high precision locations of the microseismicity preceding the 2002 2003 mt etna eruption 1 to recognize possible signals of intrusive processes leading to the last 2002 2003 flank eruption at mt etna we analyzed the spatial pattern of microseismicity between august 2001 and october 2002 and calculated 23 fault plane solutions fpss for shocks with magnitude greater than 2 5 by applying the double difference approach of waldhauser and ellsworth 2000 on 3d locations we found that most of the scattered epicentral locations further collapse in roughly linear features high precision locations evidenced a distribution of earthquakes along two main alignments oriented ne sw to ene wsw and nw se matching well both with the known tectonic and volcanic lineaments of etna and fpss results moreover microseismicity and swarms located along the nnw sse volcano genetic trend suggest together with geodetic data and volcanological evidence that progressive magma refilling has occurred since february 2002

magma degassing buffered by vapor flow through brecciated conduit margins obsidian pyroclasts a common component of rhyolitic tephra preserve a range of volatile contents which has been used to infer syneruptive conditions of magmatic degassing here we show that the textures of obsidian pyroclasts provide information on physical mechanisms of magma flow and degassing along conduit margins obsidian clasts often contain xenoliths sheared bands of lithic powder and textures consistent with magma autobrecciation these features suggest that pyroclastic obsidian primarily forms near conduit walls where magma fragments and reanneals during ascent we use these observations to develop a degassing model for pyroclastic obsidian from the a d 1340 mono craters california eruptions we suggest that degassing was buffered by continual flux of vapor through highly permeable brecciated magma along conduit walls continuous reequilibration of magma with vapor of relatively constant composition not only explains the co 2 h 2 o and d h 2 o data from mono craters pyroclastic obsidian but also requires much lower magmatic co 2 values than the commonly accepted model of closed system degassing taken together the chemical and physical evidence suggests that magma brecciation along conduit walls aids the degassing of ascending rhyolite

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

ice stream dynamics of the sw barents sea revealed by high resolution 3d seismic imaging of glacial deposits in the hoop area abstract recent developments in seismic acquisition systems and seismic data visualization have contributed to improve the imaging of seismic geomorphologies over a broad range of topics this study focuses on a new high resolution p cable 3d seismic cube located in the hoop area in the sw barents sea the scientific motivations of the study are 1 to document glacial landforms on a meter scale 2 to study the link of these landforms with the subsurface and 3 to understand ice stream dynamics by detailed interpretation of main horizons including the seabed intra glacial horizons and upper regional unconformity uru the horizons are assessed using the concept of seismic geomorphology and compared with interpretations derived from conventional 3d seismic and state of the art multibeam echosounder technologies to discuss the benefits and limitations of the different geophysical technologies a well defined intra glacial seismic reflection is imaged in the eastern part of the p cable cube this reflection has an overall ne trending ridge shaped morphology which is up to 50 m high and 5 10 km wide and interpreted as a shear margin moraine the top of the moraine displays well defined iceberg ploughmarks and clear slope failure events along its eastern flank the seabed geomorphology which has been directly shaped by glacial processes related to multiple phases of ice streaming appears to be influenced by the buried shear margin moraine mega scale glacial lineations msgls indicative of fast flowing ice streams characterize the seabed west of the moraine infilled msgls and different sets of iceberg ploughmarks with large berms dominate the seabed geomorphology above the moraine the seabed east of the moraine characterized by a smooth morphology and few pockmarks is inferred to reflect more slowly moving ice not resolved by other geophysical techniques seismic attribute maps of p cable 3d allowed the identification of smaller ploughmarks and corrugated ridges related to paleo tides eroded by the larger iceberg ploughmarks these small ploughmarks are suggested to be linked to an earlier rapid disintegration of the barents sea ice stream the new high resolution 3d seismic data have led to the development of a revised ice stream model of the barents sea linking the glacial deposits to different ice stream events

insights into the emplacement dynamics of volcanic landslides from high resolution 3d seismic data acquired offshore montserrat lesser antilles we present results from the first three dimensional 3d marine seismic dataset ever collected over volcanic landslide deposits acquired offshore of the soufriere hills volcano on the island of montserrat in the lesser antilles the 3d data enable detailed analysis of various features in and around these mass wasting deposits such as surface deformation fabrics the distribution and size of transported blocks change of emplacement direction and erosion into seafloor strata deformational features preserved on the surface of the most recent debris avalanche deposit deposit 1 reveal evidence for spatially variant deceleration as the mass failure came to rest on the seafloor block distributions suggest that the failure spread out very rapidly with no tendency to develop longitudinal ridges an older volcanic flank collapse deposit deposit 2 appears to be intrinsically related to large scale secondary failure of seafloor sediments we observe pronounced erosion directly down slope of a prominent headwall where translational sliding of well stratified sediments was initiated deep reaching faults controlled the form and location of the headwall and stratigraphic relationships suggest that sliding was concurrent with volcanic flank collapse emplacement we also identified a very different mass wasting unit between deposit 1 and deposit 2 that was likely emplaced as a series of particle laden mass flows derived from pyroclastic flows much like the recent since 1995 phase of deposition offshore montserrat but at a much larger scale this study highlights the power of 3d seismic data in understanding landslide emplacement processes offshore of volcanic islands highlights 3d seismic data show new detail of volcanic landslide deposits offshore montserrat volcanic flank collapse material has been diverted around seafloor topographic highs this bending during emplacement has caused pronounced erosion into seafloor strata erosion can destabilize seafloor slopes which then fail as translational slides block distributions and surface deformation give insight into debris avalanche style

oceanic propagation of a potential tsunami from the la palma island 1 the likelihood of a large scale tsunami from the la palma island is considered small by most nevertheless the potential catastrophic consequences call for attention here we report on numerical simulations of a tsunami that might result from the extreme case of a flank collapse of the cumbre vieja volcano at the la palma island done by combining a multimaterial model for the wave generation with boussinesq models for the far field propagation our simulations show that the slide speed is close to critical effectively generating an initial wave of several hundred meters height our main focus is the wave propagation which is genuinely dispersive in the far field propagation becomes increasingly complex due to the combined effects of dispersion refraction and interference in the direction of propagation constructive interference of the trailing waves are found to decrease the decay of the maximum amplitude with distance compared to classical asymptotic theory at transatlantic distances thus the commonly used hydrostatic models fail to describe the propagation consequences of the la palma scenario would be largest at the canary islands but our findings also suggests that the whole central atlantic would face grave consequences however the largest surface elevations are smaller than the most pessimistic reports found in literature we also find undular bores towards the shorelines of america

a multidisciplinary approach to detect active pathways for magma migration and eruption at mt etna sicily italy before the 2001 and 2002 2003 eruptions two strong flank eruptions occurred in july august 2001 and from late october 2002 to late january 2003 at mt etna volcano the two eruptions mainly involved the upper southern flank of the volcano a particularly active area during the last 30 years damaging several tourist facilities and threatening some villages the composite eruptive activity on the upper southern flank of mt etna during 2001 2003 has confirmed a posteriori the results of a multidisciplinary study started well before its occurrence by combining geological seismic and geochemical data gathered in this part of the volcano we were able in fact to highlight fractured zones likely to be re activated in the near future in this area where the largest majority of eruptive fissures in the recent past opened along n120 to n180 ranging directions the spatial distribution of earthquake epicentres during the period june 30th 2000 june 30th 2001 showed the greatest frequency in a sector compatible with both the direction of the main fissures of the pre 2001 period and that of the 2001 and 2002 lateral eruptions soil co2 and soil temperature surveys carried out in the studied area during the last 3 years have revealed anomalous release of magmatic fluids mainly co2 and water vapour along some nnw sse trending volcano tectonic structures of the area even during inter eruptive periods indicating persistent convective hydrothermal systems at shallow depth connected with the main feeder conduits of etna the temporal changes in both seismic and geochemical data from june 30th 2000 to june 30th 2001 were compared with the evolution of volcanic activity the comparison allowed to recognize at least two sequences of anomalous signals august to december 2000 and april to june 2001 likely related to episodes of step like magma ascent towards the surface as indicated by the following eruptive episodes the n120 to n180 structural directions are in accord with one of the main structural lines affecting eastern sicily they would be important pathways for magma uprise to the surface that will keep on feeding the eruptive activity of etna in the near future this study also pointed out the high instability of the southern slope of etna a sector where the potential hazard by lava flow invasion will remain high also in the near future

topographic reflection of the socompa debris avalanche chile one of the most remarkable features of the exceptionally well preserved 26 km3 socompa debris avalanche deposit is the evidence for topographically driven secondary flow the avalanche formed by sector collapse of socompa stratovolcano and spread 40 km across a pre existing basin forming a sheet of 50 m average thickness as the avalanche impinged on the western and northern margins of the basin it was reflected back forming a secondary flow that continued to travel 15 km down a gentle slope at an oblique angle to the primary flow the front of the return wave being preserved frozen on the surface of the deposit as a prominent escarpment satellite images aerial photos digital elevation models and field observations were used to reconstruct the sequence of events during avalanche emplacement and in particular during secondary flow the avalanche sheet was divided into distinct terrane groups each believed to have experienced a particular strain history during emplacement evidence for avalanche reflection includes clearly recognizable secondary slide masses sub parallel sets of curvilinear shear zones headwall scarps separating the primary levee from the secondary terranes extensional jigsaw breakup of surface lithologies during return flow and cross cutting or deflection of primary flow fabrics by secondary terranes reflection off the basin margin took place in an essentially continuous manner most major return motions being simultaneous with or shortly following primary flow the secondary flow occurred as a wave that swept obliquely across the primary avalanche direction remobilizing the primary material which was first compressed then stretched as it passed over and rearward of the wave front as return flow occurred surface lithologies were rifted in a brittle manner and the slabs were sheared pervasively as they glided and rotated back into the basin some sank into the more fluidal interior of the avalanche which drained out into a prominent distal lobe extension by factors of up to 1 8 took place during return flow secondary flow took place on slopes of only a few degrees and the distal lobe flowed 8 km on a slope of 1 overall the avalanche is inferred to have slid into place as a fast moving sheet of fragmental rock debris with a leading edge and crust with near normal friction and an almost frictionless fluidal interior and base the avalanche emplacement history deduced from field evidence is consistent with the results of a previously published numerical model of the socompa avalanche

viscosity of hydrous etna basalt implications for plinian style basaltic eruptions water dissolved in a silicate melt can strongly influence its physical properties and thus magma behavior during crystallization degassing foaming and fragmentation etna is a basaltic volcano whose activity is dominated by effusive eruptions which have long represented a threat to the densely populated surrounding area recently recognition of the products of a plinian eruption 122 b c has raised further issues for hazard assessment at etna and other basaltic volcanoes constraining the behavior of etna magma under conditions relevant to both effusive and explosive hazards requires viscosity data under conditions near the glass transition here we have investigated the viscosity of hydrous etna lava in order to better understand eruptive processes which characterize this volcano the experimental methods which have been used include piston cylinder synthesis of the hydrated melts micropenetration viscometry for low temperature viscosity measurements and near infrared spectroscopy for the evaluation of sample homogeneity and measurements of water content additionally scanning calorimetric determinations were performed to check whether incipient crystallization had occurred sample compositions were determined using electron microprobe analysis and 57fe mossbauer spectroscopy results from this study are compared with previous reports of trachytic phonolitic and model calc alkaline rhyolite hpg8 compositions the viscosity of the basaltic melt dry and wet has been parameterized in terms of temperature and water content via the non arrhenian equation log10 4 643 5 812 44 427 04 h2o t k 499 31 28 74 ln h2o where is the viscosity in pa s h2o is the water content in wt and t is the temperature in kelvin we observe that the viscosity of alkali basalt at more than 0 5 wt h2o is similar to that of an alkaline trachyte agnano monte spina eruption phlegrean fields and much higher than that of a peralkaline phonolite teide tenerife at similar silica contents and nbo t for water contents above 1 5 wt the viscosity of the basalt is similar to that of rhyolitic melts with similar water contents at temperatures ranging from 1 050 to 1 150 c and with water contents between 0 5 and 2 3 wt eruptive conditions the viscosities calculated using the equation defined in this study are 1 in reasonable agreement with those calculated using shaw s model and 2 much lower than those experimentally determined in a previous study however outside these temperature and water content ranges the agreement with shaw s model 1972 breaks down

longitudinal ridges in mass movement deposits prominent longitudinal features are often reported on the surfaces of mass movement deposits however the genesis and implications of these have not hitherto been considered and herein we present preliminary observations of their occurrence both in the field and in the laboratory elongated ridges are often oriented sub parallel to the flow direction and aligned radially from the source due to debris spreading they are particularly prominent in large 106m3 rock avalanches emplaced onto deformable substrates and are also found in the proximal reaches of volcanic debris avalanches flowbands which are longer and thinner expressions of longitudinal ridges are continuous along the entire flow length and are observed in rock avalanches emplaced onto glaciers in snow and some ice avalanches in pyroclastic flows and some block and ash flows in ejecta sheets in extraterrestrial landslides and in some volcanic debris avalanches other volcanic debris avalanches and the distal areas of rock avalanches often display hummocks that are aligned radially from the source we propose that these aligned hummocks are remnants of longitudinal ridges the formation of elongate ridges and their expressions as flowbands aligned hummocks or distal lobes and digits in qualitatively similar fashion in both laboratory and field environments suggests they represent an intrinsic tendency of granular flows in a wide range of situations

recent seismicity and tomographic modeling of the mount etna plumbing system the monitoring of seismic activity in eastern sicily southern italy has been recently improved in the framework of the poseidon project to investigate both tectonics and volcanic processes of mount etna this effort has produced a homogeneous and complete data set which we use to image the deep structure of the volcano and to define the space and time distribution of the recent seismicity encompassing the 1995 eruption diffuse eruptions between 1995 and 1997 a further magma intrusion started in 1997 and an increase of volcanic activity in july 1998 we inverted p wave arrival times from 307 selected local earthquakes to obtain a three dimensional velocity model of the volcano with a simultaneous inversion for hypocenters and velocity parameters the new tomographic images permit us to define the structure beneath the volcano from the surface down to 18 km depth the main structural feature revealed by our inversion is a high velocity body located beneath the central craters whose lateral extent increases from 6 km between 18 and 9 km depth to 12 km between 9 and 3 km depth near the surface the fast anomaly branches in two separate high vp regions which are located below the summit craters and the eastern flank valle del bove respectively the high velocity features are interpreted as high density cumulates of solidified magma that intruded the shallow crust we hypothesize that magma ascends the crust within the relatively small high velocity conduit below 9 km depth and is stored at depth shallower than 9 km within the broad high velocity region as also suggested by petrological data a sharp increase of seismicity in 1997 with earthquakes occurring at the border of the high velocity body suggests that mount etna sustained recent episodes of intrusions which possibly herald future eruptions no large low velocity anomaly interpretable as a melted magma chamber is imaged in the upper 18 km of the crust while a broad low velocity anomaly in the uppermost mantle revealed by regional seismic data possibly indicates the magma source region at depth earthquake occurrence from the deep source to the shallow intrusive area helps to trace the magma migration and the feeding of the volcanic system

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

a co2 rich gas trigger of explosive paroxysms at stromboli basaltic volcano italy in addition to rhythmic slug driven strombolian activity stromboli volcano occasionally produces discrete explosive paroxysms 2 per year on average for the most frequent ones that constitute a major hazard and whose origin remains poorly elucidated partial extrusion of the volatile rich feeding basalt as aphyric pumice during these events has led to consider their triggering by the fast ascent of primitive magma blobs from possibly great depth here i examine and discuss the alternative hypothesis that most of the paroxysms could be triggered and driven by the fast upraise of co2 rich gas pockets generated by bubble foam growth and collapse in the sub volcano plumbing system data for the so2 and co2 crater plume emissions are used to show that stromboli s feeding magma may originally contain as much as 2 wt of carbon dioxide and early coexists with an abundant co2 rich gas phase with high co2 so2 molar ratio 60 at 10 km depth below the vents compared to 7 in time averaged crater emissions pressure related modelling indicates that the time averaged crater gas composition and output are well accounted for by closed system decompression of the basalt gas mixture until the volcano crust interface 3 km depth followed by open degassing and crystallization in the volcano conduits however both the low viscosity and high vesicularity of the basaltic magma permit bubble segregation and bubble foam growth at deep sill like feeder discontinuities and at shallower physical boundaries such as the volcano crust interface where the gas rich aphyric basalt interacts with the unerupted crystal rich and viscous magma drained back from the volcano conduits gas pressure build up and bubble foam collapse at these boundaries will intermittently trigger the sudden upraise of co2 rich gas blobs that constitute the main driving force of the paroxysms deeper sourced gas blobs driving the most powerful explosions will be the richest in co2 and have highest co2 so2 ratios this mechanism is shown to account well for the dynamic seismic and petrologic features of stromboli s paroxysms and hence to provide a potential alternative interpretation for their genesis and their forecasting enhanced bubble foam leakage prior to a paroxysm or foam emptying in several steps should lead indeed to precursory upstream of co2 rich gas and increasing co2 so2 ratio in crater plume emissions the recent detection of such signals prior to two explosions in december 2006 and march 2007 strongly supports this expectation and the model proposed in this study

combining 3d seismics eyewitness accounts and numerical simulations to reconstruct the 1888 ritter island sector collapse and tsunami the 1888 ritter island volcanic sector collapse triggered a regionally damaging tsunami historic eyewitness accounts allow the reconstruction of the arrival time phase and height of the tsunami wave at multiple locations around the coast of new guinea and new britain 3d seismic interpretations and sedimentological analyses indicate that the catastrophic collapse of ritter island was preceded by a phase of deep seated gradual spreading within the volcanic edifice and accompanied by a submarine explosive eruption as the volcanic conduit was cut beneath sea level however the potential impact of the deep seated deformation and the explosive eruption on tsunami genesis is unclear for the first time it is possible to parameterise the different components of the ritter island collapse with 3d seismic data and thereby test their relative contributions to the tsunami the modelled tsunami arrival times and heights are in good agreement with the historic eyewitness accounts our simulations reveal that the tsunami was primarily controlled by the displacement of the water column by the collapsing cone at the subaerial submarine boundary and that the submerged fraction of the slide mass and its mobility had only a minor effect on tsunami genesis this indicates that the total slide volume when incorporating the deep seated deforming mass is not directly scalable for the resulting tsunami height furthermore the simulations show that the tsunamigenic impact of the explosive eruption energy during the ritter island collapse was only minor however this relationship may be different for other volcanogenic tsunami events with smaller slide volumes or larger magnitude eruptions and should not be neglected in tsunami simulations and hazard assessment

multi event oceanic island landslides new onshore offshore insights from el hierro island canary archipelago abstract this paper presents a combined onshore offshore morpho structural characterization of the el golfo giant landslide island of el hierro canary archipelago spain offshore data from multibeam echosounders chirp sub bottom profiles and multichannel seismic reflection data and onshore data coming from water wells and galleries have been analyzed the geomorphology and the internal architecture of this giant flank collapse are defined in order to determine its multi event nature the subaerial headscarp shows a non continuous arcuate profile formed by two nested semi circular amphitheaters that extend offshore along a smooth chute suggesting the occurrence of at least two large retrogressive events channels gullies and escarpments developed along the submarine sector of the scar also indicate smaller scale events and predominance of sediment bypass in the lower slope two subunits of submarine mass transport deposits mtds debris avalanche are identified on multichannel seismic reflection profiles with a total estimated volume of 318 km3 84 km3 and 234 km3 for the younger and older mtds respectively data from wells and galleries show abrasion platforms with beach deposits at sea level 0 masl formed after the landslide scar and buried by the post collapse el golfo lavas infill suggesting an age at least older than 23 5 82 5 ka for the landslide

conduit convection magma mixing and melt inclusion trends at persistently degassing volcanoes abstract magmas progressively exsolve volatiles as they ascend towards the earth s surface such that their volatile content is a function of pressure water and carbon dioxide concentrations measured in melt inclusions from degassing volcanoes rarely coincide with modelled degassing trends i show that observed melt inclusion trends can be reproduced through mixing of magmas either during convection within the volcanic conduit or within a subterranean magma reservoir no fluxing gas phase or post entrapment loss of water need be invoked a permeable network allowing gas transport is still required to avoid fragmentation of magma at shallow depths

volatiles degassing and crystallization at a primitive cinder cone implications for melt evolution and the plumbing systems of monogenetic volcanoes volcan jorullo mexico

submarine landslides around the canary islands the morphology and structure of the submarine flanks of the canary islands were mapped using the gloria long range side scan sonar system bathymetric multibeam systems and sediment echosounders twelve young 2 ma giant landslides have been identified on the submarine flanks of the canary islands up to now older landslide events are long buried under a thick sediment cover due to high sedimentation rates around the canary islands most slides were found on the flanks of the youngest and most active islands of la palma el hierro and tenerife but young giant landslides were also identified on the flanks of the older 15 20 ma but still active eastern islands large scale mass wasting is an important process during all periods of major magmatic activity the long lived volcanic constructive history of the islands of the canary archipelago is balanced by a correspondingly long history of destruction resulting in a higher landslide frequency for the canary islands compared to the hawaiian islands where giant landslides only occur late in the period of active shield growth the lower stability of the flanks of the canaries is probably due to the much steeper slopes of the islands a result of the abundance of highly evolved intrusive and extrusive rocks another reason for the enhanced slope instability is the abundance of pyroclastic deposits on canary islands resulting from frequent explosive eruptions due to the elevated volatile contents in the highly alkalic magmas dike induced rifting is most likely the main trigger mechanism for destabilization of the flanks flank collapses are a major geological hazard for the canary islands due to the sector collapses themselves as well as triggering of tsunamis in at least one case a giant lateral blast occurred when an active magmatic or hydrothermal system became unroofed during flank collapse

inverse modeling of interbed storage parameters using land subsidence observations antelope valley california 1 we use land subsidence observations from repeatedly surveyed benchmarks and interferometric synthetic aperture radar insar in antelope valley california to estimate spatially varying compaction time constants and inelastic specific skeletal storage coefficients s kv in a previously calibrated regional groundwater flow and subsidence model the observed subsidence patterns reflect both the spatial distribution of head declines and the spatially variable inelastic skeletal storage coefficient using the nonlinear parameter estimation program ucode we estimate compaction time constants between 3 8 and 285 years the s kv values are estimated by linear estimation and range from 0 to almost 0 09 we find that subsidence observations over long time periods are necessary to constrain estimates of the large compaction time constants in antelope valley the insar data used in this study cover only a three year period limiting their usefulness in constraining these time constants this problem will be alleviated as more sar data become available in the future or where time constants are small by incorporating the resulting parameter estimates in the previously calibrated regional model of groundwater flow and land subsidence we can significantly improve the agreement between simulated and observed land subsidence both in terms of magnitude and spatial extent the sum of weighted squared subsidence residuals a common measure of model fit was reduced by 73 with respect to the original model however the ability of the model to adequately reproduce the subsidence observed over only a few years is impaired by the fact that the simulated hydraulic heads over small time periods are often not representative of the actual aquifer hydraulic heads errors in the simulated hydraulic aquifer heads constitute the primary limitation of the approach presented here

three dimensional imaging of miocene volcanic effusive and conduit facies implications for the magmatism and seafloor spreading of the south china sea abstract an integrated and practical seismic based three dimensional 3d visualization technique of volcanic effusive and conduit facies is proposed in the miocene lower zhujiang formation of the baiyun sag pearl river mouth basin prmb south china sea scs the technique is based mainly on the 3d visualization to separately described the strong amplitude reflection volcanic effusive facies and the weak amplitude chaotic reflection volcanic conduit facies with different seismic cube attributes instantaneous amplitude attribute and variance cube attribute the detail work flow of the method has been proposed with eight steps including the original data type seismic attributes selection the visualizing skills and the final validation with borehole and thin sections it is convenient to operate and describe the spatial distribution and interrelation of various volcanic facies effectively and intuitively the 3d imaging result of different volcanic facies described in the baiyun sag can be viewed from any perspectives and better understand the related genesis mechanism which associated with the nw se trend normal fault system during the breakup stage the two volcanic facies indicate that the spatial distribution of the volcanic rocks is parallel to the normal faults strike and the magma probably flows along the normal fault plane and then feds into the volcanic mounds with eruption the volcanic mounds are mostly belonged to the central fissure eruption types and mainly correspond to the second magmatic episode 23 8 ma of early miocene in the prmb and were induced associated with the seafloor spreading of the northern scs we may easier to find effective volcanic reservoirs or other volcano related metallic minerals based on the proposed new method this significant work can also serve as a useful reference for other continental margins or sedimentary basins with typical volcanic influence

late pleistocene stratigraphy of iodp site u1396 and compiled chronology offshore of south and south west montserrat lesser antilles marine sediments around volcanic islands contain an archive of volcaniclastic deposits which can be used to reconstruct the volcanic history of an area such records hold many advantages over often incomplete terrestrial data sets this includes the potential for precise and continuous dating of intervening sediment packages which allow a correlatable and temporally constrained stratigraphic framework to be constructed across multiple marine sediment cores here we discuss a marine record of eruptive and mass wasting events spanning 250 ka offshore of montserrat using new data from iodp expedition 340 as well as previously collected cores by using a combination of high resolution oxygen isotope stratigraphy ams radiocarbon dating biostratigraphy of foraminifera and calcareous nannofossils and clast componentry we identify five major events at soufriere hills volcano since 250 ka lateral correlations of these events across sediment cores collected offshore of the south and south west of montserrat have improved our understanding of the timing extent and associations between events in this area correlations reveal that powerful and potentially erosive density currents traveled at least 33 km offshore and demonstrate that marine deposits produced by eruption fed and mass wasting events on volcanic islands are heterogeneous in their spatial distribution thus multiple drilling coring sites are needed to reconstruct the full chronostratigraphy of volcanic islands this multidisciplinary study will be vital to interpreting the chaotic records of submarine landslides at other sites drilled during expedition 340 and provides a framework that can be applied to the stratigraphic analysis of sediments surrounding other volcanic islands

comment on conduit convection magma mixing and melt inclusion trends at persistent degassing volcanoes by fred witham published in earth planetary science letters 2011 301 345 352 we discuss the influence of magma mixing on the co 2 h 2 o behavior in magmas witham s model does not fit our melt inclusion data set for mt etna and stromboli magma fluxing by a deep derived co 2 rich gas better explains the co 2 h 2 o evolution

lava production at soufriere hills volcano montserrat 1995 2009 1 we estimate that about 1 km3 of andesitic lava has been produced at soufriere hills volcano montserrat from 1995 to 2009 there were three major episodes of extrusion each lasting about 2 to 3 5 years and producing about 280 to 340 m m3 of lava and one minor episode our estimates account for the dense rock equivalent volumetric contributions from the core and talus components of the lava dome pyroclastic flow deposits and air fall deposits by 2005 at least two thirds of the erupted mass has already entered the sea the average lava flux across the major extrusion episodes has been 3 5 m3s 1 with short period 10 15 days pulses up to 10 20 m3s 1 the first and third episodes of extrusion show similar flux histories suggesting similar behaviour of the system ten years apart waning flux towards the end of each episode may be caused by declining overpressure in the magma reservoir

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

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

dynamics of magma mixing and degassing recorded in plagioclase at stromboli aeolian archipelago italy crystal rich materials scoriae and lava flows emitted during the 1985 2000 activity of stromboli were taken into consideration for systematic study of bulk rock matrix glass chemistry and in particular for the study of chemical and textural zoning of plagioclase the most abundant mineral phase over the considered time period bulk rock composition remained fairly constant in both major sio2 49 2 50 9 wt and k2o 1 96 2 18 wt and trace elements the quite constant chemistry of matrix glasses also indicates that the degree of crystallization of magma was maintained at around 50 vol plagioclase ranges in composition between an62 and an88 and is characterized by alternating 10 100 m thick bytownitic and labradoritic concentric layers although the dominant and representative plagioclase of scoriae is an68 the labradoritic layers an62 70 show small scale 1 5 m oscillatory zoning are free of inclusions and appear to record episodes of slow crystal growth in equilibrium with a degassed liquid having the composition of the matrix glass in contrast the bytownitic layers an70 an88 are patchy zoned show sieve structure with abundant micrometric glass inclusions and voids and are attributed to rapid crystal growth

melt inclusion record of the conditions of ascent degassing and extrusion of volatile rich alkali basalt during the powerful 2002 flank eruption of mount etna italy 1 two unusual highly explosive flank eruptions succeeded on mount etna in july august 2001 and in october 2002 to january 2003 raising the possibility of changing magmatic conditions here we decipher the origin and mechanisms of the second eruption from the composition and volatile h2o co2 s cl content of olivine hosted melt inclusions in explosive products from its south flank vents our results demonstrate that powerful lava fountains and ash columns at the eruption onset were sustained by closed system ascent of a batch of primitive volatile rich 4 wt basaltic magma that rose from 10 km depth below sea level bsl and suddenly extruded through 2001 fractures maintained opened by eastward flank spreading this magma the most primitive for 240 years probably represents the alkali rich parental end member responsible for etna lavas evolution since the early 1970s few of it was directly extruded at the eruption onset but its input likely pressurized the shallow plumbing system several weeks before the eruption this latter was subsequently fed by the extrusion and degassing of larger amounts of the same but slightly more evolved magma that were ponding at 6 4 km bsl in agreement with seismic data and with the lack of preeruptive so2 accumulation above the initial depth of sulphur exsolution 3 km bsl we find that while ponding this magma was flushed and dehydrated by a co2 rich gas phase of deeper derivation a process that may commonly affect the plumbing system of etna and other alkali basaltic volcanoes

low pressure crystallization paths of h2o saturated basaltic hawaiitic melts from mt etna implications for open system degassing of basaltic volcanoes melt inclusions indicate that the basaltic hawaiitic magmas from mt etna sicily contained up to 2 3 wt h2o dissolved in the melt prior to eruption the effect of h2o degassing during magma ascent has been experimentally constrained between 1135 and 1009 c for ph2o ptotal varying from 800 to 270 bars the starting material was a primitive hawaiitic lava sample mgo 7 1 wt representative of the less evolved lava emitted at mt etna experiments were conducted in tzm pressure vessels with ag70pd30 capsules in order to minimize the feo loss at temperatures of 1135 1090 c ph2o 800 bars with ninio and fmq buffers olivine fo83 80 is the liquidus phase in equilibrium with a residual hawaiitic melt mg 0 60 0 57 cao al2o3 0 82 salitic pyroxene begins to crystallize at 1075 c plagioclase at 1025 c and at 1009 c the magma is 33 5 crystallized with olivine ca rich pyroxene and plagioclase 16 60 24 at ph2o 270 bars fmq buffer olivine fo79 3 80 and salitic pyroxene are the main liquidus phases between 1100 and 1090 c they are in equilibrium with hawaiitic melts mg 0 51 cao al2o3 0 73 at 1070 c the experimental charges are highly crystallized 51 5 with olivine fo70 salite and plagioclase an78 4 76 3 in 14 44 42 relative proportions increasing the water content of hawaiitic basaltic magmas expands the stability field of the olivine relative to the other phases lowers the crystallization temperatures of pyroxene and plagioclase and results in the development of a more an rich plagioclase when compared to the natural samples these results support a model of early and moderate crystallization of olivine from etnean primitive hawaiitic magmas containing close to 2 5 wt h2o with nno oxygen buffering conditions at low pressure ph2o ptotal we propose a model of crystallization driven by decompression and water degassing during the emplacement of magma in the volcanic pile itself and possibly concomitant with the opening of fractures

conditions of magma storage degassing and ascent at stromboli new insights into the volcano plumbing system with inferences on the eruptive dynamics stromboli is known for its persistent degassing and rhythmic strombolian activity occasionally punctuated by paroxysmal eruptions the basaltic pumice and scoria emitted during paroxysms and strombolian activity respectively differ in their textures crystal contents and glass matrix compositions which testify to distinct conditions of crystallization degassing and magma ascent we present here an extensive dataset on major elements and volatiles co2 h2o s and cl in olivine hosted melt inclusions and embayments from pyroclasts emplaced during explosive eruptions of variable magnitude magma saturation pressures were assessed from the dissolved amounts of h2 oa nd co2 taking into account the melt composition evolution both pressures and melt inclusion compositions indicate that 1 ca basaltic melts entrapped in high mg olivines fo89 90 generate stromboli basalts through crystal fractionation and 2 the stromboli plumbing system can be imaged as a succession of magma ponding zones connected by dikes the 7 10 km interval where magmas are stored and differentiate is periodically recharged by new magma batches possibly ranging from ca basalts to basalts with a co2 rich gas phase these deep recharges promote the formation of bubbly basalt blobs which are able to intrude the shallow plumbing system 2 4 km where co2 gas fluxing enhances h2o loss crystallization and generation of crystal rich dense degassed magma chlorine partitioning into the h2o co2 bearing gas phase accounts for its efficient degassing 69 under the open system conditions of strombolian activity paroxysms however are generated through predominantly closed system ascent of basaltic magma batches from the deep storage zone in this situation crystallization is negligible and sulfur exsolution starts at 170 mpa chlorine remains dissolved in the melt until lower pressures only 16 being lost upon eruption finally we propose a continuum in explosive eruption energy from strombolian activity to large paroxysmal events ultimately controlled by variable pressurization of the deep feeding system associated with magma and gas recharges

contrasting triggering mechanisms of the 2001 and 2002 2003 eruptions of mount etna italy abstract mount etna produced two significant eruptions in 2001 and 2002 2003 which we have analysed using geological seismic and deformation data these eruptions showed some similarities such as the activating of two magmatic plumbing systems central lateral and eccentric but they differed in their triggering mechanisms while the 2001 eruption was largely the result of the emplacement of a n s eccentric dike independent from the central conduits consistent with e w regional extension the 2002 2003 eruption occurred in response to a major flank slip on the eastern and southeastern sides of the volcano this is demonstrated by the spatial and temporal distribution of seismicity and deformation preceding and accompanying the two eruptions during the months prior to the 2001 eruption most epicenters were concentrated on the southern flank at depths of 5 15 km below sea level during the 4 days before the eruption earthquake hypocenters migrated to shallower levels from 5 km bsl upward indicating the emplacement of the eccentric dike this is confirmed by the patterns of ground fracturing observed in the field and deformation documented by electronic distance measurements edm in contrast the months before the 2002 2003 eruption were characterised by shallower seismicity mainly concentrated along the active faults bordering the slipping flank sector flank slip accelerated in september 2002 and a second more vigorous acceleration of flank slip occurred on 26 27 october 2002 accompanying the opening of eruptive vents the very short 2 h seismic crisis preceding the onset of eruptive activity stands in neat contrast with the 4 days of intense seismicity before the 2001 eruption subsequently flank slip deformation extended all over the eastern and southeastern flanks of the volcano causing serious damage in this sector the events of 2001 2003 can be seen as a continuous chain of intimately interacting processes including regional tectonics magma accumulation and eruption and flank instability in this scenario the 2001 eruption led to increased flank instability that subsequently accelerated and culminated with the massive flank slip which in turn facilitated the 2002 2003 eruption this sequence of events points to a long term feedback mechanism between magmatism and flank instability at etna

a giant landslide on the north flank of tenerife canary islands the extent of mass wasting along the north flank of tenerife has been mapped using swath bathymetry gloria side scan sonar and 3 5 khz echo sounder data the marine surveys show that north of tenerife a giant landslide is exposed over an area of 5500 km2 of the seafloor more than twice the surface area of the island the landslide truncates an older ridge and valley topography that is associated with the shield building basalts on tenerife we interpret the ridge and valley topography as the result of subaerial erosion the landslide is estimated to have a length of 100 km a width of up to 80 km and a volume of about 1000 km3 it extends onshore into the orotava and icod valleys which have been interpreted as of landslide origin k ar dating of basaltic flows in the steep headwall of orotava suggests an age of formation for the valley is younger than 0 78 ma and may even be younger than 0 27 ma the icod valley is located immediately to the north of the most recent volcano on tenerife las canadas and has been associated with the collapse of its caldera between 1 2 and 0 2 ma a young age for the landslide is supported by the 3 5 khz echo sounder data which show that the landslide is draped by a thin 10 m layer of younger sediment the landslide did not form however during a single catastrophic event but represents the amalgamation of a number of separate landslides the occurrence of the ridge and valley topography in water depths of up to 2 5 km suggests that the shield building basalts have subsided by at least this amount since they formed 3 3 8 0 ma we speculate that this subsidence is caused by some form of stress relaxation that occurs in the underlying lithosphere the giant landslide imaged in our sonar data is associated with the late stages in the development of the most recent volcano on tenerife las canadas which only began at about 1 8 ma thus landsliding may be a particular feature of the time soon after emplacement when because of incomplete isostatic adjustment oceanic volcanoes have their greatest elevations above sea level and therefore are most susceptible to slope failure

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

comments on quantifying groundwater exploitation induced subsidence in the rafsanjan plain southeastern iran using insar time series and in situ measurements by motagh m shamshiri r haghighi m h wetzel h u akbari b nahavandchi h arabi s engineering geology 218 2017 134 151 abstract in confined aquifers there is a direct correspondence between changes in both hydraulic head and aquifer thickness as well as between changes in aquifer thickness and vertical land deformation in fact the vertical land deformation in confined aquifers incorporates changes in both compressibility of the aquifer skeleton and expansion of the pore water as main factors controlling the storage coefficient of the aquifers this is not the case in unconfined aquifers where the water is predominantly drained by gravity from the pore spaces implying that it may not be possible to calculate the storage coefficient of unconfined aquifers using the land deformation data in a paper published in this journal motagh et al 2017 conducted a join of insar land deformation data and hydrogeological measurements to estimate the storage coefficient and the average volume storage loss of the rafsanjan aquifer southeast of iran from 2004 to 2010 the authors estimated the storage coefficient of the unconfined rafsanjan aquifer using specific storage equations but adopted for confined aquifers which led to an overestimation in the storage coefficient 0 1 in comparison with the average value obtained from standard well pumping tests 0 05 reported by zayandehroodi 2012 likewise this overestimation in the storage coefficient led to a deviation of 116 million cubic meters per year mcm yr of the average volume storage loss for the unconfined aquifer

sediment waves on the conrad rise southern indian ocean implications for the migration history of the antarctic circumpolar current abstract the antarctic circumpolar current acc is the worlds longest and largest current system therefore it plays a prominent role in the global distribution of heat nutrients and greenhouse gasses while past changes in the acc have been reconstructed by a number of studies using sedimentary records in the southern ocean a detailed understanding of the relationship between its temporal and spatial variability and the changes in the earths climatic system remains unclear in this study we conducted multibeam bathymetry multi channel seismic reflection and sediment coring surveys on the conrad rise located in the southern indian ocean sector of the acc these data reveal large scale sediment wave structures with continuous and parallel reflectors that have low to moderate reflection amplitudes in the upper part of the seismic section unit a these phenomena are most likely formed by bottom current interactions with the sea floor and sediment transport under the acc the basal age of unit a is estimated to be younger than pliocene pleistocene boundary based on the extrapolation of sedimentation rates from a shallow sedimentary core the lower part of the section unit b is characterized by moderate to high amplitude sub horizontal to horizontal reflectors that are interpreted as pelagic sedimentation with stronger current influence to the upper part of the unit based on the correlation with odp sites in the southern ocean we estimate that the upper part of unit b mainly comprises calcareous ooze though the age of the change in the sedimentary environment from seismic units b to a is not specified it is thought to be caused by a northward shift of the acc

2001 flank eruption of the alkali and volatile rich primitive basalt responsible for mount etna s evolution in the last three decades abstract since the early 1970s enhanced eruptive activity of mount etna has been accompanied by selective geochemical changes in erupted lavas among which a gradual increase of alkalis whose origin is still debated here we provide further insight into the origin of this recent evolution based on a detailed study of the chemistry and dissolved volatile content of melt inclusions trapped in olivine crystals of unusual plagioclase poor primitive basalt that was extruded during a highly explosive flank eruption in july august 2001 two types of lava were erupted simultaneously along a n s fracture system trachybasalts from the upper vents 2950 2700 m were simply drained out by fracturing of the central volcanic conduit they are identical to summit crater lavas and contain mg poor olivines fo 70 72 with evolved and volatile poor melt inclusions that represent late stage crystallisation during shallow open conduit degassing in contrast plagioclase poor basalt 80 of total extruded through the lower vents 2550 2100 m derived from lateral dyke intrusion of a more primitive and volatile rich magma across the sedimentary basement this primitive melt is best preserved in rare fo 82 4 80 5 skeletal olivines present in lapilli deposits from the most powerful activities at the 2550 m vent its high dissolved contents of h 2 o 3 4 wt co 2 0 11 to 0 41 wt s 0 32 wt cl 0 16 wt and f 0 094 wt point to its closed system ascent from 400 to 250 mpa 12 to 6 5 km depth b s l however the predominance of euhedral olivine phenocrysts with common reverse zoning cores fo 76 78 and rims fo 78 80 and decrepited inclusions shows that most of the erupted basalt derived from a slightly more evolved crystallizing body of the same magma that was invaded by the uprising primitive melt prior to erupting the few preserved inclusions in these olivines indicate pre eruptive storage of that magma body at about 5 km depth b s l in coherence with seismic data we propose that the 2001 flank eruption resulted from gradual overpressuring of etna s shallow plumbing system due to the influx of volatile rich primitive basalt that may have begun several months in advance we find that this basalt is much richer in alkalis 2 0 wt k 2 o and has higher s cl 2 0 but lower cl k and cl f ratios than all pre 1970s etnean lavas 1 4 wt k 2 o s cl 1 5 as further exemplified by melt inclusions in entrained olivine xenocrysts combining these new observations with previously published data we argue that the 2001 basalt represents a new alkali rich basic end member feeding mt etna only few amount of which had previously been extruded during a 1974 peripheral eruption and more recently during brief paroxysmal summit events over the last three decades this new magma has progressively mixed with and replaced the former k poorer trachybasalts filling the plumbing system leading to extrusion of gradually more primitive and alkali richer lavas its geochemical singularities cannot result from shallow crustal contaminations instead they suggest the involvement of an alkali richer but cl poorer arc type component during recent magma genesis beneath etna

the relationship between eruptive activity flank collapse and sea level at volcanic islands a long term 1 ma record offshore montserrat lesser antilles hole u1395b drilled southeast of montserrat during integrated ocean drilling program expedition 340 provides a long 1 ma and detailed record of eruptive and mass wasting events 130 discrete events this record can be used to explore the temporal evolution in volcanic activity and landslides at an arc volcano analysis of tephra fall and volcaniclastic turbidite deposits in the drill cores reveals three heightened periods of volcanic activity on the island of montserrat 930 ka to 900 ka 810 ka to 760 ka and 190 ka to 120 ka that coincide with periods of increased volcano instability and mass wasting the youngest of these periods marks the peak in activity at the soufriere hills volcano the largest flank collapse of this volcano 130 ka occurred towards the end of this period and two younger landslides also occurred during a period of relatively elevated volcanism these three landslides represent the only large 0 3 km3 flank collapses of the soufriere hills edifice and their timing also coincides with periods of rapid sea level rise 5 m ka available age data from other island arc volcanoes suggests a general correlation between the timing of large landslides and periods of rapid sea level rise but this is not observed for volcanoes in intra plate ocean settings we thus infer that rapid sea level rise may modulate the timing of collapse at island arc volcanoes but not in larger ocean island settings

melt inclusion investigation of the volatile behaviour in historic alkali basaltic magmas of etna crystallization paths of basaltic 1763 eruption and hawaiitic 1865 and 1329 eruptions scoria from etna were deduced from mineralogy and melt inclusion chemistry the volatile behaviour was investigated through the study of melt inclusions trapped in the phenocrysts and those of the whole rocks and the matrix glasses the results from the 1763 eruption point to the early crystallization of olivine fo 81 7 from a water rich alkaline basalt with high cl 1750 2000 ppm and s 2100 2400 ppm concentrations the hawaiitic melt inclusions trapped in olivine fo 74 salite and plagioclase are characterized by a decrease in cl k2o and s k2o ratios in each investigated system there is good correlation between k2o and p2o5 in the whole rocks cl ranges from 980 to 1680 ppm from basaltic to hawaiitic lavas whereas s 110 136 ppm remains low cl and s behaviour in the 1763 magma suggests an early degassing stage of cl and s with co2 and a water rich gaseous phase for a pressure close to 100 mpa consistent with a permanent outgassing at the summit craters of etna during the eruption the sulphur remaining in the hawaiitic liquid is lost and the degassing of chlorine is limited such a degassing model can be extended to the 1865 and 1329a d eruptions

flank instability assessment at kick em jenny submarine volcano grenada lesser antilles a multidisciplinary approach using experiments and modeling kick em jenny kej located ca 8 km north of the island of grenada is the only active submarine volcano of the lesser antilles volcanic arc previous investigations of kej revealed that it lies within a collapse scar inherited from a past flank instability episode to assess the likelihood of future collapse we employ here a combined laboratory and modeling approach lavas collected using a remotely operated vehicle rov provided samples to perform the first rock physical property measurements for the materials comprising the kej edifice uniaxial and triaxial deformation experiments showed that the dominant failure mode within the edifice host rock is brittle edifice fractures such as those at champagne vent will therefore assist the outgassing of the nearby magma filled conduit favoring effusive behavior these laboratory data were then used as input parameters in models of slope stability first relative slope stability analysis revealed that the sw to n sector of the volcano displays a deficit of mass volume with respect to a volcanoid ideal 3d surface slope stability analysis using a limit equilibrium method lem showed that kej is currently stable since all values of stability factor or factor of safety fs are greater than unity the lowest values of fs were found for the sw nw sector of the volcano the sector displaying a mass volume deficit although currently stable kej may become unstable in the future instability severe reductions in fs could result for example from overpressurization due to the growth of a cryptodome our modeling has shown that instability induced flank collapse will most likely initiate from the sw nw sector of kej therefore mobilizing a volume of at least ca 0 7 km3 the mobilization of ca 0 7 km3 of material is certainly capable of generating a tsunami that poses a significant hazard to the southern islands of the west indies

melt inclusions track pre eruption storage and dehydration of magmas at etna at mount etna italy vigorous gas rich eruptions in a d 2001 2002 and 2003 were followed by gas poor eruptions in 2004 2006 and 2007 analyses of volatile co2 h2o s cl f semivolatile cu and involatile nb la elements trapped in olivine hosted melt inclusions from these latest eruptions reveal the effects of the sustained interaction between a percolating gas phase and the stored magma melt inclusion compositions indicate that magmas erupted from 2004 to 2007 were residual from the 2001 2003 eruptions and show significant evolution in the volatile content of the melt these melt inclusion observations and variations in the c s of volcanic gases can be accounted for if melts reequilibrated with co2 rich gases during storage and prior to entrapment as melt inclusions sustained gas percolation caused loss of water and enhancement of co2 in the evolving melt and may strongly influence the behavior of cu which potentially partitions into the gas phase vapor melt interactions during magma storage are important controls on magma evolution at persistently degassing volcanoes

geomorphological evolution of montserrat west indies importance of flank collapse and erosional processes analysis of topography and new swath bathymetry as well as geophysical data provides information about aerial and submarine morphological features and mass transfer processes on montserrat the island has a characteristic shallow c 4000 years ago or the boxing day event during the current eruption 26 december 1997 montserrat9s older volcanic centres the centre hills and silver hills illustrate the third stage of evolution extinction and erosion magma production long term erosion and total sedimentation rates on montserrat have been estimated as 0 17 km 3 ka 1 0 0125 km 3 ka 1 and 0 11 km 3 ka 1 i e 1 1 cm ka 1 respectively

from gradual spreading to catastrophic collapse reconstruction of the 1888 ritter island volcanic sector collapse from high resolution 3d seismic data abstract volcanic island flank collapses have the potential to trigger devastating tsunamis threatening coastal communities and infrastructure the 1888 sector collapse of ritter island papua new guinea in the following called ritter is the most voluminous volcanic island flank collapse in historic times the associated tsunami had run up heights of more than 20 m on the neighboring islands and reached settlements 600 km away from its source this event provides an opportunity to advance our understanding of volcanic landslide tsunami hazards here we present a detailed reconstruction of the 1888 ritter sector collapse based on high resolution 2d and 3d seismic and bathymetric data covering the failed volcanic edifice and the associated mass movement deposits the 3d seismic data reveal that the catastrophic collapse of ritter occurred in two phases 1 ritter was first affected by deep seated gradual spreading over a long time period which is manifest in pronounced compressional deformation within the volcanic edifice and the adjacent seafloor sediments a scoria cone at the foot of ritter acted as a buttress influencing the displacement and deformation of the western flank of the volcano and causing shearing within the volcanic edifice 2 during the final catastrophic phase of the collapse about 2 4 km3 of ritter disintegrated almost entirely and traveled as a highly energetic mass flow which incised the underlying sediment the irregular topography west of ritter is a product of both compressional deformation and erosion a crater like depression underlying the recent volcanic cone and eyewitness accounts suggest that an explosion may have accompanied the catastrophic collapse our findings demonstrate that volcanic sector collapses may transform from slow gravitational deformation to catastrophic collapse understanding the processes involved in such a transformation is crucial for assessing the hazard potential of other volcanoes with slowly deforming flanks such as mt etna or kilauea

volcanogenic mass flow deposits and seafloor diapirism following the largest insular quaternary eruption of the eastern mediterranean at nisyros island aegean volcanic arc abstract nisyros volcanic island at the eastern end of the aegean volcanic arc was mainly constructed after the ultra plinian kos plateau tuff kpt eruption at 161 ka the surrounding submarine area consists mostly of marginal mass transport deposits that commonly characterize insular stratovolcanoes this study aims at providing insights into the deposition and volume of such deposits by elucidating the products of a mega eruption and subsequent paroxysmal volcanicity typical of subduction zone island arc systems seismic reflection and multibeam bathymetry around nisyros identify pyroclastic and debris flow deposits covering areas several orders of magnitude greater than the island the entire seabed between the basins of east kos and tilos is underlain by a 7 km3 volcaniclastic unit that defines a ubiquitous basal unconformity at an average depth of 30 m below the seafloor southwest of nisyros two groups of avalanche deposits from the same unit are bathymetrically identified on the slopes of the northernmost karpathos basin apron seismic stratigraphic markers that trace the unit on the shelf of tilos suggest it is concomitant with the kpt eruption this formerly unknown submarine expansion of the kpt deposits into three neighboring basins when added to the volume of this massive unit to the rest of the nisyros surroundings gives it an explosivity index vei 6 as such it represents the largest quaternary subaqueous volcanogenic mass flow deposit of the eastern mediterranean from this dataset it can be inferred that the submarine advance of the erupted material occurred mainly through erosive gravity flows envisioned as the main dispersion mechanism of large scale subaqueous pyroclastic deposits of plinian eruptions east of nisyros unique small scale diapiric domes and seafloor mounds are attributed to loading by the kpt in combination with regional faulting subsequent nisyros effusive activity produced pyroclastic units around the northeast as well as debris avalanche and lava flows south of the island these have been correlated to known onshore formations the present study documents the intensity and impacts of a volcanic island mega eruption and paroxysmal epilogue over a cycle of 100 kyr

dynamic disintegration processes accompanying transport of the holocene flims sturzstrom swiss alps abstract a sturzstrom is a large scale landslide that evolves during transport into a rapid granular flow rock avalanche by a dynamic disintegration process numerous theoretical hypotheses have been proposed to explain the excessive mobility of these catastrophic mass movements but the role of disintegration processes remains poorly understood exceptional outcrop conditions at the giant 12 km3 flims sturzstrom swiss alps permit the analysis of disintegration processes that result from shearing during transport in confined zones of the rock mass shearing is concentrated along preferred surfaces originating as bedding planes which evolve into shear band layers differential velocities of slabs separated by these shear layers induce oblique fractures in the slabs by accommodation contacts between grains are maintained in the shear layers in unconfined zones near the top and the lateral margins shearing generates dilatancy the rock mass is affected by anisotropic dispersion without mixing and disintegrated material is preferentially produced to the top due to inflation the rock slide then evolves to a granular flow the consequence of these processes is the formation of two distinct depositional facies in the sturzstrom the structured facies exhibits a stratified aspect close to the base reflecting confined slab on slab shearing motion towards the top and distally it evolves into a chaotic facies with some isolated pockets of the structured facies reduction of confining forces on the moving sturzstrom allows transformation of the structured facies into the chaotic facies this characteristic transition observable in many sturzstrom deposits seems to be necessary for the rock avalanche process to occur and offers insights into the long runout characteristics of these catastrophic mass movements

the 2007 eruption of stromboli volcano insights from real time measurement of the volcanic gas plume co2 so2 ratio abstract the recent eruption of stromboli in february april 2007 offered a unique chance to test our current understanding of processes driving the transition from ordinary persistent strombolian to effusive activity and the ability of instrumental geophysical and geochemical networks to interpret and predict these events here we report on the results of two years of in situ sensing of the co 2 so 2 ratio in stromboli s volcanic gas plume in the attempt to put constraints on the trigger mechanisms and dynamics of the eruption we show that large variations of the plume co 2 so 2 ratio range 0 9 26 preceded the onset of the eruption since december 2007 interrupting a period of relatively steady and low ratios time averaged ratio 4 3 lasting from at least may to november 2006 by contrasting our observations with numerical simulations of volcanic degassing at stromboli derived by use of an equilibrium saturation model we suggest that the pre eruptive increase of the ratio reflected an enhanced supply of deeply derived co 2 rich gas bubbles to the shallow plumbing system this larger than normal ascent of gas bubbles was likely sourced by a 1 3 km deep gas melt separation region probably a magma storage zone and caused faster convective overturning of magmas in the shallow conduit an increase in the explosive rate and in seismic tremor and finally the collapse of the la sciara del fuoco sector triggering the effusive phase the high co 2 so 2 ratios up to 21 observed during the effusive phase and particularly in the days and hours before a paroxysmal explosion on march 15 2007 indicate the persistence of the same gas source and suggest that de pressurization of the same 1 3 km deep magma storage zone could have been the trigger mechanism for the paroxysm itself

petrologic evidence of a complex plumbing system feeding the july august 2001 eruption of mt etna sicily italy after the major 1991 1993 eruption mt etna resumed flank activity in july 2001 through a complex system of eruptive fissures cutting the ne and the s flanks of the volcano and feeding effusive activity fire fountains strombolian and minor phreatomagmatic explosions throughout the eruption magmas with different petrography and composition were erupted the vents higher than 2 600 m a s l hereafter upper vents uv erupted porphyritic plagioclase rich trachybasalt typical of present day summit and flank activity differently the vents located at 2 550 and 2 100 m a s l hereafter lower vents lv produced slightly more primitive trachybasalt dominated by large clinopyroxene olivine and uncommon minerals for etna such as amphibole apatite and orthopyroxene and containing siliceous and cognate xenoliths petrologic investigations carried out on samples collected throughout the eruption provided insights into one of the most intriguing aspects of the 2001 activity namely the coeval occurrence of distinct magmas we interpret this evidence as the result of a complex plumbing system it consists in two separate magma storage systems a shallow one feeding the activity of the uv and a deeper and more complex storage related to the activity of lv in this deep storage zone which is thermally and compositionally zoned the favourable conditions allow the crystallization of amphibole and the occurrence of cognate xenoliths representing wall cumulates throughout 2001 eruption uv and lv magmas remain clearly distinct and ascended following different paths ruling out the occurrence of mixing processes between them furthermore integrating the 2001 eruption in the framework of summit activity occurring since 1995 we propose that the 2001 magma feeding the vents lower than 2 600 m a s l is a precursor of a refilling event which reached its peak during the 2002 2003 etna flank eruption

a quasi elastic aquifer deformational behavior madrid aquifer case study summary the purpose of this paper is to analyze the quasi elastic deformational behavior that has been induced by groundwater withdrawal of the tertiary detrital aquifer of madrid spain the spatial and temporal evolution of ground surface displacement was estimated by processing two datasets of radar satellite images sar using persistent scatterer interferometry psi the first sar dataset was acquired between april 1992 and november 2000 by ers 1 and ers 2 satellites and the second one by the envisat satellite between august 2002 and september 2010 the spatial distribution of psi measurements reveals that the magnitude of the displacement increases gradually towards the center of the well field area where approximately 80 mm of maximum cumulated displacement is registered the correlation analysis made between displacement and piezometric time series provides a correlation coefficient greater than 85 for all the wells the elastic and inelastic components of measured displacements were separated observing that the elastic component is on average more than 4 times the inelastic component for the studied period moreover the hysteresis loops on the stress strain plots indicate that the response is in the elastic range these results demonstrate the quasi elastic behavior of the aquifer during the aquifer recovery phase ground surface uplift almost recovers from the subsidence experienced during the preceding extraction phase taking into account this unique aquifer system a one dimensional elastic model was calibrated in the period 1997 2000 subsequently the model was used to predict the ground surface movements during the period 1992 2010 modeled displacements were validated with psi displacement measurements exhibiting an error of 13 on average related with the inelastic component of deformation occurring as a long term trend in low permeability fine grained units this result further demonstrates the quasi elastic deformational behavior of this unique aquifer system

a parametric study of tsunamis generated by submarine slides in the ormen lange storegga area off western norway tsunami generation by submarine slides have been a major concern in the risk assessment for the ormen lange gas field off western norway tsunamis are analysed with a numerical model supplemented by an analytical one both models show how slide extensions and slide dynamics influence the tsunamigenic potential for a large region several combinations of slide parameters were tested and the product of initial acceleration and the volume of the slide gave the best correlation with the maximum surface elevation for the near coastal domain

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

the role of the pernicana fault system in the spreading of mt etna italy during the 2002 2003 eruption flank instability and collapse are observed at many volcanoes among these mt etna is characterized by the spreading of its eastern and southern flanks the eastern spreading area is bordered to the north by the e w trending pernicana fault system pfs during the 2002 2003 etna eruption ground fracturing along the pfs migrated eastward from the ne rift to as far as the 18 km distant coastline the deformation consisted of dextral en echelon segments with sinistral and normal kinematics both of these components of displacement were one order of magnitude larger 1 m in the western previously known portion of the pfs with respect to the newly surveyed 9 km long eastern section 0 1 m this eastern section is located along a pre existing but previously unknown fault where displaced man made structures give overall slip rates 1 1 9 cm year only slightly lower than those calculated for the western portion 1 4 2 3 cm year after an initial rapid motion during the first days of the 2002 2003 eruption movement of the western portion of the pfs decreased dramatically while parts of the eastern portion continued to move these data suggest a model of spreading of the eastern flank of etna along the pfs characterized by eruptions along the ne rift instantaneous short lived meter scale displacements along the western pfs and more long lived centimeter scale displacements along the eastern pfs the surface deformation then migrated southwards reactivating one after the other the nnw sse trending timpe and trecastagni faults with displacements of 0 1 and 0 04 m respectively these structures along with the pfs mark the boundaries of two adjacent blocks moving at different times and rates the new extent of the pfs and previous activity over its full length indicate that the sliding eastern flank extends well below the ionian sea the clustering of seismic activity above 4 km b s l during the eruption suggests a deep decollement for the moving mass the collected data thus suggests a significant movement volume 1 100 km3 of the eastern flank of etna both on shore and off shore

seismic stratigraphy and geodynamic evolution of christiana basin south aegean arc abstract the analysis and interpretation of vintage and recent seismic profiles across christiana basin in the south aegean arc provided information on the seismic stratigraphy and chrono stratigraphy of the basin the occurrence of volcanic deposits within the sedimentary basin infill and its post miocene geodynamic evolution plio quaternary sediments overlie a messinian erosion surface on the basin s margins while in the basin they have been deposited above the messinian evaporites the basin evolved in two stages during the early stage subsidence of the three main depocenters in the nw w and se part of the basin has been controlled by e w to ese wnw trending faults the end of the early stage is marked by the cessation of activity on the southern marginal fault and the migration of the northern faults towards north where the basin expanded significantly towards south and north the seismic stratigraphy of the younger stage deposits is characterized by the presence of three thick pyroclastic flows they occur only in the eastern part of the basin and have therefore derived from santorini volcanic center since middle pleistocene the youngest one is associated with the minoan eruption while the next one is slightly younger than 0 42 ma and may be linked with activity in peristeria volcano the lower pyroclastic flow has deposited shortly after 1 2 ma and is the thickest 100 msec and widest distributed pyroclastic flow deposit in the basin it is most probably the biggest pyroclastic flow known in the south aegean sea it may be associated with an eruption of the early volcanic centers of akrotiri no evidence of volcanic or volcano clastic deposits derived from west i e from milos volcanic center has been found in christiana basin by taking into consideration the similar two stage structural evolution of the santorini to amorgos area proposed in the literature it is suggested here that since early to middle quaternary the e w trending christiana basin may be considered as an area of extension developed on the right side of the southwestern termination of the ne sw trending dextral santorini amorgos fault zone

behaviour of particle laden flows into the ocean experimental simulation and geological implications the behaviour of subaerial particle laden gravity currents e g pyroclastic flows lahars debris flows sediment bearing floods and jokulhlaups flowing into the sea has been simulated with analogue experiments flows of either saline solution simple suspensions of silicon carbide sic in water or complex suspensions of sic and plastic particles in methanol were released down a slope into a tank of water the excess momentum between subaerial and subaqueous flow is dissipated by a surface wave at relatively low density contrasts between the tank water and the saline or simple suspensions the flow mixture enters the water and forms a turbulent cloud involving extensive entrainment of water the cloud then collapses gravitationally to form an underwater gravity current which progresses along the tank floor at higher density contrasts the subaerial flow develops directly into a subaqueous flow the flow slows and thickens in response to the reduced density contrast which is driving motion and then continues in the typical gravity current manner complex suspensions become dense flows along the tank floor or buoyant flows along the water surface if the mixtures are sufficiently denser or lighter than water respectively flows of initially intermediate density are strongly influenced by the internal stratification of the subaerial flow material from the particulate depleted upper sections of the subaerial flow becomes a buoyant gravity current along the water surface whereas material from the particulate enriched lower sections forms a dense flow along the tank floor sedimentation from the dense flow results in a reduction in bulk density until the mixture attains buoyancy lifts off and becomes a secondary buoyant flow along the water surface jokulhlaups lahars and debris flows are typically much denser than seawater and thus will usually form dense flows along the seabed after sufficient sedimentation the freshwater particulate mixture can lift off to form a buoyant flow at the sea surface leading to a decoupling of the fine and coarse particles flood waters with low particulate concentrations 2 may form buoyant flows immediately upon entering the ocean subaerial pyroclastic flows develop a pronounced internal stratification during subaerial run out and thus a flow splitting behaviour is probable which agrees with evidence for sea surface and underwater flows from historic eruptions of krakatau and mont pelee a pyroclastic flow with a bulk density closer to that of sea water may form a turbulent cloud resulting in the deposition of much of the pyroclasts close to the shore dense subaqueous pyroclastic flows will eventually lift off and form secondary buoyant flows either before or after the transformation to a water supported nature

seasonal subsidence and rebound in las vegas valley nevada observed by synthetic aperture radar interferometry analyses of areal variations in the subsidence and rebound occurring over stressed aquifer systems in conjunction with measurements of the hydraulic head fluctuations causing these displacements can yield valuable information about the compressibility and storage properties of the aquifer system historically stress strain relationships have been derived from paired extensometer piezometer installations which provide only point source data because of the general unavailability of spatially detailed deformation data areal stress strain relations and their variability are not commonly considered in constraining conceptual and numerical models of aquifer systems interferometric synthetic aperture radar insar techniques can map ground displacements at a spatial scale of tens of meters over 100 km wide swaths insar has been used previously to characterize larger magnitude generally permanent aquifer system compaction and land subsidence at yearly and longer timescales caused by sustained drawdown of groundwater levels that produces intergranular stresses consistently greater than the maximum historical stress we present insar measurements of the typically small magnitude generally recoverable deformations of the las vegas valley aquifer system occurring at seasonal timescales from these we derive estimates of the elastic storage coefficient for the aquifer system at several locations in las vegas valley these high resolution measurements offer great potential for future investigations into the mechanics of aquifer systems and the spatial heterogeneity of aquifer system structure and material properties as well as for monitoring ongoing aquifer system compaction and land subsidence

catastrophic collapse of the volcanic island of hierro 15 ka ago and the history of landslides in the canary islands landslides play an important role in the evolution of many volcanic islands producing huge fields of blocky volcanic debris on their submarine slopes sidescan sonar images presented in this paper provide evidence for a large debris avalanche el golfo on the northern flank of hierro island in the canary islands angular blocks as much as 1 2 km across and 200 m high cover the debris avalanche surface el golfo avalanche is related to both the canary debris flow and a volcaniclastic turbidite found in the madeira abyssal plain 600 km west of the canaries dating of the turbidite and the failure scarp onshore indicates that the failure probably occurred between 13 and 17 ka there appears to be a general correlation between volcaniclastic turbidites in the abyssal plain sequence and landslides in the canaries during the past 750 ka tentatively this correlation suggests that seven major landslides have affected the canaries in that time

quantifying groundwater exploitation induced subsidence in the rafsanjan plain southeastern iran using insar time series and in situ measurements abstract decades of groundwater overexploitation for agriculture and industrial development have resulted in substantial land subsidence in the rafsanjan plain of southeastern iran this work presents the results of an insar time series analysis obtained by the exploitation of envisat alos and sentinel 1 s1 sar data archives between june 2004 and may 2016 to investigate land subsidence in the plain the insar analysis revealed an area of approximately 1000 km 2 within the study area showing subsidence of 5 cm year and locally exceeding 30 cm yr in the last decade this area of significant subsidence is limited in its spatial extent to the agricultural land and is partly influenced by quaternary faults the temporal and areal relationships of subsidence and groundwater level data suggest that a significant part of the observed subsidence in the rafsanjan region is caused by intense groundwater extraction that has led to widespread compaction within the upper parts of the up to 300 m thick unconsolidated sediments causing irreversible and inelastic deformation of the aquifer the average volume storage loss of the aquifer system due to overexploitation is estimated to have been approximately 300 million cubic metre mcm yr over the last decade

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

magma ascent and the pressurization of mount etna s volcanic system after a period of deflation during the 1991 1993 flank eruption mount etna underwent a rapid inflation seismicity and ground deformation show that since 1994 a huge volume of magma intruded beneath the volcano producing from 1998 onward a series of eruptions at the summit and on the flank of the volcano the last of these started on 27 october 2002 is still in progress and can be considered one of the most explosive eruptions of the volcano in recent times here we show how geodetic data and seismic deformation between 1994 and 2001 indicate a radial compression around an axial intrusion consistent with a repressurization of mount etna s plumbing system at a depth of 6 to 15 kilometers which triggered most of the seismicity and provoked the dilatation of the volcano and the recent explosive eruptive activity

prodigious submarine landslides on the hawaiian ridge the extensive area covered by major submarine mass wasting deposits on or near the hawaiian ridge has been delimited by systematic mapping of the hawaiian exclusive economic zone using the side looking sonar system gloria these surveys show that slumps and debris avalanche deposits are exposed over about 100 000 km2 of the ridge and adjacent seafloor from kauai to hawaii covering an area more than 5 times the land area of the islands some of the individual debris avalanches are more than 200 km long and about 5000 km3 in volume ranking them among the largest on earth the slope failures that produce these deposits begin early in the history of individual volcanoes when they are small submarine seamounts culminate near the end of subaerial shield building and apparently continue long after dormancy consequently landslide debris is an important element in the internal structure of the volcanoes the dynamic behavior of the volcanoes can be modulated by slope failure and the structural features of the landslides are related to elements of the volcanoes including rift zones and fault systems the landslides are of two general types slumps and debris avalanches the slumps are slow moving wide up to 110 km and thick about 10 km with transverse blocky ridges and steep toes the debris avalanches are fast moving long up to 230 km compared to width and thinner 0 05 2 km they commonly have a well defined amphitheater at their head and hummocky terrain in the lower part oceanic disturbance caused by rapid emplacement of debris avalanches may have produced high level wave deposits such as the 365 m elevation hulopoe gravel on lanai that are found on several islands most present day submarine canyons were originally carved subaerially in the upper parts of debris avalanches subaerial canyon cutting was apparently promoted by the recently steepened and stripped slopes of the landslide amphitheaters

s cl f degassing pattern of water rich alkali basalt modelling and relationship with eruption styles on mount etna volcano abstract our knowledge of the degassing pattern of sulphur chlorine and fluorine during ascent and eruption of basaltic magmas is still fragmental and mainly limited to water poor basalts here we model and discuss the pressure related degassing behaviour of s cl and f during ascent differentiation and extrusion of h2o co2 rich alkali basalt on mount etna sicily as a function of eruptive styles our modelling is based on published and new melt inclusion data for dissolved volatiles co2 h2o s cl f in quenched explosive products from both central conduit 1989 2001 and lateral dyke 2001 and 2002 eruptions pressures are obtained from the dissolved h2o and co2 concentrations and vapour melt partition coefficients of s cl and f are derived from best fitting of melt inclusion data for each step of magma evolution this allows us to compute the compositional evolution of the gas phase during either open or closed system degassing and to compare it with the measured composition of emitted gases we find that sulphur chlorine and fluorine begin to exsolve at respective pressures of 140 mpa 100 mpa and 10 mpa during etna basalt ascent and are respectively degassed at 95 22 55 and 15 upon eruption pure open system degassing fails to explain gas compositions measured during either lateral dyke or central conduit eruptions instead closed system ascent and eruption of the volatile rich basaltic melt well accounts for the time averaged gas composition measured during 2002 type lateral dyke eruptions s cl molar ratio of 5 1 35 bulk cl loss extensive magma fragmentation during the most energetic fountaining phases enhances cl release 55 and produces a lower s cl ratio of 3 7 as actually measured comparatively slower magma rise in the central conduits of etna favours both sulphide saturation of the melt and greater chlorine release 55 resulting in a distinct s cl evolution path and final ratio in eruptive gas in both eruption types any previous bubble melt separation at depth leads to increased s cl and s f ratios in emitted gas high s cl ratios measured during some discrete eruptive events can thus be explained by transitions from closed deep to open shallow system degassing with differential gas transfer extending down to 2 km depth below the vents this depth coincides with the base of the volcanic pile where structural discontinuities and the high magma vesicularity 60 may favour separate gas flow finally the excess s cl f gas discharge through etna summit craters during non eruptive periods requires a mixed supply from shallow magma degassing in the volcanic conduits and deeper derived so2 rich bubbles from the sub volcano plumbing system our modelling provides a useful reference framework for interpreting the monitored variations of s cl and f in mount etna gas emissions as a function of volcanic activity more broadly the observations made for s cl and f degassing on etna may apply to other basaltic volcanoes with water rich magmas such as in arcs

depositional processes in large scale debris flow experiments this study examines the depositional process and characteristics of deposits of large scale experimental debris flows to 15 m3 composed of mixtures of gravel to 32 mm sand and mud the experiments were performed using a 95 m long 2 m wide debris flow flume that slopes 31 following release experimental debris flows invariably developed numerous shallow 10 cm deep surges sediment transported by surges accumulated abruptly on a 3 runout slope at the mouth of the flume deposits developed in a complex manner through a combination of shoving forward and shouldering aside previously deposited debris and through progressive vertical accretion progressive accretion by the experimental flows is contrary to commonly assumed en masse sedimentation by debris flows despite progressive sediment emplacement deposits were composed of unstratified accumulations of generally unsorted debris hence massively textured poorly sorted debris flow deposits are not emplaced uniquely en masse the depositional

subduction like fluids in the genesis of mt etna magmas evidence from boron isotopes and fluid mobile elements abstract new whole rock b sr nd isotope ratios and 87sr 86sr on clinopyroxenes have been collected to study the enrichment of fluid mobile elements fmes observed in mt etna volcanics etna volcano one of the most active in the world is located in an extremely complex tectonic context at the boundary between colliding african and european plates the analytical work focuses on current 1974 1998 and historic 1851 1971 eruptive activity including some key prehistoric lavas in order to interpret the secular shift of its geochemical signature to more alkaline compositions boron is used as a tool to unravel the role of fluids in the genesis of magmas revealing far reaching consequences beyond the case study of mt etna small variations are observed in 11b 3 5 to 8 0 87sr 86sr 0 70323 0 70370 and 143nd 144nd 0 51293 0 51287 moreover temporal evolution to higher 11b and 87sr 86sr and to lower 143nd 144nd is observed in the current activity defining a regular trend sr isotopic equilibrium between whole rock and clinopyroxene pairs indicates the successive introduction of three distinct magma types into the etna plumbing system over time these are characterized by differing degrees of fme enrichment in addition certain lavas exhibit evidence for country rock assimilation magma fluid interaction or magma mixing in the shallow feeding system at times these processes apparently lowered magmatic 11b and or induced sr isotopic disequilibrium between whole rock and clinopyroxene the regular increase of 11b values is correlated with nb fme and 87sr 86sr ratios these correlations are consistent with simple mixing between the mantle source and aqueous fluids derived from nearby ionian slab the best fit of mt etna data is obtained using an enriched morb mantle source and a fluid phase with 11b of about 2 and 87sr 86sr of 0 708 we argue that the slab window generated by differential roll back of subducting ionian lithosphere with respect to sicily allows the upwelling of asthenosphere from below the subduction system and provides a suitable path of rise for subduction related fluids the increasing geochemical signature of fluid mobile elements enrichment to mt etna lavas is considered a consequence of the progressive opening of slab window through time

late pleistocene tephrochronology of marine sediments adjacent to montserrat lesser antilles volcanic arc the recent history of the soufriere hills volcano montserrat lesser antilles volcanic arc is deduced using data obtained from a submarine core collected in 2002 the core contains concentrations of ash and several tephra layers which are identified by the abundance of glass shards dense and poorly vesiculated particles and scoria the tephra layers have been dated using micropalaeontology and stable isotope stratigraphy tephra layers in a marine sediment core off the coast of montserrat record the volcanic history of south soufriere hills soufriere hills volcano back to 250 ka eight layers are composed of dense juvenile ash related to dome eruptions five of which can be directly correlated to dated domes or related pyroclastic flow sequences on land six layers are composed of pumiceous glassy ash and relate to significant explosive eruptions a marker sequence of basalt tephra layers is dated at 124 147 ka and is correlated with construction of the south soufriere hills basaltic stratocone pelagic sediments between the main tephra layers have low abundances of volcanogenic components c 10 4 years of dormancy or low activity

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

recurrence of major flank landslides during the last 2 ma history of reunion island new detailed swath bathymetry and backscatter data corroborate the existence of four large bulges on the submarine flanks of reunion island these fan shaped promontories are 20 25 km wide at the coastline and 70 150 km across the seafloor 40 50 km offshore their surfaces are characterized by a speckle sonar pattern indicating the presence of large blocks up to several hundred meters across each bulge results from the superposition of multiple landslide deposits whose older ones are dissected and delimited by erosive channels as much as 200 m deep and 20 km long the submarine flanks of reunion island are thus mostly built by accumulation of debris avalanche fans morphologic and geologic evidence define large subaerial source areas for these mass wasting events in particular inferred headwalls of most landslides having affected the piton des neiges massif generally coincide with the boundaries of its cirques mafate salazie and cilaos whereas recurrent landslides have resulted in the formation of large concentric amphitheatre structures through the piton de la fournaise massif thus about 15 slide events accompanied growth of the reunion island shield since 2 ma

buoyancy controlled eruption of magmas at mt etna buoyancy controls the ability of magma to rise its ascent rate and the style of the eruptions geophysical geological and petrological data have been integrated to evaluate the buoyancy of magmas at mt etna the density difference between host rocks and magmas is mainly related to the amount of h2o dissolved in the magma and to the bubble liquid separation processes in the depth interval 22 2 km b s l highly hydrated h2o 3 basaltic magmas or mixtures of bubbles liquid have positive buoyancy and rise rapidly conversely bubble depleted liquids with an intermediate h2o content 1 5 having neutral buoyancy will spread out and form magmatic reservoirs at different depths until cooling crystallization further modify composition and density these different processes account for the magma compositions location of magmatic reservoirs as determined by geophysical methods and the complex eruptive cycles slow effusions fire fountains and plinian eruptions that have been observed in the history of the volcano

new insights into landslide processes around volcanic islands from remotely operated vehicle rov observations offshore montserrat submarine landslide deposits have been mapped around many volcanic islands but interpretations of their structure composition and emplacement are hindered by the challenges of investigating deposits directly here we report on detailed observations of four landslide deposits around montserrat collected by remotely operated vehicles integrating direct imagery and sampling with sediment core and geophysical data these complementary approaches enable a more comprehensive view of large scale mass wasting processes around island arc volcanoes than has been achievable previously the most recent landslide occurred at 11 5 14 ka deposit 1 1 7 km3 and formed a radially spreading hummocky deposit that is morphologically similar to many subaerial debris avalanche deposits hummocks comprise angular lava and hydrothermally altered fragments implying a deep seated central subaerial collapse inferred to have removed a major proportion of lavas from an eruptive period that now has little representation in the subaerial volcanic record a larger landslide deposit 2 10 km3 occurred at 130 ka and transported intact fragments of the volcanic edifice up to 900 m across and over 100 m high these fragments were rafted within the landslide and are best exposed near the margins of the deposit the largest block preserves a primary stratigraphy of subaerial volcanic breccias of which the lower parts are encased in hemipelagic mud eroded from the seafloor landslide deposits south of montserrat deposits 3 and 5 indicate the wide variety of debris avalanche source lithologies around volcanic islands deposit 5 originated on the shallow submerged shelf rather than the terrestrial volcanic edifice and is dominated by carbonate debris