the mechanism of surtseyan volcanism during eruption the vent of a surtseyan volcano is occupied by a highly mobile slurry of tephra hyaloclastite and water as magma ascends rapidly through the slurry mixing occurs due to velocity shear acceleration of the fluid fluid contacts and mass incorporation consequent expansion of the admixed water causes the jetting and continuous up rush activity that characterizes surtseyan volcanism there is no evidence of the widely accepted fuel coolant interaction mechanism

the 25 september 2007 eruption of mount ruapehu new zealand directed ballistics surtseyan jets and ice slurry lahars abstract at 20 26 nzdt on 25 september 2007 a moderate gas driven eruption beneath the summit crater lake of mt ruapehu new zealand generated a directed ballistic fallout apron and surtseyan jet that impacted an area of c 2 5 km2 to the north of the vent two climbers were caught in the blast at a hut 600 m from the vent primary ice slurry lahars were generated in two catchments draining the summit region including a flow that entered a commercial ski field the ejecta consists of blocks of andesitic lava and scoria erupted during previous volcanic episodes a variety of mineral cemented lake floor sediments vent fill debris and rare glassy material interpreted to be derived from a fresh batch of magma a minority of clasts contain formerly molten elemental sulphur indicating that vent temperatures at the base of the lake were in excess of 119 c the ballistic deposit is confined to a c 40 wide swath directed northwards that extends up to 2 km from the inferred vent location beneath crater lake the strong directionality of the jetted deposits and ballistic free shadow zones sheltered by intervening topography all point to a relatively low angle directed blast previous similar eruptions at ruapehu also show preferred deposit orientations that are here correlated with an inclined and off centre vent beneath crater lake the 25 september 2007 eruption appears to have resulted from failure of a relatively shallow hydrothermal seal composed of elemental sulphur and other mineral precipitates developed in the vent breccia which breached following overpressurization by a pulse of magmatic gases released from deeper in the conduit this event highlights the potential hazard from relatively minor gas driven eruptions at ruapehu that can occur with little or no warning improved understanding of the eruption mechanism for this style of eruption will inform future risk assessments for ruapehu and other similar volcanoes worldwide

a monogenetic surtla type surtseyan volcano from the eocene oligocene waiareka deborah volcanics otago new zealand a model the relics of a small monogenetic continental shelf surtseyan volcano are preserved on the north otago coast south island new zealand in the late eocene early oligocene waiareka deborah volcanics the succession consists of two parts i e a lower interval of bedded lapilli tuffs and lapillistones representing the eruptive aggradational cone building phase and an upper epiclastic sequence representing the post eruptive degradational phase all of the preserved succession appears to have been deposited below storm wave base the lapilli tuffs and lappillistones are subaqueous fall deposits modified contemporaneously by downslope grain flow and turbidity current redeposition and perhaps by local reworking caused by turbulent thermal eddies the absence of major discordances in the lapilli tuffs suggests that the active eruptive period was very short lived perhaps lasting only a few days the epiclastic succession consists of redeposited volcanic skeletal lime mud and glauconitic detritus transported by debris flows and other mass flows the initial epiclastic unit a debris flow appears to represent the sector collapse of a significant part of the cone the appearance of fossils and rounded clasts low in the epiclastic succession coincides with stabilisation of the top of the submarine volcanic edifice development of a wave planed top and its colonisation by a diverse fauna periodic storm activity swept material off the platform redepositing it as marginal talus ramps surtla a wholly submarine satellite volcanic centre of the 1963 1967 eruptive activity of surtsey is an excellent modern analogue for both the eruptive and post eruptive phases of the bridge point aorere point volcanic centre by analogy with surtla the 120 metres of lapilli tuffs and lapillistones exposed on bridge point and aorere point accumulated in only several days the 25 metres of reworked glauconitic and fossiliferous volcaniclastics represent thousands of years based on the time required for glauconite to form

nature of and controls on volcanism in the ca 2 32 2 06ga pretoria group transvaal supergroup kaapvaal craton south africa abstract the time of deposition of the pretoria group between 2 32 and 2 06 ga on south africa s kaapvaal craton was characterized by the first major increase in atmospheric oxygen it was accompanied by the extrusion of significant thicknesses of volcanic deposits namely the bushy bend lavas of the timeball hill formation the hekpoort formation and the machadodorp volcanic member of the silverton formation marking the three major volcanic events within the transvaal supergroup which are thought to be precursors to the succeeding bushveld complex magmatism the bushy bend lava member of the timeball hill formation is characterized by subaqueous basaltic andesitic fissure eruptions with fumarolic activity and probably minor subaerial explosive eruptions in the hinterland of the transvaal supergroup basin the subaerial volcanism of the hekpoort formation appears to have been dominated by fissure eruptions with a preponderance of lava flows and locally important pyroclastic material intermittent hiatuses in volcanism were marked by local lacustrine shale deposition finally the machadodorp lava member can be interpreted as the deposits of several seamounts aligned along a fissure probably within an extensional environment the geodynamic control inferred for the evolution of the pretoria group basin encompasses two cycles of prerift uplift subsequent mechanical rifting and long lived thermal subsidence the limited extent of the bushy bend lavas in the south of the pretoria group depository attests to the likelihood that volcanism accompanying the first rifting event was short lived in contrast the second rifting cycle postulated for the pretoria group basin has a strong association with widespread and large scale volcanism of the hekpoort ongeluk flood basalts which may have been plume related the scale of the second cycle volcanism and its importance in influencing the upper part of the pretoria group basin fill is underlined by the machadodorp volcanism probably related to hot spot volcanism as the ongeluk hekpoort plume waned

shallow marine phreatomagmatic eruptions through a semi solidified carbonate platform odp leg 144 site 878 early cretaceous mit guyot west pacific abstract leg 144 1995 of the ocean drilling program recovered basalts and volcaniclastic material from the volcanic basement of several guyots in the northwest pacific including mit guyot in site 878 tectonic reconstruction suggests that this seamount originated as an intraplate volcano on the pacific superswell in the early cretaceous tephra emplaced by mass flow within the sedimentary cap is the subject of this study the tephra unit consists of palagonitized moderately to strongly vesicular basaltic clasts of apparent phreatomagmatic origin carbonate mud to grainstone clasts and armoured lapilli armoured lapilli are inferred to have been formed during eruption within a steam envelope that developed above the vent due to magma water interaction and high gas content of the magma another distinctive feature of the tephra unit are abundant truncation surfaces that cut the lithotypes due to subsidence and are juxtaposed to the same lithotypes these truncation surfaces are inferred to represent intra eruption slip surfaces which formed during eruption of the volcano that generated the tephra pile the resulting slumps initiated grainflows and dilute turbidity currents whose deposits are interspersed with those of high concentration density currents a subaqueous setting of deposition and eruption is indicated by the abundance of sideromelane glass shards cauliflower chilled clasts the underlying marine carbonates the lack of tachylite within the deposits and sedimentary structures within the breccia

shallow water eruption fed mafic pyroclastic deposits along a paleoproterozoic coastline kangerluluk volcano sedimentary sequence southeast greenland abstract the 200 300 m thick volcano sedimentary sequence at kangerluluk is part of the psammite zone one of four major zones which constitute the 1 8 ga ketilidian orogen in south greenland three lithofacies are emphasized in the study 1 the conglomerate sandstone 2 the volcanic and 3 the pyroclastic lithofacies the 2 40 m thick conglomerate sandstone lithofacies represents a subaerial to subaqueous fan delta deposit matrix and clast supported conglomerates are interpreted as debris flow and longitudinal gravel bar deposits erosive based conglomerate channel fills attest to stream incision trough crossbedded sandstone interpreted as lunate megaripples planar bedded sandstone indicative of upper flow regime bar top sands and small scale trough crossbeds reflecting ripples follow up section form collectively with the conglomerate 0 40 2 50 m thick fining upward sequences the sandstone dominated unit up section from the conglomerates and composed of planar and low angle crossbeds minor ripples and graded beds as well as mudstone is indicative of a lower shoreface deposit below normal wave base the clastic sedimentary rocks are suggestive of a fan delta setting the 100 200 m thick volcanic lithofacies composed of pillowed and pillow brecciated lava flows is consistent with shallow water deposition interstratification of lava flows with both conglomerate sandstone and pyroclastic lithofacies intrusion of dykes into volcaniclastic rocks and peperite formation accentuate contemporaneity between volcanism and sedimentation and is a common feature of island arcs the 1 50 m thick pyroclastic lithofacies with sharp depositional contacts to the overlying volcanic and underlying conglomerate sandstone lithofacies was emplaced in a subaqueous setting the lithofacies is divided into a planar to crossbedded tuff lapilli tuff and a bedded lapilli tuff breccia whereby both deposits are inferred to result from shallow water surtseyan type eruptions the 5 15 m thick bedded lapilli tuff breccia with abundant bomb sag structures and graded beds is considered a result of subaqueous eruptions strong enough to form an insulating steam cupola characterized by ballistically emplaced bombs that rapidly collapsed allowing for transport via mass flow processes the deposits are considered proximal to the vent the 2 50 cm thick planar to crossbedded tuff lapilli tuff featuring abundant euhedral and broken crystals of feldspar 2cm and minor pyroxene 1 cm are massive graded crossbedded and stratified the planar but laterally discontinuous beds characterized by abundant low angle scours are interpreted as low to high concentration sediment gravity flows produced directly from subaqueous tephra jets that collapsed due to massive water ingestion local breccia size pyroclasts disrupting beds are interpreted as bomb sags the mafic eruption fed surtseyan type deposits postulated to be a subaqueous counterpart of cold subaerial base surges originate from subaqueous tuff cones formed along a rugged volcanic dominated shoreline featuring high energy fan deltas

collapse and reconstruction of monowai submarine volcano kermadec arc 1998 2004 monowai submarine volcano is one of the three most historically active volcanoes of the kermadec arc repeat multibeam surveys of monowai cone from september 1998 and september 2004 and t wave data recorded by the reseau sismique polynesien network for the same period document the collapse and subsequent regrowth of the cone within this 6 a period grid differencing of the two bathymetric data sets acquired 6 a apart reveals that a landslide 2230 m long occurred between the surveys within which a postcollapse cone and talus ridge 0 023 km3 in volume subsequently formed the volume of this collapse minus postcollapse construction is 0 085 km3 we interpret an unusual strong amplitude t wave event on 24 may 2002 as recording hot landsliding where the 100 to 160 m thick collapse has unroofed the uppermost parts of the vent conduit with the subsequent explosive interaction and cooling of hot magma and volcaniclastic rubble with ambient seawater this interpretation is consistent with the lack of emergent events sharp onset and large amplitude of the 24 may 2002 t waves the subsequent 2500 t wave events between november 2002 and september 2004 occurred in swarms with emerging and waning activity and with typical explosive volcanic acoustic signatures which are interpreted as recording the regrowth of an 90 m high cone back to a near 1998 elevation at an average rate of 47 m a 1 this study provides 1 a lower bound for frequency magnitude relationships of landsliding for submarine arc volcanoes and 2 estimates of 0 013 km3 a 1 of submarine cone growth during eruptive cycles

evolution and facies architecture of paleogene surtseyan volcanoes on chatham islands new zealand southwest pacific ocean abstract this paper reports for the first time phreatomagmatic deposits and preserved surtseyan tuff cones in the chatham islands new zealand fieldwork has located the relicts of at least six closely spaced paleogene surtseyan cones and associated volcaniclastic sediments within the red bluff tuff formation the complete stratigraphic section of the cones consists of two parts 1 the lower part represents volcanic aggradational processes that constructed tuff cones in a short period of time and is composed of a bedded interval of explosively fragmented vesicular glassy basaltic pyroclasts ash and lapilli sizes as well as feeder dykes pillow lavas and pillow sills and 2 the upper part represents the rapid denudation of these cones by shallow marine currents or gravity flows reflecting the instability of the tephra pile forming the cones and a much later marine faunal colonization stage e g corals brachiopods molluscs etc erosion could have occurred almost immediately after or even during the emplacement of the volcanic pile similar to what occurred at surtla vent a satellite submerged cone of the basaltic island volcano surtsey iceland the waiareka deborah volcanics bridge point aorere point and lookout bluff surtseyan cones otago new zealand and marion and prince edward islands southwest indian ocean amongst others by contrast the complete faunal colonization and stabilization of a diverse marine community could have taken hundreds or perhaps even thousands of years to reach their acme following the volcanic pulses the structural textural and compositional characteristics of the red bluff tuff formation support a phreatomagmatic mode of fragmentation similar to that at surtsey volcano iceland the red bluff tuff sequence represents one of the most complete marine tuff cones described in the geologic record

post eruptive morphological evolution of island volcanoes surtsey as a modern case study abstract surtsey is a small volcanic island in the vestmannaeyjar archipelago off the south coast of iceland the eruption leading to the island s emersion lasted for 3 5 yr 1963 1967 while destructive forces have been active for over 50 yr 1963 present day during which surtsey has suffered rapid subaerial and submarine erosion and undergone major morphological changes surtsey is a well documented modern example of the post eruptive degradational stage of island volcanoes and has provided the unique opportunity to continuously observe and quantify the effects of intense geomorphic processes in this paper we focus on coastal and marine processes re shaping the shoreline and shallow water portions of the surtsey complex since its formation and on the related geomorphological record analogies with the post eruptive morphological evolution of recently active island volcanoes at the emerging stage encompassing different climatic conditions wave regimes and geological contexts are discussed

enhanced productivity led to increased organic carbon burial in the euxinic north atlantic basin during the late cenomanian oceanic anoxic event 1 three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in 13c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins

a shallow marine alkali basalt tuff cone in the middle miocene jinzai formation izumo sw japan abstract the jinzai basalt is an alkali basalt tephra unit erupted on the japan sea side of sw japan immediately after the opening of the japan sea ceased 15 ma the jinzai basalt comprises a large volume of glassy alkali basalt clasts of phreatomagmatic origin and is interpreted to have constituted a tuff cone the tuff cone grew to a height of 100 m above the 50 to 150 m deep submarine substrate but the summit and a part of the flank were lost due to syn and post eruptive sliding slumping and erosion the restored tuff cone has a crater 400 500 m wide and 100 m high and the cone rim reaches 1500 m in width with bedding dipping outward at a maximum angle of 20 30 the primary deposits include thinly bedded lapillistone to lapilli tuff and tuff and thickly bedded lapilli tuff and tuff which are thought to be correlated to a small volume phreatomagmatic explosion and more voluminous one respectively the shallow marine jinzai basalt tuff cone is essentially similar in constituents internal structures configuration and size to other tuff cones built in shallow surface water this tuff cone however appears dominated by phreatomagmatic products due to dynamic interaction of rapidly ascending magma and water saturated unconsolidated sediments or vent filling slurry of water and ejecta and has been entirely altered through syn and post eruptive reactions of hot basalt glass and interstitial seawater

englacial vs lacustrine origin of volcanic table mountains evidence from iceland detailed facies analysis of hyaloclastites and associated lavas from eight table mountains and similar hyaloclastite volcanoes in the icelandic rift zone contradict a rapid and continuous monogenetic entirely subglacial evolution of most volcanoes studied the majority of the exposed hyaloclastite deposits formed in large stable lakes as indicated by widespread up to 300 m thick continuous sections of deep water shallow water and emergent facies salient features include extensively layered or bedded successions comprising mainly debris flow deposits turbidites base surge and fallout deposits consisting of texturally and compositionally variable slightly altered hyaloclastites as well as sheet and pillow lavas in contrast chaotic assemblages of coarser grained more poorly sorted and more strongly palagonitized hyaloclastite tuffs and breccias as well as scoria and lava are interpreted to have formed under sub or englacial conditions in small chimney like ice cavities or ice bound lakes irregularly shaped and erratically arranged hyaloclastite bodies produced at variable water levels appear to have resulted mainly from rapid changes of the eruptive environment due to repeated build up and drainage of ice bound lakes as well as the restricted space between the ice walls we distinguish a deep water facies formed during high water levels of the lake a hydroclastic shallow water and emergent facies leakage of the lake or growth of the volcano above the water surface our model implies the temporary existence of large stable lakes in iceland probably formed by climatically induced ice melting the highly complex edifices of many table mountains and similar volcanoes were constructed during several eruptive periods in changing environments characterized by contrasting volcanic and sedimentary processes

eruption processes and facies architecture of the orion central kimberlite volcanic complex fort a la corne saskatchewan kimberlite mass flow deposits in a sedimentary basin abstract the fort a la corne diamondiferous kimberlite field consists of at least 70 bodies of volcaniclastic kimberlite hosted within a contemporaneous non volcanic sedimentary succession this study of the three dimensional stratigraphy and facies architecture across the orion central kimberlite volcanic complex highlights the variations in upper and extra vent processes the sedimentary succession consists of continental to marginal marine quartz sandstones and mudstones overlain by marginal to deep marine dark mudstone and muddy sandstones and siltstones relatively thin conformable volcaniclastic kimberlite packages are interbedded throughout the host rock stratigraphy extremely thick up to at least 211 m thick discordant to concordant volcaniclastic packages series infill at least three elongate northwest trending craters 145a 145b and 219 craters and contain laterally equivalent conformable extra crater deposits bound by marine mudstones indicative of a prevailing dominantly marine environment the volcaniclastic deposits within the 145a and 145b craters respectively are separated by a considerable hiatus whereas the deposit infilling the 219 crater was formed around the same time as 145b crater deposit multiple depositional units of massive to stratified olivine rich sand to pebble sized volcaniclastic facies infill craters and were emplaced by megaturbidite pulses fed by crystal rich eruption fountains which interacted with the crater relief stacked normally graded thick to very thick bedded matrix supported olivine rich facies characterized by brief depositional breaks between some beds represent syn to post eruptive turbidite pulses associated with the early eruptive event in the 145a crater thin layers of light grey kimberlitic mudstone underlie or occur near the base of and above the main volcaniclastic packages associated with the 145b and 219 eruptions crater infilling volcaniclastic deposits were later reworked by storm induced currents into thin to medium graded moderately sorted fine to coarse olivine rich sandstone with intercalated discontinuous muddy laminae laminated to cross laminated olivine rich silt to sand sized volcaniclastic facies constitutes a small volume volcaniclastic turbidite which marks the last preserved kimberlite emplacement event at orion central

contrasting eruption styles of the 147 kimberlite fort a la corne saskatchewan canada abstract the cretaceous fort a la corne falc kimberlite field was active over a time span of 20 ma with contemporaneous terrestrial mannville group to marine lower colorado group background sedimentation steep sided pipes craters and positive landform volcanoes such as scoria or tuff cones are thought to have formed during that period the 147 kimberlite is located in the se section of the field s main cluster and is part of the large 377 5 ha orion north volcanic complex based on logging of 25 drill cores the morphology of the country rock kimberlite interface suggests excavation of a complex crater field down to the upper portion of the mannville group sedimentary deposits at least two types of volcaniclastic deposits are identified a main kimberlite unit that is typically characterized by crustal xenolith poor 1 2 normal graded beds possibly deposited as turbidites in a subaqueous environment originating from the nearby 148 tephra cone and infilling the adjacent 147 crater and a second unit located on the ne margin of the 147 kimberlite that represents a thick 60 m sequence of large up to 22 m sedimentary country rock blocks located at least 60 m above their original stratigraphic position we suggest the following time sequence of events crater excavation as a consequence of a shallow magma fragmentation level within the uppermost country rock sequences together with several closely spaced eruptive centres initially formed the complex intercalated crater field subsequently ongoing eruptions with a fragmentation level above the country rock produced the lithic fragment poor main infill of the 148 kimberlite resedimentation from the outer flanks of the 148 tephra cone resulted in the deposition of turbidites in the 147 area a consolidation phase solidified the lowermost portion of the main infill in 147 a subsequent explosion s occurred within the mannville group in the 147 area ejecting large blocks of sedimentary country rocks and fracturing the overlying volcaniclastic main infill finally blocks of the main infill tilted and possibly slumped into the subsidence structure developed above the emptied explosion chamber of 147 the different volcanic deposits reflect a change in eruption style and fragmentation level from highly explosive to spatter activity with little fragmentation potential cap rocks to build up the volatile overpressure necessary to blast the craters were not present at the time of emplacement no diatremes were observed in the study area assuming that the magma properties remained constant over time the change in eruption style has to be attributed to external factors such as water access to the rising magma the volcanic behaviour of the kimberlite magma appears to be comparable to that of other magmatic systems both in eruptive style and production rate no evidence was found for a high possibly plinian production rate or dispersion

particle water heat transfer during explosive volcanic eruptions 1 thermal interaction between volcanic particles and water during explosive eruptions has been quantified using a numerical heat transfer model for spherical particles the model couples intraparticle conduction with heat transfer from the particle surface by boiling water in order to explore heat loss with time for a range of particle diameters the results are combined with estimates of particle settling times to provide insight into heat removal during eruption from samples of volcanic particles produced by explosive eruption heat removal is restricted by resistance to heat transfer from the volcanic particles with intraparticle thermal conduction important for large particles and surface cooling by boiling dominating for small particles in most cases volcanic particles approach thermal equilibrium with the surrounding fluid during an explosive eruption application of the results to a sample from the gjalp 1996 iceland eruption indicates that relative to 0 c 70 80 of the heat is transferred from the particles to boiling water during the settling time before burial in the stratigraphic succession the implication is that for subglacial explosive eruptions much of the heat content of the magma is coupled into melting ice extremely rapidly if all particles of the gjalp 1996 deposit were cooled to the local boiling point by the end of the eruption then approximately 78 of the initial heat content was removed from the erupting magma during the eruption this is consistent with calorimetric calculations based on volumes of ice melted during and after the eruption

ongoing dispersal of the 7 august 2019 pumice raft from the tonga arc in the southwestern pacific ocean on the 7 august 2019 a 195 km2 raft of andesitic pumice was produced at 200 m below sea level at an unnamed submarine volcano in the tonga islands southwest pacific ocean drifting chiefly westward the raft reached the fiji islands on the 19 september yachts that crossed the raft as early as 2 days post eruption provided an outstanding data set of raft characteristics and pristine samples further exceptional tracking of raft dispersal by satellite images allows us to contrast virtual particle tracking methods with ocean model currents to explore the relative influence of surface currents wind and wave action on pumice flotsam dispersal over up to 2 years attenuation of ocean waves by large and compact pumice rafts appears to reduce the effect of stokes drift the coupling of real time satellite observations with oceanographic lagrangian simulations allows near real time forecasting for global maritime hazard mitigation

condor seamount azores ne atlantic a morpho tectonic interpretation abstract high resolution datasets collected by multibeam and acoustic backscatter surveys were used to produce fine scale seafloor nature and morpho tectonic interpretations of the condor seamount condor constitutes an elongated volcanic ridge that extends for 39 km and rises more than 1800 m from the surrounding seafloor constructive morphologies include i linear eruptive centres ii volcanic cones with or without summit depressions iii lava flows and iv hummocky sectors eruptive type is interpreted to vary with depth on the deeper seamount extremities the predominance of highly acoustically backscattering volcanic cones and hummocky terrain is interpreted to result from effusive eruptions not yet covered by sediment deposits in contrast the smoother relief of the central seamount flanks is interpreted as draping and infilling of the underlying effusive relief by i primary volcaniclastic deposits produced by explosive eruptions on the shallowest parts of the ridge together with ii secondary volcanigenic sediments resulting from truncation of the seamount top by swell erosion and iii sediments resulting from biogenic production a set of wnw ese to nw se trending volcano tectonic structures are shown to control most of the fissural volcanism that formed the ridge a network of nnw sse trending faults is identified on the sea floor around condor but they show little relation with the distribution of volcanic edifices or with post emplacement dismantling of the seamount these fault sets are related to the transtensional regime acting on the azorean segment of the eurasia nubia plate boundary erosional features include i palaeo wave cut platforms on the seamount summit ii landslide scars produced by lateral collapses of the ne and sw facing flanks iii gullies and turbidity current channels and iv mass wasting deposits iceberg drag and bump marks are also identified on the seamount upper flanks representing the first reference to such features in the azores and an additional low latitude record given the lack of major erosional and tectonic dismantling condor is suggested to be a relatively young seamount a revised factoring of eustatic erosional and isostatic processes does not exclude that the summit may have been eroded as late as the last glacial maximum

subaqueous eruption and shallow water reworking of a small volume surtseyan edifice at kakanui new zealand kakanui volcaniclastic deposits on the south island of new zealand are the remnants of two late eocene to early oligocene surtseyan type cones eruptive dominated material of the i stratified tuff and lapilli tuff and ii lapilli tuff breccia lithofacies and post eruptive debris of the iii shell rich tuff and lapilli tuff and iv chaotic and cross bedded tuff and lapilli tuff lithofacies compose the deposits the 9 250 m thick stratified tuff and lapilli tuff contains grain flow deposits originating from low volume tephra jets and local thinning and fining upward sequences that formed from density currents during sustained uprush the lapilli tuff breccia up to 4 5 m thick contains inward dipping beds deposited via debris flows along inner cone walls burrows and articulated shells in the 2 4 m thick shell rich tuff and lapilli tuff indicate volcanic quiescence and low sedimentation rates whereas shell fragments upsection signal increased wave and current activity burrows pyrite concretions and mudstone in the lower part of the 26 m thick chaotic tuff and lapilli tuff indicate suspension deposition and cessation in pyroclastic volcanism high angle trough cross beds and limestone rip up fragments upsection are consistent with wave induced current reworking the depositional model involves a surtseyan type eruption on a continental shelf followed by colonization of organisms on the tops of planed off cones the kakanui deposits comprise a cluster of cones constituting part of a late eocene early oligocene monogenetic volcanic field the kakanui succession provides an opportunity to study deposits that form from explosive subaqueous pyroclastic eruptions and wave dominated deposition and erosion

cone morphologies associated with shallow marine eruptions east pico island azores eruptions in shallow water typically produce cones of volcaniclastic material in order to identify any systematic effects of water depth and other environmental parameters on cone morphology we have measured the heights and widths of cones in multibeam echo sounder data from a submarine ridge extending southeast from pico island azores xrf analyses of dredged samples show that lavas here vary compositionally from alkali basalt to trachybasalt and trachyandesite cones in deeper water are generally steep sided with upper flanks close to 30 the dip of talus at the angle of repose however height width ratios of cones vary more in shallow water 200 400 m summit depth with extreme values below 0 1 while some shallow water cones are steep sided as in deep water others are much flatter three such cones lie on a bench at 300 m depth immediately east of pico island and have flank slopes of only 10 20 we speculate that exceptionally shallow cone slopes here were produced by forced spreading of the erupting columns on reaching the water air density barrier

sedimentation and volcanism in a permian arc related basin southern new zealand an exceptionally well exposed ancient intra arc basin in the permian takitimu group of new zealand contains 14 km of interbedded primary volcanic and marine volcaniclastic rocks of basaltic to rhyodacitic composition these are the products of subaerial and submarine arc volcanism and closely associated turbidite sedimentation the takitimu oceanic arc basin setting formed a dynamic closed sedimentary system in which large volumes of volcaniclastic material generated at the arc was rapidly redeposited in marine basins flanking the eruptive centres volcanism probably included 1 moderate to deep water extrusion of lava and deposition of hyaloclastite 2 extrusive and explosive eruptions from shallow marine to marginally emergent volcanoes in or on the margin of the basin and 3 plinian and phreato plinian eruptions from more distant subaerial vents along the arc much of the newly erupted material was rapidly transported to the adjacent marine basin by debris flows slumping and sliding hemipelagic sedimentation predominated on the outer margin of the basin infrequently interrupted by deposition of ash from the most explosive arc volcanism and the arrival of extremely dilute turbidites turbidite sedimentation prevailed in the remainder of the basin producing a thick prograding volcaniclastic apron adjacent to the arc the volcaniclastic strata closely resemble classic turbidite deposits and show similar lateral facies variations to submarine fan deposits study of such sequences provides insight into poorly understood processes in modern arc related basins

early proterozoic basaltic andesite tuff breaccia downslope subaqueous mass transport of phreatomagmatically generated tephra at bear lake in the flin flon snow lake greenstone belt of manitoba 400 m of thick to very thick bedded generally ungraded basaltic andesite tuff breccia breccia and lapilli tuff are intercalated with pillowed lava flows in the upper part of an early proterozoic submarine basaltic andesite shield volcano the fragmental rocks comprise angular amygdaloidal blocks and lapilli many with partial chilled selvages in a matrix of blocky non amygdaloidal to highly amygdaloidal vitric basaltic andesite ash and small lapilli minor thin to medium bedded commonly normally graded tuff occurs in the upper part of the sequence clasts in fragmental beds consistently have higher amygdule contents than intercalated lava flows although similar to pillow fragment breccias the bear lake fragmental rocks were produced by extended surtseyan type phreatomagmatic eruptions with associated fire fountain activity at a progressively subsiding shallow water vent periodic tephra slumping generated debris flows that transported particles down the uppe gentle slope of the volcano to a depositional site at a water depth of less than 1 km turbidity currents probably carried much fine tephra to deeper water tuff was deposited in the preserved section only after explosive volcanism ceased

construction of an oceanic island insights from the el hierro canary islands 2011 2012 submarine volcanic eruption eight consecutive swath bathymetry data sets were obtained to monitor the submarine eruption that occurred from 10 october 2011 to 5 march 2012 south of el hierro island in the canary islands an increase in seismic activity since july 2011 preceded the onset of the eruption which was marked by seismic tremor and stained waters the first bathymetry 15 d after the eruption started depicts a cone topping at 205 m depth growing on a preexisting valley recurrent mapping shows changes in the morphology and depth of the cone allowing us to identify collapses and calculate eruptive volumes and rates which peaked at 12 7 10 6 m 3 d 1 of non dense rock equivalent ndre on 29 30 october the final cone consists of at least four vents along a north northwest south southeast lineation with the shallowest summit at 89 m depth the total accumulated volume was 329 10 6 ndre m 3 of which one third formed the cone similar cones have been identified on the submerged flanks of the island with volumes ranging from 6 to 1000 10 6 ndre m 3 as in many other volcanic islands large scale landslides play an important role in the evolution of el hierro a giant flank landslide el golfo 13 134 ka 150 180 km 3 mobilized in a single event a volume equivalent to 450 550 eruptions of the size of the reported one showing striking differences in the construction and destruction rates of the island this study is relevant for future monitoring programs and geohazard assessment of new submarine eruptions

the morphology of insular shelves as a key for understanding the geological evolution of volcanic islands insights from terceira island azores shelves from volcanic ocean islands result from the competition between two main processes wave erosion that forms and enlarges them and volcanic progradation that reduces their dimension in places where erosion dominates over volcanism shelf width can be used as a proxy for the relative age of the subaerial volcanic edifices and reconstruction of their extents prior to erosion can be achieved in this study new multibeam bathymetry and high resolution seismic reflection profiles are exploited to characterize the morphology of the insular shelves adjacent to each volcanic edifice of terceira island in order to improve the understanding of its evolution subaerial morphological and geological stratigraphic data were also used to establish the connection between the onshore and offshore evolution shelf width contiguous to each main volcanic edifice is consistent with the known subaerial geological history of the island most of the older edifices have wider shelves than younger ones the shelf edge proved to be a very useful indicator in revealing the original extent of each volcanic edifice in plan view its depth was also used to reconstruct vertical movements showing that older edifices like serra do cume ribeirinha guilherme moniz and pico alto have subsided while more recent ones have not the morphology of the shelf namely the absence presence of fresh lava flow morphologies and several types of erosional depositional and tectonic features integrated with the analysis of the coastline morphology allowed us to better constrain previous geological interpretations of the island evolution

felsic fire fountaining beneath archean seas pyroclastic deposits of the 2730 ma hunter mine group quebec canada abstract the lapilli tuff breccias ltb 1 and ltb 2 of the archean hunter mine group in the south central part of the abitibi greenstone belt are inferred to be the product of subaqueous lava fountaining intercalated sub wave base iron formations interstratified turbiditic tuffs the absence of wave induced sedimentary structures and the stratigraphic position of lapilli tuff breccias beneath basaltic komatiites support this contention a complete eruptive sequence shows a tripartite division into a massive breccia b stratified lapilli tuff and c turbiditic tuff lapilli tuff division the massive breccia division is characterized by clusters of isolated and compressed irregular shaped clasts inferred to be deposited directly from the hot magmatic lava fountain abundant vesicular pyroclasts with a vesicle content of up to 60 exhibit locally coalescing vesicles indicating bubble nucleation prior to eruption the prevalence of irregular to amoeboid clast shapes suggests transport from the vent in a steamy rich high density current to the site under a self generated steam cupola ubiquitous subequant lapilli size pyroclasts of the stratified lapilli tuff division suggest that significant ingress of water into the fountain changed the prevalent fragmentation process from magmatic to hydrovolcanic the turbiditic tuff lapilli tuff division composed of pumice lithic fragments and vitric ash is envisaged to have formed by gravitational collapse of a subaqueous turbulent eruptive plume this type of eruptive mechanism constituted a minor but important process of volcanic construction on the ocean floor during the archean and possibly during incipient arc and backarc formation in modern day settings

types of phreatomagmatic volcanoes in the western snake river plain idaho usa abstract the western snake river plain graben in southwestern idaho includes a large hydrovolcanic field which was produced in late miocene to pleistocene time by the interaction of rising basaltic magmas with the waters and water saturated deposits of an enormous freshwater lake lake idaho the phreatomagmatic volcanoes in this field may be grouped into three types emergent subaqueous and subaerial emergent volcanoes which began erupting under water and built up above the lake level are relatively large and symmetrical are dominated by bedded tuffs and late magmatic deposits and are excellent indicators of water depth at the time of the eruption subaqueous volcanoes which never built up above the lake level are relatively small and asymmetrical are dominated by basal massive deposits and are potentially useful in discriminating between deep and very deep water settings subaerial volcanoes which were formed when magmas intercepted buried aquifers and interacted explosively with water are small tuff rings and maars with variable shapes are composed of subequal although variable proportions of basal massive deposits bedded tuffs and late magmatic deposits and are useful in determining the stratigraphic successions underlying them

satellite observations of a surtseyan eruption hunga ha apai tonga abstract on march 17 2009 a surtseyan eruption occurred around hunga ha apai island tonga a series of observations from the high spatial resolution advanced spaceborne thermal emission and reflection radiometer aster and the high temporal resolution moderate resolution imaging spectroradiometer modis was used to estimate the magnitude location start time and duration of the eruption and measure the evolving characteristics of the new hunga ha apai island the eruption start time was estimated to be between 01 50 and 11 10 local time on march 17 2009 i e between 12 50 and 22 10 utc march 16 the initial explosive phase lasted 3 5 days and consisted of multiple steam and tephra explosions from two distinct vent sources one on the northwest side and another about 100 m off the south shore of the pre existing island the eruption plume reached 4 0 to 7 6 km altitude above sea level and tephra added new land around each of the vents initially tripling the area of the pre existing island the next phase of steaming from newly formed crater lakes around the vents lasted a few days three warm crater lakes formed initially but disappeared with time as the shoreline eroded after 2 months vegetation that was initially buried by tephra was recovering after 10 months the size of the island had eroded down to twice that of the pre existing island and the one remaining crater lake had a temperature of 68 17 c the volume of erupted material was estimated to be 0 0176 km3 and the volcanic explosivity index vei was estimated to be vei 2

geometry internal architecture and evolution of buried volcanic mounds in the northern south china sea abstract high resolution seismic and borehole data were used to characterize a volcanic mound in the northern south china sea including its internal architecture lithological characteristics and evolutionary history on seismic profiles the mound shows a convex geometry similar to an isolated carbonate buildup it was therefore previously seen as a carbonate buildup and a significant hydrocarbon target until an industrial well by7 1 proved its volcanic nature ten seismic facies are identified to analyze the internal architecture of the mound under the constraint of borehole data petrologic analysis based on cuttings and thin sections reveals that the mound is composed of volcanic tuffs siliciclastics carbonates and basalt layers depositions and architecture of the mound are interpreted as a result of an interplay between tephra accumulation during volcanic eruptions wave induced re deposition of volcaniclastics when the volcanic mound emerged above sea level and subsequent siliciclastic carbonate deposition when the volcanic mound was flooded during the phases of volcanic quiescence furthermore the correlation of seismic and well data allows us to reconstruct the entire evolutionary history of the mound from its formation to its demise and final burial this work presents a detailed description of the mound architecture and its genesis and thus provides an analogue for detailed interpretations of similar structures encountered during petroleum explorations in the south china sea or elsewhere

submarine silicic volcanism of the healy caldera southern kermadec arc sw pacific i volcanology and eruption mechanisms the submarine healy volcano southern kermadec arc with a 2 2 5 km wide caldera is pervasively mantled with highly vesicular silicic pumice within a water depth of 1 150 1 800 m pumices comprise type 1 white light grey pumice with 30 mm vesicles and weak moderate foliation type 2 grey pumice with millimetre scale laminae flow banded foliation including stretched vesicles 55 mm in length and a minor finely vesicular type 3 pumice all types are sparsely porphyritic with undevitrified glassy groundmass 68 70 sio2 which is microlite and lithic free coexisting pyroxenes yield magma temperatures of 950 c pumice density is 0 5 g cm 3 and vesicularity is 78 83 vesicle size distributions for types 1 and 2 pumice range from 20 m to 20 mm with a strong power law relation with d 2 5 0 4 for vesicles 9 mpa will limit vesicularity to less than the observed 78 83 whereas pressure 6 mpa require a more shallower reconstruction of the edifice and larger volume syn eruptive collapse uniformly high vesicularity is interpreted as evidence of insulation within an eruption column comprising steam and hot pyroclasts most pyroclasts cool condensing and ingesting water into steam inflated vesicles and then sink progression into pyroclastic mode would expand the eruption column displace ambient water reduce the hydrostatic load and further promote vesiculation and fragmentation pyroclasts within the column would quench at these reduced pressures we argue that healy eruptions deeper than 1 000 m cannot be pyroclastic volumes for the lower and upper bounds of edifice size are 2 36 and 3 58 km3 respectively but do not account for intra caldera pumice fill these volumes are considered to be predominantly primary eruption output as shown by a dearth of accessory lithics in all pumice yielding at an average 81 vesicularity eruptive pumice volumes of between 10 and 15 km3 some pyroclasts may have risen to the sea surface and be a correlative of the sea rafted loisels pumice the latter occurs in some new zealand holocene beach sequences and has a estimated age of 590 80 calendar years

the submarine eruption and erosion of surtla surtsey iceland abstract surtla is the site of a short lived submarine vent which built basaltic elastic deposits almost to sea level in 1963 early in the eruption of surtsey since then wave and current activity have eroded the volcanic pile such that in july 1981 its top was a fairly level plateau 45 m below sea level and its surface comprised a lag deposit of sparse blocks of lava in a bed mainly of glass granules this winnowed layer was underlain by a nonreworked poorly sorted and finer deposit of glassy clasts formed by a combination of disruption by magmatic volatiles steam explosions and quench brecciation during the eruption the explosion violence and associated comminution increased as the pile built up to shallower water depths it is argued that at times of continuous effusion a cupola of steam was situated over the vent as indicated by scoriaceous spatter which shows agglutination and bread crust features that can only have developed in conditions more akin to subaerial than hitherto envisaged in a subaqueous eruption

the petrology of basalts from surtla surtsey iceland abstract surtla is the entirely submarine volcanic pile of a satellite vent which was active shortly after initiation of the main surtsey eruption blocks of lava and glassy elastic deposits collected from surtla are of mildly alkaline olivine basalt and are compositionally the most evolved material determined from the surtsey volcano petrographical and chemical analyses confirm the previously postulated continuum between the evolved derivative and more primitive parental compositions widely occurring in the vestmannaeyjar volcanic system but not hitherto found in a single eruption a compositionally zoned magma chamber is invoked

oceanic ridge crest processes oceanic ridge crest processes constitute a vigorous frontier of multidisciplinary research with global ramifications in the earth atmospheric and biologic sciences this deep ocean frontier is gradually opening in response to investigations which are elucidating the role of these processes in the lithosphere hydrosphere atmosphere and biosphere and the application of advanced instrumental and interpretive techniques which are increasing the quality and quantity of data these techniques include crustal drilling with borehole logging deep sea drilling project reports high resolution bathymetry sea beam etc side scan sonar seamarc i and ii gloria etc imagery with video and photography multichannel seismics determination of water column properties ctd with rosette sampler etc and submersible applications

morpho sedimentary characteristics of the volcaniclastic apron around stromboli volcano italy abstract submarine portions of stromboli volcano account for about 98 of the whole extent of the volcanic edifice and are mostly covered by volcaniclastic sediments that made up a modern volcaniclastic apron the architecture and main sedimentary processes acting within the apron are depicted through the integration of geophysical evidence multibeam long range side scan sonar and seismic data and seafloor sampling the apron shows on the whole a large variability both across and along slope of morphologies and deposits related to mass wasting and reworking processes passing into areas covered by hemipelagic sedimentation a large spectrum of erosive depositional features was recognized on the surface of the apron on shallower areas i e submerged shelves shore platforms and depositional terraces submarine features related to wave action and sea level fluctuations are present they mainly act as temporary storing and reworking areas for volcaniclastic material derived from subaerial portions unconfined cohesionless inertial flows commonly dominate the upper slope where gradients are very high up to 35 and grain to grain and grain to bed collisions are favoured within the flows these flows tend to evolve into turbidity currents on the lower slope in response to a marked decrease of slope gradients below 8 generating various erosive depositional features such as erosive furrows troughs channel levee features and coarse grained sediment waves the most active area of the apron lies offshore sciara del fuoco on the nw flank where a large amount of coarse grained volcaniclastic material derived by the persistent strombolian activity is collected and deposited by means of high and low density turbidity currents on the lower slope down to 2600 m bsl more than 20 km far from the island conversely other areas are mostly dominated by deposition via settling of suspended sediments related both to hemipelagic sedimentation and to the dispersion of fine tephras by the prevailing wind and marine currents such processes interfinger and overlie in space and time giving rise to a very complex morpho sedimentary facies distribution however the structural bilateral symmetry of stromboli volcano allows defining distinct morpho sedimentary zones where one or more type of processes dominates and related different stratal architecture of the apron the unbuttressed portions of the island nw and se are characterized by the emplacement of wide and thick debris avalanche deposits volume in the order of 1 2 km 3 for each event related to large scale sector collapses representing the most important and efficient mass wasting processes making up the apron such deposits are embedded within different volcaniclastic sequences and can be eroded or exhumed by successive gravity flows the result is a highly complex both spatially and vertically succession of facies where it is often difficult to depict an arranged series of processes conversely on buttressed flanks sw and ne a more ordered evolution of processes and deposits making up the apron is observed giving rise to a less complex apron architecture

subaqueous strombolian eruptions and eruption fed pyroclastic deposits in a paleoproterozoic rifted arc hidden formation flin flon canada abstract the hidden formation of the paleoproterozoic flin flon arc assemblage comprises the stratigraphic hanging wall to the volcanogenic massive sulfide vms deposits at flin flon manitoba canada it represents a basaltic volcanic edifice erupted within a large subsidence structure developed in a rifted arc environment it is predominately pillow lavas with subordinated amounts volcaniclastic rocks rocks that stratigraphically overly the schist and mandy vms deposits 5 km southeast of the main flin flon deposits have been correlated through litho and chemo stratigraphy with the hidden formation they display evidence of pyroclastic volcanism and concomitant subsidence pillow lavas and hyaloclastite are unequivocal evidence of subaqueous eruption the hidden formation in the schist mandy area comprises mafic tuff mafic megabreccia basalt lava fluidal clast breccia and plagioclase crystal rich volcaniclastic lithofacies intruded by synvolcanic dikes and sills the megabreccia lithofacies is characterized by angular basalt clasts 1 20 m in a matrix of finer basalt clasts and is interpreted to have been deposited by mass flows due to slumping of the caldera wall a within flow vertical transition in the lavas from massive to pillowed flows suggests a slowing of emplacement velocity decrease in temperature and an increase in the viscosity during eruption based on the monolithic nature of the fluidal clast breccias and the fluidal shapes of clasts with delicate tails and intact glassy margins they are interpreted to be the result of strombolian eruptions an increase in the ingestion of water in the vent s lead to a change from magmatic to phreatomagmatic fragmentation planar and cross laminations graded beds and the abundance of broken plagioclase crystals in combination with scoria and lithic clasts suggest the mafic tuff and plagioclase crystal rich volcaniclastic lithofacies were deposited by subaqueous eruption fed density currents derived from a phreatomagmatic eruption detailed mapping of the volcanic lithofacies in the schist mandy area has facilitated the identification of synvolcanic faults defining inner caldera margins and volcanic vents these structures when traced downwards through stratigraphy define structural corridors corresponding with the schist and mandy vms deposits indicating they represent long lived structures that also acted as magmas and fluid pathways

the 1969 subglacial eruption on deception island antarctica events and processes during an eruption beneath a thin glacier and implications for volcanic hazards a short lived eruption of basaltic andesite to andesite on deception island in 1969 occurred from a series of fissures underneath a glacier the glacier was thin c 100 m and the eruption created a large and sudden discharge of meltwater that overflowed the glacier severely damaging buildings on the island the eruption was unusually well documented and it illustrates several features of subglacial eruptions that are only poorly known and not well understood in particular overflowing meltwater is contrary to predictions based on existing simple hydrological models for eruptions beneath thin glaciers the eruption is analysed in this paper and used as a model for the fluid dynamics and thermodynamics of eruptions beneath a thin glacier mainly composed of impermeable ice it is suggested that in eruptions of relatively fluid magmas with a low magma rise rate volatiles and magma are able to decouple and subglacial melting is strongly influenced by the superheated magmatic and hydrothermal gases mainly steam thus melting is much faster than that due solely to coupled conductive magma and convective meltwater heat transfer the influence of gasdriven melting also has an important effect on the shape of the meltwater cavity and may be at least partly responsible for the cylindrical ice chimneys developed above vents on deception island the results of the study are important for reconstructing the shapes of englacial cavities melted above a vent they also highlight the importance of glacier structure and densification rather than simply glacier thickness in determining the hydraulic evolution of an eruption even eruptions beneath thin glaciers can generate significant meltwater floods

magma water interactions in subaqueous and emergent basaltic in the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of 1 explosive release of magmatic volatiles 2 explosive expansion and collapse of steam formed at magma water contact surfaces 3 explosive expansion of steam following enclosure of water in magma or entrapment of water close to magma and 4 cooling contraction these processes named respectivelymagmatic explosivity contact surface steam explosivity bulk interaction steam explosivity andcooling contraction granulation can be enhanced by mutual interaction and feedback the first three explosive processes are limited at certain water depths hydrostatic pressures and become increasingly vigorous at shallower levels the depth of onset of magmatic explosivity depends largely on juvenile volatile content it is up to 200 m for tholeiitic magmas and up to 1 km for alkalic magmas at the depth where formation of clastic deposits becomes predominant over effusion of lavas magmatic explosivity is subordinate to steam explosivity as a clast forming process the upward transition to accumulation of dominantly clastic deposits is not simply related to the onset of substantial exsolution of magmatic volatiles and can occur without it contact surface explosivity commonly requires initiation by a vigorous impact between magma and water and although no certain depth limit is known likelihood of such explosivity decreases rapidly with depth clast generation by bulk interaction explosivity appears to be restricted to depths much shallower than that of the critical pressure of water which in sea water is at about 3 km cooling contraction granulation can occur in any depth of water but at shallow levels may be replaced by contact surface explosivity during continuous eruption under water tephra can be ejected and deposited within a cupola of steam such that rapid quenching does not occur emergent volcanoes are characterized by distinctive steam explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material water and steam the water gets into the vent by flooding across or through the top of the tephra pile and violent explosions cease when this access is sealed the eruptions during emergence of surtsey and capelinhos typify the distinctive explosive activity the style and controls of which are different from those of maar volcanoes

patterns of local and global redox variability during the cenomanian turonian boundary event oceanic anoxic event 2 recorded in carbonates and shales from central italy careful evaluation of the local geochemical conditions in past marine settings can provide a window to the average redox state of the global ocean during episodes of extensive organic carbon deposition these comparisons aid in identifying the interplay between climate and biotic feedbacks contributing to and resulting from these events well documented examples are known from the mesozoic era which is characterized by episodes of widespread organic carbon deposition known as oceanic anoxic events this organic carbon burial typically leads to coeval positive carbon isotope excursions geochemical data are presented here for several palaeoredox proxies cr ti v mo zn mn fe speciation i ca and sulphur isotopes from a section exposed at furlo in the marche umbrian apennines of italy that spans the cenomanian turonian boundary here oceanic anoxic event 2 is represented by a ca 1 m thick radiolarian rich millimetre laminated organic rich shale known locally as the bonarelli level iron speciation data for thin organic rich intervals observed below the bonarelli level imply a local redox shift going into the oceanic anoxic event with ferruginous conditions i e anoxic with dissolved ferrous iron transiently developed prior to the event and euxinia i e anoxic and sulphidic bottom waters throughout the event itself pre oceanic anoxic event enrichments of elements sensitive to anoxic water columns were due to initial development of locally ferruginous bottom waters as a precursor to the event however the greater global expanse of dysoxic to euxinic conditions during the oceanic anoxic event greatly reduced redox sensitive trace metal concentrations in seawater pyrite sulfur isotopes document a positive shift leading into the oae carbonate i ca ratios were generally low suggesting locally reduced bottom water oxygen conditions preceding the event and relatively increased o2 concentrations post event combined the furlo geochemical data suggest a redox stratified water column with oxic surface waters and a shallow chemocline overlying locally ferruginous bottom waters preceding the event globally widespread euxinic bottom waters during the oceanic anoxic event followed by chemocline shallowing but sustained local redox stratification following the event this article is protected by copyright all rights reserved

volcanic tectonic and mass wasting processes offshore terceira island azores revealed by high resolution seafloor mapping terceira island in the azores archipelago lies at the intersection of four submarine volcanic ridges new high resolution bathymetric and seismic reflection data have been used to analyze the main volcanic tectonic and mass wasting features of the island offshore volcanic features such as linear volcanic centers and pointy and flat topped cones are mainly concentrated on the narrow western and north western ridges characterized by an overall rugged morphology fault scarps dominate mainly the broad eastern and south eastern ridges which are characterized by an overall smooth and terrace like morphology on the eastern ridge faults form a series of horsts and grabens related to the onshore lajes graben the strikes of the fault scarps linear volcanic centers and alignment of volcanic cones on the ridges reveal two main structural trends wnw ese and nnw sse consistent with the main tectonic structures observed on the azores plateau in contrast a large variability of strike was observed in inter ridge areas reflecting the relative importance of regional and local stresses in producing these structures mass wasting features are subordinate and mostly represented by hundred meter wide scars that indent the edge of the insular shelf surrounding the island apart from two large deeper scars identified on the southern steep flank of the western ridge finally the remarkable morpho structural differences between the western and eastern ridges are discussed in the framework of the evolution of the terceira volcanic edifice and hypothesized to reflect successive stages of ridge evolution

the miocene costa giardini diatreme iblean mountains southern italy model for maar diatreme formation on a submerged carbonate platform in this paper we present a model for the growth of a maar diatreme complex in a shallow marine environment the miocene age costa giardini diatreme near sortino in the region of the iblei mountains of southern sicily has an outer tuff ring formed by the accumulation of debris flows and surge deposits during hydromagmatic eruptions vesicular lava clasts accretionary lapilli and bombs in the older ejecta indicate that initial eruptions were of gas rich magma abundant xenoliths in the upper late deposited beds of the ring suggest rapid magma ascent and deepening of the eruptive vent is shown by the change in slope of the country rock the interior of the diatreme contains nonbedded breccia composed of both volcanic and country rock clasts of variable size and amount the occurrence of bedded hyaloclastite breccia in an isolated outcrop in the middle lower part of the diatreme suggests subaqueous effusion at a low rate following the end of explosive activity intrusions of nonvesicular magma forming plugs and dikes occur on the western side of the diatreme and at the margins close to the contact between breccia deposits and country rock they indicate involvement of volatile poor magma possibly during late stages of activity we propose that initial hydromagmatic explosive activity occurred in a shallow marine environment and the ejecta created a rampart that isolated for a short time the inner crater from the surrounding marine environment this allowed explosive activity to draw down the water table in the vicinity of the vent and caused deepening of the explosive center a subsequent decrease in the effusion rate and cessation of explosive eruptions allowed the crater to refill with water at which time the hyaloclastite was deposited emplacement of dikes and plugs occurred nonexplosively while the breccia sediment was mostly still soft and unconsolidated locally forming peperites the sheltered low energy lagoon filled with marine limestones mixed with volcaniclastic material eroded from the surrounding ramparts ultimately lagoonal sediments accumulated in the crater until subsidence or erosion of the tuff ring caused a return to normal shallow marine conditions

fluidal clast breccia generated by submarine fire fountaining trooper creek formation queensland australia abstract a distinctive monomictic breccia composed of fluidal and blocky basaltic andesite clasts occurs in a cambro ordovician submarine volcanic succession in northern queensland australia associated with this fluvial clast buccia facies are coherent facies and coarse and fine breccia facies of the same composition the fluidal clast breccia facies is internally massive and 250 m thick varying only in the ratio of fluidal clasts to blocky clasts fluidal clasts range in size from 2 cm to 170 cm and have moderately to highly vesicular cores and thick up to 1 cm non vesicular formerly glassy rims blocky clasts are highly vesicular to non vesicular subaqueous fire fountain breccias are distinguished from subaerial fire fountain breccias by thick glassy margins on fluidal clasts the lack of welding and agglutination and the distinctive association of highly vesicular fluidal clasts with non vesicular angular blocky clasts recognition of submarine fire fountain breccias in volcanic successions constrains the eruption style proximity tens of metres to source and environment of deposition

in situ modification of modern submarine hyaloclastic pyroclastic deposits by oceanic currents an example from the southern kermadec arc sw pacific submarine volcaniclastic deposits both modern and ancient pose a conundrum in distinguishing between syn and post eruptive processes high standing submarine volcanic edifices of the late quaternary southern kermadec arc sw pacific are point sources of pyroclastic hyaloclastic deposits that are bathed and modified by a complex current system of the south pacific gyre flowing southeast along the northern margin of new zealand which in part comprises the anticyclonic flow of the warm cored east cape eddy ece flow of the ece across the southern kermadec arc provides a present day case of extensive and in situ post eruptive textural modification of modern pyroclastic hyaloclastic deposits on the crests and upper flanks of submarine stratovolcanoes photographic observations and limited textural data from seven kermadec volcanoes reveal pervasive evidence of sediment winnowing including crag and tail structures scour and moating around volcanic blocks coarse sand granule lag deposits epifaunal deflection lineated mud streaking and moulded bioturbation mounds and asymmetric current ripple bedforms at water depths of at least 1500 m all bedforms indicate increasing current speed at progressively higher elevations decreasing water depth for each volcano current ripples mostly have discontinuous asymmetric shorted crested linguoid lunate forms below 1000 m water depth progressing to semi continuous asymmetric shorted crested linear sinuous forms above 500 m current elutriation of the kermadec deposits progressively removes fines with decreasing water depth resulting in relatively fines depleted volcaniclastic sands and granules this post eruptive process overprints syn eruptive processes that notionally generate more comminuted fine grained clasts with decreasing water depth as phreatomagmatic explosive eruptions become more vigorous current elutriation also modifies volcaniclastic detritus prior to subsequent removal by episodic mass gravity flow in addition the sand granule traction load driven by current flow moves sediment nearly continuously to gully and rill heads for removal down slope independently of syn eruptive sediment flux the underlying observation is that volcaniclastic deposits rarely reflect just syn eruptive processes and that significant in situ current elutriation of at the least surficial pyroclastic hyaloclastic eruption products can occur on submarine volcanoes threshold current velocities derived assuming unidirectional flow over cohesionless sand lapilli grainsizes and accounting for bed friction yield current velocities at 100 cm above the bed of 15 cm s 1 for water depths 1500 m through to 70 cm s 1 for depths

numerical model of crater lake eruptions we present results from a numerical investigation of subaqueous eruptions involving superheated steam released through a lake mimicking the volcanic setting at mt ruapehu the simulations were conducted using an adaptive mesh multi material hydrodynamics code with thermal conduction sage simple adaptive grid eulerian parameters investigated include eruption pressure lake level and mass of superheated vapor the simulations produced a spectrum of eruption styles from vapor cavities to radial jets that resulted in hazards that ranged from small scale waves to high amplitude surges that reached and cascaded over the edge of the crater rim there was an overall tendency for lake surface activity to increase including wave amplitude with increasing mass of superheated vapor and eruption pressure surface waves were induced by the formation and collapse of a gas cavity the collapse of the cavity is considered to play a major role in the characteristic features observed during a subaqueous eruption the additional mass of superheated vapor produced a larger cavity that displaced a larger area of the lake surface resulting in fast moving surges upon the collapse of the cavity high lake levels 90 m appear to suppress the development of explosive jetting activity when eruption pressures are 10 mpa vertical jets and radial ejections of steam and water can occur in water depths 90 m less explosive eruption styles can produce hazardous events such as lahars by the outward movement of surface waves over the crater rim

coastal erosion rates of lava deltas around oceanic islands abstract rates of coastal erosion are needed for planning purposes and to improve understanding of how the shelves of islands develop ultimately becoming submerged banks near shore submarine platforms created by erosion of lava deltas of known age provide an opportunity to quantify erosion rates and to investigate how those rates vary between different types and ages of lava flows as well as how they vary with wave climate we have compiled data on deltas formed during historical and holocene eruptions age 6 ka from both a and p hoehoe lava flows and from diverse localities azores and hawaiian islands and ascension island near shore platforms were interpreted from multibeam sonar bathymetric light detection and ranging lidar and historical sounding data from them we estimated time averaged shoreline retreat rates from the seaward distances between the modern coastlines and the submarine platform edges the 35 interpreted platforms have rugged dipping surfaces left behind by erosion with an average gradient of 5 range 2 10 eroded distance of 436 m 78 1119 m and depth of platform edge of 25 m 5 56 m to evaluate the latter depths we computed seabed orbital speeds due to surface waves at the platform edges depths of platform edges correlate only modestly with those speeds suggesting that platform surfaces have adjusted to wave conditions with a wide range of particle sizes and hence thresholds of motion the largest retreat distances 800 m are associated with platforms of the central azores islands which are exposed to higher waves however retreat rates are highly varied 0 08 12 5 m yr and weakly correlated with measures of wave power suggesting that waves are only a secondary influence given that lack of correlation we suspect that the main factor contributing to variability arises from varied cliff resistance to erosion blocks between joints in lava flows and hence resistance to erosion vary greatly in size from the thicker and less densely jointed a flows to the thinner and shell like layered lavas in p hoehoe flows

marine emplacement of welded ignimbrite the ordovician pitts head tuff north wales the pitts head welded ignimbrite records a subaerial large volume eruption and associated pyroclastic current that flowed into the sea the current 15 km from source was steadily sustained with high mass flux and high particle concentration towards its base and it entered the sea without substantial mixing with water and thus without large scale hydroexplosivity and without general cooling it continued to aggrade ignimbrite at 580 c for at least 3 4 km from the original shoreline in water initially 50 m deep entirely subaqueous hot state progressive aggradation and welding of the ignimbrite occurred where the water could not be wholly displaced by the current although eventually the deposit displaced the shore 4 km seawards wet sea floor sediments buried by the ignimbrite were heated and locally fluidized by steam and several square kilometres of hot ignimbrite with variable thicknesses of sedimentary substrate detached and slid downslope directions of sliding and the order of piling up of slide sheets are shown by hot state rheomorphic deformation fabrics and the geometric relations of detachment surfaces extensional disruption of the ignimbrite is marked by breaks in the sheet via which fluidized sediments were mobilized locally to form rootless vents both the initial incursion of the pyroclastic current into the sea and the subsequent submarine sliding of the ignimbrite are likely to have caused tsunamis similar occurrences at modern coastlines presently susceptible to incursion of high mass flux pyroclastic currents e g taupo volcanic zone new zealand neapolitan region italy vicinity of manila taal philippines would according to tsunami propagation behaviour cause significant near and far field coastal hazard

syn and posteruptive hazards of maar diatreme volcanoes abstract maar diatreme volcanoes represent the second most common volcano type on continents and islands this study presents a first review of syn and posteruptive volcanic and related hazards and intends to stimulate future research in this field maar diatreme volcanoes are phreatomagmatic monogenetic volcanoes they may erupt explosively for days to 15 years above the preeruptive surface a relatively flat tephra ring forms below the preeruptive surface the maar crater is incised because of formation and downward penetration of a cone shaped diatreme and its root zone during activity both the maar crater and the diatreme grow in depth and diameter inside the diatreme which may penetrate downwards for up to 2 5 km fragmented country rocks and juvenile pyroclasts accumulate in primary pyroclastic deposits but to a large extent also as reworked deposits ejection of large volumes of country rocks results in a mass deficiency in the root zone of the diatreme and causes the diatreme fill to subside thus the diatreme represents a kind of growing sinkhole due to the subsidence of the diatreme underneath the maar crater is a subsidence crater and also grows in depth and diameter with ongoing activity as long as phreatomagmatic eruptions continue the tephra ring grows in thickness and outer slope angle syneruptive hazards of maar diatreme volcanoes are earthquakes eruption clouds tephra fall base surges ballistic blocks and bombs lahars volcanic gases cutting of the growing maar crater into the preeruptive ground formation of a tephra ring fragmentation of country rocks thus destruction of area and ground changes in groundwater table and potential renewal of eruptions the main hazards mostly affect an area 3 to possibly 5 km in radius distal effects are comparable to those of small eruption clouds from polygenetic volcanoes syneruptive effects on infrastructure people animals vegetation agricultural land and drainage are pointed out posteruptive hazards concern erosion and formation of lahars inside the crater a lake usually forms and diverse types of sediments accumulate in the crater volcanic gases may be released in the crater compaction and other diagenetic processes within the diatreme fill result in its subsidence this posteruptive subsidence of the diatreme fill and thus crater floor is relatively large initially but will decrease with time it may last millions of years various studies and monitoring are suggested for syn and posteruptive activities of maar diatreme volcanoes erupting in the future the recently formed maar diatreme volcanoes should be investigated repeatedly to understand more about their syneruptive behaviour and hazards and also their posteruptive topographic limnic and biologic evolution and potential posteruptive hazards for future maar diatreme eruptions a hazard map with four principal hazard zones is suggested with the two innermost ones having a joint radius of up to 5 km areas that are potentially endangered by maar diatreme eruptions in the future are pointed out

submarine eruption near socorro island mexico geochemistry and scanning electron microscopy studies of floating scoria and reticulite abstract products of an underwater eruption near socorro island in the ne pacific were observed directly on january 29 1993 ten days after precursors were first recorded by sofar sound fixing and ranging hydrophones located in hawaii and tahiti eruptive activity was noticed from boats and ships as small steam plumes rising from the sea at an area centered at 18 48 n 111 05 w 2 4 km nw of punta tosca and 4 6 km ssw of cape henslow on socorro island the observed steam was produced by 1 3 m large blocks of hot dark grey highly vesiculated basalt rising buoyantly to the surface from two submarine shallow vents at 210 and 30 m depth tens of blocks accompanied by bubbles could be observed rising to the surface in irregular pulses these scoriaceous blocks remained floating at the surface until they would crack into smaller pieces by thermal contraction emitting hissing noises from vapourizing seawater in contact with the hot interior of the blocks steam jets several metres in height were produced and occasionally blocks were propelled laterally by the steam jet depending on vesicularity and permeability blocks remained floating and drifting with the surface current for 1 15 minutes before sinking back floating rocks covered an area of about 6000 m2 this intermittent activity has been observed ever since and has not stopped as of april 1994 buoyant scoria and reticulite are indicative of volatile mostly co2 supersaturation and exsolution in the magma prior to rapid quenching which inhibits loss of volatiles by bubble escape a high velocity ascent of low viscosity magma in a relatively narrow conduit is also required to prevent substantial gas escape and allow formation of reticulite the buoyant scoria is most probably ejected by intermittent lava fountaining at fixed vents as a result of changes in eruption velocities due to changes in the exsolved gas content of the lava between january and july 1993 floating blocks of scoria and reticulite were collected on several occasions from the surface of the sea for chemical and mineralogical analyses major and minor element analyses including ree as well as electron microprobe analyses of different phases revealed that the composition of the emitted lava has not changed through time blocks of basalt sio2 45 47 are highly vitric and vesicular with tabular anorthite phenocrysts up to 3 mm in length and minor grains of forsteritic olivine ree and trace element composition of these rocks suggest an anomalous mantle source for the erupted alkali basalt lava the ongoing eruption will either continue in a similar fashion as described and eventually cease or built up a mound that reaches the surface and forms an island with accompanying change in eruptive style

spatial patterns of atmospheric pollen transport in a montane region abstract annual pollen deposition pollen cm 2 yr 1 was sampled for 6 yr in the southern sierra nevada the owens valley and the inyo mountains of central california spatial pollen distributions were examined for anemophilous plants which are limited to growth sites 1 at high elevations on one or both mountain ranges 2 on lower mountain slopes and 3 on the owens valley floor pollen deposition values for high and low elevation plants changed by a factor of 5 to 10 between adjacent sample sites which straddle boundaries of the plant communities in which the source plants grow pollen deposition values were high and variable within communities in which the species grew pollen deposition beyond source populations was low and uniform despite great differences in distance of sites from pollen sources the step function that seems to characterize pollen distribution patterns implies that pollen from distant populations may be of little value in interpreting vegetation stability and change reflected by fossil pollen stratigraphy the physical isolation of pollen embedded in the local mountain valley wind system from that in the prevailing westerlies may explain part of the spatial distribution of the pollen

submarine explosive volcanism in the southeastern terceira rift sao miguel region azores abstract morphologic studies with sonar data and in situ observations of modern eruptions have revealed some information suggesting how submarine volcanic cones develop but the information only addresses the modern surfaces of these features here we describe a study combining morphological data with high resolution seismic reflection data collected over cones within the southeastern terceira rift a succession of deep basins volcanic bathymetric highs and islands e g sao miguel representing the westernmost part of the eurasian nubian plate boundary the cones 252 are distributed in depths down to 3200 m and exhibit an average diameter of 743 m an average slope of 20 and heights mainly between 50 and 200 m the cones are here classified into three different categories by physiographic or tectonic setting we find no particular morphometric differences in cone shapes between these areas first numerous cones located at the submarine flanks of sao miguel s sete cidades and fogo volcano are considered to be parasitic structures second in the southeast of the island they form a superstructure possibly reflecting an early submarine stadium of a posterior subaerial stratovolcano third some cones are controlled by faults mostly in a graben system southwest of the island high resolution multichannel seismic data indicates that the graben cones evolved synchronously with the graben formation bottom currents then probably removed the surficial fine grain size fraction leaving rough surface textures of the cones which backscatter sonar signals strongly in the data recorded here however a young cone investigated in detail is characterized by a smooth surface a marked increase of internal stratification with increasing distance from the summit and upwards concave flanks others exhibit central craters suggesting an explosive than an effusive evolution of these structures the morphological characteristics of these submarine cones show that they have similar sizes and shapes to cinder cones onshore sao miguel

stratigraphy petrochemistry and quaternary depositional record of the songaksan tuff ring jeju island korea abstract the songaksan tuff ring str is one of several recent hydrovolcanic centers on jeju island korea which provides an excellent example of proximal to distal facies changes in wet pyroclastic surge deposits a multidisciplinary study has been carried out on the str and adjacent lithostratigraphic units to constrain absolute age geochemical characteristics and quaternary depositional history a number of rock units were identified inside the crater of the str including scoria deposit i trachybasalt lava scoria deposit ii and a late stage basaltic tuff indicative of a rather complex sequence of magmatic and phreatomagmatic eruptions after the construction of the tuff ring petrochemical analysis shows that the str was generated from different magma batches that fractionated from a homogenous magma chamber and the early erupted magma was more evolved and volatile rich reworking of the str commenced shortly after the hydromagmatic eruption in a high energy nearshore environment resulting in deposition of the hamori formation the formation is composed of planar stratified and low to high angle cross stratified tuffaceous pebbly sandstones and occurs up to an altitude of about 4 m above present sea level 14c dating of molluscan shells beneath the formation indicates that it began to be deposited after about 4000 yr bp detailed sedimentary logging reveals that the formation consists of several stratal packages bounded by laterally persistent and distinct lithologic boundaries probably formed by millennial scale sea level fluctuations occurrence of another hydrovolcanic sequence the sinyangri formation on the opposite side of jeju island having similar sedimentary characteristics and ages suggests that the sea level fluctuations as seen in the hamori formation have affected a wide area of jeju island probably related to the high frequency sea level oscillations during the post 6 ka bp regression period in the east asian region it can be concluded that the formation of the str was possible because of the holocene transgression which made the present coastal areas water saturated and adequate for hydrovolcanic eruptions the str in turn contributed to record high frequency sea level fluctuations during the holocene via acting as a local and short lived but affluent source of loose sediment

subglacial intermediate volcanism at kerlingarfjoll iceland magma water interactions beneath thick ice the products of andesite and dacite glaciovolcanism at kerlingarfjoll are unlike others previously described in the literature three sequences of lithofacies are described and interpreted here the andesitic deposits at campsite gully are divided into massive vitriclastic lapilli tuff with intrusions fluidal clast bearing vitriclastic lapilli tuff and stratified pumice rich vitriclastic lapilli tuff at tindur andesitic eruptions produced contorted pillow fragment breccia and the clast supported lithic breccia finally pillow lava with intrusions and crudely bedded vitriclastic lapilli tuff of dacitic composition are described at haraldur abundant vitriclasts the presence of pillow lavas hackly fracturing of lava bodies and lack of oxidation of clasts demonstrate that each of these lithofacies formed in the presence of abundant water this contrasts with all other descriptions of subglacially erupted intermediate magmas which are characterised by jointed and glassy lava flows and domes with a marked scarcity of fragmental material the kerlingarfjoll sequences therefore demonstrate that it is possible for intermediate magmas to generate and interact with significant volumes of water at the base of a glacier preliminary estimates of volatile contents in glassy clasts correspond to quenching pressures equivalent to 500 m water or 550 m ice this is consistent with eruption beneath an ice sheet that was thick enough to overwhelm the underlying topography and where meltwater drainage was controlled by the morphology of the glacier surface it is argued that the drainage of water due to steep topography and or thin and fractured ice as opposed to thermodynamic considerations is the most likely explanation for the absence of evidence for significant magma water interaction in previously described instances of intermediate glaciovolcanism the apparent low viscosity of the kerlingarfjoll magmas may relate to relatively high eruption temperatures and or the inhibition of degassing of the magma due to high ambient pressures and the consequent limitation of groundmass crystallisation

underwater records of submarine volcanic activity el hierro canary islands 2011 2012 eruption abstract we present the monitoring of a submarine volcanic eruption that took place near the southernmost emerged land of el hierro island canary islands spain from october 2011 to february 2012 right after the onset of the eruption in mid october 2011 we deployed an offshore geophone array for the purpose of monitoring the submarine eruptive activity signals it acquired continuous data from october 2011 to may 2012 sometime after the end of the eruption the array consisted of 8 high frequency 3 component geophones assembled into a cable string with 6 m of separation the geophone string was installed in la restinga harbor at a distance of less than 2 km from the volcanic edifice the dataset acquired with the array is a unique continuous acoustic record of the activity associated with this eruption we analyzed the continuous signal of the eruptive activity with special interest in those events reflecting the eruption dynamics our results show that the geophone array was recording acoustic waves from a back azimuth source corresponding to the position of the submarine vent traveling at a speed of 1510 m s compatible with the speed of sound in water acoustic data shows a good correlation with the seismic data recorded on land for the case of earthquake occurrence in addition it provides relevant information towards the understanding of the eruptive surface activity therefore this methodology can be successfully used in cases of submarine eruptions

observations of eruptive plume dynamics and pyroclastic deposits from submarine explosive eruptions at nw rota 1 mariana arc abstract observations at the submarine volcano nw rota 1 mariana arc have provided a unique opportunity to study basaltic explosive eruptions at 550 m below sea level in particular during one week of observations in 2006 the active vent evolved from a region of diffuse gas venting and slow lava effusion to a focused vent that emitted a nearly continuous stream of gas with entrained juvenile pyroclasts the eruptions were small strombolian bursts that ejected bomb sized pyroclasts meters above the vent and produced buoyant plumes that rose tens of meters above the vent and contained variable amounts of ash sampled pyroclasts are dominantly coarse ash and lapilli with fluidal textures that provide evidence of magmatic fragmentation however the blocky morphologies of some clasts combined with visual evidence of secondary fragmentation suggest that quench granulation due to rapid cooling was also important in pyroclast formation rapid cooling is also suggested by the slow rise of buoyant plumes which indicates a low heat content and small density contrast with surrounding seawater rapid plume deceleration in seawater limited deposition of coarse ash lapilli and bombs to within a few meters of the vent and allowed recycling of 15 of the ejected clasts petrologic evidence for pyroclast recycling is provided by numerous microcrystalline inclusions incorporated within microlite poor matrix glass the matrix glass within these inclusions is strongly enriched in chlorine

coastal evolution on volcanic oceanic islands a complex interplay between volcanism erosion sedimentation sea level change and biogenic production abstract the growth and decay of oceanic hotspot volcanoes are intrinsically related to a competition between volcanic construction and erosive destruction and coastlines are at the forefront of such confrontation in this paper we review the several mechanisms that interact and contribute to the development of coastlines on oceanic island volcanoes and how these processes evolve throughout the islands lifetime volcanic constructional processes dominate during the emergent island and subaerial shield building stages during the emergent island stage surtseyan activity prevails and hydroclastic and pyroclastic structures form these structures are generally ephemeral because they can be rapidly obliterated by marine erosion with the onset of the subaerial shield building stage coastal evolution is essentially characterized by rapid but intermittent lateral growth through the formation of lava deltas largely expanding the coastlines until they typically reach their maximum extension with the post shield quiescence in volcanic activity destructive processes gradually take over and coastlines retreat adopting a more prominent profile mass wasting and marine and fluvial erosion reshape the landscape and if conditions are favorable biogenic processes assume a prominent role post erosional volcanic activity may temporarily reverse the balance by renewing coastline expansion but islands inexorably enter in a long battle for survival above sea level reef growth and or uplift may also prolong the island s lifetime above the waves the ultimate fate of most islands however is to be drowned through subsidence and or truncation by marine erosion

trace element abundances in the rock canyon anticline pueblo colorado marine sedimentary section and their relationship to caribbean plateau construction and oxygen anoxic event 2 1 rapid eruption of submarine lava flows during formation of the caribbean plateau correlates closely with ocean anoxic event 2 oae2 which bracketed the cenomanian turonian boundary 93 5 ma these events also correspond with a positive excursion in carbon isotopic composition of seawater hydrothermal activity associated with large scale submarine volcanism may have been responsible for this abrupt change in ocean chemistry we determined the distribution of major minor and trace element abundances in the rock canyon marine sedimentary section pueblo colorado after normalizing element concentrations to zr to remove the variable contribution of terrigenous material to these sediments we detected an interval of concentrated metal abundance anomalies that coincides with the abrupt beginning of the positive 13c isotope excursion the metal abundance anomalies indicate that intermittent hydrothermal activity in the form of both water rock exchange and magmatic degassing introduced large concentrations of trace metals into the cretaceous ocean at the same time that extinctions of benthic species turnover in plankton communities and increases in isotopically light organic carbon burial occurred the stratigraphic position of this interval of trace metal anomalies matches events associated with oae2 and indicates that intermittent hydrothermal activity on a massive scale triggered abrupt changes in carbon burial and deep ocean oxygen contents

structure and eruptive mechanisms at surtsey volcano iceland glassy basalt tuff was the primary material cored in 1979 from a 181 m deep drill hole on the east tuff ring of surtsey volcano despite the fact that the hole extends 122 m below sea level all the core is similar to the exposed tephra composing the two tuff rings of the island the tuff includes abundant accretionary lapilli and tuff vesicles indicating that it was all deposited subaerially during the growth of the tuff rings repeated hydromagmatic explosion cycles began with a series of intermittent tephra finger explosions leading up to continuous uprush explosions which lasted for several minutes to several hours this nozzle like continuous activity produced eruption columns 100 250 m in diameter and 500 2000 m in height which probably quarried several hundred metres below the ground surface the continuous uprush explosion type provides a reasonable mechanism to excavate a diatreme from the top down during construction of the tuff rings concentric faults repeatedly downdropped a funnel like structure 400 800 m in diameter several hundred metres thus accounting for the presence of subaerially deposited tephra in the drill core far beneath sea level ring dykes later intruded upward along these faults and fed small lava flows heat in the surface tephra probably originated primarily from these shallow intrusions