landslide generated tsunamis at reunion island 1 landslides that occur on oceanic volcanoes can reach the sea and trigger catastrophic tsunamis reunion island has been the location of numerous huge landslides involving tens to hundreds of cubic kilometers of material we use a new two fluid seawater and landslide numerical model to estimate the wave amplitudes and the propagation of tsunamis associated with landslide events on reunion island a 10 km3 landslide from the eastern flank of piton de la fournaise volcano would lift the water surface by about 150 m where it entered the sea the wave thus generated would reach saint denis the capital of reunion island population of about 150 000 people in only 12 min with an amplitude of more than 10 m and would reach mauritius island in 18 min although mauritius is located about 175 km from the impact waves reaching its coast would be greater than those for reunion island this is due to the initial shape of the wave and its propagation normal to the coast at mauritius but generally coast parallel at reunion island a submarine landslide of the coastal shelf of 2 km3 would trigger a 40 m high wave that would severely affect the proximal coast in the western part of reunion island for a landslide of the shelf of only 0 5 km3 waves of about 2 m in amplitude would affect the proximal coast

imaging subduction from the trench to 300 km depth beneath the central north island new zealand with vp and vp vs summary recent dense deployments of portable digital seismographs have provided excellent control on earthquakes beneath the central north island of new zealand here we use a subset of the best recorded earthquakes in an inversion for the 3 d vp and vp vs structure the data set includes 39 123 p observations and 18 331 s observations from 1239 earthquakes and nine explosions the subducted plate is imaged as a high vp low vp vs feature vp within the mantle of the subducted slab is almost always 8 5 km s 1 which requires the ca 120 myr slab to be unusually cold the low vp vs within the subducted plate closely parallels the lower plane of the dipping seismic zone it most likely indicates fluid resulting from dehydration of serpentine in the slab mantle and the earthquakes themselves are likely to be promoted by dehydration embrittlement we identify a region with vp 8 0 km s 1 directly above the dipping seismic zone can be interpreted as sinking entrained with the motion of the subducted slab and forming a viscous blanket that insulates the slab from the high temperature mantle wedge material in the overlying low vp region can be interpreted as rising within a return flow within the wedge the volcanic front appears to be controlled by where this dipping low vp region meets the base of the crust the thickness of the backarc crust also shows significant variation along strike in the central taupo volcanic zone tvz the crust is ca 35 km thick while southwest of mt ruapehu the crust thickens by ca 10 km there is no significant low vp zone in the mantle wedge in this southwestern region suggesting that this thicker crust has choked off mantle return flow the seismic tomography results when combined with constraints on mantle flow from previous shear wave splitting results provide a plausible model for both the distribution of volcanism in the central north island and the exceptional magmatic productivity of the central tvz

landward and seaward directed thrusting accompanying the onset of subduction beneath new zealand a short 5 m y episode of deformation accompanied the onset of the present phase of subduction beneath northern and eastern new zealand in the earliest miocene at many places along the continental margin the structures produced were dominated by subhorizontal thrust sheets with tens of kilometres of displacement thrusting was directed both landward with or without involvement of the upper part of the downgoing plate and seaward the structures are different in style from those typical of active trench slopes which are predominantly seaward directed imbricate thrusts and associated folds the structures show that delamination of the downgoing plate occurred at some places and suggest that a high degree of coupling between upper and lower plates occurred at others

numerical modeling of the emplacement of socompa rock avalanche chile 1 the 7 5 ka socompa sector collapse emplaced 25 km3 of fragmented rock as a thin but widespread 500 km2 avalanche deposit followed by late stage sliding of 11 km3 as toreva blocks most of the avalanche mass was emplaced dry although saturation of a basal shear layer cannot be excluded modeling was carried out using the depth averaged granular flow equations in order to provide information on the flow behavior of this well preserved long run out avalanche results were constrained using structures preserved on the surface of the deposit as well as by deposit outline and run up a proxy for velocity models assuming constant dynamic friction fail to produce realistic results because the low basal friction angles 1 to 3 5 necessary to generate observed run out permit neither adequate deposition on slopes nor preservation of significant morphology on the deposit surface a reasonable fit is obtained however if the avalanche is assumed simply to experience a constant retarding stress of 50 100 kpa during flow this permits long run out as well as deposition on slopes and preservation of realistic depositional morphology in particular the model explains a prominent topographic escarpment on the deposit surface as the frozen front of a huge wave of debris reflected off surrounding hills the result that socompa avalanche experienced a small approximately constant retarding stress during emplacement is consistent with a previously published analysis of avalanche data

numerical analysis of the mobility of the palos verdes debris avalanche california and its implication for the generation of tsunamis abstract analysis of morphology failure and post failure stages of the palos verdes debris avalanche reveals that it may have triggered a significant tsunami wave our analysis of the failure itself indicates that the slope is stable under aseismic conditions but that a major earthquake with a magnitude around 7 could have triggered the slide a post failure analysis considering the debris avalanche as a bi linear flow shows that peak velocities of up to 45 m s could have been reached and that the initial movement involved a mass of rock less than 10 km wide 1 km long and about 50 80 m thick initial wave height estimates vary from 10 to 50 m tsunami waves propagating to the local shoreline would be significantly smaller such a range demonstrates our lack of proper knowledge of the transition from failure to post failure behavior related to mass movements further investigations and analyses of terrestrial and submarine evidence are required for a proper hazard assessment related to tsunami generation in the los angeles area

tectonic rotations about vertical axes during the last 4 ma in part of the new zealand plate boundary zone the declinations of the primary magnetization of sedimentary rocks in the northern part of the new zealand plate boundary zone after thermal or alternating field cleaning have been used to determine tectonic rotations about vertical axes of rigid crustal blocks the pattern of rotations during the last 4 ma combined with structural style and continuity defines seven structural domains each ca 100 100 200 km across which contain crustal blocks up to 100 km across and 20 km thick large crustal blocks tens of km across in two of these domains have rotated clockwise more than 20 relative to one of the margins of the plate boundary zone in the last 4 ma their behaviour appears to be controlled by the nature of the plate boundaries such as the presence of an underlying subducted slab and the strength of the crust at the back of the overlying crustal wedge small crustal blocks 10 km across may have rotated clockwise through angles greater than 20 during the last 4 ma floating on an underlying zone of more distributed deformation the tectonic rotations of the large crustal blocks and the nature of the deformation at their boundaries combined with an interpolation of the relative plate positions can be used to reconstruct the plate boundary zone at ca 4 ma

inconsistent magnetic polarities between greigite and pyrrhotite magnetite bearing marine sediments from the tsailiao chi section southwestern taiwan abstract to establish a magnetobiostratigraphy for a 620 m thick middle to late pleistocene mudstone sequence in the lower gutingkeng formation of the tsailiao chi tlc section in southwestern taiwan we conducted paleomagnetic and mineral magnetic measurements together with sediment granulometry and calcareous nannofossil identification paleomagnetic samples from 65 sites revealed two types of thermal demagnetization 25 400 c behavior 1 single component stable characteristic remanence in magnetite and pyrrhotite dominated samples type s and 2 abrupt changes in polarity when samples with significant greigite concentrations were heated above 320 340 c type c the characteristic polarities derived from type s samples and from magnetite dominated type c samples obtained above 340 c are consistent with those determined from nannofossil biostratigraphy this implies that the nrm carried by magnetite and pyrrhotite is reliable the essentially antiparallel remanence components in type c samples below 340 c are attributed to greigite the almost antiparallel direction could have resulted from delayed formation of greigite but in this case the different direction of this component must have resulted from variable remanence lock in times alternatively the opposite polarities may result from self reversal which warrants further investigation pyrrhotite and greigite may have both formed authigenically but there is no clear explanation for the observed differences in direction

review of paleostrain stress directions in northland new zealand and of the structure of the northland allochthon abstract folding shearing and fracturing in the northland allochthon occurred prior to deposition of the upper oligocene miocene akarana supergroup observations on fold vergence indicate that the allochthon moved from nnw to sse part of the pre miocene post lower cretaceous deformation in the autochthonous basement consisted of thrusting and strike slip faulting with compression trending ne sw across northland peninsula nw se thrusting followed by nw se extension affected the miocene rocks nw se extension persisted into the quaternary

shortening of an overriding plate and its implications for slip on a subduction thrust central hikurangi margin new zealand 1 at subduction plate boundaries strains accumulate within the overriding plate in response to motion of the down going plate to a first approximation margin normal interplate slip and shortening in the overriding plate sum to the total plate convergence therefore margin normal interplate slip can be estimated by measuring shortening in the overriding plate and total plate convergence here we quantify margin normal interplate slip by measuring shortening of the upper plate along a profile which extends up to 480 km across and approximately normal to the central hikurangi margin new zealand long term deformation is estimated for periods of millions of years using data from seismic reflection lines and cross sections while contemporary strain rates are derived from global positioning system gps geodetic velocities these data permit comparison of plate convergence rates determined by seafloor spreading data with the rates of contraction over short 7 years and long 2 5 and 5 myr periods of time on this part of the plate boundary total margin normal shortening in the overriding plate over the last 5 myr was 9 28 km and accounts for 6 19 of the total convergence 145 160 km at rates of 2 6 mm yr the remaining 80 or more of plate convergence has been accommodated by slip on the subduction thrust gps contraction along approximately the same profile indicates 14 16 mm yr of contemporary shortening across the terrestrial part of the upper plate which is approximately modeled by 80 interplate coupling on the subduction interface down to depths of 30 km the contrasting proportions of inferred interplate coupling for contemporary and geological data sets are consistent with stick slip behavior on the plate interface and with slip being principally achieved during intermittent large earthquakes the general shapes of short and long term shortening profiles are similar and suggest that the highest strains occur at or immediately east of the mohaka fault these strain profiles are consistent with a model where high strains in the upper plate are concentrated near the down dip end of the contemporary locked zone on the plate interface this model requires that the down dip end of the interseismic locked zone has on average been approximately stable over a period of at least 2 5 5 myr

shallow subduction tectonics in the raukumara peninsula new zealand as illuminated by earthquake focal mechanisms the raukumara peninsula affords an excellent opportunity to study the subduction process as subduction of the buoyant hikurangi plateau on the pacific plate has resulted in exposure of the forearc above the shallow part of the subduction thrust here we report on the focal mechanisms of 117 earthquakes of m l 2 4 4 9 and shallower than 80 km recorded during a 5 month deployment of 36 portable seismographs on the peninsula mechanisms have been constrained using both first motion polarity data and amplitudes of seismogram envelopes downdip tensional strain predominates in the subducted plate with taxes of events in both the upper and lower planes of the dipping seismic zone generally paralleling the local dip of the zone trenchward extensional strain is seen in the uppermost part of the overlying australian plate in line with geodetic and geological results this can be related to extension and gravity sliding of surficial rocks due to uplift of the raukumara range resulting from underplating of subducted sediment there is a marked change in earthquake mechanisms along strike in the lower part of the overlying plate and at the plate interface a concentration of low angle thrust events at the plate interface in the northeastern half of the peninsula suggests that the plate interface is less coupled there than to the southwest this along strike change in plate coupling corresponds closely to a change in the crustal structure of the overlying plate and also to a change in tectonic rotation domain determined paleomagnetically

petrologic evolution of krakatau indonesia implications for a future activity abstract krakatau volcano is located along a n35e volcanic lineament running through the sunda straits indonesia its last activity has been characterized by successive phases each beginning with the construction of a cone and ending with its destruction and the formation of a caldera the two last pre and post 1883 cycles are well known but the more ancient ones are not so clearly defined lavas of krakatau belong to an andesitic series in which fractional crystallization plays the most important role the petrologic evolution is characterized by a cyclicity in good agreement with the structural evolution the succession is regular basalts basic andesites acid andesites dacites a gap between acid and basic andesites occurs in each cycle the destructive stages correspond to the occurrence of dacitic terms the anak cycle was characterized from 1927 to 1979 by basalts and basic andesites the 1981 eruption involved a more differentiated magma close to dacitic detailed study of the petrologic evolution since 1883 emphasizes the predominant role of fractional crystallization this process occurred during a very short period between 1979 and 1981 separation of labradorite augite olivine and magnetite from parental basic andesite may generate the dacitic descendant in a shallow reservoir p h 2 o estimated about 0 5 kbar implications for a future activity are considered

widespread remagnetizations and a new view of neogene tectonic rotations within the australia pacific plate boundary zone new zealand 14 ma 1 than the presently observed rate of 3 4 ma 1 which is only likely to be characteristic of the tectonic regime established since 1 2 ma these new results are consistent with both long and short term deformation on the hikurangi margin being driven by realignment of the subducting pacific plate with collision of the hikurangi plateau in the late miocene potentially being key to both the initiation of tectonic rotations and the widespread remagnetization of neogene sediments however accommodating faster more coherent rotation of the hikurangi margin in neogene reconstructions of the new zealand plate boundary region particularly in the late miocene remains a challenge

a geophysical interpretation of the 1883 krakatau eruption abstract from the present submarine topography in the vicinity of the krakatau islands it is concluded that the focus of the large explosions was situated to the northwest of the present rakata island the channel between krakatau and sebesi islands was completely blocked by banks of volcanic material immediately after the eruptions and it is suggested that this material was mainly lithic fragments the explosion sequences of krakatau are deduced from the records of sea waves and air waves observed at jakarta the large tsunami was caused by the most violent explosion simultaneously with the largest air waves it is inferred that the origin of the tsunami was a sudden upheaval of the seawater due to a violent explosion and that the height of the tsunami near its source was 30 40 m energy of the explosion is estimated from analyses of the air waves as one order of magnitude greater than that of the 1956 bezymianny eruption thus the 1883 krakatau eruption may have caused explosive removal of more than 10 km3 of material the subsurface structure of krakatau islands after the 1883 eruption is deduced from gravity anomalies it is concluded that at the bottom of the caldera there are deposits of low density in the shape of an inverted cone 8 km in diameter and 1 km in depth from the residual gravity anomaly observed over the caldera one can estimate the mass deficiency there this allows estimates to be made as to the amount of ejecta although large uncertainties remain these data indicate that explosive removal of material was the main process responsible for the disappearance of the northern half of the former rakata krakatau island in the 1883 eruption

near and far field survey report of the 30 december 2002 stromboli southern italy tsunami abstract in may 2002 stromboli one of the two active volcanoes in the aeolian islands southern tyrrhenian sea entered a new phase of explosive activity initially characterized by gas and ash emission from the summit craters on 30 december 2002 a massive submarine landslide followed by a subaerial one from the elevation of about 650 m above sea level a s l detached from the submerged part of the northwest slope of stromboli island producing a tsunami this huge mass movement was recorded by the ingv seismic stations installed respectively at stromboli and panarea in the following days a working group of ingv researchers and technicians was organized in order to perform a field survey of the tsunami effects in the near field including all the aeolian islands meanwhile a survey in the far field was planned along the coastline of campania and sicily where the effects of the 30 december tsunami were observed but not directly quantified visible material effects of the 30 december tsunami could be observed only along the northeast coast of stromboli island inundated by the wave with run up heights locally up to several meters many buildings were severely damaged on the other aeolian islands and in the far field the effects of the sea wave were documented only through eyewitness accounts to ensure a coherent collection of these accounts a standard interview form based on the advice of the intergovernmental oceanographic commission ioc was used a databank of all observations measurements interview forms and photographs was compiled in order to provide a useful base to test computer simulations hazard analyses and damage scenarios additional information was also made available at the emergeo link of ingv web pages http www ingv it emergeo and http www ov ingv it

advances in the study of mega tsunamis in the geological record abstract extreme geophysical events such as asteroid impacts and giant landslides can generate mega tsunamis with wave heights considerably higher than those observed for other forms of tsunamis in this paper we review recent advances in the study of mega tsunamis in the geological record focusing on well documented examples that have captured particular attention over the past decade we provide up to date background on the source mechanisms of tsunami generation during asteroid impacts and ocean island landslides which are the largest landslides on earth we also discuss the main sources of uncertainty for modelling such mega tsunamis and for addressing associated hazards

the 1674 ambon tsunami extreme run up caused by an earthquake triggered landslide we present an analysis of the oldest detailed account of tsunami run up in indonesia that of the 1674 ambon tsunami rumphius in waerachtigh verhael van de schuckelijcke aerdbebinge batavia dutch east indies 1675 at 100 m this is the largest run up height ever documented in indonesia and with over 2300 fatalities even in 1674 it ranks as one of indonesia s most deadly tsunami disasters we consider the plausible sources of earthquakes near ambon that could generate a large destructive tsunami including the seram megathrust the south seram thrust and faults local to ambon we conclude that the only explanation for the extreme run up observed on the north coast of amon is a tsunami generated by an earthquake triggered coastal landslide we use a two layer tsunami model to show that a submarine landslide with an approximate volume of 1 km3 offshore the area on ambon s northern coast between seith and hila where dramatic changes in coastal landscape were observed can explain the observed tsunami run up along the coast thus the 1674 ambon tsunami adds weight to the evidence from recent tsunamis including the 1992 flores 2018 palu and sunda strait tsunamis that landslides are an important source of tsunami hazard in indonesia

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

the december 22 2018 anak krakatau indonesia landslide and tsunami preliminary modeling results on the evening of december 22 2018 the coasts of the sunda strait indonesia were hit by a tsunami generated by the collapse of a part of the anak krakatau volcano hundreds of people were killed thousands were injured and displaced this paper presents a preliminary modeling of the volcano flank collapse and the tsunami generated based on the results of a 2d depth averaged coupled model involving a granular rheology and a coulomb friction for the slide description and dispersive effects for the water flow part with a reconstructed total volume subaerial and submarine of the landslide of 150 million hbox m 3 inferred from pre and post collapse satellite and aerial images the comparison of the simulated water waves with the observations tide gauges located all around the strait photographs and field surveys is satisfactory due to the lack of information for the submarine part of the landslide the reconstructed submarine slope is assumed to be approximately constant a significant time delay on the results and particularly in the bandar lampung bay could be attributed to imprecisions of bathymetric data the sensitivity to the basal friction and to dispersive effects is analyzed through numerical tests results show that the influence of the basal friction angle on the simulated wave heights decreases with distance and that a value of 2 circ gives consistent results with the observations the dispersive effects are assessed by comparing water waves simulated by a shallow water model and a boussinesq model simulations with frequency dispersion produce longer wave periods and smaller wave amplitudes in the sunda strait and particularly in deep waters

new magnetostratigraphic and numerical age of the fuente nueva 3 site guadix baza basin spain abstract sediments of the plio pleistocene guadix baza basin have provided a wealth of information on the first hominin populations in western europe to better constrain the age of the fuente nueva 3 archaeological site within the basin and to complement previous magnetostratigraphic studies two vertical boreholes were taken that provide a continuous record of the lower part of the sequence results indicate that the sequence is dominated by negative inclinations but some additional intervals with positive inclination are also identified in the lower part of the sequence a new cosmogenic nuclide burial age of 1 50 0 31 ma helps constrain the magnetostratigraphic record the abundance of normal polarity directions at the bottom of a borehole may indicate proximity to the olduvai subchron however further analyses are required to confirm this hypothesis

generation mechanism of tsunamis from the 1883 krakatau eruption the 1883 eruption of krakatau generated a destructive tsunami which claimed about 34 000 lives we compute the generation and propagation of tsunamis from three models previously proposed they are 1 large scale caldera collapse of the northern part of krakatau island 2 emplacement of pyroclastic flow deposits 3 submarine explosion we numerically solve the non linear shallow water equations on actual bathymetry all three models displace the same volume 11 5 km 3 of water in different ways we compare the results of our computation with the observed tsunami waveforms at batavia and tsunami wave heights along the coasts of java and sumatra the comparison shows that the submarine explosion model of 1 to 5 min duration best explains the generation of the largest tsunami

seismic stratigraphy of a buried volcanic arc northland new zealand and implications for neogene subduction abstract for over 6 million years in the early miocene the northland peninsula of new zealand s north island was the site of a volcanic arc comprising north westerly trending twin belts of marine and subaerial andesitic volcanoes approximately 50 volcanic edifices from major massifs to small cones have been newly identified on marine seismic profiles of the western belt which is largely buried the volcanoes were important point sources of sediment and the volcaniclastic deposits of each of the major and intermediate sized volcanoes form distinct seismic sequences the three main elements of the volcanic sequence are i a main body ii a sloping apron and iii a wide almost flat ring plain the downlap of the oldest discernible internal clinoform reflector relative to a known regional marker reflector underlying it indicates the approximate time of onset of activity whereas downlap of the top bounding reflector relative to those of other volcanic sequences provides a relative order of extinction sequence stratigraphic principles and super position determine relative stratigraphic hierarchy the volcanoes studied here were active only in the early miocene with few exceptions most were active by 22 ma and extinct by 16 ma with many extinct by 19 ma there was no pattern in their order of inception or extinction although a few became dominant burying or surrounding their neighbours at the south eastern end of the chain there is a rapid change over a short distance in both age and orientation from the northwest trending early miocene volcanism in the northland basin to north east trending middle and late miocene volcanism in the contiguous taranaki basin the northland volcanoes are interpreted to have been an arc facing the south westwards subducting south fiji basin whereas the taranaki volcanoes are interpreted to have been part of a separate pacific facing volcanic arc the lau colville ridge

evidence calibrated numerical model of december 22 2018 anak krakatau flank collapse and tsunami on december 22 2018 a sector of the anak krakatau volcano edifice collapsed into the sea generating a tsunami that hit the sunda strait coasts in indonesia the collapse followed a period of 6 months of volcanic activity that was insufficient to warn the tsunami threatened coastal population the anak krakatau tsunami resulted in hundreds of casualties thousands of injured and displaced people and massive coastal damage this paper uses the tsunami records the collected field survey data and satellite imagery based interpretations to develop a model of the anak krakatau flank failure and tsunami we address the dynamics of the flank failure the tsunami generation and propagation and the coastal impact using evidence calibrated numerical modelling an in house developed multi layer viscoplastic shallow water numerical code is employed to simulate the anak krakatau collapse mass movement and the whole source to coast tsunami process our results suggest that a flank collapse scenario involving a volume of material of 0 135 km3 and occurring as a sequence of two failures fairly reproduces the local and regional tsunami records and survey data

large tectonic rotation of part of new zealand in the last 5 ma abstract detailed paleomagnetic data from the wairoa syncline a middle miocene to the present forearc basin on the east coast of the north island new zealand show that the rate of clockwise rotation for the last 5 ma has been 7 8 ma of which less than 1 5 ma can be explained by apparent polar wander due to motion of the australian or pacific plates this rotation is similar to a present day rate of 7 ma determined from geodetic data between 5 and 20 ma ago the rate of tectonic rotation is poorly determined and may be between 0 and 2 ma the change in the rate of rotation of the wairoa syncline around 5 ma is probably related to a markedly different tectonic style in the new zealand region within the last 5 ma associated with a change in position of the euler poles of rotation for the pacific australian plates

numerical modelling of the tsunami triggered by the guimar debris avalanche tenerife canary islands comparison with field based data abstract some tsunami deposits have been previously identified 41 188 m asl in the agaete valley on the northwest coast of the island of gran canaria in the canary islands in this paper the guimar sector collapse tenerife 0 83 ma and its expected associated tsunami that is thought to be at the origin of these tsunami deposits are tentatively reproduced using a two fluid numerical code two failure processes are considered 1 the whole 44 km 3 volume is released in one go or 2 the 44 km 3 are released in five retrogressive failures of equal volume occurring each 120 s in both cases two rheologies are used to simulate the landslide propagation the mohr coulomb frictional law and a constant retarding stress two hypotheses concerning the origin of the offshore mapped deposits are also considered 1 the mapped deposits are the direct result of a single collapse event occurring either in one go or by near retrogressive failures or 2 the mapped deposits result from a collapse followed by later partial remobilization of its deposits in all scenarios the subaerial destabilisation spreads out eastwards into the sea triggering waves 390 500 m high when considering a collapse in one go and 225 380 m when considering successive retrogressive failures the first wave reaches the coast of gran canaria located at 70 km from the scar 495 560 s after the collapse onset whatever the scenario considered water enters the agaete valley on gran canaria 555 690 s after the onset of collapse reaching up to 9 1 km inland for a collapse in one go and 5 0 km when considering five retrogressive failures in this valley the simulated waves inundate all the locations where tsunami deposits were identified with the flow depth measured reaching a maximum of 50 m collapse by retrogressive failures to 150 m collapse in one go at these particular places the directions of maximum kinetic energy as a function of time for the simulated waves are consistent with the current directions recorded by the cobble fabrics present in the run up and backwash layers of the tsunami deposits at one outcrop this study shows that the major source of uncertainty when reproducing landslide triggered tsunamis is linked to the way the landslide happens failure mechanisms that should be thus more precisely taken into account for landslide triggered tsunamis hazard assessment the rheology chosen to simulate the landslide propagation has only a second order impact on the produced waves

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

apparent magnetic polarity reversals due to remagnetization resulting from late diagenetic growth of greigite from siderite summary a mixed polarity zone representing alternations between remagnetized and non remagnetized strata has been documented within the lower few metres of the crp 1 core ross sea antarctica detailed rock magnetic investigation of this interval indicates that the normal polarity remagnetization is carried by magnetostatically interacting single domain particles of a ferrimagnetic iron sulphide mineral while the reversed polarity magnetization of non remagnetized strata is carried by magnetite with a broad range of grain sizes and negligible magnetostatic interactions scanning electron microscope observations of polished sections indicate that the ferrimagnetic iron sulphide mineral is greigite fe3s4 based on microtextural relationships it is not possible to determine the relative timing of formation for much of the greigite however a significant proportion of the greigite has grown on the surface of authigenic siderite feco3 grains that occur as microconcretions and as cement surrounding detrital matrix grains in such cases microtextural relationships indicate that siderite post dates early diagenetic pyrite and that greigite post dates the siderite siderite usually forms in environments with abundant dissolved iron and carbonate but without dissolved pore water h2s this set of geochemical conditions occurs in methanic settings below the sulphate reduction zone in which early diagenetic pyrite forms we interpret the observed remagnetization of the lower part of the crp 1 core as due to a late diagenetic pore water migration event where abundant iron on the surface of siderite grains reacted with fluids containing limited dissolved sulphide thereby causing precipitation of greigite the distribution of siderite and associated greigite in the lower part of the crp 1 core is patchy which accounts for the apparent alternation of polarities this study is part of a growing catalogue of remagnetizations involving greigite which suggests that occurrences of greigite should be treated with caution in palaeomagnetic and environmental magnetic studies

computer simulations of tsunamis due to sector collapse at stromboli italy abstract stromboli is an island volcano of the aeolian volcanic arc characterised by persistent activity the cone rises about 2500 3000 m from its submarine base with very steep slopes its summit at 924 m above the sea level the subaerial growth of stromboli occurred in the last 100 ka has been marked by repeated episodes of large gravitational collapses especially affecting the nw flank of the island in the last 13 ka the last one occurred less than 5000 years ago forming the deep depression on the nw seaward flank named sciara del fuoco sdf and it produced very likely large water waves this paper envisages a scenario where a huge mass of volcanic material collapses into the sea in the same sector in which the sdf collapse took place in holocenic times and it computes possible tsunami evolutions assuming the present day bathymetry numerical simulations are performed by means of two distinct models one for the mass collapse and one for the tsunami slope failure dynamics are calculated with the aid of a lagrangian model the landslide is subdivided into blocks and the motion of each constituent block is calculated by applying the basic principle of mechanical momentum conservation with block block and block ambient interactions being taken into account water waves are computed by solving a system of shallow water equations including a forcing term dependent on the sliding mass motion the finite element fe technique is employed since it permits the use of non uniform grids which are adequate to account for marine basins with irregular coastlines in addition to the sensitivity analysis concerning the main parameters governing the slide motion two main cases are explored differing in the slide path followed by the mass the resulting tsunami is very large with giant waves as high as several meters tens of meters in the worst cases impinging the coast due to the strong wave refraction induced by bathymetry waves travel around the island affecting even the island coast opposite the source

magnetostratigraphic chronology of late miocene to early pliocene biostratigraphic and oceanographic events in new zealand successions of uplifted shallow marine sediments in new zealand were among the first to provide evidence of latest miocene climatic deterioration and were also among the first onshore successions where late miocene to early pliocene magnetostratigraphic records were established a revised chronology of late miocene to early pliocene events has been determined from new magnetostratiigraphic results from two important successions at blind river and upton brook south island new zealand lat 41 45 s long 174 05 e magnetostratigraphic results from upton brook are the fast from strata containing the kapitean index mollusks and provide the first reliable estimate of the age of the tongaporutuan kapitean boundary a coherent chronology from blind river and upton brook indicates that two synchronous low sea level and cool paleoclimatic events occurred in the late miocene kapitean stage this inference is supported from other well known coeval successions in the new zealand region the revised new zealand chronology supports recent determinations from the mediterranean that indicate a two stage messinian salinity crisis and a 5 2 ma age for the miocene pliocene boundary data from new zealand the mediterranean and ocean cores around the world suggest that these latest miocene events are related to glacio eustatic sea level fluctuations a 6 05 ma age for the first occurrence datum of globorotalia conomiozea indicates that significant diachroneity exists in the placement of this datum between the southwest pacific and the mediterranean confirming the observation that g conomiazea is unsuitable for correlation between ocean basins

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

magnetite dissolution diachronous greigite formation and secondary magnetizations from pyrite oxidation unravelling complex magnetizations in neogene marine sediments from new zealand detailed rock magnetic and electron microscope analyses indicate that the magnetic signature of neogene marine sediments from the east coast of new zealand is dominated by the authigenic iron sulphide greigite the greigite is present as a mixed population of stable single domain and superparamagnetic grains which is consistent with authigenic growth from solution this growth can result from pyritization reactions soon after deposition which also leads to dissolution of most detrital magnetite however where constrained by field tests our data suggest that remanence acquisition can occur 1 myr after deposition and can vary in timing at the outcrop scale strong viscous overprints result from oxidation of the iron sulphides probably during percolation of oxic ground water this process can sometimes destroy any ancient remanent magnetization this complex magnetic behaviour particularly the presence of late forming magnetizations carried by greigite means that the remanence in new zealand cenozoic sediments and in similar sediments elsewhere cannot be assumed to be primary without confirmation by field tests the reversals test should be employed with caution in such sediments as patchy remagnetizations can lead to false polarity stratigraphies

subduction evolution and mantle dynamics at a continental margin central north island new zealand 1 central north island new zealand provides an unusually complete geological and geophysical record of the onset and evolution of subduction at a continental margin whereas most subduction zones are innately two dimensional north island of new zealand displays a distinct three dimensional character in the back arc regions specifically we observe mariana type subduction in the back arc areas of central north island in the sense of back arc extension high heat flow prolific volcanism geothermal activity and active doming and exhumation of the solid surface evidence for emplacement of a significant percent of new lithosphere beneath the central north island comes from heat flux of 25 mw km of strike of volcanic zone and thinned crust underlain by rocks with a seismic wave speed consistent with underplated new crust seismic attenuation qp 1 is high 240 and rhyolitic and andesitic volcanism are widespread almost complete removal of mantle lithosphere is inferred here in pliocene times on the basis of the rock uplift history and upper mantle seismic velocities as low as 7 4 0 1 km s in contrast southwestern north island exhibits chilean type back arc activity in the sense of compressive tectonics reverse faulting low heat flow thickened lithosphere and strong coupling between the subducted and overriding plates this rapid switch from mariana type to chilean type subduction occurs despite the age of the subducted plate being constant under north island moreover stratigraphic evidence shows that processes that define the extensional back arc area the central volcanic region are advancing southward into the compressional system wanganui basin at about 10 mm yr we link the progression from one system to another to a gradual and viscous removal of thickened mantle lithosphere in the back arc regions thickening occurred during the miocene within the taranaki fault zone the process of thickening and convective removal is time and temperature dependent and has left an imprint in both the geological record and geophysical properties of central north island which we document and describe

pacific basin tsunami hazards associated with mass flows in the aleutian arc of alaska abstract we analyze mass flow tsunami generation for selected areas within the aleutian arc of alaska using results from numerical simulation of hypothetical but plausible mass flow sources such as submarine landslides and volcanic debris avalanches the aleutian arc consists of a chain of volcanic mountains volcanic islands and submarine canyons surrounded by a low relief continental shelf above about 1000 2000 m water depth parts of the arc are fragmented into a series of fault bounded blocks tens to hundreds of kilometers in length and separated from one another by distinctive fault controlled canyons that are roughly normal to the arc axis the canyons are natural regions for the accumulation and conveyance of sediment derived from glacial and volcanic processes the volcanic islands in the region include a number of historically active volcanoes and some possess geological evidence for large scale sector collapse into the sea large scale mass flow deposits have not been mapped on the seafloor south of the aleutian islands in part because most of the area has never been examined at the resolution required to identify such features and in part because of the complex nature of erosional and depositional processes extensive submarine landslide deposits and debris flows are known on the north side of the arc and are common in similar settings elsewhere and thus they likely exist on the trench slope south of the aleutian islands because the aleutian arc is surrounded by deep open ocean mass flows of unconsolidated debris that originate either as submarine landslides or as volcanic debris avalanches entering the sea may be potential tsunami sources to test this hypothesis we present a series of numerical simulations of submarine mass flow initiated tsunamis from eight different source areas we consider four submarine mass flows originating in submarine canyons and four flows that evolve from submarine landslides on the trench slope the flows have lengths that range from 40 to 80 km maximum thicknesses of 400 800 m and maximum widths of 10 40 km we also evaluate tsunami generation by volcanic debris avalanches associated with flank collapse at four locations makushin cleveland seguam and yunaska sw volcanoes which represent large to moderate sized events in this region we calculate tsunami sources using the numerical model topics and simulate wave propagation across the pacific using a spherical boussinesq model which is a modified version of the public domain code funwave our numerical simulations indicate that geologically plausible mass flows originating in the north pacific near the aleutian islands can indeed generate large local tsunamis as well as large transoceanic tsunamis these waves may be several meters in elevation at distal locations such as japan hawaii and along the north and south american coastlines where they would constitute significant hazards

large tectonic rotations since the early miocene in a convergent plate boundary zone south island new zealand abstract a palaeomagnetic study in part of the new zealand plate boundary zone provides new constraints on the temporal and spatial distribution of neogene and quaternary tectonic rotations thermal demagnetization of samples from cretaceous basaltic dykes palaeocene oligocene micritic limestone and miocene and pliocene siltstones in the marlborough region south island have defined stable high temperature magnetic components which are interpreted as the primary magnetization declination anomalies after tectonic corrections are interpreted as rigid body rotations about a vertical axis of sample sites relative to the pacific plate all palaeomagnetic data from marlborough cluster into three main groups a 60 100 clockwise rotation affected palaeocene to middle miocene sedimentary sequences across marlborough between 18 ma and 8 ma coeval with a phase of low angle thrusting the absence of this rotation in a late cretaceous dyke swarm defines the present western limit of the early rotating zone a regional 20 clockwise rotation occurred in the last 4 ma during the development of the marlborough fault system in a zone of dextral transpression although locally clockwise rotations 40 may have occurred near some of the major dextral strike slip faults however a negligible rotation is observed in the same period in the region to the southeast of the major kekerengu dextral strike slip fault which appears to have acted as a hinge zone accommodating relative rotation by dextral strike slip on an arcuate fault bending and internal deformation the observed tectonic rotations record the overall clockwise rotation of the trend of the southern end of the hikurangi margin from w to nw in the early miocene to ne today determined independently from the long term relative plate motion data for the pacific and australian plates

the origin of the 1883 krakatau tsunamis abstract hypotheses for the origin of the krakatau tsunamis of 27 august 1883 are reviewed the 151 minute sea wave travel time between krakatau and batavia jakarta first proposed by verbeek cannot be substantiated thus hypotheses for the origin of the tsunamis which rest on very accurate timings of the origins of the air and sea waves such as that of latter 1981 also cannot be substantiated there was one exceptionally large sea wave tsunami on 27 august and many smaller ones most of the smaller waves appear to have been air sea coupled waves rather than true tsunamis of the few sea waves that were probably true tsunamis only one may have originated by emplacement of a pyroclastic flow at a point nearer batavia than krakatau the catastrophic event in the eruption of august 27th was preceded some 40 minutes earlier by a subordinate event which also propagated an air sea coupled wave and a tsunami the largest heard explosion produced an air sea coupled wave but was not associated with a tsunami although the precise time relations between the origins of the air and sea waves cannot be definitely established the most likely scenario for the catastrophic phase of the eruption is broadly similar to that originally proposed by verbeek in which collapse of part of the original volcanic edifice propagated a major volcanic explosion

past and potential tsunami sources in the south china sea a brief synthesis abstract extending across some 3 5 million square km and with coastlines populated by in excess of 80 million people the south china sea scs is bordered by seven independent states understanding the risk of tsunamis in the scs is therefore an imperative especially given the new priorities for the science community following the endorsement by the un general assembly of the sendai framework for disaster risk reduction 2015 2030 our review presents a synthesis of existing literature on the current state of knowledge concerning known tsunamigenic threats but also highlights a number of other potential sources that have so far received less attention or gone largely un or under recognised an overview of the geological evolution of the scs is presented in order to appreciate how the existing structural configuration of the ocean basin is responsible for the presence of a variety of potential tsunamigenic mechanisms traditional thinking places the generation of a large magnitude earthquake at the manila trench subduction zone at the top of the spectrum for tsunami potential with several simulations already available in the literature illustrating wave characteristics resulting from the worst case rupture in addition to the manila trench and other possible earthquake sources however volcanic activity and submarine landsliding of sediment burden on continental shelves on the scs margins represent hitherto fundamentally unquantified tsunami threats although revealed nonetheless by for example the existence of the giant brunei and baiyun submarine slides furthermore in the central scs previously considered essentially devoid of tsunami sources numerous near surface carbonate platforms and coral atolls show evidence of arcuate bight like structures in their planform geometry likewise suggesting their propensity for possible tsunamigenic lateral flank collapse in the current absence of well constrained tsunami probability estimates and scenarios of wave size and propagation features for non earthquake tsunami sources future research priorities lie in two main areas these are 1 improvement of modelling for tsunamigenic submarine failures as well as for earthquakes and 2 a greater focus on geomorphic investigation to identify palaeotsunami deposits on coastlines considered likely to have been impacted in the past and where good preservation potential exists this is needed to establish the magnitude timing frequency of events on holocene timescales the last 10 000 years well beyond historical records thereby improving our capabilities for understanding and forecasting the likelihood and severity of future tsunami risk in the south china sea

late neogene exhumation patterns in taranaki basin new zealand evidence from offset porosity depth trends taranaki basin new zealand is located adjacent to the australian pacific plate boundary where the tectonic regime changes from dominantly subduction related to the north to transpression related along the alpine fault to the south during the neogene burial and exhumation varied extensively in both time and space in response to subsidence and uplift along this evolving plate boundary zone the basin can be divided into two regions 1 the western platform outside the plate boundary deformation zone where no uplift nor exhumation has occurred and 2 the eastern mobile belt which lies inside the deformation zone and has been variably uplifted and exhumed exhumation magnitudes for sedimentary deposits of the basin are estimated from offset porosity depth trends the analysis is based on correlating sonic log travel times with compensated density logs permitting sonic travel time to be used as a proxy for porosity twelve western platform wells are used to define a standard exponential porosity depth trend with an extrapolated surface porosity of 50 and an exponential decay factor of 2265 m valid for mudstone shale sections spanning a depth range of 300 3000 m this curve is a calibration curve against which offset porosity depth trends from wells in exhumed regions can be compared to determine apparent exhumation amounts porosity depth trends for 43 eastern mobile belt wells are offset 0 2800 m shallower relative to the western platform trend but generally are parallel to it in the southern region of the eastern mobile belt net exhumation amounts which are the sum of the porosity depth trend offset and depth to unconformity range from 850 to 3000 m most of this exhumation occurred on discrete contractional structures in late miocene to early pliocene time probably associated with an increased rate of convergence across the alpine fault system to the south in the eastern region of the eastern mobile belt net exhumation progressively increases from 0 m in the south to 1800 m in the northeast part of the basin consistent with the 2 4 sw structural tilt of onshore strata the regional and consistent pattern of exhumation in the eastern region contrasts with the discrete structure related exhumation in the southern region and is consistent with models of thermal and flexural uplift

source mechanisms of volcanic tsunamis volcanic tsunamis are generated by a variety of mechanisms including volcano tectonic earthquakes slope instabilities pyroclastic flows underwater explosions shock waves and caldera collapse in this review we focus on the lessons that can be learnt from past events and address the influence of parameters such as volume flux of mass flows explosion energy or duration of caldera collapse on tsunami generation the diversity of waves in terms of amplitude period form dispersion etc poses difficulties for integration and harmonization of sources to be used for numerical models and probabilistic tsunami hazard maps in many cases monitoring and warning of volcanic tsunamis remain challenging further technical and scientific developments being necessary and must be coupled with policies of population preparedness

modelling 2018 anak krakatoa flank collapse and tsunami effect of landslide failure mechanism and dynamics on tsunami generation the 2018 anak krakatoa volcano flank collapse generated a tsunami that impacted the sunda strait coastlines in the absence of a tsunami early warning system it caused several hundred fatalities there are ongoing discussions to understand how the failure mechanism of this event affected landslide dynamics and tsunami generation in this paper the sensitivity to different failure scenarios on the tsunami generation is investigated through numerical modelling to this end the rate of mass release the landslide volume the material yield strength and orientation of the landslide failure plane are varied to shed light on the failure mechanism landslide evolution and tsunami generation we model the landslide dynamics using the depth averaged viscoplastic flow model bingclaw coupled with depth averaged long wave and shallow water type models to simulated tsunami propagation we are able to match fairly well the observed tsunami surface elevation amplitudes and inundation heights in selected area with the numerical simulations however as observed by other authors discrepancies in simulated and observed arrival times for some of the offshore gauges are found which raises questions related to the accuracy of the available bathymetry for this purpose further sensitivity studies changing the bathymetric depth near the source area are carried out with this alteration we are also able to match better the arrival times of the waves

bending within the axial tectonic belt of new zealand in the last 9 myr from paleomagnetic data abstract tongaporutuan stage late miocene 11 6 myr sedimentary rocks at two localities within the axial tectonic belt of new zealand have a direction of magnetisation in which the declination is 020 11 and 030 8 d 95 the directions of magnetisation in rocks of similar age outside the belt have a declination like that of the earth s present axial dipole 360 the clockwise deviation of the declination is inferred to indicate bending of the rocks within the zone of deformation between the pacific and indian plates due to the oblique convergence of these plates

a seismic crustal section across the east cape convergent margin new zealand abstract crustal seismic reflection measurements were made along a 250 km profile across the pacific australian plate boundary north of new zealand data were recorded to 16 s two way time and have defined a major sedimentary basin corresponding to the southern end of the raukumara basin a fore arc basin reaching a depth of about 13 km this basin contains a lower generally conformable sequence of sediments and an upper sequence dominated by several major uncomformities the eastern part of this basin is cut by several recently active eastward dipping high angle thrust faults which are interpreted to be caused by the recent convergence at the adjacent pacific australian plate boundary the eastern margin of the basin is marked by a sharp change in character on the seismic data we interpret this feature as a terrane boundary coinciding with a major transcurrent fault which has juxtaposed a detached fragment of an island arc fore arc with a thin 15 km crust to the east against a passive margin sedimentary sequence to the west the southern raukumara basin is floored by cretaceous age oceanic crust fragments of which were obducted onto the north island about 22 ma ago the area has had a complex history a schematic model for the evolution of this margin during the past 22 ma is developed suggesting that the raukaumara basin has developed as a combination of fore arc basin processes and oblique crustal extension

pyroclastic flows and surges over water an example from the 1883 krakatau eruption pyroclastic deposits from the 1883 eruption of krakatau are described from areas northeast of the volcano on the islands of sebesi sebuku and lagoendi and the southeast coast of sumatra massive and poorly stratified units formed predominantly from pyroclastic flows and surges that traveled over the sea for distances up to 80 km granulometric and lithologic characteristics of the deposits indicate that they represent the complement of proximal subaerial and submarine pyroclastic flow deposits laid down on and close to the krakatau islands the distal deposits exhibit a decrease in sorting coefficient median grain size and thickness with increasing distance from krakatau crystal fractionation is consistent with the distal facies being derived from the upper part of gravitationally segregated pyroclastic flows in which the relative amount of crystal enrichment and abundance of dense lithic clasts diminished upwards the deposits are correlated to a major pyroclastic flow phase that occurred on the morning of 27 august at approximately 10 a m energetic flows spread out away from the volcano at speeds in excess of 100 km h and traveled up to 80 km from source the flows retained temperatures high enough to burn victims on the sw coast of sumatra historical accounts from ships in the sunda straits constrain the area affected by the flows to a minimum of 4x103 km2 at the distal edge of this area the flows were relatively dilute and turbulent yet carried enough material to deposit several tens of centimeters of tephra the great mobility of the krakatau flows from the 10 a m activity may be the result of enhanced runout over the sea it is proposed that the generation of steam at the flow seawater interface may have led to a reduction in the sedimentation of particles and consequently a delay in the time before the flows ceased lateral motion and became buoyantly convective the buoyant distal edge of these ash and steam laden clouds lifted off into the atmosphere leading to cooling condensation and mud rain

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

reconstruction of the 2018 tsunamigenic flank collapse and eruptive activity at anak krakatau based on eyewitness reports seismo acoustic and satellite observations abstract after several months of eruptive activity the subaerial cone of anak krakatau collapsed on december 22 2018 the landslide event generated a tsunami that had deadly consequences within the sunda strait in indonesia such significant collapse events are common in the geologic record but are a rare phenomenon in the instrumented record however these events can have a potentially large impact on society we have reconstructed the collapse along with the activity preceding and following it by combining information from official reports remote geophysical observations and local eyewitness accounts it appears that the collapse of anak krakatau s subaerial cone led to a drastic change in the eruptive style from continuous strombolian explosions to sustained surtseyan those changes are detectable in the seismo acoustic measurements which when combined with eyewitnesses allows us to reconstruct the timing and phenomenology of the sequence our analysis reveals that intense eruptive activity generated sustained infrasound unusual but not unique at anak krakatau starting approximately eight hours before the collapse within this timeframe two seismic signals consistent with minor mass movements as well as a momentary quiescence were identified prior to the main collapse the data presented here indicate that anak krakatau failed in one collapse event producing a tsunami with multiple waves around the volcano the last one being the largest following the collapse three volcanic plumes could be clearly identified in the satellite data and by eyewitnesses as well as spectral lines in the seismic data these lines observed up to 371 km suggest a repeating energetic explosive source lasting for seven days the collapse produced multiple infrasound arrivals observed at regional infrasound stations but was not recorded on the regional hydroacoustic network our analysis of the eruptive sequence demonstrates that a detailed eruption chronology can be reconstructed using remote methods even in the event of failure or destruction of local monitoring infrastructure this event also highlights that tsunamigenic flank collapses can occur with little to no warning and be difficult to interpret in real time as a significant amount of non operational analysis was required after the event to complete the chronology

twenty five years of progress in the science of geological tsunamis following the 1992 nicaragua and flores events we review a set of 47 tsunamis of geological origin triggered by earthquakes landslides or volcanoes which have occurred over the past 25 years and provided significant new insight into theoretical experimental field or societal aspects of tsunami science among the principal developments in our command of various aspects of tsunamis we earmark the development of the w phase inversion for the low frequency moment tensor of the parent earthquake the abandonment of the concept of a maximum earthquake magnitude for a given subduction zone controlled by simple plate properties the development and implementation of computer codes simulating the interaction of tsunamis with initially dry land at beaches thus introducing a quantitative component to realistic tsunami warning procedures and the recent in situ investigation of current velocities in addition to the field of surface displacements during the interaction of tsunamis with harbors continued research remains warranted notably in the field of the real time identification of tsunami earthquakes whose tsunamis are larger than expected from their seismic magnitudes especially conventional ones the recent tragedy during the 2018 krakatau flank collapse along a scenario which had been quantitatively forecast also emphasizes the need for a continued effort in the education of the populations at risk

coupling eruption and tsunami records the krakatau 1883 case study indonesia the well documented 1883 eruption of krakatau volcano indonesia offers an opportunity to couple the eruption s history with the tsunami record the aim of this paper is not to re analyse the scenario for the 1883 eruption but to demonstrate that the study of tsunami deposits provides information for reconstructing past eruptions indeed though the characteristics of volcanogenic tsunami deposits are similar to those of other tsunami deposits they may include juvenile material e g fresh pumice or be interbedded with distal pyroclastic deposits ash fall surges due to their simultaneity with the eruption five kinds of sedimentary and volcanic facies related to the 1883 events were identified along the coasts of java and sumatra 1 bioclastic tsunami sands and 2 pumiceous tsunami sands deposited respectively before and during the plinian phase 26 27 august 3 rounded pumice lapilli reworked by tsunami 4 pumiceous ash fall deposits and 5 pyroclastic surge deposits only in sumatra the stratigraphic record on the coasts of java and sumatra which agrees particularly well with observations of the 1883 events is tentatively linked to the proximal stratigraphy of the eruption

continental subduction and three dimensional crustal structure the northern south island new zealand the three dimensional vp and vp vs structure of a region where subduction transitions to oblique transform faulting has been determined using arrival times from 579 local earthquakes recorded during a temporary deployment and 3146 earthquakes have been relocated between 40 km and 100 km depth the subducted plate is imaged as a relatively low velocity feature in the uppermost mantle reflecting the continental nature of the subducted crust in this region an increase in amplitude of this low velocity feature from northeast to southwest can be related to an increase in the thickness of the crust of the subducted plate in this direction velocity variations within the subducted and overlying plates show some spatial correlation this suggests an interaction between the plates which extends well beyond the plate interface and is consistent with other geophysical and geological evidence that the plate interface beneath marlborough is currently not accommodating much active subduction in the overlying plate the awatere fault is a major structural feature associated with a low velocity zone extending to 23 km depth there is a marked change in structure near this fault with seismic velocities being lower to the southeast a relatively high level of seismicity occurs in this region of lower seismic velocities suggesting a relationship between the two a possible explanation for this is elevated pore pressures caused by fluids derived from dehydration of the continental subducted crust the low velocity region in the overlying plate coincides with the region of most intense active deformation suggesting it is relatively weak

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

magnetostratigraphic lithostratigraphic and tephrostratigraphic constraints on lower and middle pleistocene sea level changes wanganui basin new zealand wanganui basin north island new zealand contains a complex sedimentary record of lower and middle pleistocene sea level changes palaeomagnetic results allow identification of the matuyama brunhes transition the jaramillo subchron and the cobb mountain subchron correlations of rhyolitic tuff horizons across the basin are consistent with magnetostratigraphic correlations between sections isothermal plateau fission track itpft ages of 1 05 0 05 ma and 1 63 0 15 ma on two tuffs potaka pumice and pakihikura pumice respectively are consistent with the interpreted magnetostratigraphy and also with the astronomically tuned timescale of odp site 677 magnetostratigraphy and itpft ages allow correlation of sedimentary cycles at wanganui with odd numbered oxygen isotope stages 17 31 in deep sea cores the stratotype section for the new zealand castlecliffian stage is shown to be incomplete relative to other studied sections in the basin below stage 31 the character of the cyclothems changes at wanganui from marine dominated to a greater representation of non marine and estuarine strata this change may be partly related to a change in amplitude and frequency of climatic cycles identified in oxygen isotope records but the primary cause is likely to be increased basinal uplift

source of the tsunami generated by the 1650 ad eruption of kolumbo submarine volcano aegean sea greece the 1650 ad explosive eruption of kolumbo submarine volcano aegean sea greece generated a destructive tsunami in this paper we propose a source mechanism of this poorly documented tsunami using both geological investigations and numerical simulations sedimentary evidence of the 1650 ad tsunami was found along the coast of santorini island at maximum altitudes ranging between 3 5 m a s l perissa southern coast and 20 m a s l monolithos eastern coast corresponding to a minimum inundation of 360 and 630 m respectively tsunami deposits consist of an irregular 5 to 30 cm thick layer of dark grey sand that overlies pumiceous deposits erupted during the minoan eruption and are found at depths of 30 50 cm below the surface composition of the tsunami sand is similar to the composition of the present day beach sand but differs from the pumiceous gravelly deposits on which it rests the spatial distribution of the tsunami deposits was compared to available historical records and to the results of numerical simulations of tsunami inundation different source mechanisms were tested earthquakes underwater explosions caldera collapse and pyroclastic flows the most probable source of the 1650 ad kolumbo tsunami is a 250 m high water surface displacement generated by underwater explosion with an energy of 2 1016 j at water depths between 20 and 150 m the tsunamigenic explosion s occurred on september 29 1650 during the transition between submarine and subaerial phases of the eruption caldera subsidence is not an efficient tsunami source mechanism as short and probably unrealistic collapse durations 5 min are needed pyroclastic flows cannot be discarded but the required flux 106 to 107 m3 s 1 is exceptionally high compared to the magnitude of the eruption

numerical investigations of tsunamis generated by pyroclastic flows from the kikai caldera japan 1 tsunamis generated by a voluminous pyroclastic flow entering the sea during a caldera forming eruption at the kikai caldera japan were investigated by using a two layer shallow water model which is limited to the source conditions and their impact on coastal areas volume flux of the dense component of the pyroclastic flow was controlled by a sine function results showed that the maximum height of the tsunami was largest in models with the largest volume flux of the flows the approximate source conditions of the tsunami which can stir sediment particles on the sea floor were investigated using the non dimensional boundary shear stress results from our simulation showed that the shear stress to initiate movement of sediment particles was not easily achieved in areas where there was evidence of a tsunami a caldera collapse is thought more likely to have generated the huge tsunami rather than a pyroclastic flow

diagenetic formation of ferrimagnetic iron sulphide minerals in rapidly deposited marine sediments south island new zealand abstract detailed magnetostratigraphic studies of late neogene siliciclastic sediments of the awatere group south island new zealand 41 45 s 174 05 e have revealed a wide range of palaeomagnetic behaviour examination of rock magnetic properties was undertaken using conventional palaeomagnetic techniques and thermomagnetic x ray diffraction and electron microprobe analyses these analyses indicate that the ferrimagnetic iron sulphide minerals greigite and pyrrhotite are responsible for a stable and intense magnetic remanence in fine grained sediments whereas titanomagnetite is the only remanence bearing mineral identified in coarser grained sediments which are less strongly and less stably magnetised than the fine grained sediments detrital titanomagnetite grains are likely to have undergone dissolution during early diagenesis as a result of iron sulphide formation which occurs commonly in rapidly deposited anoxic sediments that support active sulphate reduction and h 2 s formation preservation of greigite and pyrrhotite is inferred to result from the arrest of the pyritisation process probably due to the low permeability of the fine grained sediments and consumption of available h 2 s before full reaction to pyrite occurred relative palaeomagnetic instability and weak remanence intensities in coarser grained sediments is likely to be due to low titanomagnetite concentrations resulting from titanomagnetite dissolution

the 15 august 2007 peru tsunami runup observations and modeling 1 on 15 august 2007 an earthquake with moment magnitude mw of 8 0 centered off the coast of central peru generated a tsunami with locally focused runup heights of up to10 m a reconnaissance team was deployed two weeks after the event and investigated the tsunami effects at 51 sites three tsunami fatalities were reported south of the paracas peninsula in a sparsely populated desert area where the largest tsunami runup heights were measured numerical modeling of the earthquake source and tsunami suggest that a region of high slip near the coastline was primarily responsible for the extreme runup heights the town of pisco was spared by the paracas peninsula which blocked tsunami waves from propagating northward from the high slip region the coast of peru has experienced numerous deadly and destructive tsunamis throughout history which highlights the importance of ongoing tsunami awareness and education efforts to ensure successful self evacuation

tsunamis of volcanic origin summary of causes with particular reference to krakatoa 1883 known tsunamis of volcanic origin are reviewed and classified according to their causes earthquakes accompanying eruptions excluding tectonic events which apparently triggered eruptions pyroclastic flows and submarine explosions have each accounted for about 20 of cases ten causes of volcanic tsunamis are discussed from the risk point of view those due to landslides are particularly dangerous eruptions at calderas are more likely to generate tsunamis than eruptions elsewhere of those killed directly by volcanic eruptions nearly a quarter have died as a result of tsunamis by transfer of energy to sea waves a violent eruption which would be comparatively harmless on land extends greatly the radius over which destruction occurs

the opening of cook strait interglacial tidal scour and aligning basins at a subduction to transform plate edge abstract cook strait the central seaway through the axial ranges of new zealand has many inferred origins a compilation of marine geological and geophysical datasets suggests that cook strait developed when five sedimentary basins at a rapidly changing obliquely convergent plate boundary were moved into line and were linked by strong tidal scour in middle pleistocene times the basins relate partly to oblique subduction north of cook strait and partly to intercontinental transform to the south prior to opening muddy subduction pull down and foreland basins in the northwest were separated from equally quiet water rotating forearc to transform basins in the southeast the land barrier between them narrowed and was finally breached as subduction related basins migrated southwards and transform related basins extended northwards in response to rotation and divergent branching of a major transcurrent fault following breaching a history of alternating scour and quiet water deposition is recorded by a series of deep irregular unconformities in muddy basin fill scour is correlated with interglacial periods of high sea level when land barriers were submerged and strong tides caused by a 140 phase difference at either end of the strait eroded muddy sediments deposited in glacial periods when an emergent landbridge limited tidal exchange

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

field survey and numerical modelling of the december 22 2018 anak krakatau tsunami on december 22 2018 the eruption and flank collapse of the anak krakatau volcano generated a tsunami in the sunda strait causing catastrophic damage to uninhabited coastlines proximal to the source along the heavily populated shores of banten and lampung provinces in java and sumatra tsunami waves caused severe damage extensive inundation and more than 430 deaths an international tsunami survey team itst deployed 6 weeks after the event documented the tsunami effects including runup heights flow depths and inundation distances as well as sediment deposition patterns and impacts on infrastructure and the natural environment the team also interviewed numerous eyewitnesses and educated residents about tsunami hazards this itst was the first to visit and document the extreme tsunami effects on the small islands in the sunda strait closest to anak krakatau rakata panjang sertung sebesi and panaitan along the steep slopes of rakata and sertung islands located less than 5 km from and facing directly towards the southwest flank of anak krakatau all of the dense coastal vegetation was stripped to bare earth up to elevations of more than 80 m while on the northeast tip of sertung island facing away from the source a single tree remained standing after flow depths of 11 m above ground struck there the runup distributions on the islands encircling anak krakatau highlight the directivity of the tsunami source suggesting that the collapse occurred towards the southwest this manifested as tsunami runup of 10 m that stripped away coastal forests to bare rock for up to 400 m inland in the ujung kulon national park located 50 km to the south southwest inundation and damage were mostly limited to within 400 m of the shoreline likely the result of the relatively short wavelengths caused by the landslide generated tsunami a significant variation in tsunami impact was observed along the shorelines of the sunda strait with runup heights rapidly decreasing with distance from the inferred tsunami source to model the event we applied a hot start initial condition that roughly reproduced the measured tsunami runup heights along rakata and sertung the waveforms were then propagated through the sunda straight using a boussinesq type wave model the results showed a good fit to the observed heights along the java and sumatra coastlines the northern coast of panaitan island and ujung kulon nation park the model also produced an acceptable fit to the observed amplitudes at tide gauges despite the regional volcanic and tsunamigenic history of the region and 6 months of eruptive activity prior to the event the tsunami largely caught the local population off guard this further highlights the need for community based education and awareness programs as essential to save lives in locales at risk from locally generated tsunamis

transferability of a calibrated numerical model of rock avalanche run out application to 20 rock avalanches on the nuussuaq peninsula west greenland long run out rock avalanches are one of the most hazardous geomorphic processes and risk assessments of the potential threat they pose are often reliant on numerical modelling of their potential run out distance the development of such models requires a thorough understanding of past flow behaviour inferred from deposits emplaced by previous events despite this few records exist of multiple rock avalanches that occurred in conditions sufficiently consistent to develop a set of more generalised and hence transferrable rules we conduct field and imagery based mapping and use numerical modelling to investigate the emplacement of 20 adjacent rock avalanches on the southern flanks of the nuussuaq peninsula west greenland the rock avalanches run out towards the vaigat strait and are sourced from a range of coastal mountains of relatively uniform geology we calibrate a three dimensional continuum dynamic flow code volcflow with data from a modern well constrained event that occurred at paatuut ad 2000 the best fit model assumes a constant retarding stress with a collisional stress coefficient simulating run out to within 0 3 of that observed this calibration was then used to model the emplacement of deposits from five other neighbouring rock avalanches before simulating the general characteristics of a further 14 rock avalanche deposits on simplified topography our findings illustrate that a single calibration of volcflow can account for the observed deposit morphology of a uniquely large collection of rock avalanche deposits emplaced by a series of events spanning a large volume range although the prevailing approach of tuning models to a specific case may be useful for detailed back analysis of that event we show that more generally applied models even using a single pair of rheological parameters can be used to model potential rock avalanches of varied volumes in a region and therefore to assess the risks that they pose

tsunamigenic sea floor deformations in addition to the primary damage they do earthquakes can cause tsunamis massive ocean swells that can inundate coastal regions in their perspective synolakis et al describe results presented at a workshop on the interface between seismology and tsunami hydrodynamics held in santa monica in may 1997 the authors discuss the highlights of the meeting and summarize future directions for research

temporal stability of deformation rates comparison of geological and geodetic observations hikurangi subduction margin new zealand abstract we examine how well contemporary horizontal velocity fields from global positioning system gps geodetic measurements describe long term deformation rates million year rates of extension shortening strike slip and vertical axis rotations are compared with modelling of gps velocities from the last 10 15 years in the hikurangi subduction margin new zealand within measurement uncertainties of mainly 50 the rates of deformation and vertical axis rotations for each time interval are usually indistinguishable the comparable deformation rates are consistent with the notion of near constant rates since 1 5 ma during this time oblique relative plate motion was partitioned with the majority 85 of margin normal motion accommodated on the plate interface and most 60 margin parallel motion by strike slip faulting and vertical axis rotations in the upper plate prior to 1 5 ma gps velocities cannot be reliably used to describe deformation and rotations of the hikurangi margin because at this time the taupo rift commenced opening the boundary between raukumara and wairoa rotational domains was abandoned and the rates of upper plate shortening increased the broad compatibility of gps and geological deformation and rotation rates since 1 5 ma suggests that the build up of contemporary elastic strains in the north island measured by gps is largely uniform for much of the duration of each seismic cycle the good agreement between the gps and geological deformation rates in the north island is consistent with the view that contemporary elastic strains will mainly be converted to permanent dip slip on the subduction thrust and to displacement on upper plate faults during future large magnitude earthquakes

magnetic properties of sedimentary greigite fe3s4 new data are presented here that document the previously poorly known magnetic characteristics of sedimentary greigite fe3s4 several diagnostic magnetic properties can be used in conjunction to rapidly screen sediments to detect the presence of greigite such discriminants are necessary because greigite displays a similar or higher range of coercivities compared to most ferrimagnetic minerals and the commonly used method of alternating field demagnetization cannot be used to distinguish between palaeomagnetic remanence components due to greigite and other ferrimagnetic minerals sedimentary greigite has high ratios of the saturation isothermal remanent magnetization to magnetic susceptibility mrs which are accompanied by hysteresis ratios of mrsms 0 5 and bcr bc 1 5 ms is the saturation magnetization bc is the coercive force and bcr is the coercivity of remanence greigite has no low temperature phase transition whereas the ferrimagnetic iron sulphide pyrrhotite undergoes a major phase transition at about 34 k and unoxidized magnetite displays the verwey transition at 118 k low temperature measurements may therefore prove valuable in distinguishing between magnetite pyrrhotite and greigite although the absence of a low temperature transition cannot be taken as definitive evidence for the presence of greigite greigite also displays characteristic high temperature behaviour with a major drop in magnetization between 270 and 350 c determination of the mrs ratio is an excellent means of rapidly screening sediments to identify stratigraphic intervals that may contain greigite subsequent low and high temperature analyses can then provide unambiguous identification of greigite and enable the evaluation of the presence of other magnetic minerals