bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaluation of volcano flank instability triggered by dyke intrusion
Authors: Elsworth Derek , Voight Barry 
Published: April 2008

Abstract
Instability of volcano flanks may result from the mechanically and thermally generated pore fluid pressures that accompany dyke intrusion. These complementary methods of pore pressure generation act on potential basal failure planes, decreasing effective stresses and consequently decreasing frictional resistance to failure. The twin agents of pore pressure generation provide a rational and quantifiable means of initiating and sustaining flank instability, even as the driving forces provided by magma pressurization ultimately drop as flank displacement is initiated, Pore pressures developed by mechanical and thermal effects are readily evaluated using simple, but mechanistically rigorous, models. Mechanically induced pore fluid pressures are evaluated through an analogy with a moving line dislocation within a saturated porous-elastic medium. Thermally induced pore fluid pressures are evaluated from a one-dimensional advective-diffusive solution for low Peclet transport, representing behaviour around a plane feeder dyke of infinite extent. Induced pore pressure magnitudes condition stability through the parameters representing the geometry and dimensions of the flank and failing flank block, together with the parameters modulating volumetric magma intrusion rate and heat supply. Where appropriate parameter magnitudes are selected, the resulting mechanical and thermal pore fluid pressures are sufficient to initiate failure. Where the pervasive influence of thermally induced pore pressures is included, or where shear collapse of the saturated pore structure occurs, the disturbance is sufficient to sustain failure. This presents the possibility for long runout instabilities of extremely large volume.
Mutual influence of dyking and collapses at Stromboli volcano, Italy
Authors: Tibaldi Alessandro 
Published: April 2008

Abstract

The island of Stromboli represents the emergent part of a 2.6 km high composite volcano. The evolution of this summit zone is characterized by a complex dyke pattern and repeated collapses. Three summit collapses and one southeastward minor lateral collapse occurred between 85 and 21 ka
bp
. From 13 ka to a few thousand years ago, three large lateral collapses occurred northwestwards. During the last 100 ka of volcanic history, which is reconstructed on the basis of data derived from the emergent part of the cone, the majority of dykes have been injected along a NE-SW zone of weakness which cuts the summit of the volcano. In the southern part of the island a N-S dyke zone connected, for a short period, the main Stromboli conduit to an off-shore crater. Another dyke zone developed after 13 ka
bp
along the walls of the earliest lateral collapse which occurred towards the NW at around this time. Dykes are vertical, especially along the NE-trending weak zone, whereas the other more external dykes tend to parallel the cone slopes and the collapse depression. Cumulative dyke thicknesses have a NW-SE horizontal maximum. Dyking along the NE-SW weak zone may have exerted a geometric control and provided a trigger for the NW-SE lateral collapse event. In turn the more external dyking was extremely sensitive to the local σ3 induced by debuttressing, in the case of injection planes parallel to the lateral collapse escarpments, and by the gross volcano morphology, in the case of dykes which parallel the cone slopes.
The influence of regional stresses on the mechanical stability of volcanoes: Stromboli (Italy)
Authors: Russo Guido , Giberti Grazia , Sartoris Giovanni 
Published: April 2008

Abstract

An elastic model was developed to study the mechanical stability of a volcanic system that includes a volcanic edifice and a magmatic feeding system (conduits and reservoirs) with axial symmetry around a vertical axis. Stability depends critically on the horizontal regional stress which comes into the problem as a boundary condition imposed at large horizontal distance. We considered three types of boundary conditions: (1) zero horizontal displacement (NHD); (2) lithostatic regional stress (LITH); (3) non-axisymmetrical regional stress corresponding to a strike-slip regime (NAS). For the third case (NAS), we used a 3-D model. The stress distributions were calculated by a numerical finite element method. The development of tensile tangential stress in the elements adjacent to the walls of conduits and reservoirs is assumed to be a sufficient condition for the instability of the plumbing system. In compression, we have adopted the Navier-Coulomb criterion for failure. We apply this model to Stromboli volcano, which is characterized by a steep volcanic edifice and open conduits filled with magma. There is geochemical evidence for a deep reservoir (
c.
10 km depth) of unknown size and indirect evidence of a shallower reservoir (at the base of the edifice) with volume of the order of 1 km
3
. The persistent explosive activity has been steady for the last 2000 years: this implies that the feeding system is mechanically stable. It is found that the deep reservoir has no influence on the stability of the edifice. With NHD boundary condition, implying that the horizontal regional stress is one-third of the vertical component, Stromboli’s volcanic system is unstable. In general, any volcanic system with an open and magma-filled plumbing system, with NHD boundary conditions, is mechanically unstable. With lithostatic regional stresses (LITH), the magmatic feeding system is mechanically stable and the slopes of the subaerial edifice are unstable, being subject to landslides. Both NHD and LITH conditions imply that the regional horizontal stress is isotropic which is not appropriate for the Southern Tyrrhenian Sea. With the NAS boundary condition, the stability of the plumbing system of Stromboli volcano allows us to place an upper limit on the maximum shear stress Δ
0
= (|σ

h

|

max

− |σ

h

|

min

)/2 For Δ
0
= 10 MPa, the magmatic feeding system is at the limit of mechanical instability. The subaerial edifice has steep slopes and it is at the limit of gravitative instability independent of the boundary conditions.
Hydrothermal pore fluid pressure and the stability of porous, permeable volcanoes
Authors: Day S. J. 
Published: April 2008

Abstract
Lateral collapses of large volcanoes are commonly associated with phreatic explosions and other evidence for the presence of pressurized hydrothermal pore fluids within the volcanoes prior to collapse. Furthermore, hydrothermal alteration of volcanic edifices is a major factor in increasing susceptibility to collapse. This is generally held to be because of a reduction in effective friction coefficient μ through alteration. However, this is inconsistent with an analysis of the factors affecting the strength of fluid-saturated rocks and volcanic debris in terms of the Rubey & Hubbert equations for shear failure of such materials. Instead, this analysis indicates that reductions in the strength of volcanic materials are mainly due to the effect of high pore pressure relative to confining pressure, expressed as the ratio λ of the two. Consideration of field and seismic evidence, together with simple calculations, indicates that high values of, and large increases in, λ are produced by a variety of mechanisms: heating of confined pore water by intrusions; degassing of intrusions; discharges of highly pressurized fluids from depth through clastic dykes; and by deformation associated with faulting. The sensitivity of pore fluid pressures to perturbation by these mechanisms is however highly dependent upon the permeability of their host rocks, which may itself be subject to rapid changes by fracturing, faulting and other processes. The rapidity of temperature changes and other mechanisms for pressurization in volcanic edifices means that the resultant pore pressure changes are large even in quite highly permeable rocks, but the effects are unpredictable. Detection of the development and spreading of high pore pressures within active volcanoes may however be possible by careful monitoring of patterns of seismicity.
The role of basement in volcano deformation
Authors: Vries Benjamin Van Wyk De , Borgia Andrea 
Published: April 2008

AbstractGrowing volcanoes load their basements, causing isostatic flexure, compaction and brittle and ductile deformation. Deformation of basement in turn exerts stress onto the edifice, which also responds by deforming. This deformation will be gradual or catastrophic, depending on the nature of the cone, and the properties of the underlying rocks. The physical properties of substratum, most especially the viscosity, can vary greatly. Thus a substratum of lava will support a volcano to a greater extent than fine clastic rocks. Compaction, crustal flexure, and sagging (a result of viscous flow of substratum) create a depression below the volcano. In the cone this induces compression, which increases with increasing sagging. However over long time spans, or in low viscosity substratum, sagging generates volcano spreading, where elastic compression is relaxed. The role of basement in volcano stability at four Nicaraguan stratocones 1.5–2 km high, constructed of similar materials on three types of basement has been studied. San Cristobal volcano has a volcanic basement of lava and ignimbrite, which has sagged by small amounts. Mombacho volcano has a basement of volcanic and marine strata. Sagging occurs, but spreading is slow. Compressive stresses have been released in the cone by thrust faulting. These structures have probably been exploited by three sector collapses. Concepción and Maderas volcanoes rest on sedimentary strata of weak mudstones, and large amounts of sagging and spreading have occurred. The study shows that spreading promotes gradual deformation in the volcano, because slopes are reduced and stresses relaxed. Catastrophic failure is favoured when compression is dominant, because stresses are large enough to fracture rock and produce decollements. Fracturing also promotes hydrothermal circulation, which further weakens the construct.
Coastal elevation changes in eastern Sicily: implications for volcano instability at Mount Etna
Authors: Firth C. , Stewart I. , McGuire W. J. , Kershaw S. , Vita-Finzi C. 
Published: April 2008

Abstract

The eastern flank of Mount Etna, Sicily has been recognized as being unstable, and three contrasting models have been proposed to account for this phenomenon, these being deep-seated spreading, shallow sliding and tectonic block movements. These models are examined by making reference to the rates and patterns of crustal movement along the eastern coastline of Sicily as determined from palaeoshoreline data. The south-eastern coastline of Sicily (Portopalo to Catania) provides no evidence of Holocene emergence. In contrast the volcanic coastline (Catania to Capo Schiso) and the northeastern shoreline (Taormina to Milazzo) display widespread evidence of coastal emergence. Radiocarbon dated remains indicate that both the volcano and northeastern Sicily have been uplifted at a rate exceeding 1.5 mm a
−1
during Holocene times, although more recent rates of uplift may have been greater. The pattern of uplift suggests that the northeastern coastline of Sicily, including the volcanic edifice, is apparently uplifting as a coherent unit, with superficial flank movements being superimposed on a regionally uplifting sub-volcanic basement.
Transport and emplacement mechanisms of mass-flow deposits on Monte Vulture volcano, Basilicata, southern Italy
Authors: Duncan A. M. , Cole P. D. , Guest J. E. , Chester D. K. 
Published: April 2008

Abstract
The Lahar Facies of Mt Vulture, which forms a broad apron around the base of the cone, is composed predominantly of mass-flow deposits. There is a spectrum of lithological types ranging from monolithologic units which may be of a primary pyroclastic flow origin and are composed entirely of juvenile material, to polylithologic deposits, containing a range of clast types, interpreted to be cold debris-flow deposits. Some debrisflow deposits show evidence of being hot on emplacement. Debris-flow deposits are interbedded with lapilli-fall layers and lava flows suggesting formation contemporaneous with eruptive activity. Some debris-flow deposits travelled no more than 3 km from their source. Many flows were apparently non-erosive, although there is one example where a debris-flow eroded clasts from the top of a lava flow. The presence of fractured ‘jigsaw’ blocks and large fragile blocks of pyroclastic material rules out turbulent flow and high shear for much of the transport prior to emplacement. Multiple grading and abundant development of reverse grading with large lava blocks rafted on, or protruding through, the upper surface of flow units implies that the lahars were high-concentration, high-strength flows in which differential shearing produced discontinuous multiple grading. Locally, individual debris-flow deposits have convex upper surface profiles with internal grading paralleling the surface, strongly supporting a conclusion that these debris-flow deposits were emplaced en masse.
Destructive mass movements associated with Quaternary volcanoes in Hokkaido, Japan
Authors: Yamagishi Hiromitsu 
Published: April 2008

Abstract
Hokkaido, the northern island of Japan, is situated on the North American Plate between the Pacific Plate and the Eurasian Plate; it is set on an island arc subducted by the two latter plates. Hence, Hokkaido has many Quaternary volcanoes. Most of these volcanoes have the andesitic to dacitic composition diagnostic of island arcs. They are remarkably unstable due to steepness of the upper slopes, structural fragility, and post-hydrothermal alteration. Consequently, in Hokkaido, many destructive mass movements occur from the Quaternary volcanoes. They are represented by debris avalanches from stratovolcano or lava dome collapses, hydrologic mass flows due to rainfalls, and slides associated with caldera formation.
Turbidites from slope failure on Hawaiian volcanoes
Authors: Garcia Michael O. 
Published: April 2008

Abstract

Turbidites are common in the sediments surrounding the Hawaiian Islands. Cores were taken during leg 136 of the Ocean Drilling Program 320 km west of the island of Hawaii on the outer side of the arch that surrounds the southern end of the Hawaiian chain. They contain Pleistocene to late Oligocene graded volcanic sand layers with fresh glass (or its alteration products) and mineral fragments (olivine, plagioclase, and clinopyroxene). Some layers have mixed assemblages of Pleistocene to Eocene radiolarians or Eocene and Cretaceous ichthyoliths. The glass fragments are weakly vesicular and blocky to platy in shape. The glass fragments from individual Pleistocene to Pliocene layers have large compositional ranges (i.e. larger than expected for a single eruption). These features indicate that the turbidites probably were deposited from turbidity currents that originated on the flanks of Hawaiian volcanoes. The low to moderate sulfur content of the sand glasses indicates that they were derived from partially degassed lavas that were erupted under shallow marine to subaerial conditions. The turbidity currents ran over the
c.
500 m high Hawaiian Arch, which indicates that the currents were at least 325 m thick. Similar turbidite deposits are located 930 km south of the Hawaiian Islands. Thus, debris avalanche from Hawaiian volcanoes can generate enormous turbidity currents that transport sediments long distances from their source. This phenomenon is an alternative explanation to Antarctic bottom waters for generating mixed assemblages of Pleistocene and Eocene radiolarians in deep-sea sediments.
Spectral analysis of volcanic tremor associated with the 1993 paroxysmal events at Stromboli
Authors: Carniel Roberto , Casolo Siro , Iacop Franco 
Published: April 2008

Abstract
The year 1993 was characterized by three paroxysmal phases at Stromboli: two (February and October) consisted of a series of violent explosions, the third (May) of strong Strombolian activity, accompanied by a small lava flow. Here we investigate the characteristics of the tremor before, during and after these paroxysmal phases. One evident feature is that the three phases analysed are significant expressions of the Strombolian activity. In fact, they mark a considerable change in the dynamics of the volcano. The energy content, both in terms of volcanic tremor and of number of events drops to very low values after the periods of intense activity. Concerning the evolution of the spectral content of the tremor before the paroxysmal phases, there seems to be a concentration of energy in the low frequency range (below 5 Hz for the crisis in May; below 3 Hz for the February and October events), with clearly identifiable peaks in some cases, while after the crisis the spectrum becomes again much more scattered. This transition, especially in the case of the strong explosions of February and October, happens abruptly. A continuous monitoring of the spectral content of volcanic tremor on Stromboli can therefore be a useful tool to identify the beginning of an instability which may lead to a paroxysmal phase.
Tonalite-trondhjemite-granodiorite magmatism and the genesis of Lewisian crust during the Archaean
Authors: Rollinson H. R. 
Published: April 2008

Abstract

This paper reviews the major and trace element and isotopic geochemistry of the Lewisian tonalite-trondhjemite-grandiorite/granite (TTG) gneisses from the mainland Lewisian. The main crust-forming event in the Lewisian was at
c.
3.0 Ga, although some supracrustal rocks preserve evidence for an earlier history. The granulites of the Central Region of the Lewisian preserve evidence of a younger episode of crust generation and a model is proposed for these rocks in which new crust generated at
c.
2.6 Ga is contaminated with
c.
3.0 Ga crust. It is proposed that the ‘depletion’ in the elements U, Th, K & Rb in the Central Region TTG granulites is original, i.e. related to the process of crust generation rather than of granulite facies metamorphism as previously supposed.

TTG genesis in the Lewisian is the product of the dehydration melting of amphibolite at > 18 kb depth and > 800°C. Differences in the levels of U, Th, K & Rb (LILE) between the TTG gneisses of the different regions of the mainland Lewisian is attributed to differences in the partial melting process. LILE-depleted rocks experienced dehydration followed by dehydration melting, whereas LILE-rich rocks are the product of dehydration melting alone.
The evolution of the Grenville Province in eastern Labrador, Canada
Authors: Gower Charles F. 
Published: April 2008

Abstract

Rifting at
c.
1.71 Ga separated the Mealy Mountains terrane from pre-Labradorian Laurentia and resulted in a short-lived (backarc?) basin, followed by southward subduction giving rise to 1.68-1.66 Ga Labradorian calc-alkaline arcs, partly built on older crust in the Mealy Mountains terrane. The arcs and subduction were also short lived, terminating when accretion against the Makkovikian and Eastern Churchill provinces occurred at 1.65 Ga. The Trans-Labrador batholith developed as a result of crustal thickening during suturing of the 1.68-1.66 Ga arc-related rocks to pre-Labradorian Laurentia. Further bimodal magmatism, in response to crustal thickening, continued until
c.
1.62 Ga, followed by waning granitic magmatism until 1.60 Ga.

The Labrador Orogen and older rocks in the Mealy Mountains terrane are flanked to the south by Pinwarian (1.51-1.45 Ga) granitoid rocks, possibly the inboard manifestation of a northward-subducting continental-margin arc at the southern margin of Laurentia. Extension, mostly coincident with the 1.71 Ga zone of weakness, started at
c.
1.45 Ga. Although rifting was successful further west, it is only represented by basaltic magmatism (Michael and Shabogamo gabbros) along a linear zone in Labrador. Similar tectonism characterized the same zone periodically for at least the next 150 million years during which time the 1.27 Ga Harp-Nutak dykes were emplaced and slightly younger rocks of the Seal Lake Group formed north of the Grenville Province.

After
c.
1.23 Ga tectonic conditions changed, partly in response to Elzevirian accretion of arc terranes preserved in the southwest Grenville Province, that are speculated to have once also existed south of the exposed eastern Grenville Province. Alternating compressional and extensional conditions terminated at
c.
1.0 Ga during collisional orogenesis associated with the final stages of development of the Grenville Orogen. Grenvillian deformation in Labrador (1.08-0.97 Ga) resulted in northwesterly thrusting, the effects of which are focused in the Exterior Thrust Belt, and widespread plutonism in the Interior Magmatic Belt. Thrusting in the Exterior Thrust Belt is sited along the zone of 1.71 and 1.43 Ga rifting. Uplift and cooling continued until 0.90 Ga as crustal stability was gradually achieved.
40
Ar/
39
Ar geochronological constraints on the tectonothermal evolution of the Eastern Segment of the Sveconorwegian Orogen, south-central Sweden
Authors: Page Laurence M. , Stephens Michael B. , Wahlgren Carl-Henric 
Published: April 2008

Abstract

A
40
Ar/
39
Ar study to constrain the tectonothermal evolution across the Eastern Segment of the Sveconorwegian Orogen has been initiated in the area north and east of lake Vänern, south-central Sweden. This segment of the orogen is confined by two major deformation zones, the Sveconorwegian Frontal Deformation Zone (SFDZ) in the east and the Mylonite Zone in the west. Previous structural work and the prograde character of the metamorphism within the study area suggest that an older (<
c.
1.57 Ga), regional foliation was formed by ductile shear deformation in a compressional tectonic regime. The orientation of this foliation was subsequently modified by later rotation along younger ductile shear zones in the easternmost, frontal part of the orogen (SFDZ). The
40
Ar/
39
Ar ages for hornblende suggest that the regional foliation is Sveconorwegian. Furthermore, white mica ages demonstrate that the Sveconorwegian tectonothermal overprint continues at least 40 km east of the traditionally accepted limit situated along the ‘Protogine Zone’. These results also provide age constraints for different phases of Sveconorwegian tectonothermal evolution with an older group of ages from 1009–965 Ma and a younger set from 930–905 Ma. The older ages are inferred to constrain a minimum age for crustal thickening during which the regional foliation and metamorphism developed, while the younger are associated with later compressional movement along the SFDZ.