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1.
Jan Lindsay Warner Marzocchi Gill Jolly Robert Constantinescu Jacopo Selva Laura Sandri 《Bulletin of Volcanology》2010,72(2):185-204
The Auckland Volcanic Field (AVF) is a young basaltic field that lies beneath the urban area of Auckland, New Zealand’s largest
city. Over the past 250,000 years the AVF has produced at least 49 basaltic centers; the last eruption was only 600 years
ago. In recognition of the high risk associated with a possible future eruption in Auckland, the New Zealand government ran
Exercise Ruaumoko in March 2008, a test of New Zealand’s nation-wide preparedness for responding to a major disaster resulting from a volcanic
eruption in Auckland City. The exercise scenario was developed in secret, and covered the period of precursory activity up
until the eruption. During Exercise Ruaumoko we adapted a recently developed statistical code for eruption forecasting, namely
BET_EF (Bayesian Event Tree for Eruption Forecasting), to independently track the unrest evolution and to forecast the most
likely onset time, location and style of the initial phase of the simulated eruption. The code was set up before the start
of the exercise by entering reliable information on the past history of the AVF as well as the monitoring signals expected
in the event of magmatic unrest and an impending eruption. The average probabilities calculated by BET_EF during Exercise
Ruaumoko corresponded well to the probabilities subjectively (and independently) estimated by the advising scientists (differences
of few percentage units), and provided a sound forecast of the timing (before the event, the eruption probability reached
90%) and location of the eruption. This application of BET_EF to a volcanic field that has experienced no historical activity
and for which otherwise limited prior information is available shows its versatility and potential usefulness as a tool to
aid decision-making for a wide range of volcano types. Our near real-time application of BET_EF during Exercise Ruaumoko highlighted
its potential to clarify and possibly optimize decision-making procedures in a future AVF eruption crisis, and as a rational
starting point for discussions in a scientific advisory group. It also stimulated valuable scientific discussion around how
a future AVF eruption might progress, and highlighted areas of future volcanological research that would reduce epistemic
uncertainties through the development of better input models. 相似文献
2.
In a companion paper, a methodology for ranking volcanic hazards and events in terms of risk was presented, and the likelihood and extent of potential hazards in the Auckland Region, New Zealand investigated. In this paper, the effects of each hazard are considered and the risk ranking completed. Values for effect are proportions of total loss and, as with likelihood and extent, are based on order of magnitude.Two outcomes were considered – building damage and loss of human life. In terms of building damage, tephra produces the highest risk by an order of magnitude, followed by lava flows and base surge. For loss of human life, risk from base surge is highest. The risks from pyroclastic flows and tsunami are an order of magnitude smaller. When combined, tephra fall followed by base surge produces the highest risk. The risks from lava flows and pyroclastic flows are an order of magnitude smaller. For building damage, the risk from Mt. Taranaki volcano, 280 km from the Auckland CBD, is largest, followed by Okataina volcanic centre, an Auckland volcanic field eruption centred on land, then Tongariro volcanic centre. In terms of human loss, the greatest risk is from an Auckland eruption centred on land. The risks from an Auckland eruption centred in the ocean, Okataina volcanic centre, and Taupo volcano are more than an order of magnitude smaller. When combined, the risk from Mt. Taranaki remains highest, followed by an Auckland eruption centred on land. The next largest risks are from the Okataina and Tongariro volcanic centres, followed by Taupo volcano.Three alternative situations were investigated. As multiple eruptions may occur from the Auckland volcanic field, it was assumed that a local event would involve two eruptions. This increased risk of a local eruption occurring on land so that it was equal to that of an eruption from Mt. Taranaki. It is possible that a future eruption may be of a similar, or larger size, to the previous Rangitoto eruption. Risk was re-calculated for local eruptions based on the extent of hazards from Rangitoto. This increased the risk of lava flow to greater than that of base surge, and the risk from an Auckland land eruption became greatest. The relative probabilities used for Mt. Taranaki volcano and the Auckland volcanic field may only be minimum values. When the probability of these occurring was increased by 50%, there was no change in either ranking.Editorial responsibility: J. S. Gilbert 相似文献
3.
J. G. Moore 《Bulletin of Volcanology》1967,30(1):337-363
A base surge, first identified at the Bikini thermonuclear undersea explosion, is a ring-shaped basal cloud that sweeps outward as a density flow from the base of a vertical explosion column. Base surges are also common in shallow underground test explosions and are formed by expanding gases which first vent vertically and then with continued expansion rush over the crater lip (represented by a large solitary wave in an underwater explosion), tear ejecta from it, and feed a gas-charged density flow, which is the surge cloud. This horizontally moving cloud commonly has an initial velocity of more than 50 meters per second and can carry clastic material many kilometers. Base surges are a common feature of many recent shallow, submarine and phreatic volcanic eruptions. They transport ash, mud, lapilli, and blocks with great velocity and commonly sandblast and knock down trees and houses, coat the blast side with mud, and deposit ejecta at distances beyond the limits of throw-out trajectories. Close to the eruption center, the base surge can erode radial channels and deposit material with dune-type bedding. 相似文献
4.
Basal layered deposits of the large-volume Peach Springs Tuff occur beneath the main pyroclastic flow deposit over a minimum lateral distance of 70 km in northwestern Arizona (USA). The basal deposits are interpreted to record initial blasting and pyroclastic surge events at the beginning of the eruption; the pyroclastic surges traveled a minimum of 100 km from the (as yet unknown) source. Changes in bedding structures with increasing flow distance are related to the decreasing sediment load of the surges. Some bed forms in the most proximal part of the study area (Kingman, Arizona) can be interpreted as being shock induced, reflecting a blast origin for the surges. Component analyses support a hydrovolcanic origin for some of the blasting and subsequent pyroclastic surges. The eruption apparently began with magmatic blasts, which were replaced by hydrovolcanic blasts. Hydrovolcanic activity may be partially related to failure of the conduit walls that temporarily plugged the vent. A single large-volume pyroclastic flow immediately followed the blast phase, and no evidence has been observed for a Plinian eruption column. The stratigraphic sequence indicates that powerful hydrovolcanic blasting rapidly widened the vent, thus bypassing a Plinian fallout phase and causing rapid evolution to a collapsing eruption column. Similar processes may occur in other large-volume ignimbrite eruptions, which commonly lack significant Plinian fallout deposits. 相似文献
5.
Akihiko Fujinawa Masao Ban Tsukasa Ohba Kazuo Kontani Kotaro Miura 《Journal of Volcanology and Geothermal Research》2008
Three eruption events occurring in the central part of the northeastern Japan arc were investigated and compared: Adatara AD1900, Zao AD1895, and Bandai AD1888. Producing low-temperature (LT) pyroclastic surges, these events are characterized by steam eruptions ejecting no juvenile material. These eruptions' well-preserved eruptive deposits and facies facilitated granulometric analyses of the beds, which revealed the transport and deposition mechanisms of LT surges. Combining these results with those of investigations of documents reporting the events, we correlated each eruption to the relevant individual bed and reconstructed the LT surge development sequence. Important findings related to the transport and deposition modes are the following. (1) Bed sets consisting of thin, laminated ash and its overlying thick massive tuff were recognized in the Adatara 1900 proximal deposits. The bed set was probably produced by a strong wind that discharged and propagated quickly from the vent (leading wind) and a gravitationally segregated, highly concentrated flow originated from the eruption column, within a discrete eruption episode. A similar combination might have occurred during the first surge of the Bandai 1888 event. (2) Comparison of the proximal and distal facies for the largest eruption of Adatara 1900 event indicates that the initial turbulence of the eruption cloud decreased rapidly, transforming into a density-stratified surge with a highly concentrated part near the base. Similar surges occurred in the climatic stage of Zao 1895. (3) Bandai 1888 ejecta indicate massive beds deposited preferentially at topographic lows. Co-occurring planar beds showed no topographic affection, as indicated by the topographic blocking of a stratified surge. The observed facies–massive tuffs, crudely stratified tuffs, and thin bedded tuffs–are compatible with those for high-temperature surges. At Bandai, absence of dune bedded tuffs and commonly poorer sorting in the LT surge deposits might be attributable to poor thermally induced turbulence of eruption columns. Condensation of vapor in the surges might have contributed to the poor sorting. The estimated explosion energies were 6 × 1013 J for Adatara AD1900, 6.5 × 1010 J for Zao AD1895, and 6.5 × 1015 J for Bandai AD1888, implying that the three events were hydrothermal eruptions with distinctive eruptive mechanisms. Regarding eruption sources, the Adatara 1900 event was caused solely by thermal energy of the hydrothermal fluid, although magma intrusion likely triggered evolution of hydrothermal systems at Zao in 1895. Steam eruptions in the Bandai 1888 event occurred simultaneously with sudden exposure of the hydrothermal system, whose triggers require no internal energy. 相似文献
6.
Volcanic base surge deposits, recorded from the Pacific volcanic belts, Iceland, and the Azores, are here reported for the first time from Italy. Dune forms produced by deposition from base surges occur in the products of phreatic eruptions of Vulsini, Vico, and Sabatini volcanoes north of Rome. The occurrence of cross bedding, drag and slump features, normal dunes, symmetric and asymmetric antidunes, and radial troughs can in some cases be related to individual volcanic craters. Antidune features are more common on crater rims than farther from the craters, and the antidunes appear to be favored by high particle velocities and high water contents in the eruption, and perhaps by density and cohesiveness of the underlying material. 相似文献
7.
8.
Hannes B. Mattsson 《Journal of Volcanology and Geothermal Research》2010,189(1-2):81-91
Here I present textural data (i.e., vesicularity, vesicle size distributions (VSD), plagioclase crystallinity, crystal size distributions (CSD), combined with fractal analyses of particle outlines) from a natural succession of alternating fall and surge deposits in the emergent Capelas tuff cone (Azores).The textural variation in the Capelas succession is surprisingly small considering the wide variety of fragmentation processes, vent activity and emplacement mechanisms that are characteristic of emergent eruptions. The plagioclase crystal content varies between 24 and 33 vol.%. CSD analyses of plagioclase show near-linear trends with a slight increase in time for the smallest crystal sizes (with surge deposits having more groundmass plagioclase when compared with fall deposits). This is consistent with crystallization induced by degassing and decompression at lower eruption rates. The vesicularities of the Capelas pyroclasts are more variable (18 to 59 vol.%), with VSDs displaying kinked trends characteristic of coalescence. This is especially evident in the fall deposits, and consistent with being formed in continuous uprush (jetting) with an overall shallow fragmentation level within the conduit. Bubble coalescence can also be identified in the surge deposits, although to a much lesser extent. The amount of bubble coalescence is negatively correlated with the amount of groundmass crystallization (i.e., plagioclase) in the Capelas deposits.A relatively broad range of fractal dimensions (with average Dbox = 1.744 and σ = 0.032) for the outlines of pyroclastic fragments emplaced by fall or as surges indicate that there is little difference in the fragmentation process itself at Capelas. In addition to this, the fact that the fractal dimensions for both the fall and surge end-members completely overlap suggests that shape modification due to abrasion and chipping of grain edges was minor during emplacement of base surges. These results are consistent with emergent eruptions, building tuff cones, to be a relatively low-energy phreatomagmatic landform (e.g., at least when compared with more energetic phreatomagmatic eruptions producing tuff rings and maar volcanoes). 相似文献
9.
L. Gurioli R. Sulpizio R. Cioni A. Sbrana R. Santacroce W. Luperini D. Andronico 《Bulletin of Volcanology》2010,72(9):1021-1038
During the past 22 ka of activity at Somma–Vesuvius, catastrophic pyroclastic density currents (PDCs) have been generated
repeatedly. Examples are those that destroyed the towns of Pompeii and Ercolano in AD 79, as well as Torre del Greco and several
circum-Vesuvian villages in AD 1631. Using new field data and data available from the literature, we delineate the area impacted
by PDCs at Somma–Vesuvius to improve the related hazard assessment. We mainly focus on the dispersal, thickness, and extent
of the PDC deposits generated during seven plinian and sub-plinian eruptions, namely, the Pomici di Base, Greenish Pumice,
Pomici di Mercato, Pomici di Avellino, Pompeii Pumice, AD 472 Pollena, and AD 1631 eruptions. We present maps of the total
thickness of the PDC deposits for each eruption. Five out of seven eruptions dispersed PDCs radially, sometimes showing a
preferred direction controlled by the position of the vent and the paleotopography. Only the PDCs from AD 1631 eruption were
influenced by the presence of the Mt Somma caldera wall which stopped their advance in a northerly direction. Most PDC deposits
are located downslope of the pronounced break-in slope that marks the base of the Somma–Vesuvius cone. PDCs from the Pomici
di Avellino and Pompeii Pumice eruptions have the most dispersed deposits (extending more than 20 km from the inferred vent).
These deposits are relatively thin, normally graded, and stratified. In contrast, thick, massive, lithic-rich deposits are
only dispersed within 7 to 8 km of the vent. Isopach maps and the deposit features reveal that PDC dispersal was strongly
controlled by the intensity of the eruption (in terms of magma discharge rate), the position of the vent area with respect
to the Mt Somma caldera wall, and the pre-existing topography. Facies characteristics of the PDC deposits appear to correlate
with dispersal; the stratified facies are consistently dispersed more widely than the massive facies. 相似文献
10.
Mark Bebbington Shane J. Cronin Ian Chapman Michael B. Turner 《Journal of Volcanology and Geothermal Research》2008
Quantifying the potential ash fall hazards from re-awakening volcanoes is a topic of great interest. While methods for calculating the probability of eruptions, and for numerical simulation of tephra dispersal and fallout exist, event records at most volcanoes that re-awaken sporadically on decadal to millennial cycles are inadequate to develop rigorous forecasts of occurrence, much less eruptive volume. Here we demonstrate a method by which eruption records from radiocarbon-dated sediment cores can be used to derive forecasting models for ash fall impacts on electrical infrastructure. Our method is illustrated by an example from the Taranaki region of New Zealand. Radiocarbon dates, expressed as years before present (B.P.), are used to define an age-depth model, classifying eruption ages (with associated errors) for a circa 1500–10 500 year B.P. record at Mt. Taranaki (New Zealand). In addition, data describing the youngest 1500 years of eruption activity is obtained from directly dated proximal deposits. Absence of trend and apparent independence in eruption intervals is consistent with a renewal model using a mix of Weibulls distributions, which was used to generate probabilistic forecasts of eruption recurrence. After establishing that interval length and tephra thickness were independent in the record, a thickness–volume relationship (from [Rhoades, D.A., Dowrick, D.J., Wilson, C.J.N., 2002. Volcanic hazard in New Zealand: Scaling and attenuation relations for tephra fall deposits from Taupo volcano. Nat. Hazards, 26:147–174]) was inverted to provide a frequency–volume relationship for eruptions. Monte Carlo simulation of the thickness–volume relationship was then used to produce probable ash fall thicknesses at any chosen site. Several critical electrical infrastructure sites in the Taranaki Region were analysed. This region, being the only gas and condensate-producing area in New Zealand, is of national economic importance, with activities in and around the area depending on uninterrupted power supplies. Forecasts of critical ash thicknesses (1 mm wet and 2 mm dry) that may cause short-circuiting, surges or power shutdowns in substations show that the annual probabilities of serious impact are between ~ 0.5% and 27% over a 50 year period. It was also found that while large eruptions with high ash plumes tend to affect “expected” areas in relation to prevailing winds, the direction impacts of small ash falls are far less predictable. In the Taranaki case study, areas out of normal downwind directions, but close to the volcano, have probabilities of impact for critical thicknesses of 1–2 mm of around half to 60% of those in downwind directions and therefore should not be overlooked in hazard analysis. Through this method we are able to definitively show that the potential ash fall hazard to electrical infrastructure in this area is low in comparison to other natural threats, and provide a quantitative measure for use in risk analysis and budget prioritisation for hazard mitigation measures. 相似文献
11.
G. Mastrolorenzo 《Bulletin of Volcanology》1994,56(6-7):561-572
The tuff ring of Averno (3700 years BP) is a wide maar-type, lake-filled volcano which formed during one of the most recent explosive eruptions inside the Campi Flegrei caldera.The eruptive products consist of (a) a basal coarse unit, intercalated ballistic fallout breccia, subplinian pumice deposits and pyroclastic surge bedsets and (b) an upper fine-grained, stratified, pyroclastic surge sequence.During the deposition of the lower unit both purely magmatic (lapilli breccia) and hydromagmatic episodes (wavy and planar bedded, fine ash pyroclastic surge bedsets) coexisted. The hydromagmatic deposits exhibit both erosive and depositional features. The upper unit mostly comprises fine grained, wet pyroclastic surge deposits. The pyroclastic surges were controlled by a highly irregular pre-existing topography, produced by volcano-tectonic dislocation of older tuff rings and cones.Both the upper and lower units show decreasing depletion of fines with increasing distance from the vent. The ballistic fallout layers, however, exhibit only a weak increase in fines with distance from the vent, in spite of marked fining of the lapilli and blocks. The deposits consist dominantly of moderately to highly vesicular juvenile material, generated by primary magmatic volatile driven fragmentation followed by episodes of near-surface magma-water interaction.The evolution of the eruption toward increased fragmentation and a more hydromagmatic character may reflect that the progressive depletion in magmatic volatiles and a decrease in conduit pressure during the last stage of the eruption, possibly associated with a widening of the vent at sea level. 相似文献
12.
J.L. Macías L. Capra J.L. Arce J.M. Espíndola A. García-Palomo M.F. Sheridan 《Journal of Volcanology and Geothermal Research》2008
El Chichón volcano consists of a 2-km wide Somma crater compound cone 0.2 Ma old with peripheral domes with a central crater reactivated several times during the Holocene. The most recent eruption at El Chichón occurred from March 28 to April 4, 1982, resulting in the worst volcanic disaster during historical times in Mexico, killing more than 2000 people and destroying nine towns and small communities. The volcanic hazard map of El Chichón is based on detailed field work that documented twelve eruptions during the last 8000 years, and computer simulations. To validate the results, computer simulations were first performed over pre-1982 topography mimicking the extent of the actual deposits produced and afterwards run over post-1982 topography. These eruptions have produced pyroclastic fall, surge, flow and lahar deposits. Pyroclastic flows have different volumes and Heim coefficients varying from 0.2 (pumice flows), to 0.15 (block-and-ash flows) and 0.10 (ash flows). Simulations using FLOW3D and TITAN2D indicate that pumice flows and block-and-ash flows can fill the moat area and follow main ravines up to distances of ca. 3 km from the crater, with no effect on populations around the volcano. On the other hand, more mobile ash flows related to column-collapse events can reach up to 4 km from the vent, but will always follow the same paths and still not affect surrounding populations. The energy-cone model was used to simulate the outflow of pyroclastic surges based on the 1982 event (H/L = 0.1 and 0.2), and shows that surges may reach some towns around the volcano. 相似文献
13.
The May 22, 1915 eruptions of Lassen Peak involved a volcanic blast and the emplacement of three geographically and temporally distinct lahar deposits. The volcanic blast occurred when a Vulcanian explosion at the summit unroofed a shallow magma source, generating an eruption cloud that rose to an estimated height of 9 km above sea level. The blast cloud was probably caused by the collapse of a small portion of the eruption column; absence of a flank vent associated with these eruptions argues against it originating as an explosion that has been directed by vent geometry or location. The volcanic blast devasted 7 km2 of the northeast flank of the volcano, and emplaced a deposit of juvenile tephra and accidental lithic and mineral fragments. Decrease in blast deposit thickness and median grain size with increasing distance from the vent suggests that the blast cloud lost transport competence as it crossed the devastated area. Scanning electron microscope examination of pyroclasts from the blast deposit indicates that the blast cloud was a dry, turbulent suspension that emplaced a thin deposit which cooled rapidly after deposition. Lahar deposits were emplaced primarily in Lost Creek, with minor lahars flowing down gullies on the west, northwest and north flanks of the volcano. The initial lahar was apparently triggered early in the eruption when the blast cloud melted the residual snowpack as it moved down the northeast flank of the peak. The event that triggered the later lahars is enigmatic; the presence of approximately five times more juvenile dacite bombs on the surface of the later lahars suggests that they may have been triggered by a change in eruption style or dynamics. 相似文献
14.
Roberto Sulpizio Arnau Folch Antonio Costa Chiara Scaini Pierfrancesco Dellino 《Bulletin of Volcanology》2012,74(9):2205-2218
Long-range dispersal of volcanic ash can disrupt civil aviation over large areas, as occurred during the 2010 eruption of Eyjafjallaj?kull volcano in Iceland. Here we assess the hazard for civil aviation posed by volcanic ash from a potential violent Strombolian eruption of Somma-Vesuvius, the most likely scenario if eruptive activity resumed at this volcano. A Somma-Vesuvius eruption is of concern for two main reasons: (1) there is a high probability (38?%) that the eruption will be violent Strombolian, as this activity has been common in the most recent period of activity (between AD 1631 and 1944); and (2) violent Strombolian eruptions typically last longer than higher-magnitude events (from 3 to 7?days for the climactic phases) and, consequently, are likely to cause prolonged air traffic disruption (even at large distances if a substantial amount of fine ash is produced such as is typical during Vesuvius eruptions). We compute probabilistic hazard maps for airborne ash concentration at relevant flight levels using the FALL3D ash dispersal model and a statistically representative set of meteorological conditions. Probabilistic hazard maps are computed for two different ash concentration thresholds, 2 and 0.2?mg/m3, which correspond, respectively, to the no-fly and enhanced procedure conditions defined in Europe during the Eyjafjallaj?kull eruption. The seasonal influence of ash dispersal is also analysed by computing seasonal maps. We define the persistence of ash in the atmosphere as the time that a concentration threshold is exceeded divided by the total duration of the eruption (here the eruption phase producing a sustained eruption column). The maps of averaged persistence give additional information on the expected duration of the conditions leading to flight disruption at a given location. We assess the impact that a violent Strombolian eruption would have on the main airports and aerial corridors of the Central Mediterranean area, and this assessment can help those who devise procedures to minimise the impact of these long-lasting low-intensity volcanic events on civil aviation. 相似文献
15.
Ana Teresa Mendoza-Rosas Servando De la Cruz-Reyna 《Journal of Volcanology and Geothermal Research》2008
The probabilistic analysis of volcanic eruption time series is an essential step for the assessment of volcanic hazard and risk. Such series describe complex processes involving different types of eruptions over different time scales. A statistical method linking geological and historical eruption time series is proposed for calculating the probabilities of future eruptions. The first step of the analysis is to characterize the eruptions by their magnitudes. As is the case in most natural phenomena, lower magnitude events are more frequent, and the behavior of the eruption series may be biased by such events. On the other hand, eruptive series are commonly studied using conventional statistics and treated as homogeneous Poisson processes. However, time-dependent series, or sequences including rare or extreme events, represented by very few data of large eruptions require special methods of analysis, such as the extreme-value theory applied to non-homogeneous Poisson processes. Here we propose a general methodology for analyzing such processes attempting to obtain better estimates of the volcanic hazard. This is done in three steps: Firstly, the historical eruptive series is complemented with the available geological eruption data. The linking of these series is done assuming an inverse relationship between the eruption magnitudes and the occurrence rate of each magnitude class. Secondly, we perform a Weibull analysis of the distribution of repose time between successive eruptions. Thirdly, the linked eruption series are analyzed as a non-homogeneous Poisson process with a generalized Pareto distribution as intensity function. As an application, the method is tested on the eruption series of five active polygenetic Mexican volcanoes: Colima, Citlaltépetl, Nevado de Toluca, Popocatépetl and El Chichón, to obtain hazard estimates. 相似文献
16.
P.J. Baxter W.P. Aspinall A. Neri G. Zuccaro R.J.S. Spence R. Cioni G. Woo 《Journal of Volcanology and Geothermal Research》2008
Disasters from explosive volcanic eruptions are infrequent and experience in emergency planning and mitigation for such events remains limited. The need for urgently developing more robust methods for risk assessment and decision making in volcanic crises has become increasingly apparent as world populations continue to expand in areas of active explosive volcanism. Nowhere is this more challenging than at Vesuvius, Italy, with hundreds of thousands of people living on the flanks of one of the most dangerous volcanoes in the world. We describe how a new paradigm, evidence-based volcanology, has been applied in EXPLORIS to contribute to crisis planning and management for when the volcano enters its next state of unrest, as well as in long-term land-use planning. The analytical approach we adopted enumerates and quantifies all the processes and effects of the eruptive hazards of the volcano known to influence risk, a scientific challenge that combines field data on the vulnerability of the built environment and humans in past volcanic disasters with theoretical research on the state of the volcano, and including evidence from the field on previous eruptions as well as numerical simulation modelling of eruptive processes. Formal probabilistic reasoning under uncertainty and a decision analysis approach have provided the basis for the development of an event tree for a future range of eruption types with probability paths and hypothetical casualty outcomes for risk assessment. The most likely future eruption scenarios for emergency planning were derived from the event tree and elaborated upon from the geological and historical record. Modelling the impacts in these scenarios and quantifying the consequences for the circumvesuvian area provide realistic assessments for disaster planning and for showing the potential risk–benefit of mitigation measures, the main one being timely evacuation, but include for consideration protecting buildings against dilute, low dynamic pressure surges, and temporary roof supports in the most vulnerable buildings, as well as hardening infrastructure and lifelines. This innovative work suggests that risk-based methods could have an important role in crisis management at cities on volcanoes and small volcanic islands. 相似文献
17.
Volcanic eruptions typically produce a number of hazards, and many regions are at risk from more than one volcano or volcanic field. So that detailed risk assessments can be carried out, it is necessary to rank potential volcanic hazards and events in terms of risk. As it is often difficult to make accurate predictions regarding the characteristics of future eruptions, a method for ranking hazards and events has been developed that does not rely on precise values. Risk is calculated individually for each hazard from each source as the product of likelihood, extent and effect, based on the parameters order of magnitude. So that multiple events and outcomes can be considered, risk is further multiplied by the relative probability of the event occurring (probabilitye) and the relative importance of the outcome (importanceo). By adding the values obtained, total risk is calculated and a ranking can be carried out.This method was used to rank volcanic hazards and events that may impact the Auckland Region, New Zealand. Auckland is at risk from the Auckland volcanic field, Okataina volcanic centre, Taupo volcano, Tuhua volcano, Tongariro volcanic centre, and Mt. Taranaki volcano. Relative probabilities were determined for each event, with the highest given to Mt. Taranaki. Hazards considered were, for local events: tephra fall, scoria fall and ballistic impacts, lava flow, base surge and associated shock waves, tsunami, volcanic gases and acid rain, earthquakes and ground deformation, mudflows and mudfills, lightning and flooding; and for distal events: tephra fall, pyroclastic flows, poisonous gases and acid rain, mudflows and mudfills, climate variations and earthquakes. Hazards from each source were assigned values for likelihood, with the largest for tephra fall from all sources, earthquakes and ground deformation, lava flows, scoria fall and base surge for an Auckland eruption on land, and earthquakes and ground deformation from an Auckland eruption in the ocean. The largest values for extent were for tephra fall and climate variation from each of the distal centres. However, these parameters do not give a true indication of risk. In a companion paper the effect of each hazard is fully investigated and the risk ranking completed. 相似文献
18.
J. -C. Thouret F. Lavigne K. Kelfoun S. Bronto 《Journal of Volcanology and Geothermal Research》2000,100(1-4)
Of 1.1 million people living on the flanks of the active Merapi volcano, 440,000 are at relatively high risk in areas prone to pyroclastic flows, surges, and lahars. For the last two centuries, the activity of Merapi has alternated regularly between long periods of viscous lava dome extrusion, and brief explosive episodes at 8–15 year intervals, which generated dome-collapse pyroclastic flows and destroyed part of the pre-existing domes. Violent explosive episodes on an average recurrence of 26–54 years have generated pyroclastic flows, surges, tephra-falls, and subsequent lahars. The 61 reported eruptions since the mid-1500s killed about 7000 people. The current hazard-zone map of Merapi (Pardyanto et al., 1978) portrays three areas, termed ‘forbidden zone’, ‘first danger zone’ and ‘second danger zone’, based on successively declining hazards. Revision of the hazard map is desirable, because it lacks details necessary to outline hazard zones with accuracy, in particular the valleys likely to be swept by lahars, and excludes some areas likely to be devastated by pyroclastic gravity-currents such as the 22 November 1994 surge. In addition, risk maps should be developed to incorporate social, technical, and economic factors of vulnerability.Eruptive hazard assessment at Merapi is based on reconstructed eruptive history, on eruptive behavior and scenarios, and on existing models and preliminary numerical modeling. Firstly, the reconstructed eruptive activity, in particular for the past 7000 years and from historical accounts of eruptions, helps to define the extent and recurrence frequency of the most hazardous phenomena (Newhall et al., 2000; Camus et al., 2000). Pyroclastic flows traveled as far as 9–15 km from the source, pyroclastic surges swept the flanks as far as 9–20 km away from the vent, thick tephra fall buried temples in the vicinity of Yogyakarta 25 km to the south, and subsequent lahars spilled down the radial valleys as far as 30 km to the west and south. At least one large edifice collapse has occurred in the past 7000 years (Newhall et al., 2000; Camus et al., 2000). Secondly, four eruption scenarios are portrayed as hazardous zones on two maps and derived from the past eruptive behavior of Merapi and from the most affected areas in the past. Thirdly, simple numerical simulation, based on a Digital Elevation Model, a stereo-pair of SPOT satellite images, and one 2D-orthoimage helps to simulate pyroclastic and lahar flowage on the flanks and in radial valley channels, and to outline areas likely to be devastated.Three major threats are identified: (1) a collapse of the summit dome in the short-to mid-term, that can release large-volume pyroclastic flows and high-energy surges towards the south–southwest sector of the volcano; (2) an explosive eruption, much larger than any since 1930, may sweep all the flanks of Merapi at least once every century; (3) a potential collapse of the summit area, involving the fumarolic field of Gendol and part of the southern flank, which can contribute to moderate-scale debris avalanches and debris flows. 相似文献
19.
J. Martí W.P. Aspinall R. Sobradelo A. Felpeto A. Geyer R. Ortiz P. Baxter P. Cole J. Pacheco M.J. Blanco C. Lopez 《Journal of Volcanology and Geothermal Research》2008
We propose a long-term volcanic hazards event tree for Teide-Pico Viejo stratovolcanoes, two complex alkaline composite volcanoes that have erupted 1.8–3 km3 of mafic and felsic magmas from different vent sites during the last 35 ka. This is the maximum period that can be investigated from surface geology and also represents an upper time limit for the appearance of the first phonolites on that volcano. The whole process of the event tree construction was divided into three stages. The first stage included the determination of the spatial probability of vent opening for basaltic and phonolitic eruptions, based on the available geological and geophysical data. The second, involved the analysis of the different eruption types that have characterised the volcanic activity from Teide during this period. The third stage focussed on the generation of the event tree from the information obtained in the two previous steps and from the application of a probabilistic analysis on the occurrence of each possible eruption type. As for other volcanoes, the structure of the Teide-Pico Viejo Event Tree was subdivided into several steps of eruptive progression from general to more specific events. The precursory phase was assumed as an unrest episode of any geologic origin (magmatic, hydrothermal or tectonic), which could be responsible for a clear increase of volcanic activity revealed by geophysical and geochemical monitoring. According to the present characteristics of Teide-Pico Viejo and their past history, we started by considering whether the unrest episode would lead to a sector collapse or not. If the sector collapse does not occur but an eruption is expected, this could be either from the central vents or from any of the volcanoes' flanks. In any of these cases, there are several possibilities according to what has been observed in the period considered in our study. In the case that a sector collapse occurs and is followed by an eruption we considered it as a flank eruption. We conducted an experts elicitation judgement to assign probabilities to the different possibilities indicated in the event tree. We assumed long term estimations based on existing geological and historical data for the last 35 Ka, which gave us a minimum estimate as the geological record for such a long period is incomplete. However, to estimate probabilities for a short term forecast, for example during an unrest episode, we would need to include in the event tree additional information from the monitoring networks, as any possible precursors that may be identified could tell us in which direction the system will evolve. Therefore, we propose to develop future versions of the event tree to include also the precursors that might be expected on each path during the initial stages of a new eruptive event. 相似文献
20.
D.M. Burt L.P. Knauth K.H. Wohletz M.F. Sheridan 《Journal of Volcanology and Geothermal Research》2008
Before base surges were described in association with nuclear blasts and explosive volcanic eruptions (especially, the 1980 eruption of Mount St. Helens, Washington), laminar and cross-bedded volcanogenic surge deposits were commonly misinterpreted as being of fluvial or aeolian origin. One well-documented example involves the “water-laid tuffs” in and near the Spor Mountain beryllium mine, Utah; other examples abound. In light of how frequently volcanogenic surge deposits have been misinterpreted on Earth, extreme caution is urged for Mars studies. Contrary to what has been claimed, the markedly cross-bedded, salty deposits at Meridiani Planum on Mars need not have been formed by a combination of aeolian and aqueous processes, and their contained hematitic spherules need not have formed as aqueous concretions. Given the lack of indications of volcanism in the vicinity, and the planet-wide abundance of impact craters, deposition by surges associated with distant impact targets consisting of brine-soaked, locally sulfidic regolith is a reasonable explanation for all features observed, especially if diagenesis and weathering are considered. The uniformly sized and shaped, Ni-enriched blue-gray hematitic spherules would then be some type of vapor condensation spherules (including accretionary lapilli). A similar interpretation is possible for deposits in the Home Plate area, Gusev Crater. Unlike on the dry and atmosphereless Moon, salty impact surge deposits containing spherules should be common, and well-preserved, on Mars. 相似文献