tectonics and slumping in the source region of the 1998 papua new guinea tsunami from seismic reflection images in september 1999 we collected seven high resolution seismic reflection profiles along the northern continental margin of papua new guinea which targeted the source region of the 1998 tsunami that inundated sissano lagoon we utilized swath bathymetry collected by the jamstec sopac groups in january 1999 the seismic profiles image several faults bottom simulating reflectors and a large rotational slump the slump has a head scarp of 100 m vertical extent coinciding with the headwall and tension cracks observed previously by submersible at the southern edge of the amphitheater the central back rotated part of the slump is coherent with parallel reflections the interpreted basal failure plane has a maximum depth of 760 m below the seafloor and it crops out at a steep escarpment about 100 meters high located 4 5 km north of the head scarp this escarpment separates the slide toe from a series of seafloor parallel coherent reflections that are top lapped by basin deposits at the foot of the amphitheater to the north the cross sectional area of the displaced mass is 2 3 km2 from the bathymetry the width is approximately 2 5 3 km yielding a total volume assuming parabolic shape of 3 8 4 6 km3 based on these interpretations the slump was restored to its undeformed position this technique yields a center of mass vertical drop of 380 m horizontal movement of 840 m and slip of 980 m along the slide plane

monitoring volcano slope instability with synthetic aperture radar a review and new data from pacaya guatemala and stromboli italy volcanoes abstract volcano slope instability manifests in many forms ranging from steady state to punctuated movement or shallow erosion to deep seated spreading the interplay of gravity magmatic or hydrothermal fluids and often active tectonics on a volcanic edifice results in complex spatial and temporal variations in deformation kinematics while this makes the recognition assessment and monitoring of volcano slope instability challenging advancements in synthetic aperture radar sar technology have significantly accelerated our knowledge of instability phenomena and our ability to assess their hazards this review discusses the applications and challenges of sar imagery to various slope instabilities at volcanoes around the world sar amplitude images are powerful tools for mapping areas of geomorphological changes these snapshots can be combined using interferometric sar insar to create multi temporal deformation maps that provide unique information on the evolution of slope failures space borne insar has become an economic way to detect changes at volcanoes at very high resolution ground based insar gbinsar can produce frequent sar images on the order of seconds to minutes propelling insar from monitoring to surveillance and early warning applications however interpreting insar derived ground deformation signals related to volcano slope instability is still challenging deformation from magma rise or variations in hydrothermal systems may be inseparable from persistent deep seated flank motion similarly shallow or localized ground motion may occur in overlap with thermal contraction or subsidence of newly emplaced lava or tephra deposits if triggered to failure landslides can vary over several magnitudes from small volume rock falls that pose only a localized hazard to large volume debris avalanches capable of travelling tens of kilometers away from the source these collapses can have cascading hazards if accompanied by directed blasts or tsunamis emphasizing the need for continued advancement of our understanding of these events and their consequences to highlight the utility of sar for measuring and monitoring mass movement two case studies of stromboli italy and pacaya guatemala volcanoes are discussed in detail where recent instability events persistent volcanic activity and ground truth constraints have resulted in excellent case histories in applying sar imagery to understand these potentially hazardous slope instabilities

anomalous sulfur poor platinum group element mineralization in komatiitic cumulates mount clifford western australia an unusual occurrence of sulfur poor platinum group element pge mineralization has been discovered at mount clifford in the agnew wiluna belt western australia within the lower part of a 1 000 m thick komatiitic dunite body the host body consists primarily of strongly serpentinized olivine adcumulates with accessory chromite high precision whole rock icp ms data show that the pge mineralization extends over tens of meters whereas the lateral extent is unknown palladium and pt abundances are closely associated with base metal sulfides but show offset distribution patterns with maximum concentrations associated with the relatively sulfide poor base of a disseminated sulfide bearing layer whole rock concentrations range up to 4 100 ppb pd and 920 ppb pt iridium rh and ru follow the trends in pd and pt but are strongly depleted ir 0 4 ppb ru 0 5 ppb rh 0 1 ppb platinum group minerals pgm were located in essentially sulfide free serpentine 2 m below the peak in sulfide abundance and can be categorized into three groups pd antimonides pt dominated pgm and pt bearing ni antimonides the pge mineralization zone is underlain by an interval of strong ni depletion within olivine mesocumulates that is characterized by an unusual negative correlation between ni and the mg number of the rock this relationship is interpreted to be the result of an equilibration of olivine of variable forsterite content with a relatively large mass of magmatic sulfide however there is no direct evidence of this sulfide mass anywhere in the entire mount clifford dunite body the ni depletion is accompanied by strong depletion in ipge ir ru and rh the association of the pge zone with a reversal in the mg fe ratio of the host cumulates and a distinctive offset relationship of multiple pt pd and cu s peaks is suggestive of a primary magmatic origin however this is inconsistent with current models for offset reef pge concentrations which involve the onset of sulfide liquid saturation from a previously sulfur undersaturated pge undepleted magma the association of enriched pt and pd with highly depleted ni and ipge in immediately underlying cumulates conflicts with this model we suggest a combination of processes early sulfide segregation at low r values producing ni and ipge depleted olivine partial redissolution and removal of most of this sulfide component during a major replenishment event and subsequent overprint by a migrating pt pd cu rich fluid

from catastrophic collapse to multi phase deposition flow transformation seafloor interaction and triggered eruption following a volcanic island landslide abstract the current understanding of tsunamis generated by volcanic island landslides is reliant on numerical models benchmarked against reconstructions of past events as the largest historical event with timed tsunami observations the 1888 sector collapse of ritter island papua new guinea provides an outstanding opportunity to better understand the linked process of landslide emplacement and tsunami generation here we use a combination of geophysical imaging bathymetric mapping seafloor observations and sampling to demonstrate that the ritter landslide deposits are spatially and stratigraphically heterogeneous reflecting a complex evolution of mass flow processes the primary landslide mass was dominated by well bedded scoriaceous deposits which rapidly disintegrated to form an erosive volcaniclastic flow that incised the substrate over much of its pathway the major proportion of this initial flow is inferred to have been deposited up to 80 km from ritter the initial flow was followed by secondary failure of seafloor sediment over 40 km from ritter the most distal part of the 1888 deposit has parallel internal boundaries suggesting that multiple discrete units were deposited by a series of mass flow processes initiated by the primary collapse the last of these flows was derived from a submarine eruption triggered by the collapse this syn collapse eruption deposit is compositionally distinct from pre and post collapse eruptive products suggesting that the collapse immediately destabilised the underlying magma reservoir subsequent eruptions have been fed by a modified plumbing system constructing a submarine volcanic cone within the collapse scar through at least six post collapse eruptions our results show that the initial tsunami generating landslide at ritter generated a stratigraphically complex set of deposits with a total volume that is several times larger than the initial failure given the potential for such complexity there is no simple relationship between the volume of the tsunamigenic phase of a volcanic island landslide and the final deposit volume and deposit area or run out cannot be used to infer primary landslide magnitude the tsunamigenic potential of prehistoric sector collapse deposits cannot therefore be assessed simply from surface mapping but requires internal geophysical imaging and direct sampling to reconstruct the event

origin of spectacular fields of submarine sediment waves around volcanic islands understanding how large eruptions and landslides are recorded by seafloor morphology and deposits on volcanic island flanks is important for reconstruction of volcanic island history and geohazard assessment spectacular fields of bedforms have been recognised recently on submerged flanks of volcanic islands at multiple locations worldwide these fields of bedforms can extend over 50 km and individual bedforms can be 3 km in length and 150 m in height the origin of these bedform fields however is poorly understood here we show that bedforms result from eruption fed supercritical density flows turbidity currents in some locations but most likely rotational landslides at other locations general criteria are provided for distinguishing between submarine bedforms formed by eruptions and landslides and emphasise a need for high resolution seismic datasets to prevent ambiguity bedforms associated with rotational landslides have a narrower source with a distinct headscarp they are more laterally confined and internal bedform structure does not suggest upslope migration of each bedform eruption fed density currents produce wide fields of bedforms which extend radially from the caldera internal layers imaged by detailed seismic data show that these bedforms migrated up slope indicating that the flows that produced them were froude supercritical due to the low density contrast between interstitial fluid and sediment the extent and dimensions of submarine eruption fed bedforms is much greater than those produced by pyroclastic density currents on land

modern changes of the high mountain landscapes and glaciation in southern siberia russia by the example of the eastern sayan mountains the period of observations of glaciation of the munku sardyk mountain massif in siberia is one of the longest i e 155 years however the data obtained are scattered and not systematic the paper presents an integrated analysis of the materials collected since the first description by the explorer of siberian mountains g i radde istoriy 1896 and extended by peretolchin 1908 and komarov 1953 as well as by glaciologists maksimov 1965 arefiev and mukhametov 1996 the authors considered the current state of the glaciers and interaction of natural geosystems of the massif taking into account the nival glacial processes since the beginning of the current millennium regular observations have been conducted on the munku sardyk massif by the v b sochava institute of geography sb ras limnological institute sb ras and east siberian state academy of education the studies revealed the leading landscape forming factors and examined the landscape structure of the surroundings of the contemporary nival glacial geosystems with due regard for the manifestations of altitudinal zonation a medium scale landscape typological mapping was carried out presented are the quantitative parameters of the dynamics of the nival glacial geosystems obtained on the basis of modern remote sensing instruments gps measurements and surface laser scanning using gis analysis the stump and stem of larch detected in the valley of the bugovek river 300 m above the contemporary upper forest limit and 1330 m up the valley show that most likely there was no glaciation during the atlantic period 7000 7300 years ago the modern glacier complex has formed only during the last 4000 5000 years the trend of shrinkage of glaciers since the end of the little ice age can be traced especially in recent years the length and area of the open part of the glaciers have decreased by half from 0 68 to 0 34 km2 the presence of small forms of glaciation on the southernmost limit of the siberian glaciation 1500 m below the theoretical climate boundary suggests that this area can be considered a unique key site to identify trends in development of the mountain and nival glacial geosystems and provides an opportunity to built reconstructive and predictive models of development of mountain landscapes under the conditions of ever increasing anthropogenic influence

detecting micrometer scale platinum group minerals in mantle peridotite with microbeam synchrotron radiation x ray fluorescence analysis 1 platinum group elements pge in the earth s mantle are key tracers for understanding the differentiation history of the earth pge in mantle peridotite are strongly concentrated in fe ni cu sulfides whereas platinum group minerals rarely found in peridotite are additional potential phases that host pge in the mantle however the abundances of platinum group minerals are not well constrained because they are generally too small to be detected with conventional analytical tools we employed microbeam synchrotron radiation x ray fluorescence to efficiently detect micrometer scale platinum group minerals in rock samples this nondestructive technique allows location of micrometer scale minerals from the interior of rock thin sections with this method we detected micrometer scale platinum group minerals in an orogenic lherzolite sample the platinum group minerals range from 1 m to 10 m in maximum dimension they are located near or within fe ni cu sulfides which were not exposed on the thin section surface nine grains of platinum group minerals in total were detected in just one peridotite thin section demonstrating the high efficiency of this method for detecting micrometer scale minerals from the inside of rock samples

large scale sediment waves and scours on the modern seafloor and their implications for the prevalence of supercritical flows large scale 20 m to 7 km wavelength bedforms are common on the seafloor yet there is a lack of consensus on how they form and thus what to call them we conducted statistical analysis on a dataset of 82 seafloor bedforms that span a range of water depths and environments the data form three distinct groups 1 small scale 20 300 m wavelength sediment waves with mixed relief made of medium sand to cobble sized sediment that form in confined settings which we call small sediment waves 2 large scale 300 7000 m wavelength sediment waves with mixed relief made of fine grained sediment that form in relatively unconfined settings which we call large sediment waves and 3 large scale fully enclosed depressions in the seafloor which we call scours there is a statistically significant data gap in the size of bedforms between small sediment waves and large sediment waves that does not appear to be a sampling artefact this data gap probably results from the environments in which sediment waves form being either confined e g channel or canyon or unconfined e g open slope bedform migration direction is available for 36 of the data and includes small and large scale sediment waves of these examples all are shown to migrate up current up current migration is indicative of supercritical flow thus this data suggests that supercritical flows operate in a wide range of environments and can generate both small and large sediment waves therefore we suggest that small and large sediment waves form by similar processes despite the gap in bedform wavelength and sediment size the migration direction for scours remains unknown scours may form from similar processes to small and large sediment waves or alternatively they may be a completely separate bedform type that form when erosive flows exploit pre existing defects in the seafloor this novel statistical analysis of a global database shows that up current migrating bedforms associated with supercritical flow are unusually widespread and are recognised at two distinct scales

syn eruptive soft sediment deformation structures in a deep submarine caldera havre 2012 the 2012 rhyolitic eruption of havre submarine caldera in the kermadec arc generated an assemblage of new soft sediment deformation structures on the caldera floor these structures are the first documented examples of syn eruptive soft sediment deformation structures within a submarine caldera they are exquisitely portrayed on a high resolution 1 m bathymetric map made in 2015 their timing has been resolved by means of stratigraphic relationships with an overlying giant pumice deposit that correlates with the pumice raft first observed on 18th july 2012 utc weeks to months earlier in 2012 the largest lava was erupted from a vent on the southwestern caldera wall flowed down to the caldera floor and advanced almost 1 km farther a surficial layer of the caldera floor sediment surrounding the leading edge of the lava failed most likely in response to load and heat transfer from the lava failure produced a slump sheet comprising folds with arcuate crests at the toe an undeformed domain in the middle and a basin and ridge domain at the head adjacent to the lava subsequently 1 the lava ruptured on two main faults that propagated across the caldera floor and 2 strike slip on the faults moved the lava that was in between forward simultaneously offsetting segments of the slump sheet these two events were probably triggered by the earthquake swarm recorded on the 17th july 2012 utc a day before the pumice raft appeared the leading edge of the lava then sank slowly into the underlying sediment sinking was accommodated by sideways expulsion of sediment from beneath the lava modifying the topography around the edge of the lava the caldera floor sediment was also disturbed when part of the southwestern caldera wall collapsed generating a small debris avalanche which is represented by a cluster of hummocks on the caldera floor collapse was a response to shallow intrusion of a rhyolite dyke into the southwestern caldera wall

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

structural evolution of a modern arc continent collision in papua new guinea the finisterre mountains and western solomon sea of northern papua new guinea are the site of an active oblique arc continent collision comparison of structures along the length of the collision zone provides a history of its structural evolution here we compare the results of structural mapping in the finisterre mountains where collision is in an advanced state with side scan sonar images and potential field data from the western solomon sea which illuminate the structure of the juvenile collision zone an accretionary wedge complex composed of a southwestward younging stack of imbricate thrust sheets developed along a westward extension of the modern new britain trench prior to collision this accretionary wedge crops out in the finisterre mountains as the erap structural complex consequences of collision were doubling of the crustal thickness to 50 52 km rapid up lift of the finisterre terrane and initiation of a major out of sequence thrust that displaced the finisterre volcanics over younger sediments of the accretionary wedge this out of sequence thrust is mapped in the finisterre mountains as the wongat thrust and it is recognized in the western solomon sea on side scan sonar images a second generation out of sequence thrust formed after substantial uplift had subaerially exposed the collision zone this thrust crosscuts the wongat thrust forming a window of accretionary wedge sediments bounded to both the ne and sw by finisterre volcanics this younger out of sequence thrust is the gain thrust of the finisterre mountains at least 15 km of crustal shortening has occurred across the wongat thrust at 146 30 e longitude and the gain thrust has accommodated up to 7 4 km of shortening in the same area it is probable that the well lithified finisterre volcanics serve as the backstop for the accretionary wedge collision complex that is forming in the collision zone of the western solomon sea potential field models indicate that this backstop is arcward dipping thrusting of the back stop material over the accretionary wedge as we observe along the wongat thrust is expected for wedges with arcward dipping backstops a series of ne sw trending cross faults perpendicular to the dominant structural trend exist in the collision zone these faults have components of left lateral strike slip and se down dip slip motion it is likely that the finisterre terrane is being segmented along these faults with the segmentation caused by differential resistance to convergence between the downgoing continental crust of the collision zone and the oceanic crust of the subduction zone to the east the origin of the faults is uncertain previous authors believed that they formed during paleogene volcanic activity in the finisterre terrane the colinearity of several of these cross faults with major mapped faults on the downgoing plate raises the possibility that the finisterre range cross faults are upper plate manifestations of lower plate structures and as such reveal strong interplate coupling in the collision zone

bedforms on the submarine flanks of insular volcanoes new insights gained from high resolution seafloor surveys a comparative analysis of bedform fields along the submarine flanks of insular volcanoes characterized by different morpho structural settings volcanic and meteo marine regimes vanuatu kermadec bismark madeira and aeolian archipelagos is presented here to provide insights on the size distribution morpho dynamic and genesis of such bedforms two main types of bedforms are recognized according to their size location and preconditioning triggering processes small scale bedforms have wavelengths of tens to hundreds of metres and wave heights of metres because of their small size they are typically not recognizable at water depths greater than 400 m from vessel mounted bathymetric surveys however few examples of small scale bedforms are reported from upper volcanic flanks where steep gradients commonly hinder their formation their recognition is mostly limited to the thalweg of shallow and flat bottomed channels that carve the insular shelf on slope gradients 15 small scale bedforms are mostly related to erosional depositional processes due to sedimentary gravity flows that are often the result of a cascading effect between volcanic and non volcanic processes for example flood discharges and retrogressive landslides large scale bedforms occur at all water depths having wavelengths of hundreds thousands of metres and wave heights up to few hundreds of metres the origin of large bedforms is more difficult to ascertain especially if only bathymetric data are available some diagnostic criteria are presented to distinguish between bedforms associated with landslide deposits and those associated with density currents in this latter case relevant sediment sources and slope gradients 8 are key factors for bedform development erosional depositional bedforms are typically related to eruption fed density flows formed during large caldera collapses or to large turbidity flows bedforms generated by turbidity flows are often observed in the lower volcanic flanks where an abrupt decrease of gradients is present often matching a change from confined to unconfined settings in summary this study provides insights to interpret bedforms in modern and ancient marine volcaniclastic settings elsewhere

catastrophic debris avalanche from ancestral mount shasta volcano california a debris avalanche deposit extends 43 km northwestward from the base of mount shasta across the floor of shasta valley california where it covers an area of at least 450 km 2 the surface of the deposit is dotted with hundreds of mounds hills and ridges all formed of blocks of pyroxene andesite and unconsolidated volcaniclastic deposits derived from an ancestral mount shasta individual hills are separated by flat topped laharlike deposits that also form the matrix of the debris avalanche and slope northwestward about 5 m km radiometric ages of rocks in the deposit and of a postavalanche basalt flow indicate that the avalanche occurred between about 300 000 and 360 000 yr ago an inferred average thickness of the deposit plus a computed volume of about 4 km 3 for the hills and ridges indicate an estimated volume of about 26 km 3 making it the largest known quaternary landslide on earth

interactions between a transform fault and arc volcanism in the bismarck sea papua new guinea 1 we present a new interpretation of the geological evolution of the western branch of the bismarck sea seismic lineation bssl region offshore the northwestern coast of papua new guinea from mapping and interpretation of bathymetry and backscatter data acquired aboard r v kilo moana in 2004 at present the schouten islands parallel the papua new guinea coast but this distribution results from the left lateral displacement of some of these volcanic islands by the bismarck sea seismic lineation the trend of the islands and seamounts was initially aligned n s and then displaced by the bssl wei island lies on a large submarine edifice that may have formed as part of a leaky transform subsequent to forming wei island was bisected and its pieces were displaced 45 km using this distance together with the strike slip rate for the bismarck sea seismic lineation predicted from the north bismarck plate south bismarck plate pole the division occurred approximately 385 000 years ago

deep structure of an arc continent collision earthquake relocation and inversion for upper mantle p and s wave velocities beneath papua new guinea we examine mechanisms of lithospheric growth and modes accommodating subcrustal convergence following the cessation of subduction by analyzing the seismicity and upper mantle velocities in the new guinea arc continent collision earthquakes in the papua new guinea png region from 1967 to 1984 have been relocated in a joint inversion with seismic velocities using p and s wave arrival times recorded by seismographs in png a total of 957 well recorded earthquakes were chosen for use in three dimensional velocity inversions from an initial catalog of 12 960 events based on the stability of initial hypocenter relocations constant velocity blocks were defined as irregular polyhedra to give fine detail in heavily sampled areas without introducing a large number of poorly controlled parameters and to exploit a priori knowledge of the geometry of velocity anomalies spherical geometry was used to accurately calculate long ray paths up to 1500 km in length most of the 700 best located hypocenters from the png data set are in the upper mantle beneath the finisterre huon fh ranges the newly accreted island arc terrane beneath the papuan peninsula and in the new britain seismic zone an oceanic subduction system these hypocenters show a well defined seismic zone dipping vertically or steeply to the north beneath the northern fh ranges from 125 to 250 km depth continuous along strike with the new britain seismic zone to the east which shows earthquakes to 600 km depth the steeply dipping intermediate depth seismicity flattens near 100 km depth beneath the fh ranges and forms a subhorizontal seismic zone beneath the fh ranges by contrast seismicity continues upward to the surface beneath new britain where the arc has not yet collided with new guinea the 100 km deep flat zone does not continue south of the fh ranges but appears to be truncated below the eastern and southern boundaries of the island arc terrane and no clear evidence for a south dipping seismic zone could be found the relationship of the flat part of the slab 100 km beneath the fh ranges and surface faulting is difficult to discern the apparent surface suture bounding the south side of the fh ranges is 100 km directly above the southern termination of intermediate depth seismicity nowhere in png could clear evidence for arc polarity reversal be found from seismicity all of the well located subcrustal earthquakes beneath the papuan peninsula lie in a narrow horizontal line between 125 and 175 km depth that follows the center of the peninsula and are distinctly separated from the fh seismic zone to the north these events do not require a southward subducting plate beneath the papuan peninsula an alternate and reasonable explanation for these events is that they are a result of unstable thickening of the lithosphere information on lateral heterogeneity in the mantle is limited because large variations in crustal velocities dominate the observed pattern of travel time residuals allowing for only crustal heterogeneity reduces travel time residual variances by 40 from a simple one dimensional structure while allowing for additional mantle heterogeneity results in 10 further reduction for the various parameterization s attempted here inversions with several different block geometries show low velocities at 35 to 171 km km depth beneath the bismarck sea back arc basin and high velocities just south of the intermediate depth fh seismic zone the pattern of lateral heterogeneity supports the inference from seismicity of north dipping slabs beneath both northeast new guinea and new britain

flank collapse and large scale landsliding in the cape verde islands off west africa large scale landslides occur on the flanks of many volcanic oceanic islands worldwide none have taken place in historical time but their geohazard potential especially their ability to generate tsunamis is large the cape verde islands are a group of 10 large and several smaller volcanic islands off the coast of west africa between 15 and 17 n a single flank landslide has previously been described from the island of fogo but systematic analysis of the cape verde group has until now been lacking this paper describes and interprets a multibeam bathymetry data set covering the slopes of the western cape verde islands including those of the islands with the most recent volcanic activity fogo in the southwest and santo antao in the northwest all of the larger islands show evidence of large flank landslides although only fogo and the southwest part of santo antao have failed in the last 400 ka tope de coroa the volcano at the southwest end of santo antao has been inactive for the past 170 ka and is judged to have a low landslide potential unless volcanic activity resumes in contrast there would seem to be a high probability of a future east directed landslide on fogo from the area of the highly active pico do fogo volcano although it is impossible to predict a timescale for such an event a tsunami generated by such a landslide could have a catastrophic effect on the adjacent island of santiago and possibly even farther afield on the west african coast

slope failures on the flanks of the western canary islands abstract landslides have been a key process in the evolution of the western canary islands the younger and more volcanically active canary islands el hierro la palma and tenerife show the clearest evidence of recent landslide activity the evidence includes landslide scars on the island flanks debris deposits on the lower island slopes and volcaniclastic turbidites on the floor of the adjacent ocean basins at least 14 large landslides have occurred on the flanks of the el hierro la palma and tenerife the majority of these in the last 1 million years with the youngest on the northwest flank of el hierro as recent as 15 thousand years in age older landslides undoubtedly occurred but are difficult to quantify because the evidence is buried beneath younger volcanic rocks and sediments landslides on the canary island flanks can be categorised as debris avalanches slumps or debris flows debris avalanches are long runout catastrophic failures which typically affect only the superficial part of the island volcanic sequence up to a maximum thickness of 1 to 2 km they are the commonest type of landslide mapped in contrast slumps move short distances and are deep rooted landslides which may affect the entire thickness of the volcanic edifice debris flows are defined as landslides which primarily affect the sedimentary cover of the submarine island flanks some landslides are complex events involving more than one of the above end member processes individual debris avalanches have volumes in the range of 50 500 km3 cover several thousand km2 of seafloor and have runout distances of up to 130 km from source overall debris avalanche deposits account for about 10 of the total volcanic edifices of the small relatively young islands of el hierro and la palma some parameters such as deposit volumes and landslide ages are difficult to quantify the key characteristics of debris avalanches include a relatively narrow headwall and chute above 3000 m water depth on the island flanks broadening into a depositional lobe below 3000 m debris avalanche deposits have a typically blocky morphology with individual blocks up to a kilometre or more in diameter however considerable variation exists between different avalanche deposits at one extreme the el golfo debris avalanche on el hierro has few large blocks scattered randomly across the avalanche surface at the other icod on the north flank of tenerife has much more numerous but smaller blocks over most of its surface with a few very large blocks confined to the margins of the deposit icod also exhibits flow structures longitudinal shears and pressure ridges that are absent in el golfo the primary controls on the block structure and distribution are inferred to be related to the nature of the landslide material and to flow processes observations in experimental debris flows show that the differences between the el golfo and icod landslide deposits are probably controlled by the greater proportion of fine grained material in the icod landslide this in turn relates to the nature of the failed volcanic rocks which are almost entirely basalt on el hierro but include a much greater proportion of pyroclastic deposits on tenerife landslide occurrence appears to be primarily controlled by the locations of volcanic rift zones on the islands with landslides propagating perpendicular to the rift orientation however this does not explain the uneven distribution of landslides on some islands which seems to indicate that unstable flanks are a weakness that can be carried forward during island development this may occur because certain island flanks are steeper extend to greater water depths or are less buttressed by the surrounding topography and because volcanic production following a landslide my be concentrated in the landslide scar thus focussing subsequent landslide potential in this area landslides are primarily a result of volcanic construction to a point where the mass of volcanic products fails under its own weight although the actual triggering factors are poorly understood they may include or be influenced by dyke intrusion pore pressure changes related to intrusion seismicity or sealevel climate changes a possible relationship between caldera collapse and landsliding on tenerife is not in our interpretation supported by the available evidence

the evolution of volcanic systems following sector collapse abstract sector collapses affect volcanic edifices across all tectonic settings and involve a rapid redistribution of mass comparable in scale to the largest magmatic eruptions the eruptive behaviour of a volcano following sector collapse provides a test of theoretical relationships between surface loading and magma storage which imply that collapse driven unloading may lead to changes in eruption rate and erupted magma compositions large sector collapses are infrequent events globally with all historical examples being relatively small in comparison to many of the events documented in the geological record as a result exploration of the impacts of sector collapse on eruptive behaviour requires detailed investigation of prehistoric collapses but this is often hindered by poorly resolved stratigraphic relationships and dating uncertainties nevertheless observations from a number of volcanoes indicate sharp changes in activity following sector collapse here a global synthesis of studies from individual volcanoes in both arc and intraplate settings is used to demonstrate a number of common processes in post collapse volcanism multiple examples from large 5 km3 sector collapses in arc settings show that collapse may be followed by compositionally anomalous large volume and often effusive eruptions interpreted to originate via disruption of a previously stable upper crustal reservoir these anomalous eruptions highlight that magma compositions erupted during periods of typical i e unperturbed by sector collapse volcanism may not be representative of the range of compositions stored within a vertically extensive crustal reservoir if eruptible magma is not present upper crustal reservoirs may rapidly solidify following collapse without further eruption allowing more mafic compositions to ascend to the surface with only limited upper crustal modification resulting in edifice regrowth at temporarily elevated eruption rates subsequent re establishment of an upper crustal reservoir further supports a relationship between surface loading and crustal storage but long term chemical and mineralogical differences between pre and post collapse evolved magmas imply that a newly developed reservoir can overprint the influence of a preceding reservoir forming a spatially and compositionally distinct plumbing system these broad patterns are replicated in intraplate settings despite differences in scale and melting processes current evidence suggests that post collapse evolution of intraplate volcanoes can be explained by unloading induced destabilisation of the magma plumbing system rather than increased melt production what emerges from an apparently diverse set of observations is a systematic behaviour that strongly supports a coupling between edifice growth and magma ascent storage and pressurisation eruption rates erupted compositions and the style of volcanism at any particular system may thus be modulated from the surface and long term shifts in surface behaviour may occur without any changes in the deep parts of magmatic systems observations of sharp post collapse changes in erupted compositions including the ascent of primitive mafic magmas also require a crystal dominated mid to upper crustal reservoir consistent with recent models of crustal magmatic systems

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

significance and timing of the mid 17th century eruption of long island papua new guinea tibito tephra was first recorded in the central highlands of papua new guinea png in 1971 by the late 1970s the tephra had been mapped across tens of thousands of square kilometres traced to i

ritter island volcano lateral collapse and the tsunami of 1888 summary in the early morning of 1888 march 13 roughly 5 km 3 of ritter island volcano fell violently into the sea northeast of new guinea this event the largest lateral collapse of an island volcano to be recorded in historical time flung devastating tsunami tens of metres high on to adjacent shores several hundred kilometres away observers on new guinea chronicled 3 min period waves up to 8 m high that lasted for as long as 3 h these accounts represent the best available first hand information on tsunami generated by a major volcano lateral collapse in this article we simulate the ritter island landslide as constrained by a 1985 sonar survey of its debris field and compare predicted tsunami with historical observations the best agreement occurs for landslides travelling at 40 m s 1 but velocities up to 80 m s 1 cannot be excluded the ritter island debris dropped little more than 800 m vertically and moved slowly compared with landslides that descend into deeper water basal friction block models predict that slides with shorter falls should attain lower peak velocities and that 40 ms 1 is perfectly compatible with the geometry and runout extent of the ritter island landslide the consensus between theory and observation for the ritter island waves increases our confidence in the existence of mega tsunami produced by oceanic volcano collapses two to three orders of magnitude larger in scale

active deformation in the new guinea fold and thrust belt seismological evidence for strike slip faulting and basement involved thrusting the new guinea fold and thrust belt forms a 1000 km long mountain chain running the length of new guinea but its trend is oblique to the predicted convergence direction a large component of left lateral shear across the mountain belt is expected but geological evidence for such motion is ambiguous surface structures in the fold and thrust belt show mountain building by folding and thrusting supposedly thin skinned of pre pliocene continental shelf sediments although some evidence indicates that active faulting penetrates the basement we examine the active deformation of this mountain belt by using teleseismic long period p and sh waveforms short period p waveforms and p wave first motions to determine reliable focal mechanisms and source depths for the 18 largest earthquakes in the new guinea fold and thrust belt since 1964 eight thrust events with seismic moments m0 between 1017 and 2 1018 n m are distributed throughout the thrust belt at depths ranging from 0 5 to 45 km and have steeply dipping fault planes that strike parallel to surface structural trends six of the eight events are between 11 and 25 km deep the steep dips of nodal planes the depths of these earthquakes and the known thicknesses of the sedimentary section show that thrust faulting is not exclusively thin skinned i e confined above a shallow detachment surface but penetrates the crystalline basement at high angles most earthquakes in the western half of the thrust belt including the three largest earthquakes examined m0 5 1018 n m show strike slip faulting with the probable fault plane oriented east west so that displacement is left lateral the nine strike slip earthquakes account for almost 90 of the observed seismic moment in the period 1964 1985 and indicate a seismic slip rate of 5 25 mm a all but one of these strike slip earthquakes are shallower than the thrust earthquakes suggesting that east northeast convergence across the fold and thrust belt is accommodated by a decoupled system of strike slip and dip slip faults while the great height of the mountain belt is an obvious indication that crustal thickening is an important consequence of plate motion in new guinea seismological evidence suggests that translation by strike slip faulting may play a much greater role than previously recognized by analogy in older collisional orogens whose motions can be inferred only from remnant structures and not from seismicity strike slip faulting may have been equally important in accommodating convergence we estimate from seismic moments of earthquakes and from the volume of the mountains that deformation of the new guinea highlands may account for 5 20 of the total convergence between the pacific plate and australia in new guinea

progressive mixing of meteoritic veneer into the early earth s deep mantle komatiites are ancient volcanic rocks mostly over 2 7 billion years old from the archaean era that formed through high degrees of partial melting of the mantle and therefore provide reliable information on bulk mantle compositions1 in particular the platinum group element pge contents of komatiites provide a unique source of information on core formation mantle differentiation and possibly core mantle interaction2 3 4 5 6 7 8 most of the available pge data on komatiites are from late archaean 2 7 2 9 gyr old or early proterozoic 2 0 2 5 gyr old samples here we show that most early archaean 3 5 3 2 gyr old komatiites from the barberton greenstone belt of south africa and the pilbara craton of western australia are depleted in pge relative to late archaean and younger komatiites early archaean komatiites record a signal of pge depletion in the lower mantle resulting from core formation this signal diminishes with time owing to progressive mixing in to the deep mantle of pge enriched cosmic material that the earth accreted as the late veneer during the early archaean 4 5 3 8 gyr ago meteorite bombardment

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

large scale volcanic cone collapse the 1888 slope failure of ritter volcano and other examples from papua new guinea a largely submarine avalanche amphitheatre that formed catastrophically in 1888 on ritter volcano has been identified from a bathymetric survey collapse of the volcano in 1888 therefore is considered to have been caused by rapid large scale slope failure rather than by cauldron subsidence as previously supposed escarpments of pre historic slope failures are common on other papua new guinea volcanoes directions of avalanching on some volcanoes in the bismarck volcanic arc appear to be controlled by a regional stress pattern and those for some volcanoes in the fly highlands province on mainland papua new guinea point away from the regional centre of pliocene uplift large amphitheatres such as at doma peaks in the fly high lands province probably originated by multiple collapses

primary cumulus platinum minerals in the monts de cristal complex gabon magmatic microenvironments inferred from high definition x ray fluorescence microscopy an unusual occurrence of pt enriched pyroxenites in the monts de cristal igneous complex is characterized by unusually high ratios of pt to other platinum group elements pges and very low cu and sulfide contents synchrotron x ray fluorescence microscopy was used to identify over a hundred discrete grains of platinum minerals and relate their occurrence to textural associations in the host heteradcumulate orthopyroxenites element associations backed up by fib sem and pixe probe observations indicate that most of the pt is associated with either as or trace cu ni rich sulfides or both some of the pt as grains can be identified as sperrylite and most are likely to be pt fe alloy the relative abundances and volumes of pt minerals to sulfide minerals are very large compared with typical magmatic sulfides almost all of the grains observed lie at or within a few tens of m of cumulus orthopyroxene grain boundaries and there is no significant difference between the populations of grains located inside or outside plagioclase oikocrysts these oikocrysts are inferred to have crystallized either at the cumulus stage or very shortly thereafter on the basis of their relationship to ti enrichment in the margins of pyroxene grains not enclosed in oikocrysts this relationship precludes a significant role of trapped intercumulus liquid in pt deposition or mobilization and also allows a confident inference that pt rich and pt as enriched phases precipitated directly from the magma at the cumulus stage these observations lead to the conclusion that fractionation of pt from other pges in this magmatic system is a consequence of a solubility limit for solid pt metal and or pt arsenide

pt and pd mobility in hydrothermal fluids evidence from komatiites and from thermodynamic modelling abstract komatiite host rocks and ores provide a natural laboratory for the study of pt and pd during hydration and carbonation of ultramafic rocks the degree of correlation between pt and pd and of those elements with lithophile elements such as ti in komatiitic rocks and ores is strongly dependent on the magmatic sulfide content of the rock pt and pd are typically very strongly correlated within s poor komatiites and in disseminated ores containing 5 volume or less magmatic sulfides in contrast they are almost completely decoupled in sulfide rich ore samples thermodynamic modelling based on the existing body of published experimental data on pt and pd solubilities suggests that pd and pt can be readily transported as bisulfide complexes in acidic neutral solutions under reduced and moderate oxidation condition at 300 c and chloride complexes are only important under extremely acidic oxidised conditions pd is much more soluble than pt in the case of fluids in sulfide rich environments in equilibrium with the characteristic assemblages found within altered and metamorphosed komatiites solubilities of both elements are much lower in sulfide poor environments especially where ph values are constrained to neutral values by the near ubiquitous presence of carbonate minerals in the alteration assemblage this accounts for the evident near immobility of pt and pd in even the most altered silicate host rocks as compared with their wide dispersion in sulfide rich ores

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

growth and collapse of a littoral lava dome during the 2018 19 eruption of kadovar volcano papua new guinea analyzed by multi sensor satellite imagery abstract growing volcanic islands and lava domes become structurally unstable associated with sectoral collapses explosive volcanism and related hazards this article describes the rare case of a growing and collapsing lava dome at kadovar volcano a small inhabited volcanic island located north of papua new guinea the eruption began on january 5 2018 and was monitored by multi sensor satellite imagery including optical thermal and synthetic aperture radar sar sensors results show that kadovar began a new episode of volcanic activity at the central crater and then also at the eastern coast of the island sar amplitude imagery has made it possible to monitor the birth of a new peninsula on the eastern coast this new peninsula has a blocky appearance and is associated with a localized thermal anomaly which is indicative of an emerging lava dome we analyzed the changes on the island and the peripheral lava dome and found that after a great increase in the size of the area parts of the island and the lava dome then collapsed eastwardly into the ocean on february 9 2018 the sector collapse caused small tsunami waves that hit the neighboring islands a subsequent slower re growth of the lava dome is evident from the satellite data which has reached a final area of 40 000 m this study provides details on the rapid growth and collapse of a peripheral lava dome and a destabilization episode in an island and dome sector and underlines the great value of remote sensing data on remote volcanic islands

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

volcano collapse and tsunami generation in the bismarck volcanic arc papua new guinea during a cruise on the r v kilo moana in 2004 we mapped 12 debris avalanches from volcanoes in the bismarck volcanic arc estimated their sizes and computed the size of potential tsunami run up in major local population centers from these features we used the towed side scan instrument hawaii mr1 the hull mounted em120 system for swath bathymetry and backscatter intensity a shallow penetration chirp system several bottom camera tows and selected cores we calibrate our computations with the known tsunami run up of the ritter collapse even the small collapses may have had significant run up on near by coastlines had any of the collapses we have identified occurred in modern times each would affect a presently populated region of the coastline to a moderate or significant degree

the aitape 1998 tsunami reconstructing the event from interviews and field mapping on the evening of 17 july 1998 on the aitape coast of papua new guinea a strongly felt earthquake was followed some 10 25 minutes later by a destructive tsunami the tsunami comprised three waves each estimated to be about 4 m high the second of the three waves rose to a height of 10 15 m above sea level after it had crossed the shoreline and caused most damage maximum wave heights and the greatest damage were recorded along a 14 km sector of coast centered on sissano lagoon in this sector the wavefronts moved from east to west along the coast all structures were destroyed and in the two main villages 20 40 percent of the population was killed partial destruction extended 23 km to the southeast and 8 km to the northwest and effects of the tsunami were felt as far as 250 km to the west northwest beyond the international border more than 1600 people are known to have died with some estimates as high as 2200 1000 were seriously injured and 10 000 survivors were displaced this paper presents information from interviews with eye witnesses and from mapping of damage and inundation and includes new information on the height shape and timing of the waves on the possible escape of petroleum and other gases from beneath the seafloor before and during the tsunami on unusual sound effects that preceded the waves and lighting effects that followed on possible deep circulation to 250 m of sea water in the waves on subsidence of the order of 50 70 cm at the coastal sand barrier and on the resilience and potential protective capacity of certain species of trees eye witness accounts indicate that the tsunami reached the shore at between 09 00 and 09 08 ut which is earlier than is proposed in published models of the timing and location of the source of the tsunami

submarine landslide deposits of the historical lateral collapse of ritter island papua new guinea abstract the march 13th 1888 collapse of ritter island in papua new guinea is the largest known sector collapse of an island volcano in historical times one single event removed most of the island and its western submarine flank and produced a landslide deposit that extends at least 70 km from the headwall of the collapse scar we have mapped and described the deposits of the debris avalanche left by the collapse using full coverage multibeam bathymetry side scan sonar backscatter intensity mapping chirp seismic reflection profiles towcam photographs of the seafloor and samples from a single dredge applying concepts originally developed on the 1980 mount st helens collapse landslide deposits we find that the ritter landslide deposits show three distinct morphological facies large block debris avalanche matrix rich debris avalanche and distal debris flow facies restoring the island s land and submarine topography we obtained a volume of 4 2 km3 for the initial collapse about 75 of which is now forming the large block facies at distances less than 12 km from the collapse scar the matrix rich facies volume is unknown but large scale erosion of the marine sediment substrate yielded a minimum total volume of 6 4 km3 in the distal debris flow and or turbidite deposits highlighting the efficiency of substrate erosion during the later history of the landslide movement although studying submarine landslide deposits we can never have the same confidence that subaerial observations provide our analysis shows that well exposed submarine landslide deposits can be interpreted in a similar way to subaerial volcano collapse deposits and that they can in turn be used to interpret older incompletely exposed submarine landslide deposits studying the deposits from a facies perspective provides the basis for reconstructing the kinematics of a collapse event landslide understanding the mechanisms involved in its movement and deposition and so providing key inputs to tsunami models

gps and seismological constraints on active tectonics and arc continent collision in papua new guinea implications for mechanics of microplate rotations in a plate boundary zone 1 the island of new guinea is located within the deforming zone between the pacific and australian plates that converge obliquely at 110 mm yr new guinea has been fragmented into a complex array of microplates some of which rotate rapidly about nearby vertical axes we present velocities from a network of 38 global positioning system gps sites spanning much of the nation of papua new guinea png the gps derived velocities are used to explain the kinematics of major tectonic blocks in the region and the nature of strain accumulation on major faults in png we simultaneously invert gps velocities earthquake slip vectors on faults and transform orientations in the woodlark basin for the poles of rotation of the tectonic blocks and the degree of elastic strain accumulation on faults in the region the data are best explained by six distinct tectonic blocks the australian pacific south bismarck north bismarck and woodlark plates and a previously unrecognized new guinea highlands block significant portions of the ramu markham fault appear to be locked which has implications for seismic hazard determination in the markham valley region we also propose that rapid clockwise rotation of the south bismarck plate is controlled by edge forces initiated by the collision between the finisterre arc and the new guinea highlands

seismotectonics of new guinea a model for arc reversal following arc continent collision the structure and evolution of the northern new guinea collision zone is deduced from international seismological center isc seismicity 1964 1985 new and previously published focal mechanisms and a reexamination of pertinent geological data a tectonic model for the new guinea margin is derived which illustrates the sequential stages in the collision and suturing of the bewani toricelli adelbert finisterre huon new britain arc to central new guinea followed by subduction polarity reversal in the west east of 149 e the solomon plate is being subducted both to the north and south bringing the new britain and trobriand forearcs toward collision west of 149 e the forearcs have collided and together they override a fold in the doubly subducted solomon plate lithosphere which has an axis that is parallel to the strike of the ramu markham suture and that plunges westward at an angle of 5 beneath the coast ranges of northern new guinea active volcanism off the north coast of new guinea is related to subduction of the solomon plate beneath the bismarck plate active volcanism of the papuan peninsula and quaternary volcanism of the new guinea highlands are related to slow subduction of the solomon plate beneath the indo australian plate along the trobriand trough and the trough s former extension to the west respectively from 144 148 e seismicity and focal mechanisms reveal that convergence between the sutured bismarck and indo australian plates is accommodated by thrusting within the finisterre and adelbert ranges and compression of the new guinea orogenic belt together with basement involved foreland folding and thrusting to the south the finisterre block overthrusts the new guinea orogenic belt whereas the adelbert block is sutured to new guinea and overthrusts the oceanic lithosphere of the bismarck sea along the new guinea trench west of 144 e seismicity defines a southward dipping wadati benioif zone and focal mechanisms indicate oblique subduction only this oldest westernmost portion of the collision has progressed past suturing to a full reversal in subduction polarity

differential preservation in the geologic record of intraoceanic arc sedimentary and tectonic processes abstract records of ancient intraoceanic arc activity now preserved in continental suture zones are commonly used to reconstruct paleogeography and plate motion and to understand how continental crust is formed recycled and maintained through time however interpreting tectonic and sedimentary records from ancient terranes after arc continent collision is complicated by preferential preservation of evidence for some arc processes and loss of evidence for others in this synthesis we examine what is lost and what is preserved in the translation from modern processes to the ancient record of intraoceanic arcs composition of accreted arc terranes differs as a function of arc continent collision geometry forward facing collision can accrete an oceanic arc on to either a passive or an active continental margin with the arc facing the continent and colliding trench and forearc side first in a backward facing collision involving two subduction zones with similar polarity the arc collides backarc first with an active continental margin the preservation of evidence for contemporary sedimentary and tectonic arc processes in the geologic record depends greatly on how well the various parts of the arc survive collision and orogeny in each case preservation of arc terranes likely is biased towards those that were in a state of tectonic accretion for tens of millions of years before collision rather than tectonic erosion the prevalence of tectonic erosion in modern intraoceanic arcs implies that valuable records of arc processes are commonly destroyed even before the arc collides with a continent arc systems are most likely to undergo tectonic accretion shortly before forward facing collision with a continent and thus most forearc and accretionary prism material in ancient arc terranes likely is temporally biased toward the final stages of arc activity when sediment flux to the trench was greatest and tectonic accretion prevailed collision geometry and tectonic erosion vs accretion are important controls on the ultimate survival of material from the trench forearc arc massif intra arc basins and backarc basins and thus on how well an ancient arc terrane preserves evidence for tectonic processes such as subduction of aseismic ridges and seamounts oblique plate convergence and arc rifting forward facing collision involves substantial recycling melting and fractionation of continent derived material during and after collision and so produces melts rich in silica and incompatible trace elements as a result forward facing collision can drive the composition of accreted arc crust toward that of average continental crust

the volcanic environment for 40 000 years of human occupation on the willaumez isthmus west new britain papua new guinea abstract the stratigraphic sequence of 22 tephra beds and their associated paleosols at two sites selected from our studies in west new britain papua new guinea provide the essential environmental background for understanding human responses to c 40 ka years of volcanic activity lithology grain size and mineralogy of the tephras interpreted for the first time elucidate the varying volcanic provenance especially of the pleistocene beds and the environmental conditions which former inhabitants experienced this sequence provides an important long term record of how humans coped with volcanic adversity in papua new guinea the stratigraphic record contains abundant evidence for human settlement during the intervals between volcanic eruptions following plinian and subplinian eruptions people abandoned the region for significant periods of time in some cases these cataclysmic events caused major cultural disasters characterised by local population extinction and loss of some significant types of cultural behaviour despite the punctuated record of settlement and changes in material culture over the long term human populations found effective ways to maintain themselves within an active volcanic environment key responses included persistence of mobile and flexible settlement patterns planned and staged uses of raw materials social exchange and increasing levels of landscape management

new multibeam mapping and geochemistry of the 30 35 s sector and overview of southern kermadec arc volcanism new multibeam mapping and whole rock geochemistry establish the first order definition of the modem submarine kermadec arc between 30 degrees and 35 degrees s twenty two volcanoes with basal diameters 5 km are newly discovered or fully mapped for the first time giggenbacb macauley havre haungaroa kuiwai ngatoroirangi sonne kibblewhite and yokosuka for each large volcano edifice morphology and structure surficial deposits lava fields distribution of sector collapses and lava compositions are determined macauley and havre are large silicic intra oceanic caldera complexes for both concentric ridges on the outer flanks are interpreted as recording mega bedforms associated with pyroclastic density flows and edifice foundering other stratovolcanoes reveal complex histories with repeated cycles of tectonically controlled construction and sector collapse extensive basaltic flow fields and the development of summit craters and or small nested calderas combined with existing data for the southernmost arc segment we provide an overview of the spatial distribution and magmatic heterogeneity along similar to 780 km of the kermadec arc at 30 degrees 36 degrees 30 s coincident changes in arc elevation and lava composition define three volcano tectonic segments a central deeper segment at 32 degrees 20 34 degrees 10 s has basement elevations of 3200 m water depth and relatively simple stratovolcanoes dominated by low k series basalt basaltic andesite in contrast the adjoining arc segments have higher basement elevations typically 3 km coincide with the shallower arc segments the dominant mode of large caldera formation is interpreted as mass discharge pyroclastic eruption with syn eruptive collapse hence the shallower arc segments are characterized by both the generation of volatile enriched magmas from crustal melting and a reduced hydrostatic load allowing magma vesiculation and fragmentation to initiate and sustain pyroclastic eruptions proposed initiation parameters for submarine pyroclastic eruptions are water depths 70 wt sio2 and a high discharge rate c 2005 elsevier b v all rights reserved

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

sulfide oxidation as a process for the formation of copper rich magmatic sulfides typical magmatic sulfides are dominated by pyrrhotite and pentlandite with minor chalcopyrite and the bulk atomic cu fe ratio of these sulfides is typically less than unity however there are rar

sulfide saturation history of the stillwater complex montana chemostratigraphic variation in platinum group elements a platinum group element pge investigation of a 5 3 km thick stratigraphic section of the stillwater complex montana was undertaken to refine and test a geochemical technique to explore for platiniferous horizons in layered mafic ultramafic complexes pge au major and trace elements were determined in 92 samples from outcrops along traverses in the chrome mountain and contact mountain areas in the western part of the stillwater complex where the j m reef occurs 1 460 m above the floor of the intrusion a further 29 samples from a drill hole cored in the immediate vicinity of the j m reef were analyzed to detail compositional variations directly above and below the j m reef below the j m reef background concentrations of pt 10 ppb and pd 7 ppb are features of peridotites with intermediate s concentrations mostly 100 200 ppm and rocks from the bronzitite norite i and gabbronorite i zones mostly pt au within the middle and upper banded series s abundances fluctuate considerably but exhibit an overall upward increase the behavior of these elements records periodic sulfide saturation during deposition of the peridotite zone followed by crystallization under sulfide undersaturated conditions until saturation is achieved at the base of the j m reef following formation of the reef sulfide saturated conditions persisted throughout the deposition of most of the remaining lower layered series this resulted in a pronounced impoverishment in pge abundance in the remaining magma a condition that continued throughout deposition of the remainder of a succession which is characterized by very low pt 1 5 ppb and pd 0 7 ppb abundances because only unmineralized rock was selected for study in the 5 3 km thick section the results provide an unbiased picture of the variation in background pge levels during crystallization of the stillwater complex in contrast the variations in the drill core samples through the reef provide a detailed record of ore formation plots of pt pd pd s and pt pd as a function of stratigraphic height in the intrusion show that the location of the j m reef is defined by an abrupt change in these concentrations and ratios although this is the most abrupt change three other anomalies in pge abundance and ratios are apparent in the profiles and coincide with known laterally extensive sub economic sulfide concentrations above the j m reef the uppermost of these is the pge bearing picket pin sulfide horizon the relative ease with which mineralized horizons can be pinpointed in these diagrams indicates that a similar approach could be used in exploration programs in other ultramafic mafic intrusions our observations exclude the possibilities of either magma mixing within the stillwater chamber or the fluxing of a volatile rich fluid as the mechanisms responsible for the genesis of the j m reef rather our data indicate that the j m reef formed from a parental magma that was strongly enriched in pge this magma likely formed at depth below the stillwater magma chamber by the interaction of the parental magma with s rich meta sedimentary rocks followed by the re dissolution of these sulfides in the stillwater magma

the triple group and the platinova gold and palladium reefs in the skaergaard intrusion stratigraphic and petrographic relations this paper describes the setting structure and textural relations of the platinova reefs in the skaergaard intrusion the reefs comprise a strata bound occurrence of au pge estimated at 91 million tons of rock with 1 8 ppm au and similar amounts of pd the precious metals occur in two major zones a lower major pd reef which is concordant with the modal layering and followed by at least ten minor pd reefs also concordant and an au concentration which fringes the pd reefs outward and upward through the triple group units the major pd concentration and the au concentration are separated in a systematic way across the intrusion near the center of the intrusion the au concentration occurs some 60 m higher in the stratigraphy than the main pd reef but the separation decreases gradually outward being only a few meters near the margins the dominant precious metal minerals are small grains of cu fe au pd pt alloys which typically are included in interstitial sulfides bornite digenite and smaller amounts of chalcopyrite the textural relations suggest a close genetic association between the sulfides and au pge minerals an association which is confirmed by whole rock compositional data our observations demonstrate that the platinova reefs formed after significant concentration of the au pge and s in the residual magma during fractional crystallization before it became saturated with respect to a sulfide fe cu s o liquid this sulfide liquid acted as a collector of au pge and settled into the layered series cumulates we propose that the structure of the deposit evolved through fractional crystallization of the au pge bearing sulfide liquid as it was filter pressed along with the interstitial silicate melt upward into the overlying unconsolidated cumulates the fractional crystallization resulted in an evolution of the au pge bearing phases with progressive fractionation from pd rich alloys at the base of the deposit to au rich alloys at the top we argue that the sulfides evolved to their present extreme cu rich fe poor composition during oxidation desulfurization reactions in the same event which oxidized the iron titanium oxides of the intrusion this oxidation desulfurization probably had no overall effect on the distribution of au and pge

the ischia debris avalanche first clear submarine evidence in the mediterranean of a volcanic island prehistorical collapse sector or flank collapse with related debris avalanches is increasingly recognized as a relatively common volcanic behaviour in particular for large hot spot related oceanic islands here we report the case of a catastrophic collapse that occurred at ischia volcanic island in prehistorical times and was driven by the volcano tectonic uplift of mt epomeo the major relief of the island the collapse left a subaerial to submarine horseshoe scar on the southern flank of the island and generated a debris avalanche incorporating thousands of giant blocks dispersed as far as 50 km from the island during the emplacement part of the debris avalanche evolved into a debris flow covering an area of 250 300 km2 this constitutes the first clear evidence of a submarine debris avalanche in the mediterranean sea the major collapse was followed and probably also preceded by recurrent less catastrophic terrestrial and underwater failures two other undersea hummocky deposits are found north and west of the island and might tentatively be correlated to the major southern collapse such volcanic behaviour previously unknown for ischia volcano has likely triggered tsunami waves over the entire bay of naples raising the question of their impact on prehistorical historical communities

volcanic evolution of the south sandwich volcanic arc south atlantic from multibeam bathymetry abstract new multibeam bathymetry data are presented for the south sandwich intra oceanic arc which occupies the small sandwich plate in the south atlantic and is widely considered to be a simple end member in the range of intra oceanic arc types the images show for the first time the distribution of submarine volcanic tectonic and erosional depositional features along the whole length of the 540 km long volcanic arc allowing systematic investigation of along arc variations the data confirm that the volcanic arc has a simple structure composed of large volcanoes which form a well defined volcanic front but with three parallel cross cutting seamount chains extending 38 60 km from near the volcanic front into the rear arc there is no evidence for intra arc rifting or extinct volcanic lines topographic evidence for faulting is generally absent except near the northern and southern plate boundaries most of the volcanic arc appears to be built on ocean crust formed at the associated back arc spreading centre as previously proposed from magnetic data but the southern part of the arc appears to be underlain by older arc or continental crust whose west facing rifted margin facing the back arc basin is defined by the new bathymetry the new survey shows nine main volcanic edifices along the volcanic front and ca 20 main seamounts the main volcanoes form largely glaciated islands with summits 3 0 3 5 km above base levels which are 2500 3000 m deep in the north and shallower at 2000 2500 m deep in the south some of the component seamounts are interpreted to have been active since the last glacial maximum and so are approximately contemporaneous with the volcanic front volcanism seven calderas all either submarine or ice filled have been identified adventure volcano a newly discovered submarine volcanic front caldera volcano is described for the first time all but one of the calderas are situated on summits of large volcanoes in the southern part of the arc and most are associated with current or historic volcanic or hydrothermal activity shallow shelves around the islands are generally 1 10 km wide submerged banks up to 1100 m deep are interpreted as subsided erosional surfaces seamounts and emergent volcanoes experienced a range of mass wasting processes including by landsliding and smaller mass flows

collision propagation in papua new guinea and the solomon sea the mountain system in papua new guinea png is growing by accretion of australian margin strata to the front of the papuan fold and thrust belt in the south and by accretion of exotic terranes along its ne margin presently the finisterre terrane is being accreted along the ne margin of png and the collision point is migrating eastward within the solomon sea east of the collision point the new britain trench marks the tectonic front between the solomon sea and south bismarck sea plates whereas to the west the tectonic front lies in the southern part of the papuan fold and thrust belt present day sedimentary environments within the western solomon sea are inferred from interpretation of seismic reflection data similar facies are observed accreted to the front of the finisterre terrane in the markham valley the frontal leron formation is largely fluvial and shallow marine and the erap complex contains elements of turbidites and pelagic deposits there appears to be a smaller volume of coarse proximal marine strata accreted to the front of the finisterre terrane than is expected from interpretation of reflection profiles in the western solomon sea this difference may be attributed to a combination of submarine erosion in the markham canyon partial incorporation of these deposits into the erap complex and a difference in depositional rates and products carried to the solomon sea in the past relative to what is observed today based on plate motions alternative collision geometries and the youngest dates available for the erap complex we determine a rate of progression of the collision point of about 212 km m y during the past 1 m y

holocene explosive eruptions of witori and dakataua caldera volcanoes in west new britain papua new guinea abstract witori and dakataua caldera volcanoes have been very active in the middle to late holocene using tephrochronology this paper establishes the chronostratigraphy of these eruptions and their magnitude and the frequency of explosive volcanism at witori and dakataua after a long dormancy witori started explosive activity at ca 5600 conventional radiocarbon years bp producing in the next 4500 years five major tephra layers w k1 to w k4 w g with veis of 5 to 6 after the w g eruption at around 1200 bp the activity decreased in magnitude but increased in frequency with some eruptions forming central cones the major eruption of dakataua began with alternating ejections of phreatomagmatic ashfalls and plinian deposits followed by the cataclysmic eruption resulting in lithic rich pyroclastic flows ca 1100 1200 bp the major tephra layers cover extensive areas in west new britain due to their large volumes and the prevailing easterly winds providing valuable time markers for establishing holocene chronology the largest eruption the w k2 event of ca 3300 bp shaped much of the present landscape with an extensive area significantly devastated by tephra falls and pyroclastic flows obsidian and other artefacts buried by the tephras indicate that the area was repeatedly occupied the major tephra events formed new coastal plains favourable for human occupation

wetting facilitates late stage segregation of precious metal enriched sulfosalt melt in magmatic sulfide systems the wetting behavior of as rich sulfosalt melts against monosulfide solid solution mss is investigated using experiments to elucidate late stage fractionation processes in magmatic sulfide systems which may control the distribution of platinum group elements a range of as rich melt compositions is found to wet mss including those that contain significant proportions 1 45 of precious metals pt pd and au however extremely au rich or pt rich sulfosalt melts 40 au 50 pt 5 au do not wet mss these results imply that if magma contamination and or fractionation processes were able to produce a late stage as rich melt sulfosalt melts crystallize cooler than mss that exceeds 0 2 of the rock volume then an interconnected melt drainage network would be able to form along mss crystal triple junctions the dense sulfosalt melt could thereby drain downward progressively sequestering incompatible bi sb te pt pd and au to form sulfosalt melt accumulations that continue to fractionate to form the platinum group minerals this late stage fractionation model is consistent with the observed mineral distribution in numerous magmatic sulfide deposits

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

pyroxene oikocrysts in troctolitic cumulates evidence for supercooled crystallisation and postcumulus modification studies of pyroxene oikocrysts in plagioclase olivine cumulates crystallised from high alumina olivine tholeiite magmas in layered intrusions inferred to represent periodically replenished magma chambers show that small plagioclases enclosed within the oikocrysts differ significantly from plagioclases in the host rock plagioclases within oikocrysts are very elongate with a high surface area show extensive mutual attachment at high angles resembling skeletal growth and tend to be randomly orientated some are rounded and embayed are reversely zoned and more sodic by an 5 10 than some of the plagioclase in the host rock plagioclase crystal centres tend to be closer spaced in the oikocrysts than in the host rock in contrast plagioclases in the host rock are discrete coarser grained less elongate strongly aligned and locally polygonised

asteroid impact tsunami of 2880 march 16 summary nasa scientists have given a 1 1 km diameter asteroid 1950 da a 0 0 to 0 3 per cent probability of colliding with the earth in the year 2880 this article examines a scenario where 1950 da strikes the sea 600 km east of the united states coast travelling at 17 8 km s 1 the asteroid would blow a cavity 19 km in diameter and as deep as the ocean 5 km at the impact site tsunami waves hundreds of metres high would follow as the transient impact cavity collapses the tsunami disperses quickly but because the waves are so large initially destructive energy carries basin wide within two hours of the scenario impact 100 m waves make landfall from cape cod to cape hatteras within 12 hours 20 m waves arrive in europe and africa water velocity at the deep ocean floor exceeds 1 m s 1 to 800 km distance strong enough to leave a widespread tsunami signature in the sedimentary record

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

solubility of pt in sulphide mattes implications for the genesis of pge rich horizons in layered intrusions the partitioning of pt in sulphide melt matte has been studied as a function of fs2 and fo2 at 1200 and 1300 c the results show that the solubility of pt in mattes increases strongly with increasing fs2 and decreases weakly with increasing fo2 the increase in pt solubility with increasing fs2 is attributed to pt dissolving in the melt as a sulphide species and the weak inverse dependence of pt solubility on fo2 to the diluting effect of increasing o in the melt at high fo2 these results coupled with measurements of pt solubility in silicate melts taken from the literature allow the calculation of pt matte silicate melt partition coefficients d pt matte sil for a range of conditions pertinent to the formation of pt rich horizons in layered intrusions the calculated values range between 107 and 1011 depending on fo2 and fs2 several orders of magnitude higher than previously published values our preferred value for d pt matte sil for conditions appropriate to the merensky reef is 107 and for the stillwater pt rich horizon 108 the new results are consistent with the magmatic hypothesis for pt rich horizons in layered intrusions

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