Richard Herd

... July (Table 1) and presumably was caused by the large volume of pyroclastic flow material displacing ... the shoreline was eroded by the tsunami, indicating that the surge was emplaced before the ... to have been generated during the most intense stages of the lava dome unloading ...

Terrain is a surface phenomenon that is measured, modelled, and mapped. However, it is continuously variable and must be simulated by points or mathematical equations that are inherently approximations. The error induced by digitally represented terrain can propagate to surface derivatives and geographical information science (GIS) applications where topography is considered. This can lead to uncertainty in model predictions and

During the 1995 to 1998 phase of dome growth at Soufrière Hills Volcano on Montserrat, we documented instability of the steep southern rim of English's Crater, known as Galway's Wall. The horseshoe-shaped…

Proximal deposits of small-volume trachytic eruptions are an under-studied record of eruption dynamics despite being common across a range of settings. The 59 ± 4 ka Echo Canyon deposits, Ascension Island, resulted from a small-volume explosive-effusive trachytic eruption. Variations in juvenile clast texture reveal changes in ascent dynamics and transitions in eruption style. Five dominant textural types are identified within the pumice lapilli population. Early Strombolian-Vulcanian eruption phases are typified by macro- and micro-vesicular equant clast types. Sheared clasts are most abundant at the eruption peak, transitioning to dense clasts in later phases due to shear-induced coalescence, outgassing and vesicle collapse. Melt densification and outgassing via tuffisite veins increased plume density, contributing to partial column collapse and the explosive-effusive transition. Bulk vesicularity distributions indicate a shift in dominant fragmentation mechanism during the erupti...

... the new techniques developed are making this eruption one of historic importance to ... the continuing activity, but the social and economic pressure building on officials ... Murray. , eds (1995) Monitoring Active Volcanoes: Strategies, Procedures and Techniques (University College ...

ABSTRACT The andesitic Soufrière Hills Volcano, Montserrat has been active since 1995, with five phases of dome growth to date. Mafic enclaves are ubiquitous, and supply of mafic magma is interpreted as the main driver for the current eruption. Recent (Phases IV to V) activity has changed from longer periods of dome growth to shorter more intensive episodes. This is coincident with an increase in the abundance and heterogeneity of mafic enclaves, implying that the changes in activity may reflect differences within the magmatic system. The intense Phase V episode lasted ~18 weeks, culminating in the energetic collapse of Feb. 11th 2010. Within these deposits three distinct mafic enclave types have been identified using textural and geochemical variations: (A) Weakly porphyritic basaltic enclaves; with chilled margins and inherited phenocryst proportions of < 8%. (B) Medium to highly porphyritic basaltic-andesite enclaves; with diffuse margins and inherited phenocryst proportions of 16-25%. (C) Composite; a mixture of types A and B indicating two-stage mixing. Textural and petrological variations also includes differences in: vesicularity, modal mineral assemblages, glass abundance, groundmass size and distribution. Inherited phenocrysts show petrological and geochemical characteristics consistent with late stage heating and inheritance from the andesite. Bulk XRF analyses of Phase V enclaves shows a wide compositional range of 48-58wt% SiO2. An observed SiO2 compositional gap between the mafic enclaves and host andesite in the earlier eruptive phases is no longer present, reflecting increasing hybridisation of the mafic enclaves. The majority of enclaves also have some geochemical characteristics distinctive from the earlier phase enclaves, e.g. higher MgO and lower FeO values. Successive replenishments of mafic magma have led to a more complex mixing regime as observed in the composite enclaves. The overall evolution of the geochemistry, coupled with increased textural variability across enclave types implies a correlation with the change in activity in the latter phases.

During the 1995 to 1998 phase of dome growth at Soufrière Hills Volcano on Montserrat, we documented instability of the steep southern rim of English's Crater, known as Galway's Wall. The horseshoe-shaped English's Crater provided good evidence for previous sector collapses, and assessments undertaken in late 1996 anticipated the possibility of a partial sector collapse and a SW-directed explosion, hazards previously unrecognized on Montserrat.A change from predominantly endogenous to exogenous growth of the lava dome at the end of 1996 eased the stress on the southern sector. However, rapid dome growth in November and December 1997 led to severe reloading and eventual sector failure at the base of the buried Galway's Wall and in the adjacent hot-spring area. This failure resulted in the debris avalanche and lateral blast of 26 December 1997.Similar sector collapses at a number of small volcanoes in the Caribbean, as well as worldwide, are evidence that edifice insta...

Since 1995 the eruption of the andesitic Soufrière Hills Volcano (SHV), Montserrat, has been studied in substantial detail. As an important contribution to this effort, the Seismic Experiment with Airgunsource-Caribbean Andesitic Lava Island Precision Seismo-geodetic Observatory (SEA-CALIPSO) experiment was devised to image the arc crust underlying Montserrat, and, if possible, the magma system at SHV using tomography and reflection seismology. Field operations were carried out in October–December 2007, with deployment of 238 seismometers on land supplementing seven volcano observatory stations, and with an array of 10 ocean-bottom seismometers deployed offshore. The RRS James Cook on NERC cruise JC19 towed a tuned airgun array plus a digital 48-channel streamer on encircling and radial tracks for 77 h about Montserrat during December 2007, firing 4414 airgun shots and yielding about 47 Gb of data. The main objecctives of the experiment were achieved. Preliminary analyses of these d...

Eruption of the Soufriere Hills volcano began on 18 July 1995 after three years of elevated seismic activity. Four months of increasingly vigorous phreatic activity culminated in mid-November 1995 with the initiation of dome growth. Growth rates increased unevenly through early March ...

The prolonged and ongoing volcanic activity at SoufriSre Hills Volcano (SHV), Montserrat, provides a rare chance for collecting multi-stream monitoring data in support of volcano research. Conventional surface geophysical instrumentation and detailed observational and geochemical data have enabled the development of a good understanding of surface and near-surface physical processes controlling eruptive style and intensity at SHV. However, the geophysical

Project CALIPSO (Caribbean Andesite Lava Island-volcano Precision Seismo-geodetic Observatory) was developed in order to investigate the magmatic system at the exceedingly active Soufriere Hills Volcano (SHV), Montserrat. The collaborative project involves a number of institutions acting in partnership with the Montserrat Volcano Observatory (MVO), and is funded by NSF with a contribution to drilling costs provided by UK NERC. SHV

Project CALIPSO (Caribbean Andesite Lava Island-volcano Precision Seismo-geodetic Observatory) investigates with borehole and surface instruments the magmatic system at the very active Soufriere Hills Volcano (SHV), Montserrat, supplementing surface monitoring systems of the Montserrat Volcano Observatory, and those of other institutions including PSU and U Ark. Many aspects of andesitic magmatic system dynamics remain little understood despite significant monitoring and

... Dunkley, P.; Voight, B.; Edmonds, M.; Herd, R.; Strutt, M.; Thompson, G.; Bass, V.; Aspinall, WP; Neuberg, J.; Sparks, R.; Mattioli, G.; Hidayat, D.; Elsworth ... One of the regular six-monthly meetings of the Risk Assessment Panel (RAP) took place on 3-4 Sept 02 and concluded that if ...

ABSTRACT The violent eruption of Merapi volcano (Central Java) that started on 26 October 2010 was the volcano's largest since 1872 and the deadliest event since 1930. Before 2010, Merapi's more recent (historical) eruptive activity was repeatedly characterised by periods of slow lava dome extrusion punctuated by gravitational dome failures, generating small-volume pyroclastic density currents (PDCs) with runout distances of typically less than 10 km. The unforeseen, large-magnitude events in 2010 were unusual in many respects: (1) the eruption was short-lived and started with an explosive phase that was not preceded by a lava dome at the surface; (2) between 31 October and 4 November, a lava dome appeared and grew rapidly within the summit crater, exceeding growth rates observed at the peak of the penultimate eruption in 2006 by a factor of ~ 22; (3) during the most vigorous eruptive phase on 5 November, at least one PDC travelled more than 15 km (more than twice the distance of the largest flows in 2006) beyond the summit along the Gendol river valley, causing widespread devastation on Merapi's south flank; (4) in a late phase of the eruption, pumice-rich PDCs were produced, forming a thin veneer on top of the deposits of the largest PDCs from 5 November; (5) ash emissions from sustained eruption columns resulted in ash fall tens of kilometres from the volcano, affecting, amongst other areas, the volcano's western slopes and the city of Yogyakarta ~ 25 km to the south; and (6) the total deposited volume in 2010, based on provisional estimates, may have been ~ 10 times higher than that of other recent eruptions. Here we report and present new geochemical, Sr-Nd-O isotope and U-series data for the volcanic products (lava dome fragments, magmatic inclusions, scoria, pumice and ash) from various stages of the 2010 eruption of Merapi. These data are discussed in the context of other recent to historical, typically less explosive, dome-forming eruptions to elucidate the driving forces behind the unusual explosive behaviour in 2010 and their timescales. The 2010 events highlight that dome extrusion and relatively small, prolonged dome-forming eruptions at Merapi can be interrupted at relatively short notice by larger and more vigorous eruption phases or eruptions, which appear more common in the geological record. An improved knowledge of these processes and of changes in the pre-eruptive magma system has important implications for the assessment of hazards and risks from future eruptive activity at Merapi.

abstractEruption 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 km3 of crystal-rich andesitic lava. Discharge rates gradually accelerated from >1 m3 s-1 during the first few months to >5 m3 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 ...

GPS measurements at Soufriere Hills volcano on Montserrat show that displacements that occurred since 1995 are irreversible. Displacements measured between June 1996 and June 1997 (Shepherd et al., 1998) are re-interpreted using a 3D Boundary Element Method (BEM) for elastic medium. Using a spherical source model, it is shown that the source of the displacements is located at the base of the dome (350 meters below the dome summit in 1997), therefore these displacements could be created by the dome weight. Further models show that the weight of the dome on the crater floor only accounts for 14 percent of the measured displacements. We have then assumed the dome was fed by a vertical cylindrical conduit. Increase in the dome volume increases pressure in the conduit. We find that this pressure could explained the GPS observations if the conduit radius was 350 meters in diameter. In 1996 and 1997, tiltmeters recorded cyclic deformations of the edifice (Voight et al, 1999). Two tiltmeters operated simultaneously at different distances from the summit allowing determination of the source depth. Assuming these deformations are created by the pressurization of a portion of a cylindrical conduit in an elastic medium and using again a 3D BEM, we show that this source is located at 900 meters depth below the dome summit. Scaling the conduit diameter so that the rock matrix does not fail, the measured tilt amplitudes are explained by a conduit diameter larger than 100 meters. These interpretations of Montserrat deformations lead us to estimate a conduit diameter much larger than the 30 meter-diameter estimated from geological and petrological interpretations (Devine et al., 1998). This paradox can be explained if the conduit size estimated from the deformations corresponds to a "pseudo-pressurized-conduit" made of a central cylindrical conduit where magma is flowing, embedded in a visco-plastic cylindrical medium where stresses are close to hydrostatic so that magma pressures are transmitted to the surrounding elastic rock matrix. This explanation is compatible with the geological and petrological interpretations as these methods provided the conduit diameter required to transport magma to the surface. This Anelastic rheology is particularly relevant to studies of the stability of the edifice and further risk assessment

Lavas from the current eruption of the Soufrière Hills Volcano, Montserrat exhibit evidence for magma mingling, related to the intrusion of mafic magma at depth. We present detailed field, petrological, textural and geochemical descriptions of mafic enclaves in andesite erupted during 2009-2010, and subdivide the enclaves into three distinct types. Type A are mafic, glassy with chilled margins and few inherited phenocrysts. Type B are more evolved with high inherited phenocryst contents and little glass, and are interpreted as significantly hybridised. Type C are composite, with a mafic interior (type A) and a hybrid exterior (type B). All enclaves define tight linear compositional trends, interpreted as mixing between a mafic end-member (type A) and host andesite. Enclave glasses are rhyolitic, owing to extensive crystallisation during quenching. Type A quench crystallisation is driven by rapid thermal equilibration during injection into the andesite. Conversely, type B enclaves fo...

Abstract Dome growth at Soufrière Hills Volcano halted in early March 1998. After dome growth ceased, seismicity reduced significantly, but activity related to dome disintegration and degassing of magma at depth continued. A sustained episode of pyroclastic flows on ...

Lavas from the current eruption of the Soufrière Hills Volcano (SHV), Montserrat exhibit evidence for magma mingling, related to the intrusion of mafic magma at depth. We present detailed field, petrological, textural and geochemical descriptions of mafic enclaves in andesite erupted during 2009–2010, and subdivide the enclaves into three distinct types: type A are mafic, glassy with chilled margins and few inherited phenocrysts; type B are more evolved with high inherited phenocryst content and little glass, and are interpreted as significantly hybridized; type C are composite, with a mafic interior (type A) and a hybrid exterior (type B). All enclaves define tight linear compositional trends, interpreted as mixing between a mafic end member (type A) and host andesite. Enclave glasses are rhyolitic, owing to extensive crystallization during quenching. Type A quench crystallization is driven by rapid thermal equilibration during injection into the andesite. Conversely, type B enclav...

The Soufriere Hills volcano (SHV) CGPS network consists of 6 dual-frequency code-phase receivers, with Dorn-Margolin choke-ring antennae, which share a common RF telemetry network. All GPS data were processed using GIPSY-OASISII to obtain free-network point positions using final orbit, clock, and earth orientation parameters from JPL. Positions were recast into ITRF97 and these positions were used to calculate component velocities.

Lavas from the current eruption of the Soufrie`re Hills Volcano (SHV), Montserrat exhibit evidence for magma mingling, related to the intrusion of mafic magma at depth. We present detailed field, petrological, textural and geochemical descriptions of mafic enclaves in andesite erupted during 2009–2010, and subdivide the enclaves into three distinct types: type A are mafic, glassy with chilled margins and few inherited phenocrysts; type B are more evolved with high inherited phenocryst content and little glass, and are interpreted as significantly hybridized; type C are composite, with a mafic interior (type A) and a hybrid exterior (type B). All enclaves define tight linear compositional trends, interpreted as mixing between a mafic end member (type A) and host andesite. Enclave glasses are rhyolitic, owing to extensive crystallization during quenching. Type A quench crystallization is driven by rapid thermal equilibration during injection into the andesite. Conversely, type B enclaves form in a hybridized melt layer, which ponded near the base of the chamber and cooled more slowly. Vesiculation near the mafic–silicic interface resulted in disruption of the hybridized layer and the formation of the type B enclaves. The composite enclaves represent an interface between types A and B, suggesting multiple episodes of mafic injection.

A large dome collapse took place on 12-13 July 2003 at Soufriere Hills Volcano. This event was the largest in magnitude during the 1995-2003 eruption and involved over 120 million m3 andesite dome and talus material. The collapse took place over 18 hours and culminated in an explosive phase that continued intermittently until 15 July 2003. Prior to the collapse, the total volume of the dome was 230 million m3 and was made up of remnants of lava erupted 1997-2001, talus material and fresh andesite dome lava erupted during the last two years. Talus made up around 50% of the total dome volume. This paper describes and interprets the pyroclastic flow and airfall deposits from this event, using other monitoring data and empirical evidence to reconstruct the dome collapse. The airfall and pyroclastic flow deposits were studied in detail over the weeks following the collapse. Airfall deposits were studied at 45 locations around the island and 75 samples were collected for analysis. The sur...

ABSTRACT The interplay between magma ascent, degassing and changing magmatic properties are widely recognized as critical factors controlling the style of silicic volcanic eruptions. Microlite textures in samples from the prolonged dome-forming eruption of Merapi in 2006 provide a record of changing magmatic ascent conditions and shallow conduit processes throughout the eruption. Analysis of microlite textural parameters, including measurements of areal number density (NA), mean microlite size, crystal aspect ratio and groundmass crystallinity (φ), combined with the monitoring record and field observations, indicate that magma ascent paths change between continuous ascent at varying rates from a deeper magma storage region, to ascent being temporarily stalled at shallow depths in the latter stages of the eruption, supporting the idea of an ephemeral shallow magma storage region at Merapi. Plagioclase microlite compositions show evidence of decompression-induced degassing, often displaying rims of anorthoclase and more K-rich alkali feldspar (sanidine). Anorthite contents also support the textural data of later erupted magma being temporarily stalled at shallow depths. Crystal size distributions (CSDs) are interpreted to show that both growth-dominated and nucleation-dominated crystallisation regimes existed during the 2006 eruption, resulting from changing conditions of undercooling (ΔT) during variable magma ascent paths. By contrast, microlite textural analysis and feldspar microlite compositions of samples from the fast-growing lava dome of the second phase of the 2010 eruption prior to the cataclysmic events on 5 November indicate faster ascent rates, a crystallisation regime more strongly dominated by nucleation due to high ΔT and interaction of the 2010 magma with more hotter magma from depth.

Kilauea is one of the better studied volcanoes on Earth, and regular SO2 flux measurements over the past 26 years have, along with concurrent geophysical measurements, improved our understanding of eruptive processes. In particular, the temporal pattern of summit SO2 release has served to test the model of Kilauea's summit reservoir as a way station for magma bound for the east rift eruption site. East rift SO2 emissions, on the other hand, are now regularly used to track the overall lava effusion rate. These gas-based eruption rate data confirm concurrent geophysical measurements made by Very Low Frequency (VLF) profiling of master lava tubes. Although data from weekly SO2 measurements clearly track eruptive changes over weeks to months, much of Kilauea's activity varies on a shorter timescale-minutes to days. In order to capture these transients, including complex deflation-inflation events, effusive bursts, and gas pistoning, high sampling rates are required, comparable...