formation of an a ā lava delta insights from time lapse multibeam bathymetry and direct observations during the stromboli 2007 eruption five consecutive multibeam bathymetries collected before during and after the 2007 stromboli eruption combined with visual inspections allowed us to document the morphological evolution of an a lava fed delta and to reconstruct the main processes acting during its submarine emplacement the 2007 stromboli delta extended down to 600 m water depth and covered an area of 420 103 m2 with a maximum thickness of 65 m and a total estimated volume of 7 106 m3 i e three times larger than its subaerial counterpart the lava delta grew mainly through the emplacement of discrete lobes about 50 150 m in size lobes were fed from point sources along the paleoshoreline and their subaqueous pathways seem to be mainly controlled by the submarine morphology with flows mostly filling in depressions left by previous lobes the main controlling factors on the lobe morphology and thickness are the effusion rates and the pre eruption morphology i e the geometry and gradients of the basal surface data also shows that sudden slope failure of portions of the submarine delta may occur simultaneously with accretion implying that a significant part of the delta material can be transported to greater depths by submarine gravity flows the present study is relevant for future monitoring and hazard assessment during the growth of active lava fed deltas as well as for a better interpretation of ancient volcaniclastic successions inland

growth and collapse of the reunion island volcanoes this work presents the first exhaustive study of the entire surface of the reunion island volcanic system the focus is on the submarine part for which a compilation of all multibeam data collected during the last 20 years has been made different types of submarine features have been identified a coastal shelf debris avalanches and sedimentary deposits erosion canyons volcanic constructions near the coast and seamounts offshore criteria have been defined to differentiate the types of surfaces and to establish their relative chronology where possible debris avalanche deposits are by far the most extensive and voluminous formations in the submarine domain they have built four huge submarine bulges to the east north west and south of the island they form fans 20 30 km wide at the coastline and 100 150 km wide at their ends 70 80 km offshore they were built gradually by the superimposition and or juxtaposition of products moved during landslide episodes involving up to several hundred cubic kilometers of material about 50 individual events deposits can be recognized at the surface the landslides have recurrently dismantled piton des neiges les alizes and piton de la fournaise volcanoes since 2 ma about one third are interpreted as secondary landslides affecting previously emplaced debris avalanche deposits on land landslide deposits are observed in the extensively eroded central area of piton des neiges and in its coastal areas analysis of the present day topography and of geology allows us to identify presumed faults and scars of previous large landslides the submarine bulges are dissected and bound by canyons up to 200 m deep and 40 km long filled with coarse grained sediments and generally connected to streams onshore a large zone of sedimentary accumulation exists to the north east of the island it covers a zone 20 km in width extending up to 15 km offshore volcanic constructions are observed near the coast on both piton des neiges and piton de la fournaise volcanoes and are continuations of subaerial structures individual seamounts are present on the submarine flanks and the surrounding ocean floor a few seem to be young volcanoes but the majority are probably old eroded seamounts this study suggests a larger scale and frequency of mass wasting events on reunion island compared to similar islands the virtual absence of downward flexure of the lithosphere beneath the island probably contributes to this feature the increased number of known flank failure events has to be taken into consideration when assessing hazards from future landslides in particular the probability of landslide generated tsunamis

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

radar observations of prevailing winds and waves in the southern hemisphere mesosphere and lower thermosphere hf radar stations utilizing the spaced antenna partial reflection technique located at adelaide 35 s 138 e and mawson station 67 s 63 e have observed horizontal mesospheric winds continuously since mid 1984 observations in the period 1984 87 are compared with the northern hemisphere latitude conjugate stations of kyoto 35 n 136 e and poker flat 65 n 147 w and with satellite derived circulation models particular reference is made to the equinoctial changeovers in zonal flow and to the temporal and altitude variations in the planetary wave activity at mawson and adelaide

hydroacoustic detection of submarine landslides on kilauea volcano landslides produced at the site where lava flows intothe o cean at kilauea vo lcanohave been detected hy droacoustically up to 10 landslides per day were detected by a hydrophone on the hawaii undersea geo observatory hugo located 50 km south of the entry site the largest of these landslides partly subaerial events known as bench collapses were detected by a network of hydrophones in the eastern pacific 5000 7000 km away from the source the landslides display a characteristic spectral signature eas ily recognizable among other signals such as earthquake t phases and anthropogenic noises the fact that signals are detected at great distances suggests that hydroacoustic de tection of landslides could be a powerful tool in tsunami monitoring and modeling efforts

growth and mass wasting of volcanic centers in the northern south sandwich arc south atlantic revealed by new multibeam mapping new multibeam swath bathymetric sonar data acquired using an em120 system on the rrs james clark ross supplemented by sub bottom profiling reveals the underwater morphology of a not vert similar 12 000 km2 area in the northern part of the mainly submarine south sandwich volcanic arc the new data extend between 55 45 s and 57 20 s and include protector shoal and the areas around zavodovski visokoi and the candlemas islands groups each of these areas is a discrete volcanic center the entirely submarine protector shoal area close to the northern limit of the arc forms a 55 km long east west trending seamount chain that is at least partly of silicic composition the seamounts are comparable to small subaerial stratovolcanoes in size with volumes up to 83 km3 indicating that they are the product of multiple eruptions over extended periods zavodovski visokoi and the candlemas island group are the summits of three 3 3 5 km high volcanic edifices the bathymetric data show evidence for relationships between constructional volcanic features including migrating volcanic centers structurally controlled constructional ridges satellite lava flows and domes and mass wasting of the edifices mass wasting takes place mainly by strong erosion at sea level and dispersal of this material along chutes probably as turbidity currents and other mass flows that deposit in extensive sediment wave fields large scale mass wasting structures include movement of unconsolidated debris in slides slumps and debris avalanches volcanism is migrating westward relative to the underlying plate and major volcanoes are asymmetrical being steep with abundant recent volcanism on their western flanks and gently sloping with extinct eroded volcanic sequences to their east this is consistent with the calculated rate of subduction erosion of the fore arc

the 15 march 2007 explosive crisis at stromboli volcano italy assessing physical parameters through a multidisciplinary approach basaltic volcanoes are dominated by lava emission and mild explosive activity nevertheless many basaltic systems exhibit from time to time poorly documented and little understood violent explosions a short lived multiblast explosive crisis paroxysmal explosion occurred on 15 march 2007 during an effusive eruptive crisis at stromboli italy the explosive crisis which started at 20 38 14 ut had a total duration of 5 min the combined use of multiparametric data collected by the permanent instrumental networks seismic acoustic and thermal records and a field survey carried out immediately after the event enabled us to constrain the eruptive dynamics and quantify physical parameters the eruption consisted of three major pulses in the first lithic blocks and ash were ejected at speeds of 100 155 m s and 130 210 m s respectively the high solid load of the eruptive jet resulted in the partial collapse of the column with the formation of a small volume pyroclastic density current the second 12 s long pulse emitted 2 2 2 7 107 kg of tephra mass discharge rate 1 9 2 3 106 kg s forming a 3 km high convective plume dispersing tephra up to the west coast and a dilute density current with limited dispersal downslope of the craters a final 30 s long phase formed a scoria flow with a volume of 1 5 1 7 104 m3 mass discharge rate 5 9 6 7 105 kg s a total runout of 200 m and a velocity of 45 m s the total gas volume involved in the explosion was 1 3 1 9 104 m3 with an initial overpressure of 7 9 0 4 mpa we compared the 15 march 2007 event with historical paroxysms in particular with that of 5 april 2003 which was remarkably similar

the 1741 oshima oshima eruption extent and volume of submarine debris avalanche oshima oshima is a small volcanic island southwest off hokkaido in japan sea the violent eruption on august 29 1741 caused a sector collapse of the north flank very destructive tsunami with 2000 casualties was also documented but the generation mechanism has been controversial volume of subaerial sector collapse about 0 4 km was considered too small to generate such a devastating tsunami we compile and analyze recently obtained swath bathymetry data around the island the volcano is more than 2 3 km high from ocean bottom with its base diameter of 18 km the total slide volume both subaerial and submarine is estimated as 2 4 km nearly an order of magnitude larger than the subaerial part to the north of island hummocky terrain of debris deposits extends in an area of 69 km with the total volume of 2 5 km a value similar to the total slide volume it is one of the largest debris avalanches in historic time and probably responsible to the tsunami generation

multiple sector collapses at stromboli volcano italy how they work this paper demonstrates that four large sector collapses have affected the nw flank of the stromboli volcano in the past 13 ka alternating with growth phases in order to contribute to the evaluation of the critical conditions which trigger lateral collapses a reconstruction of the geometry of each collapse of the volcano edifice in the four stages that preceded the relative collapse events is also presented and a computation of the landslide volume this reconstruction is based on new field data plotted in three dimensions prior to the initial 13 ka collapse the volcano was 1125 100 m high above sea level the collapse had a volume of 2 23 0 87 km3 whereas the pre collapse volcano volume was 218 8 7 7 km3 the next edifice that failed was 900 70 m high a s l the collapse volume was 1 0 54 km3 with a precollapse volcano volume of 201 4 5 4 km3 the edifice then grew to 1000 60 m a s l the third collapse had a volume of 1 08 0 39 km3 and occurred within a volcano with a volume of 209 1 4 6 km3 this was followed by a new growth phase followed by the last collapse with a volume of 0 73 0 22 km3 the volcano volume was about the same as the present one the present active crater zone is at 780 m a s l in the first three collapses sliding surfaces cut the main magma conduit in the last collapse the upper scarp coincided with the conduit location dyking along a main ne trending weakness zone across the volcano summit exerted a lateral force for collapse inception the decrease of the landslide volumes with the age and the concentric scarps of the four collapses suggest that the younger sliding planes tended to become more superficial and to decrease the areal extent this is interpreted as due to a successively weaker eruptive products from dominantly lavas to dominantly pyroclastics and b the feedback effects between collapses and dykes that injected along the lateral segments of the first collapse slide plane

stability of a collapsing volcano stromboli italy limit equilibrium analysis and numerical modelling abstract stromboli is an active island volcano belonging to the aeolian archipelago italy in the last 13 ka it experienced four lateral collapses affecting its northwestern flank with its most recent volcanic crisis december 2002 associated with landslides and related tsunami events this paper presents the first stability analysis of the stromboli volcanic edifice the main input is the geotechnical model of the volcano defined on the basis of stratigraphical lithological material properties and structural data collected from in situ surveys and laboratory tests two dimensional stability analysis was performed by limit equilibrium methods lem and finite difference modelling flac 4 0 code mainly focusing on the subaerial part of stromboli s nw flank sciara del fuoco the variability of the safety factor was studied by deterministic sensitivity and probabilistic analysis focusing on the effect of external forces such as magma pressure and seismicity as potential triggering mechanisms of lateral collapse the lem analyses were developed considering a maximum depth of 150 350 m for the sliding surface to which correspond collapse volumes of 95 000 185 000 m 3 m respectively the study shows that without external forces the investigated rock mass is stable and that the tectonic seismicity of the area alone does not destabilize the studied slope on the contrary magma pressure in dykes can represent a destabilizing factor numerical modelling results are concordant with those from lem in addition the simulation reveals that deformations and superficial landslides preannounce and contribute to retrogressive plasticization and maybe to failure surface deepening shallow submarine landslides represent a possible triggering mechanism and the landslide events of 30 december 2002 consistently fit the simulated evolution flac has revealed to be a useful tool for modelling such a complex system it allowed to calibrate the response of the geotechnical model test the validity of the assumptions simulate the stress strain evolution and prepare a possible model for future scenarios

offshore evidence of large scale lateral collapses on the eastern flank of stromboli italy due to structurally controlled bilateral flank instability abstract new detailed swath bathymetry and long range side scan sonar data on the submerged flanks of stromboli integrated with seismic data and seabed sampling indicate that repeated lateral instability processes occurred on the eastern flank of the volcano although no debris avalanche deposits were known before the high resolution exploration of the seabed this flank of the island is opposite to the northwestern side more evidently affected by repeated flank collapses and this setting is evidence for a structurally controlled bilateral flank instability of the volcanic edifice evidence of at least two large scale lateral collapses is represented by a superficial hummocky megablock field partially outcropping on the middle lower eastern submerged slope and by a chaotic unit estimated volume is 1 2 km3 actually embedded within the volcaniclastic sequence at the foot of the submerged flank a main submarine scar open towards the se is carved in the upper slope on the eastern flank of the island being partially filled with gravity flow deposits owing to the present day depositional setting of the volcano s submerged flank a morphological continuity can be envisaged between this submerged scar and an inferred subaerial one likely encompassing the rina grande depression and several minor nested landslide scars recognized on the eastern stromboli flank a spatial and temporal reconstruction of possible events is proposed the chaotic debris avalanche unit buried within the volcaniclastic apron at the slope base and partially reworked in its distal part within the stromboli canyon floor is thought to be the result of a lateral collapse event called paleostromboli lateral collapse plc as it likely occurred in the earlier stages of the subaerial development of the island affecting a wide sector of the eastern stromboli flank the megablock field might instead result from a more superficial debris avalanche deposit partially eroded by gravity flows currently acting on the seabed it is tentatively related to the recent subaerial scar morphologies affecting the vancori units and for this reason named vancori lateral collapse vlc displaced materials have lower volume and mobility than the plc

development of volcanic insular shelves insights from observations and modelling of faial island in the azores archipelago a variety of geological processes contribute to the development of volcanic island shelves although their relative importance remains unclear we have mapped the morphology of faial island s shelf in the azores from geophysical multibeam sonar chirp and boomer seismic reflection and geological data sediment sampling a wave erosional model and a eustatic record of glacially induced oscillations of sea level which modulated the elevation at which the waves operated through time was used to determine the contribution of mechanical wave erosion to shelf development wave regimes varied according to the orientation of the coast the model was run for 10 to 800 ka depending on the age of the various coastal sectors based on published radiometric data the modelling replicated the shape of the island s shelf reasonably well supporting the contention that it developed primarily through mechanical wave erosion operating in an intertidal zone that migrated landwards and seawards with changes in the level of the sea disparities between modelled and actual shelf morphologies may reflect varied geological resistance to erosion errors in the radiometric dates more recent unrecognised volcanic deposits sediment deposition and tectonic vertical movements there were some variation in rates of shelf development over different time scales but over the long term the relationship between shelf age and width was essentially linear the depth of the shelf break in some areas suggests that there have been differential vertical movements of the land around the island probably related to local faults the poor development or absence of terraces on the shelf may be attributed either to recent volcanic progradation or to sediment infilling of the space created by earlier erosion however poorly developed terraces on the southern shelf of faial are similar to those predicted by the model given appropriate adjustments for vertical movements of the land

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

large scale active slump of the southeastern flank of pico island azores we report evidence for ongoing lateral slump of part of the southeastern flank of the pico volcanic ridge in the azores data from a high resolution digital elevation model field work gps and radar interferometry show that 1 the slumping sector is several cubic kilometers in size 2 the structure involves several curved scars with normal fault kinematics 3 the central part is undergoing little horizontal displacement toward the southeast 1 6 1 3 mm yr but significant downward movement 5 12 mm yr and 4 the outer part of the southeastern flank of pico is subsiding faster than the inner parts this likely reflects recent individualization of a steep seaward dipping fault in the moving mass the slump shares similarities with active slumps recognized elsewhere although the studied area may represent only the proximal part of a much larger complex potentially affecting the deep submarine base of the island displacement of the subaerial part of the southeastern flank of pico seems to be accommodated by the movement and rotation of large blocks along listric normal faults

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

the landslides and tsunamis of the 30th of december 2002 in stromboli analysed through numerical simulations on the 30th of december 2002 two tsunamis were generated only 7 min apart in stromboli southern tyrrhenian sea italy they represented the peak of a volcanic crisis that started 2 days before with a large emission of lava flows from a lateral vent that opened some hundreds of meters below the summit craters both tsunamis were produced by landslides that detached from the sciara del fuoco this is a morphological scar and is the result of the last collapse of the northwestern flank of the volcanic edifice that occurred less than 5 ka b p the first tsunami was due to a submarine mass movement that started very close to the coastline and that involved about 20 106 m3 of material the second tsunami was engendered by a subaerial landslide that detached at about 500 m above sea level and that involved a volume estimated at 4 9 106 m3 the latter landslide can be seen as the retrogressive continuation of the first failure the tsunamis were not perceived as distinct events by most people they attacked all the coasts of stromboli within a few minutes and arrived at the neighbouring island of panarea 20 km ssw of stromboli in less than 5 min the tsunamis caused severe damage at stromboli

the role of nonquasigeostrophic forcing in southern hemisphere blocking onsets abstracta generalized frictionless adiabatic geostrophic zonal wind tendency equation is derived to diagnose the nonquasigeostrophic forcings to blocking onset in the southern hemisphere through case study and composite analysis in general the quasigeostrophic model is capable of representing the key physical processes associated with blocking onset in the troposphere reasonably well in most blocking cases the consideration of nonquasigeostrophic forcings moderately improves the quasigeostrophic representation in a majority of the blocking events selected for this study but not all events this suggests that the nonquasigeostrophic terms could be important in a specific blocking event but not in a composite meaning furthermore the nonquasigeostrophic forcing of geostrophic advection of ageostrophic relative vorticity term is extensively examined in this study this forcing is found to be the leading nonquasigeostrophic forcing term among all nonquasigeostrophic forcings in a composite sense th

lava delta deformation as a proxy for submarine slope instability abstract the instability of lava deltas is a recurrent phenomenon affecting volcanic islands which can potentially cause secondary events such as littoral explosions due to interactions between hot lava and seawater and tsunamis it has been shown that interferometric synthetic aperture radar insar is a powerful technique to forecast the collapse of newly emplaced lava deltas this work goes further demonstrating that the monitoring of lava deltas is a successful strategy by which to observe the long term deformation of subaerial submarine landslide systems on unstable volcanic flanks in this paper displacement measurements derived from synthetic aperture radar sar imagery were used to detect lava delta instability at stromboli volcano italy recent flank eruptions 2002 2003 2007 and 2014 affected the sciara del fuoco sdf depression created a stacked lava delta which overlies a pre existing scar produced by a submarine subaerial tsunamigenic landslide that occurred on 30 december 2002 space borne x band cosmo skymed csk and c band sentinel 1a snt sar data collected between february 2010 and october 2016 were processed using the squeesar algorithm the obtained ground displacement maps revealed the differential ground motion of the lava delta in both csk and snt datasets identifying a stable area characterized by less than 2 mm y in both datasets within the northern sector of the sdf and an unstable area characterized by velocity fields on the order of 30 mm y and 160 mm y in the csk and snt datasets respectively in the central sector of the sdf the slope stability of the offshore part of the sdf as reconstructed based on a recently performed multibeam bathymetric survey was evaluated using a 3d limit equilibrium method lem in all the simulations factor of safety f values between 0 9 and 1 1 always characterized the submarine slope between the coastline and 250 m a s l the critical surfaces for all the search volumes corresponded to the 30 december 2002 landslide which involved the lava delta and its surrounding areas insar data provided the post effusive deformation field after the 2007 and 2014 flank eruptions whereas lem results highlighted that the accumulation of lava flows on the prone to failure sdf submarine slope is the main cause of the detected lava delta deformation lava delta instability measured also at pico island azores and kilauea volcano hawaii is evidence of the broader spectrum of instability phenomena that take place in the coastal or submarine area of the flanks of the volcanoes at kilauea past lava deltas have moved faster than the surrounding slope and the recorded movements relate only to the collapses of the deltas themselves producing rapid mass wasting near the coasts in contrast at stromboli and pico lava deltas move at the same velocity as the surrounding slope in these cases the displacement at lava deltas can be considered as a proxy for the deformation of submarine slides there are very few studies dealing with lava delta deformation thus the analysis presented in this work will benefit the monitoring of submarine slopes in other prone to failure coastal or island volcanic systems which have the potential to generate tsunamis

submarine depositional terraces in the tyrrhenian sea as a proxy for paleo sea level reconstruction problems and perspective abstract in the last decade great effort was put in the study of relative sea level changes on mediterranean coastlines through the integration of geophysical modelling and proxy data of paleo shorelines in this paper we show potential and limitations of using additional marine geomorphic sedimentary markers for earlier and lower sea levels these markers are submarine depositional terraces sdts i e deposits formed by a set of small prograding sedimentary wedges having a terraced shape and found at variable shallow water depths mainly the first 150 m on continental and insular shelves in the tyrrhenian sea the shallowest terraces near shore have their edges at depths between 10 m and 30 m approximating the modern local storm wave base level their formation is thought to be associated with the modern sea level highstand and thus can be used as the modern analogue for deeper terraces formed in the past when the sea level was on the middle and outer shelf mid shelf terraces have their edges at variable depths between 40 m and 90 m and probably formed during the last sea level rise they show a patchy spatial distribution and a large variability in their internal structure so that they are not suitable for correlation on a regional scale shelf edge terraces have their edges at depths between 120 m and 170 m which is close or deeper than the last glacial maximum lgm sea level stand they show a remarkable lateral continuity and a prograding internal structure similar to those at shallower depth and thus represent a proxy for the sea level position at around 20 ka however the position of sdts edges is not a direct measure of paleo sea level positions because their depth depends on a complex interplay of several factors such as the base of the storm wave and its variation in response to coastal physiography as well as the occurrence of subsequent erosional or depositional processes depending on the geophysical and mapping methods used to determine their depth the associated error range can also differ based on the analysis of these complexities and a wide range of physiographic settings of the tyrrhenian sea we discuss these error ranges in order to assess potential and limitation of the sdt for analyses of vertical mobility of an area

paroxysmal activity at stromboli lessons from the past the persistent normal activity of stromboli is occasionally interrupted by sudden and highly energetic explosive events called strombolian paroxysms these phenomena together with landslide generated tsunamis represent the most hazardous manifestations of present day volcanic activity at stromboli the most recent paroxysms on 5 april 2003 and 15 march 2007 have drawn attention to these energetic events because they significantly threatened inhabitants and tourists historical accounts and field evidence indicate however that even larger paroxysms in terms of volume dispersal of products and intensity of explosive phenomena occurred in the recent past during these paroxysms incipiently welded spatter deposits mantled the north and south rims of the sciara del fuoco down to low elevations extending much farther than the similar deposits from recent observed events 5 april 2003 and 15 march 2007 in order to identify characterize and discriminate among products of these outstanding spatter forming eruptions more than 50 stratigraphic sections were measured and sampled stratigraphic sedimentological and radiometric 14c data indicate that only two paroxysms produced spatter that reached very low elevations and inhabited areas the first occurred in the 16th century and the last in ad 1930 analysis of texture and deposit components reveals that the early phases of the two eruptions were driven by distinctly different eruptive dynamics both identified paroxysms are at least one order of magnitude greater than any similar event observed by monitoring systems at stromboli these two large paroxysms were the most powerful volcanic events at stromboli in the last eighteen centuries

the 2007 stromboli eruption event chronology and effusion rates using thermal infrared data accepted for publication in journal of geophysical research copyright 2009 american geophysical union further reproduction or electronic distribution is not permitted

dynamics of the december 2002 flank failure and tsunami at stromboli volcano inferred by volcanological and geophysical observations 1 the 2002 effusive flank eruption at stromboli volcano started on december 28 after several months of strong explosive activity at the summit craters on december 30 the seismic network recorded two large flank failures and associated tsunami waves this is the first time that a flank collapse and tsunami and their associated phenomena have been recorded by a multi disciplinary monitoring system volcanological and geophysical monitoring as well as thermal surveys performed immediately before and after the failure allowed us to define and interpret the sequence of events the still on going eruption has provided for the first time the opportunity to look into the dynamics of stromboli s effusive eruptions flank failure and landslide formation and their potential hazard

large scale catastrophic flank collapses in a steep volcanic ridge the pico faial ridge azores triple junction abstract large scale flank collapses are common in the geological evolution of volcanic ocean islands in the atlantic to date catastrophic lateral collapses in the azores islands have been difficult to identify leading to suggestions that a lack of events may relate to the relatively small size of the islands here we show evidence for two major collapses on the northern flank of pico island pico faial volcanic ridge central azores suggesting that this island had a collapse incidence similar to that of other atlantic volcanic islands the study is based on the analysis of 1 offshore and onshore high resolution digital elevation models 2 field data focused on the n flank and 3 new k ar ages on selected lava flow samples pico sub aerial northern flank is marked by two conspicuous arcuate shaped depressions concave towards the sea here interpreted as landslide scars a main debris field is observed offshore the largest depression this deposit has 20 km of maximum length covers ca 150 km2 is composed of meter to hectometer blocks and has an exposed volume here estimated between 4 and 10 km3 though the actual volume probably exceeds 10 km3 debris flow towards the ese was apparently determined by the slope of the narrow wnw ese s jorge channel young lava flows cascade over the interpreted scars thus concealing the older volcanic sequence s affected by the landslide s new k ar ages measured on these lava flows provide a minimum age of ca 70 ka for the large scale collapse s in pico s northern flank

the evolution of the sciara del fuoco subaerial slope during the 2007 stromboli eruption relation between deformation processes and effusive activity abstract focusing on the island of stromboli this research investigates whether airborne remote sensing systems such as those based on digital photogrammetry and laser scanner sensors can be adopted to monitor slope deformation and lava emplacement processes in active volcanic areas thanks to the capability of extracting accurate topographic data and working on flexible time schedules these methods can be used to constrain the regular and more frequent measurements derived from satellite observations this work is dedicated to the monitoring of stromboli s volcanic edifice which is beneficial when obtaining quantitative data on the geometry of deformation features and the displaced failures and landslides and emplaced lava flows volumes in particular we focus on the capability of extracting average effusion rates from volume measurements that can be used to validate or integrate satellite derived estimates since 2001 a number of airborne remote sensing surveys namely digital photogrammetry dp and airborne laser scanning als have been carried out on stromboli s volcano to obtain high resolution digital elevation models dem and orthophotos with sub meter spatial resolution and a time schedule suitable for monitoring the morphological evolution of the surface during the quiescent phases during the last two effusive eruptions 2002 2003 and 2007 the surface modifications created on the sciara del fuoco slope and on the crater area as a consequence of effusive activity were quantified and monitored using the same methodologies this work which is based on the results obtained from the multi temporal quantitative analysis of the data collected from 2001 to 2007 mainly focuses on the 2007 eruption but also accounts for analogies and differences regarding the 2002 2003 event the 2007 eruption on the sciara del fuoco slope from 27 february until 2 april produced a compound lava field including a lava delta on the shoreline discharging most of the lava into the sea the comparison of the 2007 dems with a pre eruption surface 2006 lidar survey allowed for the evaluation of the total lava volume that accumulated on the subaerial slope while two syn eruption dems were used to calculate the average effusion rates during the eruption since the evolution of a lava field produced during an eruption can be seen as a proxy for the magma intrusion mechanism hypotheses are formulated on the connection between the lava discharge and the instabilities suffered by the slope

hydroacoustic investigation of submarine landslides at west mata volcano lau basin submarine landslides are an important process in volcano growth yet are rarely observed and poorly understood we show that landslides occur frequently in association with the eruption of west mata volcano in the ne lau basin these events are identifiable in hydroacoustic data recorded between 5 and 20 km from the volcano and may be recognized in spectrograms by the weak and strong powers at specific frequencies generated by multipathing of sound waves the summation of direct and surface reflected arrivals causes interference patterns in the spectrum that change with time as the landslide propagates observed frequencies are consistent with propagation down the volcano s north flank in an area known to have experienced mass wasting in the past these data allow us to estimate the distance traveled by west mata landslides and show that they travel at average speeds of 10 25 m s

the stromboli 2002 tsunamigenic submarine slide characteristics and possible failure mechanisms 1 on 30 december 2002 a major instability event deeply involving the submarine slope occurred on the sciara del fuoco on the western flank of stromboli volcano in the aeolian islands tsunami waves with a maximum runup of over 10 m in stromboli were generated having a measurable impact as far as the sicily coast just 10 months before the event a multibeam bathymetry had been collected in the area down to 1000 m of depth a repetition of the survey after the slide allowed the unique opportunity to verify the occurrence of a large submarine slide and to define volumes involved and morphology generated by the event through the comparison of the preevent and postevent bathymetric grids a morphological characterization of the slope before and after the submarine landslide is presented showing how the preexisting features interacted with the slide event in controlling the instability mechanisms of the submarine failure are discussed on the basis of the geometrical characters of the landslide event structural and stratigraphic setting of the submerged slope and geotechnical considerations on the behavior of slope material

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

the 1883 eruption of krakatau the 1883 eruption of krakatau was a modest ignimbrite forming event the deposits are primarily coarse grained dacitic non welded ignimbrite large explosions produced pyroclastic flows that entered the sea generating destructive tsunami grain size studies of the ignimbrite suggest that these explosions were not driven by magma seawater interaction the total bulk volume of pyroclastic deposits including co ignimbrite ash is estimated to be 18 21 km3

island edifice failures and associated tsunami hazards volcanic ocean islands are prone to structural failure of the edifice that result in landslides that can generate destructive tsunamis these island landslides range enormously in size varying from small rock falls to giant sector failures involving tens of cubic kilometers of debris a survey of literature has allowed us to identify twenty three processes that contribute to edifice collapse these have been divided into endogenetic and exogenetic sources of edifice failure endogenetic sources of instability and failure include unstable foundations volcanic intrusions thermal alteration edifice pore pressures unbuttressed structures and buried faults exogenetic sources of instability and failure include collapse of subaerial or submarine deposits endo upwelling karst megaporosity fractures oversteepening overloading sea level change marine erosion weathering including hurricanes glacial response volcanic activity regional uplift or subsidence tectonic seismicity and anthropogenic agents while the endogenetic sources dominate during periods of active volcanism and cone building the exogenetic sources may cause failure at any time tsunamis both small and large are associated with these edifice failures

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

direct sediment transfer from land to deep sea insights into shallow multibeam bathymetry at la reunion island abstract submarine canyon heads are key areas for understanding the triggering factors of gravity currents responsible for the transfer of detrital sediment to the deep basins this contribution offers a detailed picture of canyon heads off la reunion island with high resolution multibeam bathymetry in the water depth range of 4 220 m the present feeding of the cilaos turbidite system one of the largest modern volcaniclastic systems in the world is deduced from morphological and sedimentological interpretations of newly acquired data the study highlights small scale sedimentary features indicating hydrodynamic and sedimentary processes a direct connexion between the saint etienne river mouth and submarine canyons is evidenced by the complete incision of the shelf and the presence of canyon heads connected to the modern deltaic bar this direct connection supplied by river torrential floods cyclonic floods every two or three years suggests the continuity of high density fluvial flows to submarine gravity flows forming hyperpycnal flows in the canyon the initiation of secondary submarine gravity flows by storm waves large austral waves and cyclonic waves is also proposed for submarine canyons with large canyon heads developed in the surf zone from a sandy coastal bar bedforms in active canyon axis are considered as an indicator of the frequent activity of high density turbidity currents moreover a morphological record of last glacial and deglacial sea level variations is preserved and particularly the last glacial maximum sea level with the presence of small vertical cliffs observed in this bathymetric data which likely corresponds to a paleo shoreline or paleo reefs

geomechanical characterization of the volcaniclastic material involved in the 2002 landslides at stromboli during the 2002 eruption the nw flank of stromboli volcano southern italy experienced large landslides that produced tsunami waves with a maximum runup of 10 m in height this paper focuses on the geomechanical behavior of the loose volcaniclastic layers the weakest component of the deposit forming the volcano flank tests on the coarse grained volcaniclastic soil and on the rock material forming the grains were conducted in dry conditions a feature of the subaerial slope the rock material in spite of its high porosity exhibits relatively high stiffness and strength due to the remarkable continuity of the solid skeleton accordingly the volcaniclastic soil is characterized by high shear strength during shear tests however significant grain crushing occurs which partly explains the nonlinear shear strength envelope and the strain softening associated with contractive behavior grain crushing was also found to affect compressibility and its time dependency investigated under oedometric conditions

observations of physical effects from tsunamis of december 30 2002 at stromboli volcano southern italy on december 30 2002 following an intense period of activity of stromboli volcano south tyrrhenian sea italy complex mass failures occurred on the northwest slope of the mountain which also involved the underwater portion of the volcanic edifice for a total volume of about 2 3 107 m3 two main landslides occurred within a time separation of 7 min and both set tsunami waves in motion that hit the coasts of stromboli causing injuries to three people and severe damage to buildings and structures the tsunamis also caused damage on the island of panarea some 20 km to the sse from the source they were observed all over the aeolian archipelago at the island of ustica to the west along the northern sicily coasts to the south as well as along the tyrrhenian coasts of calabria to the east and in campania to the north this paper presents field observations that were made in the days and weeks immediately following the events the results of the quantitative investigations undertaken in the most affected places namely along the coasts of stromboli and on the island of panarea are reported in order to highlight the dynamics of the attacking waves and their impact on the physical environment on the coastal structures and on the coastal residential zone in stromboli the tsunami waves were most violent along the northern and northeastern coastal belt between punta frontone and the village of scari with maximum runup heights of about 11 m measured on the beach of spiaggia longa measured runups were observed to decay rapidly with distance from the source typical of tsunami waves generated by limited area sources such as landslides

characterisation of a volcanic residual soil and its implications for large landslide phenomena application to tenerife canary islands large landslides are common processes during the evolution of volcanoes and individual events can exceed several cubic kilometres in volume volcanic slope failures are a significant risk for the neighbouring population due to their huge volumes and great runout distances around the canary archipelago a total of seventeen deposits of large landslides have been found and on tenerife seven large landslides have affected the subaerial and submarine morphology during the last 6 ma however the causes of such mass movements are still poorly understood this work analyses the events around the canary islands and focuses on the ones that occurred on tenerife in order to obtain new insights into the mechanisms of large volcanic landslides the study is divided into a first part that includes site investigations examining the general features favouring large scale failures at volcanoes the second part describes the laboratory tests used to analyse a residual soil that may be the potential slip surface of the slides on tenerife the site investigation revealed that regional tectonics and the climate have a significant influence on the spatial distribution of the landslides moreover morphological and geological features such as deep fluvial canyons a high coastal cliff and persistent dike intrusion may favour the initiation of slope failure a typical residual soil sample from the lateral scarp of the la orotava amphitheatre on tenerife was studied by carrying out standard laboratory tests the microstructure was analysed using environmental scanning electron microscopy and a particular bonding was found this bonding was also detected by the geotechnical tests consolidation tests and direct shear tests revealed that the mechanical behaviour of the residual soil changes greatly if the bonding of the soil is broken the bonded structure generally fails when the effective normal stress surpasses the yield strength of the bonding in the case of large volcanic landslides with thicknesses up to several hundred meters the high overburden easily exceeds this yield strength and generates a broken bonding therefore volcanic residual soils such as the one analysed in this study are perfect candidates for the potential failure surfaces of large volcanic landslides referring to the la orotava events we assume that residual soil layers and morphological geological and climatic features reduced the slope stability to critical conditions whereas a strong earthquake associated with a caldera collapse episode may have finally triggered the landslide the results obtained indicate that the residual soils play an important role in affecting the stability of volcano slopes and their destabilising influence significantly favours large scale sliding we suggest that the results obtained from this study can be applied to other locations since volcanic residual soils are common in volcanic areas

entrance of hot pyroclastic flows into the sea experimental observations the entrance of hot pyroclastic flows into water has been observed in a series of experiments in which shooting granular flows of hot ignimbrite ash 403 c of bulk density near that of water run down a smooth chute and enter a water filled tank at an angle of 26 flows of relatively cool ash 250 c mixing across the water surface over some distance from shore generates steam explosions forming fountains of wet and dry ash and convectively rising fine ash plumes steam explosions increase in strength and lateral extent towards higher ash temperatures and mass fluxes the explosions generate water waves that remain driven by massive fountain fallout across some distance from shore the ash fountains feed pyroclastic surges which advance down tank over water at high speeds underwater plumes of sediment falling from the ash fountains and surges drop coarse load onto the floor whereas the finer load forms a turbidity current high temperature and poor size sorting of pyroclastic flows are key parameters that determine the processes of interaction with water and the associated hazards poor sorting allows for the formation of ash cloud surges moving over water even from cool flows high temperatures cause littoral explosions and facilitate extensive mass transport over water all flows generate tsunami waves by different mechanisms

sector collapse sedimentation and clast population evolution at an active island arc volcano stromboli italy sciara del fuoco is the subaerial part of a partially filled sector collapse scar that extends to 700 m below sea level on stromboli volcano the collapse occurred 2200 m and 10 km from the shore to the nnw a fan shaped mounded feature comprises debris avalanche deposits 4 km3 from two or more sector collapses volcaniclastic density currents originating from sciara del fuoco follow the topographic margin of the debris avalanche deposits although overbank currents and other unconfined currents widely cover the mounded feature with turbidites historical recorded eruptive activity in sciara del fuoco is considerably less than that which occurred earlier and much of the partial fill may have formed from eruptions soon after the sector collapse it is possible that a mass of eruptive products similar to that in the collapse scar is dispersed as volcanogenic sediment in deep water of the tyrhennian basin evidence that the early post collapse eruptive discharge was greater than the apparent recent flux 2kg s counters suggestions that a substantial part of stromboli s growth has been endogenous the partial fill of sciaria del fuoco is dominated by lava and spatter layers rather than by the scoria and ash layers classically regarded as main constituents of strombolian cinder cones much of the volcanic slope beneath the vents is steeper than the angle of repose of loose tephra which is therefore rapidly transported to the sea delicate pyroclasts that record the magmatic explosivity are selectively destroyed and diluted during sedimentary transport mainly in avalanches and by shoreline wave reworking and thus the submarine deposits do not record well the extent and diversity of explosive activity and associated clast forming processes considerable amounts of dense non vesicular fine sand and silt grains are produced by breakage and rounding of fragments of lava and agglutinate the submarine extension of the collapse scar and the continuing topographic depression to 2200 m below sea level are zones of considerable by passing of fine sand and silt which are transported in turbidity currents evidently volcanogenic sediments dispersed around island volcanoes by density currents are unlikely to record well the true spectrum and relative importance of clast forming processes that occurred during an eruption marine sedimentary evidence of magmatic explosivity is particularly susceptible to partial or complete obliteration unless there is a high rate of discharge of pyroclastic material into the sea

tsunamis in the aeolian islands southern italy a review the aeolian islands located in the south tyrrhenian sea to the west of calabria and to the north of sicily constitute the aeolian volcanic arc characterized by a relevant volcanic activity with an established tsunamigenic potential according to the documentary sources that are available for the aeolian tsunamis and that cover unfortunately only about the last 100 years stromboli is responsible for the majority of the events some cases are also known to have occurred at the islands of salina and vulcano in terms of intensities the most destructive events are those originated by the stromboli volcano reported to have produced severe destruction to boats and houses and to have even caused injuries and fatalities in this work we focus on the historical events and discard the paleotsunami occurrences that were probably associated with the ascertained flank collapses of the volcanic cones we also neglect the recent destructive tsunamis of 30 december 2002 which were caused by a series of mass failures at the sciara del fuoco since observations and analyses are of such an amount that deserve to be illustrated in devoted papers the bulk of the present research consisted in collecting all the available data on the historical cases the first in order of time is the july 1916 stromboli tsunami with the purpose of casting more light on their generation mechanism and on their effects and consequently of contributing to the studies on assessment of tsunami hazard and risk in the aeolian islands and in the southern tyrrhenian sea

the 1998 casita volcano flank failure revisited new insights into geological setting and failure mechanisms abstract a flank collapse occurred at the casita volcano in nicaragua on 30 october 1998 during hurricane mitch the collapse transformed into a disastrous lahar that completely buried two small towns 6 km downstream killing about 2500 people destroyed small settlements and disrupted the pan american highway based on the knowledge acquired during previous investigations with additional unpublished field data and observations this study provides a comprehensive review of all previous studies published and unpublished on the 1998 casita lahar and new insights into the initial flank collapse and the current stability the knowledge on pre and post failure geometry geology lithology tectonics and stratigraphy of the scarp area is improved and a summary of available geotechnical data is provided lithological characteristics that were significant in the initial flank collapse and failure mechanism were identified the location of the failure surface was more precisely defined and the number and sequence of stages in the initial failure presented in previous studies have been confirmed slope stability analyses were carried out using limit equilibrium methods geological interpretations analysis of digital elevation models and geotechnical back analyses confirmed that the flank collapse took place in three stages involving both the northern and southern areas of the scarp and occurred continuously during a time interval of seconds to a few minutes in the first stage failure initiated in a highly fractured and altered volcanic breccia in the northern area of the scarp which released a volume of 260 000 m3 the flow that developed from this failure removed colluvium deposits at the toe of the slope in the southern part in not more than 40 s this rapid removal of the colluvium triggered a second stage which comprised 640 000 m3 and consisted in the failure of the southern part of the scarp by the sliding of a fractured volcanic breccia over a unit of clay rich pyroclastic deposits the third and final stage consisted in a failure of the remaining breccia and the overlying fractured lavas in the northern area and involved a volume of 690 000 m3 the fact that future events can affect some remaining settlements and the segment of the pan american highway between chinandega and leon motivated an analysis of the stability of the remaining slope using parameters calibrated in the back analyses of the 1998 flank failure the results indicated that the remaining slope is stable as long as groundwater levels in the northern and southern area are deeper than 65 m and 90 m respectively relative to the points of maximum elevation on the analysed section and the colluvium deposits in the southern area are not removed from the toe of the slope

volcano tectonic controls and emplacement kinematics of the iriga debris avalanches philippines mt iriga in southeastern luzon is known for its spectacular collapse scar that was possibly created in 1628 ad by a 1 5 km3 debris avalanche the debris avalanche deposit dad covered 70 km2 and dammed the barit river to form lake buhi the collapse has been ascribed to a non volcanic trigger related to a major strike slip fault under the volcano using a combination of fieldwork and remote sensing we have identified a similar size older dad to the southwest of the edifice that originated from a sector oblique to the underlying strike slip fault both deposits cover wide areas of low waterlogged plains to a distance of about 16 km for the oldest and 12 km for the youngest hundreds of metre wide and up to 50 m high hummocks of intact conglomerate sand and clay units derived from the base of the volcano show that the initial failure planes cut deep into the substrata in addition large proportions of both dad consist of ring plain sediments that were incorporated by soft sediment bulking and extensive bulldozing an ignimbrite unit incorporated into the younger dad forms small less than 5 m high discrete hummocks between the larger ones both debris avalanches slid over water saturated soft sediment or ignimbrite and spread out on a basal shear zone accommodated by horst and graben formation and strike slip faults in the main mass the faults are listric and flatten into a well developed basal shear zone this shear zone contains components from the substrate and has a diffuse contact with the intact substrata long transport normal ridges in the distal parts are evidence of compression related to deceleration and bulldozing the collapse orientation and structure on both sectors and dad constituents are consistent with collapse being a response to combined transtensional faulting and gravity spreading iriga can serve as a model for other volcanoes such as mayon that stand in sedimentary basins undergoing transtensional strike slip faulting

la fossa caldera breaching and submarine erosion vulcano island italy abstract la fossa caldera lfc on vulcano island in the aeolian archipelago italy is a multi collapse caldera whose north eastern part lies underwater through the integration of marine geophysical surveys and sampling carried out in the last decade its submarine extension and offshore areas have been reconstructed in unprecedented detail strong erosive processes breached the submarine portion of lfc and gradually dismantled the caldera rims and infill leading to the emplacement of a wide volcaniclastic fan from the base of lfc down to over 1000 m the bathy morphologic setting seismoacoustic facies and analyses of sediment samples from the fan together with volumetric considerations suggest that this feature is the pathway deposit of submarine unconfined gravity flows and turbidity currents deriving from the gradual dismantling of lfc submarine erosive processes are still active and the progressive erosion of the northern caldera sector threatens the stability of the active la fossa cone and the nearby coastal settlements

the 15 march 2007 paroxysm of stromboli video image analysis and textural and compositional features of the erupted deposit on 15 march 2007 a paroxysmal event occurred within the crater terrace of stromboli in the aeolian islands italy infrared and visible video recordings from the monitoring network reveal that there was a succession of highly explosive pulses lasting about 5 min from at least four eruptive vents initially brief jets with low apparent temperature were simultaneously erupted from the three main vent regions becoming hotter and transitioning to bomb rich fountaining that lasted for 14 s field surveys estimate the corresponding fallout deposit to have a mass of 1 9 107 kg that coupled with the video information on eruption duration provides a mean mass eruption rate of 5 4 105 kg s textural and chemical analyses of the erupted tephra reveal unexpected complexity with grain size bimodality in the samples associated with the different percentages of ash types juvenile lithics and crystals that reflects almost simultaneous deposition from multiple and evolving plumes juvenile glass chemistry ranges from a gas rich low porphyricity end member typical of other paroxysmal events to a gas poor high porphyricity one usually associated with low intensity strombolian explosions integration of our diverse data sets reveals that 1 the 2007 event was a paroxysmal explosion driven by a magma sharing common features with large scale paroxysms as well as with ordinary strombolian explosions 2 initial vent opening by the release of a pressurized gas slug and subsequent rapid magma vesiculation and ejection which were recorded both by the infrared camera and in the texture of fallout products and 3 lesser paroxysmal events can be highly dynamic and produce surprisingly complex fallout deposits which would be difficult to interpret from the geological record alone

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

seismic and acoustic signatures of surficial mass movements at volcanoes abstract surficial mass movements such as debris avalanches rock falls lahars pyroclastic flows and outburst floods are a dominant hazard at many volcanoes worldwide understanding these processes cataloging their spatio temporal occurrence and detecting tracking and characterizing these events would advance the science of volcano monitoring and help mitigate hazards seismic and acoustic methods show promise for achieving these objectives many surficial mass movements generate observable seismic and acoustic signals and many volcanoes are already monitored significant progress has been made toward understanding modeling and extracting quantitative information from seismic and infrasonic signals generated by surficial mass movements however much work remains in this paper we review the state of the art of the topic covering a range of scales and event types from individual rock falls to sector collapses we consider a full variety of volcanic settings from submarine to subaerial shield volcano to stratovolcano finally we discuss future directions toward operational seismo acoustic monitoring of surficial mass movements at volcanoes

evolution of a sediment wave in an experimental channel the routing of bed material through channels is poorly understood we approach the problem by observing and modeling the fate of a low amplitude sediment wave of poorly sorted sand that we introduced into an experimental channel transporting sediment identical to that of the introduced wave the wave essentially dispersed upstream and downstream without translation although there was inconclusive evidence of translation late in the experiment when the wave was only 10 20 grain diameters high alternate bars migrated through zones of differing bed load transport rate without varying systematically in volume celerity or transport rate sediment that overpassed migrating bars was apparently responsible for dispersion of the wave the evolution of the wave was well predicted by a one dimensional model that contains no adjusted empirical constants numerical experiments demonstrate however that the theory does not predict sediment waves that migrate long distances downstream such waves can only be explained by the following processes not represented by the theory selective bed load transport spatial variations in bar and other form roughness the mechanics of mobile armor and perhaps other mechanisms

monthly mean winds in the mesosphere at 44s and 78s a medium frequency partial reflection spaced antenna wind radar was installed at scott base 78s on ross island antarctica in november 1982 results from this radar for the period december 1982 to october 1984 inclusive are compared with simultaneous measurements made with a similar radar at christchurch 44s n z monthly mean zonal winds measured at 80 km are compared with recent models for the southern hemisphere middle atmosphere there is a general agreement with the models but there is evidence that the christchurch winter flow was atypical in 1983

gravitational erosional sedimentary and volcanic processes on the submarine environment of selvagens islands madeira archipelago portugal abstract volcanic oceanic islands are the emerged portions of large volcanoes that rise abruptly from the ocean floor although the geological record of these islands provide some insights into the evolution of their entire volcanic edifices for a complete picture it is essential to study the islands submarine pedestals and surrounding settings in this study we document the submarine morphology of the selvagens islands madeira archipelago portugal and relate it with their subaerial evolution in order to gain a more complete insight on the evolutionary history of these islands to this purpose we employed bathymetric surfaces backscatter mosaics and subbottom profiler data integrated with geological observations of the subaerial part of the islands our study reveals the presence of a complex submarine morphology composed mainly of two deeply eroded central volcanoes the edifices of selvagem grande and selvagem pequena and a less eroded saddle like ridge related to a fissural volcanic system located between them other secondary landforms generated by volcanism erosion gravitational collapses and possible faulting activity are also present whilst the building of the two central volcanoes relates to the older volcanic stages of both islands the fissural system with a general ne sw trend is probably contemporaneous of the younger volcanic stages of selvagem grande the shelf of selvagem grande also features the eroded remains of numerous relatively young volcanic cones seemingly forming several nw se and ne sw lineaments the same direction observed onshore for the younger volcanic stage of this edifice the shelves break of both selvagens was affected by multiple landslide scars and channel headwalls the channels constitute a large drainage network that fans out in a radial pattern along the flanks of both central edifices in the deeper parts of this submarine drainage large sediment wave fields are observed in some locations with wavelengths of 300 1 900 m and 2 45 m in height these tend to form cyclic steps that change gradually downslope to antidunes and their origin is attributed to sediment density flows that suffer hydraulic jumps when their channel confinement ends and the slope gradient decreases from 7 to 2 5 several scour features are also found at 3 300 4 000 m water depth being 3 20 km in width 10 20 km in length rectangular or u shaped in cross section and 40 100 m deep they occur around the base of the submarine edifices where seafloor gradients change to 3 0 0 5 their origin is also related to hydraulic jumps of unconfined sediment density flows which are able to erode the seafloor and create these features these morphologies are a testimony to how volcanic erosional and depositional processes conjugate to shape the flanks of a very long lived volcanic island system one of the oldest in the north atlantic ocean

the validity of the geostrophic approximation in the winter stratosphere and troposphere abstract the validity of the geostrophic approximation is examined for the northern hemisphere from the lower troposphere to the stratopause in january using a general circulation model substantial errors are found when the geostrophic winds are compared to the true winds in the stratosphere the errors in the winter stratosphere are in fact much larger than the errors in the troposphere the relative errors in quantities derived from the wind field such as eddy momentum and heat fluxes are found to be even larger than the errors in the zonal wind field the eliasen palm ep flux divergence is now commonly used to diagnose the interactions of the eddies with the mean flow the errors in the quasi geostrophic ep flux divergence am found to be as large or larger than the true divergence in the winter stratosphere the true ep flux from the model is convergent almost everywhere in the stratosphere although observational studies have shown a region of divergence at high latitudes indicating an appare

construction and destruction of a volcanic island developed inside an oceanic rift graciosa island terceira rift azores abstract there is a great lack of knowledge regarding the evolution of islands inside active oceanic rifts in particular the meaning of the different evolutionary steps therefore we conducted an investigation in graciosa island which lies at the northwestern end of the terceira rift in the azores triple junction with the objective of constraining the evolution of the island in terms of volcanic growth and mass wasting in particular the meaning and age of the destruction events from digital elevation model dem analysis stratigraphic and tectonic observations k ar dating on key samples and available bathymetry and gravity data we propose that graciosa comprises five main volcanic complexes separated by major unconformities related to large scale mass wasting 1 the older volcanic edifice serra das fontes complex grew until ca 700 ka and was affected by a major flank collapse towards the southwest which removed the whole sw flank the summit and a part of the ne flank 2 the baia do filipe complex developed between at least 472 ka and 433 ka in two different ways in the sw presently offshore as a main volcano and in the ne unconformably over the sub aerial remnants of the serra das fontes complex as secondary volcanic edifices 3 the baia do filipe complex was affected by a major flank collapse towards the sw again removing most of the edifice 4 the remnants of the baia do filipe complex were covered in unconformity by the serra dormida complex between ca 330 and 300 ka which in turn was unconformably covered by the younger basaltic cover complex between ca 300 ka and 214 ka these two units were affected by a third major sector collapse that removed the whole western flank the summit and part of the eastern flank of the serra dormida and basaltic cover complexes 5 despite the relatively young age of graciosa the collapse scars are not well preserved and not active anymore 6 a central type volcano has been growing since at least 60 ka at the southeastern end of the island inside the scar left by a fourth sector collapse towards the se which affected most previous complexes contemporaneously parasitic strombolian cones formed all over the island despite the location of graciosa inside the active terceira rift the new data indicate that the evolution of the island has been driven by a competition between volcano growth and repeated destruction by catastrophic sector collapses rather than by slow incremental faulting associated with the tectonics of the rift

morphology of the faial island shelf azores the interplay between volcanic erosional depositional tectonic and mass wasting processes 1 the extents of volcanic island shelves result from surf erosion which enlarges them and volcanic progradation which reduces them however mass wasting tectonics and sediment deposition also contribute to their morphology in order to assess the relative significance of these various processes we have mapped in detail faial island s shelf in the azores archipelago based on interpretation of geophysical and geological data the nearshore substrates of the island down to 30 50 m depth are rocky and covered by volcaniclastic boulder deposits formed by surf action on now submerged lava flows below those depths sandy and gravel volcaniclastic beds dominate building clinoforms up to the shelf edge in some sectors of the coast prograding lava has narrowed the shelf but in contrast to nearby pico island we find fewer submarine emplaced lavas on the shelf in this island we interpret the distance between the coastline and the shelf edge as almost entirely a result of a straightforward competition between surf erosion and lava progradation in which erosion dominates therefore shelf width can be used as a proxy for coastline age as well as for wave energy exposure the stratigraphy of shelf deposits in boomer seismic data is examined in detail to assess the roles of different sediment sources accommodation space and wave exposure in creating these deposits we also show evidence of mass wasting at the shelf edge and discuss the possible origins of slope instability finally we discuss the contributing role of tectonics for the development of the shelf

gravitational erosional and depositional processes on volcanic ocean islands insights from the submarine morphology of madeira archipelago abstract the submarine flanks of volcanic ocean islands are shaped by a variety of physical processes whilst volcanic constructional processes are relatively well understood the gravitational erosional and depositional processes that lead to the establishment of large submarine tributary systems are still poorly comprehended until recently few studies have offered a comprehensive source to sink approach linking subaerial morphology with near shore shelf slope and far field abyssal features in particular few studies have addressed how different aspects of the subaerial part of the system island height climate volcanic activity wave regime etc may influence submarine flank morphologies we use multibeam bathymetric and backscatter mosaics of an entire archipelago madeira to investigate the development of their submarine flanks crucially this dataset extends from the nearshore to the deep sea allowing a solid correlation between submarine morphologies with the physical and geological setting of the islands in this study we also established a comparison with other island settings which allowed us to further explore the wider implications of the observations the submarine flanks of the madeira archipelago are deeply dissected by large landslides most of which also affected the subaerial edifices below the shelf break landslide chutes extend downslope forming poorly defined depositional lobes around the islands a large tributary system composed of gullies and channels has formed where no significant rocky ridge outcrops are present in madeira island these were likely generated by turbidity currents that originated as hyperpycnal flows whilst on porto santo and desertas their origin is attributed to storm induced offshore sediment transport at the lower part of the flanks 3000 to 4300 m where seafloor gradients decrease to 0 5 3 several scour and sediment wave fields are present with the former normally occurring upslope of the latter sediment waves are often associated with the depositional lobes of the landslides but also occur offshore poorly developed tributary systems sediment wave fields and scours are mostly absent in areas where the tributary systems are well developed and or are dominated by rocky outcrops this suggests that scours and sediment wave fields are probably generated by turbidity currents which experience hydraulic jumps where seafloor gradients are significantly reduced and where the currents become unconfined the largest scours were found in areas without upslope channel systems and where wave fields are absent and are also interpreted to have formed from unconfined turbidity currents our observations show that tributary systems are better developed in taller and rainy islands such as madeira on low lying and dry islands such as porto santo and desertas tributary systems are poorly developed with unconfined turbidite currents favouring the development of scours and sediment wave fields these observations provide a more comprehensive understanding of which factors control the gravitational erosional and depositional features shaping the submarine flanks of volcanic ocean islands

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

catastrophic flank collapses and slumping in pico island during the last 130 kyr pico faial ridge azores triple junction abstract the pico island constitutes the easternmost sub aerial domain of a steep wnw ese volcanic ridge which has developed within the nubia eurasia diffuse plate boundary azores triple junction the island comprises three volcanic systems from older to younger the topo volcano the fissural system and the pico stratovolcano from a high resolution digital elevation model 10 m and new bathymetric stratigraphic structural and high precision k ar data we reconstruct the main successive stages of growth and partial destruction of the island over the last 200 kyr we especially concentrate on the central sector of the island which has recorded gradual movements through slumping and catastrophic flank collapses since ca 130 kyr the remmants of the topo volcano are partly exposed on pico s se flank and are here dated between 186 5 and 115 4 ka topo was significantly destroyed by n and s directed large scale flank collapses between ca 125 and 70 ka on pico s n flank collapse seems to have removed all the unstable material but in the s the collapse structure is composite including a major flank collapse and a remnant slump complex that is still active a first episode of deformation occurred between ca 125 and 115 ka along the master fault of the slump between ca 115 and 69 ka most of the unstable material was removed by a major flank collapse leaving behind a still considerable volume of unstable material that comprises the active slump this first collapse was catastrophic and generated a large debris deposit recognized on the high resolution bathymetry with a minimum run out of ca 17 km the scar was partially filled by volcanic products erupted from volcanic cones developed within the slump depression and possibly also from the early wnw ese fissural system subsequent deformation in the slump area affected in part the filling units leading to the individualization of secondary curved faults younger volcanic products have gradually masked the mass wasting scars unlike the well known hilina slump hawaii pico s slump evolution might be controlled by an active regional tectonics

the 5 april 2003 vulcanian paroxysmal explosion at stromboli volcano italy from field observations and thermal data abstract the 5 april 2003 paroxysmal explosion at stromboli volcano was one of the strongest explosive events of the last century it occurred while the effusive eruption begun on 28 december 2002 and finished on 22 july 2003 was still on going and the summit craters of the volcano were obstructed in this paper we present a reconstruction of the sequence of events based on thermal and visual images collected from helicopter before during and immediately after the paroxysm one month before the blast ash emission and temperature increase at the bottom of the summit craters were observed an increasing amount of juvenile components in the emitted ash during march suggested that the magma level within the crater was rising accordingly hot degassing vents at the bottom of the summit craters were not persistent and the craters remained almost entirely obstructed by talus accumulation until the paroxysm occurred three minutes before the explosion we recorded a significant increase in temperature inside crater 1 accompanied by a thicker gas plume thirty two seconds before the blast reddish ash was emitted from crater 1 the paroxysm produced a vulcanian explosion that opened the feeder conduit obstructed for over three months the blast was accompanied by a shock wave recorded by the ingv seismic network at 07 13 37 gmt explosions with hot material started from crater 1 and after 15 s propagated to crater 3 about 100 m away the velocity of ejecta was 80 m s 1 and increased when the eruptive plumes from both craters merged together during the vulcanian phase an eruptive column rose 1 km above the top of the volcano and explosions continued mainly at crater 3 the paroxysm lasted about 9 min with bombs up to 4 m wide falling on the village of ginostra on the west flank of the island and destroying two houses this event signalled the start of the declining phase of the effusive eruption suggesting that the feeder conduit was returning to its former steady conditions with open vents and continuous mild strombolian activity

geologic factors contributing to landslide generation in a pyroclastic area august 1998 nishigo village japan vertical contrasts in permeability particularly where permeable surface materials overlie impermeable materials that prohibit the downward infiltration of groundwater concentrate the groundwater and become an important focus of landslides that are triggered by intense rainfall just such a hydrogeological structure is present within the pyroclastics in nishigo village in fukushima prefecture japan where intense rainfall of 1200 mm in 6 days generated more than 1000 landslides in august 1998 three types of landslides occurred the first type occurred along the edges of small plateaus where horizontal beds of permeable ash scoria and pumice overlie impermeable mudflow deposits consisting of tuffaceous fines and andesite blocks and massive weakly consolidated ignimbrites the rainfall on the plateaus infiltrated downward first then laterally within the permeable beds finally gushing out at the plateau edges and triggering landslides the second type of landslide occurred where weathered tuff of the same ignimbrite was present with a slip surface at the base of the heavily weathered zone within this heavily weathered zone the tuff exfoliated into thin weak plates running parallel to the slope surface the third type of landslide involved failure of colluvium or ash that filled hollows this type occurred as a result of subsurface erosion caused by the groundwater infiltrating the superficial beds above the impermeable tuff

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

tracking morphological changes and slope instability using spaceborne and ground based sar data abstract stromboli aeolian archipelago italy is an active volcano that is frequently affected by moderate to large mass wasting which has occasionally triggered tsunamis with the aim of understanding the relationship between the geomorphologic evolution and slope instability of stromboli remote sensing information from space born synthetic aperture radar sar change detection and interferometry insar and ground based insar gbinsar was compared with field observations and morphological analyses ground reflectivity and squeesar an insar algorithm for surface deformation monitoring displacement measurements from x band cosmo skymed satellites csk were analysed together with displacement measurements from a permanent sited ku band gbinsar system remote sensing results were compared with a preliminary morphological analysis of the sciara del fuoco sdf steep volcanic flank which was carried out using a high resolution digital elevation model dem finally field observations supported by infrared thermographic surveys irt allowed the interpretation and validation of remote sensing data the analysis of the entire dataset collected between january 2010 and december 2014 covers a period characterized by a low intensity of strombolian activity this period was punctuated by the occurrence of lava overflows occurring from the crater terrace evolving downslope toward sdf and flank eruptions such as the 2014 event the amplitude of the csk images collected between february 22nd 2010 and december 18th 2014 highlights that during periods characterized by low intensity strombolian activity the production of materials ejected from the crater terrace towards the sdf is generally low and erosion is the prevailing process mainly affecting the central sector of the sdf csk squeesar and gbinsar data allowed the identification of low displacements in the sdf except for high displacement rates up to 1 5 mm h that were measured following both lava delta formation after the 2007 eruption and the lava overflows of 2010 and 2011 after the emplacement of the 2014 lava field high displacements in the central and northern portions of the sdf were recorded by the gbinsar device whereas the spaceborne data were unable to detect these rapid movements a comparison between irt images and gbinsar derived displacement maps acquired during the same time interval revealed that the observed displacements along the sdf were related to the crumbling of newly emplaced 2014 lava and of its external breccia detected slope instability after the 2014 flank eruption was related to lava accumulation on the sdf and to the difference in the material underlying the 2014 lava flow i lava flows and breccia layers related to the 2002 03 and 2007 lava flow fields in the northern sdf sector and ii loose volcaniclastic deposits in the central part of the sdf this work emphasizes the importance of smart integration of spaceborne sar derived hazard information with permanent sited operational monitoring by gbinsar devices to detect areas impacted by mass wasting and volcanic activity

small fast moving flow like landslides in volcanic deposits the 2001 las colinas landslide el salvador abstract fast moving landslides are one of the most significant dangers deriving from slope instabilities landslides involving large volumes can develop in rock or debris avalanches with extreme mobility and enormous destructiveness nevertheless a relevant number of casualties and damages derive from small fast moving landslides with flow like behaviour the las colinas landslide occurred at santa tecla el salvador central america during a strong earthquake it slid off the northern flank of the balsamo ridge and resulted in almost 500 casualties and can be considered one of the most destructive landslides ever known earthquake shaking was amplified by the rock mass and the steep ridge topography we collected original geological geomorphological and geophysical data in the cordillera del balsamo area the involved materials ranging from lapilli to tuff layers of different strength have been mapped and characterized slope stability analyses have been performed both under static and dynamic conditions through limit equilibrium and finite element methods hazard zonation for this type of landslides requires the forecast of the movement velocity and final deposition area we used a fully two dimensional fem model to simulate landslide spreading downslope the developed code allows the use of different constitutive models and yield rules with the possibility to model and study internal deformation of the landslide mass as well material entrainment and deposition

understanding shallow magma emplacement at volcanoes orthogonal feeder dikes during the 2002 2003 stromboli italy eruption 1 understanding how shallow magma is emplaced within volcanoes is crucial for hazard assessment the 2002 2003 stromboli eruption provides the opportunity to investigate shallow magma emplacement resulting from orthogonal feeder dikes and its possible effects stromboli erupted in 2002 2003 when effusive activity replaced strombolian activity on december 28 a ne sw fissure propagated from the lava filled northernmost summit crater on december 29 a nw se fissure propagated north of the craters feeding nw se aligned vents on december 30 this area collapsed reaching the sea and generating a tsunami in mid february 2003 the nw se fissure became inactive while the ne sw effusive fissure continued until july a model for shallow magma emplacement is proposed the lateral propagation of a ne sw dike from the northernmost crater was triggered below a nw se dike propagating from the magma filled ne tip of the ne sw elongated conduit fed the nw se aligned vents in february the conduit periphery became solidified freezing the nw se dike and the transport of magma was limited to the central part focusing its rise below the craters this fed the ne sw fissure until the supply decreased further july returning to the ordinary level sustaining strombolian activity orthogonal dike emplacement followed the trajectories of the maximum gravitational stress 1 partly controlled by the irregular topography of the uppermost edifice the emplacement of orthogonal dikes in a limited area is feasible at non perfectly conical active volcanoes where the maximum gravitational stress may show variations from a purely radial path

failure of volcano slopes magmatic intrusions can initiate and sustain massive and catastrophic volcano collapse their role is twofold involving both driving and resisting forces first flank stability is diminished by magmastatic and magma overpressures and steepened slopes that accompany intrusion second excess pore pressures in potential failure zones can be generated as a result of intrusion related mechanical or thermal straining of the rock fluid medium pressurized retrograde boiling in high level magma chambers or hydrothermal fluid circulation also earthquakes may aid collapse through inertial forces and shaking induced pore pressure generation these excess pore pressures reduce the sliding resistance as shown for wedge shaped slide blocks for selected cases the destabilizing influence of mechanically induced pore pressures is maximized as the intruded width or corresponding overpressure of the intrusion is increased the destabilizing influence of thermally induced pore pressures is conditioned by the seve

a new type of volcano flank failure the resurgent caldera sector collapse ischia italy 1 this study is the first description of recurrent and rapid lateral failure of the resurgent portion of a caldera complex the sliding planes and the characteristics of debris avalanche deposits resemble those of cone sector collapses but the main triggering mechanism proposed at ischia caldera italy is related to intermittent resurgence during the last 33 ka the increase in resurgence rate produced major collapses southward due to three main mechanisms that contributed to an increase in shear stress i magma driven uplift which produced increase in static loading ii faulting and associated deformation which induced tilting and steepening of the original layering and iii earthquake shaking due to coseismic faulting the largest episodes of flank failure occurred in the interval 8 6 5 7 ka bp these were followed by magma eruption and a decrease in the resurgence rate recognition of this phenomenon is particularly important in recent active calderas located near the coast as it can trigger tsunamis

enhancement of sub daily positioning solutions for surface deformation monitoring at deception volcano south shetland islands antarctica deception island is one of the most visited places in antarctica there are biological geological and archeological features that are major attractions within port foster its horse shoe shaped natural inner bay and two scientific bases that are occupied during austral summers deception island is an active volcano however and needs to be monitored in order to reduce risk to people on the island surface deformation in response to fluid pressure is one of the main volcanic activities to observe automated data acquisition and processing using the global navigation satellite systems allow measurements of surface deformation in near real time nevertheless the positioning repeatability in sub daily solutions is affected by geophysical influences such as ocean tidal loading among others such periodic influences must be accurately modeled to achieve similar repeatability as daily solutions that average them however a single solution each 24 h will average out the deformation suffered during that period and the position update waiting time can be a limitation for near real time purposes throughout the last five austral summer campaigns in deception using simultaneous wireless communications between benchmarks a processing strategy was developed to achieve millimeter level half hourly positioning solutions that have similar repeatability as those given by 24 h solutions for these half hourly solutions a tidal analysis was performed to assess any mismodeling of ocean tide loading and a discrete kalman filter was designed and implemented to enhance the sub daily positioning repeatability with these solutions the volcano dynamic activity resulting in localized surface deformation for the last five austral summer campaigns is addressed although based on only three carefully located benchmarks it is shown that deception has been shortening and subsiding during these last 4 years the method s accuracy in baselines up to a few hundred kilometers assures its applicability to other volcanoes worldwide

the morphological evolution of the sciara del fuoco since 1868 reconstructing the effusive activity at stromboli volcano the morphological evolution of the sciara del fuoco stromboli is described from a time series dataset formed by digital elevation models and orthophotos derived by digitising historical contour maps compiled in 1868 and 1937 and by processing data from aerial surveys carried out between 1954 and 2009 all maps were co registered in the same reference system and used to build a quantitative reconstruction of the morphological changes of the sciara del fuoco slope the changes mainly relate to the emplacement of many lava flows and their successive erosion a comparative quantitative analysis yields estimates of areas and volumes of the lava fields formed on the sub aerial part of the sciara del fuoco during a number of effusive events between 1937 and 2001 some of them never assessed before the results of the analysis constrain the interpretation of the evolution and the magnitude of the recent effusive activity at the stromboli volcano despite some uncertainties due to widely spaced observation periods the results integrate all available topographic knowledge and contribute to an understanding of the main characteristics of the recent effusive eruptive styles at stromboli volcano

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

morpho structural setting of stromboli volcano revealed by high resolution bathymetry and backscatter data of its submarine portions the first high resolution bathymetric and backscatter maps of offshore stromboli island are presented together with an interpretation of its volcanic structural and sedimentary features the volcanic edifice is characterized by a sub conical shape with a quasi bilateral symmetry with respect to a ne sw axis the dimensions of the strombolicchio volcanic centre to the ne of stromboli have been restored by redrawing its morphology before wave action that eroded it in late quaternary time on the ne submarine flank of strombolicchio a n64 e structural trend controls the shape of strombolicchio canyon on the southern side of stromboli the submarine flank has a radial structural trend possibly reflecting a volcanic stress regime landslide scars at various scales are ubiquitous on the submarine slopes of stromboli repeated large scale lateral collapses have affected both the northwestern and southeastern unbuttressed flanks of the volcano producing large debris avalanche deposits

a comparison of pyroclastic flow and debris avalanche mobility many pyroclastic flows have runout distances longer than expected from basic frictional arguments in these cases the ratio of the height descended h and the runout l are as small as 0 2 a feature which has been attributed to fluidization however significant fluidization by gases is now considered unlikely during emplacement of debris avalanches where h l and volume are inversely related we determine whether pyroclastic flows are more mobile than debris avalanches of the same volume and if different emplacement mechanisms are needed to describe their runout h l and volume data were compiled for 34 nonvolcanic and 40 volcanic debris avalanche deposits as well as 15 pyroclastic flow deposits systematic differences in the volume versus h l plots were explored by statistical analysis results show an inverse relationship between h l and volume for both nonvolcanic and volcanic debris avalanche deposits as expected and also for pyroclastic flow deposits regression lines for plots of pyroclastic flow and volcanic debris avalanche data are statistically indistinguishable and the non volcanic debris avalanche line is parallel to the other two we argue that the nonvolcanic and volcanic debris avalanche differences are due to material properties rather than emplacement mechanisms therefore since pyroclastic flows and volcanic debris avalanches have indistinguishable h l versus volume it is unlikely that pyroclastic flows have a significantly different primary emplacement mechanism based on the data in hand we conclude that it is unnecessary to invoke gas fluidization to explain the mobility of the types of pyroclastic flows examined or the excess runout of large volume debris avalanches

deformation of stromboli volcano italy during the 2007 eruption revealed by radar interferometry numerical modelling and structural geological field data abstract the activity of stromboli volcano is characterized by very low energy explosions occurring every 10 15 min throwing out lava above the crater rim during 2007 the volcano showed an anomalous activity in which new effusive vents developed 27 february and 9 march and a major explosion took place on 15 march this paper presents an integrated study based on a structural geological field survey interferometric radar monitoring and numerical modelling on the deformations of the upper nw flank of the volcano sciara del fuoco sdf the field survey carried out during the 2007 events shows the development of mainly ne striking fissures and fractures on the northern part of the upper sdf in january 2007 the ground based synthetic aperture radar gb insar installed on the flank of the sdf showed a progressive acceleration of movement on the ne crater preceding the eruption of 27 february 2007 by the first half of february the acceleration also involved the upper portion of the sdf and on 27 february the eruption started with the opening of new vents and deformation rates higher than the measurement capability of the radar device on 8 9 march 2007 the gb insar highlighted the formation of a bulge on the nw sector of the sdf preceding the opening of an additional vent to understand the deformation pattern recorded during the eruption a numerical simulation was carried out by using the flac 3d code based on the integration of all the data the deformations observed in the pre effusive phase before 27 february seem to be related to the intrusion of a sw ne striking dyke the bulging recorded before the 9 march vent opening is instead to be associated with the intrusion of a sub horizontal sill

subaerial submarine evidence of structures feeding magma to stromboli volcano italy and relations with edifice flank failure and creep abstract structural field data including parameters of 109 sheets strike mostly n10 55 e average dip angle mostly 70 90 average thickness two peaks at 1 2 m and 4 2 m and of 14 eruptive fissures and vents as well as bathymetric and numerical data suggest that stromboli experienced the development of a volcanic rift zone across the cone summit with a tendency to widen towards the lower submarine flanks during the last 100 ka inside this rift zone intrusive sheets mostly strike ne and become more abundant more steeply dipping and thicker on approaching the rift axis this rift persistence reflects the edifice s state of stress with a nw se horizontal least principal stress on the magma intrusion paths after 13 ka ago sheets mainly intruded with a horseshoe shaped geometry in plan view along the boundaries of the northwestern unstable volcano flank where four main lateral collapses occurred during the last 13 ka they also intruded with a ne strike across the volcano summit and the northeastern volcano flank the horseshoe shaped geometry is influenced by the lateral creep of the volcano flank which provides space for intrusion along the transtensional boundaries of the unstable sector where thinner sheets were emplaced when the collapse depression was filled up by new deposits ne striking thicker dykes emplaced across the northwestern volcano flank indicating a rapid re establishment of regional tectonic forces across the cone unbuttressing due to the present sciara del fuoco depression and ongoing flank creeping can account for intrusions also inside the sciara del fuoco the latter in 2007

editorial flank dynamics sector collapses lahars and rockfalls analysis monitoring and modelling of small to large scale volcanic slope instability slope dynamics in volcanic environments comprise a wide spectrum of phenomena from large lateral collapse to shallow debris remobilization which may represent a major threat for human communities and infrastructures many volcanos built up from the ocean floor and large portions of the volcano edifice are submerged in these settings only the edifice s summit can be investigated by terrestrial remote sensing and in situ approaches growth and destruction including tectonics and gravitational phenomena affect entire volcano flanks and are not limited to the physical boundary of the sea level but could comprise their subaqueous parts

cyclical slope instability and volcanism related to volcano tectonism in resurgent calderas the ischia island italy case study abstract the results of a detailed stratigraphic study carried out in the areas located to the east and south west of mt epomeo at ischia are presented and compared with those of previous geological archaeological and historical investigations to show the relationships among caldera resurgence volcanism and slope instability in the past 5 5 ka resurgence at ischia began at about 30 ka b p and occurred through intermittent uplifting and tectonic quietness phases during the past 5 5 ka reactivation of faults and related volcanic activity was accompanied by emplacement of deposits generated by surface gravitational movements these deposits were generated in four main phases dated between 5 5 and 2 9 ka around 2 9 ka between 2 6 and 2 3 ka and between 2 3 and 1 9 ka respectively deposits formed by gravitational movements preceded and followed the emplacement of volcanic rocks testifying that slope instability was induced by vertical movements which also activated and or reactivated faults and fractures that fed volcanism the results of this study therefore suggest that although slope failure can occur as a consequence of a variety of factors resurgence has to be considered a factor inducing a particularly intense slope instability resurgence is accompanied by activation of faults and renewal of volcanism causing oversteepening of the slopes and generating seismicity that could trigger surface gravitational movements furthermore the availability of large amount of loose material rapidly accumulated along the slopes during eruptions favors landslide generation

reconstructing the anak krakatau flank collapse that caused the december 2018 indonesian tsunami volcanogenic tsunamis are one of the deadliest volcanic phenomena understanding their triggering processes and mitigating their effect remains a major challenge on 22 december 2018 flank failure of the anak krakatau volcano in indonesia generated a tsunami which killed more than 400 people this event was captured in unprecedented detail by high resolution satellite imagery and eyewitness accounts here we combine historic observations with these recent data to for the first time interpret the internal architecture of anak krakatau and reconstruct the failure tsunamigenesis and regrowth processes observed we calculate the volume of material initially lost from the volcano flank failure and find that it was relatively small 0 1 km3 compared to the overall changes observed during the entire eruption but was nonetheless able to generate rapid tsunami waves with devastating impacts the flank failure also changed the eruption style and upper volcanic plumbing system with these subsequent explosive eruptions destroying the summit and then partially rebuilding the lost flank the nature of the flank failure was controlled by the internal structure of the island and although regrowth rate will be a primary control on flank failure intervals the reconfiguring of the volcano s internal vent network is likely to have re stabilised it in the medium term the findings demonstrate that hazard assessments at ocean islands must consider that even small flank failures during unexceptional eruptions can have catastrophic consequences

a case history of paroxysmal explosion at stromboli timing and dynamics of the april 5 2003 event abstract on april 5 2003 stromboli volcano italy produced the most violent explosion of the past 50 years the event was exceptionally well documented thanks to the presence on the island of several scientists and a large number of instruments deployed over the preceding months to monitor the effusive eruption that began in december 2002 integration of visual documentation deposit features and geophysical data allowed an accurate reconstruction of the explosive event and its dynamics the eruption consisted of a 8 min long explosive event which evolved through four phases whose timing was precisely recorded by an infrared thermometer located about 450 m from the summit crater phases 2 and 3 lasted 39 and 42 s respectively both had an impulsive character were responsible for ejecting almost the entire mass of the pyroclastic products phases 1 and 4 represented respectively a short lived precursory event and a waning tale during phase 2 meter sized ballistic blocks were launched with velocities of 170 m s to altitudes of up to 1400 m above the craters these fell on the volcano flanks and on the village of ginostra about 2 km distant from the vent a vertical jet rose above the craters which developed to feed a convective plume that reached a height of up to 4 km the calculated mass of the phase 2 fallout deposit and mass discharge rate were 1 1 1 4 108 kg and 2 8 3 6 106 kg s respectively during phase 3 a scoria flow deposit with an estimated volume of 0 9 1 1 104 m3 was erupted from the same vent that fed the ongoing sustained lava flow the average mass discharge rate for this phase was 2 5 3 1 105 kg s products emitted during phases 2 and 3 consisted of lithic and fresh magmatic material in similar proportions the juvenile fraction consisted of a deep originated almost aphyric highly vesicular pumice mingled with a shallow derived crystal rich moderately vesicular scoria similarities with the eruption dynamics of other historical paroxysms at stromboli makes the april 5 2003 explosion representative of these highly energetic events that constitute the most hazardous volcanic phenomena at stromboli volcano

discharge of pyroclastic flows into the sea during the 1996 1998 eruptions of the soufriere hills volcano montserrat explosive eruptions of the soufriere hills volcano on the island of montserrat in the west indies generated pyroclastic flows that reached the sea on the east and southwest coasts between november 1995 and july 1998 discharge of the flows produced two pyroclastic deltas off of the tar and white river valleys a marine geological survey was conducted in july 1998 to study the submarine extensions of both deltas detailed profiles of depth and sub bottom structure were obtained using a chirp ii bubble pulser system these profiles were compared with pre eruption bathymetric data in order to identify areas of recent deposition and erosion deposition off the tar and white river valleys was thickest nearest the coastline and deltas and extended into deeper water up to 5 km from shore the total volume of submarine pyroclastic deposits as of july 1998 was 73 106 m3 dre submarine pyroclastic deposits off the tar river valley made up more than two thirds of the total volume 55 106 m3 dre and covered an area of approximately 5 0 km2 which included the delta the volume of submarine pyroclastic deposits in the white river area 18 106 m3 dre is probably underestimated due to the lack of precise pre eruption bathymetric data in areas greater than 2 km from shore growth of pyroclastic deltas at the mouths of the tar and white river valleys continued to the edge of the submarine shelf where there was a steep break in slope in the tar river area pyroclastic material was distributed down the steep shelf break and into deeper water at least a few kilometers from shore the material spread out radially forming a submarine fan where distribution was primarily controlled by bathymetry and slope

depositional processes on oceanic island shelves evidence from storm generated neogene deposits from the mid north atlantic oceanic islands such as the azores in the mid north atlantic are periodically exposed to large storms that often remobilize and transport marine sediments along coastlines and into deeper environments such disruptive events create deposits denominated tempestites whose characteristics reflect the highly dynamic environment in which they were formed tempestites from oceanic islands however are seldom described in the literature and little is known about storm related sediment dynamics affecting oceanic island shelves therefore the geological record of tempestite deposits at oceanic islands can provide invaluable information on the processes of sediment remobilization transport and deposition taking place on insular shelves during and after major storms in santa maria island azores a sequence of neogene tempestite deposits was incorporated in the island edifice by the ongoing volcanic activity thus preserved and later exposed through uplift and erosion because it was overlain by a contemporary coastal lava delta the water depth at the time of deposition could be inferred constituting an excellent case study to gain insight on the still enigmatic processes of insular shelf deposition sedimentological palaeontological petrographic and palaeo water depth information allowed the reconstruction of the depositional environment of these sediments the sequence typifies the characteristics of a tempestite or successive tempestites formed at ca 50 m depth in a steep energetic open insular shelf and with evidence for massive sediment remobilization from the nearshore to the middle or outer shelf the authors claim that cross shelf transport induced by storm events is the main process of sediment deposition acting on steep and narrow shelves subjected to high energetic environments such as the insular shelves of open sea volcanic islands

morphologic resilience and depositional processes due to the rapid evolution of the submerged sciara del fuoco stromboli island after the december 2002 submarine slide and tsunami abstract in order to monitor the stromboli submarine slope after the 30 december 2002 landslide and tsunami repeated marine surveys were carried out offshore of sciara del fuoco the morphological changes and depositional processes that brought to the gradual filling of the slide scar have been studied in detail thirteen surveys in a period of little more than 4 years provided a unique opportunity to reconstruct the morpho sedimentary evolution of the submarine slope and its recovery after the mass wasting event the scar has been progressively filled with lava and volcanoclastic debris in the first month and a half the filling rate was very high due to the entrance of lava flows into the sea and to the morphological readjustment of the slope in the following months years the rate dramatically decreased when the eruptive vents moved upwards and the eruption finally stopped after 4 years february 2007 more than 40 of the scar was already filled in early 2007 a new eruption occurred and a lava delta was constructed in the 2002 scar influencing the natural readjustment of the slope therefore our reconstruction only encompasses the period between the 2002 and 2007 eruptions the swath bathymetry reconstruction of geometry and volume of scar filling during the period 2002 2007 evidenced a punctuated and fast shift of depocenters and debris emplacement through avalanching processes this process quickly obliterated the features produced by the 2002 tsunamigenic landslide so that a major question about the preservation potential of mass wasting features on active volcanic flanks emerges

subaqueous density flow processes and deposits of an island volcano landslide stromboli island italy stromboli is a 3000 m high island volcano rising to 900 m above sea level it is the most active volcano of the aeolian archipelago in the tyrrhenian sea italy major large volume 1 km 3 sector collapses four occurring in the last 13 kyr have played an important role in shaping the north western flank sciara del fuoco of the volcano potentially generating a high risk tsunami hazard for the aeolian islands and the italian coast however smaller volume partial collapses of the sciara del fuoco have been shown to be more frequent tsunami generating events one such event occurred on 30 december 2002 when a partial collapse of the north western flank of the island took place the resulting landslide generated 10 m high tsunami waves that impacted the island multibeam bathymetry side scan sonar imaging and visual observations reveal that the landslide deposited 25 to 30 10 6 m 3 of sediment on the submerged slope offshore from the sciara del fuoco two contiguous main deposit facies are recognized i a chaotic coarse grained metre sized to centimetre sized clasts deposit and ii a sand deposit containing a lower cross bedded sand layer and an upper structureless pebbly sand bed capped by sea floor ripple bedforms the sand facies develops adjacent to and partially overlying the coarse deposits characteristics of the deposits suggest that they were derived from cohesionless sandy matrix density flows flow rheology and dynamics led to the segregation of the density flow into sand rich and clast rich regions a range of density flow transitions both in space and in time caused principally by particle concentration and grain size partitioning within cohesionless parent flows was identified in the deposits of this relatively small scale submarine landslide event

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

the morphology of the submarine flanks of volcanic ocean islands a comparative study of the canary and hawaiian hotspot islands the submarine flanks of volcanic islands are shaped by volcanic constructional processes landslides erosion sediment deposition and tectonic movements we use a newly acquired multibeam sonar dataset from the westerly canary islands el hierro la palma and tenerife to develop a comparison with the hawaiian islands which suggests differences in the processes constructing and modifying their flanks landslides affect the flanks of both island groups debris avalanches fast moving shallow landslides have left smooth chutes and blocky deposits in both cases but blocks within some hawaiian avalanche deposits are markedly larger we attribute the larger block sizes in the hawaiian islands to the fact that their avalanches were relatively unconfined whereas many canary and hawaiian avalanches with small block sizes appear to have been constrained down narrow chutes forcing interactions between blocks within the flows and encouraging disintegration furthermore the hawaiian avalanches with the largest blocks initiated near sea level whereas many of the canary avalanches initiated above sea level so hydraulic resistance of water entering cracks may be an additional factor in resisting block disintegration during flow slow moving deep seated slumps or volcanic spreading have produced submarine benches and tabular escarpments due to thrust faulting adjacent to several hawaiian rift zones but are not well developed in the canaries although volcanic morphology is partly obscured by sedimentation in the canaries we are able to interpret lava terraces around the deep flanks of el hierro which are similar to those found in the hawaiian islands however cones rather than terraces are the most common volcanic forms in the canary islands implying that flank eruptions have involved magma with significant volatile contents assuming that volatile contents dictate whether cones or terraces are formed these differences may ultimately originate from the different building rates of the two island groups for example the lack of evidence for high level magma chambers in the canaries associated with their lower outputs implies that there is less possibility for degassing of magma below the summit before lateral intrusion down rift zones hence cones rather than lava terraces are more commonly observed the apparent lack of slumping or volcano spreading could also reflect a lack of driving pressure from extensive high level magma chambers in the canaries

triggering mechanism at the origin of paroxysms at stromboli aeolian archipelago italy the 5 april 2003 eruption 1 the 5 april 2003 paroxysm of stromboli occurred during an ongoing effusive episode that initiated on 28 december 2002 it mainly consisted in two a few seconds apart cannon like explosions followed by a vertical gas pyroclast jet the hk basaltic pumices that were generated mainly contain crystals that were drained back from the shallow parts of the plumbing system few euhedral to anhedral olivines and their melt inclusions testify to crystal fractionation and possible mixing between hk basaltic magmas variable in their volatile content extent of evolution and volume the most primitive volatile rich hk basalt term is sizable at micrometer scale only we propose that the triggering mechanism of the paroxysm was initiated at moderate pressures 240 mpa and was related to bubble driven ascent of magma blobs the latter rose through and interacted with overlying slightly more evolved melts and finally mingled with the shallow crystal rich magma just before the eruption