A. Neal 《Bulletin of Volcanology》1998,59(8):537-555
The 1992 eruption of Crater Peak, Mount Spurr, Alaska, involved three subplinian tephra-producing events of similar volume
and duration. The tephra consists of two dense juvenile clast types that are identified by color, one tan and one gray, of
similar chemistry, mineral assemblage, and glass composition. In two of the eruptive events, the clast types are strongly
stratified with tan clasts dominating the basal two thirds of the deposits and gray clasts the upper one third. Tan clasts
have average densities between 1.5 and 1.7 g/cc and vesicularities (phenocryst free) of approximately 42%. Gray clasts have
average densities between 2.1 and 2.3 g/cc, and vesicularities of approximately 20%; both contain abundant microlites. Average
maximum plagioclase microlite lengths (13–15 μm) in gray clasts in the upper layer are similar regardless of eruptive event
(and therefore the repose time between them) and are larger than average maximum plagioclase microlite lengths (9–11 μm) in
the tan clasts in the lower layer. This suggests that microlite growth is a response to eruptive processes and not to magma
reservoir heterogeneity or dynamics. Furthermore, we suggest that the low vesicularities of the clasts are due to syneruptive
magmatic degassing resulting in microlitic growth prior to fragmentation and not to quenching of clasts by external groundwater.
Received: 5 September 1997 / Accepted: 1 February 1998 相似文献
18.
Results are presented from 11 microgravity surveys on Mt. Etna between 1987 and 1993, a period including the major 1989 and
1991–1993 flank eruptions and subordinate 1990 activity. Measurements were made with LaCoste and Romberg D-62 and D-157 gravity
meters along a network around the volcano between 1000 and 1900 m a.s.l. and, since 1992, a N–S summit profile. Gravity changes
of as much as 200 μGal were observed at scales from the size of the summit region to that of the volcano. None was associated
with significant changes in ground elevation. The data show an increase in gravity for 2 years before the 1989 eruption. The
increase is attributed to the accumulation of magma (0.25–1.7×109 m3) in an elongate zone, oriented NNW–SSE, between 2.5 and 6 km below sea level. Part of this magma was injected into the volcanic
pile to supply the 1989 and 1990 eruptions. It also probably fed the start of the 1991–1993 eruption, since this event was
not preceded by significant gravity changes. A large gravity increase (up to 140 μGal) detected across the volcano between
June and September 1992 is consistent with the arrival in the accumulation zone of 0.32–2.2×109 m3 of new magma, thus favoring continued flank effusion until 1993. A large gravity decrease (200 μGal) in the summit region
marked the closing stages of the 1991–1993 event and is associated with magma drainage from the upper levels of Etna's central
feeding system.
Received: 15 July 1995 / Accepted: 27 October 1997 相似文献
19.
The Bag Tephra, a widespread tephrochronological marker in Middle Europe: chemical and mineralogical investigations 总被引:1,自引:0,他引:1
The Bag Tephra is a widespread tephra layer interbedded in Quaternary loess deposits along the Danubian valley of Hungary
and Slovakia. Its age is poorly defined between 788 and 380 ka B.P. The glass and mineral composition – micropumice clasts
of phono-tephrite and blocky shards of tephri-phonolite associated with two kinds of clinopyroxene, fassaitic diopside, and
salite – is very distinctive. This tephra could be used as a chronological marker, as soon as its age is refined. The probable
origin is the middle Italian volcanic area.
Received: 3 November 1998 / Accepted: 18 January 1999 相似文献
20.
Pyroclastic deposits as a guide for reconstructing the multi-stage evolution of the Somma-Vesuvius Caldera 总被引:1,自引:0,他引:1
The evolution of the Somma-Vesuvius caldera has been reconstructed based on geomorphic observations, detailed stratigraphic
studies, and the distribution and facies variations of pyroclastic and epiclastic deposits produced by the past 20,000 years
of volcanic activity. The present caldera is a multicyclic, nested structure related to the emptying of large, shallow reservoirs
during Plinian eruptions. The caldera cuts a stratovolcano whose original summit was at 1600–1900 m elevation, approximately
500 m north of the present crater. Four caldera-forming events have been recognized, each occurring during major Plinian eruptions
(18,300 BP "Pomici di Base", 8000 BP "Mercato Pumice", 3400 BP "Avellino Pumice" and AD 79 "Pompeii Pumice"). The timing of
each caldera collapse is defined by peculiar "collapse-marking" deposits, characterized by large amounts of lithic clasts
from the outer margins of the magma chamber and its apophysis as well as from the shallow volcanic and sedimentary units.
In proximal sites the deposits consist of coarse breccias resulting from emplacement of either dense pyroclastic flows (Pomici
di Base and Pompeii eruptions) or fall layers (Avellino eruption). During each caldera collapse, the destabilization of the
shallow magmatic system induced decompression of hydrothermal–magmatic and hydrothermal fluids hosted in the wall rocks. This
process, and the magma–ground water interaction triggered by the fracturing of the thick Mesozoic carbonate basement hosting
the aquifer system, strongly enhanced the explosivity of the eruptions.
Received: 24 November 1997 / Accepted: 23 March 1999 相似文献