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排序方式: 共有95条查询结果,搜索用时 15 毫秒
1.
Andrew J. L. Harris Anna L. Butterworth Richard W. Carlton Ian Downey Peter Miller Pedro Navarro David A. Rothery 《Bulletin of Volcanology》1997,59(1):49-64
Satellite data offer a means of supplementing ground-based monitoring during volcanic eruptions, especially at times or locations
where ground-based monitoring is difficult. Being directly and freely available several times a day, data from the advanced
very high resolution radiometer (AVHRR) offers great potential for near real-time monitoring of all volcanoes across large
(3000×3000 km) areas. Herein we describe techniques to detect and locate activity; estimate lava area, thermal flux, effusion
rates and cumulative volume; and distinguish types of activity. Application is demonstrated using data for active lavas at
Krafla, Etna, Fogo, Cerro Negro and Erebus; a pyroclastic flow at Lascar; and open vent systems at Etna and Stromboli. Automated
near real-time analysis of AVHRR data could be achieved at existing, or cheap to install, receiving stations, offering a supplement
to conventional monitoring methods.
Received: 21 January 1997 / Accepted: 3 April 1997 相似文献
2.
Roberto Sulpizio Daniela Mele Pierfrancesco Dellino Luigi La Volpe 《Bulletin of Volcanology》2005,67(8):743-767
The combined use of field investigation and laboratory analyses allowed the detailed stratigraphic reconstruction of the Pollena eruption (472 AD) of Somma-Vesuvius. Three main eruptive phases were recognized, related either to changes in the eruptive processes and/or to relative changes of melt composition. The eruption shows a pulsating behavior with deposition of pyroclastic fall beds and generation of dilute and dense pyroclastic density currents (PDC). The eruptive mechanisms and transportation dynamics were reconstructed for the whole eruption. Column heights were between 12 and 20 km, corresponding to mass discharge rates (MDR) of 7×106 kg/s and 3.4×107 kg/s. Eruptive dynamics were driven by magmatic fragmentation of a phono-tephritic to tephri-phonolitic magma during Phases I and II, whereas phreatomagmatic fragmentation dominated Phase III. Magma composition varies between phonolitic and tephritic-phonolitic, with melt viscosity likely not in excess of 103 Pa s. The volume of the pyroclastic fall deposits, calculated by using of proximal isopachs, is 0.44 km3. This increases to 1.38 km3 if ash volumes are extrapolated on a log thickness vs. square root area diagram using one distal isopach and column height.Editorial responsibility: R Cioni 相似文献
3.
The presence of volcaniclastic rocks related to the silicic magmatism within the Serra Geral Formation has been a matter of long-standing debate. In this paper, we present extensive documentation that supports the presence and abundance of these rocks in the Jacuí Group, a newly discovered volcaniclastic and epiclastic accumulation in southern Brazil. The Jacuí Group is composed of two interfingered stratigraphic units, the Volta Alegre and Tupanciretã formations, and it represents the uppermost stratigraphic unit of the Paraná Basin. The Volta Alegre Formation is primarily composed of resedimented volcaniclastic tuffites, the pyroclasts which were sourced from the Santa Maria subgroup of the Palmas-type of the Serra Geral Formation. The Tupanciretã Formation is composed of fluvial and aeolian deposits transported towards the north–northwest. Deposition of the Jacuí Group began in the Early Cretaceous (∼132 Ma) and was coeval with the acidic volcanism of the Santa Maria subgroup. This group was deposited in a probable interior sag basin that represents either the beginning of the extension in the inner part of the continent that subsequently migrated to the east or the far-field impact of extensional processes that preceded the break-up of Gondwana and the opening of the South Atlantic Ocean. 相似文献
4.
Pyroclastic deposits from the 1883 eruption of Krakatau are described from areas northeast of the volcano on the islands of Sebesi, Sebuku, and Lagoendi, and the southeast coast of Sumatra. Massive and poorly stratified units formed predominantly from pyroclastic flows and surges that traveled over the sea for distances up to 80 km. Granulometric and lithologic characteristics of the deposits indicate that they represent the complement of proximal subaerial and submarine pyroclastic flow deposits laid down on and close to the Krakatau islands. The distal deposits exhibit a decrease in sorting coefficient, median grain size, and thickness with increasing distance from Krakatau. Crystal fractionation is consistent with the distal facies being derived from the upper part of gravitationally segregated pyroclastic flows in which the relative amount of crystal enrichment and abundance of dense lithic clasts diminished upwards. The deposits are correlated to a major pyroclastic flow phase that occurred on the morning of 27 August at approximately 10 a.m. Energetic flows spread out away from the volcano at speeds in excess of 100 km/h and traveled up to 80 km from source. The flows retained temperatures high enough to burn victims on the SW coast of Sumatra. Historical accounts from ships in the Sunda Straits constrain the area affected by the flows to a minimum of 4x103 km2. At the distal edge of this area the flows were relatively dilute and turbulent, yet carried enough material to deposit several tens of centimeters of tephra. The great mobility of the Krakatau flows from the 10 a.m. activity may be the result of enhanced runout over the sea. It is proposed that the generation of steam at the flow/seawater interface may have led to a reduction in the sedimentation of particles and consequently a delay in the time before the flows ceased lateral motion and became buoyantly convective. The buoyant distal edge of these ash-and steam-laden clouds lifted off into the atmosphere, leading to cooling, condensation, and mud rain. 相似文献
5.
Risk assessment of the impact of pyroclastic currents on the towns located around Vesuvio: a non-linear structural inverse analysis 总被引:2,自引:0,他引:2
L.?NunzianteEmail author M.?Fraldi L.?Lirer P.?Petrosino S.?Scotellaro C.?Cicirelli 《Bulletin of Volcanology》2003,65(8):547-561
In a.d. 79, the catastrophic eruption of Vesuvio, which later was described in two famous letters by Pliny the Younger to Tacitus the Historian, destroyed Pompeii, Hercolaneum, Oplontis and Stabiae, resulting in many thousand of victims. After a few hours of the eruption, the several-kilometre-high volcanic column began to collapse, provoking strong air shocks as well as destructive pyroclastic density currents, which travelled down the volcano slopes. In 2000, an archaeological excavation survey, which was performed on the east slope of the volcano in the Terzigno–Vesuvio area at a distance of about 5 km from the vent, brought to light the ruins of several Roman villas that were completely destroyed by these currents during the a.d. 79 eruption. The present paper proposes a new structural analysis, which starts from the study of the damage produced on partially collapsed masonry walls, and determines the dynamic pressures of the currents that overran this site. The non-linear structural analysis, which is based on strength values obtained by means of experimental tests, is of the 'inverse type' and takes into account the limit behaviour of the ancient Roman masonry. The values of the dynamic pressures that were capable of producing the collapse of the masonry walls were obtained by utilising a modern limit analysis theory. The obtained results show that dynamic pressures of a few kPa (1–5) were able to cause masonry buildings to collapse. These values are consistent with those proposed in some of the latest volcanological studies made by numerical simulations of pyroclastic flow propagation. It is shown here that these dynamic pressures are even able to determine the collapse of both modern reinforced concrete and masonry wall buildings that are largely present in the area. Therefore, in possible future eruptions, dynamic pressures of this magnitude would flatten a large urbanised area, where ~700,000 people are currently living. The obtained results give a better definition of both the risk to pyroclastic currents in possible Vesuvio eruptions and provide new guidelines for construction in the neighbouring zones.Editorial responsibility: A. Woods 相似文献
6.
Large phreatomagmatic vent complex at Coombs Hills, Antarctica: Wet, explosive initiation of flood basalt volcanism in the Ferrar-Karoo LIP 总被引:2,自引:2,他引:2
The Mawson Formation and correlatives in the Transantarctic Mountains and South Africa record an early eruption episode related
to the onset of Ferrar-Karoo flood basalt volcanism. Mawson Formation rocks at Coombs Hills comprise mainly (≥80% vol) structureless
tuff breccia and coarse lapilli tuff cut by irregular dikes and sills, within a large vent complex (>30 km2). Quenched juvenile fragments of generally low but variable vesicularity, accretionary lapilli and country rock clasts within
vent-fill, and pyroclastic density current deposits point to explosive interaction of basalt with groundwater in porous country
rock and wet vent filling debris. Metre-scale dikes and pods of coherent basalt in places merge imperceptibly into peperite
and then into surrounding breccia. Steeply dipping to sub-vertical depositional contacts juxtapose volcaniclastic rocks of
contrasting componentry and grainsize. These sub-vertical tuff breccia zones are inferred to have formed when jets of debris
+ steam + water passed through unconsolidated vent-filling deposits. These jets of debris may have sometimes breached the
surface to form subaerial tephra jets which fed subaerial pyroclastic density currents and fall deposits. Others, however,
probably died out within vent fill before reaching the surface, allowing mixing and recycling of clasts which never reached
the atmosphere. Most of the ejecta that did escape the debris-filled vents was rapidly recycled as vents broadened via lateral
quarrying of country rock and bedded pyroclastic vent-rim deposits, which collapsed along the margins into individual vents.
The unstratified, poorly sorted deposits comprising most of the complex are capped by tuff, lapilli tuff and tuff breccia
beds inferred to have been deposited on the floor of the vent complex by pyroclastic density currents. Development of the
extensive Coombs Hills vent-complex involved interaction of large volumes of magma and water. We infer that recycling of water,
as well as recycling of pyroclasts, was important in maintaining water supply for phreatomagmatic interactions even when aquifer
rock in the vent walls lay far from eruption sites as a consequence of vent-complex widening. The proportion of recycled water
increased with vent-complex size in the same way that the proportion of recycled tephra did. Though water recycling leaves
no direct rock record, the volcaniclastic deposits within the vent complex show through their lithofacies/structural architecture,
lithofacies characteristics, and particle properties clear evidence for extensive and varied recycling of material as the
complex evolved.
Editorial responsibility: J. Donnelly-Nolan 相似文献
7.
8.
Ignimbrites of the 13-ka Upper Laacher See Tephra were deposited from small, highly concentrated, moderately fluidized pyroclastic
flows. Their unconsolidated nature, and the prominence of accidental Devonian slate fragments, make these ignimbrites ideal
for clast fabric studies. The upper flow unit of ignimbrite M14 has characteristics typical of a type-2 ignimbrite. Layer
2a and the lower part of layer 2b of the flow unit have strong, upstream-inclined a[p] fabrics (a[p] means long particle axes
parallel to flow direction). Only clasts with a/b axial ratios of 2.5 or greater preserve good a[p] fabrics, whereas the a–b
planes of flat fragments dip upstream irrespective of axial ratio. The a-axis fabric becomes weaker, flatter, and more girdle-like
in the upper half of layer 2b. At one locality the a-axis fabric appears to rotate 40° up through the flow unit, suggesting
either shear decoupling of different levels in the moving flow or unsteadiness effects in a flow depositing progressively
at its base. The existence of similarly strong a[p] fabrics in layer 2a and the lower half of layer 2b appears inconsistent
with the common interpretation that ignimbrite flow units are emplaced as a plug of essentially non-shearing material (layer
2b) on a thin shear layer (layer 2a), and that the entire flow freezes en masse to form the deposit. The data suggest that,
if the flow froze en masse, it was shearing pervasively through at least half its thickness. Another possibility is that the
flow unit aggraded progressively from the base up, and that the fabrics record the integrated history of shear directions
and intensities immediately above the bed throughout the duration of deposition.
Received: 13 February 1997 / Accepted: 4 April 1998 相似文献
9.
Sheathfolds in rheomorphic ignimbrites 总被引:1,自引:1,他引:0
Structural reappraisal of several classic rheomorphic ignimbrites in Colorado, Idaho, the Canary Islands and Italy has, for the first time, revealed abundant oblique folds, curvilinear folds and sheathfolds which formed during emplacement. Like their equivalents in tectonic shear-zones, the sheathfold axes lie sub-parallel to a pervasive elongation lineation, and appear as eye structures on rock surfaces normal to the transport direction. With the recognition of sheathfolds, ignimbrites previously inferred to have undergone complex rheomorphic deformation histories are re-interpreted as recording a single, progressive deformation event. In some examples, the trends of sheathfolds and related lineations change with height through a single ignimbrite suggesting that rheomorphism did not affect the entire thickness of ignimbrite synchronously. Instead, we infer that in these ignimbrites a thin ductile shear-zone rose gradually through the aggrading agglutinating mass whilst the flow direction varied with time. This suggests that, in some cases, both welding and rheomorphism can be extremely rapid, with ductile strain rates significantly exceeding rates of ignimbrite aggradation.Editorial responsibility: T. Druitt 相似文献
10.
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