首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
Surface deformations on the western flank of Mt Etna volcano, spanning 1980–2004, have been analysed as they pertain to stress interactions between magma intrusions within the shallow crust along the S–SE Rift and faulting sensitivity. During this period, an accurate analysis of strain parameters, computed by inversion of SW electro‐optical distance data, suggested that the observed strong displacements on this flank of the edifice can also be related to dextral shear movements along a roughly NE–SW buried fault crossing the area covered by this network, as supported by seismic observations of the 20–24 April 2001 swarm. Moreover, Coulomb stress change model analysis confirms that the displacement along this fault, heralding the July–August 2001 eruption 2 months earlier can be related to major stresses applied by a dike intrusion at depth along the S–SE Rift, as testified by the microseismicity occurring between November 2000 and 19 April 2001.  相似文献   

2.
On December 24th, Mt. Etna volcano underwent a seismic crisis beneath the summit and upper southern flank of the volcano, accompanied by significant ash emission. Eruptive fissures opened at the base of summit craters, propagating SE‐wards. This lateral eruption lasted until December 27th. Despite the small eruption, seismic swarm and ground deformation were very strong. Sentinel‐1 interferograms show a wide and intense ground deformation with some additional features related to volcano‐tectonic structures. We inverted DInSAR data to characterise the magma intrusion. The resulting model indicates that a large dyke intruded but aborted its upraise at about the sea level; however, this big intrusion stretched the edifice, promoting the opening of the eruptive fissures fed by a shallower small dyke, and activating also several faults. This model highlights that a big intrusion beneath a structurally complex volcano represents a main issue even if the eruption is aborted.  相似文献   

3.
This paper documents a phreatomagmatic flank eruption that occurred 18 700 ± 100 a BP , on the lower north-eastern slope of Etna during the Ellittico volcano activity, which produced fall and surge deposits. This type of eruption is connected to a sedimentary basement ridge at Etna. The interaction between the rising magma and the shallow groundwater hosted in the volcanic pile overlying the impermeable sediments resulted in phreatomagmatic instead of strombolian activity. Three eruptive phases are distinguished based on field and analytical data: (i) an explosive phreatomagmatic opening, (ii) a main phase producing coarse lithic-rich fallout and a strombolian deposit, and (iii) the final pulsating surge-forming phase. The discovery of this phreatomagmatic flank eruption, which occurred at lower altitude, raises important issues for previous hazard assessments at Etna.  相似文献   

4.
Continuous GPS (CGPS) data, collected at Mt. Etna between April 2012 and October 2013, clearly define inflation/deflation processes typically observed before/after an eruption onset. During the inflationary process from May to October 2013, a particular deformation pattern localised in the upper North Eastern sector of the volcano suggests that a magma intrusion had occurred a few km away from the axis of the summit craters, beneath the NE Rift system. This is the first time that this pattern has been recorded by CGPS data at Mt. Etna. We believe that this inflation process might have taken place periodically at Mt. Etna and might be associated with the intrusion of batches of magma that are separate from the main feeding system. We provide a model to explain this unusual behaviour and the eruptive regime of this rift zone, which is characterised by long periods of quiescence followed by often dangerous eruptions in which vents can open at low elevation and thus threaten the villages in this sector of the volcano.  相似文献   

5.
Benchmarks installed on the upper eastern flank of Mt. Etna in 1982 have subsided continually since then, with the rate of subsidence twice accelerating prior to eruptions. The first of these eruptions was in December 1985, and the second in September 1989. This pattern of accelerating downslope movement has also been observed prior to landslides, and recent work applying knowledge of the failure of materials has shown that analysis of the inverse rate of these movements can be used to predict the time of failure. Post-eruption analyses of geodetic or seismic data from volcanoes has shown that in several cases, this approach could have been used to forecast eruptions weeks in advance. Applying the same principles to the accelerating subsidence on Mt. Etna's eastern flank prior to the eruptions of 1985 and 1989 shows that rough estimates of eruption dates could have been obtained several months in advance. These observations also suggest a speculative eruption-triggering mechanism involving an interplay between slope creep deformation and extensional weakening over the zone of intrusion.  相似文献   

6.
Indoor Radon concentrations have been carried out simultaneously at the villages of S. Venerina and Acireale, which are located on the south-eastern flank of Mt. Etna volcano. Both investigation sites are partially affected by the same fault system, which plays an important role in the dynamics of the volcano, especially before and during eruptive periods. Measurements were performed in the period from January 2006 until April 2006, just prior to an eruption which took place on 14th July 2006. Indoor Radon monitoring at S. Venerina, was carried out at two buildings located nearby, characterized by a different type of construction. These buildings were chosen because they can be considered as representative of both the historical centre and the new neighbourhoods of the village. At the same time, a Radon active monitor was operating in-soil near the two aforesaid edifices. Cross-correlation analysis between the in-soil one with both the indoor S. Venerina Radon series indicated different temporal correlation, probably due to the different types of building foundations and constructive materials of their walls, both causing the different indoor accumulation. S. Venerina’s indoor Radon values taken at the new building showed similar trends and the same anomalies as the ones recorded at Acireale. The simultaneous increase in indoor Radon concentration was observed at both sites from the last ten days of March, when a significant increase in the CO2 efflux was recorded. Increases in volcanogenic gases occurred very probably throughout an inflating state of the volcano during the pre-eruptive period, which caused the wide opening of the fractures. Lastly, variations in indoor Radon concentrations observed before an eruption, indicate the suitability of the investigated sites for in-soil Radon monitoring at a low altitude of the south-eastern flank of Mt. Etna. Moreover, in this place repeated and long period Radon indoor measurements should be carried out due to high potential indoor accumulation which depends from the volcanic activity, as this could constitute a serious danger to public health.  相似文献   

7.
The eastern flank of Mt. Etna volcano rests on Pleistocene marine sediments, which unconformably cover the Apenninic–Maghrebian Chain units. A quantitative biostratigraphic analysis was carried out based on the calcareous nannofossil content of the Pleistocene deposits outcropping along the S and NE periphery of the volcano. Sediments were constrained to the MNN19e and MNN19f biozones, deposited from 1.2 to 0.589 Ma. According to the depth of deposition and the present altitude of the Pleistocene succession, uplift rates are estimated between 1.1 and 1.7 mm yr−1 for the northeastern sector of the Etna edifice, and between 0.36 and 0.61 mm yr−1 for the southern one. This inhomogeneous long-term uplift rate affecting the Etna region, probably results from a buried thrust below the northern flank of Etna, which is related to the post-Tortonian geodynamic evolution of NE Sicily.  相似文献   

8.
Volcán Tequila is an extinct stratovolcano in the western Mexican Volcanic Belt that has erupted lavas ranging from andesite to rhyolite during the last 0.9 Ma. Following an early period of rhyolitic volcanism, the main edifice of the volcano was constructed by central vent eruptions that produced 25 km3 of pyroxene-andesite. At about 0.2 Ma central activity ceased and numerous flows of hornblende-bearing andesite, dacite, and rhyodacite erupted from vents located around the flanks of the volcano. Bimodal plagioclase phenocryst rim compositions in lavas from both the main edifice and the flanks indicate that magma mixing commonly occurred shortly prior to or during eruption. Compositions of endmember magmas involved in mixing, as constrained by whole-rock major and trace element abundances, phenocryst compositions, and mineral-melt exchange equilibria, are similar to those of some lavas erupted from the central vent and on the flanks of the volcano. Estimated pre-eruptive temperatures for hornblende-bearing lavas (970°–830°C) are systematically lower than for lavas that lack hornblende (1045°–970°C), whereas magmatic H2O contents are systematically higher for hornblende-bearing lavas. In addition to stabilizing hornblende, high magmatic water contents promoted crystallization of calcic plagioclase (An70–82). Frequent injections of magma into the base of the subvolcanic plumbing system followed by eruption of mixed magma probably prevented formation of large volumes of silicic magma, which have caused paroxysmal, caldera-forming eruptions at other stratovolcanoes in western Mexico. The later stages of volcanic activity, represented by the flank lavas, indicate a change from a large magma storage reservoir to numerous small ones that developed along a NW-trending zone parallel to regional fault trends. Sr and Nd isotopic data for lavas from the Tequila region and other volcanoes in western Mexico demonstrate that differentiated calc-alkaline magmas are formed primarily through crystal fractionation of mantle-derived calc-alkaline basalt coupled with assimilation of crustal material. Present Address:Department of the Geophysical Sciences The University of Chicago, Chicago IL, 60637, USA  相似文献   

9.
Volcanic tremor and SO2 data, measured between 1987 and 1992 on Mt. Etna, have been studied. A cross-correlation analysis between the two time series has revealed large cross-correlation coefficients corresponding to enhanced volcanic activity. Tremor and SO2 emissions thus seem to have a common physical origin linked to the magma dynamics of the volcano.  相似文献   

10.
After a recharge phase that began in 2007, on 13 May 2008, a new eruption started on Mt. Etna volcano. The final intrusion was very fast, accompanied by a violent seismic swarm and marked by ground deformation recorded at permanent tilt and GPS stations. The violence of the eruptive event generated concern that the eruptive fissures might propagate downslope towards populated areas. The ground deformation modelling explains both the mechanism of the intrusion as well as the attempt of the dyke to propagate in the shallower part of the northern sector of the volcano. We show that the 2008 intrusion was characterized by a mechanism, which is new and different to the ones modelled in previous eruptions, following the path of the central conduit in the first part of the intrusion (below 1.6 km) and then breaking off towards the east in the last shallow part.  相似文献   

11.
Large variations of the CO2 flux through the soil were observed between November 2002 and January 2006 at Mt. Etna volcano. In many cases, the CO2 flux was strongly influenced by changes in air temperature and atmospheric pressure. A new filtering method was then developed to remove the atmospheric influences on soil CO2 flux and, at the same time, to highlight the variations strictly related to volcanic activity. Successively, the CO2 corrected data were quantitatively compared with the spectral amplitude of the volcanic tremor by cross correlation function, cross-wavelet spectrum and wavelet coherence. These analyses suggested that the soil CO2 flux variations preceded those of volcanic tremor by about 50 days. Given that volcanic tremor is linked to the shallow (a few kilometer) magma dynamics and soil CO2 flux related to the deeper (~12 km b.s.l.) magma dynamics, the “delayed similarity” between the CO2 flux and the volcanic tremor amplitude was used to assess the average speed in the magma uprising into the crust, as about 170–260 m per day. Finally, the large amount of CO2 released before the onset of the 2004–2005 eruption indicated a deep ingression of new magma, which might have triggered such an eruption.  相似文献   

12.
This paper relates the hydrology of a volcano to its eruptive activity, which seem to be correlated. Based on the groundwater pattern previously determined by hydrologic and thermal modelling, we formulate hypotheses for the mechanisms linking rainfall and volcanic eruptions. We focus on: mechanical loading by the weight of the infiltrated rain, which might favour magma overpressure or slope instability on the eastern volcanic flank; unloading of the infiltrated water, discharged toward the ocean, which could increase the tangential tensile stress above the magma chamber. We test the sensitivity of the model to the magma chamber geometry and the rainfall distribution. The mechanical unloading of the infiltrated water is the mechanism most likely to trigger eruptions. However, the presence of a sliding surface and rainfall loading could favour the development of tensile stress in the 'shell' surrounding the magma chamber but with a lower intensity than in the previous case.  相似文献   

13.
Thermochemical calculations and laboratory phase equilibration experiments on lavas of the 131 day 1983 Mt. Etna flank eruption of 0.1 km3 were undertaken to investigate possible systematic variations in inferred melt-phenocryst equilibration conditions as a function of time. The 1983 Mt. Etna lavas are multiply saturated; plagioclase, clinopyroxene and olivine, the dominant phenocrysts, occur in the ratio 1:1/2:1/4. Melts (glasses) plot close to the plagioclase saturated olivine-clinopyroxene low pressure cotectic on a Walker-O'Hara diopside-forsterite-silica diagram suggesting equilibration of melt and phenocrysts in a high level magma reservoir. Total pressures, temperatures and dissolved H2O concentrations were calculated using the isoactivity method of Carmichael and coworkers based on about 300 elelctron microprobe analyses of coexisting olivine, clinopyroxene and plagioclase phenocrysts, microphenocrysts and groundmass microlites for samples collected 6, 46 and 125 days after the start of the eruption. Total pressures (P t), temperatures and H2O contents based on representative olivine-clinopyroxene pairs are 140 MPa, 1105°C, 2.4 wt% H2O; 255 MPA, 1112°C, 1.0 wt% H2O and 85 MPa, 1096°C, 1.8 wt% H2O respectively for the early (283), middle (I83) and late (L83) samples. Corresponding equilibration depths are in the range 3 to 10 kilometers. Plagioclase feldspar phenocrysts, while showing more evidence of disequilibrium, provide compatible estimates of P t and T when analysis is restricted to the low anorthite mode of the plagioclase frequency-composition histograms: 133 MPa and 1115°C; 260 MPa and 1117°C and 103 MPa and 1104°C, repectively for 283, I83 and L83. The pre-eruptive (i.e., in situ) temperature-pressure gradient calculated from olivine-clinopyroxene equilibria is 10.6 K/kbar. This compares well with independent estimates of the temperature-pressure derivative of the (pseudo) invariant point composition (10 to 12 K/kbar) in both model (e.g., diopside-forsterite-anorthite, Presnall et al. 1978) and natural (e.g., Walker et al. 1979; Grove et al. 1982) systems. Apparently, magma within the Etna reservoir was in a quasiequilibrium state buffered by its multiply-saturated character immediately preceding eruption. The temporal variation of computed P t, T and H2O concentrations for melt-phenocryst equilibrium agrees well with predictions based on simulations of the withdrawal of magma from a body zoned with respect to dissolved H2O provided the temporal record of magma discharge is taken into account. Discharge varied by a factor of about 100 during the sample collection interval. The intermediate P t but high H2O content inferred for sample 283 reflects the withdrawal of H2O enriched magma during an early phase of high average discharge of about (350 m3/s) before evaculation isochrons became quasistationary. The high P t and relatively dry I83 magma reflects the deepening of the evacuation isochrons after 50 days of intermediate discharge with the development of quasi-stationary isochrons in time and space. Sample L83 from day 125 near the end of the eruption reflects the shoaling of evacuation isochrons (hence low P t and relatively high H2O content) associated with the observed low (0.5 m3/s) discharge. Our results show that thermochemical modeling efforts provide important opportunities for testing the predictions of magma with-drawal simulations.  相似文献   

14.
Buoyancy controls the ability of magma to rise, its ascent rate and the style of the eruptions. Geophysical, geological and petrological data have been integrated to evaluate the buoyancy of magmas at Mt Etna. The density difference between host rocks and magmas is mainly related to the amount of H2O dissolved in the magma and to the bubble‐liquid separation processes. In the depth interval 22–2 km b.s.l. highly hydrated (H2O ～ 3%) basaltic magmas or mixtures of bubbles + liquid have positive buoyancy and rise rapidly. Conversely, bubble‐depleted liquids, with an intermediate H2O content (～ 1.5%), having neutral buoyancy, will spread out and form magmatic reservoirs at different depths until cooling/crystallization further modify composition and density. These different processes account for the magma compositions, location of magmatic reservoirs as determined by geophysical methods, and the complex eruptive cycles (slow effusions, fire fountains and Plinian eruptions) that have been observed in the history of the volcano.  相似文献   

15.
The size distributions of crystals of olivine, plagioclase and oxides of the 1991/93 eruption at Mt. Etna (Italy) are analyzed. The simultaneous collection of this information for different minerals gives precious insight into the cooling history of lavas. Three distinct episodes are detectable: a storage of the magma in a deep reservoir, characterized by nearly constant and low nucleation and growth rates (near to equilibrium); an ascent phase, with an ever increasing nucleation rate related to volatile exsolution; and finally a quenching phase. In addition to geochemical and geophysical evidence, the similarity of the crystal size distributions of the present eruption with those of previous ones of this century makes it possible to exclude that crystal size distributions of Etnean lavas are due to mixing of different populations. This strongly suggests that the main features of the volcano feeding system have not changed despite observed variations in the magma output rates.  相似文献   

16.
《Gondwana Research》2014,25(3-4):1223-1236
Repeating volcano-tectonic (VT) earthquakes, taking place at Mt. Etna during 1999–2009, were detected and analyzed to investigate their behavior. We found 735 families amounting to 2479 VT earthquakes, representing ~ 38% of all the analyzed VT earthquakes. The number of VT earthquakes making up the families ranges from 2 to 23. Over 70% of the families comprise 2 or 3 VT earthquakes and only 20 families by more than 10 events. The occurrence lifetime is also highly variable ranging from some minutes to ten years. In particular, more than half of the families have a lifetime shorter than 0.5 day and only ~ 10% longer than 1 year. On the basis of these results, most of the detected families were considered “burst-type”, i.e., show swarm-like occurrence, and hence their origin cannot be explained by a temporally constant tectonic loading. Indeed, since the analyzed earthquakes take place in a volcanic area, the rocks are affected not only by tectonic stresses related to the fairly steady regional stress field but also by local stresses, caused by the volcano, such as magma batch intrusions/movements and gravitational loading. We focused on the five groups of families characterized by the longest repeatability over time, namely high number of events and long lifetime, located in the north-eastern, eastern and southern flanks of the volcano. Unlike the first four groups, which similarly to most of the detected families show swarm-like VT occurrences, group “v”, located in the north-eastern sector, exhibits a more “tectonic” behavior with the events making up such a group spread over almost the entire analyzed period. It is clear how both occurrence and slip rates do not remain constant but vary over time, and such changes are time-related to the occurrence of the 2002–2003 eruption. Finally, by FPFIT algorithm a good agreement between directions identified by nodal planes and the earthquake epicentral distribution was generally found.  相似文献   

17.
Mount Etna is an open conduit volcano, characterised by persistent activity, consisting of degassing and explosive phenomena at summit craters, frequent flank eruptions, and more rarely, eccentric eruptions. All eruption typologies can give rise to lava flows, which represent the greatest hazard by the volcano to the inhabited areas. Historical documents and scientific papers related to the 20th century effusive activity have been examined in detail, and volcanological parameters have been compiled in a database. The cumulative curve of emitted lava volume highlights the presence of two main eruptive periods: (a) the 1900–1971 interval, characterised by a moderate slope of the curve, amounting to 436 × 106 m3 of lava with average effusion rate of 0.2 m3/s and (b) the 1971–1999 period, in which a significant increase in eruption frequency is associated with a large issued lava volume (767 × 106 m3) and a higher effusion rate (0.8 m3/s). The collected data have been plotted to highlight different eruptive behaviour as a function of eruptive periods and summit vs. flank eruptions. The latter have been further subdivided into two categories: eruptions characterised by high effusion rates and short duration, and eruptions dominated by low effusion rate, long duration and larger volume of erupted lava. Circular zones around the summit area have been drawn for summit eruptions based on the maximum lava flow length; flank eruptions have been considered by taking into account the eruptive fracture elevation and combining them with lava flow lengths of 4 and 6 km. This work highlights that the greatest lava flow hazard at Etna is on the south and east sectors of the volcano. This should be properly considered in future land-use planning by local authorities.  相似文献   

18.
Air entrainment in fragmented magmas controls the dynamics of volcanic eruptions. Pyroclast oxidation kinetics may be applied to quantify the degree of magma–air interaction. Pyrrhotite (Po) in volcanic rocks is often oxidized to form magnetite (Mt) and hematite (Hm), and its reaction mechanisms are well constrained. To test utilizing Po oxidation as a marker for magma–air interactions, we compared the occurrence of Po oxidation products from three different eruption styles during the Sakurajima 1914–1915 eruption. Pumices from the Plinian eruption include columnar-type Fe oxides (Mt with subordinate width of Hm) often accompanied by relict Po. This columnar type is also found in clastogenic lava, where it is almost completely oxidized to Hm. The effusive lava contains framboidal aggregates of subhedral to anhedral Mt crystals without Hm. The formation mechanisms of columnar and framboidal Fe oxides were estimated. The columnar type Fe oxides were formed syn-eruptively through gaseous reactions, as opposed to the melt in a magma chamber, as demonstrated by the Ti-free nature of the columnar Mt and its synchronous oxidation to Hm. By contrast, the framboidal type was formed in a melt with decreasing fS2. The calculation of Hm growth in a conductively cooling pumice clast constrains the surface temperature of pumice in the eruption column. The paragenesis and oxidation degree of Po and Fe oxides are consistent with the eruption processes in terms of magma fragmentation, air entrainment, and welding, and can, therefore, be a responsive marker for the magma–air interaction.  相似文献   

19.
An instrusive dacite and a salic pumice, emplaced late in the evolution of the Miocene (c. 10 m.y.) Króksfjördur volcano, NW Iceland, contain a varied assemblage of xenolithic metaigneous rocks. Mineral and rock chemistry shows that the dacite is very similar to calc-alkaline salic rocks from the SW Pacific. It contains phenocrystic plagioclase, quartz, pyroxene, cummingtonite, hornblende, biotite, two oxides, apatite and zircon in a rhyolitic glass. The rock equilibrated at 700 to 750°C. P ～ 1.6 Kbar and PH2O ～ 1 Kbar. The xenoliths are layered gabbros, granophyres and various fine-grained hornfelses and show that the dacite magma was residing within a gabbro intrusion capped by granophyre prior to the eruption. The hornfelses are amphibole-plagioclase, amphibole-pyroxene-plagioclase and pyroxene-plagioclase rocks formed during high-temperature metamorphism of basic dykes cutting the gabbro intrusion. The gabbros and hornfelses mostly record higher metamorphic temperatures (850–940°C) than the dacite, and indicate that they were equilibrated during the ascent of a magma body into a hydrous high-level region within the volcano. During a following thermal decline, the hydrated magma cooled to form the first cummingtonite-bearing low-T magma to be recorded from the ocean ridge systems.  相似文献   

20.
Kīlauea is the youngest of five basaltic shield volcanoes on the island of Hawai’i. It is located to the south‐east of the much larger Mauna Loa volcano, and rose above sea level about 100 ka ago. Kīlauea is one of the most monitored, and arguably the best understood volcanoes on Earth, providing scientists with a good understanding of its current eruption, in which magma rises from depth and is stored beneath its 4 × 3.2 km summit caldera in an underground reservoir. The reservoir is connected to a lava lake within a crater called Halema’uma’u, which is situated on the floor of the caldera. When magma drains from the summit area it travels in underground conduits and emerges on the flanks of the volcano at a rift zone, where it erupts through fissures. The magma is sometimes stored in other reservoirs along the way. This link between summit magma storage and fissure eruptions on the flanks has occurred thousands of times at many Hawai’ian volcanoes. The current eruptive episode is, however, a ‘once‐in‐a‐century’ show, because it is the first time since 1924 that fissure‐fed lava flow eruptions have been accompanied by significant explosive eruptions within Halema’uma’u Crater. This gives scientists a unique opportunity to use modern methods to understand exactly how such hazardous explosions happen at Kīlauea, a volcano that receives about 2 million visitors a year.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号