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1.
R. Cioni A. Bertagnini D. Andronico P. D. Cole F. Mundula 《Bulletin of Volcanology》2011,73(7):789-810
We describe the products of the hitherto poorly known 512 AD eruption at Vesuvius, Italy. The deposit records a complex sequence
of eruptive events, and it has been subdivided into eight main units, composed of stratified scoria lapilli or thin subordinate
ash-rich layers. All the units formed by deposition from tephra fallout, pyroclastic density currents of limited extent being
restricted to the initial stages of the eruption (U2). The main part of the deposit (U3 and U5) is characterized by a striking
grain size alternation of fine to coarse lapilli, similar to that often described for mid-intensity, explosive eruptions.
The erupted products have a phonotephritic composition, with progressively less evolved composition from the base to the top
of the stratigraphic sequence. Based on different dispersal, sedimentological and textural features of the products, we identify
five phases related to different eruptive styles: opening phase (U1, U2), subplinian phase (U3 to U5), pulsatory phreatomagmatic
phase (U6), violent strombolian phase (U7) and final ash-dominated phase (U8). A DRE volume of 0.025 km3 has been calculated for the total fallout deposit. Most of the magma was erupted during the subplinian phase; lithic dispersal
data indicate peak column heights of between 10 and 15 km, which correspond to a mass discharge rate (MDR) of 5 × 106 kg s−1. The lower intensity, violent strombolian phase coincided with the eruption of the least evolved magma; a peak column height
of 6–9 km, corresponding to an MDR of 1 ×10 6 kg s −1, is estimated from field data. Phreatomagmatic activity played a minor role in the eruption, only contributing to the ash-rich
deposits of U1, U4, U6 and U8. 相似文献
2.
Karen Fontijn Gerald G. J. Ernst Costanza Bonadonna Marlina A. Elburg Evelyne Mbede Patric Jacobs 《Bulletin of Volcanology》2011,73(9):1353-1368
The ~4-ka trachytic Rungwe Pumice (RP) deposit from Rungwe Volcano in South-Western Tanzania is the first Plinian-style deposit
from an African volcano to be closely documented focusing on its physical characterization. The RP is a mostly massive fall
deposit with an inversely graded base. Empirical models suggest a maximum eruption column height H
T of 30.5–35 km with an associated peak mass discharge rate of 2.8–4.8 × 108 kg/s. Analytical calculations result in H
T values of 33 ± 4 km (inversion of TEPHRA2 model on grain size data) corresponding to mass discharge ranging from 2.3 to 6.0 × 108 kg/s. Lake-core data allow extrapolation of the deposit thinning trend far beyond onland exposures. Empirical fitting of
thickness data yields volume estimates between 3.2 and 5.8 km3 (corresponding to an erupted mass of 1.1–2.0 × 1012 kg), whereas analytical derivation yields an erupted mass of 1.1 × 1012 kg (inversion of TEPHRA2 model). Modelling and dispersal maps are consistent with nearly no-wind conditions during the eruption.
The plume corner is estimated to have been ca. 11–12 km from the vent. After an opening phase with gradually increasing intensity,
a high discharge rate was maintained throughout the eruption, without fountain collapse as is evidenced by a lack of pyroclastic
density current deposits. 相似文献
3.
Causes and consequences of bimodal grain-size distribution of tephra fall deposited during the August 2006 Tungurahua eruption (Ecuador) 总被引:2,自引:2,他引:0
Julia Eychenne Jean-Luc Le Pennec Liliana Troncoso Mathieu Gouhier Jean-Marie Nedelec 《Bulletin of Volcanology》2012,74(1):187-205
The violent August 16–17, 2006 Tungurahua eruption in Ecuador witnessed the emplacement of numerous scoria flows and the deposition
of a widespread tephra layer west of the volcano. We assess the size of the eruption by determining a bulk tephra volume in
the range 42–57 × 106 m3, which supports a Volcanic Explosivity Index 3 event, consistent with calculated column height of 16–18 km above the vent
and making it the strongest eruptive phase since the volcano’s magmatic reactivation in 1999. Isopachs west of the volcano
are sub-bilobate in shape, while sieve and laser diffraction grain-size analyses of tephra samples reveal strongly bimodal
distributions. Based on a new grain-size deconvolution algorithm and extended sampling area, we propose here a mechanism to
account for the bimodal grain-size distribution. The deconvolution procedure allows us to identify two particle subpopulations
in the deposit with distinct characteristics that indicate dissimilar transport-depositional processes. The log-normal coarse-grained
subpopulation is typical of particles transported downwind by the main volcanic plume. The positively skewed, fine-grained
subpopulation in the tephra fall layer shares close similarities with the elutriated co-pyroclastic flow ash cloud layers
preserved on top of the scoria flow deposits. The area with the higher fine particle content in the tephra layer coincides
with the downwind prolongation of the pyroclastic flow deposits. These results indicate that the bimodal distribution of grain
size in the Tungurahua fall deposit results from synchronous deposition of lapilli from the main plume and fine ash elutriated
from scoria flows emplaced on the western flank of the volcano. Our study also reveals that inappropriate grain-size data
processing may produce misleading determination of eruptive type. 相似文献
4.
《Journal of Volcanology and Geothermal Research》2007,159(1-3):198-209
Cora Maar is a Quaternary volcano located to the 20 km northwest of Mount Erciyes, the largest of the 19 polygenetic volcanic complexes of the Cappadocian Volcanic Province in central Anatolia. Cora Maar is a typical example of a maar-diatreme volcano with a nearly circular crater with a mean diameter of c.1.2 km, and a well-bedded base surge-dominated maar rim tephra sequence up to 40 m in thickness. Having a diameter/depth ratio (D/d) of 12, Cora is a relatively “mature” maar compared to recent maar craters in the world.Cora crater is excavated within the andesitic lava flows of Quaternary age. The tephra sequence is not indurated, and consists of juvenile clasts up to 70 cm, non-juvenile clasts up to 130 cm, accretionary lapilli up to 1.2 cm in diameter, and ash to lapilli-sized tephra. Base surge layers display well-developed antidune structures indicating the direction of the transport. Both progressive and regressive dune structures are present within the tephra sequence. Wavelength values increase with increasing wave height, and with large wavelength and height values. Cora tephra display similarities to Taal and Laacher See base surge deposits. Impact sags and small channel structures are also common. Lateral and vertical facies changes are observed for the dune bedded and planar bedsets.According to granulometric analyses, Cora Maar tephra samples display a bimodal distribution with a wide range of Mdφ values, characteristic for the surge deposits. Very poorly sorted, bimodal ash deposits generally vary from coarse tail to fine tail grading depending on the grain size distribution while very poorly sorted lapilli and block-rich deposits display a positive skewness due to fine tail grading. 相似文献
5.
Fuego volcano in Guatemala erupted in 1974 in a basaltic sub-Plinian event, which has been well documented and studied. In
1999, after a period of quiescence lasting 20 years, Fuego erupted again, this time less violently, but with persistent low-level
activity. This study investigates the link between these episodes. Previous melt inclusion studies have shown magma erupted
in 1974 to have been a volatile-rich hybrid tapped from a vertically extensive system. By contrast, magma erupted in 1999
and 2003 is similar in composition to that erupted in 1974, but melt inclusions are more evolved. Although melt inclusions
from the later period are CO2 rich (up to ∼1,500 ppm), they have low H2O concentration (max 1.5 wt.%, compared to ∼6 wt.% in 1974). These melt inclusions have a modified H2O concentration due to diffusive re-equilibration at shallow pressures. Despite this diffusive exchange, both eruptions show
evidence of recent mingling of the same low and higher K melts, one of which was slightly cooler than the other and as a result
traversed the amphibole stability field. (210Pb/226Ra) data on selected bulk rock samples from 1974 suggest that whereas the cooler, more evolved end-member may have been degassing
since the last major eruption in the 1930s, the warmer end-member intruded at most a decade prior to the 1974 eruption. The
two end-members are thus batches of the same magma emplaced shallowly ∼30 years apart during which time the older batch was
cooled and differentiated before mixing with the younger influx. The presence of the same two melts in the later eruptions
suggests that magma in 1999 and 2003 is partly residual from 1974. The current eruptive activity is clearing the system of
this residual magma prior to an expected new magma batch. 相似文献
6.
New physical characterization of the Fontana Lapilli basaltic Plinian eruption,Nicaragua 总被引:1,自引:1,他引:0
The Fontana Lapilli deposit was erupted in the late Pleistocene from a vent, or multiple vents, located near Masaya volcano
(Nicaragua) and is the product of one of the largest basaltic Plinian eruptions studied so far. This eruption evolved from
an initial sequence of fluctuating fountain-like events and moderately explosive pulses to a sustained Plinian episode depositing
fall beds of highly vesicular basaltic-andesite scoria (SiO2 > 53 wt%). Samples show unimodal grain size distribution and a moderate sorting that are uniform in time. The juvenile component
predominates (> 96 wt%) and consists of vesicular clasts with both sub-angular and fluidal, elongated shapes. We obtain a
maximum plume height of 32 km and an associated mass eruption rate of 1.4 × 108 kg s−1 for the Plinian phase. Estimates of erupted volume are strongly sensitive to the technique used for the calculation and to
the distribution of field data. Our best estimate for the erupted volume of the majority of the climactic Plinian phase is
between 2.9 and 3.8 km3 and was obtained by applying a power-law fitting technique with different integration limits. The estimated eruption duration
varies between 4 and 6 h. Marine-core data confirm that the tephra thinning is better fitted by a power-law than by an exponential
trend. 相似文献
7.
Petrology and sulfur and chlorine emissions of the 1963 eruption of Gunung Agung,Bali, Indonesia 总被引:3,自引:0,他引:3
The 1963 eruption of Gunung Agung produced 0.95 km3 dense rock equivalent (DRE) of olivine±hornblende-bearing, weakly phyric, basaltic andesite tephra and lava. Evidence for
magma mixing in the eruptive products includes whole-rock compatible and incompatible trace element trends, reverse and complex
compositional zoning of mineral phases, disequilibrium mineral assemblages, sieve-textured plagioclase phenocrysts, and augite
rims on reversely zoned orthopyroxene. Basalt magma mixed with pre-existing andesite magma shortly before eruption to yield
basaltic andesite with a temperature of 1040–1100 °C at an assumed pressure of 2 kb, f O2>NNO, and an average melt volatile content (H2O±CO2) of 4.3 wt.%. Magma-mixing end members may have provided some of the S and Cl emitted in the eruption. Glass inclusions in
phenocrysts contain an average of 650 ppm S and 3130 ppm Cl as compared with 70 ppm and 2220 ppm, respectively, in the matrix
glass. Maximum S and Cl contents of glass inclusions approach 1800 and 5000 ppm, respectively. Application of the petrologic
method to products of the 1963 eruption for estimating volatile release yields of 2.5×1012 g (Mt) of SO2 and 3.4 Mt of Cl released from the 0.65 km3 of juvenile tephra which contributed to stratospheric injection of H2SO4 aerosols on 17 March and 16 May, when eruption column heights exceeded 20 km above sea level. An independent estimate of
SO2 release from atmospheric aerosol loading (11–12 Mt) suggests that approximately 7 Mt of SO2 was injected into the stratosphere. The difference between the two estimates can be most readily accounted for by the partitioning
of S, as well as some Cl, from the magma into a water-rich vapor phase which was released upon eruption. For other recent
high-S-release eruptions of more evolved and oxidized magmas (El Chichón, Pinatubo), the petrologic method gives values two
orders of magnitude less than independent estimates of SO2 emissions. Results from this study of the Agung 1963 magma and its volatile emissions, and from related studies on eruptions
of more mafic magmas, suggest that SO2 emissions from eruptions of higher-S-solubility magma may be more reliably estimated by the petrologic method than may those
from more-evolved magma eruptions.
Received: 29 June 1994 / Accepted: 25 April 1996 相似文献
8.
The Middle Scoria deposit represents an explosive eruption of basaltic andesite magma (54 wt. % SiO2) from Okmok volcano during mid-Holocene time. The pattern of dispersal and characteristics of the ejecta indicate that the
eruption opened explosively, with ash textural evidence for a limited degree of phreatomagmatism. The second phase of the
eruption produced thick vesicular scoria deposits with grain texture, size and dispersal characteristics that indicate it
was violent strombolian to subplinian in style. The third eruptive phase produced deposits with a shift towards grain shapes
that are dense, blocky, and poorly vesicular, and intermittent surge layers, indicating later transitions between magmatic
(violent strombolian) to phreatomagmatic (vulcanian) eruptive styles. Isopach maps yield bulk volume estimates that range
from 0.06 to 0.43 km3, with ~ 0.04 to 0.25 km3 total DRE. The associated column heights and mass discharge values calculated from isopleth maps of individual Middle Scoria
layers are 8.5 – 14 km and 0.4 to 45 × 106 kg/s. The Middle Scoria tephras are enriched in plagioclase microlites that have the textural characteristics of rapid magma
ascent and relatively high degrees of effective undercooling. Those textures probably reflect the rapid magma ascent accompanying
the violent strombolian and subplinian phases of the eruption. In the later stages of the eruption, the plagioclase microlite
number densities decrease and textures include more tabular plagioclase, indicating a slowing of the ascent rate. The findings
on the Middle Scoria are consistent with other explosive mafic eruptions, and show that outside of the two large caldera-forming
eruptions, Okmok is also capable of producing violent mafic eruptions, marked by varying degrees of phreatomagmatism. 相似文献
9.
Perrine Paquereau-Lebti Michel Fornari Pierrick Roperch Jean-Claude Thouret Orlando Macedo 《Bulletin of Volcanology》2008,70(8):977-997
40Ar/39Ar ages and paleomagnetic correlations using characteristic remanent magnetizations (ChRM) show that two main ignimbrite sheets
were deposited at 4.86 ± 0.07 Ma (La Joya Ignimbrite: LJI) and at 1.63 ± 0.07 Ma (Arequipa Airport Ignimbrite: AAI) in the
Arequipa area, southern Peru. The AAI is a 20–100 m-thick ignimbrite that fills in the Arequipa depression to the west of
the city of Arequipa. The AAI is made up of two cooling units: an underlying white unit and an overlying weakly consolidated
pink unit. Radiometric data provide the same age for the two units. As both units record exactly the same well-defined paleomagnetic
direction (16 sites in the white unit of AAI: Dec = 173.7; Inc = 31.2; α95 = 0.7; k = 2749; and 10 sites in the pink unit of AAI; Dec = 173.6; Inc = 30.3; α95 = 1.2; k = 1634), showing no evidence of secular variation, the time gap between emplacement of the two units is unlikely to exceed
a few years. The >50 m thick well-consolidated white underlying unit of the Arequipa airport ignimbrite provides a very specific
magnetic zonation with low magnetic susceptibilities, high coercivities and unblocking temperatures of NRM above 580°C indicating
a Ti-poor titanohematite signature. The Anisotropy of Magnetic Susceptibility (AMS) is strongly enhanced in this layer with
anisotropy values up to 1.25. The fabric delineated by AMS was not recognized neither in the field nor in thin sections, because
most of the AAI consists in a massive and isotrope deposit with no visible textural fabric. Pumices deformation due to welding
is only observed at the base of the thickest sections. AMS within the AAI ignimbrite show a very well defined pattern of apparent
imbrications correlated to the paleotopography, with planes of foliation and lineation dipping often at more than 20° toward
the expected vent, buried beneath the Nevado Chachani volcanic complex. In contrast with the relatively small extent of the
thick AAI, the La Joya ignimbrite covers large areas from the Altipano down the Piedmont. Ti-poor titanomagnetites are the
dominant magnetic carriers and AMS values are generally lower than 1.05. Magnetic foliations are sub horizontal and lineations
directions are scattered in the LJI. The AMS fabrics are probably controlled by post-depositional compaction and welding of
the deposit rather than transport dynamics.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
10.
Charles R. Stern 《Bulletin of Volcanology》2008,70(4):435-454
For regionally widespread Holocene tephra layers in southernmost Patagonia, correlations based on both chemical and chronological
data indicate their derivation from five large-volume (>1 km3) explosive eruptions of four different volcanoes in the southernmost Andes. Bulk-tephra and tephra-glass major and trace-element
chemistry and Sr isotopic ratios unambiguously distinguish different source volcanoes, and imply that two of the regionally
widespread tephra (MB1 and MB2) were derived from Mt. Burney (52°S), one (R1) from Reclus (51°S), one (A1) from Aguilera (50°S) and one (H1) from Hudson volcano (46°S). The H1 tephra derived from the Hudson volcano, which is located at the southern end of the Andean Southern Volcanic Zone (SVZ; 33–46°S),
contains distinctive greenish andesitic glass with FeO > 4.5 wt.% and TiO2 > 1.2 wt.%. In contrast, rhyolitic glass in tephra derived from the eruptions of Mt. Burney, Reclus and Aguilera volcanoes,
which are located in the Andean Austral Volcanic Zone (AVZ; 49–55°S), is clear and transparent and has significantly lower
FeO and TiO2. Tephra derived from these three AVZ volcanoes all contain plagioclase, orthopyroxene, minor clinopyroxene and amphibole.
Biotite occurs only in the Aguilera A1 tephra, which also has the highest bulk-tephra and tephra-glass K2O and Rb contents. Averages of new and published 14C ages determined on organic material in soil and sediment samples above and below these tephra constrain the uncalibrated
14C age of the R1 eruption of Reclus volcano to 12,685 ± 260 years BP, the MB1 and MB2 eruptions of Mt. Burney to 8,425 ± 500 and 3,830 ± 390 years BP, the Hudson H1 eruption to 6,850 ± 160 years BP, and the A1 eruption of Aguilera volcano to 3,000 ± 100 years BP. The volume of the largest of these eruptions, H1 of the Hudson volcano, is estimated as >18 km3. The volume of the Reclus R1 eruption is estimated at >10 km3, the Aguilera A1 eruption at between 4 and 9 km3, and the younger Mt. Burney MB2 eruption at ≥2.8 km3. The volume of the older MB1 Mt. Burney eruption is the least well constrained, but must have been larger than the younger MB2 eruption. The data indicate that the frequency of explosive activity of volcanic centers in the AVZ is lower than in the
southern SVZ. 相似文献
11.
Celine Longchamp C. Bonadonna O. Bachmann A. Skopelitis 《Bulletin of Volcanology》2011,73(9):1337-1352
Explosive eruptions associated with tephra deposits that are only exposed in proximal areas are difficult to characterize.
In fact, the determination of physical parameters such as column height, mass eruption rate, erupted volume, and eruption
duration is mainly based on empirical models and is therefore very sensitive to the quality of the field data collected. We
have applied and compared different modeling approaches for the characterization of the two main tephra deposits, the Lower
Pumice (LP) and Upper Pumice (UP) of Nisyros volcano, Greece, which are exposed only within 5 km of the probable vent. Isopach
and isopleth maps were compiled for two possible vent locations (on the north and on the south rim of the caldera), and different
models were applied to calculate the column height, the erupted volume, and the mass eruption rate. We found a column height
of about 15 km above sea level and a mass eruption rate of about 2 × 107 kg/s for both eruptions regardless of the vent location considered. In contrast, the associated wind velocity for both UP
and LP varied between 0 and 20 m/s for the north and south vent, respectively. The derived erupted volume for the south vent
(considered as the best vent location) ranges between 2 and 27 × 108 m3 for the LP and between 1 and 5 × 108 m3 for the UP based on the application of four different methods (integration of exponential fit based on one isopach line,
integration of exponential and power-law fit based on two isopach lines, and an inversion technique combined with an advection–diffusion
model). The eruption that produced the UP could be classified as subplinian. Discrepancies associated with different vent
locations are smaller than the discrepancies associated with the use of different models for the determination of erupted
mass, plume height, and mass eruption rate. Proximal outcrops are predominantly coarse grained with ≥90 wt% of the clasts
ranging between −6ϕ and 0ϕ. The associated total grainsize distribution is considered to result from a combination of turbulent
fallout from both the plume margins and the umbrella region, and as a result, it is fines-depleted. Given that primary deposit
thickness observed on Nisyros for both LP and UP is between 1 and 8 m, if an event of similar scale were to happen again,
it would have a significant impact on the entire island with major damage to infrastructure, agriculture, and tourism. Neighboring
islands and the continent could also be significantly affected. 相似文献
12.
The source parameters of the Bohai Sea earthquake, July 18, 1969 and Yongshan, Yunnan earthquake, May 11, 1974 were determined
by full — wave theory synthetic seismograms of teleseismic P waves. P+pP+sP wereform were calculated with WKBJ approximation
and real integral paths. One — dimensional unilateral, finite propagation source was also considered. By trail — and — error
in comparing the theoretical seismograms with the observational ones of WWSSN stations, the source parameters were obtained
as follow: for Bohai earthquake, φ=195°, δ=85°, λ=65°,M
o=0.9×1019Nm,L=59.9km.V
R=3.5km/s, ∧
R
=160°; for Yongshan earthquake, φ=240°, δ=80°, ∧=150°,M
o=1.3×1018Nm,L=48.8km,V
R=3km/s, ∧
R
=−10°, where φ is strike, δ dip angle, λ slip angle,M
o seismic moment,L rupture length,V
R rupture propagation speed. As III type fractures the faulting propagated along the fault planes, and ∧
R
is the angle from the strike to the propagation direction. Yongshan earthquake showed complexity in its focal process, having
four sub—ruptures during the first 60 seconds.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 1–8, 1991. 相似文献
13.
Strombolian explosive styles and source conditions: insights from thermal (FLIR) video 总被引:1,自引:3,他引:1
Matthew R. Patrick Andrew J. L. Harris Maurizio Ripepe Jonathan Dehn David A. Rothery Sonia Calvari 《Bulletin of Volcanology》2007,69(7):769-784
Forward Looking Infrared Radiometer (FLIR) cameras offer a unique view of explosive volcanism by providing an image of calibrated
temperatures. In this study, 344 eruptive events at Stromboli volcano, Italy, were imaged in 2001–2004 with a FLIR camera
operating at up to 30 Hz. The FLIR was effective at revealing both ash plumes and coarse ballistic scoria, and a wide range
of eruption styles was recorded. Eruptions at Stromboli can generally be classified into two groups: Type 1 eruptions, which
are dominated by coarse ballistic particles, and Type 2 eruptions, which consist of an optically-thick, ash-rich plume, with
(Type 2a) or without (Type 2b) large numbers of ballistic particles. Furthermore, Type 2a plumes exhibited gas thrust velocities
(>15 m s−1) while Type 2b plumes were limited to buoyant velocities (<15 m s−1) above the crater rim. A given vent would normally maintain a particular gross eruption style (Type 1 vs. 2) for days to
weeks, indicating stability of the uppermost conduit on these timescales. Velocities at the crater rim had a range of 3–101 m
s−1, with an overall mean value of 24 m s−1. Mean crater rim velocities by eruption style were: Type 1 = 34 m s−1, Type 2a = 31 m s−1, Type 2b = 7 m s−1. Eruption durations had a range of 6–41 s, with a mean of 15 s, similar among eruption styles. The ash in Type 2 eruptions
originates from either backfilled material (crater wall slumping or ejecta rollback) or rheological changes in the uppermost
magma column. Type 2a and 2b behaviors are shown to be a function of the overpressure of the bursting slug. In general, our
imaging data support a broadening of the current paradigm for strombolian behavior, incorporating an uppermost conduit that
can be more variable than is commonly considered. 相似文献
14.
On the significance of CO2 inclusions in plagioclase microphenocrysts in tholeiite from Moeraki,New Zealand 总被引:1,自引:0,他引:1
Liquid plus vapour inclusions of CO2 are widespread in plagioclase microphenocrysts in small tholeiitic intrusions and tephra of the Moeraki and adjacent areas
of northeast Otago, New Zealand. They imply the presence of immiscible CO2 droplets in the magma at depths of about 7–14 km. Their presence within 5 μm of the edges of microphenocrysts as little as
35 μm thick and 118 μm long indicates minimal feldspar crystal growth during the final ascent and quenching of the magma.
Delicate branching clusters of lath-like microphenocrysts escaped disruption during this ascent. Such CO2 inclusions are a potential source of ‘excess argon’ perturbing K-Ar age determinations.
Received March 24, 1993/Accepted September 10, 1993 相似文献
15.
Frédéric Dondin Jean-Frédéric Lebrun Karim Kelfoun Nicolas Fournier Auran Randrianasolo 《Bulletin of Volcanology》2012,74(2):595-607
Kick 'em Jenny volcano is the only known active submarine volcano in the Lesser Antilles. It lies within a horseshoe-shaped
structure open to the west northwest, toward the deep Grenada Basin. A detailed bathymetric survey of the basin slope at Kick
'em Jenny and resulting high-resolution digital elevation model allowed the identification of a major submarine landslide
deposit. This deposit is thought to result from a single sector collapse event at Kick 'em Jenny and to be linked to the formation
of the horseshoe-shaped structure. We estimated the volume and the leading-edge runout of the landslide to be ca. 4.4 km3 and 14 km, respectively. We modelled a sector collapse event of a proto Kick 'em Jenny volcano using VolcFlow, a finite difference code based on depth-integrated mass and momentum equations. Our models show that the landslide can be
simulated by either a Coulomb-type rheology with low basal friction angles (5.5°–6.5°) and a significant internal friction
angle (above 17.5°) or, with better results, by a Bingham rheology with low Bingham kinematic viscosity (0 < ν
B < 30 m2/s) and high shear strength (130 < γ ≤ 180 m2/s2). The models and the short runout distance suggest that the landslide travelled as a stiff cohesive flow affected by minimal
granular disaggregation and slumping on a non-lubricated surface. The main submarine landslide deposit can therefore be considered
as a submarine mass slide deposit that behaved like a slump. 相似文献
16.
Uplift of a broad area centered ~6 km west of the summit of South Sister volcano started in September 1997 (onset estimated
from model discussed in this paper) and was continuing when surveyed in August 2006. Surface displacements were measured whenever
possible since August 1992 with satellite radar interferometry (InSAR), annually since August 2001 with GPS and leveling surveys,
and with continuous GPS since May 2001. The average maximum displacement rate from InSAR decreased from 3–5 cm/yr during 1998–2001
to ~1.4 cm/yr during 2004–2006. The other datasets show a similar pattern, i.e., surface uplift and extension rates decreased
over time but deformation continued through August 2006. Our best-fit model to the deformation data is a vertical, prolate,
spheroidal point-pressure source located 4.9–5.4 km below the surface. The source inflation rate decreased exponentially during
2001–2006 with a 1/e decay time of 5.3 ± 1.1 years. The net increase in source volume from September 1997 to August 2006 was 36.5–41.9 x 106 m3. A swarm of ~300 small (M
max = 1.9) earthquakes occurred beneath the deforming area in March 2004; no other unusual seismicity has been noted. Similar
deformation episodes in the past probably would have gone unnoticed if, as we suspect, most are small intrusions that do not
culminate in eruptions. 相似文献
17.
Jennifer L. Lewicki George E. Hilley Laura Dobeck Bruno D. V. Marino 《Bulletin of Volcanology》2012,74(1):135-141
Use of eddy covariance (EC) techniques to map the spatial distribution of diffuse volcanic CO2 fluxes and quantify CO2 emission rate was tested at the Horseshoe Lake tree-kill area on Mammoth Mountain, California, USA. EC measurements of CO2 flux were made during September–October 2010 and ranged from 85 to 1,766 g m−2 day−1. Comparative maps of soil CO2 flux were simulated and CO2 emission rates estimated from three accumulation chamber (AC) CO2 flux surveys. Least-squares inversion of measured eddy covariance CO2 fluxes and corresponding modeled source weight functions recovered 58–77% of the CO2 emission rates estimated based on simulated AC soil CO2 fluxes. Spatial distributions of modeled surface CO2 fluxes based on EC and AC observations showed moderate to good correspondence (R
2 = 0.36 to 0.70). Results provide a framework for automated monitoring of volcanic CO2 emissions over relatively large areas. 相似文献
18.
Lucas Vieira Barros Marcelo Assumpção Ronnie Quintero Vinicius Martins Ferreira 《Journal of Seismology》2011,15(2):391-409
Small local earthquakes from two aftershock sequences in Porto dos Gaúchos, Amazon craton—Brazil, were used to estimate the
coda wave attenuation in the frequency band of 1 to 24 Hz. The time-domain coda-decay method of a single backscattering model
is employed to estimate frequency dependence of the quality factor (Q
c) of coda waves modeled using Qc = Q0 fhQ_{\rm c} =Q_{\rm 0} f^\eta , where Q
0 is the coda quality factor at frequency of 1 Hz and η is the frequency parameter. We also used the independent frequency model approach (Morozov, Geophys J Int, 175:239–252, 2008), based in the temporal attenuation coefficient, χ(f) instead of Q(f), given by the equation
c(f)=g+\fracpfQe \chi (f)\!=\!\gamma \!+\!\frac{\pi f}{Q_{\rm e} }, for the calculation of the geometrical attenuation (γ) and effective attenuation (Qe-1 )(Q_{\rm e}^{-1} ). Q
c values have been computed at central frequencies (and band) of 1.5 (1–2), 3.0 (2–4), 6.0 (4–8), 9.0 (6–12), 12 (8–16), and
18 (12–24) Hz for five different datasets selected according to the geotectonic environment as well as the ability to sample
shallow or deeper structures, particularly the sediments of the Parecis basin and the crystalline basement of the Amazon craton.
For the Parecis basin Qc = (98±12)f(1.14±0.08)Q_{\rm c} =(98\pm 12)f^{(1.14\pm 0.08)}, for the surrounding shield Qc = (167±46)f(1.03±0.04)Q_{\rm c} =(167\pm 46)f^{(1.03\pm 0.04)}, and for the whole region of Porto dos Gaúchos Qc = (99±19)f(1.17±0.02)Q_{\rm c} =(99\pm 19)f^{(1.17\pm 0.02)}. Using the independent frequency model, we found: for the cratonic zone, γ = 0.014 s − 1, Qe-1 = 0.0001Q_{\rm e}^{-1} =0.0001, ν ≈ 1.12; for the basin zone with sediments of ~500 m, γ = 0.031 s − 1, Qe-1 = 0.0003Q_{\rm e}^{-1} =0.0003, ν ≈ 1.27; and for the Parecis basin with sediments of ~1,000 m, γ = 0.047 s − 1, Qe-1 = 0.0005Q_{\rm e}^{-1} =0.0005, ν ≈ 1.42. Analysis of the attenuation factor (Q
c) for different values of the geometrical spreading parameter (ν) indicated that an increase of ν generally causes an increase in Q
c, both in the basin as well as in the craton. But the differences in the attenuation between different geological environments
are maintained for different models of geometrical spreading. It was shown that the energy of coda waves is attenuated more
strongly in the sediments, Qc = (78±23)f(1.17±0.14)Q_{\rm c} =(78\pm 23)f^{(1.17\pm 0.14)} (in the deepest part of the basin), than in the basement, Qc = (167±46)f(1.03±0.04)Q_{\rm c} =(167\pm 46)f^{(1.03\pm 0.04)} (in the craton). Thus, the coda wave analysis can contribute to studies of geological structures in the upper crust, as the
average coda quality factor is dependent on the thickness of sedimentary layer. 相似文献
19.
Kenichiro Tani Richard S. Fiske Yoshihiko Tamura Yukari Kido Jiro Naka Hiroshi Shukuno Rika Takeuchi 《Bulletin of Volcanology》2008,70(5):547-562
Sumisu volcano was the site of an eruption during 30–60 ka that introduced ∼48–50 km3 of rhyolite tephra into the open-ocean environment at the front of the Izu-Bonin arc. The resulting caldera is 8 × 10 km
in diameter, has steep inner walls 550–780 m high, and a floor averaging 900 m below sea level. In the course of five research
cruises to the Sumisu area, a manned submersible, two ROVs, a Deep-Tow camera sled, and dredge samples were used to study
the caldera and surrounding areas. These studies were augmented by newly acquired single-channel seismic profiles and multi-beam
seafloor swath-mapping. Caldera-wall traverses show that pre-caldera eruptions built a complex of overlapping dacitic and
basaltic edifices, that eventually grew above sea level to form an island about 200 m high. The caldera-forming eruption began
on the island and probably produced a large eruption column. We interpret that prodigious rates of tephra fallback overwhelmed
the Sumisu area, forming huge rafts of floating pumice, choking the nearby water column with hyperconcentrations of slowly
settling tephra, and generating pyroclastic gravity currents of water-saturated pumice that traveled downslope along the sea
floor. Thick, compositionally similar pumice deposits encountered in ODP Leg 126 cores 70 km to the south could have been
deposited by these gravity currents. The caldera-rim, presently at ocean depths of 100–400 m, is mantled by an extensive layer
of coarse dense lithic clasts, but syn-caldera pumice deposits are only thin and locally preserved. The paucity of syn-caldera
pumice could be due to the combined effects of proximal non-deposition and later erosion by strong ocean currents. Post-caldera
edifice instability resulted in the collapse of a 15° sector of the eastern caldera rim and the formation of bathymetrically
conspicuous wavy slump structures that disturb much of the volcano’s surface. 相似文献
20.
Numerous measurements of CO2 degassing from the soil, carried out with the accumulation chamber method, indicate that in the period April–July 1995 the upper part of the Fossa cone released a total output of 200 t d–1 of CO2, which corresponds to approximately 1000 t d–1 of steam. These large amounts of fluids are of the same order of magnitude as those released by the high temperature fumarolic
field located inside the crater. The spatial distribution of soil gas fluxes shows that the main structures releasing CO2 are the inner slopes of the crater and a NW–SE line, located NE of the crater rim, which correspond to the main direction
of Vulcano Island active faults. The comparison of the φCO2 maps with the soil temperature distribution, derived from both direct measurements and airborne infrared images, indicates
the occurrence of extensive condensation of fumarolic steam within the upper part of the Fossa cone, whose total amount is
comparable to the rainfall budget. Part of the condensate which originates from this process contributes to the recharge of
the phreatic aquifer of Porto Plain, modifying the chemical and isotopic composition of the groundwater.
Received: 1 September 1995 / Accepted: 8 January 1996 相似文献