bluuebunny/crossref_metadata_2025 huggingface dataset:
Ordovician
Authors: Bevins R. E. , Bluck B. J. , Brenchley P. J. , Fortey R. A. , Hughes C. P. , Ingham J. K. , Rushton A. W. A.
Published: August 2007

Since the publication of the Cambrian and Ordovician correlation charts by the Geological Society (Cowie
et al.
1972; Williams
et al.
1972) it has become more general practice to include the Tremadoc Series in the Ordovician, and although the precise level at which the base of the Ordovician is to be drawn is not finally decided, the limits of the system are generally understood. The upper limit has now been precisely defined at the base of
Parakidograptus acuminatus
Biozone, as exposed at Dob's Linn in the central belt of the Southern Uplands in south Scotland, the underlying
Glyptograptus persculptus
Biozone being relegated to the Hirnantian Stage of the Ashgill Series in the Ordovician System (Cocks & Rickards 1988).

Standard international series for the Ordovician are yet to be decided upon but in Britain the series usually employed are those which have been defined and refined over a period of more than a hundred years, based on successions in Wales, the Welsh Borderland and the north of England, namely: Tremadoc Arenig, Llanvirn, Llandeilo, Caradoc and Ashgill. These have ready application in the Anglo-Welsh area and further afield, particularly in continental Europe and Asia, but the demonstration that the faunas of Scotland and northwestern Ireland have much more in common with those of Laurentia (North America, Greenland and Spitsbergen) makes the direct application of many of these chronostratigraphical terms less relevant than the scheme which has developed for the classification of the North American Ordovician. The latter is still to some extent
Silurian
Authors: Bassett M. G. , Bluck B. J. , Cave R. , Holland C. H. , Lawson J. D.
Published: August 2007

The history of establishment of the Silurian System (and hence of the Silurian Period) and its principal divisions has been reviewed by Cocks
et al
. (1971) and Holland (1984, 1989
a
). The System itself, three of the four Series into which it is divided, and the Stages within these three, are all based upon localities in Britain. The names of all the divisions shown in Fig. I have been ratified by the International Union of Geological Sciences. The two major divisions, Lower Silurian and Upper Silurian, remain informal, but they are useful when degree of precision in correlation does not allow reference at the level of Series (Holland 1989
a
). The boundary stratotypes are all described in Holland & Bassett (1989). Graptolite Biozones have proved especially useful for international correlation in the Silurian and the sequence of Biozones used in Britain is shown in Fig. 1. Correlation of the Biozones wth the global Standard Series and Stages is shown approximately, but is not known with exactitude in all cases.

Geodetically the position of the British Isles in the Silurian remained astride the 25°S latitude, a position it had reached in the later Ordovician (Briden
et al
. 1973); movementwas confined to rotation. During this time the south magnetic pole wandered, in terms of present geography, from near to southwest Africa, to the Horn of Africa in early Silurian times, then back along the equator to west Africa/Brazil at the end of the Silurian.

The Llandovery Epoch was chracterized by marine transgressions. Thus in
Permian
Authors: Smith D. B. , Taylor J. C. M. , Arthurton R. S. , Brookfield M. E. , Glennie K. W.
Published: August 2007

Permian strata in the British Isles crop out mainly in northern and central England but are extensive in the subsurface both on land and in several adjoining offshore areas. Their base is defined as in Smith et al. (1974) and their top is within red beds, overlying the Zechstein evaporites.

We emphasize that both the base and the top of the nominally Permian rocks lie in continental strata almost devoid of stratigraphically useful fossils and that, accordingly, these boundaries are only doubtfully correlated with internationally acceptable biostratigraphic standards.

Subdivision of British Permian strata into Lower and Upper series follows the traditional view summarized by Smith et al. (1974). The junction between the series is taken at the incoming of marine strata in northern England and adjoining offshore areas, and at approximately equivalent levels in continuous continental sequences elsewhere; recent limited palynological studies suggest that the early Permian-late Permian transition adopted here and in most of northwest Europe may be mid or late Kazanian or even Tatarian in age which is somewhat younger than the base-Kazanian/Ufimian position taken in more continuous marine sequences.

There has been no comprehensive revision of the stratigraphy and nomenclature of early Permian strata in and around the British Isles since the work of Smith et al. (1974) and Rhys (1974), but these aspects of the early Permian continental deposits of several cuvettes and inland drainage basins in southwest Scotland were reviewed by Brookfield (1978) and the age of continental deposits in the Elgin area was reconsidered
Palaeogene and Neogene
Authors: Murray J. W.
Published: August 2007

Most of the British Isles has been a land area throughout the Tertiary and the basic shape of the coastline had been determined by the late Palaeocene. Only in southeast England are there marine Palaeogene and Neogene successions and these were deposited in embayments marginal to the North Sea and English Channel.

Much of the key information for the interpretation of the Tertiary history of the British Isles lies offshore. Thousands of kilometres of seismic profiles have been run and hundreds of boreholes drilled, mainly in the search for oil. The only part of the Tertiary which has been of economic interest is the Palaeocene of the northern North Sea. Summaries of the offshore data are given in Woodland (1975) and Illing & Hobson (1981).

Thick Tertiary successions are known from the central Graben of the North Sea, the Rockall Trough and the Faeroe Basin (Map Pg 1). The North Sea was the site of great subsidence caused by thermal relaxation following stretching of the continental crust (Sclater & Christie 1980). None of the Tertiary sediments was deposited in very deep water. By contrast, the Rockall Trough and the Faeroe Basin are underlain by oceanic crust and deep water has existed there throughout the Tertiary. The successions are known only from seismic studies (Roberts 1975) but are thought to be mainly fine-grained and with some contourites.

On a regional scale, the Tertiary history of northwest Europe must be considered in relation to the plate tectonic events proceeding in the adjacent ocean.
Part 3: Sulphate and Carbonate Scale Prediction in North Sea Oil and Gas Fields
Authors: Todd A. C. , Yuan M. D. , McCracken I. R.
Published: August 2007

Water-borne scales of sulphate and carbonate are major production problem in North Sea oil fields. Scale formation results from two processes: reduction in mineral solubility in produced formation water due to drops in temperature and pressure during production, and chemical incompatibility between formation water and injected seawater. Temperature and pressure drops are chiefly responsible for carbonate scale precipitation. Chemical incompatibility between the reservoir formation water and the injected sea-water is the most common cause of sulphate scaling. Furthermore, the precipitation of one mineral scale may be aggravated or alleviated by competitive co-precipitation of other mineral(s) and specific ion effects. This chapter examines the susceptibility of North Sea formation waters to carbonate and sulphate scale precipitation.

Seawater contains a few thousand milligrams per litre (c.2800 mg 1
-1
) of sulphate anions (SO
2-
4
), a small amount (c.420 mg 1
-1
) of calcium ions (Ca
2+
) and trace amounts of barium (Ba
2+
) and strontium (Sr
2+
) ions. In many offshore fields in the northern and central North Sea, the original formation water has trace SO
2-
4
but excessive Ba
2+
and Sr
2+
ions (up to 2000 - 3000 mg 1
-1
) as well as Ca
2+
ions (up to tens of thousands mg l
-1
). In normal oil field conditions, these two types of brines are usually chemically stable when they are kept apart. However, as seawater is injected into the reservoir formation during a waterflooding process, it commingles with the formation water in various locations of both reservoir and production systems to deposit sulphate mineral scales of barite (BaS0
4
), celestite (SrS0
4
)
Part 4: Compositional variations of North Sea formation waters
Authors: Warren Edward A. , Smalley Craig P. , Howarth R. J.
Published: August 2007

A total of 236 individual water analyses from over 70 fields in the North Sea and Norwegian Haltenbanken area were provided by field operators or collated from the literature (Table 4.1). All the data from the field operators were supplied as representative analyses of the formation water for that field. Most of the analyses supplied were routine ten ion analyses with accompanying data on sample type, water resistivity and reservoir conditions. Where these accompanying data were not supplied but were available from other sources, they have been added to the original contribution. Previously published formation water analyses have also been included with accompanying data where available.

Minor ions, such as bromide and lithium, trace metals, organic species such as acetate, and isotopic data were seldom reported. Consequently, maps and figures have only been constructed of the major cations, anions, total dissolved solids and R
w
.

All users of the water data compiled here should be aware of possible variations in data quality. There are a number of concerns, most notably the chemical analysis method, sampling artifacts and sample contamination.

The majority of the chemical analyses of formation waters compiled were not performed by the North Sea field operators themselves, but were produced under contract by a number of service companies. Although routine laboratory methods were used to obtain the data reported here, different methods have been used between laboratories and over time due to improved instrumentation and analytical methods over the last 25 years of oil and gas production from the
The eruption of Soufrière Hills Volcano, Montserrat (1995-1999): overview of scientific results
Authors: Sparks R. S. J. , Young S. R.
Published: August 2007

The eruption of Soufrière Hills Volcano, Montserrat (1995-1999) has displayed a wide range of volcanic phenomena: growth of an andesitic lava dome, generation of pyroclastic flows by lava dome collapse and by fountain collapse in explosive eruptions, Vulcanian and sub-Plinian explosivity with accompanying tephra fall, entrance of pyroclastic flows into the sea, sector collapse with formation of a debris avalanche and a high-velocity pyroclastic density current, and generation of lahars. New phenomena include: cyclic patterns of ground deformation linked with shallow seismicity and eruptive activity; pyroclastic flows formed by rapid sedimentation from pyroclastic surges; and an unprecedented slow escalation of eruption intensity. Magma pulsations with timescales of hours to years have been recognized. Transitions from extrusive to explosive activity were triggered by major dome collapses. Relationships between magma ascent dynamics and geophysical signals have been elucidated. Ascending water-rich andesitic magma becomes Theologically stiffened by degassing and groundmass crystallization. Large magma overpressures are consequently developed in the upper conduit, causing shallow seismicity, radial patterns of ground deformation, and cyclic pulsations of eruptive activity. Lava dome growth involved heterogeneous deformation with formation of spines and lobes along shear zones. Collapse of the pressurized dome resulted in substantial pyroclastic surges forming above pyroclastic flows. Influx of hydrous mafic magma remobilized hot crystalline igneous rocks at depths of 5 to 6 km to form crystal-rich andesitic magma and triggered the eruption.
The Montserrat Volcano Observatory: its evolution, organization, role and activities
Authors: Aspinall W. P. , Loughlin S. C. , Michael F. V. , Miller A. D. , Norton G. E. , Rowley K. C. , Sparks R. S. J. , Young S. R.
Published: August 2007

The Montserrat Volcano Observatory (MVO) is a statutory body of the Government of Montserrat and is the organization responsible for volcano monitoring operations on the island. It was formed shortly after the first phreatic explosions from Soufrière Hills Volcano occurred on 18 July 1995, and evolved from a hastily created, interim entity to a fully established volcano monitoring operation. Participating scientific teams have been drawn mainly from the Seismic Research Unit of the University of the West Indies, the US Geological Survey, the British Geological Survey and universities from various countries including the USA, UK, France and Puerto Rico. Despite its hurried inception, the MVO has been able to provide timely, high quality hazard advice to the civil authorities and has maintained an exceptional documentary record of all scientific aspects of the eruption. Its public education and information efforts have been extensive and there have been unusually high levels of interaction between scientists and the civil authorities, and between scientists and the public, both within Montserrat and outside in the wider world. The experience of setting up and running the MVO, under difficult and stressful conditions, has exemplified the advantages of teamwork and flexibility within monitoring operations and the benefits of openness and clarity in public interactions. Novel techniques have been applied to the appraisal of hazards and advances in scientific understanding have proved invaluable for risk assessment and management.
Growth patterns and emplacement of the andesitic lava dome at Soufrière Hills Volcano, Montserrat
Authors: Watts R. B. , Herd R. A. , Sparks R. S. J. , Young S. R.
Published: August 2007

abstract

Eruption of the Soufrière Hills Volcano on Montserrat allowed the detailed documentation of a Pélean dome-forming eruption. Dome growth between November 1995 and March 1998 produced over 0.3 km
3
of crystal-rich andesitic lava. Discharge rates gradually accelerated from >1 m
3
s
-1
during the first few months to >5 m
3
s
-1
in the later stages. Early dome growth (November 1995 to September 1996) was dominated by the diffuse extrusion of large spines and mounds of blocky lava. A major dome collapse (17 September 1996) culminated in a magmatic explosive eruption, which unroofed the main conduit. Subsequent dome growth was dominated by the extrusion of broad lobes, here termed shear lobes. These lobes developed through a combination of exogenous and endogenous growth over many weeks, with movement accommodated along curved shear faults within the dome interior. Growth cycles were recognized, with each cycle initiated by the slow emplacement of a large shear lobe, constructing a steep flank on one sector of the dome. A growth spurt, heralded by the onset of intense hybrid seismicity, pushed the lobe rapidly out, triggering dome collapse. Extrusion of another lobe within the resulting collapse scar reconstructed the steep dome flanks prior to the next cycle.
Dynamics of magma ascent and lava extrusion at Soufrière Hills Volcano, Montserrat
Authors: Melnik O. , Sparks R. S. J.
Published: August 2007

Growth of the andesitic lava dome during eruption of Soufrière Hills Volcano, Montserrat involved general increases in discharge rate and dome height with superposed fluctuations on timescales from hours to months. We have modelled magma conduit flow incorporating viscosity variations caused by degassing and crystallization. Gas loss is modelled by permeable flow, with variations of permeability constrained by measurements. Crystallization kinetics is modelled by an Avrami law. Observations and petrological studies constrain conduit diameter (
c
. 30 m), magma chamber crystal content (
c
. 60-65%), melt water content (
c
. 5%), magma temperature (
c
. 850°C) and chamber depth (
c
. 5 km). Gas loss and rheological stiffening cause a maximum in magma overpressure (magma pressure minus lithostatic pressure) at depths of a few hundred metres below the dome. This maximum can explain ground deformation patterns, shallow seismicity, and short-lived Vulcanian explosions. Crystallization kinetics causes a strong feedback mechanism and multiple steady solutions for discharge rate. Small changes in chamber pressure, magma viscosity and conduit diameter strongly amplify discharge rate. Multiple solutions allow cyclic variation of discharge rate. Escalation of activity is attributed principally to influx of hot mafic magma into the chamber, resulting in chamber pressure increasing with time. Dome growth can be intrinsically unpredictable due to non-linear effects.
Mechanisms of lava dome instability and generation of rockfalls and pyroclastic flows at Soufrière Hills Volcano, Montserrat
Authors: Calder E. S. , Luckett R. , Sparks R. S. J. , Voight B.
Published: August 2007

Between 3 January 1996 and 1 December 1998 at Soufrière Hills Volcano, Montserrat, there were 27150 seismic signals attributable to rockfalls and pyroclastic flows. Large (1-4 x 10
6
m
3
) and major (>4 x 10
6
m
3
) dome collapses began to occur after the extrusion rate reached 2 m
3
s
-1
and the lava dome exceeded 30 x 10
6
m
3
in volume. Large to major collapses occurred on 26 occasions and were usually associated with periods of elevated extrusion rate (6 13 m
3
s
-1
), intense hybrid earthquake swarms and/or inflation-deflation cycles of crater-rim ground deformation. During these cycles, gas-rich pulses of magma, 140 000 320 000 m
3
in volume, were intruded into the dome and, soon thereafter, dome collapses from the headwalls of shear lobes were generated. Large dome collapses also occurred after 10 March 1998, when magma extrusion ceased, but these had no seismic precursors. These events represent structural failures from over steepened canyon-like walls and were followed by intense degassing, suggesting that gas pressure build-up within the relict dome may have played some role. Rockfall counts and durations established from seismic data show variations that correlate with extrusion rate. Using pyroclastic flow runout and rockfall duration data as proxies for event magnitude, power law relationships between frequency (total number of events) and magnitude have been found. Seismic signals associated with rockfalls and pyroclastic flows commonly comprise both high-frequency and long-period components. Intense degassing from the dome is interpreted as the source for the long-period component. These results indicate that rockfalls and pyroclastic flows generated by dome collapse at Montserrat are not simply the result of passive dome failure, but are intimately related to discharge of pressurized gas and pulses of magma extrusion. Pyroclastic flows were usually sourced from lobe headwalls, where lava was hot and gas-rich and where fragmentation of the micro vesicular andesite lava occurred more readily.
Pyroclastic flows and surges generated by the 25 June 1997 dome collapse, Soufrière Hills Volcano, Montserrat
Authors: Loughlin S. C. , Calder E. S. , Clarke A. , Cole P. D. , Luckett R. , Mangan M. T. , Pyle D. M. , Sparks R. S. J. , Voight B. , Watts R. B.
Published: August 2007

On 25 June 1997, an unsteady, retrogressive, partial collapse of the lava dome at Soufrière Hills Volcano lasted 25 minutes and generated a major pulsatory block-and-ash flow, associated pyroclastic surges and a surge-derived pyroclastic flow that inundated an area of 4 km
2
on the north and NE flanks of the volcano. Three main pulses are estimated to have involved 0.78, 2.36 and 2.36 x 10
6
m
3
of debris and the average velocities of the fronts of the related block-and-ash flow pulses were calculated to be 15 ms
-1
, 16.1 ms
-1
and 21.9 ms
-1
respectively.

Deposits of block-and-ash flow pulses 1 and 2 partially filled the main drainage channel so that material of the third pulse spilled out of the channel at several places, inundating villages on the eastern coastal plain. Bends and constrictions in the main drainage channel, together with depositional filling of the channel, assisted detachment of pyroclastic surges from the pulsatory block-and-ash flow. The most extensive pyroclastic surge detached at an early stage from the third block-and-ash flow pulse, swept down the north flank of the volcano and then climbed 70 m in elevation before dissipating. Rapid sedimentation from this surge generated a high-concentration granular flow (surge-derived pyroclastic flow) that drained westwards into a valley not anticipated to be at high risk.

Observations support the hypothesis that the interior of the Soufrière Hills Volcano lava dome was pressurized and that pyroclastic surge development became more substantial as deeper, more highly pressurized parts of the dome were incorporated into the pyroclastic flow. Surge development was at times so violent that expanded clouds detached from the block-and-ash flow within a few tens of metres of the lava dome.
Eyewitness accounts of the 25 June 1997 pyroclastic flows and surges at Soufrière Hills Volcano, Montserrat, and implications for disaster mitigation
Authors: Loughlin S. C. , Baxter P. J. , Aspinall W. P. , Darroux B. , Harford C. L. , Miller A. D.
Published: August 2007

Eyewitness and survivor accounts allow reconstruction of the sequence of events on 25 June 1997, when a sustained partial collapse of the lava dome occurred leading to the death of 19 people. An unsteady pyroclastic flow was generated with three distinct pulses. The third flow pulse caused most of the damage to infrastructure and most, if not all, of the casualties. Pyroclastic surges detached along most of the path of the third flow pulse, and one travelled 70 m up an adjacent hillside.

Observations were made that will be important for the development of mitigation measures at future events involving high-temperature flows and surges. Temperatures remained high (300-400°C) at the periphery of the most voluminous and extensive surge, even though dynamic pressure and velocity were low, causing the death of seven victims. Some people survived at the margins of the surge zone but suffered serious burns when they were forced to walk across the hot surge deposits to safety. Deflagration of buildings and vegetation was immediate within the pyroclastic surge and intense fires burned long after the volcanic activity had ceased. Fires could be a serious secondary hazard in an urban area. Search-and-rescue efforts were hampered in the immediate aftermath of the pyroclastic flows and surges by smoke and ash in the atmosphere. The hot, locally gas-rich surge deposits posed a major hazard to search-and-rescue workers and volcanologists for days afterwards.

Despite the efforts of officials, scientists and concerned members of the public, about 80 people were in Zones A and B of the Exclusion Zone on 25 June 1997. Our findings suggest that many had become accustomed to the pyroclastic flows and had become overconfident in their own ability to judge the threat by observing repeated flows that had gradually increased runout but remained restricted to valleys. Many people had contingency plans and believed that there would be observable or audible warning signs from the volcano if the activity were to escalate significantly. However, there were no such discernible warnings and individual contingency plans proved inadequate. Public education should concentrate on correcting such public misapprehension of hazardous phenomena and attendant risks in future volcanic crises.
Small-volume, highly mobile pyroclastic flows formed by rapid sedimentation from pyroclastic surges at Soufrière Hills Volcano, Montserrat: an important volcanic hazard
Authors: Druitt T. H. , Calder E. S. , Cole P. D. , Hoblitt R. P. , Loughlin S. C. , Norton G. E. , Ritchie L. J. , Sparks R. S. J. , Voight B.
Published: August 2007

Gravitational collapses of the lava dome at Soufrière Hills Volcano on 25 June and 26 December 1997 generated pyroclastic surges that spread out over broad sectors of the landscape and laid down thin, bipartite deposits. In each case, part of the settling material continued to move upon reaching the ground and drained into valleys as high-concentration granular flows of hot (120-410°C) ash and lapilli. These surge-derived pyroclastic flows travelled at no more than 10 m s
-1
but extended significantly beyond the limits of the parent surge clouds (by 3 km on 25 June and by 1 km on 26 December). The front of the 25 June flow terminated in a valley about 50 m below a small town that was occupied at the time. Despite their small deposit volumes (5-9 x 10
4
m
3
), the surge-derived pyroclastic flows travelled as far as many of the Soufrière Hills block-and-ash flows on slopes as low as a few degrees, reflecting a high degree of mobility. An analysis of the deposits from 26 December suggests that sediment accumulation rates of at least several millimetres per second were sufficient to generate pyroclastic flows by suspended-load fallout from pyroclastic surges on Montserrat. Surge-derived pyroclastic flows are an important, and hitherto underestimated, hazard around active lava domes. At Montserrat they formed by sedimentation over large catchment areas and drained into valleys different from those affected by the primary block-and-ash flows and pyroclastic surges, thereby impacting areas not anticipated to be vulnerable in prior hazards analyses. The deposits are finer-grained than those of other types of pyroclastic flow at Soufrière Hills Volcano; this may aid their recognition in ancient volcanic successions but, along with valley-bottom confinement, reduces the preservation potential.
Episodes of cyclic Vulcanian explosive activity with fountain collapse at Soufrière Hills Volcano, Montserrat
Authors: Druitt T. H. , Young S. R. , Baptie B. , Bonadonna C. , Calder E. S. , Clarke A. B. , Cole P. D. , Harford C. L. , Herd R. A. , Luckett R. , Ryan G. , Voight B.
Published: August 2007

In 1997 Soufriére Hills Volcano on Montserrat produced 88 Vulcanian explosions: 13 between 4 and 12 August and 75 between 22 September and 21 October. Each episode was preceded by a large dome collapse that decompressed the conduit and led to the conditions for explosive fragmentation. The explosions, which occurred at intervals of 2.5 to 63 hours, with a mean of 10 hours, were transient events, with an initial high-intensity phase lasting a few tens of seconds and a lower-intensity, waning phase lasting 1 to 3 hours. In all but one explosion, fountain collapse during the first 10-20 seconds generated pyroclastic surges that swept out to 1-2 km before lofting, as well as high-concentration pumiceous pyroclastic flows that travelled up to 6 km down all major drainages around the dome. Buoyant plumes ascended 3-15 km into the atmosphere, where they spread out as umbrella clouds. Most umbrella clouds were blown to the north or NW by high-level (8-18 km) winds, whereas the lower, waning plumes were dispersed to the west or NW by low-level (<5 km) winds. Exit velocities measured from videos ranged from 40 to 140 ms-
1
and ballistic blocks were thrown as far as 1.7 km from the dome. Each explosion discharged on average 3 x 10
5
m
3
of magma, about one-third forming fallout and two-thirds forming pyroclastic flows and surges, and emptied the conduit to a depth of 0.5-2 km or more. Two overlapping components were distinguished in the explosion seismic signals: a low-frequency (c. 1 Hz) one due to the explosion itself, and a high-frequency (>2 Hz) one due to fountain collapse, ballistic impact and pyroclastic flow. In many explosions a delay between the explosion onset and start of the pyroclastic flow signal (typically 10-20 seconds) recorded the time necessary for ballistics and the collapsing fountain to hit the ground. The explosions in August were accompanied by cyclic patterns of seismicity and edifice deformation due to repeated pressurization of the upper conduit. The angular, tabular forms of many fallout pumices show that they preserve vesicularities and shapes acquired upon fragmentation, and suggest that the explosions were driven by brittle fragmentation of overpressured magmatic foam with at least 55 vol% bubbles present in the upper conduit prior to each event.
Computational modelling of the transient dynamics of the August 1997 Vulcanian explosions at Soufrière Hills Volcano, Montserrat: influence of initial conduit conditions on near-vent pyroclastic dispersal
Authors: Clarke A. B. , Neri A. , Voight B. , Macedonio G. , Druitt T. H.
Published: August 2007

This paper presents numerical models of the Vulcanian explosions that occurred in 1997 at Soufrière Hills Volcano. Plume evolution and velocities were calculated for the well-documented and typical explosions of 6 and 7 August 1997, and these data and other observations were compared to transient, axisymmetric, multiphase flow simulations of coupled conduit evacuation and pyroclastic dispersal. Pre-explosion conduit conditions were estimated from Montserrat data, using a simple gas solubility law and assuming that conduit magma flow had stagnated with a constant overpressure prior to the explosions. Reference simulation input parameters include conduit diameter of 30 m, crater diameter of 300 m, meltwater content of 4.3±0.5°, grain sizes of 30, 2000 and 5000 µm, and conduit overpressure of l0MPa. The numerical simulations of the explosions resolved highly unsteady vent exit conditions such as velocity, pressure and mass flux, and the spatial and temporal dispersal of pyroclasts during the initial few minutes was investigated using one gas phase and two or three solid phases representing pyroclasts of different size. Our simulations produced transitional eruptive regime behaviour, dividing the erupted mass into a portion that generated a radial pyroclastic current fed by a collapsing column, and a convective portion that generated a buoyant plume. This behaviour generally mimicked the observed explosions. The movement of different particle sizes was tracked, with fine particles dominantly influencing the convective behaviour of the central plume and ash plume thermals generated above the pyroclastic currents. Simulated initial vent velocities ranged from 85 to 120ms
-1
, collapse heights ranged from 450 to 1370 m above the vent, initial pyroclastic current velocities ranged from 40 to 60 ms
-1
with surge runouts to 1.8 km, drawdown depths in the conduit were a few hundred metres, and simulated pyroclastic current deposit temperatures ranged between 135 and 430°C. Subsets of these results are in reasonable agreement with observed and measured parameters of the 1997 explosions. The best match was intermediate between our reference simulation, which assumed no loss of volatiles from the conduit during rise from the magma reservoir and which appeared too energetic, and another simulation in which much volatile leakage was assumed. The results suggest that volatile depletion in the conduit was an important factor in influencing the dynamic behaviour of the Vulcanian explosions on Montserrat.
Numerical modelling of tephra fallout associated with dome collapses and Vulcanian explosions: application to hazard assessment on Montserrat
Authors: Bonadonna C. , Macedonio G. , Sparks R. S. J.
Published: August 2007

Hazardous effects of tephra fallout on Montserrat include roof collapse, aviation threats, health hazards from respirable crystalline silica, crop pollution, road safety and lahar generation. An advection-diffusion model was developed to investigate tephra dispersal from dome collapses and Vulcanian explosions, which generated most of the fallout tephra during the 1995-1999 eruptive period of Soufrière Hills Volcano. Wind field, atmospheric diffusion, gravity settling, aggregation and elutriation processes are considered. Computed isomass maps compare well with field observations and require aggregation of fine ash for good agreement. Probability maps were also compiled. Individual probability maps (for individual dome collapses and Vulcanian explosions) are based on the statistics of wind profiles and show that fallout tephra generated by individual eruptive events on a Montserrat scale do not cause serious damage in any area on Montserrat. Cumulative probability maps (for a given scenario of activity) are generated by sampling statistical distributions of wind profiles and eruptive events over an extended period of time. They show that persistent tephra fallout can accumulate enough material to cause roof collapses and serious damage to vegetation in the SW part of the island, and minor damage to vegetation in the north, as also confirmed by field data.
Seismicity, gas emission and deformation from 18 July to 25 September 1995 during the initial phreatic phase of the eruption of Soufrière Hills Volcano, Montserrat
Authors: Gardner C. A. , White R. A.
Published: August 2007

On 18 July 1995, after more than three years of irregularly increasing seismicity, phreatic explosions opened a new vent on Soufrière Hills Volcano, about 4 km east of the capital city of Plymouth, Montserrat. By early August 1995, the volcano was monitored by a nine-station seismic network, three telemetered electronic tiltmeters, and daily correlation spectroscopy (COSPEC) flights to measure S02 emission rates and to observe vent areas. Seismicity and S02 emission rates implicated magma intrusion as the cause of the seismic unrest. Strong evidence of magma ascent to shallow levels, however, did not appear until late September 1995, when increasing numbers of hybrid events heralded the formation of a small dome and spine. We infer from the data that intrusion of a small volume of magma occurred in July, but stalled on ascent. Degassing of the stalled magma formed a carapace that thickened with time. We suggest that either volatile build-up beneath the degassed carapace, or aseismic intrusion of fresh material, finally forced the stalled magma to the surface in late September 1995. A similar cycle of activity appears to have occurred during the second phreatic phase between late September and mid-November 1995.
Spaceborne radar measurements of the eruption of Soufrière Hills Volcano, Montserrat
Authors: Wadge G. , Scheuchl B. , Stevens N. F.
Published: August 2007

Radar measurements from space are used to help monitor the evolution of a Peléean eruption on Soufrière Hills Volcano, Montserrat, during 1996 to April 1999. Data from four radar systems are used: ERS-1, ERS-2, Radarsat and JERS-1. We demonstrate that ratio images of backscattered radar energy collected at different times provide useful qualitative summary maps of gross topographic change (e.g. infilling of valleys with deposits) and changes in backscattering properties with time. Radar phase data using the interferometry technique can also provide valuable change detection information. Phase coherence images for ERS-1 and ERS-2 pairs with only one day separation on 25 and 26 September 1997 and 8 and 9 April 1999 allow the areal extent of some pyroclastic flows deposits emplaced during those 24-hour periods to be mapped. Generally, the radar phase can only be retrieved from those parts of the volcano where the vegetation is destroyed by pyroclastic flow deposits and local slopes are not too steep. Quantitative information on the topography of the volcano can also be extracted from the phase data, though not routinely from the new lava dome that grew during 1995-1998. By comparing the radar-measured post-eruption topography with the pre-eruption topography the thickness of the pyroclastic flow deposits (up to 85 m in some valleys on the northeastern slopes) are mapped. Radar interferometry also supplies a means of measuring surface deformation between radar images.
How Does It Feel to Be Like a Rolling Stone? Ten Questions About Dispersal Evolution
Authors: Ronce Ophélie
Published: August 2007

This review proposes ten tentative answers to frequently asked questions about dispersal evolution. I examine methodological issues, model assumptions and predictions, and their relation to empirical data. Study of dispersal evolution points to the many ecological and genetic feedbacks affecting the evolution of this complex trait, which has contributed to our better understanding of life-history evolution in spatially structured populations. Several lines of research are suggested to ameliorate the exchanges between theoretical and empirical studies of dispersal evolution.
Punishment Beyond the Legal Offender
Authors: Comfort Megan
Published: August 2007

In the United States, lawbreakers are treated as social isolates, and the sentences imposed upon them are conceived of as affecting a discrete individual. However, people who commit or are suspected of committing crimes are generally embedded in kinship webs and social networks that draw others into the ambit of the state's punishment apparatus. Through their association with someone convicted of a crime, legally innocent people have firsthand and often intense contact with criminal justice authorities and correctional facilities, they experience variants of the direct and indirect consequences of incarceration, and they are confronted by the paradox of a penal state that has become the primary distributor of social services for the poor in the United States. Collectively, studies investigating punishment beyond the offender contribute to the understanding of the wide and multi-faceted impact of punitive sanctions and spotlight the importance of considering this full range of repercussions when evaluating the scope of the nation's policing, judicial, and correctional policies.
The Biological Basis of Audition
Authors: Recanzone Gregg H. , Sutter Mitchell L.
Published: August 2007

Interest has recently surged in the neural mechanisms of audition, particularly with regard to functional imaging studies in human subjects. This review emphasizes recent work on two aspects of auditory processing. The first explores auditory spatial processing and the role of the auditory cortex in both nonhuman primates and human subjects. The interactions with visual stimuli, the ventriloquism effect, and the ventriloquism aftereffect are also reviewed. The second aspect is temporal processing. Studies investigating temporal integration, forward masking, and gap detection are reviewed, as well as examples from the birdsong system and echolocating bats.
[Cl−]imodulation of Ca2+-regulated exocytosis in ACh-stimulated antral mucous cells of guinea pig
Authors: Shimamoto Chikao , Umegaki Eiji , Katsu Ken-ichi , Kato Masumi , Fujiwara Shoko , Kubota Takahiro , Nakahari Takashi
Published: August 2007

The effects of intracellular Cl−concentration ([Cl−]i) on acetylcholine (ACh)-stimulated exocytosis were studied in guinea pig antral mucous cells by video microscopy. ACh activated Ca2+-regulated exocytosis (an initial phase followed by a sustained phase). Bumetanide (20 μM) or a Cl−-free (NO3−) solution enhanced it; in contrast, 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB, a Cl−channel blocker) decreased it and eliminated the enhancement induced by bumetanide or NO3−solution. ACh and Ca2+dose-response studies demonstrated that NO3−solution does not shift their dose-response curves, and ATP depletion studies by dinitrophenol or anoxia demonstrated that exposure of NO3−solution prior to ATP depletion induced an enhanced initial phase followed by a sustained phase, whereas exposure of NO3−solution after ATP depletion induced only a sustained phase. Intracellular Ca2+concentration ([Ca2+]i) measurements showed that bumetanide and NO3−solution enhanced the ACh-stimulated [Ca2+]iincrease. Measurements of [Cl−]irevealed that ACh decreases [Cl−]iand that bumetanide and NO3−solution decreased [Cl−]iand enhanced the ACh-evoked [Cl−]idecrease; in contrast, NPPB increased [Cl−]iand inhibited the [Cl−]idecrease induced by ACh, bumetanide, or NO3−solution. These suggest that [Cl−]imodulates [Ca2+]iincrease and ATP-dependent priming. In conclusion, a decrease in [Cl−]iaccelerates ATP-dependent priming and [Ca2+]iincrease, which enhance Ca2+-regulated exocytosis in ACh-stimulated antral mucous cells.
Transcytosis of gastric leptin through the rat duodenal mucosa
Authors: Cammisotto Philippe G. , Gingras Diane , Bendayan Moïse
Published: August 2007

Leptin is secreted into the gastric juice by epithelial Chief cells and reaches the duodenum in a biologically intact active form. We assessed the possibility that this gastric leptin crosses the intestinal mucosa by transcytosis through enterocytes to reach blood circulation. Endogenous gastric leptin secretion was triggered by cholinergic stimulation. In another set of experiments, recombinant leptin was inserted in vivo into the duodenal lumen. Plasma levels of leptin were assessed by enzyme immunoassay and Western blot, and duodenal tissue was processed for immunocytochemistry. We first observed that leptin was found inside duodenal enterocytes from fed rats but not inside those from fasted ones. Stimulation of gastric secretion by a cholinergic agent led to rapid increases in plasma leptin levels (202 ± 39%) except when the pylorus was clamped. Insertion of recombinant leptin into the duodenal lumen raised plasma leptin concentrations (558 ± 34%) quite rapidly, whereas carrier solution without leptin had no effect. The use of FITC-tagged leptin reinforced these results. Light and electron microscopy revealed the cellular compartments involved in its transcytosis, namely, the enterocyte microvilli, the endocytotic vesicles, the Golgi complex, and the basolateral interdigitations. Leptin was also present in the lamina propria, in capillary endothelial cell plasmalemmal vesicles, and in capillary lumina. These results demonstrate that gastric exocrine leptin is internalized by duodenal enterocytes and delivered to the lamina propria and blood circulation. It may thus be able to play important paracrine and endocrine functions for the control of gastric emptying and nutrient absorption.
Targeted deletion of A2A adenosine receptors attenuates the protective effects of myocardial postconditioning
Authors: Morrison R. Ray , Tan Xing Lin , Ledent Catherine , Mustafa S. Jamal , Hofmann Polly A.
Published: August 2007

Endogenous adenosine is an important ligand trigger for the cardioprotective effects of postconditioning (POC), yet it is unclear which adenosine receptor subtype is primarily responsible. To evaluate the role of A2A adenosine receptors in POC-induced protection, global ischemia-reperfusion was performed with and without POC in isolated wild-type (WT) and A2A adenosine receptor knockout (A2AKO) mouse hearts. Injury was measured in terms of postischemic functional recovery and release of cardiac troponin I (cTnI). Activation of protective signaling with POC was assessed by Akt and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation. In WT hearts, POC improved recovery of postischemic developed pressure in early (81.6 ± 6.4% of preischemic baseline vs. 37.5 ± 5.6% for non-POC WT at 1 min) and late (62.2 ± 4.2% of baseline vs. 45.5 ± 5.3% for non-POC WT at 30 min) reperfusion, reduced cTnI release by 37%, and doubled the phosphorylation of both Akt and ERK1/2. These beneficial effects of POC were blocked by treatment with the selective A2A adenosine receptor antagonist ZM-241385 during reperfusion. Postischemic functional recovery, cTnI release, and phosphorylation of Akt and ERK1/2 were not different between non-POC WT and A2AKO hearts. In A2AKO hearts, POC did not improve functional recovery, reduce cTnI release, nor increase phosphorylation of Akt or ERK1/2. Thus the protective effects of POC are attenuated by both selective A2A receptor antagonism and targeted deletion of the gene encoding A2A adenosine receptors. These observations support the conclusion that endogenous activation of A2A adenosine receptors is an essential trigger leading to the protective effects of POC in isolated murine hearts.
Ebselen reduces nitration and restores voltage-gated potassium channel function in small coronary arteries of diabetic rats
Authors: Bubolz Aaron H. , Wu Qingping , Larsen Brandon T. , Gutterman David D. , Liu Yanping
Published: August 2007

Small coronary arteries (SCA) from diabetic rats exhibit enhanced peroxynitrite (ONOO−) formation and concurrent impairment of voltage-dependent potassium (Kv) channel function. However, it is unclear whether ONOO− plays a causative role in this impairment. We hypothesized that functional loss of Kv channels in coronary smooth muscle cells (SMC) in diabetes is due to ONOO− with subsequent tyrosine nitration of Kv channel proteins. Diabetic rats and nondiabetic controls were treated with or without ebselen (Eb) for 4 wk. SCA were prepared for immunohistochemistry (IHC), immunoprecipitation (IP) followed by Western blot (WB), videomicroscopy, and patch-clamp analysis. IHC revealed excess ONOO− in SCA from diabetic rats. IP and WB revealed elevated nitration of the Kv1.2 α-subunit and reduced Kv1.2 protein expression in diabetic rats. Each of these changes was improved in Eb-treated rats. Protein nitration and Kv1.5 expression were unchanged in SCA from diabetic rats. Forskolin, a direct cAMP activator that induces Kv1 channel activity, dilated SCA from nondiabetic rats in a correolide (Cor; a selective Kv1 channel blocker)-sensitive fashion. Cor did not alter the reduced dilation to forskolin in diabetic rats; however, Eb partially restored the Cor-sensitive component of dilation. Basal Kv current density and response to forskolin were improved in smooth muscle cells from Eb-treated DM rats. We conclude that enhanced nitrosative stress in diabetes mellitus contributes to Kv1 channel dysfunction in the coronary microcirculation. Eb may be beneficial for the therapeutic treatment of vascular complications in diabetes mellitus.
Metabolic forearm vasodilation is enhanced following Bier block with phentolamine
Authors: Moradkhan Raman , McQuillan Patrick , Hogeman Cynthia , Leuenberger Andrea , Linton-Frazier Latoya , Leuenberger Urs A.
Published: August 2007

The extent to which sympathetic nerve activity restrains metabolic vasodilation in skeletal muscle remains unclear. We determined forearm blood flow (FBF; ultrasound/Doppler) and vascular conductance (FVC) responses to 10 min of ischemia [reactive hyperemic blood flow (RHBF)] and 10 min of systemic hypoxia (inspired O2 fraction = 0.1) before and after regional sympathetic blockade with the α-receptor antagonist phentolamine via Bier block in healthy humans. In a control group, we performed sham Bier block with saline. Consistent with α- receptor inhibition, post-phentolamine, basal FVC (FBF/mean arterial pressure) increased (pre vs. post: 0.42 ± 0.05 vs. 1.03 ± 0.21 units; P < 0.01; n = 12) but did not change in the saline controls (pre vs. post: 0.56 ± 0.14 vs. 0.53 ± 0.08 units; P = not significant; n = 5). Post-phentolamine, total RHBF (over 3 min) increased substantially (pre vs. post: 628 ± 75 vs. 826 ± 92 ml/min; P < 0.01) but did not change in the controls (pre vs. post: 618 ± 66 vs. 661 ± 35 ml/min; P = not significant). In all conditions, compared with peak RHBF, peak skin reactive hyperemia was markedly delayed. Furthermore, post-phentolamine (pre vs. post: 0.43 ± 0.06 vs. 1.16 ± 0.17 units; P < 0.01; n = 8) but not post-saline (pre vs. post: 0.93 ± 0.16 vs. 0.87 ± 0.19 ml/min; P = not significant; n = 5), the FVC response to hypoxia (arterial O2 saturation = 77 ± 1%) was markedly enhanced. These data suggest that sympathetic vasoconstrictor nerve activity markedly restrains skeletal muscle vasodilation induced by local (forearm ischemia) and systemic (hypoxia) vasodilator stimuli.