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111.
112.
Nicole C. Lautze Bruce F. Houghton 《Journal of Volcanology and Geothermal Research》2008,170(3-4):262-268
A combination of fortuitous eruptive and wind conditions at Stromboli volcano in September 2002 enabled the collection of samples of multiple lapilli from individual observed explosions. These ejecta present the first opportunity to analyze the vesicularity of material ejected in a single Strombolian explosion. Samples of between 40 and 92 lapilli were collected from each of six sequential explosions on 30 September 2002, and 28 lapilli were obtained from a single explosion 24 h later (1 October). Density measurements and microtextural observations show that considerable heterogeneity existed within each of the seven samples. Centimeter to millimeter size bubble-rich and bubble-poor zones are present and are, in places, mingled together. These data confirm that the shallow conduit at Stromboli is a texturally diverse environment at the instant of a single explosion, and that a similar range of heterogeneity can persist through closely-spaced sequences of explosions on a timescale of hours and, probably, days, despite the dynamic processes of ascent of melt and decoupled gas phases. 相似文献
113.
Guido Giordano Massimiliano Porreca Pietro Musacchio Massimo Mattei 《Bulletin of Volcanology》2008,70(10):1221-1236
The edifice of Stromboli volcano gravitationally collapsed several times during its volcanic history (>100 ka–present). The
largest Holocene event occurred during the final stage of the Neostromboli activity (∼13–5 ka), and was accompanied by the
emplacement of phreatomagmatic and lahar deposits, known as the Secche di Lazzaro succession. A stratigraphic and paleomagnetic
study of the Secche di Lazzaro deposits allows the interpretation of the emplacement and the eruptive processes. We identify
three main units within the succession that correspond to changing eruption conditions. The lower unit (UA) consists of accretionary
lapilli-rich, thinly bedded, parallel- to cross-stratified ash deposits, interpreted to indicate the early stages of the eruption
and emplacement of dilute pyroclastic density currents. Upward, the second unit (UB) of the deposit is more massive and the
beds thicker, indicating an increase in the sedimentation rate from pyroclastic density currents. The upper unit (UC) caps
the succession with thick, immediately post-eruptive lahars, which reworked ash deposited on the volcano’s slope. Flow directions
obtained by Anisotropy of Magnetic Susceptibility (AMS) analysis of the basal bed of UA at the type locality suggest a provenance
of pyroclastic currents from the sea. This is interpreted to be related to the initial base-surges associated with water–magma
interaction that occurred immediately after the lateral collapse, which wrapped around the shoulder of the sector collapse
scar. Upward in the stratigraphy (upper beds of UA and UB) paleoflow directions change and show a provenance from the summit
vent, probably related to the multiple collapses of a vertical, pulsatory eruptive column. 相似文献
114.
Katla volcano,Iceland: magma composition,dynamics and eruption frequency as recorded by Holocene tephra layers 总被引:1,自引:0,他引:1
Bergrún Arna Óladóttir Olgeir Sigmarsson Gudrun Larsen Thor Thordarson 《Bulletin of Volcanology》2008,70(4):475-493
The Katla volcano in Iceland is characterized by subglacial explosive eruptions of Fe–Ti basalt composition. Although the
nature and products of historical Katla eruptions (i.e. over the last 1,100 years) at the volcano is well-documented, the
long term evolution of Katla’s volcanic activity and magma production is less well known. A study of the tephra stratigraphy
from a composite soil section to the east of the volcano has been undertaken with emphasis on the prehistoric deposits. The
section records ∼8,400 years of explosive activity at Katla volcano and includes 208 tephra layers of which 126 samples were
analysed for major-element composition. The age of individual Katla layers was calculated using soil accumulation rates (SAR)
derived from soil thicknesses between 14C-dated marker tephra layers. Temporal variations in major-element compositions of the basaltic tephra divide the ∼8,400-year
record into eight intervals with durations of 510–1,750 years. Concentrations of incompatible elements (e.g. K2O) in individual intervals reveal changes that are characterized as constant, irregular, and increasing. These variations
in incompatible elements correlate with changes in other major-element concentrations and suggest that the magmatic evolution
of the basalts beneath Katla is primarily controlled by fractional crystallisation. In addition, binary mixing between a basaltic
component and a silicic melt is inferred for several tephra layers of intermediate composition. Small to moderate eruptions
of silicic tephra (SILK) occur throughout the Holocene. However, these events do not appear to exhibit strong influence on
the magmatic evolution of the basalts. Nevertheless, peaks in the frequency of basaltic and silicic eruptions are contemporaneous.
The observed pattern of change in tephra composition within individual time intervals suggests different conditions in the
plumbing system beneath Katla volcano. At present, the cause of change of the magma plumbing system is not clear, but might
be related to eruptions of eight known Holocene lavas around the volcano. Two cycles are observed throughout the Holocene,
each involving three stages of plumbing system evolution. A cycle begins with an interval characterized by simple plumbing
system, as indicated by uniform major element compositions. This is followed by an interval of sill and dyke system, as depicted
by irregular temporal variations in major element compositions. This stage eventually leads to a formation of a magma chamber,
represented by an interval with increasing concentrations of incompatible elements with time. The eruption frequency within
the cycle increases from the stage of a simple plumbing system to the sill and dyke complex stage and then drops again during
magma chamber stage. In accordance with this model, Katla volcano is at present in the first interval (i.e. simple plumbing
system) of the third cycle because the activity in historical time has been characterized by uniform magma composition and
relatively low eruption frequency. 相似文献
115.
Servando De la Cruz-Reyna Izumi Yokoyama Alicia Martínez-Bringas Esteban Ramos 《Bulletin of Volcanology》2008,70(6):753-767
Popocatépetl Volcano is located in the central Mexican Volcanic Belt, within a densely populated region inhabited by over
20 million people. The eruptive history of this volcano indicates that it is capable of producing a wide range of eruptions,
including Plinian events. After nearly 70 years of quiescence, Popocatépetl reawakened in December 21, 1994. The eruptive
activity has continued up until the date of this submission and has been characterized by a succession of lava dome growth-and-destruction
episodes, similar to events that have apparently been typical for Popocatépetl since the fourteenth century. In this regime,
the episodes of effusive and moderately explosive activity alternate with long periods of almost total quiescence. In this
paper we analyze five years of volcano-tectonic seismicity preceding the initial eruption of the current episode. The evolution
of the V-T seismicity shows four distinct stages, which we interpret in terms of the internal processes which precede an eruption
after a long period of quiescence. The thermal effects of a magma intrusion at depth, the fracturing related to the slow development
of magma-related fluid pathways, the concentration of stress causing a protracted acceleration of this process, and a final
relaxation or redistribution of the stress shortly before the initial eruption are reflected in the rates of V-T seismic energy
release. A hindsight analysis of this activity shows that the acceleration of the seismicity in the third stage asymptotically
forecast the time of the eruption. The total seismic energy release needed to produce an eruption after a long period of quiescence
is related to the volume of rock that must be fractured so imposing a characteristic threshold limit for polygenetic volcanoes,
limit that was reached by Popocatépetl before the eruption. 相似文献
116.
Four groups of thermal springs with temperatures from 50 to 80 °C are located on the S–SW–W slopes of El Chichón volcano, a composite dome-tephra edifice, which exploded in 1982 with a 1 km wide, 160 m deep crater left. Very dynamic thermal activity inside the crater (variations in chemistry and migration of pools and fumaroles, drastic changes in the crater lake volume and chemistry) contrasts with the stable behavior of the flank hot springs during the time of observations (1974–2005). All known groups of hot springs are located on the contact of the basement and volcanic edifice, and only on the W–SW–S slopes of the volcano at almost same elevations 600–650 m asl and less than 3 km of direct distance from the crater. Three groups of near-neutral (pH ≈ 6) springs at SW–S slopes have the total thermal water outflow rate higher than 300 l/s and are similar in composition. The fourth and farthest group on the western slope discharges acidic (pH ≈ 2) saline (10 g/kg of Cl) water with a much lower outflow rate (< 10 l/s). 相似文献
117.
D. Rouwet Y. Taran S. Inguaggiato N. Varley J.A. Santiago Santiago 《Journal of Volcanology and Geothermal Research》2008
El Chichón volcano (Chiapas, Mexico) erupted violently in March–April 1982, breaching through the former volcano–hydrothermal system. Since then, the 1982 crater has hosted a shallow (1–3.3 m, acidic (pH ∼ 2.2) and warm (∼ 30 °C) crater lake with a strongly varying chemistry (Cl/SO4 = 0–79 molar ratio). The changes in crater lake chemistry and volume are not systematically related to the seasonal variation of rainfall, but rather to the activity of near-neutral geyser-like springs in the crater (Soap Pool). These Soap Pool springs are the only sources of Cl for the lake. Their geyser-like behaviour with a long-term (months to years) periodicity is due to a specific geometry of the shallow boiling aquifer beneath the lake, which is the remnant of the 1983 Cl-rich (24,000 mg/l) crater lake water. The Soap Pool springs decreased in Cl content over time. The zero-time extrapolation (1982, year of the eruption) approaches the Cl content in the initial crater lake, meanwhile the extrapolation towards the future indicates a zero-Cl content by 2009 ± 1. This particular situation offers the opportunity to calculate mass balance and Cl budget to quantify the lake–spring system in the El Chichón crater. These calculations show that the water balance without the input of SP springs is negative, implying that the lake should disappear during the dry season. The isotopic composition of lake waters (δD and δ18O) coincide with this crater lake-SP dynamics, reflecting evaporation processes and mixing with SP geyser and meteoric water. Future dome growth, not observed yet in the post-1982 El Chichón crater, may be anticipated by changes in lake chemistry and dynamics. 相似文献
118.
Kaguyak Caldera lies in a remote corner of Katmai National Park, 375 km SW of Anchorage, Alaska. The 2.5-by-3-km caldera collapsed ~ 5.8 ± 0.2 ka (14C age) during emplacement of a radial apron of poorly pumiceous crystal-rich dacitic pyroclastic flows (61–67% SiO2). Proximal pumice-fall deposits are thin and sparsely preserved, but an oxidized coignimbrite ash is found as far as the Valley of Ten Thousand Smokes, 80 km southwest. Postcaldera events include filling the 150-m-deep caldera lake, emplacement of two intracaldera domes (61.5–64.5% SiO2), and phreatic ejection of lakefloor sediments onto the caldera rim. CO2 and H2S bubble up through the lake, weakly but widely. Geochemical analyses (n = 148), including pre-and post-caldera lavas (53–74% SiO2), define one of the lowest-K arc suites in Alaska. The precaldera edifice was not a stratocone but was, instead, nine contiguous but discrete clusters of lava domes, themselves stacks of rhyolite to basalt exogenous lobes and flows. Four extracaldera clusters are mid-to-late Pleistocene, but the other five are younger than 60 ka, were truncated by the collapse, and now make up the steep inner walls. The climactic ignimbrite was preceded by ~ 200 years by radial emplacement of a 100-m-thick sheet of block-rich glassy lava breccia (62–65.5% SiO2). Filling the notches between the truncated dome clusters, the breccia now makes up three segments of the steep caldera wall, which beheads gullies incised into the breccia deposit prior to caldera formation. They were probably shed by a large lava dome extruding where the lake is today. 相似文献
119.
Agnès Mazot Alain Bernard Tobias Fischer Salvatore Inguaggiato Igan S. Sutawidjaja 《Journal of Volcanology and Geothermal Research》2008
Papandayan is a stratovolcano situated in West Java, Indonesia. Since the last magmatic eruption in 1772, only few hydrothermal explosions have occurred. An explosive eruption occurred in November 2002 and ejected ash and altered rocks. The altered rocks show that an advanced argillic alteration took place in the hydrothermal system by interaction between acid fluids and rocks. Four zones of alteration have been defined and are limited in extension and shape along faults or across permeable structures at different levels beneath the active crater of the volcano. 相似文献
120.