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Understanding the process of volcanic lateral collapse, which may be governed by numerous possible factors, can be significantly improved by identifying the role of each factor. Here we test the perturbation induced in a volcano by tectonic normal faulting in the basement, magma inflation and multiple flank deformation, based on fieldwork and analogue experiments. Ollagüe Volcano (Chile‐Bolivia) provides a good example of a sector collapse with exposed substrate extensional tectonics, and our experiments have been done with conditions consistent with field data. Results show that none of the possible tectonic conditions led to complete lateral failure; in agreement also with the field data, sector collapse of the model cone occurred only when a shallow magmatic intrusion within the volcano was reproduced. We also found out that volcano flank deformation is enhanced if a previous flank destabilization occurred, interleaved by new cone growth. Terra Nova, 18, 282–289, 2006 相似文献
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G. Giovannini G. B. Taylor E. Arbizzani M. Bondi W. D. Cotton L. Feretti L. Lara T. Venturi 《New Astronomy Reviews》1999,43(8-10)
We report on centimeter VLA and VLBI observations of the giant, low power radio galaxy 1144+35. On the parsec scale, we see a complex jet component moving away from the center of activity at 2.7h50−1 c. We detect a faint parsec-scale counter-jet and derive a jet velocity of 0.95c and an angle to the line of sight of 25°, consistent with an intrinsically symmetric ejection. These findings lend credence to the claim that even the jets of low-power radio galaxies start out relativistically. 相似文献
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Mauro Coltelli Paola Del Carlo Luigina Vezzoli 《International Journal of Earth Sciences》2000,89(3):665-677
The pyroclastic deposits of Etna have been correlated over the whole volcanic edifice for the first time, allowing the construction of a continuous record of tephra-producing events, which extends from approximately 100 ka to the Present. In this interval, five main periods of explosive activity have been identified: (a) ~100-ka strombolian to subplinian activity; (b) 80- to 100-ka plinian benmoreitic activity; (c) 16- to 80-ka strombolian to subplinian from basaltic to mugearitic activity; (d) 15.5- to 15-ka plinian benmoreitic activity accompanying the caldera-forming eruptions of the Ellittico Volcano; and (e) the most recent 13-ka basaltic explosive activity of strombolian and subplinian type of the present edifice that also includes the 122-B.C. plinian eruption. This study results in a semi-quantitative and in some cases quantitative definition of the intensity and chronology of the explosive activity at Etna. Moreover, this work gives a new significance to the volcanic hazards of Etna, a volcano generally considered to be the site of gentle effusive eruptions. 相似文献
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Tephrochronological study in the quaternary Val d’Agri intermontane basin (Southern Apennines,Italy)
Irene Zembo Pietro Vignola Sergio Andò Riccardo Bersezio Luigina Vezzoli 《International Journal of Earth Sciences》2011,100(1):173-187
In the south-eastern depocentre of the Val d’Agri basin (Southern Apennines), a volcanic ash layer crops out interbedded within
poorly structured alluvial fan deposits of Late Pleistocene age. Textural, depositional and pedological features of this weathered
layer suggest a primary deposition from a pyroclastic fall-out of volcanic ash. Chemical analyses of feldspars show an alkali
trachytic composition and accessory minerals association allow to correlate this tephra layer with the regionally dispersed
Y-7 marine tephra layer (Tufo Verde Epomeo eruption, Ischia volcano), dated at 56 ± 4 ka. The Val d’Agri tephra here described
for the first time was deposited during MIS Stage 3. Its recovery and characterization permit to contribute to regional correlation
of the Mediterranean climatic and volcanic events from marine to continental successions and to describe landscape evolution
of the Southern Apennines during glacial–interglacial cycles. 相似文献
16.
Luigina Vezzoli Massimo Matteini Natalia Hauser Ricardo Omarini Roberto Mazzuoli Valerio Acocella 《Bulletin of Volcanology》2009,71(5):509-532
The Middle-Upper Miocene Las Burras–Almagro-El Toro (BAT) igneous complex within the Eastern Cordillera of the central Andes
(∼24°S; NW Argentina) has revealed evidence of non-explosive interaction of andesitic magma with water or wet clastic sediments
in a continental setting, including peperite generation. We describe and interpret lithofacies and emplacement mechanisms
in three case studies. The Las Cuevas member (11.8 Ma) comprises facies related to: (i) andesite extruded in a subaqueous
setting and generating lobe-hyaloclastite lava; and (ii) marginal parts of subaerial andesite lava dome(s) in contact with
surface water, comprising fluidal lava lobes, hyaloclastite, and juvenile clasts with glassy rims. The Lampazar member (7.8 Ma)
is represented by a syn-volcanic andesite intrusion and related peperite that formed within unconsolidated, water-saturated,
coarse-grained volcaniclastic conglomerate and breccia. The andesite intrusion is finger-shaped and grades into intrusive
pillows. Pillows are up to 2 m wide, tightly packed near the intrusion fingers, and gradually become dispersed in the host
sediment ≥50 m from the parent intrusion. The Almagro A member (7.2 Ma) shows evidence of mingling between water-saturated,
coarse-grained, volcaniclastic alluvial breccia and intruding andesite magma. The resulting intrusive pillows are characterized
by ellipsoidal and tubular shape and concentric structure. The high-level penetration of magma in this coarse sediment was
unconfined and irregular. Magma was detached in apophyses and lobes with sharp contacts and fluidal shapes, and without quench
fragmentation and formation of a hyaloclastite envelope. The presence of peperite and magma–water contact facies in the BAT
volcanic sequence indicates the possible availability of water in the system between 11–7 Ma and suggests a depositional setting
in this part of the foreland basin of the central Andes characterized by an overall topographically low coastal floodplain
that included extensive wetlands. 相似文献
17.
A. Capetti E. Trussoni A. Celotti L. Feretti M. Chiaberge 《Monthly notices of the Royal Astronomical Society》2000,318(2):493-500
We consider archival ROSAT and Hubble Space Telescope ( HST ) observations of five FR I radio galaxies and isolate their nuclear emission from that of the host galaxy. This enables us to determine the spectral energy distributions (SEDs) of their nuclei spanning the region from the radio to the X-ray band. They cannot be described as single power laws, but require the presence of an emission peak located between the infrared (IR) and soft X-ray band. We found consistency between the SED peak position and the values of the broad-band spectral indices of radio galaxies compared with those of BL Lacs, once the effects of beaming are properly taken into account. FR I SEDs are thus qualitatively similar to those of BL Lacs, supporting the identification of FR I sources as their misoriented counterparts. No dependence of the shape of the SED on the FR I orientation is found. 相似文献