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231.
An experimental facility has been developed to investigate magma-water interaction (MWI). The facility operates in a high-pressure
and high-temperature environment, with temperatures up to 1,200°C and pressures up to 200 MPa. Cylindrical sample-holders
(20 by 180 mm in size) are heated conductively to yield a three phase (melt, crystals and gas) system, and then water (or
other fluid) is injected into the sample through a capillary tube (diameter 0.5 mm, length ca. 1,000 mm) under controlled
conditions. Pressure, volume and temperature changes are continuously recorded during every phase of the experiments. To test
this facility, MWI is studied at subliquidus temperatures (800 and 900°C) and pressure (8 MPa), using a leucite tephrite sample
with two different initial grain sizes. Because of the grain-size dependence of sintering, the two starting materials produce
magmas with different textures at the same temperature: porous magma for large initial grain sizes and dense magma for small
initial grain sizes. In these experiments 1.5 g of water at room temperature is injected into 6.0 g of partially molten sample
at velocities ranging from 1 to 3 m/s. We find that the extent of fragmentation and transport caused by MWI are mainly controlled
by the texture of the interacting sample with explosive interaction occurring only for porous magmas. 相似文献
232.
Alessandro Bonforte Salvatore Gambino Francesco Guglielmino Francesco Obrizzo Mimmo Palano Giuseppe Puglisi 《Bulletin of Volcanology》2007,69(7):757-768
On 22 September 2002, 1 month before the beginning of the flank eruption on the NE Rift, an M-3.7 earthquake struck the northeastern
part of Mt. Etna, on the westernmost part of the Pernicana fault. In order to investigate the ground deformation pattern associated
with this event, a multi-disciplinary approach is presented here. Just after the earthquake, specific GPS surveys were carried
out on two small sub-networks, aimed at monitoring the eastern part of the Pernicana fault, and some baselines belonging to
the northeastern EDM monitoring network of Mt. Etna were measured. The leveling route on the northeastern flank of the volcano
was also surveyed. Furthermore, an investigation using SAR interferometry was performed and also the continuous tilt data
recorded at a high precision sensor close to the epicenter were analyzed to constrain the coseismic deformation. The results
of the geodetic surveys show a ground deformation pattern that affects the entire northeastern flank of the volcano, clearly
shaped by the Pernicana fault, but too strong and wide to be related only to an M-3.7 earthquake. Leveling and DInSAR data
highlight a local strong subsidence, up to 7 cm, close to the Pernicana fault. Significant displacements, up to 2 cm, were
also detected on the upper part of the NE Rift and in the summit craters area, while the displacements decrease at lower altitude,
suggesting that the dislocation did not continue further eastward. Three-dimensional GPS data inversions have been attempted
in order to model the ground deformation source and its relationship with the volcano plumbing system. The model has also
been constrained by vertical displacements measured by the leveling survey and by the deformation map obtained by SAR interferometry. 相似文献
233.
M. Bisson M. T. Pareschi G. Zanchetta R. Sulpizio R. Santacroce 《Bulletin of Volcanology》2007,70(2):157-167
The Campania Region (southern Italy) is characterized by the frequent occurrence of volcaniclastic debris flows that damage
property and loss of life (more than 170 deaths between 1996 and 1999). Historical investigation allowed the identification
of more than 500 events during the last four centuries; in particular, more than half of these occurred in the last 100 years,
causing hundreds of deaths. The aim of this paper is to quantify debris-flow hazard potential in the Campania Region. To this
end, we compared several elements such as the thickness distribution of pyroclastic fall deposits from the last 18 ka of the
Vesuvius and Phlegrean Fields volcanoes, the slopes of relieves, and the historical record of volcaniclastic debris flows
from A.D. 1500 to the present. Results show that flow occurrence is not only a function of the cumulative thickness of past
pyroclastic fall deposits but also depends on the age of emplacement. Deposits younger than 10 ka (Holocene eruptions) apparently
increase the risk of debris flows, while those older than 10 ka (Late Pleistocene eruptions) seem to play a less prominent
role, which is probably due to different climatic conditions, and therefore different rates of erosion of pyroclastic falls
between the Holocene and the Late Pleistocene. Based on the above considerations, we compiled a large-scale debris-flow hazard
map of the study area in which five main hazard zones are identified: very low, low, moderate, high, and very high. 相似文献
234.
Matthew R. Patrick John L. Smellie Andrew J. L. Harris Robert Wright Ken Dean Pavel Izbekov Harold Garbeil Eric Pilger 《Bulletin of Volcanology》2005,67(5):415-422
The MODVOLC satellite monitoring system has revealed the first recorded eruption of Mount Belinda volcano, on Montagu Island in the remote South Sandwich Islands. Here we present some initial qualitative observations gleaned from a collection of satellite imagery covering the eruption, including MODIS, Landsat 7 ETM+, ASTER, and RADARSAT-1 data. MODVOLC thermal alerts indicate that the eruption started sometime between 12 September and 20 October 2001, with low-intensity subaerial explosive activity from the islands summit peak, Mount Belinda. By January 2002 a small lava flow had been emplaced near the summit, and activity subsequently increased to some of the highest observed levels in August 2002. Observations from passing ships in February and March 2003 provided the first visual confirmation of the eruption. ASTER images obtained in August 2003 show that the eruption at Mount Belinda entered a new phase around this time, with fresh lava effusion into the surrounding icefield. MODIS radiance trends also suggest that the overall activity level increased significantly after July 2003. Thermal anomalies continued to be observed in MODIS imagery in early 2004, indicating a prolonged low-intensity eruption and the likely establishment of a persistent summit lava lake, similar to that observed on neighboring Saunders Island in 2001. Our new observations also indicate that lava lake activity continues on Saunders Island.Editorial responsibility: J. Gilbert 相似文献
235.
Temporal Evolution of Magmatism in the Northern Volcanic Zone of the Andes: The Geology and Petrology of Cayambe Volcanic Complex (Ecuador) 总被引:4,自引:1,他引:3
SAMANIEGO PABLO; MARTIN HERVE; MONZIER MICHEL; ROBIN CLAUDE; FORNARI MICHEL; EISSEN JEAN-PHILIPPE; COTTEN JOSEPH 《Journal of Petrology》2005,46(11):2225-2252
In the Northern Volcanic Zone of the Andes, the Cayambe VolcanicComplex consists of: (1) a basal, mostly effusive volcano, theViejo Cayambe, whose lavas (andesites and subordinate dacitesand rhyolites) are typically calc-alkaline; and (2) a younger,essentially dacitic, composite edifice, the Nevado Cayambe,characterized by lavas with adakitic signatures and explosiveeruptive styles. The construction of Viejo Cayambe began >1·1Myr ago and ended at 1·0 Ma. The young and still activeNevado Cayambe grew after a period of quiescence of about 0·6Myr, from 0·4 Ma to Holocene. Its complex history isdivided into at least three large construction phases (Angurealcone, Main Summit cone and Secondary Summit cone) and compriseslarge pyroclastic events, debris avalanches, as well as periodsof dome activity. Geochemical data indicate that fractionalcrystallization and crustal assimilation processes have a limitedrole in the genesis of each suite. On the contrary, field observations,and mineralogical and geochemical data show the increasing importanceof magma mixing during the evolution of the volcanic complex.The adakitic signature of Nevado Cayambe magmas is related topartial melting of a basaltic source, which could be the lowercrust or the subducted slab. However, reliable geophysical andgeochemical evidence indicates that the source of adakitic componentis the subducted slab. Thus, the Viejo Cayambe magmas are inferredto come from a mantle wedge source metasomatized by slab-derivedmelts (adakites), whereas the Nevado Cayambe magmas indicatea greater involvement of adakitic melts in their petrogenesis.This temporal evolution can be related to the presence of thesubducted Carnegie Ridge, modifying the geothermal gradientalong the WadatiBenioff zone and favouring slab partialmelting. KEY WORDS: adakites; 40Ar/39Ar dating; Cayambe volcano; Ecuador; mantle metasomatism; Andes 相似文献
236.
237.
238.
S. M. Fazlullin S. V. Ushakov R. A. Shuvalov M. Aoki A. G. Nikolaeva E. G. Lupikina 《Journal of Volcanology and Geothermal Research》2000,97(1-4)
A subaqueous eruption in Karymsky lake in the Academii Nauk caldera dramatically changed its water column structure, water chemistry and biological system in less than 24 h, sending major floodwaves down the discharging river and eruption plumes with ash and gases high into the atmosphere. Prior to the eruption, the lake had a pH of about 7, was dominated by bicarbonate, and well stocked with fish, but turned in early 1996 into a stratified, initially steaming waterbody, dominated by sulfate with high Na and K levels, and devoid of fish. Blockage of the outlet led to rising waterlevels, followed by dam breakage and catastrophic water discharge. The total energy input during the eruption is estimated at about 1016 J. The stable isotope composition of the lake water remained dominated by the meteoric meltwaters after the eruption. 相似文献
239.
T. Sriwana M. J. van Bergen J. C. Varekamp S. Sumarti B. Takano B. J. H. van Os M. J. Leng 《Journal of Volcanology and Geothermal Research》2000,97(1-4)
Kawah Putih is a summit crater of Patuha volcano, West Java, Indonesia, which contains a shallow, 300 m-wide lake with strongly mineralized acid–sulfate–chloride water. The lake water has a temperature of 26–34°C, pH=<0.5–1.3, Stot=2500–4600 ppm and Cl=5300–12 600 ppm, and floating sulfur globules with sulfide inclusions are common. Sulfur oxyanion concentrations are unusually high, with S4O62−+S5O62−+S6O62−=2400 – 4200 ppm. Subaerial fumaroles (<93°C) on the lake shore have low molar SO2/H2S ratios (<2), which is a favorable condition to produce the observed distribution of sulfur oxyanion species. Sulfur isotope data of dissolved sulfate and native sulfur show a significant 34S fractionation (ΔSO4–Se of 20‰), probably the result of SO2 disproportionation in or below the lake. The lake waters show strong enrichments in 18O and D relative to local meteoric waters, a result of the combined effects of mixing between isotopically heavy fluids of deep origin and meteoric water, and evaporation-induced fractionation at the lake surface. The stable-isotope systematics combined with energy-balance considerations support very rapid fluid cycling through the lake system. Lake levels and element concentrations show strong seasonal fluctuations, indicative of a short water residence time in the lake as well.Thermodynamic modeling of the lake fluids indicates that the lake water is saturated with silica phases, barite, pyrite and various Pb, Sb, Cu, As, Bi-bearing sulfides when sulfur saturation is assumed. Precipitating phases predicted by the model calculations are consistent with the bulk chemistry of the sulfur-rich bottom sediments and their identified mineral phases. Much of the lake water chemistry can be explained by congruent rock dissolution in combination with preferential enrichments from entering fumarolic gases or brines and element removal by precipitating mineral phases, as indicated by a comparison of the fluids, volcanic rocks and lake bed sediment.Flank springs on the mountain at different elevations vary in composition, and are consistent with local rock dissolution as a dominant factor and pH-dependent element mobility. Discharges of warm sulfate- and chloride-rich water at the highest elevation and a near-neutral spring at lower level may contain a small contribution of crater-lake water. The acid fluid-induced processes at Patuha have led to the accumulation of elements that are commonly associated with volcano-hosted epithermal ore deposits. The dispersal of heavy metals and other potentially toxic elements from the volcano via the local drainage system is a matter of serious environmental concern. 相似文献
240.
M. Martínez E. Fernndez J. Valds V. Barboza R. Van der Laat E. Duarte E. Malavassi L. Sandoval J. Barquero T. Marino 《Journal of Volcanology and Geothermal Research》2000,97(1-4)
Concentrations of chloride and sulfate and pH in the hot crater lake (Laguna Caliente) at Poás volcano and in acid rain varied over the period 1993–1997. These parameters are related to changes in lake volume and temperature, and changes in summit seismicity and fumarole activity beneath the active crater. During this period, lake level increased from near zero to its highest level since 1953, lake temperature declined from a maximum value of 70°C to a minimum value of 25°C, and pH of the lake water increased from near zero to 1.8. In May 1993 when the lake was nearly dry, chloride and sulfate concentrations in the lake water reached 85,400 and 91,000 mg l−1, respectively. Minimum concentrations of chloride and sulfate after the lake refilled to its maximum volume were 2630 and 4060 mg l−1, respectively. Between January 1993 and May 1995, most fumarolic activity was focused through the bottom of the lake. After May 1995, fumarolic discharge through the bottom of the lake declined and reappeared outside the lake within the main crater area. The appearance of new fumaroles on the composite pyroclastic cone coincided with a dramatic decrease in type B seismicity after January 1996. Between May 1995 and December 1997, enhanced periods of type A seismicity and episodes of harmonic tremor were associated with an increase in the number of fumaroles and the intensity of degassing on the composite pyroclastic cone adjacent to the crater lake. Increases in summit seismic activity (type A, B and harmonic tremor) and in the height of eruption plumes through the lake bottom are associated with a period of enhanced volcanic activity during April–September 1994. At this time, visual observations and remote fumarole temperature measurements suggest an increase in the flux of heat and gases discharged through the bottom of the crater lake, possibly related to renewed magma ascent beneath the active crater. A similar period of enhanced seismic activity that occurred between August 1995 and January 1996, apparently caused fracturing of sealed fumarole conduits beneath the composite pyroclastic cone allowing the focus of fumarolic degassing to migrate from beneath the lake back to the 1953–1955 cone. Changes in the chemistry of summit acid rain are correlated changes in volcanic activity regardless of whether fumaroles are discharging into the lake or are discharging directly into the atmosphere. 相似文献