R. S. J. Sparks

University of Bristol

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B. Voight

Pennsylvania State University

Willy Aspinall

University of Bristol

Oleg Melnik

Lomonosov Moscow State University

Herbert E. Huppert

University of Cambridge

Jon Blundy

University of Oxford

Jenni Barclay

University of East Anglia

Haraldur Sigurdsson

University of Rhode Island

G. S. Mattioli

The University of Texas at Arlington

Catherine Annen

Czech Academy of Sciences, Institute of Geophysics

M. Field

University of Bristol

Cooperative Institutions

University of Bristol

197

University of Cambridge

Montserrat Volcano Observatory

Centre National de la Recherche Scientifique

United States Geological Survey

British Geological Survey

University of Oxford

University of Leeds

University of the West Indies

Imperial College London

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Sedimentation from gravity currents generated by turbulent plumes

Sedimentology (1991)

R. S. J. Sparks Steven N. Carey Haraldur Sigurdsson

ABSTRACT Sedimentation from radially spreading gravity currents generated at the top of ascending sediment‐laden plumes is described by a model which assumes that sediment is dispersed homogeneously by turbulence in the gravity current, resulting in an exponential decrease in the concentration of sediment with time as particles settle out of the lower boundary of the current. For radial spreading this model predicts a Gaussian distribution of sediment accumulation away from the source with an exponential constant, B , which depends on flow rate, Q , and particle settling velocity, v ( B = nv/Q ). In the experiments described, sedimentation occurs from gravity currents generated by ascent of buoyant, particle‐laden plumes of fresh water in a tank of salty water. The sediment accumulation shows close agreement with the theoretical model, and the Gaussian decay constant, B , can be determined from a maximum in the accumulated mass of sediment per unit distance and from the slope of the line In( S/S 0 ) = ‐ Br 2 , where r is the radial distance, S is the sediment mass flux per unit area and S 0 is the value of S at r =0. Data from the dispersal of volcanic ejecta from a large ( c . 24 km high) plinian eruption column in the Azores also show good agreement with the theory, confirming that it is general and independent of scale and the nature of the fluid. The experimental data also show a change in sedimentation behaviour at distances from the source corresponding to the corner of the plume where it diverts into a lateral gravity current and there is an abrupt decrease in vertical velocity. Sedimentation of coarse grain sizes, between the source and the corner, occurs from the inclined plume margins and does not behave as predicted by the theoretical model.

Sedimentation

Gravity current

Settling

Turbidity current

Froude number

10.1111/j.1365-3091.1991.tb01875.x

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Citations (111)

Pteropods from the Caribbean Sea: variations in calcification as an indicator of past ocean carbonate saturation

Biogeosciences (2012)

Deborah Wall-Palmer Malcolm B. Hart Christopher Smart R. S. J. Sparks Anne Le Friant

Abstract. The aragonite shell-bearing thecosome pteropods are an important component of the oceanic plankton. However, with increasing pCO2 and the associated reduction in oceanic pH (ocean acidification), thecosome pteropods are thought to be particularly vulnerable to shell dissolution. The distribution and preservation of pteropods over the last 250 000 years have been investigated in marine sediment cores from the Caribbean Sea close to the island of Montserrat. Using the Limacina Dissolution Index (LDX), fluctuations in pteropod calcification through the most recent glacial/interglacial cycles are documented. By comparison to the oxygen isotope record (global ice volume), we show that pteropod calcification is closely linked to global changes in pCO2 and pH and is, therefore, a global signal. These data are in agreement with the findings of experiments upon living pteropods, which show that variations in pH can greatly affect aragonitic shells. The results of this study provide information which may be useful in the prediction of future changes to the pteropod assemblage caused by ocean acidification.

Ocean Acidification

10.5194/bg-9-309-2012

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Citations (32)

New estimates of the 1815 Tambora eruption volume

Journal of Volcanology and Geothermal Research (2014)

J. Kandlbauer R. S. J. Sparks

Dense-rock equivalent

Peléan eruption

Pyroclastic fall

Caldera

10.1016/j.jvolgeores.2014.08.020

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Citations (62)

A stress-controlled mechanism for the intensity of very large magnitude explosive eruptions

Earth and Planetary Science Letters (2011)

Antonio Costa Joachim Gottsmann Oleg Melnik R. S. J. Sparks

Silicic

Overpressure

Magma chamber

Effusive eruption

Dome (geology)

10.1016/j.epsl.2011.07.024

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Citations (39)

Melt Segregation in Deep Crustal Hot Zones: a Mechanism for Chemical Differentiation, Crustal Assimilation and the Formation of Evolved Magmas

Journal of Petrology (2012)

J. Solano Matthew D. Jackson R. S. J. Sparks Jon Blundy Catherine Annen

Mantle-derived basaltic sills emplaced in the lower crust provide a mechanism for the generation of evolved magmas in deep crustal hot zones (DCHZ). This study uses numerical modelling to characterize the time required for evolved magma formation, the depth and temperature at which magma formation occurs, and the composition of the magma. The lower crust is assumed to comprise amphibolite. In an extension of previous DCHZ models, the new model couples heat transfer during the repetitive emplacement of sills with mass transfer via buoyancy-driven melt segregation along grain boundaries. The results shed light on the dynamics of DCHZ development and evolution. The DCHZ comprises a mush of crystals plus interstitial melt, except when a new influx of basaltic magma yields a short-lived (20–200 years) reservoir of melt plus suspended crystals (magma). Melt segregation and accumulation within the mush yields two contrasting modes of evolved magma formation, which operate over timescales of c. 10 kyr–1 Myr, depending upon emplacement rate and style. In one, favoured by emplacement via over-accretion, or emplacement at high rates, evolved magma forms in the crust overlying the intruded basalt sills, and is composed of crustal partial melt, and residual melt that has migrated upwards out of the crystallizing basalt. In the other, favoured by emplacement via under- or intra-accretion, or by emplacement at lower rates, evolved magma forms in the intruded basalt, and the resulting magma is composed primarily of residual melt. In all cases, the upward migration of buoyant melt yields cooler and more evolved magmas, which are broadly granitic in composition. Chemical differentiation is therefore driven by melt migration, because the melt migrates through, and chemically equilibrates with, partially molten rock at progressively lower temperatures. Crustal assimilation occurs during partial melting, and mixing of crustal and residual melt occurs when residual melt migrates into the partially molten crust, yielding chemical signatures indicative of a mixed crustal and mantle origin. However, residual melt is volumetrically more significant than crustal melt, except at the highest emplacement rates. Contamination of crustal melt by residual melt from basalt crystallization appears to be an inevitable consequence of melt segregation in DCHZ, and can explain the mixed crust–mantle origin of many granites.

Sill

Magma chamber

Igneous differentiation

10.1093/petrology/egs041

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Citations (189)

The dynamics of bubble formation and growth in magmas: A review and analysis

Journal of Volcanology and Geothermal Research (1978)

R. S. J. Sparks

Supersaturation

10.1016/0377-0273(78)90002-1

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Citations (955)

The sources of granitic melt in Deep Hot Zones

Transactions of the Royal Society of Edinburgh Earth Sciences (2008)

Catherine Annen Jonathan D. Blundy R. S. J. Sparks

Abstract A Deep Hot Zone develops when numerous mafic sills are repeatedly injected at Moho depth or are scattered in the lower crust. The melt generation is numerically modelled for mafic sill emplacement geometries by overaccretion, underaccretion or random emplacement, and for intrusion rates of 2, 5 and 10mm/yr. After an incubation period, melts are generated by incomplete crystallisation of the mafic magma and by partial melting of the crust. The first melts generated are residual from the mafic magmas that have low solidi due to concentration of H 2 0 in the residual liquids. Once the solidus of the crust is reached, the ratio of crustal partial melt to residual melt increases to a maximum. If wet mafic magma, typical of arc environments, is injected in an amphibolitic crust, the residual melt is dominant over the partial melt, which implies that the generation of I-type granites is dominated by the crystallisation of mafic magma originated from the mantle and not by the partial melting of earlier underplated material. High ratios of crustal partial melt over residual melt are reached when sills are scattered in a metasedimentary crust, allowing the generation of S-type granites. The partial melting of a refractory granulitic crust intruded by dry, high-T mafic magma is limited and subordinate to the production of larger amount of residual melt in the mafic sills. Thus the generation of A-type granites by partial melting of a refractory crust would require a mechanism of selective extraction of the A-type melt.

Solidus

Sill

Fractional crystallization (geology)

10.1017/s0263593300001462

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Citations (78)

Sedimentology of deposits from the pyroclastic density current of 26 December 1997 at Soufrière Hills Volcano, Montserrat

Geological Society London Memoirs (2002)

L. J. Ritchie Paul Cole R. S. J. Sparks

abstract At 03:01 (local time) on 26 December 1997, major sector collapse followed by collapse of the andesitic lava dome occurred at Soufrière Hills Volcano, Montserrat. The collapse of the dome involved explosive disintegration and formation of a highly energetic pyroclastic density current (PDC), which was dispersed principally to the SW and devastated an area of 10 km 2 . The deposits of the PDC are divisible into valley-confined and unconfined facies. The latter is characterized by two bipartite units (Units I and II), both of which are composed of a fines-poor layer (layer 1) typically overlain by a finer-grained, fines-rich layer (layer 2). The sequence is interpreted as recording strongly pulsatory (unsteady) flow and is capped by Unit III, an accretionary lapilli-rich fallout layer. There are pronounced variations of lithofacies, thickness, grain size and sedimentary structures related to local topography. The PDC was highly erosive: it sculpted isolated mounds of deposit and heavily scoured the pre-existing substrate. Lithofacies are granulometrically distinct, with median diameter (Mdø) increasing as sorting coefficient (Ãø) decreases. Lithofacies characteristics depend strongly on azimuth over a 70° sector, with major lateral (cross-flow) changes at similar radial distances from the dome. The deposits are similar to those produced in the blast eruptions of Mont Pelée in 1902 and Mount St Helens in 1980. We infer that particle size sorting occurred during explosive expansion of the collapsing lava dome, such that the resulting PDC was initially stratified in both grain size and density. The marked lateral and vertical variations in grain size of the deposits indicate efficient further development of density stratification and grain-size sorting during transport, due to air entrainment and sedimentation.

10.1144/gsl.mem.2002.021.01.19

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Citations (33)

Small-volume, highly mobile pyroclastic flows formed by rapid sedimentation from pyroclastic surges at Soufrière Hills Volcano, Montserrat: an important volcanic hazard

Geological Society London Memoirs (2002)

T. H. Druitt Eliza S. Calder Paul Cole Richard P. Hoblitt Susan Loughlin

Abstract 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.

Sedimentation

Pyroclastic fall

10.1144/gsl.mem.2002.021.01.12

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Citations (100)

Three active volcanoes in China and their hazards

Journal of Asian Earth Sciences (2003)

Haiquan Wei R. S. J. Sparks Rong Liu Qingkai Fan Y. Wang

Scoria

Volcanic hazards

Felsic

10.1016/s1367-9120(02)00081-0

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Citations (122)