vulcanian explosion at soufriere hills volcano montserrat on march 2004 as revealed by strain data 1 the calipso collaborative volcano monitoring system on the caribbean island of montserrat includes observations of strain at depths 200 m using sacks evertson strainmeters strain data for the march 2004 explosion of the soufriere hills volcano are characterized by large roughly equal but opposite polarity changes at the two near sites and much smaller changes at a more distant site the strain amplitudes eliminate a spherical pressure mogi type source as the sole contributor the initial changes are followed by smaller recoveries but with differing relative recovery magnitudes this dissimilarity requires a minimum of two pressure sources which we model as a deep spherical pressure source and a shallow dike the spherical source is fixed at the location derived from data for the massive dome collapse in july 2003 we solve for the best fitting dike plus sphere source combination the dike geometry is consistent with earlier interpretations of dikes based on gps data and other lines of evidence

unique strainmeter observations of vulcanian explosions soufriere hills volcano montserrat july 2003 gravity waves propagated at 30 m s 1 eruption volumes estimated from plume height and strain data are 0 32 0 42 10 6 0 26 0 49 10 6 and 0 81 0 84 10 6 m 3 f or explosions 3 5 respectively consistent with quasi cylindrical conduit drawdown 2 km the duration of vigorous explosion is given by the strain signature indicating mass fluxes of order 10 7 kg s 1 conduit pressures released reflect static weight of porous gas charged magma and exsolution generated overpressures of order 10 mpa citation voight b et al 2010 unique strainmeter observations of vulcanian explosions soufriere hills volcano montserrat july 2003 geophys res lett 37 l00e18 doi 10 1029 2010gl042551

control on the emplacement of the andesite lava dome of the soufriere hills volcano montserrat by degassing induced crystallization lava solidification is controlled by two mechanisms external cooling and gas exsolution the latter inducing crystallization due to increasing liquidus temperature the andesite lava dome of the soufriere hills volcano montserrat is an extrusion dominated by crystallization caused by gas exsolution where cooling is unimportant in controlling emplacement in the magma chamber the magma has an estimated viscosity of 7 106 pa s during ascent gas exsolution caused the magma to extrude in a highly crystalline state with only 5 15 residual melt viscosities in the range 1013 1014 pa s and mechanical strength 1 mpa deformation can be heterogeneous with extrusion along shear zones rheological stiffening in the upper conduit also causes large overpressures shallow seismicity and cyclic patterns of dome extrusion gas rich porphyritic andesites tend to be the least mobile kind of lava because transition from magma into hot crystalline material was reached during ascent

seismic hybrid swarm precursory to a major lava dome collapse 9 12 july 2003 soufriere hills volcano montserrat abstract a swarm of 9500 hybrid earthquakes preceded the 12 13 july 2003 dome collapse at soufriere hills volcano montserrat most events had nearly identical waveforms and cross correlation was applied to measure inter event periods as well as phase arrival times to determine accurate relative location hypocenter depths were shallow

eruption of soufriere hills 1995 2009 from an offshore perspective insights from repeated swath bathymetry surveys this contribution provides an analysis of the 1995 2009 eruptive period of soufriere hills volcano montserrat from a unique offshore perspective the methodology is based on five repeated swath bathymetric surveys the difference between the 2009 and 1999 bathymetry suggests that at least 395 mm3 of material has entered the sea this proximal deposit reaches 95 m thick and extends 7km from shore however the difference map does not include either the finer distal part of the submarine deposit or the submarine part of the delta close to the shoreline we took both contributions into account by using additional information such as that from marine sediment cores by march 2009 at least 65 of the material erupted throughout the eruption has been deposited into the sea this work provides an excellent basis for assessing the future activity of the soufriere hills volcano including potential collapse and other volcanoes on small islands

satellite based constraints on explosive so2 release from soufriere hills volcano montserrat 1 numerous episodes of explosive degassing have punctuated the 1995 2009 eruption of soufriere hills volcano shv montserrat often following major lava dome collapses we use ultraviolet uv and infrared ir satellite measurements to quantify sulfur dioxide so2 released by explosive degassing which is not captured by routine ground based and airborne gas monitoring we find a total explosive so2 release of 0 5 tg which represents 6 of total so2 emissions from shv since july 1995 the majority of this so2 0 4 tg was vented following the most voluminous shv dome collapses in july 2003 and may 2006 based on our analysis we suggest that the so2 burden measured following explosive disruption of lava domes depends on several factors including the instantaneous lava effusion rate dome height above the conduit and the vertical component of directed explosions space based so2 measurements merit inclusion in routine gas monitoring at shv and other dome forming volcanoes

modelling the lava dome extruded at soufriere hills volcano montserrat august 2005 may 2006 part i dome shape and internal structure lava domes comprise core carapace and clastic talus components they can grow endogenously by inflation of a core and or exogenously with the extrusion of shear bounded lobes and whaleback lobes at the surface internal structure is paramount in determining the extent to which lava dome growth evolves stably or conversely the propensity for collapse the more core lava that exists within a dome in both relative and absolute terms the more explosive energy is available both for large pyroclastic flows following collapse and in particular for lateral blast events following very rapid removal of lateral support to the dome knowledge of the location of the core lava within the dome is also relevant for hazard assessment purposes a spreading toe or lobe of core lava over a talus substrate may be both relatively unstable and likely to accelerate to more violent activity during the early phases of a retrogressive collapse soufriere hills volcano montserrat has been erupting since 1995 and has produced numerous lava domes that have undergone repeated collapse events we consider one continuous dome growth period from august 2005 to may 2006 that resulted in a dome collapse event on 20th may 2006 the collapse event lasted 3 h removing the whole dome plus dome remnants from a previous growth period in an unusually violent and rapid collapse event we use an axisymmetrical computational finite element method model for the growth and evolution of a lava dome our model comprises evolving core carapace and talus components based on axisymmetrical endogenous dome growth which permits us to model the interface between talus and core despite explicitly only modelling axisymmetrical endogenous dome growth our core talus model simulates many of the observed growth characteristics of the 2005 2006 shv lava dome well further it is possible for our simulations to replicate large scale exogenous characteristics when a considerable volume of talus has accumulated around the lower flanks of the dome model results suggest that dome core can override talus within a growing dome potentially generating a region of significant weakness and a potential locus for collapse initiation

growth of the lava dome and extrusion rates at soufriere hills volcano montserrat west indies 2005 2008 the third episode of lava dome growth at soufriere hills volcano began 1 august 2005 and ended 20 april 2007 volumes of the dome and talus produced were measured using a photo based method with a calibrated camera for increased accuracy the total dense rock equivalent dre volume of extruded andesite magma 306 51 mm3 was similar within error to that produced in the earlier episodes but the average extrusion rate was 5 6 0 9 m3s 1 dre higher than the previous episodes extrusion rates varied in a pulsatory manner from 0 5 m3s 1 to 20 m3s 1 on 18 may 2006 the lava dome had reached a volume of 85 mm3 dre and it was removed in its entirety during a massive dome collapse on 20 may 2006 extrusion began again almost immediately and built a dome of 170 mm3 dre with a summit height 1047 m above sea level by 4 april 2007 there were few moderate sized dome collapses 1 10 mm3 during this extrusive episode in contrast to the first episode of dome growth in 1995 8 when they were numerous the first and third episodes of dome growth showed a similar pattern of low 0 5 m3s 1 but increasing magma flux during the early stages with steady high flux after extrusion of 25 mm3

real time seismic amplitude measurement rsam a volcano monitoring and prediction tool seismicity is one of the most commonly monitored phenomena used to determine the state of a volcano and for the prediction of volcanic eruptions although several real time earthquake detection and data acquisition systems exist few continuously measure seismic amplitude in circumstances where individual events are difficult to recognize or where volcanic tremor is prevalent analog seismic records provide a quick visual overview of activity however continuous rapid quantitative analysis to define the intensity of seismic activity for the purpose of predicing volcanic eruptions is not always possible because of clipping that results from the limited dynamic range of analog recorders at the cascades volcano observatory an inexpensive 8 bit analog to digital system controlled by a laptop computer is used to provide 1 min average amplitude information from eight telemetered seismic stations the absolute voltage level for each station is digitized averaged and appended in near real time to a data file on a multiuser computer system raw realtime seismic amplitude measurement rsam data or transformed rsam data are then plotted on a common time base with other available volcano monitoring information such as tilt changes in earthquake activity associated with dome building episodes weather and instrumental difficulties are recognized as distinct patterns in the rsam data set rsam data for domebuilding episodes gradually develop into exponential increases that terminate just before the time of magma extrusion mount st helens crater earthquakes show up as isolated spikes on amplitude plots for crater seismic stations but seldom for more distant stations weather related noise shows up as low level long term disturbances on all seismic stations regardless of distance from the volcano implemented in mid 1985 the rsam system has proved valuable in providing up to date information on seismic activity for three mount st helens eruptive episodes from 1985 to 1986 may 1985 may 1986 and october 1986 tiltmeter data the only other telemetered geophysical information that was available for the three dome building episodes is compared to rsam data to show that the increase in rsam data was related to the transport of magma to the surface thus if tiltmeter data is not available rsam data can be used to predict future magmatic eruptions at mount st helens we also recognize the limitations of rsam data two examples of rsam data associated with phreatic or shallow phreatomagmatic explosions were not preceded by the same increases in rsam data or changes in tilt associated with the three dome building eruptions

using a discrete element approach to model lava dome emplacement and collapse abstract lava dome collapses can lead to explosive activity and pyroclastic flow generation which makes them one of the most deadly consequences of volcanic activity the mechanisms linked to a collapse are however still poorly understood and very few numerical models exist that investigate the actual collapse of a lava dome after emplacement we use a discrete element method implemented in the modelling software particle flow code to investigate lava dome growth but also go further to test the stability of the dome under the following conditions increased internal pressure switch in extrusion direction caused by partial cooling of the dome and extrusion of lava onto variable underlying topography we initially show the morphology development of a growing lava dome and how the rheological boundary between core and talus evolves throughout the lifetime of a dome and with varied solidus pressures through visualisation of strain accumulation within the lava dome we show superficial rockfall development due to interaction with topography whereas large deep seated failures occur when the dome is exposed to internal overpressures we find that a switch in extrusion direction promotes a transition from endogenous to exogenous dome growth and leads to lava lobe formation we demonstrate that lava dome collapse exhibits many features similar to common landslides and by investigating strain patterns within the dome we can use numerical modelling to understand features that elude field observations

identification of structural controls in an active lava dome with high resolution dems volcan de colima mexico monitoring the topography of active lava domes is critical for detecting changes that may trigger or influence collapse or explosive activity internal dome structure and conditions are more difficult to elucidate but also play vital roles here we describe the exposure following an explosion of significant scarps in the active dome at volcan de colima mexico that are interpreted as evidence of brittle failure planes and a complex internal dome morphology in the first use of automated 3d computer vision reconstruction techniques structure from motion and multi view stereo sfm mvs on an active volcanic dome we derive high resolution surface models from oblique and archive photographs taken with a consumer camera the resulting 3d models were geo referenced using features identified in a web sourced orthoimage no ground based measurements were required in december 2010 the dome 2 14 106 m3 had a flat upper surface reflecting an overall ductile emplacement regime between then and may 2011 a period of low explosivity was accompanied by a small volume loss 0 4 105 m3 and arcuate steps appeared in the dome surface suggesting the presence of localized planes of weakness the complex array of summit scarps was exposed following a significant explosion in june 2011 and is interpreted to be the surface expression of fault planes in the dome the 1 m resolution dems indicated that the region of greatest volume loss was not coincident with the assumed location of the conduit and that heterogeneity within the dome may have been important during the june explosion

cyclical patterns in volcanic degassing revealed by so2 flux timeseries analysis an application to soufriere hills volcano montserrat abstract cyclical patterns of behaviour in timeseries of seismic and geodetic data at volcanoes are frequently observed during lava dome building eruptions and are particularly well documented from the current eruption of the soufriere hills volcano shv montserrat however the discontinuous nature of many so 2 measurements often preclude the identification and quantitative analysis of cyclical patterns in degassing data here using a long so 2 timeseries from shv with continuous measurements since 2002 we explore for the first time degassing behaviour at a resolution comparable to that possible for seismic and deformation datasets timeseries analysis of flux data spanning 2002 2011 reveals that so 2 emissions at shv exhibit complex cyclicity with dominant cycles evident on both multi year and multi week 50 day timescales these cycles persist through phases of both active extrusion and eruptive pause and show close similarities to periodic components previously identified at shv in timeseries of seismicity ground deformation and lava extrusion the strength of expression or amplitude of degassing cycles particularly on multi week timescales shows distinct temporal variation and appears to correlate with the occurrence and nature of explosive activity occurring in 2002 2009 this suggests that the amplitude of surface gas flux cycles is modulated by physical conditions within the conduit direct quantitative comparison between seismicity dome growth and degassing for eruptive phases 2 2002 2003 and 3 2005 2007 reveals that peaks in so 2 flux appear to correspond broadly to enhanced lava extrusion and elevated seismicity within cycles of 30 50 days however time lags of 2 4 and 7 days are observed between initial low frequency seismic swarms and peaks in dome growth so 2 flux and rockfall event rate respectively multi parameter correlations offer valuable insights into the controls on subsurface gas ascent but further research is required to fully explore the contributions of permeability and overpressure as well as other subsurface processes

field survey and numerical simulation of the 21 november 2004 tsunami at les saintes lesser antilles 1 although a few historical tsunamis have occurred in the lesser antilles region their characteristics are poorly documented due to the ephemeral nature of the associated signatures recently a tsunami was generated following a magnitude mw 6 3 earthquake that occurred on 21 november 2004 between guadeloupe and dominica this was one of the two largest historical earthquakes recorded in this area in the last century a field survey allowed us to characterize the tsunami which affected les saintes the southern coast of basse terre guadeloupe and northern dominica we used these data to constrain a numerical simulation of tsunami generation and propagation the 21 november tsunami provides a unique opportunity to further constrain the models of brittle deformation in the back arc region proposed by previous tectonic investigations to characterize the tsunami signatures and to improve regional hazards evaluation

seismicity of rockfalls and avalanches at three cascade range volcanoes implications for seismic detection of hazardous mass movements abstract this study reviews seismograms from 14 rockfalls and avalanches of moderate to large volume 10 4 to 10 7 m 3 at mount st helens mount adams and mount rainier in the cascade range of washington to investigate how variations in source volume source materials track materials and failure modes affect avalanche seismicity the largest signals were generated by rockfalls at mount st helens and debris avalanches at mount rainier that initiated as block failures at mount st helens several rockfalls that originated as block failures near the crater rim descended slopes with similar profiles and appear to show a linear or nearly linear relation between source volume and seismogram amplitude those that fell over an extended period of time were poorly recorded at the reference seismic station and did not show this correlation multiple seismograms from three of the four instrumentally recorded debris avalanches at mount rainier indicate a tendency of unstable slopes there to fail progressively a pattern that has important implications for the mass movement hazard at mount rainier seismic evidence shows that the little tahoma rock fall avalanches in december 1963 occurred on 6 december over a week earlier than previously reported mass movements that have been seismically detected span the spectrum of rapid flowage events from water surges and debris flows to dry rock debris ice and snow avalanches the success in identifying and in some cases locating these events in near real time demonstrates that local and regional seismic networks can play a valuable role in reducing hazards from large rapid mass movements

anatomy of a lava dome collapse the 20 march 2000 event at soufriere hills volcano montserrat abstract a second extrusive phase of the currently ongoing 1995 2003 eruption of soufriere hills volcano shv montserrat commenced in mid november 1999 following 19 months during which no fresh lava had reached the surface by mid march 2000 a new andesite lava dome constructed within a collapse scar girdled by remnants of the 1995 1998 dome complex had attained an estimated volume of 29 3 million m3 mm3 on 20 march 2000 during a period of heavy rainfall on the island a significant collapse event ensued that removed 95 of the new lava dome 28 3 mm3 during 5 hours of activity that generated 40 pyroclastic flows and at least one magmatic explosion the associated ash cloud reached an altitude of 9 km and deposited ash on the island of guadeloupe to the southeast and a number of lahars and debris flows occurred in valleys on the flanks of shv a large quantity of observational data including contemporaneous field observations and continuous data from the broadband seismic network on montserrat allow a detailed reconstruction of this dome collapse event in contrast to most of the large dome collapses at shv the 20 march 2000 event is distinguished by a lack of short term precursory elevated seismicity at shallow depths beneath the lava dome broadband seismic amplitude data recorded during the event are used to infer the cumulative volume of collapsed dome as the collapse progressed these data indicate that the high velocity pyroclastic flows observed at the climax of the event removed by far the largest portion 68 of the lava dome at peak discharge rates estimated from the seismic record of 2 104 m3 s 1 following the 20 march 2000 collapse lava dome growth recommenced immediately and continued without significant interruption until another larger dome collapse occurred on 29 july 2001 the 29 july 2001 event also coincided with heavy rainfall on montserrat matthews et al 2002 geophys res lett 29 doi 10 1029 2002gl014863 and lacked precursory elevated seismic activity we attribute the initiation of the 20 march 2000 collapse to a prolonged spell of heavy rainfall on the lava dome prior to and during the event the precise causal mechanism remains controversial though some combination of mechanical erosion and or destabilization of a critically poised face of the lava dome the action of pressurized steam or water on potential failure surfaces within the dome rapid cooling of hot lava and small phreatic explosions seems likely anecdotal evidence exists for other rainfall induced activity on montserrat and the triggering of explosive or pyroclastic flow activity by rainfall has been noted at dome forming volcanoes elsewhere including merapi indonesia voight et al 2000 j volcanol geotherm res 100 69 138 unzen japan yamasato et al 1997 papers meteorol geophys 48 santiaguito guatemala smithsonian institution global volcanism network bull 15 1990 and mount st helens usa mastin 1994 geol soc am bull 106 175 185 hazard mitigation plans at dome forming volcanoes would therefore benefit from the inclusion of meteorological forecasting and rain monitoring equipment particularly in the tropics

submarine pyroclastic deposits formed at the soufriere hills volcano montserrat 1995 2003 what happens when pyroclastic flows enter the ocean the soufriere hills volcano montserrat west indies has undergone a series of dome growth and collapse events since the eruption began in 1995 over 90 of the pyroclastic material produced has been deposited into the ocean sampling of these submarine deposits reveals that the pyroclastic flows mix rapidly and violently with the water as they enter the sea the coarse components pebbles to boulders are deposited proximally from dense basal slurries to form steep sided near linear ridges that intercalate to form a submarine fan the finer ash grade components are mixed into the overlying water column to form turbidity currents that flow over distances 30 km from the source the total volume of pyroclastic material off the east coast of montserrat exceeds 280 106 m3 with 65 deposited in proximal lobes and 35 deposited as distal turbidites

remobilization of andesite magma by intrusion of mafic magma at the soufriere hills volcano montserrat west indies the 1995 1999 eruption of the soufriere hills volcano montintroduction serrat has produced a crystal rich andesite containing quenchthe soufriere hills volcano montserrat located in the textured mafic inclusions which show evidence of having been molten lesser antilles island arc in the west indies began to when incorporated into the host magma individual crystals in the erupt on 18 july 1995 after about 350 years of dormancy andesite record diverse histories amphibole phenocrysts vary from young et al 1998b the eruption was preceded by a pristine and unaltered to strongly oxidized and pseudomorphed by period of seismic swarms which began in january 1992 anhydrous reaction products plagioclase phenocrysts are commonly previous earthquake crises have occurred on montserrat reverse zoned often with dusty sieve textures reverse zoned rims are in 1896 1897 1932 1935 and 1966 1967 powell 1938 also common on orthopyroxene phenocrysts pyroxene geothermometry shepherd et al 1971 initial phreatic and phregives an average temperature of 858 20 c for orthopyroxene atomagmatic activity was followed by extrusion of an phenocryst cores whereas reverse zoned rims record temperatures andesitic lava dome in november 1995 pyroclastic flows from about 880 to 1050 c the heterogeneity in mineral rim generated by gravitational collapse of the unstable dome compositions zoning patterns and textures is interpreted as reflecting have been the dominant form of activity throughout the non uniform reheating and remobilization of the resident magma eruption but periods of explosive activity producing body by intrusion of hotter mafic magma convective remobilization pumice flows and falls have also occurred robertson et results in mixing together of phenocrysts that have experienced al 1998 young et al 1998b dome growth ceased different thermal histories depending on proximity to the intruding suddenly in march 1998 and further activity up to may mafic magma the low temperature and high crystallinity are 1999 has mainly involved gravitational collapses of the interpreted as reflecting the presence of a cool highly crystalline dome and periods of ash venting with some small scale magma body beneath the soufriere hills volcano the petrological vulcanian explosive events observations in combination with data on seismicity extrusion rate the soufriere hills volcano is the only active centre and so2 fluxes indicate that the current eruption was triggered by on montserrat the volcano is a composite of at least recent influx of hot mafic magma five andesitic lava domes flanked by pyroclastic deposits rea 1974 identified four other volcanic centres all

tsunami deposits associated with the 7 3 ka caldera forming eruption of the kikai caldera insights for tsunami generation during submarine caldera forming eruptions abstract timing and mechanism of volcanic tsunamis will be a key to understand the dynamics of large scale submarine explosive volcanism tsunami deposits associated with the vei 7 eruption of the kikai caldera at 7 3 ka are found in the yakushima and kuchinoerabujima islands 40 km south southeast of the caldera rim the tsunami deposits distribute along the rivers in their northern coast up to 4 5 km from the river exit and up to 50 m above the present sea level the tsunami deposits in the yakushima area consist of pumice bearing gravels in the lower part of the section unit i and pumiceous conglomerate in the upper part unit ii the presence of rounded pebbles of sedimentary rocks which characterize the beach deposit indicates a run up current from the coastal area the rip up clasts of the underlying paleosol in unit i show strong erosion during the invasion of tsunami compositional similarity between the pumices in the tsunami deposit and the juvenile materials erupted in the early phase of the akahoya eruption indicates the formation of tsunami deposit during the early phase of the eruption which produced the initial plinian pumice fall and the lower half of the koya pyroclastic flow presence of the dense volcanic components obsidians and lava fragments besides pumices in the tsunami deposit supports that they were carried by the koya pyroclastic flow and not the pumices floating on the sea surface sequential relationship between the koya pyroclastic flow and the tsunami suggests that the emplacement of the pyroclastic flow into the sea surrounding the caldera is the most probable mechanism of the tsunami

in situ measurements of plagioclase growth using sims depth profiles of 7li 30si a means to acquire crystallization rates during short duration decompression events numerous petrologic studies have attempted to determine crystal growth rates in volcanic systems through several methods including analyses of crystal size distributions in natural samples and decompression experiments on hydrous magmas experiments have revealed that rim growth on existing crystals will occur under a wide range of decompression conditions and is favored under conditions of low to moderate undercoolings over microlite nucleation which has typically been the focus of decompression induced crystallization studies for this study samples of eruptive clasts were collected from a vulcanian explosion that occurred following the july 12 13 2003 dome collapse of soufriere hills volcano montserrat plagioclase phenocrysts were extracted and examined with secondary ion mass spectrometry sims depth profiling lithium inflection depths within the profiles along with the observed time interval between the peak in the collapse decompression and the explosion that ejected the examined samples were used to calculate the growth rates as a result of magma devolatilization with an average of 8 3 x 10 8 mm s anorthite content of the plagioclase rim growth indicates an average decompression magnitude of 40 mpa inducing an undercooling of 45 c that favors crystal growth over microlite nucleation however variability in the final anorthite contents suggests that not all phenocrysts recorded an equilibrium composition reflecting accurate pressure conditions in such events occurring over short timescales 10 h lithium is a more reliable indicator of decompression induced growth than changing anorthite content due to lithium s rapid diffusivity

growth process of the lava dome flow complex at sinabung volcano during 2013 2016 abstract mount sinabung north sumatra indonesia erupted for the first time in 2010 and reactivated again in 2013 the eruption started with a phreatic phase changed to phreatomagmatic and then andesite lava appeared at the summit crater in late december 2013 lava effusion continued and has been associated with partial to complete collapses of the lava complex which successively generated pyroclastic density currents pdcs the lava complex grew first as a lava dome and then developed into a lava flow lava extension stage it extended up to about 3 km in horizontal runout distance by late 2014 when the front of the lava complex moved onto the middle and lower slope of the volcano pdc events were initially replaced by simple rock falls inflation of the upper part of the lava complex began in mid 2014 when the movement of the lava flow front stagnated the inflation was associated with hybrid seismic events and frequent partial collapses of the upper part of the lava complex generating pdc events with long travel distances from mid september 2014 new lobes repeatedly appeared near the summit and collapsed cyclic vulcanian events began in august 2015 when hybrid events peaked and continued 1 5 years vulcanian stage these events sometimes triggered pdcs whose deposits contained vesiculated lava fragments the distribution of pdc deposits which extended over time mostly overlapped in areal extent with that of the 9th 10th century eruption eruption volumes were estimated based on measurements with a laser distance meter during 6 periods digital surface model dsm analysis of satellite images during one period and the cumulative number of seismically detected pdc events assuming a constant volume of each pdc event the total volume of eruption products reached about 0 16 km 3 dre as of the end of 2015 the lava discharge rate was largest during the initial stage 7 m 3 s and decreased exponentially over time the discharge rate during the vulcanian stage was 1 m 3 s the trend of decreasing discharge rate is in harmony with that of ground deflation recorded by a gps measurement the chemical composition of lava slightly evolved with time cyclic vulcanian events may have been triggered by limited degassing conditions in the upper conduit and by unloading of the conduit by lava dome collapses

rainfall induced volcanic activity on montserrat 1 dome forming volcanic eruptions cyclically extrude bodies of lava over several months which then become gravitationally unstable and collapse generating pyroclastic flows on 29 july 2001 extreme rainfall over montserrat coincided with a major collapse of the soufriere hills lava dome we present rainfall and seismic records that demonstrate for the first time a relationship between intense rainfall and lava dome collapse with associated pyroclastic flow generation after seven months of little rain and a period of sustained dome growth the onset of intense rain was followed within hours by dome collapse and pyroclastic flows the large scale weather system responsible for the rain was identifiable in satellite images and predicted by meteorological forecasts issued 60 hours prior to the volcanic activity it is suggested that weather prediction of intense rainfall be incorporated with existing geophysical and geochemical measurements to improve warnings of these hazardous events

monitoring lava dome growth during the 2004 2008 mount st helens washington eruption using oblique terrestrial photography abstract we present an analysis of lava dome growth during the 2004 2008 eruption of mount st helens using oblique terrestrial images from a network of remotely placed cameras this underutilized monitoring tool augmented more traditional monitoring techniques and was used to provide a robust assessment of the nature pace and state of the eruption and to quantify the kinematics of dome growth eruption monitoring using terrestrial photography began with a single camera deployed at the mouth of the volcano s crater during the first year of activity analysis of those images indicates that the average lineal extrusion rate decayed approximately logarithmically from about 8 m d to about 2 m d 2 m d from november 2004 through december 2005 and suggests that the extrusion rate fluctuated on time scales of days to weeks from may 2006 through september 2007 imagery from multiple cameras deployed around the volcano allowed determination of 3 dimensional motion across the dome complex analysis of the multi camera imagery shows spatially differential but remarkably steady to gradually slowing motion from about 1 2 m d from may through october 2006 to about 0 2 1 0 m d from may through september 2007 in contrast to the fluctuations in lineal extrusion rate documented during the first year of eruption dome motion from may 2006 through september 2007 was monotonic 0 10 m d to gradually slowing on time scales of weeks to months the ability to measure spatial and temporal rates of motion of the effusing lava dome from oblique terrestrial photographs provided a significant and sometimes the sole means of identifying and quantifying dome growth during the eruption and it demonstrates the utility of using frequent long term terrestrial photography to monitor and study volcanic eruptions

dome growth at mount cleveland aleutian arc quantified by time series terrasar x imagery synthetic aperture radar imagery is widely used to study surface deformation induced by volcanic activity however it is rarely applied to quantify the evolution of lava domes which is important for understanding hazards and magmatic system characteristics we studied dome formation associated with eruptive activity at mount cleveland aleutian volcanic arc in 2011 2012 using terrasar x imagery interferometry and offset tracking show no consistent deformation and only motion of the crater rim suggesting that ascending magma may pass through a preexisting conduit system without causing appreciable surface deformation amplitude imagery has proven useful for quantifying rates of vertical and areal growth of the lava dome within the crater from formation to removal by explosive activity to rebirth we expect that this approach can be applied at other volcanoes that host growing lava domes and where hazards are highly dependent on dome geometry and growth rates

magma fragmentation by rapid decompression the processes leading to magma fragmentation and the generation of pyroclastic debris during explosive volcanic eruptions are of fundamental importance in volcanology observations of explosive eruptions1 3 as well as theoretical analyses of the underlying processes4 have raised the question of whether the rapid decompression of highly viscous vesicular magma that results from the collapse of a lava dome or volcanic edifice can in itself produce explosive magma fragmentation and pyroclast formation here we report the results of a laboratory investigation of pyroclast formation following rapid decompression samples of magma from the 1980 eruption of mount st helens when rapidly depressurized from initial pressures of up to 12 mpa and at temperatures in the range 750 825 c fragmented to form pyroclastic products that are in many respects similar to those formed in real eruptions moreover we observe explosive fragmentation at temperatures well below those normally associated with magmatic processes suggesting that even relatively cool magma bodies can be very hazardous when subjected to rapid unloading events

combinations of volcanic flank and seafloor sediment failure offshore montserrat and their implications for tsunami generation recent seafloor mapping around volcanic islands shows that submarine landslide deposits are common and widespread such landslides may cause devastating tsunamis but accurate assessment of tsunami hazard relies on understanding failure processes and sources here we use high resolution geophysical data offshore from montserrat in the lesser antilles to show that landslides around volcanic islands may involve two fundamentally different sources of sediment island flank and larger seafloor sediment failures and can occur in multiple stages a combination of these processes produces elongate deposits with a blocky centre associated with island flank collapse surrounded by a smoother surfaced deposit that is dominated by failed seafloor sediment the failure of seafloor sediment is associated with little marginal accumulation and involves only limited downslope motion submarine landslide deposits with similar blocky and smooth surfaced associations are observed in several locations worldwide but the complex emplacement processes implied by this morphological relationship can only be revealed by high resolution geophysical data such complexity shows that the volume of landslide deposits offshore of volcanic islands cannot simply be used in tsunami models to reflect a single stage collapse of primary volcanic material by applying predictive equations for tsunami amplitude to investigate general scenarios of volcanic island landslide generation we show that the tsunami hazard associated with volcanic island collapse remains highly significant volcanic flank failures even if relatively small may generate large local tsunamis but associated seafloor sediment failures even if they have a much greater volume have a substantially lower potential for tsunami generation

resonance oscillations of the soufriere hills volcano montserrat w i magmatic system induced by forced magma flow from the reservoir into the upper plumbing dike abstract short period deformation cycles are a common phenomenon at active volcanoes and are often attributed to the instability of magma flow in the upper plumbing system caused by fluctuations in magma viscosity related to cooling degassing and crystallization here we present 20 min periodic oscillations in ground deformation based on high precision continuous borehole strain data that were associated with the 2003 massive dome collapse at the soufriere hills volcano montserrat west indies these high frequency oscillations lasted 80 min and were preceded by a 4 hour episode of rapid expansion of the shallow magma reservoir strain amplitude ratios indicate that the deformational changes were generated by pressure variations in the shallow magma reservoir and with reversed polarity the adjacent plumbing dike the unusually short period of the oscillations cannot be explained with thermally induced variations in magma properties we investigate the underlying mechanism of the oscillations via a numerical model of forced magma flow through a reservoir dike system accounting for time dependent dilation contraction of the dike due to a viscous response in the surrounding host rock our results suggest that the cyclic pressure variations are modulated by the dynamical interplay between rapid expansion of the magma chamber and the incapacity of the narrow dike to take up fast enough the magma volumes supplied by the reservoir our results allow us to place first order constraints on the viscosity of crustal host rocks and consequently its fractional melt content hence we present for the first time crustal scale in situ measurements of rheological properties of mush zones surrounding magmatic systems

submarine deposition of volcaniclastic material from the 1995 2005 eruptions of soufriere hills volcano montserrat abstract soufriere hills volcano montserrat has been erupting since 1995 during the current eruption a large part of the material produced by the volcano has been transported into the sea modifying the morphology of the submarine flanks of the volcano we present a unique set of swath bathymetric data collected offshore from montserrat in 1999 2002 and 2005 from 1999 to 2002 pyroclastic flows associated with numerous dome collapses entered the sea to produce 100 mm 3 deposit from 2002 to 2005 the 290 mm 3 submarine deposit is mainly from the 12 13 july 2003 collapse these data allow us to estimate that by may 2005 at least 482 mm 3 of material had been deposited on the sea floor since 1995 we compare on land characteristics and volumes of dome collapse events with the submarine deposits and propose a new analysis of their emplacement on the submarine flanks of the volcano the deposition mechanism shows a slope dependence with the maximum thickness of deposit before the break in the slope probably because of the type of the dense granular flow involved we conclude that from 1995 to 2005 more than 75 of the erupted volume entered the sea

emplacement processes of submarine volcaniclastic deposits iodp site c0011 nankai trough during iodp nantroseize expedition 322 four packages of tuffaceous sandstones tst 1 2 3a 3b were recovered within a moderately lithified and bioturbated silty claystone succession in the late miocene 7 6 to 9 1 ma upper part of the middle shikoku basin deposits to assess the emplacement processes of the tuffaceous sandstones we investigate modal and geochemical compositions of 24 thin sections that reveal systematic vertical changes within each bed tst 1 2 and 3b are single beds whereas tst 3a is composed of at least two beds suggesting several rapidly succeeding sedimentation events the beds are density graded such that low density pyroclasts including pumice lapilli are enriched at the top whereas dense lithic components and minerals are enriched at the bottom the volcanic glass particles pumice and shards that are the dominant modal constituents of each sandstone bed have homogeneous geochemical compositions in each bed moreover tst 1 2 and 3a glass compositions overlap completely but tst 3b glass has a different composition as is analogously observed for the mineral compositions this unique multistage approach of sedimentological and geochemical methods facilitated the detailed investigation of distal volcano derived probably tsunamogenic turbidites in order to contribute to the distinction between primary and secondary induced mass flows we interpret that all tuffaceous sandstones were emplaced by turbidity currents that were formed during major explosive volcanic eruptions however while tst 1 2 and 3a turbidity currents formed by the entry into the ocean of voluminous pyroclastic flows erupted at a volcano on mainland japan tst 3b was emplaced by a turbidity current formed by a shallow submarine or subaerial volcanic eruption at the izu bonin arc where it collided with japan these results regarding distal turbidites encourage the revisiting of older marine deposits in the scope of hazard evaluation through past events especially in regions near to volcanic sources

clastic and core lava components of a silicic lava dome the formation of a lava dome involves fractionation of the lava into core and clastic components we show that for three separate successive andesitic lava domes that grew at soufriere hills volcano montserrat between 1999 and 2007 the volumetric proportion of the lava converted to talus or pyroclastic flow deposits was 50 90 of the lava extruded currently only 8 of the total magma extruded during the 1995 2007 eruption remains as core lava the equivalent representation in the geological record will probably be even lower most of the lava extruded at the surface flowed no further than 150 300 m from the vent before disaggregation resulting in a lava core whose shape tends to a cylinder moderate to high extrusion rates at the soufriere hills domes may have contributed to the large clastic fraction observed creating talus dissipates much of the energy that would otherwise be stored in the core lava of domes the extreme hazards from large pyroclastic flows and blasts posed by wholesale collapse of a lava dome depend largely on the size of the lava core and hence on the aggregate history of the partitioning process not on the size of the dome

introduction to special section on the eruption of soufriere hills volcano montserrat the calipso project and the sea calipso arc crust imaging experiment

modelling shear bands in a volcanic conduit implications for over pressures and extrusion rates shear bands in a volcanic conduit are modelled for crystal rich magma flow using simplified conditions to capture the fundamental behaviour of a natural system our simulations begin with magma crystallinity in equilibrium with an applied pressure field and isothermal conditions the viscosity of the magma is derived using existing empirical equations and is dependent upon temperature water content and crystallinity from these initial conduit conditions we utilize the finite element method using axi symmetric coordinates to simulate shear bands via shear localisation we use the von mises visco plasticity model with constant magma shear strength for a first took into the effects of plasticity the extent of shear bands in the conduit is explored with a numerical model parameterized with values appropriate for soufriere hills volcano montserrat although the model is generic in nature our model simulates shallow up to approximately 700 in shear bands that occur within the upper conduit and probably govern the lava extrusion style due to shear boundaries we also model the change in the over pressure field within the conduit for flow with and without shear bands the pressure change can be as large as several mpa at shallow depths in the conduit which generates a maximum change in the pressure gradient of 10 s of kpa m the formation of shear bands could therefore provide an alternative or additional mechanism for the inflation deflation of the volcano flanks as measured by tilt metres shear bands are found to have a significant effect upon the magma ascent rate due to shear induced flow reducing conduit friction and altering the over pressure in the upper conduit since we do not model frictional controlled slip only plastic flow our model calculates the minimum change in extrusion rate due to shear bands however extrusion rates can almost double due to the ton nation of shear bands which may help suppress volatile loss due to the paucity of data and large parameter space available for the magma shear strength our model results can only allow for a qualitative comparison to a natural system at this stage c 2007 elsevier b v all rights reserved

insights into processes and deposits of hazardous vulcanian explosions at soufriere hills volcano during 2008 and 2009 montserrat west indies during the soufriere hills eruption vulcanian explosions have generally occurred 1 in episodic cycles 2 isolated during pauses in extrusion and 3 after major collapses of the dome in a different eruptive context significant vulcanian explosions occurred on 29 july 2008 3 december 2008 and 3 january 2009 deposits are pumiceous except for the 3 december event we reconstructed the dispersal pattern of the deposits and their textural characteristics to evaluate erupted volume and vesicularity of the magma at fragmentation we discuss the implications of these explosions in terms of eruptive processes and chronology and the hazards posed by their sudden and often unheralded occurrence we suggest that overpressurization of the conduit can develop over time scales of months to weeks by a process of self sealing of conduit walls and or the cooling dome by silica polymorphs this work provides new insights for understanding the generation of hazardous vulcanian explosions at andesitic volcanoes

timing origin and emplacement dynamics of mass flows offshore of se montserrat in the last 110 ka implications for landslide and tsunami hazards eruption history and volcanic island evolution 1 mass flows on volcanic islands generated by volcanic lava dome collapse and by larger volume flank collapse can be highly dangerous locally and may generate tsunamis that threaten a wider area it is therefore important to understand their frequency emplacement dynamics and relationship to volcanic eruption cycles the best record of mass flow on volcanic islands may be found offshore where most material is deposited and where intervening hemipelagic sediment aids dating here we analyze what is arguably the most comprehensive sediment core data set collected offshore from a volcanic island the cores are located southeast of montserrat on which the soufriere hills volcano has been erupting since 1995 the cores provide a record of mass flow events during the last 110 thousand years older mass flow deposits differ significantly from those generated by the repeated lava dome collapses observed since 1995 the oldest mass flow deposit originated through collapse of the basaltic south soufriere hills at 103 110 ka some 20 30 ka after eruptions formed this volcanic center a 1 8 km3 blocky debris avalanche deposit that extends from a chute in the island shelf records a particularly deep seated failure it likely formed from a collapse of almost equal amounts of volcanic edifice and coeval carbonate shelf emplacing a mixed bioclastic andesitic turbidite in a complex series of stages this study illustrates how volcanic island growth and collapse involved extensive large volume submarine mass flows with highly variable composition runout turbidites indicate that mass flows are emplaced either in multiple stages or as single events

crumbling of dacite dome lava and generation of pyroclastic flows at unzen volcano recent modelling of volcanic eruptions has shown that the efficiency of subsurface degassing of magmas determines whether magma erupts explosively or effuses quietly1 2 slow uprise of magma is often accompanied by effective degassing leading to the extrusion of lava flows and domes although lava dome extrusion is one of the less explosive modes of eruption it is often accompanied by explosive pyroclastic activities3 5 the 1991 eruption of unzen volcano provided an opportunity to observe at close range several types of small scale pyroclastic flow glowing avalanches originating from lava domes most of the pyroclastic flows are of merapi type caused by blocks falling from a collapsing dome others are of pelean type originating in an explosion from the side of a dome the lavas apparently show variable degrees of self explosivity we suggest that variable degrees of degassing of the magma produced a wide range of excess pore pressures in the extruded lava domes resulting in both merapi type and pelean type pyroclastic flows from the domes

emplacement of pyroclastic deposits offshore montserrat insights from 3d seismic data during the current 1995 present eruptive phase of the soufriere hills volcano on montserrat voluminous pyroclastic flows entered the sea off the eastern flank of the island resulting in the deposition of well defined submarine pyroclastic lobes previously reported bathymetric surveys documented the sequential construction of these deposits but could not image their internal structure the morphology or extent of their base or interaction with the underlying sediments we show by combining these bathymetric data with new high resolution three dimensional 3d seismic data that the sequence of previously detected pyroclastic deposits from different phases of the ongoing eruptive activity is still well preserved a detailed interpretation of the 3d seismic data reveals the absence of significant 3 m basal erosion in the distal extent of submarine pyroclastic deposits we also identify a previously unrecognized seismic unit directly beneath the stack of recent lobes we propose three hypotheses for the origin of this seismic unit but prefer an interpretation that the deposit is the result of the subaerial flank collapse that formed the english s crater scarp on the soufriere hills volcano the 1995 recent volcanic activity on montserrat accounts for a significant portion of the sediments on the southeast slope of montserrat in places forming deposits that are more than 60 m thick which implies that the potential for pyroclastic flows to build volcanic island edifices is significant

rainfall induced lahars in the belham valley montserrat west indies rain falling on loose volcanic debris over the soufriere hills volcano montserrat generates hazardous floods in the belham valley these rainfall induced lahars vary greatly in discharge and sediment concentration in space and time they differ from examples documented on other volcanoes in that 1 the eruption has been continuing since july 1995 generating repeated pulses of excess sediment 2 rainfall is the only significant trigger 3 the system is small with short distance to the sea and relatively low altitude at the catchment top repeat mapping and comparison with pre eruption data demonstrate significant geomorphological change with c 120 m shoreline progradation and c 0 4 m a 1 mean aggradation rate in the middle to lower valley the nature of the hazard and area of risk have changed as the valley has aggraded the channel widened and the runoff efficiency increased as a result of rilling and vegetation removal lahars in the belham valley correlate with days when 10 mm rain fell in 24 h with more events triggered in the late rainy season the flows are mainly newtonian but one non newtonian flow event has been demonstrated and is described in detail 20 march 2000 this flow is explained by direct volcanic ash input to the runoff

sequential dome collapse nuees ardentes analyzed from broadband seismic data merapi volcano indonesia abstract during the sequential dome collapse of merapi volcano on 22 november 1994 a broadband seismic station on the western slope was the only operational seismic equipment that provided continuous on scale recording of the event according to visual and seismic observations the collapse activity lasted about 10 h we divide the activity into two phases i a period with fluctuating but generally increasing seismic activity associated with 24 moderate to large dome collapse nuees ardentes lasting about 40 min and culminating with the largest event at 10 54 all times reported as local time and ii activity from 11 42 until 20 00 described by scattered clusters of individual rockfalls and 20 nuees ardentes the broadband data were evaluated using the assumption that avalanches with the same source areas and descent paths exhibit a linear relation between source volume and recorded seismic amplitude envelope area a result of the analysis is the determination of the volume of selected individual events from the field surveys the total volume of the collapsed dome lava is 2 6 mm3 discounting the volumetric influence of rockfalls the average size of the 44 nuees ardentes is therefore about 60 000 m3 the largest collapse event at 10 54 is estimated to involve 260 000 m3 based on an analysis of the seismicity the remaining 23 phase i events averaged 60 000 m3 with the total volume of all phase i events accounting for 63 of the unstable dome the 20 phase ii events comprised 37 of the total volume and averaged 47 000 m3 the methods described here can be put to practical use in real time monitoring situations broadband data were essential in this study primarily because of the wide dynamic range

catastrophic lava dome failure at soufriere hills volcano montserrat 12 13 july 2003 the lava dome collapse of 12 13 july 2003 was the largest of the soufriere hills volcano eruption thus far 1995 2005 and the largest recorded in historical times from any volcano 210 million m3 of dome material collapsed over 18 h and formed large pyroclastic flows which reached the sea the evolution of the collapse can be interpreted with reference to the complex structure of the lava dome which comprised discrete spines and shear lobes and an apron of talus progressive slumping of talus for 10 h at the beginning of the collapse generated low volume pyroclastic flows it undermined the massive part of the lava dome and eventually prompted catastrophic failure from 02 00 to 04 40 13 july 2003 large pyroclastic flows were generated these reached their largest magnitude at 03 35 when the volume flux of material lost from the lava dome probably approached 16 million m3 over two minutes the high flux of pyroclastic flows into the sea caused a tsunami and a hydrovolcanic explosion with an associated pyroclastic surge which flowed inland a vulcanian explosion occurred during or immediately after the largest pyroclastic flows at 03 35 13 july and four further explosions occurred at progressively longer intervals during 13 15 july 2003 the dome collapse lasted approximately 18 h but 170 of the total 210 million m3 was removed in only 2 6 h during the most intense stage of the collapse

lithosphere atmosphere ionosphere coupling after the 2003 explosive eruption of the soufriere hills volcano montserrat resonant coupling between the earth and the atmosphere at frequencies where the solid earth modes overlap the fundamental modes of the atmosphere allows for the triggering of oscillatory acoustic perturbations by ground excitation and vice versa here we describe oscillatory perturbations observed in the solid earth from volumetric borehole strainmeter data and in the atmosphere from gps derived ionospheric total electron content following the july 13 2003 soufri ere hills volcano explosion montserrat lesser antilles spectral analysis shows an amplitude peak at 4 mhz for both datasets with similar waveforms and signal duration using a normal mode summation technique we show that both signals are explained by a single explosive source in the atmosphere similarities in waveforms in particular a double wave train also reported after several other explosion triggered atmospheric perturbations result from the superposition of the dominant fundamental atmospheric modes that trigger resonant coupling with the solid earth around 4 mhz

multiple timescales of cyclical behaviour observed at two dome forming eruptions article i nfo cyclic behaviour over a range of timescales is a well documented feature of many dome forming volcanoes but has not previously been identified in high resolution seismic data from volcan de colima mexico using daily seismic count datasets from volcan de colima and soufriere hills volcano montserrat this study explores par allels in the long term behaviour of seismicity at two long lived systems datasets are examined using multiple techniques including fast fourier transform detrended fluctuation analysis and probabilistic distribution analysis and the comparison of results from two systems reveals interesting parallels in sub surface processes operating at both systems patterns of seismicity at both systems reveal complex but broadly similar long term temporal patterns with cycles on the order of 50 to 200 days these patterns are consistent with previously published spectral analyses of so2 flux time series at soufriere hills volcano and are attributed to variations in the movement of magma in each system detrended fluctuation analysis determined that both volcanic systems showeda systematic relationship betweenthe numberofseismic eventsand the relative roughness ofthetime series and explosionsatvolcande colimashoweda1 5 2 yearcycle neither observation hasaclear explanatory mechanism atvolcandecolima analysisofreposeintervalsbetweenseismiceventsshowslong termbehaviour that responds to changes in activity at the system similar patterns for both volcanic systems suggest a common process or processes driving the observed signal but it is not clear from these results alone what those processes may be furtherattempts to modelconduitprocessesateach volcanomustaccountfor thesimilarities anddiffer ences in activity within each system the identification of some commonalities in the patterns of behaviour dur ing long lived dome forming eruptions atandesiticvolcanoes provides a motivation for investigating further use of time series analysis as a monitoring tool

the effects of thermomechanical heterogeneities in island arc crust on time dependent preeruptive stresses and the failure of an andesitic reservoir using ground deformation data from soufriere hills volcano shv we present results from numerical modeling of the temperature and time dependent stress evolution in a mechanically heterogeneous crust prior to reservoir failure and renewed eruptive activity the best fit models do not allow us to discriminate between a magmatic plumbing system consisting of either a single vertically elongated reservoir or a series of stacked reservoirs a prolate reservoir geometry with volumes between 50 and 100 km3 reservoir pressure changes between 4 and 7 mpa and reservoir volume changes between 0 03 and 0 04 km3 with magma compressibility between 4 10 11 and 1 10 9 pa 1 provide plausible thermomechanical model parameters to explain the deformation time series around an order of magnitude less overpressure than is generally inferred from homogeneous elastic crustal models reservoir failure is predicted to occur at the crest of the reservoir except for reservoirs with highly compressible magma 4 10 9 pa for which subhorizontal sill formation is predicted upon reservoir failure introducing a deep crustal hot zone modulates the partitioning of strains into the hotter underlying crust and results in a further reduction in overpressure estimates to values of around 1 2 mpa upon reservoir failure deduced volume fluxes are consistent with constraints from thermal modeling of active subvolcanic systems and imply dynamic failure of a compressible magma mush column feeding eruptions at shv our interpretation of the results is that the combined thermomechanical effects of a deep crustal hot zone and hot encasing rocks around a midcrustal andesitic reservoir fundamentally alter the time dependent subsurface stress and strain partitioning upon reservoir priming these effects substantially influence surface strains recorded by volcano geodetic monitoring

excess volatiles supplied by mingling of mafic magma at an andesite arc volcano we present the results of a study of volcanic gases at soufriere hills volcano montserrat which includes the first spectroscopic measurements of the major gas species co2 and h2s at this volcano using a multisensor gas analyzer system multigas sensor the fluxes of co2 and h2s were 640 2750 t d and 84 266 t d respectively during july 2008 during a prolonged eruptive pause the flux of co2 is similar to estimates for the entire arc from previous geochemical studies while the measured h2s flux significantly alters our interpretation of the sulphur budget for this volcano the fluxes of both sulphur and carbon show considerable excesses over that which can be supplied by degassing of erupted magma we demonstrate using thermodynamic models and published constraints on preeruptive volatile concentrations that the gas composition and fluxes are best modeled by mixing between 1 gases derived from isobaric quenching of mafic magma against cooler andesite magma at depth and 2 gases derived from shallower rhyolitic interstitial melt within the porpyritic andesite the escape of deep derived gases requires pervasive permeability or vapor advection extending to several kilometers depth in the conduit and magma storage system these results provide more compelling evidence for both the contribution of unerupted mafic magma to the volatile budget of this andesitic arc volcano and the importance of the intruding mafic magma in sustaining the eruption from a broader perspective this study illustrates the importance and role of underplating mafic magmas in arc settings these magmas play an important role in triggering and sustaining eruptions and contribute in a highly significant way to the volatile budget of arc volcanoes copyright 2010 by the american geophysical union

modelling of tsunami generated by the giant late bronze age eruption of thera south aegean sea greece summary tsunami generated by the late bronze age lba eruption of thera were simulated using synthetic tide records produced for selected nearshore 20 m depths sites of northern crete the cyclades islands sw turkey and sicily inundation distances inland were also calculated along northern crete modelling was performed by incorporating fully non linear boussinesq wave theory with two tsunamigenic mechanisms the first involved the entry of pyroclastic flows into the sea assuming a thick 55 m 30 km3 flow entering the sea along the south coast of thera in three different directions all directed towards northern crete then a thin pyroclastic flow 1 m 1 2 km3 entering the sea along the north coast of thera directed towards the cyclades islands flows were modelled as a solid block that slowly decelerates along a horizontal surface the second mechanism assumed caldera collapse of 19 km3 and 34 km3 modelled as a dynamic landslide producing rapid vertical displacements calculated nearshore wave amplitudes varied from a few metres to 28 m along northern crete from pyroclastic flows and up to 19 m from caldera collapse 34 km3 volume inundation distances on crete were 250 450 m waves produced by pyroclastic flows were highly focused however as a function of sea entry direction smaller volume pyroclastic flows produced nearshore wave amplitudes up to 4 m in the cyclades islands north of thera wave amplitudes in the cyclades from smaller volume caldera collapse 19 km3 were up to 24 m whereas in sw turkey were as low as 2 1 and 0 8 m didim and fethye where lba tsunami deposits have been found wave amplitudes for the larger volume caldera collapse 34 km3 were generally 2 5 3 times larger than those generated by the smaller volume collapse 19 km3 these results provide estimates for understanding possible consequences of tsunami impact in lba coastal zones thus providing criteria at archaeological sites for detecting inundation damage as well as for contemporary hazard assessment they also provide additional criteria for deciphering homogenite layers in the abyssal stratigraphy of the ionian and eastern mediterranean seas

long term surface deformation of soufriere hills volcano montserrat from gps geodesy inferences from simple elastic inverse models 1 campaign and continuous gps geodetic measurements on soufriere hills volcano montserrat are reported from 1995 to 2009 spanning three dome growth and repose episodes uniform elastic half space inversions were used to examine how crustal pressure sources evolved by inverting subsets of all available 3d site data for any given episode using a single mogi source changes in network topology were also examined the average best fitting single mogi model yields x 0 3 0 5 km y 0 8 0 4 km and a depth of z 10 4 2 1 km 1 z positive down relative to the center of the model domain the mean mogi depth for effusive deflation versus repose inflation is different and significant at 90 confidence yielding z 11 4 2 0 km and 9 3 1 6 km respectively a vertical prolate ellipsoid improves the fit at 95 confidence over a single mogi source or stacked two source model for the 2003 2005 repose and 2005 2007 dome growth episodes

inland directed base surge generated by the explosive interaction of pyroclastic flows and seawater at soufriere hills volcano montserrat the largest and most intense lava dome collapse during the eruption of soufriere hills volcano montserrat 1995 2004 occurred 12 13 july 2003 the dome collapse involved around 200 x 106 m3 of material and was associated with a phenomenon previously unknown at this volcano large pyroclastic flows at the peak of the dome collapse interacted explosively with seawater at the mouth of the tar river valley and generated a hot dry base surge that flowed 4 km inland and 300 m uphill the surge was destructive to at least 25 m above the ground and it carbonized vegetation the resulting two layer deposits were as much as 0 9 m thick although the entire collapse lasted 18 h the base surge greatly increased the land area affected by the dome collapse in a few minutes at the peak of the event illustrating the complex nature of the interaction between pyroclastic flows and seawater

phenocryst hosted melt inclusions record stalling of magma during ascent in the conduit and upper magma reservoir prior to vulcanian explosions soufriere hills volcano montserrat west indies the mechanics of explosive eruptions influence magma ascent pathways vulcanian explosions involve a stop start mechanism that recurs on various timescales evacuating the uppermost portions of the conduit during the repose time between explosions magma rises from depth and refills the conduit and stalls until the overpressure is sufficient to generate another explosion we have analyzed major elements cl s h2o and co2 in plagioclase hosted melt inclusions sampled from pumice erupted during four vulcanian events at soufriere hills volcano montserrat to determine melt compositions prior to eruption using fourier transform infrared spectroscopy we measured values up to 6 7 wt h2o and 80 ppm co2 of 42 melt inclusions 81 cluster between 2 8 and 5 4 wt h2o 57 to 173 mpa or 2 7 km suggesting lower conduit to upper magma reservoir conditions we propose two models to explain the magmatic conditions prior to eruption in model 1 melt inclusions were trapped during crystal growth in magma that was stalled in the lower conduit to upper magma reservoir and during trapping the magma was undergoing closed system degassing with up to 1 wt free vapor this model can explain the melt inclusions with higher h2o contents since these have sampled the upper parts of the magma reservoir however the model cannot explain the melt inclusions with lower h2o because the timescale for plagioclase crystallization and melt inclusion entrapment is longer than the magma residence time in the conduit in model 2 melt inclusions were originally trapped at deeper levels of the magma chamber but then lost hydrogen by diffusion through the plagioclase host during periodic stalling of the magma in the lower conduit system in this second scenario which we favor the melt inclusions record re equilibration depths within the lower conduit to upper magma reservoir

thermal photogrammetric imaging a new technique for monitoring dome eruptions abstract structure from motion sfm algorithms greatly facilitate the generation of 3 d topographic models from photographs and can form a valuable component of hazard monitoring at active volcanic domes however model generation from visible imagery can be prevented due to poor lighting conditions or surface obscuration by degassing here we show that thermal images can be used in a sfm workflow to mitigate these issues and provide more continuous time series data than visible light equivalents we demonstrate our methodology by producing georeferenced photogrammetric models from 30 near monthly overflights of the lava dome that formed at volcan de colima mexico between 2013 and 2015 comparison of thermal models with equivalents generated from visible light photographs from a consumer digital single lens reflex dslr camera suggests that despite being less detailed than their dslr counterparts the thermal models are more than adequate reconstructions of dome geometry giving volume estimates within 10 of those derived using the dslr significantly we were able to construct thermal models in situations where degassing and poor lighting prevented the construction of models from dslr imagery providing substantially better data continuity than would have otherwise been possible we conclude that thermal photogrammetry provides a useful new tool for monitoring effusive volcanic activity and assessing associated volcanic risks

hazard predictions for volcanic explosions we have developed a method of producing hazard maps for volcanic eruptions using three dimensional numerical simulations numerical simulations of shock wave interactions with terrain were carried out assuming the volcanic explosion is analogous to point source explosions the point source explosion model is coupled with scaling distances for pyroclastic surge and ballistic fragments to produce hazard maps of the damage done both by shock waves and volcanic debris the numerical method is applied to iwatesan volcano which recently became active we demonstrate that the present method of producing hazard maps is useful for establishing better safety countermeasures for volcanic eruptions

anatomy of a submarine pyroclastic flow and associated turbidity current july 2003 dome collapse soufriere hills volcano montserrat west indies the 12 to 13 july 2003 andesite lava dome collapse at the soufriere hills volcano montserrat provides the first opportunity to document comprehensively both the sub aerial and submarine sequence of events for an eruption numerous pyroclastic flows entered the ocean during the collapse depositing approximately 90 of the total material into the submarine environment during peak collapse conditions as the main flow penetrated the air ocean interface phreatic explosions were observed and a surge cloud decoupled from the main flow body to travel 2 to 3 km over the ocean surface before settling the bulk of the flow was submerged and rapidly mixed with sea water forming a water saturated mass flow efficient sorting and physical differentiation occurred within the flow before initial deposition at 500 m water depth the coarsest components 60 of the total volume were deposited proximally from a dense granular flow while the finer components 40 were efficiently elutriated into the overlying part of the flow which evolved into a far reaching turbidity current

global positioning system detection and energy estimation of the ionospheric wave caused by the 13 july 2003 explosion of the soufriere hills volcano montserrat 1 volcanic explosions or shallow earthquakes are known to trigger acoustic and gravity waves that propagate in the atmosphere at infrasonic speeds at ionospheric heights coupling between neutral particles and free electrons induces variations of electron density detectable with dual frequency global positioning system gps measurements using gps data collected in the caribbean we identified an ionospheric perturbation after a major volcanic explosion at the soufriere hills volcano montserrat lesser antilles on 13 july 2003 spectral analysis reveals peaks centered at 1 and 4 mhz similar to those in previous observations and consistent with theory suggesting both gravity and acoustic wave components we retrieve a horizontal velocity of 624 m s for the acoustic component which implies upward propagation at 33 consistent with ray tracing results we model the acoustic wave using an n wave pressure source at ground level combined with ray tracing to propagate the neutral pressure wave this accounts for the dispersive characteristics of the atmosphere while conserving total acoustic energy plasma velocity is derived from neutral velocity using a finite difference solution of the magnetohydrodynamic momentum equation the continuity equation for charge densities is used to compute corresponding electron density variations which are then numerically integrated along satellite to receiver line of sights simultaneously accounting for the satellite displacements we minimize the misfit between observed and model waveforms to estimate a total acoustic energy release of 1 53 x 10 10 j for the primary explosion event at soufriere hills volcano associated with the peak dome collapse this method can be applied to any explosion of sufficient magnitude provided gps data are available at near to medium range from the source

the fast response of volcano seismic activity to intense precipitation triggering of primary volcanic activity by rainfall at soufriere hills volcano montserrat abstract one minute resolution time series of rainfall and seismic data from the soufriere hills volcano montserrat are analysed to explore the mechanism of external forcing of volcanic eruptions by rainfall over three years of activity the real time seismic amplitude rsam shows a narrow statistically significant peak within 30 min after the start of intense rainfall events and a much broader peak with a lag of 6 40 h the classified seismic events indicate that the volcanic response to rainfall begins at the surface and gradually penetrates deeper into the dome as there is an increase in the pseudo magnitude of surface rockfall events including pyroclastic flows with lags from the first 30 min to 40 h long period rockfalls from shallow degassing at lags of 4 and 14 h and long period and hybrid events source depth approximately 1 km with lags at 14 and 24 h after the start of rainfall events there was no rainfall related change in deeper volcano tectonic activity there was no change in the frequency of any type of classified event indicating that the rainfall acts to modulate existing internal processes rather than generating new events itself these robust results are due to many 229 different rainfall events and not just to a few large magnitude cases the rainfall triggered volcanic activity examined here is consistent with a model of fast shallow interactions with rainfall at the dome surface after which a deeper dome collapse follows

3d electrical imaging of the inner structure of a complex lava dome puy de dome volcano french massif central france abstract lava domes result from extrusion of massive lava frequent explosions and collapses this contribution focuses on a complex trachytic lava dome the puy de dome volcano located in the chaine des puys volcanic field french massif central france we performed electrical resistivity tomography ert acquisitions on the entire edifice in order to investigate its overall inner structure as well as to detail its summit area the resulting large ert dataset integrated a recently developed 3d inversion code based on an unstructured discretization of the geometrical model the 3d inversion models obtained refine the existing geological model of the puy de dome s inner structure obtained by previous geophysical studies these results also highlight the strong fracturing and fumarolic alteration that affect the summit part of the volcano

tephra deposits associated with a large lava dome collapse soufriere hills volcano montserrat 12 15 july 2003 abstract the 12 13 july 2003 dome collapse at soufriere hills volcano montserrat was the largest event of its kind during the eruption thus far 1995 2005 involving the removal of 210 million m 3 of the lava dome complex over 18 h less than 2 of the total volume of material involved in the dome collapse was deposited on land a pyroclastic density current deposit alongshore and inland from the tar river fan was generated from a single blast originating at the shoreline the blast was caused by the interaction of pyroclastic flows with seawater we propose that at the peak of the lava dome collapse a sharp increase in the volume flux of pyroclastic flows caused substantial displacement of seawater from the shoreline followed by inrush of seawater when the flux decreased a few minutes later the tsunami allowed penetration of seawater into the main body of the pyroclastic flow at the shoreline which led to explosive fragmentation of pyroclastic blocks tephra fall deposits accumulated at a high rate on montserrat causing extensive damage to vegetation and buildings their stratigraphy recorded fallout from high co pyroclastic flow clouds from a vulcanian explosion cloud at the peak in collapse rate caused by the fragmentation of degassed lava dome and from four vulcanian explosion clouds after the dome collapse caused by fragmentation of bubbly magma in the conduit the total tephra fall volume is estimated at 10 20 million m 3

source mechanism of seismic waves excited by pyroclastic flows observed at unzen volcano japan a number of pyroclastic flows have occurred at unzen volcano unzendake in kyushu japan since the end of may 1991 seismic waves which are excited by the pyroclastic flows contain low frequency components in their initial phases they were recorded by two long period seismographs in the seismic network deployed around the volcano this paper is an attempt to clarify the source mechanism of the seismic waves triggered by the pyroclastic flows visual data show that the pyroclastic flow which excites these seismic waves occurs in three successive steps first fall of a lava dome front dome collapse then its collision with the mountain slope and its fragmentation into small blocks and finally descent of the blocks along the slope we can build a simple mechanical model which gives theoretical time histories of vertical and horizontal components of a force acting on the spot of dome collapse on the mountain slope the model of a mechanism generating these seismic waves was constructed through analysis of the low frequency components with the aid of inversion methods which can estimate source time function of the force acting on the source the estimated time histories are close to those predicted by the simple mechanical model we conclude that the three steps mentioned above are essential in exciting the low frequency seismic signals this idea is supported by the fact that the volume of fallen material estimated from the visual data is proportional to the maximum vertical amplitude of seismic waves triggered by the pyroclastic flow this relation holds for the two pyroclastic flows of june 22 1991 and may 28 1992 which were studied in this paper these findings seismically confirm a visual observation that the pyroclastic flow is a result of dome collapse

unique and remarkable dilatometer measurements of pyroclastic flow generated tsunamis pyroclastic flows entering the sea may cause tsunamis at coastal volcanoes worldwide but geophysically monitored field occurrences are rare we document the process of tsunami generation during a prolonged gigantic collapse of the soufriere hills volcano lava dome on montserrat on 12 13 july 2003 tsunamis were initiated by large volume pyroclastic flows entering the ocean we reconstruct the collapse from seismic records and report unique and remarkable borehole dilatometer observations which recorded clearly the passage of wave packets at periods of 250 500 s over several hours strain signals are consistent in period and amplitude with water loading from passing tsunamis each wave packet can be correlated with individual pyroclastic flow packages recorded by seismic data proving that multiple tsunamis were initiated by pyroclastic flows any volcano within a few kilometers of water and capable of generating hot pyroclastic flows or cold debris flows with volumes greater than 5 10 6 m 3 may generate significant and possibly damaging tsunamis during future eruptions

lava dome growth and evolution with an independently deformable talus subduction zone volcanism occurs due to partial melting from subducting slabs which generally results in high viscosity magma containing a large amount of volatiles such volcanic eruptions can form a lava dome from which collapse events are a common and important part of their evolution collapse events can have devastating consequences in the form of block and ash avalanche deposits pyroclastic ows surges and the generation of tsunamis if they enter the sea in addition to this once a mass of lava dome has been removed during a collapse event this results in a drop in pressure in the remaining volatile rich magma which may then erupt explosively the internal structure of a lava dome and the extent of the surrounding carapace talus is unknown but likely to be critical for hazard assessment and is the motivation for this research presented is a computational model for the growth and evolution of an endogenous lava dome including an independently deformable talus using the finite element method dome growth is modelled to occur under two time scales continuous dome expansion via the addition of new magma into the molten core interior and relatively instantaneous talus readjustments due to rockfalls and the disintegration of the solid surface the continuous deformation of the dome is modelled as a uid with a yield strength in the talus region while talus deformation is modelled as a granular material that rests at angles below its angle of repose both surfaces dome and core talus interface are displaced using the level set method the model is axi symmetric and assumes that solidi cation and therefore talus growth occurs due to gas exsolution which promotes crystallisation rather than from surface cooling appropriate for intermediate composition lava ows for the purpose of this paper we consider and apply the model to the soufriere hills volcano montserrat but the techniques used are generic allowing the model to be applied to other dome forming eruptions the model provides information on the shape of the dome with the growth and extent of the talus and core found to be predominantly governed by the lava extrusion rate degree of solidi cation i e a solidus pressure the friction angle associated with the talus and lava dome viscosity

submarine pyroclastic deposits formed during the 20th may 2006 dome collapse of the soufriere hills volcano montserrat the 20th may 2006 lava dome collapse of the soufriere hills volcano montserrat had a total non dense rock equivalent non dre collapse volume of approximately 115 106 m3 the majority of this volume was deposited into the ocean the collapse was rapid 85 of the mobilized volume being removed in just 35 min giving peak pyroclastic flow flux of 66 103 m3 s 1 channel and levee facies on the submarine flanks of the volcano and formation of a thick steep sided ridge suggest that the largest and most dense blocks were transported proximally as a high concentration granular flow of the submerged volume 30 was deposited from the base of this granular flow forming a linear high relief ridge that extends 7 km from shore the remaining 70 of the submerged volume comprises the finer grain sizes which were transported at least 40 km by turbidity currents on gradients of 2 at several localities the may 2006 distal turbidity currents ran up 200 m of topography and eroded up to 20 cm of underlying substrate multiple turbidites are preserved representing current reflection from the graben margins and deflection around topography the high energy of the may 2006 collapse resulted in longer submarine run out than the larger 210 106 m3 soufriere hills dome collapse in july 2003

volcanic seismicity at montserrat a comparison between the 2005 dome growth episode and earlier dome growth in 2005 soufriere hills volcano on montserrat started its third major episode of dome growth since the current eruption started in 1995 the style of seismicity associated with dome growth has changed in particular the events known as hybrid earthquakes have reduced in numbers by an order of magnitude compared to previous dome growth episodes in the past hybrid earthquakes have been associated with magma ascent and so it is surprising to observe prolonged periods of rapid dome growth during which very few hybrid earthquakes are recorded in addition the frequency of the codas of hybrid earthquakes as well as of some of the so called long period events has changed the changes in recorded seismicity have had a marked effect on the techniques used to monitor the state of the volcano and those events that continue to be recorded in large numbers rockfall events have been used to assess the state of activity at the volcano

construction of volcanic records from marine sediment cores a review and case study montserrat west indies detailed knowledge of the past history of an active volcano is crucial for the prediction of the timing frequency and style of future eruptions and for the identification of potentially at risk areas subaerial volcanic stratigraphies are often incomplete due to a lack of exposure or burial and erosion from subsequent eruptions however many volcanic eruptions produce widely dispersed explosive products that are frequently deposited as tephra layers in the sea cores of marine sediment therefore have the potential to provide more complete volcanic stratigraphies at least for explosive eruptions nevertheless problems such as bioturbation and dispersal by currents affect the preservation and subsequent detection of marine tephra deposits consequently cryptotephras in which tephra grains are not sufficiently concentrated to form layers that are visible to the naked eye may be the only record of many explosive eruptions additionally thin reworked deposits of volcanic clasts transported by floods and landslides or during pyroclastic density currents may be incorrectly interpreted as tephra fallout layers leading to the construction of inaccurate records of volcanism this work uses samples from the volcanic island of montserrat as a case study to test different techniques for generating volcanic eruption records from marine sediment cores with a particular relevance to cores sampled in relatively proximal settings i e tens of kilometres from the volcanic source where volcaniclastic material may form a pervasive component of the sedimentary sequence visible volcaniclastic deposits identified by sedimentological logging were used to test the effectiveness of potential alternative volcaniclastic deposit detection techniques including point counting of grain types component analysis glass or mineral chemistry colour spectrophotometry grain size measurements xrf core scanning magnetic susceptibility and x radiography this study demonstrates that a set of time efficient non destructive and high spatial resolution analyses e g xrf core scanning and magnetic susceptibility can be used effectively to detect potential cryptotephra horizons in marine sediment cores once these horizons have been sampled microscope image analysis of volcaniclastic grains can be used successfully to discriminate between tephra fallout deposits and other volcaniclastic deposits by using specific criteria related to clast morphology and sorting standard practice should be employed when analysing marine sediment cores to accurately identify both visible tephra and cryptotephra deposits and to distinguish fallout deposits from other volcaniclastic deposits

susceptibility of lava domes to erosion and collapse by toppling on cooling joints the shape of lava domes typically leads to the formation of radial patterns of cooling joints these cooling joints define the orientation of the columnar blocks which plunge toward the center of the dome in the lower parts of the dome the columns plunge into the dome at low angles and are relatively stable higher in the dome the columns plunge into the dome at steep angles these steeply plunging columns are susceptible to toppling and if the lower part of a dome is partially removed by erosion or collapse the unstable part of the dome becomes exposed leading to toppling failure examples of this process are provided from coastal erosion of lava domes at katsura island shimane peninsula western japan an analogue model is presented to demonstrate the mechanism it is proposed that the mechanism can contribute to collapse of lava domes during or after emplacement

evidence for carbonate platform failure during rapid sea level rise ca 14 000 year old bioclastic flow deposits in the lesser antilles bioclastic flow deposits offshore from the soufriere hills volcano on montserrat in the lesser antilles were deposited by the largest volume sediment flows near this active volcano in the last 26 kyr the volume of these deposits exceeds that of the largest historic volcanic dome collapse in the world which occurred on montserrat in 2003 these flows were most probably generated by a large submarine slope failure of the carbonate shelf comprising the south west flank of antigua or the east flank of redonda adjacent islands that are not volcanically active the bioclastic flow deposits are relatively coarse grained and either ungraded or poorly graded and were deposited by non cohesive debris flow and high density turbidity currents the bioclastic deposit often comprises multiple sub units that cannot be correlated between core sites some located just 2 km apart multiple sub units in the bioclastic deposit result from either flow reflection stacking of multiple debris flow lobes and or multi stage collapse of the initial landslide this study provides unusually precise constraints on the age of this mass flow event that occurred at ca 14 ka few large submarine landslides have been well dated but the slope failures that have been dated are commonly associated with periods of rapid sea level change

volcano flank instability in the lesser antilles arc diversity of scale processes and temporal recurrence 1 the 1997 boxing day collapse a remarkable feature of the ongoing eruption of soufriere hills on montserrat has prompted new interest in the study of volcano stability in the lesser antilles building on a few cases documented in the literature we have now identified at least 47 flank collapse events on volcanoes of the caribbean arc where this type of behavior is characteristic and repetitive about 15 events occurred on active volcanoes within the last 12 000 years in the northern part of the arc flank collapses are repetitive do not exceed 1 km3 in volume occur in all directions and are promoted by intense hydrothermal alteration and well developed fracturing of the summit part of the edifices in contrast infrequent but large sector collapses with volumes up to tens of km3 are typical of the southern volcanoes they are always directed to the west as a result of the high overall slopes of the islands toward the deep back arc grenada basin because caribbean islands are small a large part of the resulting debris avalanches have flowed into the sea thus contributing voluminous and sudden inputs of volcaniclastic sediments to the grenada basin deposits from such submarine flows have been identified during the recent aguadomar and caraval oceanographic cruises and traced to their source structures on land edifice collapses have a major influence on subsequent volcanic activity but also are of high concern because of their tsunamigenic potential

palaeobiogeography of early cretaceous berriasian barremian calcareous nannoplankton in order to assess early cretaceous nannoplankton biogeography we studied a series of sites which provide a north south transect across the atlantic ocean supplemented by sections from the north sea basin barents sea falkland plateau weddell sea antarctica argo abyssal plain nw of australia and neuquen basin argentina quantitative assemblage data were gathered from each site for seven time slices within the berriasian to barremian interval each horizon being determined by a nannofossil datum trends in species relative abundance and measures of diversity evenness and richness provide revealing biogeographic information a broad low to mid palaeolatitude zone 50 degrees n 50 degrees s is flanked in both northern and southern hemispheres by distinct high palaeolatitude zones major changes in assemblage abundance and composition occur across a sharp biogeographic front at around 50 degrees n and s palaeolatitude high palaeolatitude assemblages are lower in species richness and diversity and characterised by the presence of abundant typically bipolar taxa e g crucibiscutum salebrosum a less distinct biogeographic boundary at similar to 40 degrees n is distinguished by the presence absence of rarer but biogeographically significant taxa many of which have previously been assigned to boreal or tethyan provinces continental shelf sites are characterised by lower diversity assemblages with common to dominant diagnostic taxa which vary with palaeolatitude nannoconus and micrantholithus at low palaeolatitudes and biscutum constans and zeugrhabdotus spp at higher palaeolatitudes the latter two taxa are considered to be indicative of elevated surface water fertility and the former two may have been similarly adapted the genus watznoueria is ubiquitously dominant giving the populations an unevenness which appears to be a common feature throughout coccolithophore history c 2000 published by elsevier science b v all rights reserved