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1.
Searching for strange attractor in wastewater flow 总被引:1,自引:0,他引:1
H. S. Kim Y. N. Yoon J. H. Kim 《Stochastic Environmental Research and Risk Assessment (SERRA)》2001,15(5):399-413
Chaos is a complex and irregular world in contrast with simple and regular natures of linear systems. Scientists and engineers
have invoked low-dimensional chaos for understanding the nature of real systems. In this study, the complex behavior of a
daily wastewater flow and evidence of deterministic nonlinear dynamics are investigated. The analysis involves both a metric
approach of the correlation dimension and a topological technique called the close returns plot. The estimation procedure
of delay time and delay time window is reviewed using a new technique called the C–C method for the state space reconstruction.
And both parameters are used for estimating the correlation dimension. As a result, the daily wastewater flow shows no evidence
of chaotic dynamics, which implies that stochastic models rather than deterministic chaos may be more appropriate for representing
an investigated series. 相似文献
2.
Remotely sensed observations of sea-level anomaly and sea-surface temperature have been assimilated into an implementation
of the Miami Isopycnic Coordinate Ocean Model (MICOM) for the Indian Ocean using the Ensemble Kalman Filter (EnKF). The system
has been applied in a hindcast validation experiment to examine the properties of the assimilation scheme when used with a
full ocean general circulation model and real observations. This work is considered as a first step towards an operational
ocean monitoring and forecasting system for the Indian Ocean. The assimilation of real data has demonstrated that the sequential
EnKF can efficiently control the model evolution in time. The use of data assimilation requires a significant amount of additional
processing and computational resources. However, we have tried to justify the cost of using a sophisticated assimilation scheme
by demonstrating strong regional and temporal dependencies of the covariance statistics, which include highly anisotropic
and flow-dependent correlation functions. In particular, we observed a marked difference between error statistics in the equatorial
region and at off-equatorial latitudes. We have also demonstrated how the assimilation of SLA and SST improves the model fields
with respect to real observations. Independent in situ temperature profiles have been used to examine the impact of assimilating
the remotely sensed observations. These intercomparisons have shown that the model temperature and salinity fields better
resemble in situ observations in the assimilation experiment than in a model free-run case. On the other hand, it is also
expected that assimilation of in situ profiles is needed to properly control the deep ocean circulation.
Received: 8 January 2002 / Accepted: 8 April 2002 相似文献
3.
The Chillos Valley Lahar (CVL), the largest Holocene debris flow in area and volume as yet recognized in the northern Andes,
formed on Cotopaxi volcano's north and northeast slopes and descended river systems that took it 326 km north–northwest to
the Pacific Ocean and 130+ km east into the Amazon basin. In the Chillos Valley, 40 km downstream from the volcano, depths
of 80–160 m and valley cross sections up to 337 000 m2 are observed, implying peak flow discharges of 2.6–6.0 million m3/s. The overall volume of the CVL is estimated to be ≈3.8 km3. The CVL was generated approximately 4500 years BP by a rhyolitic ash flow that followed a small sector collapse on the north
and northeast sides of Cotopaxi, which melted part of the volcano's icecap and transformed rapidly into the debris flow. The
ash flow and resulting CVL have identical components, except for foreign fragments picked up along the flow path. Juvenile
materials, including vitric ash, crystals, and pumice, comprise 80–90% of the lahar's deposit, whereas rhyolitic, dacitic,
and andesitic lithics make up the remainder. The sand-size fraction and the 2- to 10-mm fraction together dominate the deposit,
constituting ≈63 and ≈15 wt.% of the matrix, respectively, whereas the silt-size fraction averages less than ≈10 wt.% and
the clay-size fraction less than 0.5 wt.%. Along the 326-km runout, these particle-size fractions vary little, as does the
sorting coefficient (average=2.6). There is no tendency toward grading or improved sorting. Limited bulking is recognized.
The CVL was an enormous non-cohesive debris flow, notable for its ash-flow origin and immense volume and peak discharge which
gave it characteristics and a behavior akin to large cohesive mudflows. Significantly, then, ash-flow-generated debris flows
can also achieve large volumes and cover great areas; thus, they can conceivably affect large populated regions far from their
source. Especially dangerous, therefore, are snow-clad volcanoes with recent silicic ash-flow histories such as those found
in the Andes and Alaska.
Received: 28 April 1997 / Accepted: 19 August 1997 相似文献
4.
Additional data from proximal areas enable a reconstruction of the stratigraphy and the eruptive chronology of phases III
and IV of the 1982 eruption of El Chichón Volcano. Phase III began on 4 April at 0135 GMT with a powerful hydromagmatic explosion
that generated radially fast-moving (∼100 ms–1) pyroclastic clouds that produced a surge deposit (S1). Due to the sudden reduction in the confining pressure the process
continued by tapping of magma from a deeper source, causing a new explosion. The ejected juvenile material mixed with large
amounts of fragmented dome and wall rock, which were dispersed laterally in several pulses as lithic-rich block-and-ash flow
(F1). Partial evacuation of juvenile material from the magmatic system prompted the entrance of external water to generate
a series of hydromagmatic explosions that dispersed moisture-rich surge clouds and small-volume block-and-ash flows (IU) up
to distances of 3 km from the crater. The eruption continued by further decompression of the magmatic system, with the ensuing
emission of smaller amounts of gas-rich magma which, with the strong erosion of the volcanic conduit, formed a lithic-rich
Plinian column that deposited fallout layer B. Associated with the widening of the vent, an increase in the effective density
of the uprising column took place, causing its collapse. Block-and-ash flows arising from the column collapse traveled along
valleys as a dense laminar flow (F2). In some places, flow regime changes due to topographic obstacles promoted transformation
into a turbulent surge (S2) which attained minimum velocities of approximately 77 ms–1 near the volcano. The process continued with the formation of a new column on 4 April at 1135 GMT (phase IV) that emplaced
fall deposit C and was followed by hydromagmatic explosions which produced pyroclastic surges (S3).
Received: 13 May 1996 / Accepted: 12 November 1996 相似文献
5.
Calculation of lava effusion rates from Landsat TM data 总被引:1,自引:0,他引:1
Andrew J. L. Harris Luke P. Flynn Laszlo Keszthelyi Peter J. Mouginis-Mark Scott K. Rowland Joseph A. Resing 《Bulletin of Volcanology》1998,60(1):52-71
We present a thermal model to calculate the total thermal flux for lava flowing in tubes, on the surface, or under shallow
water. Once defined, we use the total thermal flux to estimate effusion rates for active flows at Kilauea, Hawaii, on two
dates. Input parameters were derived from Landsat Thematic Mapper (TM), field and laboratory measurements. Using these parameters
we obtain effusion rates of 1.76±0.57 and 0.78±0.27 m3 s–1 on 23 July and 11 October 1991, respectively. These rates are corroborated by field measurements of 1.36±0.14 and 0.89±0.09 m3 s–1 for the same dates (Kauahikaua et al. 1996). Using weather satellite (AVHRR) data of lower spatial resolution, we obtain
similar effusion rates for an additional 26 dates between the two TM-derived measurements. We assume that, although total
effusion rates at the source declined over the period, the shut down of the ocean entry meant that effusion rates for the
surface flows alone remained stable. Such synergetic use of remotely sensed data provides measurements that can (a) contribute
to monitoring flow-field evolution, and (b) provide reliable numerical data for input into rheological and thermal models.
We look forward to being able to produce estimates for effusion rates using data from high-spatial-resolution sensors in the
earth observing system (EOS) era, such as Landsat 7, the hyperspectral imager, the advanced spaceborne thermal emission spectrometer,
and the advanced land imager.
Received: 25 July 1997 / Accepted: 26 February 1998 相似文献
6.
C. Yoo 《Stochastic Environmental Research and Risk Assessment (SERRA)》2002,16(3):175-187
As the use of space-based sensors to observe soil moisture is becoming more plausible, it is becoming necessary to validate
the remotely sensed soil moisture retrieval algorithms. In this paper, measurements of point gauges on the ground are analyzed
as a possible ground-truth source for the comparison with remotely sensed data. The design compares a sequence of measurements
taken on the ground and from space. The authors review the mean square error of expected differences between the two systems
by Ha and North (1994), which is applied to the Little Washita watershed using the soil moisture dynamics model developed
by Entekhabi and Rodriguez-Iturbe (1994). The model parameters estimated by Yoo and Shin (1998) for the Washita `92 (relative)
soil moisture data are used in this study. By considering about 20 pairs of ground- and space-based measure-ments (especially,
for the same case as the Washita `92 that the space-based sensor visits the FOV once a day), the expected error was able to
be reduced to approximately 10 of the standard deviation of the fluctuations of the system alone. This seems to be an acceptable level of tolerance for
identifying biases in the retrieval algorithms. 相似文献
7.
A. W. Heemink A. J. Segers 《Stochastic Environmental Research and Risk Assessment (SERRA)》2002,16(3):225-240
The Kalman filter is used in this paper as a framework for space time data analysis. Using Kalman filtering it is possible
to include physically based simulation models into the data analysis procedure. Attention is concentrated on the development
of fast filter algorithms to make Kalman filtering feasible for high dimensional space time models. The ensemble Kalman filter
and the reduced rank square root filter algorithm are briefly summarized. A new algorithm, the partially orthogonal ensemble
Kalman filter is introduced too. We will illustrate the performance of the Kalman filter algorithms with a real life air pollution
problem. Here ozone concentrations in a part of North West Europe are estimated and predicted. 相似文献
8.
Victims from volcanic eruptions: a revised database 总被引:1,自引:1,他引:1
The number of victims from volcanism and the primary cause(s) of death reported in the literature show considerable uncertainty.
We present the results of investigations carried out either in contemporary accounts or in specific studies of eruptions that
occurred since A.D. 1783. More than 220 000 people died because of volcanic activity during this period, which includes approximately
90% of the recorded deaths throughout history. Most of the fatalities resulted from post-eruption famine and epidemic disease
(30.3%), nuées ardentes or pyroclastic flows and surges (26.8%), mudflows or lahars (17.1%), and volcanogenic tsunamis (16.9%).
At present, however, international relief efforts might reduce the effects of post-eruption crop failure and disease, and
at least some of the lahars could be anticipated in time by adequate scientific and social response. Thus, mitigation of hazards
from pyroclastic flows and tsunamis will become of paramount importance to volcanologists and civil authorities.
Received: 3 August 1997 / Accepted: 10 April 1998 相似文献
9.
Pierre Delmelle Minoru Kusakabe Alain Bernard Tobias Fischer Simon de Brouwer Esfeca del Mundo 《Bulletin of Volcanology》1998,59(8):562-576
The hydrologic structure of Taal Volcano has favored development of an extensive hydrothermal system whose prominent feature
is the acidic Main Crater Lake (pH<3) lying in the center of an active vent complex, which is surrounded by a slightly alkaline
caldera lake (Lake Taal). This peculiar situation makes Taal prone to frequent, and sometimes catastrophic, hydrovolcanic
eruptions. Fumaroles, hot springs, and lake waters were sampled in 1991, 1992, and 1995 in order to develop a geochemical
model for the hydrothermal system. The low-temperature fumarole compositions indicate strong interaction of magmatic vapors
with the hydrothermal system under relatively oxidizing conditions. The thermal waters consist of highly, moderately, and
weakly mineralized solutions, but none of them corresponds to either water–rock equilibrium or rock dissolution. The concentrated
discharges have high Na contents (>3500 mg/kg) and low SO4/Cl ratios (<0.3). The Br/Cl ratio of most samples suggests incorporation of seawater into the hydrothermal system. Water
and dissolved sulfate isotopic compositions reveal that the Main Crater Lake and spring discharges are derived from a deep
parent fluid (T≈300 °C), which is a mixture of seawater, volcanic water, and Lake Taal water. The volcanic end member is
probably produced in the magmatic-hydrothermal environment during absorption of high-temperature gases into groundwater. Boiling
and mixing of the parent water give rise to the range of chemical and isotopic characteristics observed in the thermal discharges.
Incursion of seawater from the coastal region to the central part of the volcano is supported by the low water levels of the
lakes and by the fact that Lake Taal was directly connected to the China sea until the sixteenth century. The depth to the
seawater-meteoric water interface is calculated to be 80 and 160 m for the Main Crater Lake and Lake Taal, respectively. Additional
data are required to infer the hydrologic structure of Taal. Geochemical surveillance of the Main Crater Lake using the SO4/Cl, Na/K, or Mg/Cl ratio cannot be applied straightforwardly due to the presence of seawater in the hydrothermal system.
Received: 12 February 1997 / Accepted: 26 January 1998 相似文献
10.
The role of seamounts in the formation and evolution of sea ice is investigated in a series of numerical experiments with
a coupled sea ice–ocean model. Bottom topography, stratification and forcing are configured for the Maud Rise region in the
Weddell Sea. The specific flow regime that develops at the seamount as the combined response to steady and tidal forcing consists
of free and trapped waves and a vortex cap, which is caused by mean flow and tidal flow rectification. The enhanced variability
through tidal motion in particular modifies the mixed layer above the seamount enough to delay and reduce sea-ice formation
throughout the winter. The induced sea-ice anomaly spreads and moves westward and affects an area of several 100 000 km2. Process studies reveal the complex interaction between wind, steady and periodic ocean currents: all three are required
in the process of generation of the sea ice and mixed layer anomalies (mainly through tidal flow), their detachment from the
topography (caused by steady oceanic flow) and the westward translation of the sea-ice anomaly (driven by the time-mean wind). 相似文献
11.
Lascar Volcano (22°22'S, 67°44'W) is the most active volcano of the central Andes of northern Chile. Activity since 1984
has been characterised by periods of lava dome growth and decay within the active crater, punctuated by explosive eruptions.
We present herein a technique for monitoring the high-temperature activity within the active crater using frequent measurements
of emitted shortwave infrared (SWIR) radiation made by the spaceborne along-track scanning radiometer (ATSR). The ATSR is
an instrument of low spatial resolution (pixels 1 km across) that shares certain characteristics with the MODIS instrument,
planned for use as a volcano monitoring tool in the NASA EOS Volcanology Project. We present a comprehensive time series of
over 60 cloud- and plume-free nighttime ATSR observations for 1992–1995, a period during which Lascar experienced its largest
historical eruption. Variations in short wavelength infrared flux relate directly to changes in high-temperature surfaces
within the active crater. From these data, interpretations can be made that supplement published field reports and that can
document the presence and status of the lava dome during periods where direct, ground-based, observations are lacking. Our
data agree with less frequent information collected from sensors with high spatial resolution, such as the Landsat thematic
mapper (Oppenheimer et al. 1993) and are consistent with field observations and models that relate subsidence of the dome
to subsequent explosive eruptions (Matthews et al., 1997). Most obviously, Lascar's major April 1993 eruption follows a period
in which the magnitude of emitted shortwave infrared radiation fell by 90%. At this time subsidence of the 1991–1992 lava
dome was reported by field observers and this subsidence is believed to have impeded the escape of hot volatiles and ultimately
triggered the eruption (Smithsonian Institution 1993a). Extrapolating beyond the period for which field observations of the
summit are available, our data show that the vulcanian eruption of 20 July 1995 occurred after a period of gradual increase
in short wavelength infrared flux throughout 1994 and a more rapid flux decline during 1995. We attribute this additional,
otherwise undocumented, cycle of increasing and decreasing SWIR radiance as most likely representing variations in degassing
through fumaroles contained within the summit crater. Alternatively, it may reflect a cycle of dome growth and decay. The
explosive eruption of 17 December 1993 appears to have followed a similar, but shorter, variation in SWIR flux, and we conclude
that large explosive eruptions are more likely when the 1.6-μm signal has fallen from a high to a low level. The ATSR instrument
offers low-cost data at high temporal resolution. Despite the low spatial detail of the measurements, ATSR-type instruments
can provide data that relate directly to the status of Lascar's lava dome and other high-temperature surfaces. We suggest
that such data can therefore assist with predictions of eruptive behaviour, deduced from application of physical models of
lava dome development at this and similar volcanoes.
Received: 1 October 1996 / Accepted: 13 January 1997 相似文献
12.
Fumarolic activity of Avachinsky and Koryaksky volcanoes, Kamchatka, from 1993 to 1994 总被引:1,自引:0,他引:1
Yuri A. Taran Charles B. Connor Vyacheslav N. Shapar Alexandre A. Ovsyannikov Arthur A. Bilichenko 《Bulletin of Volcanology》1997,58(6):441-448
Volcanic gas and condensate samples were collected in 1993–1994 from fumaroles of Koryaksky and Avachinsky, basaltic andesite
volcanoes on the Kamchatka Peninsula near Petropavlovsk–Kamchatsky. The highest-temperature fumarolic discharges, 220 °C
at Koryaksky and 473 °C at Avachinsky, are water-rich (940–985 mmol/mol of H2O) and have chemical and isotopic characteristics typical of Kamchatka–Kurile, high- and medium-temperature volcanic gases.
The temperature and chemical and water isotopic compositions of the Koryaksky gases have not changed during the past 11 years.
They represent an approximate 2 : 1 mixture of magmatic and meteoric end members. Low-temperature, near-boiling-point discharges
of Avachinsky Volcano are water poor (≈880 mmol/mol); Their compositions have not changed since the 1991 eruption, and are
suggested to be derived from partially condensed magmatic gases at shallow depth. Based on a simple model involving mixing
and single-step steam separation, low water and high CO2 contents, as well as the observed Cl concentration and water isotopic composition in low-temperature discharges, are the
result of near-surface boiling of a brine composed of the almost pure condensed magmatic gas. High methane content in low-temperature
Avachinsky gases and the 220 °C Koryaksky fumarole, low C isotopic ratio in CO2 at Koryaksky (–11.8‰), and water isotope data suggest that the "meteoric" end member contains considerable amounts of the
regional methane-rich thermal water discovered in the vicinity of both volcanoes.
Received: 2 May 1996 / Accepted: 5 November 1996 相似文献
13.
Guido Ventura 《Bulletin of Volcanology》1998,59(6):394-403
A basaltic andesite lava flow from Porri Volcano (Salina, Southern Tyrrhenian Sea) is composed of two different magmas. Magma
A (51 vol.% of crystals) has a dacitic glass composition, and magma B (18 vol.% of crystals), a basaltic glass composition.
Magma B is hosted in A and consists of sub-spherical enclaves and boudin-like, banding and rolling structures (RS). Four types
of RS have been recognized: σ–type;δ–type; complex σ-δ–types and transitional structures between sub-spherical enclaves and rolling structures. An analysis of the RS has been performed
in order to reconstruct the flow kinematics and the mechanism of flow emplacement. Rolling structures have been selected in
three sites located at different distances from the vent. In all sites most RS show the same sense of shear. Kinematic analysis
of RS allows the degree of flow non-coaxiality to be determined. The non-coaxiality is expressed by the kinematic vorticity
number Wk, a measure of the ratio Sr between pure shear strain rate and simple shear strain rate. The values of Wk calculated from the measured shapes of microscopic RS increase with increasing distance from the vent, from approximately
0.5 to 0.9. Results of the structural analysis reveal that the RS formed during the early–intermediate stage of flow emplacement.
They represent originally sub-spherical enclaves deformed at low shear strain. At higher strain, RS deformed to give boudin-like
and stretched banding structures. Results of the kinematic analysis suggest that high viscosity lava flows are heterogeneous
non-ideal shear flows in which the degree of non-coaxiality increases with the distance from the vent. In the vent area, deformation
is intermediate between simple shear and pure shear. Farther from the vent, deformation approaches ideal simple shear. Lateral
extension processes occur only in the near-vent zone, where they develop in response to the lateral push of magma extruded
from the vent. Lateral shortening processes develop in the distal zone and record the gravity-driven movement of the lava.
The lava flow advanced by two main mechanisms, lateral translation and rolling motion. Lateral translation equals rolling
near the vent, while rolling motion prevailed in the distal zones.
Received: 6 November 1997 / Accepted: 29 November 1997 相似文献
14.
To test the potential of heat flux prospecting in active volcanic areas using shallow temperature data taken along vertical
profiles, we carried out two thermal profile surveys, one not far from Yasur cone on Tanna Island, and another inside the
caldera of Ambrym (New Hebrides arc, southwestern Pacific). The basic steady heat flux of internal volcanic origin was determined,
taking into account both conductive and convective heat transfers. At both locations there exists, over small distances, significant
differences in the heat flux. These differences correspond to shallow sources of heat. The use of a network of vertical profiles
allowed: (a) heat flux mapping; (b) location of shallow volcanic heat sources; and (c) observation of the detailed structure
of the heat release at quiescent but active volcanoes.
Received: 18 July 1997 / Accepted: 13 May 1998 相似文献
15.
Dike propagation and dilation increases the compression of adjacent rocks. On volcanoes, especially oceanic shields, dikes
are accordingly thought to be structurally destabilizing. As compression is incremented, volcanic flanks are driven outward
or downslope and thus increase their susceptibility to destructive earthquakes and giant landslides. We show, however, that
the 2-m-thick dike emplaced along the east rift zone of Kilauea in 1983 actually stabilized that volcano's flank. Specifically,
production of flank earthquakes dropped more than twofold after 1983 as maximum downslope motion slowed to 6 cm·year–1 from approximately 40 cm·year–1 during 1980–1982. As much as 65 cm of deflationary subsidence above Kilauea's summit and upper rift zones accompanied the
dike intrusion. According to recent estimates, this deflation corresponds to a reduction in magma-reservoir pressure of approximately
4 MPa, probably about as much as the driving pressure of the 1983 dike. The volume of the dike, approximately 0.10–0.15 km3, is orders of magnitude less than the estimated 200- to 250-km3 volume of Kilauea's reservoir of magma and nearby hot, mushy rock. Thus, deflation of that reservoir reduces the compressional
load on the flank over a much larger area than intrusion of the dike adds to it, particularly at the dominant depth of seismicity,
8–9 km. A Coulomb block model for flank motion during intervals between major earthquakes requires the low-angle fault beneath
Kilauea's flank to exhibit slip weakening, conducive to earthquake instability. Accordingly, the triggering mechanism of destructive
earthquakes, several of which have struck Hawaii during the past 150 years, need not require stresses accumulated by dike
intrusions.
Received: 27 October 1998 / Accepted: 24 May 1999 相似文献
16.
Two methods were used to quantify the flux of volcanic sulphur (as the equivalent mass of SO2) to the stratosphere over different timescales during the Holocene. A combination of satellite-based measurements of sulphur
yields from recent explosive volcanic eruptions with an appropriate rate of explosive volcanism for the past 200 years constrains
the medium-term (∼102 years) flux of volcanic sulphur to the stratosphere to be ∼1 Mt a–1, with lower and upper bounds of 0.3 and 3 Mt a–1. The short-term (∼10- to 20-year) flux due to small magnitude (1010–1012 kg) eruptions is of the order of 0.4 Mt a–1. At any time the instantaneous levels of sulphur in the stratosphere are dominated by the most recent (0–3 years) volcanic
events. The flux calculations do not attempt to address this very short timescale variability. Although there are significant
errors associated with the raw sulphur emission data on which this analysis is based, the approach presented is general and
may be readily modified as the quantity and quality of the data improve. Data from a Greenland ice core support these conclusions.
Integration of the sulphate signals from presumed volcanic sources recorded in the GISP2 core provides a minimum estimate
of the 103–year volcanic SO2 flux to the stratosphere of 0.5–1 Mt a–1 over the past 9000 years. The short-term flux calculations do not account for the impact of rare, large events. The ice-core
record does not fully account for the contribution from small, frequent events.
Received: 27 September 1995 / Accepted: 13 December 1995 相似文献
17.
A discontinuous pumiceous sand, a few centimeters to tens of centimeters thick, is located up to 15 m above mean high tide
within Holocene peat along the northern Bristol Bay coastline of Alaska. The bed consists of fine-to-coarse, poorly to moderately
well-sorted, pumice-bearing sand near the top of a 2-m-thick peat sequence. The sand bed contains rip-up clasts of peat and
tephra and is unique in the peat sequence. Major element compositions of juvenile glass from the deposit and radiocarbon dating
of enclosing peat support correlation of the pumiceous sand with the caldera-forming eruption of Aniakchak Volcano. The distribution
of the sand and its sedimentary characteristics are consistent with emplacement by tsunami. The pumiceous sand most likely
represents redeposition by tsunami of climactic fallout tephra and beach sand during the approximately 3.5 ka Aniakchak caldera-forming
eruption on the Alaska Peninsula. We propose that a tsunami was generated by the sudden entrance of a rapidly moving, voluminous
pyroclastic flow from Aniakchak into Bristol Bay. A seismic trigger for the tsunami is unlikely, because tectonic structures
suitable for tsunami generation are present only south of the Alaska Peninsula. The pumiceous sand in coastal peat of northern
Bristol Bay is the first documented geologic evidence of a tsunami initiated by a volcanic eruption in Alaska.
Received: 3 December 1997 / Accepted: 11 April 1998 相似文献
18.
Segregation structures in vapor-differentiated basaltic flows 总被引:1,自引:0,他引:1
Martial Caroff René C. Maury Joseph Cotten Jean-Philippe Clément 《Bulletin of Volcanology》2000,62(3):171-187
Vesicle cylinders represent a spectacular kind of segregation structure involving residual liquids formed in situ during
the cooling of lava flows. These vertical pipes, commonly found within basalt flows typically 2–10 m thick, are interpreted
as the product of a vapor-driven differentiation process. The olivine phenocrysts and the earliest generation of groundmass
olivines found in cylinder-bearing basalts appear to have been generally affected by magmatic oxidation, resulting in high-temperature
iddingsite (HTI) alteration. This feature is also observed within cylinder-free basalt flows which exhibit other kinds of
vesicular segregation structures, such as vesicle-rich pegmatoid segregation sheets and/or segregation vesicles. Detailed
textural, petrological, and geochemical characteristics of two types of cylinders, three types of vesicle sheets, and five
types of segregation vesicles are described, based on the study of 12 occurrences of HTI-bearing basalt flows from oceanic
shield volcanoes or continental basalt plateaus. We propose a general classification of these segregation structures likely
to derive from vapor differentiation. Flow thickness is probably the main factor influencing their morphology. Finally, we
suggest that the concomitant occurrence of olivine oxidation and vapor-differentiation effects results from the late persistence
of water oversaturation after eruption, perhaps due to a high rate of magma ascent.
Received: 27 March 1999 / Accepted: 15 February 2000 相似文献
19.
We introduce a 3D model for near-vent channelized lava flows. We assume the lava to be an isothermal Newtonian liquid flowing
in a rectangular channel down a constant slope. The flow velocity is calculated with an analytical steady-state solution of
the Navier-Stokes equation. The surface velocity and the flow rate are calculated as functions of the flow thickness for different
flow widths, and the results are compared with those of a 2D model. For typical Etna lava flow parameters, the influence of
levees on the flow dynamics is significant when the flow width is less than 25 m. The model predicts the volume flow rate
corresponding to the surface velocity, taking into account that both depend on flow thickness. The effusion rate is a critical
parameter to evaluate lava flow hazard. We propose a model to calculate the effusion rate given the lava flow width, the topograhic
slope, the lava density, the surface flow velocity, and either the lava viscosity or the flow thickness.
Received: 20 January 1998 / Accepted: 8 January 1999 相似文献
20.
The 1991–1993 lava flow is the most voluminous flow erupted at Mount Etna, Sicily, in over 300 years. Estimates of the volume
obtained by various methods range from 205×106 m3 (Tanguy 1996) to over 500×106 m3 (Barberi et al. 1993). This paper describes the results of an electronic distance measurement (EDM)-based field survey of
the upper surface of the 1991–1993 flow field undertaken in 1995. The results were digitised, interpolated and converted into
a digital elevation model and then compared with a pre-eruption digital elevation model, constructed from a 1 : 25 000 contour
map of the area, based on 1989 aerial photographs. Our measurements are the most accurate to date and show that the 1991–1993
lava flow occupies a volume of 231±29×106 m3.
Received: 20 July 1996 / Accepted: 5 November 1996 相似文献