effusive history of the grande decouverte volcanic complex southern basse terre guadeloupe french west indies from new k ar cassignol gillot ages abstract the grande decouverte volcanic complex gdvc active since at least 0 2 ma is the most recent volcanic complex of the basse terre island guadeloupe lesser antilles arc a detailed geochronological study using the k ar cassignol gillot technique has been undertaken in order to reconstruct the history of effusive activity of this long lived volcanic system twenty new ages permit to suggest that the gdvc experienced at least six main effusive stages from 200 ka to present time to the north of the gdvc the gds grande decouverte soufriere volcano has been active since at least 200 ka and to the south the trmf trois rivieres madeleine field started to be emplaced 100 ka morphological investigations suggest that the whole trmf volcanism was emitted from vents distinct from the gds most probably a large e w fissure network linked to the marie galante rift the mean age of 62 5 ka obtained for the e w madeleine le palmiste alignment suggests that a fissure opening event occurred at that time however whole rock major and trace element signatures are similar for both systems suggesting that a common complex magma plumbing system has fed the overall gdvc we report very young ages for lava flows from the trmf which implies that

sector collapse at kick em jenny submarine volcano lesser antilles numerical simulation and landslide behaviour kick em jenny volcano is the only known active submarine volcano in the lesser antilles it lies within a horseshoe shaped structure open to the west northwest toward the deep grenada basin a detailed bathymetric survey of the basin slope at kick em jenny and resulting high resolution digital elevation model allowed the identification of a major submarine landslide deposit this deposit is thought to result from a single sector collapse event at kick em jenny and to be linked to the formation of the horseshoe shaped structure we estimated the volume and the leading edge runout of the landslide to be ca 4 4 km3 and 14 km respectively we modelled a sector collapse event of a proto kick em jenny volcano using volcflow a finite difference code based on depth integrated mass and momentum equations our models show that the landslide can be simulated by either a coulomb type rheology with low basal friction angles 5 5 6 5 and a significant internal friction angle above 17 5 or with better results by a bingham rheology with low bingham kinematic viscosity 0 b 30 m2 s and high shear strength 130 180 m2 s2 the models and the short runout distance suggest that the landslide travelled as a stiff cohesive flow affected by minimal granular disaggregation and slumping on a non lubricated surface the main submarine landslide deposit can therefore be considered as a submarine mass slide deposit that behaved like a slump

the 1995 1998 eruption of the soufriere hills volcano montserrat wi eruption of the soufriere hills volcano began on 18 july 1995 after three years of elevated seismic activity four months of increasingly vigorous phreatic activity culminated in mid november 1995 with the initiation of dome growth growth rates increased unevenly through early march 1996 with fluctuations on time scales from hours to months since march 1996 gravitational collapse of the unstable dome flank has affected an ever increasing area with pyroclastic flows surges and ashfalls major collapse of the eastern flank on 17 september 1996 resulted in a sub plinian explosive eruption later that day by february 1997 the dome had outgrown the confines of the crater and begun to spill into the surrounding valleys a large collapse on 25 june 1997 caused pyroclastic flows and surges on the northern flanks and resulted in the only deaths of the eruption in august september and october 1997 vulcanian explosions followed further collapses on the western and northern flanks the largest event of the eruption occurred on 26 december 1997 with failure of the southwestern flank of the volcano producing a debris avalanche and large dome collapse pyroclastic flows dome growth ceased in early march 1998 but residual volcanic activity has continued and consists of ash venting mild explosions and dome collapse pyroclastic flows

stratovolcano stability assessment methods and results from citlaltepetl mexico citlaltpetl volcano is the easternmost strato volcano in the trans mexican volcanic belt situated within 110 km of veracruz it has experienced two major collapse events and subsequent to its last collapse rebuilt a massive symmetrical summit cone to enhance hazard mitigation efforts we assess the stability of citlaltpetl s summit cone the area thought most likely to fail during a potential massive collapse event through geologic mapping alteration mineralogy geotechnical studies and stability modeling we provide important constraints on the likelihood location and size of a potential collapse event the volcano s summit cone is young highly fractured and hydrothermally altered fractures are most abundant within 5 20 m wide zones defined by multiple parallel to subparallel fractures alteration is most pervasive within the fracture systems and includes acid sulfate advanced argillic argillic and silicification ranks fractured and altered rocks both have significantly reduced rock strengths representing likely bounding surfaces for future collapse events the fracture systems and altered rock masses occur non uniformly as an orthogonal set with n s and e w trends because these surfaces occur non uniformly hazards associated with collapse are unevenly distributed about the volcano depending on uncertainties in bounding surfaces but constrained by detailed field studies potential failure volumes are estimated to range between 0 04 0 5 km 3 stability modeling was used to assess potential edifice failure events modeled failure of the outer portion of the cone initially occurs as an intact block bounded by steeply dipping joints and outwardly dipping flow con tacts as collapse progresses more of the inner cone fails and the outer intact block transforms into a collection of smaller blocks eventually a steep face develops in the uppermost and central portion of the cone this modeled failure morphology mimics collapse amphitheaters pres ent at many of the world s stratovolcanoes that have experienced massive failure events

hydrothermal circulation beneath mount pelee inferred by self potential surveying structural and tectonic implications abstract self potential sp surveys were made on mount pelee volcano martinique island french west indies in 1991 and 1992 in order to recognize its hydrothermal system the associated groundwater channeling and the main superficial structures of the massif almost 70 km of profiles were carried out with an average sample spacing of 50 m measurements essentially reveal negative sp anomalies down to 1700 mv with high gradients 1 83 mv m due to the infiltration of meteoric water into the massif rims of summit calderas morne macouba and etang sec present sharp negative sp anomalies on the western northern and eastern flanks negative sp anomalies indicate no upward water flow beneath mount pelee summit on the southwestern volcano flank a 3 5 6 km horseshoe shaped structure corresponding to a southwest flank collapse event older than 25 000 years bp is clearly identified by the sp mapping high gradients border the inner southern rim from morne calebasse to st pierre town and the caribbean sea along the northern rim of the horseshoe shaped structure the negative sp anomalies give place to a positive sp anomaly up to 200 mv of sw ne trend this zone covers the area of two active hot springs sources chaudes and puits chaud 40 65 c marine magnetic surveys and bathymetry show that the horseshoe shaped structure spreads into the caribbean sea up to about 10 km from the coast buried structural discontinuities are evidenced inside the flank collapse structure the upper one deviates the groundwater flow coming from the summit toward the south flank where the flow finds an indentation to expand again downwards this discontinuity is either an old hypothetical caldera rim partly destroyed by the collapse of the south southwestern flank and covered by recent pyroclastic deposits or more probably the trace of a bulge landslide a circulation model of the hydrothermal waters is proposed rainfall 5 6 m year is partly drained inside the summital calderas and the flank collapse zone through pyroclastic flows down to an impermeable basement there the groundwater constitutes perched aquifers at the contact of the bulge landslide or of the hypothetical old caldera rim along the inner northern border of the flank collapse structure the phreatic water is reheated warm groundwater flows along the northern avalanche structure rim and discharges near the coast in ground and marine outcrops of medium temperature finally the main part of the meteoric water is channeled along the old caldera rim or along the bulge landslide towards the south flank of mount pelee where some gaps in the rim exist there the groundwater finds again a subhorizontal gravitational circulation along mount pelee slopes into the caribbean sea

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

intra arc deformations with vertical rotation axes the case of the pre middle miocene terranes of southwest japan abstract various folds bends with vertical or subvertical rotation axes occur in the pre middle miocene terranes of southwest japan they are variable in shape conical folds accordion folds megakink bands and so on and some are accompanied with strike slip faults they range from several kilometers to more than 100 km in width and some of their hinge surfaces are traceable more than a few tens of kilometers their shapes which resemble megakink band or buckle folds indicate that they were produced by horizontal compression with vertical or subvertical 2 axes in a shallow level of the crust they were superimposed on the pre middle miocene fold and thrust structures or nappe melange complexes and are regarded to have been formed mostly during the middle miocene contemporaneous with the clockwise rotation of southwest japan related to the fan shaped opening of the sea of japan geometrical analysis clearly suggests that the drifting southwest japan behaved as a non rigid body and the formation of these structures resulted from the differential rotation of the terranes and the collision of the izu bonin arc with eastern southwest japan

the 1975 1977 crisis of la soufriere de guadeloupe f w i a still born magmatic eruption on july 8 1976 eruptive activity broke out at la soufriere de guadeloupe f w i after about one year of increasing seismic activity seismic activity continued to increase until august 1976 reaching more than 1500 events a 200 fold increase over the preceding quiet period of a few years and an energy output of about 1017 ergs in a day a total of 26 major phreatic eruptions similar to the july 8 outburst took place during an eight months period the steam blasts that characterized the eruptions gave rise to particle and sometimes block charged plumes that deposited an estimated 106 m3 of solids the h2o rich gases emitted during the blasts presumably contained other gases h2s so2 co2 that were partly adsorbed on solid particles all material was erupted at temperatures of the order of 100 to 200 c the observation of vertical migration of earthquake foci in less than a few hours and over about 6 km depth and of abnormal variations of the geomagnetic field indicate a deep energy source for the phreatic eruptions a small proportion of the gases adsorbed on solid particles had a magmatic origin however most of the steam and the tephra seemed to originate from superficial levels of a hydrothermal system similar phreatic eruptions have occurred several times in recorded history in the case of la soufriere the origin of the phreatic eruptions is best described by an abnormal energy input versus steady state from a crustal magma chamber the occurrence of truly magmatic eruptions is presumably inhibited by an extensive hydrothermal system the abrupt release of more power from the magma chamber could have resulted in an explosive pyroclastic eruption substantial improvement of the guadeloupe volcano observatory has followed the 1975 1977 crisis permanent telemetered geophysical networks and regular geochemical observations have provided a five year data base of the volcano behavior in its noneruptive state which can be compared to crisis situations

cyclic eruptions and sector collapses at monowai submarine volcano kermadec arc 1998 2007 1 repeated multibeam bathymetric surveys at monowai cone a shallow submarine basaltic volcano and part of the monowai volcanic center in the northern kermadec arc were conducted in 1998 2004 and 2007 these surveys document dramatic depth changes at the volcano including negative changes up to 176 m from two sector collapses and positive changes up to 138 m from volcanic reconstruction near the summit and debris avalanche deposits downslope of the slide scars one sector collapse occurred on the se slope between 1998 and 2004 with a volume of 0 09 km3 and another occurred on the sw slope between 2004 and 2007 with a volume of 0 04 km3 the volume of positive depth change due to addition of volcanic material by eruption is of the same order 0 05 km3 between 1998 and 2004 and 0 06 km3 between 2004 and 2007 during these time intervals monitoring by the polynesian seismic network detected frequent t wave swarms at monowai indicative of explosive eruptive activity every few months an unusual t wave swarm on 24 may 2002 was previously interpreted as the collapse event between the 1998 and 2004 surveys but no similarly anomalous t waves were detected between 2004 and 2007 probably because the polynesian seismic network stations were acoustically shadowed from the second slide event we interpret that the sector collapses on monowai are caused by the unstable loading of fragmental erupted material on the summit and steep upper slopes of the volcano 20 moreover there appears to be a cyclic pattern in which recurrent eruptions oversteepen the cone and periodically lead to collapse events that transport volcaniclastic material downslope to the lower apron of the volcano volumetric rate calculations suggest that these two processes may be more or less in equilibrium the repeated collapses at monowai are relatively modest in volume involving only 0 1 0 5 of the edifice volume have occurred much more frequently than is estimated for larger debris avalanches at subaerial volcanoes and may be characteristic of how persistently active shallow submarine arc volcanoes grow

the off shore continuation of an active basaltic volcano piton de la fournaise reunion island indian ocean structural and geomorphological interpretation from sea beam mapping abstract in 1984 a sea beam survey of the submarine east flank of piton de la fournaise was performed with r v jean charcot three main types of volcanic or volcano tectonic features have been identified 1 1 the subaerial ne and se volcanic rift zones of piton de la fournaise do not extend more than about five kilometers offshore unlike typical hawaiian rift zones which form narrow 2 4 km ridges extending tens of kilometers from the summit the active rift zones of piton de la fournaise widen downslope attaining more than 10 km at their front 2 2 the submarine extension of the grand brule slide is larger than the subaerial portion the entire slide forms a 7 24 km scar bounded by two ramparts to the north and south the slumped material may have moved as a debris flow forming a large talus downslope of the slide however the submarine counterpart of the south area of the grand brule seems to be composed by a slumped block whose structure is apparently not disturbed 3 3 another prominent feature is a conspicuous topographic high that occupies nearly all the center of the surveyed zone this cast flank submarine plateau cannot be associated with any active structure of piton de la fournaise its surface generally dips gently 2 3 and its northern and southern flanks are extensively cut by landslides cones of variable dimensions are observed on the plateau and farther to the east three hypotheses are examined to account for the origin of this morphology a remnant flank of an ancestral fournaise volcano associated with a large buried intrusion found by drilling beneath the grand brule b distinct volcanic massif or c material of a huge and ancient landslide the geophysical data show that the western part of this submarine plateau is reversely magnetized and associated with a moderate positive gravity anomaly this confirms that as suggested by the bathymetric analysis this part of the plateau is relatively coherent conversely the eastern portion of the plateau appears to be poorly magnetized and composed of low density material probably chaotic materials derived from landslides the reversed magnetization of the western part shows that the whole structure is older than 0 7 ma these results show that the volcanic history of piton de la fournaise is more complex than previously thought

morne patates volcano southern dominica lesser antilles mornes patates is the youngest volcano in dominica occupying a depression on the southwestern flank of a larger stratovolcano morne plat pays within the depression an arcuate ridge apparently of acid andesite lavas has been cored and largely buried by the explosive emplacement of two acid andesite domes and their associated pyroclastic deposits mainly block and ash flow deposits a basaltic scoria horizon exposed on the northern side of the depression has a 14 c age of 28450 1500 years b p and is not seen on the volcano itself which suggests that the domes and pyroclastic rocks are younger than this a 14 c age of 450 90 years b p from a block and ash flow deposit from the morne patates dome apparently confirms this and the youthful morphology also suggests a young age the angular shape of the depression and the steep submarine slopes are consistent with an origin as a lateral gravity slide rather than a caldera collapse vigorous fumarolic activity and swarms of local earthquakes suggest that magma exists at depth several kilometres beneath the morne patates morne plat pays area

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

large scale flank collapse events during the activity of montagne pelee martinique lesser antilles 1 a horseshoe shaped structure already identified on the southwestern flank of montagne pelee martinique lesser antilles arc was previously interpreted as resulting of a flank collapse event but no debris avalanche deposits were observed at the time new offshore high resolution bathymetry and geophysical data aguadomar cruise december 1998 to january 1999 r v l atalante lead us to identify three debris avalanche deposits on the submarine western flank of montagne pelee extending down to the grenada basin they display morphological fronts and hummocky morphology on bathymetric data speckled pattern on backscatter data and hyperbolic facies on 3 5 khz and seismic profiles new on land geological studies lead us to identify two other horseshoe shaped structures on the same flank of the volcano the three submarine deposits have been traced back to the structures identified on land which confirms the occurrence of repeated flank collapse events during the evolution of montagne pelee the ages of the last two events are estimated at 9 ka and 25 ka on the basis of 14c and 238u 230th dates every flank collapse produced debris avalanches which flowed down to the caribbean sea we propose that the repeated instabilities are due to the large asymmetry of the island with western aerial and submarine slopes steeper than the eastern slopes the asymmetry results from progressive loading by accumulation of volcanic products on the western slopes of the volcano and development of long term gravitational instabilities meteoric and hydrothermal fluid circulation on the floor of the second flank collapse structure also creates a weakened hydrothermalized area which favors the recurrence of flank collapses

revised chronostratigraphy of recurrent ignimbritic eruptions in dominica lesser antilles arc implications on the behavior of the magma plumbing system ignimbritic eruptions represent catastrophic events due to the magma volume involved and the related consequences on earth s environment in relation with the released gases and the tephra dispersal dominica has been recognized as hosting one of the major ignimbritic eruptions of the last 200 ky in the lesser antilles arc called the roseau tuff but more recent works have evidenced several pumiceous events instead of a single large one here we propose a revised chronostratigraphy of the explosive activity that occurred in the last tens of thousands years based on three field trips new 14c ages detailed lithological and geochemical investigations in particular a precise characterization of trace element glass chemistry this eruptive history reconstruction is mainly based on outcrops along the coast and in the valley since the luxury vegetation in the center of the island mostly precludes sections close to the central volcanic centers we thus confirm that the roseau event has been overestimated and that we may recognize five main ignimbritic events grande savane layou 51 ka grand bay roseau 33 ka grand fond 24 ka we discuss the possible volcanic center at their origin in addition to correlations with some plinian events of lower magnitude that were identified in the roseau valley and in the southern part of dominica this study may help to better constrain the eruptive history of the most active volcanic island of the lesser antilles arc which has important implications on hazard mitigation

radiometric dating of three large volume flank collapses in the lesser antilles arc abstract it is now recognised that flank collapses are a recurrent process in the evolution of the lesser antilles arc volcanoes large magnitude debris avalanche deposits have been identified off the coast of dominica martinique and st lucia with associated volumes up to 20 km 3 deplus c le friant a boudon g komorowski j c villemant b harford c segoufin j cheminee j l 2001 submarine evidence for large scale debris avalanches in the lesser antilles arc earth planet sci lett 192 145 157 we present new radiometric dating of three major events using the k ar cassignol gillot technique in the qualibou depression of st lucia a collapse has been constrained by dome emplacement prior to 95 2 ka in dominica where repetitive flank collapse events have occurred le friant a boudon g komorowski j c deplus c 2002 l ile de la dominique a l origine des avalanches de debris les plus volumineuses de l arc des petites antilles c r geoscience 334 235 243 the plat pays event probably occurred after 96 2 ka inside the depression caused by this event scotts head which is interpreted as a proximal megabloc from the subsequent soufriere avalanche event has been dated at 14 1 ka providing an older bound for this event on martinique three different domes within the carbets structure dated at 337 5 ka constrain the age of this high magnitude event finally these results obtained from three of the most voluminous flank collapses provide constraints to estimate the recurrence of these events which represent one of the major hazards associated with volcanoes of the lesser antilles arc

the giant submarine alika debris slide mauna loa hawaii probably represent multiple subsidence events before during and after the debris avalanches lower slopes of the slide contain distinctive lobate terraced deposits that are interpreted as having been emplaced more slowly prior to the debris avalanches estimated thicknesses of 50 200 m suggest volumes of 200 600 km 3 for the two lobes the combined volume of the entire slide and slump terrane is probably 1500 2000 km 3 the slide deposits predate a 13 ka coral reef and probably postdate the block faulted ninole basalt roughly dated as a few hundred thousand years old the alika slide or a similar deposit recognized on gloria images further north along the hawaiian ridge probably triggered a giant wave that washed 325 m high on lanai at about 100 ka slumping on mauna loa has been most intense adjacent to the large arcuate bend in its southwest rift zone as the rift zone migrated westward away from the growing kilauea volcano slumping events were probably triggered by seismic activity accompanying dike injection along the rift zone such massive slumps landslides and distal submarine turbidity flows appear to be widespread on the flanks of hawaiian volcanoes

flank failure directed blast eruption at soufriere guadeloupe french west indies a 3 000 yr old mt st helens an extensive apparently monogenic debris flow deposit in the basse terre st claude area of southern guadeloupe is contemporaneous with pyroclastic surge deposits that cover an area of at least 60 km2 these 3 000 yr old deposits were emplaced by the avalanching of a sector of soufriere volcano and an associated directed blast similar to the 1956 bezymianni and the may 18 1980 mt st helens eruptions

paleomagnetic directions and k ar dating of 0 to 1 ma lava flows from la guadeloupe island french west indies implications for time averaged field models twenty six lava flows spanning the last million years were sampled in la guadeloupe french west indies because of the lack of continuous volcano stratigraphic sections in la guadeloupe dating is necessary in order to describe the temporal evolution of the geomagnetic field in this time interval new k ar ages ranging from 50 ka to 1 ma have been obtained on andesites using the cassignol gillot technique at the universite paris sud institut de physique du globe de paris orsay laboratory additional flows with k ar ages obtained using the same dating technique were also sampled for paleomagnetic investigations more than 200 samples were analyzed using both alternating field af and thermal stepwise demagnetization techniques duplicate samplings of two flows at three different sites demonstrate that within flow dispersion is negligible for the andesitic lava flows sampled in this study direct comparison with an earlier paleomagnetic study performed on the island indicates that for the three investigated flows modern demagnetization techniques yield much better defined paleomagnetic directions the matuyama brunhes transition was recorded in a three flow section and is dated at 781 18 ka in good agreement with other recent radiometric age determinations the mean paleomagnetic pole calculated from the 23 normal polarity flows is indistinguishable from geographic north which implies that no significant persistent axial quadrupole term can be identified at this site for the last million years this result contradicts earlier results and has important implications for models of the time averaged field taf an occam algorithm was used to construct a taf model from the global volcanic database from the last 5 ma substitution of the mean direction calculated from the earlier study for the lesser antilles by our new mean value reduces the quadrupole term by more than 30 this effect which was produced by changing data from a single site demonstrates that older paleomagnetic sites may need to be reinvestigated furthermore it also highlights the limitations of taf models that can be inferred from paleomagnetic databases in their present state

late quaternary sedimentation in the lesser antilles island arc investigation of patterns and processes of late quaternary sedimentation in the lesser antilles island arc indicates that the major components of deep water sediment are volcaniclastic silt and clay redeposited shallow water carbonate mainly aragonite and high mg calcite pelagic carbonate mainly low mg calcite and windblown dust from africa although sediment derived from the adjacent south american continent is included in accreted trench deposits marine deposition of this sediment within the arc is insignificant except at the south end of the forearc distribution of sedimentary components within the lesser antilles arc is controlled primarily by arc volcanism a miocene shift in the locus of volcanism which caused the arc to bifurcate created two sedimentologic regimes in the southern part of the arc which is characterized by volcanically active islands with high relief deep water sediment is dominantly volcaniclastic in contrast in the northern part of the arc where a broad arc platform separates high relief active volcanoes from low relief extinct volcanoes surrounded by wide carbonate shelves deep water sediment is composed mainly of redeposited shallow water carbonate pelagic carbonate and eolian transported saharan dust superposed on the facies patterns determined by arc volcanism is a subtle but distinct record of quaternary climate change glacial interglacial periods are recorded in deep water sediment by variations in sedimentation rate composition and texture volcaniclastic sedimentation responded to lowstands of sea level by increased sedimentation rates and thicker and or more frequent turbidites reflecting intensified currents in interisland passages and increased erosion of exposed insular shelves deep water carbonate sedimentation records decreased carbonate productivity on exposed shelves and in the open ocean during glacial lowstands as well as variations in carbonate preservation associated with changes in ocean circulation deposition of saharan dust increased during glacial periods because of intensified wind strengths

volcanic stratigraphy and geochemistry of the soufriere volcanic centre saint lucia with implications for volcanic hazards abstract the soufriere volcanic complex svc saint lucia represents one of the largest silicic centres in the lesser antilles arc it comprises extensive pumiceous pyroclastic flow deposits lava flows as well as pelean style domes and dome collapse block and ash flow deposits these deposits occur within and around the qualibou depression a 10 km diameter wide sector collapse structure to date vent locations for svc pyroclastic deposits and their relationship to the sector collapse have been unclear because of limited stratigraphic correlation and few radiometric ages in this study we reconstruct the geologic history of the svc in light of new and recently published u th he u th and u pb zircon chronostratigraphic data aided by mineralogical and geochemical correlation compositionally svc deposits are monotonous medium k calc alkaline rocks with 61 6 to 67 7 wt sio 2 and display similar trace element abundances combined u th and u th he zircon dating together with 14 c ages and mineral fingerprinting reveals significant explosive eruptions at 640 515 265 104 60 and 40 ka producing deposits previously grouped together as the choiseul unit and at 20 ka belfond unit the mineralogically and geochemically distinct belfond unit is a large valley filling pumiceous pyroclastic flow deposit distributed to the north northeast south and southeast of the qualibou depression that was probably deposited during a single plinian eruption the unit previously referred to as choiseul tuff is much less well defined the typical choiseul unit comprises a series of yellowish white crystal poor non welded pumiceous pyroclastic deposits cropping out to the north and southeast of the qualibou depression however its age is poorly constrained a number of other units previously mapped as choiseul can be distinguished based on age and in some cases mineral and whole rock chemistry pyroclastic deposits at micoud 640 19 ka bellevue 264 8 ka anse john 104 4 ka and la pointe 59 8 2 1 ka anse noir and piaye were all previously grouped with or associated with the choiseul tuff all uncertainties 1 we suggest that these units represent individual periods of activity spanning a range of ages whereas choiseul pumice at the type locality has yielded a u th he zircon age of 515 19 ka their overall geochemical and mineralogical similarities with the choiseul at the type locality suggest that they might have all originated from the same centre morne tabac 532 21 ka is a dome truncated by the depression escarpment whereas morne bonin 273 15 ka gros piton and petit piton 71 3 ka and 109 4 ka resp belfond 13 6 0 4 ka and terre blanche 15 3 0 4 ka are domes within the qualibou depression belfond and terre blanche have whole rock geochemistry and mineral assemblages similar to the belfond pyroclastic flow deposit thus possibly representing late erupted degassed portions of the magma that produced the belfond pyroclastics the geochemical characteristics and similar zircon age distributions of the silicic lava domes and pyroclastics of the svc suggest that these share a common magma source beneath the qualibou depression the distribution of the pyroclastic flows and the wide range in their eruption ages makes it unlikely that these were erupted during caldera forming activity and we instead invoke a series of smaller volume explosive eruptions from the area of the current depression the earliest of which occurred from a large proto qualibou edifice that subsequently underwent sector collapse activity from this proto qualibou centre may have ceased sometime between 38 and 59 ka ago it therefore seems unlikely given our present understanding that there will be another eruption from the southern central highland region however the young dome forming activity in the qualibou depression may have occurred in or close to the holocene and there have been dome collapse events and explosion craters formed since then a new dome eruption or renewed activity at a dome within the depression growing in the style of the ongoing soufriere hills lava dome on the nearby island of montserrat is possible as is a future plinian eruption from this area such an eruption would not only have a devastating impact on saint lucia but would also have significant regional and global impacts

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

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

late quaternary explosive silicic volcanism on st lucia west indies many explosive eruptions of dacitic magmas have occurred on st lucia during the late quaternary these have produced widespread aprons and fans of pumice flow and ash flow deposits radiating around the central highlands with co eruptive air fall and surge layers interbedded with palaeosols and epiclastic deposits vents in the highlands have not been located because of the dense tropical jungle but we suspect they are now plugged by lava domes surrounded by aprons of block and ash flow deposits young magmatically related dacitic lava domes have been extruded in the qualibou depression the pumice succession can be divided into older quartz poor deposits forming the choiseul pumice and younger crystal rich deposits with abundant large quartz which are called the belfond pumice the choiseul pumice groups together scattered remnants of the products of many eruptions of different low silica dacitic magma types the belfond pumice is the product of several eruptions of a high silica magma type and 14 c ages have dated these between 20900 to 34200 years b p the pumice flow deposits occur as small volume valley fills a granulometric study of belfond pumice flow deposits shows them to be strongly depleted in finer ash and vitric components it is suggested that the narrow winding and vegetated valleys on the island locally induced turbulence and the flows moved with large highly fluidized and inflated heads resulting in substantial loss of fine vitric ash one ash flow deposit which is extremely rich in crystals and carbonized vegetation is highly depleted in fines and shows enhanced vitric losses this flow may have been a much more violent ash hurricane or blast which surmounted topography ingesting large amounts of lush vegetation ignition of this released the large quantities of gas needed to elutriate most of the fines a model is suggested for the recent volcanic activity on st lucia in which separate batches of silicic magma each having a distinctive petrological and chemical character rose into high level chambers over a large area eruptions of volatile rich magma led to highly explosive pumice forming activity from vents in the central highlands degassed and more crystal rich magma was extruded later from the same vents or in the attenuated flank of the qualibou depression to from lava dome complexes

pyroclastic stratigraphy of the soufriere hills volcano montserrat implications for the present eruption the stratigraphy of the soufriere hills volcano is dominated by dense andesite block and ash flow deposits forty one radiocarbon ages permit a reconstruction of the eruptive history over the past 31 000 years a single stratigraphic member yielding radiocarbon ages of 22 000 to 20 000 years b p is composed of block and ash flow deposits with semi vesiculated clasts concentrated in the upper third of each deposit the present eruption is also producing block and ash flow deposits with both dense and semi vesiculated clasts it marks a return to a more explosive driven type of activity as occurred 22 000 to 20 000 years ago deposits of this member have a broad sheet like form and volumes in excess of any produced so far by the present eruption

a new model for the evolution of la reunion volcanic complex from complete marine geophysical surveys results from recent marine geophysical surveys offer a new perspective for characterizing the evolution processes of volcanic islands in 2006 cruises forever and eroder 1 investigated the submarine flanks and the surrounding abyssal plain of la reunion indian ocean to obtain for the first time a complete geophysical survey of the area combined analyses of these data reveal major differences in the evolution of the two emerged volcanoes piton des neiges and piton de la fournaise we show that debris avalanche deposits extend on the abyssal plain only offshore the active piton de la fournaise volcano attesting the occurrence of large flank collapse events the absence of such deposits offshore piton des neiges and the presence of compressive structures within the sedimentary unit below the edifice support a mechanism of slow deformation of this volcano such as sliding or spreading the slow deformation of piton des neiges has led to numerous secondary submarine slope instabilities and favored some unconfined turbidity flows which generated large sediment waves running downward all around the island this study proposes a new model using the most complete marine data set available slow deformation controls the evolution of piton des neiges whereas piton de la fournaise formed on the flanks of a pre existing edifice experienced catastrophic large flank collapse events

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

the hydrothermal system at soufriere hills volcano montserrat west indies characterization and role in the on going eruption mineralogical microtextural and geochemical studies have been performed on altered volcanic products from active hydrothermal areas on phreatic tephra from the 1995 activity and on fragments from older castle peak dome and the present 1995 97 dome the mineral assemblages of the hydrothermal system primarily silica polymorphs are typical of the upper alteration zone of a high sulfidation system volatile and mobile elements chemistry show no evidence of interaction between the hydrothermal system and erupting magmas these results suggest that the on going eruption conduits are isolated from the hydrothermal system due to precipitation of vapor transported silica which drastically reduces the magma degassing through country rocks

the primitive volcano of mount pelee its construction and partial destruction by flank collapse abstract the geology of mount pelee the active volcano of martinique lesser antilles has been actively studied during the past decade this paper reviews the current knowledge about the oldest least well known part of the volcano here called paleo pelee and the relations between paleo pelee and the mont conil volcanic complex paleo pelee consists mostly of volcanic breccias with a few lava flows it differs in this respect from neighbouring active volcanoes such as the grande decouverte soufriere in guadeloupe and the soufriere in st vincent the oldest products of which are mainly lava flows paleo pelee initially formed a regular cone which was comparable in size with the present edifice it is now largely eroded and its products form prominent radial ridges on the western flank of mount pelee these are buried under younger deposits on the eastern flank the uniformly andesitic breccias of paleo pelee are for the most part brecciated lava flows it is inferred that the activity of mount pelee was less explosive at this stage than during following periods neo pelee the paleo pelee formations overlap those of mont conil the geology of mont conil is poorly known however its lowest exposed products are submarine andesitic breccias cut by many dikes this contrasts with paleo pelee where all breccias are of subaerial origin pleistocene limestones are interbedded within the mont conil breccias between 120 and 150 m above sea level though mont conil seems to be closely linked to mount pelee on the basis of available petrological data a major uplift must have occurred sometime during or after the construction of mont conil and forms a recognizable geological boundary between the two volcanic systems the paleo pelee edifice was partially destroyed by a flank collapse event that occurred on the southwest flank during the early stage 40 000 20 000 y b p of neo pelee this event is evidenced by a large 6 2 5 km horseshoe shaped structure which is limited by well preserved morphological scarps on land and by a 300 m offshore scarp as shown by seabeam bathymetry paleo pelee breccias and lava flows are truncated by the boundary of the collapse structure lava domes occupied the upslope part of the structure at a later time these domes are intersected by the present crater etang sec which has probably been the active vent for at least 2000 years the active crater is located at the intersection between the flank failure depression and an older caldera formed at the paleo pelee stage but probably enlarged later the flank failure structure appears as a major structure of the volcano and creates a strong structural asymmetry in the edifice this fact should be considered when dealing with such various aspects as the hydrogeology of the volcano the structural control of past and future eruptions and the volcanic hazards

30 years in the life of an active submarine volcano a time lapse bathymetry study of the kick em jenny volcano lesser antilles effective monitoring is an essential part of identifying and mitigating volcanic hazards in the submarine environment this is more difficult than onshore because observations are typically limited to land based seismic networks and infrequent shipboard surveys since the first recorded eruption in 1939 the kick em jenny kej volcano located 8km off northern grenada has been the source of 13 episodes of t phase signals these distinctive seismic signals often coincident with heightened body wave seismicity are interpreted as extrusive eruptions they have occurred with a recurrence interval of around a decade yet direct confirmation of volcanism has been rare by conducting new bathymetric surveys in 2016 and 2017 and reprocessing 4 legacy datasets spanning 30 years we present a clearer picture of the development of kej through time processed grids with a cell size of 5m and vertical precision on the order of 1 4m allow us to correlate t phase episodes with morphological changes at the volcano s edifice in the time period of observation 7 09x106 m3 of material has been added through constructive volcanism yet 5 times this amount has been lost through landslides limited recent magma production suggests that kej may be susceptible to larger eruptions with longer repeat times than have occurred during the study interval behavior more similar to sub aerial volcanism in the arc than previously thought t phase signals at kej have a varied origin and are unlikely to be solely the result of extrusive submarine eruptions our results confirm the value of repeat swath bathymetry surveys in assessing submarine volcanic hazards

lateral collapses and active sedimentary processes on the northwestern flank of stromboli volcano italy abstract the marine volcaniclastic system extending to 3 km water depth on the northwest flank of stromboli volcano has been surveyed using seismo acoustic profiling multibeam bathymetry deep towed long range side scan sonar imaging and box core sampling deposits and sea floor topography record repeated flank collapses that have occurred during the last 13 ka and created the present sciara del fuoco scar an extensive 170 km2 debris avalanche deposit characterized by subdued hummocks megablocks is buried by turbidites formed from gravity currents that originated in sciara del fuoco the currents were mainly deflected along the margin of the avalanche deposit but also spilt over onto it the turbidites reflect topographic flow stripping and their thinning towards slightly steeper slopes indicates that some material that settled there drained further downslope as secondary higher concentration flows the estimated volume of the entire fan shaped bulge amounts to 12 2 5 km3 about 3 5 km3 of which is attributed to the post collapse sedimentation the remaining 8 5 2 5 km3 is in the order of the volume computed for the material removed by the multiple sector collapses that affected the nw stromboli flank two units are identified in the distal part of the bulge through the recognition of their fronts and these indicate a layered structure for successive debris avalanche deposits granulometric and particle type characterization of seabed samples shows clast population evolution with sedimentary transport distance from the main entrance point of debris in sciara del fuoco to the confluence with the stromboli canyon and into the marsili basin some 45 km from the island changes in particle populations are due to selective sedimentation and also mixing with a wide range of terrigenous detritus brought by currents that descended the main stromboli canyon from the continental shelf abundant fine sand and silt is produced at the volcano and occurrence of mainly coarse grained material along the channel to the marsili basin indicates that a considerable volume of volcaniclastic material from stromboli lies in the sedimentary succession accumulating on the distal basin floor where a deep sea fan is growing

resonant diurnal internal tides in the north atlantic using a large acoustical array located midway between puerto rico and bermuda we have observed enhanced diurnal tidal signals associated with the lowest internal wave mode these signals result from a diurnal internal wave resonantly trapped between the shelf just north of puerto rico and the turning latitude a distance of about 1100 km the data obtained using the large acoustical array are consistent with the predicted airy function variation with latitude of diurnal internal waves near the turning latitude the existence of this wave is a striking demonstration of the long spatial and temporal coherence of oceanic internal tides in general the energy radiated by such waves is a loss of energy from the earth moon system and a source of energy for mixing in the deep ocean

calderas or gravity slide structures in the lesser antilles island arc abstract large arcuate depressions up to about 10 km in diameter on the back arc side of st lucia dominica and st vincent in the lesser antilles arc are discussed the qualibou depression on st lucia has been previously described as a caldera partly because it was believed to be the source of ignimbrites on the island remapping and stratigraphic studies of these ignimbrites show they were not erupted from the depression but from central vents in the highland rainforests and are much younger dominica is geologically similar and has two scarped depressions at the southern end of the island soufriere volcano st vincent has a prominent arcuate scarp opening to the west the southern half of which has been buried under the youngest volcanic products of the volcano we interpret these structures as the root zones of gravity slides perhaps eruption related and triggered by magmatic inflation post slide activity lava domes and fumaroles has occurred within them due to reduction in lithostatic load and pressure release on the flanks of these island volcanic complexes the presence of these structures only on the western coasts is correlated with the steeper 9 slopes into the grenada basin in contrast to the 1 submarine slopes of the atlantic side

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

cyclic formation of debris avalanches at mount st augustine volcano volcanic debris avalanches have been seen at many volcanoes since the 1980 eruption of mount st helens but typically only one or two avalanche deposits are identified at each eruptive centre suggesting that catastrophic slope failures are rare or even unique events in the lifetime of a volcano1 4 here we present a series of radiocarbon dates from volcanic deposits showing that the summit edifice of mount st augustine a 1 220 m high active volcano on augustine island in the cook inlet area of south central alaska has repeatedly collapsed and regenerated averaging 150 200 years per cycle during the past 2 000 years the unprecedented frequency of summit edifice failure was made possible by sustained lava effusion rates over 10 times greater than is typical of plate margin volcanoes

mapping the volcanic hazards from soufriere hills volcano montserrat west indies using an image processor we have used a digital model of the topography of montserrat a simple mathematical model of gravitational flow and some assumptions of the way in which the next eruption will develop to create a map of the volcanic hazards from soufriere hills volcano this has been done using an image processing computer to simulate the deposits produced by pyroclastic flows this technique has the advantages over more traditional cartographic methods of spatial precision rapid computation of multiple eruption models and the explicit nature of the physical model used soufriere hills volcano is a small andesitic volcano characterized by a cluster of summit domes and an apron of pyroclastic flow deposits and mudflows upon which several thousand people now live most of the flanks were covered by deposits from a series of eruptions from 24000 to 16000 a bp though there is some evidence that dome growth and small pyroclastic flows have occurred since the modelling is constrained by field evidence from the deposits of previous eruptions although the evidence is not good enough to model individual flow units the cumulative deposits can be used from the eruption deposit models we have created a new type of map specifically for emergency planning this sequential hazard zone map attempts to portray the regions that would be at hazard from pyroclastic flows during successive stages from the start of an eruption whose energy release was increasing with time

reconnaissance de structures tectoniques et volcaniques sous marines de l arc recent des petites antilles kick em jenny qualibou montagne pelee nordouest de la guadeloupe abstract a multibeam bathymetric survey seacarib 1 was carried out in april 1985 on board the r v conrad lamont doherty geological observatory off the western coasts of several islands of the lesser antilles complementing a previous survey of the same type arcante 2 thermosite 1980 devoted to adjoining areas in guadeloupe martinique and st lucia it allowed us to precisely map submarine volcanoes in a marginal setting behind the recent arc the main volcanic axis of the archipelago emplaced during the neogene the kick em jenny volcano south of the grenadines is the only active submarine volcano of the lesser antilles it is a small and very young cone probably only tens or hundreds of years old which was hydrothermally active during the survey the directeur volcano guadeloupe is the largest submerged volcanic centre thus far detected in the lesser antilles having been formed between 3 3 and 2 9 ma during the 1980 survey two other large volcanoes were discovered off southern basse terre guadeloupe vieux fort volcano 2 5 2 0 ma and in front of fort de france bay martinique schoelcher volcano older than 4 2 ma several other much smaller volcanoes have been mapped off the same coasts particularly the bouillante seapeaks guadeloupe moreover large tectonic structures cut the recent arc transversally and obliquely the well known qualibou depression on the island of st lucia was interpreted in various ways neither the hypothesis of a large caldera the western side of which collapsed offshore nor the suggestion of a huge rotational gravity slide are confirmed the depression seems more likely to have been controlled by tectonic factors shaping a complex graben structure the seaward extension appears to be restricted to a northern channel the soufriere channel the st pierre fault in martinique is a large transverse feature extending seaward down to some 2000 m depth to the south it bounds the mount pelee active volcanic system and the escarpment of the fault forms a dam against subaqueous pyroclastic flows running down from the volcano these flows are responsible for the unusually smooth morphology of the submarine flanks the zombi fault of northwest guadeloupe is part of a first order feature extending along at least 130 km from montserrat in the north to marie galante in the east this curved fracture cuts across the northern central part of the lesser antilles passing progressively from a subparallel to a transverse orientation with respect to the axis of the island arc these types of surveys are important because they provide better understanding of the structure and recent geological evolution of the recent volcanic arc they are also a useful complementary tool for geothermal and seismological studies

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

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

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

the qualibou caldera st lucia west indies abstract recent geological geophysical and hydrogeochemical studies conducted in the qualibou area of st lucia west indies provide new data for reevaluation of the geothermal resource and recommendation of sites for renewed drilling activities this work supports the original hypothesis of tomblin that the qualibou depression is a caldera precaldera volcanic activity was concentrated along faults associated with regional ne and nw trending structures basaltic lavas dated at 5 5 ma crop out along the western coast and are overlain by andesitic composite cones dated at 1 2 and 0 9 ma which form the highest ridges of the island superimposed upon the andesitic cones are dacitic domes 0 25 ma the eroded plugs of two of these form the spectacular pitons the major event in this volcanic field was the intermittent eruption of the choiseul pumice concurrent with the formation of the qualibou caldera 32 000 to 39 000 yrs ago about 6 km3 dense rock equivalent of lithic crystal andesitic tephra was erupted mainly as nonwelded to welded pyroclastic flows and surges some of these tuffs have been identified in geothermal drill holes within the 12 km2 caldera postcaldera eruption of dacitic tephra and dome lava 20 000 to 32 000 yrs ago occurred from vents within the caldera and appear to be a result of magmatic resurgence a 5 2 km long dipole dipole dc resistivity survey measured along a north south trending line through the caldera gave apparent resistivity results similar to those obtained in previous studies these results are compatible with a caldera substructure where low apparent resistivities analysis and interpretation of hydrogeochemical data from the qualibou caldera indicate that a geothermal reservoir underlies the sulphur springs area and consists of three layers 1 an upper steam condensate zone 2 an intermediate two phase vapor zone and 3 a lower brine zone measured temperatures at depth of 212 c are complemented by estimated temperatures of 250 c in the brine layer the water chemistry of various thermal springs indicates upwelling primarily near the caldera center at sulphur springs which feeds steam to steamcondensate hot springs along the northern caldera wall

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

geological history and potential hazards of the late pleistocene to recent plat pays volcanic complex dominica lesser antilles during 1998 2000 the island of dominica in the lesser antilles experienced a major volcanic earthquake swarm spatially associated with volcanic centres in the south of the island this swarm provided the motivation for a major re assessment of geologic history and volcanic hazards in this region this has led to a re interpretation of the south western most corner of the island as a large volcanic complex termed the plat pays volcanic complex which has exhibited a wide range of past eruptive activity and which in the quaternary experienced a major caldera collapse triggered by a voluminous pyroclastic eruption stratigraphy and new 14c age determinations reveal a complicated history of development the earliest activity is represented by the formation of the plat pays stratovolcano and associated parasitic domes a major explosive eruption 39 000 years b p produced the grand bay ignimbrite and triggered a major caldera collapse of the summit and south western flank of the plat pays stratovolcano following the major eruption re injection of plat pays magma resulted in the extrusion of approximately 12 lava domes both within and outside the resulting depression caldera collapse was followed by at least one catastrophic flank collapse but it is unclear whether or not this was triggered by caldera formation the only on shore evidence of flank collapse is the breach of the caldera rim and truncation of post caldera deposits emplaced on or near the caldera rim we find no evidence of on shore large magnitude rock avalanche deposits within the stratigraphic framework of the plat pays volcanic complex frequent seismic swarms of volcanic earthquakes and vigorous geothermal activity indicate that south dominica is still underlain by an active magma reservoir system our new geological observations combined with an interpretation of recent seismic swarm activity suggest that an eruption probably dome forming from the plat pays volcanic complex is probable within the next 100 years

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

correlation between rate of sea level change and frequency of explosive volcanism in the mediterranean volcanic activity has frequently been linked to quaternary environmental change either by driving climate modification1 2 or in response to environmental changes3 although a link has been established between large explosive eruptions and small 0 5 c brief 1 2 years falls in global temperatures4 both the evidence and mechanisms responsible for longer episodes of eruption induced planetary cooling remain questionable1 2 5 6 in contrast recent research based on ice core data suggests that rapid climate changes during the past 110 000 years increased explosive volcanic activity7 here we present a statistical analysis relating the frequency of explosive activity of mediterranean volcanoes based on dated8 9 10 11 tephra layers in deep sea sediment cores to the rate of late quaternary sea level change the nonlinear correlation between the two is tentatively explained in terms of dynamic responses of the volcanoes to stress related influences on various spatial scales the correlation supports a mechanism or mechanisms by which the climate driven growth and decay of large ice sheets can influence the eruptive chronologies of distant volcanic edifices via changes in global sea level