tsunami propagation over a wide shallow continental shelf caused by the storegga slide southeastern north sea denmark the large storegga slide which occurred on the norwegian atlantic shelf 8150 yr ago triggered a tsunami that has been identified in sediment deposits along the coasts of greenland norway the faroe islands the shetland islands scotland and the northernmost coasts of england but hitherto not along the southeastern shores of the north sea it has generally been assumed that the shallow continental shelf of the north sea attenuated and dissipated the energy of the tsunami before it reached those coastlines we used radiocarbon and optically stimulated luminescence dating as well as stratigraphic lithologic chemical and palynological analyses of sediment cores to identify tsunami deposits on the barrier island of romo located on the southwestern north sea coast of denmark we show that tsunami sediments were deposited in a freshwater paleolake that is located 16 m below present day mean sea level the tsunami sediment run up was between 1 5 m and 5 5 m above the contemporaneous sea level our results demonstrate that the storegga slide tsunami propagated across the wide 500 km and relatively shallow depth 95 m continental shelf of the north sea and resulted in run up along adjacent coastlines in contradiction to earlier theoretical studies the coastline of the southeastern north sea cannot be regarded as being sheltered from impacts of north atlantic tsunami incidents

the mjauvotn tephra and other holocene tephra horizons from the faroe islands a link between the icelandic source region the nordic seas and the european continent six different tephra horizons were found in peat and lacustrine sediments on the faroe islands in the north atlantic their geochemistry showed that they were of icelandic origin three of these can be correlated with previously described tephra horizons from the faroe islands the saksunarvatn tephra c 9000 bp the hekla 4 c 3800 bp and hekla selsund c 3600 bp a previously unrecorded basaltic tephra dated to c 5700 5300 bp was found in two lacustrine successions this horizon is named the mjauvotn tephra after mjauvotn lake on the island of streymoy two further tephras were recorded the basaltic phase of the landnam tephra viia c ad 870s and the rhyolitic tjornuvk tephra these were found in sediments deposited shortly after the first phase of human settlement at tjornuvik which is ams dated to ad 675 861 calibrated age the faroe islands are an important link between the volcanic sources on iceland and the established tephrochronological frameworks on the british isles scandinavia and germany their position within a sensitive region of the northeastern branch of the north atlantic drift make the faroe islands ideal for registering climate changes during the holocene the establishment of a modern tephrochronology may provide a tool for more precisely dating and correlating regional climate events in and around the nordic seas

first indication of storegga tsunami deposits from east greenland a 2 73 m long sediment sequence from loon lake located at 18m a s l on outer geographical society o east greenland was investigated for its chronology and changes in physical and biogeochemical properties macrofossils and grain size distribution the predominance of marine fossils throughout the sequence dated by 14c ams to between 8630 and 7535 cal yr bp shows that the loon lake at that time was a marine basin which according to existing sea level curves was about 15 35 m deep the sequence mainly consists of fine grained homogeneous sediments which are interrupted by a 0 72 m thick sandy horizon with erosive basis and distinct fluctuations in the grain size distribution and in the physical and biogeochemical properties according to the radiocarbon dates this sandy horizon was deposited after 8500 8300 cal yr bp and is interpreted as originating from the storegga tsunami the record from loon lake provides the first indication of storegga tsunami deposits from east greenland copyright 2006 john wiley sons ltd

the storegga slide tsunami comparing field observations with numerical simulations abstract deposits from the storegga tsunami have been found in coastal areas around the norwegian sea and north sea from the northeast coast of england to beyond the arctic circle in northern norway the tsunami deposits reach onshore elevations of 10 12 m above sea level of their time in western norway 3 6 m in northeast scotland and above 20 m on the shetland islands these elevations are compared with surface wave elevations derived from a numerical simulation of the storegga slide a good agreement is obtained for a retrogressive slide that descends at 25 30 m s and that has short time lags of 15 20 s between each individual slide block

seeing through tectonic plates two overlapping oceanic plates are sinking into the mantle underneath central japan where they dehydrate releasing water rich fluids that enhance mantle melting geochemical work helps determine the relative contribution of each plate to the overall fluid budget

ash layers from iceland in the greenland grip ice core correlated with oceanic and land sediments four previously known ash layers ash zones i and ii saksunarvatn and the settlement layer all originating in iceland have been identified in the central greenland ice core grip this correlation of the ash between the different environments is achieved by comparison of the chemical composition of glass shards from the ash this establishes and confirms detailed correlations between the different types of depositional records and the absolute dating of the younger part of the ice core by counting annual layers dates the eruptions accurately a precise connection with dates obtained by14c beyond the range of dendrochronology is established which provides an excellent confirmation of230th 234u dates from corals four additional icelandic ash layers have also been identified in the core but not yet correlated with known ash deposits

cliff top storm deposits on banneg island brittany france effects of giant waves in the eastern atlantic ocean this study is based on the morphosedimentary analysis of the cliff top storm deposits accumulated on the coast of banneg island located in the archipelago of molene brittany france these ctsds comprise large tabular clasts quarried from the upper part of the cliff and the backing scoured platform by giant oceanic storm waves impacting directly the western coast of the island an analysis of the distribution and the geomorphology of these accumulations were carried out using the dgps topographic surveys most of the clasts are organised into imbricate boulder clusters or ridges deposited between 7 5 and 14 5 masl 52 accumulations were inventoried from the north to the south of the island representing a global volume of 1000 m3 the median size of the clasts calculated is equivalent to 0 8 0 6 0 4 m and a weight of 0 6 t the largest one measuring 5 3 3 9 0 5 m 32 t is located in the centre of the island ridge 28 it has been deposited 14 m inland from the edge of the cliff at the elevation of 9 m sediment analysis shows that clast sizes become smaller with increasing distance from the shoreline but there is no relationship between the sorting and the distance inland a study of the hydrodynamic conditions inducing clast transport was undertaken by an analysis of the wave data from the 1989 to the 1990 winter storms models of wave runup indicate that their highest water levels may have reached up to 19 masl 5 to 10 m higher than the top of the cliff submersion by giant storm waves has been more important and frequent in the centre and the south of the island wave data over the 1979 to the 2007 period shows that no events as powerful as those of the 1989 to the 1990 winter were recorded during the last 30 years yet it appears that the 1979 1990 decade was characterized by important morphogeneous events while the following period 1990 2007 has experienced a sharp decrease in storm events these variations could be attributed to the inversion from a negative towards a positive phase in the north atlantic oscillation index

a numerical investigation of excess pore pressures and continental slope stability in response to ice sheet dynamics submarine landslides are common at glaciated continental margins the onset of large scale landslides coincides with the initiation of northern hemisphere glaciations in the quaternary this implies that processes related to glacial cycling provide favourable conditions for submarine landslides at high latitude margins potential processes include glacial deposition patterns and enhanced seismicity it is also possible that advances and retreats of ice sheets a highly dynamic process in geologic terms makes slopes discernible to failure by modifying the stress regime here we quantify this effect using 2d finite element modelling of a glaciated continental margin different model runs investigate the pore pressure development in homogeneous as well as layered slopes during glaciation when loaded by an ice stream with one or multiple ice advances ice streams cause significant variations in excess pore pressure in the very shallow sediment sequences at the continental shelf however lateral fluid flow is not efficient enough to increase pore pressures significantly at the slope where large scale submarine slides are observed hence while ice sheet dynamics appear to favour the occurrence of shallow slides close to the shelf edge ice sheets seem to be irrelevant for the generation of large scale submarine landslides at the continental slope

x ray tomography of tsunami deposits towards a new depositional model of tsunami deposits x ray computed microtomography is used to obtain high resolution imagery of a historical tsunami deposit in andalusia spain 1755 lisbon tsunami the technique allows characterization of grain size distribution structures component analysis and sedimentary fabric of fine grained unconsolidated tsunami deposits at resolutions down to particle scale the results are validated by comparing to data obtained using other techniques such as laser diffraction anisotropy of magnetic susceptibility and x ray microfluorescence on the same deposits specific technical details such as sampling scanning and image processing methods and further improvements are addressed the use of x ray computed microtomography provides new insights into the stratigraphy of the deposits and gives access to significantly more detailed view of key sedimentary features such as mudlines rip up clasts crude laminations convolutions floating outsized clasts and contacts between successive units this analysis of the 1755 tsunami deposits using x ray computed microtomography allows the proposal of new hypotheses for the sedimentary processes forming tsunami deposits deposition by settling is limited and the section analysed here is dominated by a high shear stress leading to the development of traction carpets with laminated mudlines corresponding to the basal frictional region of these carpets the onset of the tsunami backwash is marked by a micro vortex resembling kelvin helmoltz instabilities

a holocene tsunami deposit in eastern scotland a thin regionally extensive laterally persistent sand layer identified within the holocene coastal sequences of eastern scotland dated to 7000 years bp is suggested to be a tsunami deposit the likely source of the tsunami wave is the earthquake induced second storegga slide on the norwegian continental slope at least 750 km northeast of the deposit

directional ocean wave measurements in a coastal setting using a focused array imaging radar a unique focused array imaging doppler radar was used to measure directional spectra of ocean surface waves in a nearshore experiment performed on the north carolina outer banks radar images of the ocean surface s doppler velocity were used to generate two dimensional spectra of the radial component of the ocean surface velocity field these are compared to simultaneous in situ measurements made by a nearby array of submerged pressure sensors analysis of the resulting two dimensional spectra include comparisons of dominant wave lengths wave directions and wave energy accounting for relative differences in water depth at the measurement locations limited estimates of the two dimensional surface displacement spectrum are derived from the radar data the radar measurements are analagous to those of interferometric synthetic aperture radars insar and the equivalent insar parameters are shown the agreement between the remote and in situ measurements suggests that an imaging doppler radar is effective for these wave measurements at near grazing incidence angles

the tsunami phenomenon abstract with human activity increasingly concentrating on coasts tsunamis from japanese tsu harbour nami wave are a major natural hazard to today s society stimulated by disastrous tsunami impacts in recent years for instance in south east asia 2004 or in japan 2011 tsunami science has significantly flourished which has brought great advances in hazard assessment and mitigation plans based on tsunami research of the last decades this paper provides a thorough treatise on the tsunami phenomenon from a geoscientific point of view starting with the wave features tsunamis are introduced as long shallow water waves or wave trains crossing entire oceans without major energy loss at the coast tsunamis typically show wave shoaling funnelling and resonance effects as well as a significant run up and backflow tsunami waves are caused by a sudden displacement of the water column due to a number of various trigger mechanisms such are earthquakes as the main trigger submarine and subaerial mass wastings volcanic activity atmospheric disturbances meteotsunamis and cosmic impacts as is demonstrated by giving corresponding examples from the past tsunamis are known to have a significant sedimentary and geomorphological off and onshore response so called tsunamites form allochthonous high energy deposits that are left at the coast during tsunami landfall tsunami deposits show typical sedimentary features as basal erosional unconformities fining upward and landward a high content of marine fossils rip up clasts from underlying units and mud caps all reflecting the hydrodynamic processes during inundation the on and offshore behaviour of tsunamis and related sedimentary processes can be simulated using hydro and morphodynamic numerical models the paper provides an overview of the basic tsunami modelling techniques including discretisation guidelines for appropriate temporal and spatial resolution as well as the nesting method furthermore the boussinesq approximation a simplification of the three dimensional navier stokes equations is presented as a basic theory behind numerical tsunami models which adequately reflects the non linear dispersive wave behaviour of tsunamis the fully non linear boussinesq equations allow the simulation of tsunamis e g in the form of n waves based on the various subtopics presented recommendations for future multidisciplinary tsunami research are made it is especially discussed how the combination of sedimentary and geomorphological tsunami field traces and numerical modelling techniques can contribute to derive locally relevant tsunami sources and to improve the assessment of tsunami hazards considering the individual pre history and physiogeographical setting of a specific region

reconstruction of storm tsunami records over the last 4000 years using transported coral blocks and lagoon sediments in the southern south china sea large transported coral blocks on reef flats and elevated sedimentation rates in atoll lagoons were demonstrated to be excellent proxies for past strong storms tsunamis in the southern south china sea here we introduce another important proxy coarse fraction contents of lagoon sediments this proxy is based on the principle that coarse fractions of enclosed lagoon sediments are usually controlled by strong sedimentary dynamics on the surrounding reef flat and thus increases in the weight percentages of coarse grained fractions of the lagoon sediments should also reflect strong storm tsunami events or increases in storminess with the size of the content peak as the proxy for the degree of storminess bearing this in mind we measured the contents of the 1 mm grain size fractions referred to as coarse fraction content in an undisturbed lagoon core precisely dated to cover the last 4000 years the decadal resolution data show a systematic variation with some peaks strongly correlated with in timing with strong storm tsunami events dated at ad 1872 15 1685 8 similar to 1680 6 1443 9 1336 9 1210 5 similar to 1201 4 and 1064 30 using wave transported coral blocks using the mean coarsefraction content 9 2 for the entire core as a reference line a total of 77 peaks were identified for the past 4000 years twenty of these peaks are higher than 23 the mean value for peaks that are correlated in age with the six strong storm events identified using independently dated coral blocks among these 23 peaks 13 occurred within the last 1000 years the concentration of contentpeaks in the last millennium could be partially due to higher deposition rates and sampling resolution over the last similar to 4000 years there appears to be a weakly increasing trend in coarse fraction contents towards present time but this trend is not obvious within the last millennium this long term variation may be related to changes in both storminess and reef lagoon morphology however the data do suggest three extremely stormy periods centring around ad similar to 1200 similar to 400 bc and similar to 1200 bc respectively overall this study demonstrates that combined use of transported coral blocks and coarse fraction contents of lagoon sediments provides an excellent means for comprehensive reconstruction of past storm tsunami activity c 2008 elsevier ltd and inqua all rights reserved

heavy mineral assemblages of the storegga tsunami deposit abstract this study applies heavy mineral analysis to the storegga tsunami deposit across a range of locations whale firth maggie s kettle loch and scatsta voe in shetland scotland the usefulness of this proxy is tested in the identification and characterization of these palaeotsunami units furthermore provenance relationships are established based on the mineralogical content of tsunami deposits and their potential source finally the capability of identifying different phases of tsunami inundation in an 8200 years old tsunami deposit is attempted our results show that overall tsunamigenic samples presented a clear dominance of garnets and amphiboles while whale firth presented a more balanced distribution between these two mineral groups in maggie s kettle loch and scatsta voe the tsunamigenic samples are dominated by amphiboles 90 of transparent heavy minerals focusing on the two dominant heavy minerals garnets and amphiboles and their vertical variation one could observe that garnets mimic the heavy mineral concentration variability higher values at the base and decreasing values to the top this effect of concentration of the heaviest of the heavy minerals assemblage presents similarities with the formation of beach placer deposits in fact based on the heavy mineral vertical variation of the tsunami deposits in maggie s kettle loch scatsta voe and whale firth it is possible to conclude that hornblende most likely amphibole of the assemblage has the lowest concentration factor indicating that its transport process is more efficient and consequently most of its particles eventually may have moved offshore in the backwash phase of the tsunami furthermore the more platy shape of amphiboles also favours a slower deposition the opposite can be observed for garnets which require more energy to be transported i e they are more difficult to entrain by the tsunami waves and tend to be more easily preserved in the formation of a tsunamigenic placer deposit the work presented here is of particular relevance for future high resolution sedimentological studies aiming to distinguish different inundation phases of the storegga tsunami and assess the degree of preservation of these deposits especially considering the specific geomorphological and stratigraphic depositional setting of scotland

tsunami sedimentary facies deposited by the storegga tsunami in shallow marine basins and coastal lakes western norway sedimentary successions in small coastal lakes situated from 0 to 11 m above the 7000 year bp shoreline along the western coast of norway contain a distinctive deposit very different from the sediments above and below the deposit is interpreted to be the result of a tsunami inundating the coastal lakes an erosional unconformity underlies the tsunami facies and is traced throughout the basins with most erosion found at the seaward portion of the lakes the lowermost tsunami facies is a graded or massive sand that locally contains marine fossils the sand thins and decreases in grain size in a landward direction above follows coarse organic detritus with rip up clasts here termed organic conglomerate and finer organic detritus the tsunami unit generally fines and thins upwards the higher basins 6 11 m above the 7000 year shoreline show one sand bed whereas basins closer to the sea level 7000 years ago may show several sand beds separated by organic detritus these alternations in the lower basins may reflect repeated waves of sea water entering the lakes in basins that were some few metres below sea level at 7000 years bp the tsunami deposit is more minerogenic and commonly present as graded sand beds but also in some of these shallow marine basins organic rich facies occur between the sand beds the total thickness of the tsunami deposit is 20 100 cm in most studied sites an erosional and depositional model of the tsunami facies is developed

diatom assemblages in tsunami deposits associated with the 2004 indian ocean tsunami at phra thong island thailand abstract diatom assemblages in sandy deposits of the 2004 tsunami at phra thong island thailand may provide clues to flow conditions during the tsunami the tsunami deposits contain one or more beds that fine upward commonly from medium sand to silty very fine sand diatom assemblages of the lowermost portion of the deposit predominantly comprise unbroken beach and subtidal species that live attached to sand grains the dominant taxa shift to marine plankton species in the middle of the bed and to a mix of freshwater brackish and marine species near the top these trends are consistent with expected changes in current velocities of tsunami through time during high current velocities medium sand is deposited only beach and subtidal benthic diatoms attached to sediment can be incorporated into the tsunami deposit high shear velocity keeps finer material including planktonic diatoms in suspension with decreasing current velocities finer material including marine plankton can be deposited finally during the lull between tsunami waves the entrained freshwater brackish and marine species settle out with mud and plant trash low numbers of broken diatoms in the lower medium sand implies rapid entrainment and deposition whilst selective breakage of marine plankton thalassionema nitzschioides and thalassiosira and coscinodiscus spp in the middle portion of the deposit probably results from abrasion in the turbulent current before deposition

a 9000 year old ash bed on the faroe islands abstract radiocarbon datings of the saksunarvatn ash bed on the faroe islands indicate an age of 9000 9100 yr b p the saksunarvatn ash bed differs geochemically from both ash zone 1 in the north atlantic and the vedde ash bed of norway and the norwegian sea all mentioned ashes are assumed to originate from iceland the vedde ash has been dated at 10 600 60 yr b p consequently the saksunarvatn and vedde ash beds provide an opportunity for precise dating of events around the pleistocene holocene boundary in marine cores especially from the region where the two plumes overlap

evidence for three north sea tsunamis at the shetland islands between 8000 and 1500 years ago abstract coastal fen and lake deposits enclose sand layers that record at least three holocene tsunamis at the shetland islands the oldest is the well known storegga tsunami ca 8100 cal yr bp which at the shetlands invaded coastal lakes and ran up peaty hillsides where it deposited sand layers up to 9 2 m above present high tide level because sea level at ca 8100 cal yr bp was at least 10 15 m below present day sea level the runup exceeded 20 m in two lakes we also found deposits from a younger tsunami dated to ca 5500 cal yr bp the sediment facies are similar to those of the storegga tsunami rip up clasts sand layers re deposited material and marine diatoms runup was probably more than 10 m yet another sand layer in peat outcrops dates to ca 1500 cal yr bp this sand layer thins and fines inland and was found at two sites 40 km apart and traced to ca 5 6 m above present high tide the oldest tsunami was generated by the storegga slide on the norwegian continental slope we do not know what triggered the two younger events

diatoms as an aid in identifying late holocene tsunami deposits diatoms bacillariophyta help identify the onshore deposits of tsunamis from earthquakes on the cascadia subduction zone along the pacific coast of oregon washington and british columbia and on faults high in the north american plate in the puget sound area of washington at the copalis river washington diatom analyses suggest that a tsunami deposit about 300 calendric years old 300 yr bp originated from sandy shoals of the lower estuary rather than nearby beaches or coastal dunes at cultus bay and west point washington well preserved benthic estuarine diatoms in sand sheets overlying tidal marsh peat indicate that the deposits came from intertidal or nearshore areas of puget sound on an abruptly uplifted mudflat at the landward end of hood canal at lynch cove washington tidal flat diatoms refute the possibility of a terrestrial source for the sand diatoms in 300 yr bp tsunami deposits on the niawiakum river washington confirm that the sand in these deposits had a marine source and help

variation in 14c age of macrofossils and different fractions of minute peat samples dated by ams accurate 14c dating of peat samples is crucial if peat stratigraphies are to be used as historical archives to analyse the variation in 14c age within small peat samples the 14c age of different mire plant remains and peat fractions n 39 from 2 cm thick peat slices was determined using accelerator mass spectrometry the 14c ages of mosses were assumed to be the most accurate to verify this we also tested the possibility that uncertainties could be introduced by mosses at the mire surface reassimilating co2 produced during the decomposition of old peat the average 14c content of living mosses 110 5 110 9 absolute modern pm did not differ between threesphagnum species representing hummock carpet and lawn growing species their 14c contents were also identical within experimental limits to the current 14c content of the atmosphere depending on sampled depth and peat type the differences in calibrated 14c age between different fragments or fractions within specific 2 cm thick peat samples

the andoya slide and the andoya canyon north eastern norwegian greenland sea based on gloria side scan sonar imagery echo sounder records 3 5 khz profiles multichannel seismics and gravity cores the andoya slide and andoya canyon north eastern norwegian greenland sea were mapped and interpreted the andoya slide covers an area of about 9700 km2 of which the slide scar area comprise ca 3600 km2 the slide has a total run out distance of about 190 km slope failure is inferred to have occurred during the holocene because the slide scar has prominent relief on the present sea floor the area of sediment removal is characterised by an irregular relief were relatively consolidated sediments are exposed at the sea floor little or no unconsolidated sediments overlies the slide deposits earthquake activity is inferred to have triggered the slide a holocene age of the andoya slide implies that three giant slides the storegga traenadjupet and andoya slides have occurred along the continental slope of norway during the last 10 000 years a large canyon the andoya canyon is located immediately south of the andoya slide on the upper slope the canyon has been incised about 1000 m in the bedrock and the maximum width at the bottom and between the canyon shoulders is 2 and 12 km respectively the andoya canyon represents the upper part of the lofoten basin channel based on analogy with other deep sea canyon channel systems the andoya canyon lofoten basin channel is possibly of pre quaternary age holocene sediments recovered from within the canyon and draping the flanking channel deposits indicate that the andoya canyon is not presently active and has probably not been active during the holocene during the holocene the canyon acted as a trap for sediments settling from the winnowing norwegian current

wave emplaced coarse debris and megaclasts in ireland and scotland boulder transport in a high energy littoral environment abstract many coastlines of the world particularly those at higher latitudes and those located in tropical cyclone belts are regularly battered by strong storm waves drowning of low lying areas by storm surges and storm floods has been thoroughly recorded however storm deposits at rocky shorelines or on cliffs have been underrepresented in the literature this article presents observations of extraordinary wave deposits along the high wave energy coastlines of western ireland and the northern scottish isles and discusses possible wave event types and time windows of the processes responsible we used archaeological geomorphological and geochronological disciplines to compare our findings with earlier results published for these areas and to contribute to the debate on whether large clasts found well above sea level and or a considerable distance inland were deposited by storms or by tsunamis

a tsunami about 1000 years ago in puget sound washington water surged from puget sound sometime between 1000 and 1100 years ago overrunning tidal marshes and mantling them with centimeters of sand one overrun site is 10 kilometers northwest of downtown seattle another is on whidbey island some 30 kilometers farther north neither site has been widely mantled with sand at any other time in the past 2000 years deposition of the sand coincided to the year or less with abrupt probably tectonic subsidence at the seattle site and with landsliding into nearby lake washington these findings show that a tsunami was generated in puget sound and they tend to confirm that a large shallow earthquake occurred in the seattle area about 1000 years ago

large scale washover sedimentation in a freshwater lagoon from the southeast australian coast sea level change tsunami or exceptionally large storm a distinct lens of marine sand up to 90 cm thick confined vertically by peat is found in the upper fill of a closed freshwater back barrier lagoon on the southeast australian coast coring of the deposit suggests it extends continuously up to 600 m inland and tapers landward rising to 1 6 m above principle datum in places the sand is overlain by accumulations of organic rich silt that contain charophytes indicating re estab lishment of lagoon conditions hypotheses considered for the deposition of the sandsheet are higher holocene sea level storms and tsunami ground penetrating radar transects of the seaward dune system suggest a penecontemporaneous erosional contact between a series of truncated pre event dunes and several small over lying post event dunes dating the sandsheet was problematic but it is confined to the last 800 years the young age combined with a lack of associated beach deposits and evidence of wave scouring suggest that a higher sea level hypothesis is unlikely this sand lens is attributed to a large scale washover event from the southeast based on comparisons with modern storm deposits from the same coast and sedimentological diagnostic crite ria derived from studies of modern storm and tsunami deposited sandsheets it is concluded that this sand deposit is the product of a short lived large scale overwash event attributed to a late holocene tsunami

new findings regarding the saksunarvatn ash in germany the saksunarvatn ash is an important tephra layer for the correlation of early holocene environmental records in northern europe the north atlantic and greenland the saksunarvatn ash is believed to have been produced by eruptions of the grimsvotn volcanic system 10 3 ka bp which had two axes of dispersal one plume in a north west direction over northern iceland and into greenland and a second southerly plume covering the faroe isles shetland isles western norway and northern germany here we present data from potremser moor north east germany extending the easterly margin of the ash fallout zone we also present single grain trace element data from the type site at saksunarvatn as well as from potremser moor the saksunarvatn ash is indistinguishable between potremser moor and saksunarvatn suggesting the two tephras were produced by the same eruption trace element compositions from both sites are similar to data from the north atlantic marine core link 14 185 but different from the grip ice core grip 1528 61 m indicating that the south east and north west plumes may have arisen from separate eruption events copyright 2013 john wiley sons ltd

the sedimentology of middle holocene tsunami facies in northern sutherland scotland uk abstract lagoonal sediments attributed to the main holocene marine transgression in strath halladale northern sutherland contain a complex coarser layer believed to have been deposited during the tsunami associated with the second storegga slide off south west norway the coarser sequence is dated at between 7590 50 and 7290 50 radiocarbon years bp 6507 6260 cal bc and 6228 6029 cal bc detailed stratigraphical analysis has determined a distinctive suite of sedimentary sub units within the coarser layer in marked contrast to the sediments which occur above and below a pronounced erosional unconformity with the underlying sediments is recorded with the base of the tsunami layer characterised by eroded material from the underlying peat the presence of a mixed diatom assemblage although fragmentary indicates a chaotic accumulation of the deposit with all habitats represented variations in particle size within the sequence disclose striking similarities with those from contemporary tsunami deposits the run up of the tsunami sediments is calculated at a minimum of 4 6 m this is the first occasion on which a deposit of the second storegga slide tsunami has been found outside the north sea basin and indicates that the area affected by the tsunami may have been larger than has been previously described

collision of the kronotskiy arc at the ne eurasia margin and structural evolution of the kamchatka aleutian junction structural evolution of the kamchatka aleutian junction area in late mesozoic and tertiary was generally controlled by 1 the processes of subduction in kronotskiy and proto kamchatka subduction zones and 2 collision of the kronotskiy arc against ne eurasia margin two structural zones of the pre pliocene age and six structural assemblages are recognized in studied region 1 eastern ranges zone comprises se vergent thrust folded belt which evolved in accretionary and collisional setting two structural assemblages er1 and er2 developed there document shortening in the nw se direction and in the n s direction respectively 2 eastern peninsulas zone generally corresponds to kronotskiy arc terrane four structural assemblages are recognized in this zone they characterize 1 precollisional deformations in the accretionary wedge ep1 and in the fore arc basin and volcanic belt ep2 and 2 syn collisional deformation of the entire kronotskiy terrane in plunging folds ep3 and deformations in the foreland basin ep4 analysis of paleomagnetic declinations versus present day structural strike in the kronotskiy arc terrane shows that originally the arc was trending from west to east relative position of the accretionary wedge fore arc basin and volcanic belt as well as northward dipping thrusts in accretionary wedge indicate that a northward dipping subduction zone was located south of the arc the accretionary wedge developed from the late cretaceous through the eocene and it implies that the subduction zone maintained its direction and position during this time it implies that kronotskiy arc was neither a part of the pacific nor kula plates and was located on an individual smaller plate which included the arc and vetlovka back arc basin motion of the kronotskiy arc towards eurasia was connected only with nw directed subduction at kamchatka margin since middle eocene 42 44 ma emplacement of the kronotskiy arc at the kamchatka margin occurred between late eocene and early miocene this is based on the age of syn collisional plunging folds in kronotskiy terrane and provenance data for the upper eocene to middle miocene tyushevka basin which indicate in situ evolution of the basin with respect to kamchatka collision was controlled by the common motion of the kronotskiy arc with pacific plate towards the northwest and by the motion of the eurasian margin towards the south the latter motion was responsible for the southward deflection of the western part of the kronotskiy arc ep3 structures and for oblique transpressional structures in the collisional belt er2 structures

scenarios of tsunami amplitudes in the north eastern coast of sea of marmara generated by submarine mass failure in this paper the tsunamis resulting from a submarine mass failure such as slides and slumps triggered by earthquakes or other environmental effects which is settled at the bottom of the north eastern sea of marmara are examined in one sample region as the solution method one hybrid method is developed the main objective of this method is to combine an analytical solution presenting near field tsunami amplitudes above the submarine mass failure with a numerical solution indicating the tsunami amplitudes in the coastal regions for this purpose one common linear boundary between analytical and numerical solution domains is defined movements of submarine mass failures smf are modeled using one simple kinematics source model and the amplitudes of the tsunamis at the region that are closer to the landslide are computed by using the analytical method smf is modeled approximately from the bottom geometry and an average depth is used scenarios of smf are established depending on the velocities and thicknesses of the failure and near field tsunami amplitudes are obtained in the open sea during the source time after the source times the solutions are found in the numerical region using telemac 2d software system with the mentioned boundary above in this boundary the output of the analytical solutions is taken as the boundary conditions or the disturbances for the numerical method with these disturbances the numerical method is performed and the amplitudes are calculated in the coastal area the generation propagation and coastal amplifications of the tsunamis are illustrated at some certain points and regions both in the open sea and near the coast line the results have been visualized and discussed

a parametric study of tsunamis generated by submarine slides in the ormen lange storegga area off western norway tsunami generation by submarine slides have been a major concern in the risk assessment for the ormen lange gas field off western norway tsunamis are analysed with a numerical model supplemented by an analytical one both models show how slide extensions and slide dynamics influence the tsunamigenic potential for a large region several combinations of slide parameters were tested and the product of initial acceleration and the volume of the slide gave the best correlation with the maximum surface elevation for the near coastal domain

tsunami sedimentation associated with the 1923 kamchatka earthquake abstract the kuril kamchatka region is notorious for the occurrence of earthquake tsunamis and historical documents show that they have caused repeatedly considerable damage since the 1750s the great tsunami generated in april 1923 around the northern kamchatka trench flooded the coast of ust kamchatsk depositing a thin sand layer which is traceable up to 3 km or more inland beyond the present coastline local government documents indicate that the 1923 tsunami flooded low lying coastal areas covered by thick snow the unusual process of tsunami run up without loss of tractive load is interpreted to have resulted from the smoothing of fields by the ice covered surface we conclude that the tsunami flooded snowfields and deposited an extensive sheet of sand a mixture of snow and seawater flooded over the area and caused damage to vegetation

on the postglacial isostatic adjustment of the british isles and the shallow viscoelastic structure of the earth summary observations of postglacial relative sea level rsl history at sites beyond the margins of the main accumulations of wu rm wisconsin devensian ice may be invoked to test the accuracy of global models of the glacial isostatic adjustment process the existing database of rsl time series for the british isles forms a continuous network of sites that sample the coasts of scotland england and wales fairly uniformly and which may be especially important in this regard not only are these 14c data for the holocene epoch of very high quality in terms of our knowledge of the coastal environment and relationship to palaeo sea level of each age measurement but they are especially numerous and relate to an island that was itself partly glaciated in the north essentially ice free in the south and located well outboard of the massive ice sheet that covered fennoscandia at the last glacial maximum lgm taken together the time series from 55 distinct locations allow us to perform a fairly stringent test of the recently formulated ice 4g vm2 global model of the isostatic adjustment process even without modification this model has been shown to fit most of the time series in the uk data set rather well in order to satisfy very recently published a priori constraints on the maximum thickness of the scottish ice sheet however we find that the lithospheric thickness the feature of the radial viscoelastic structure to which the rebound data from scotland are most sensitive must be somewhat reduced whereas the assumed thickness of the lithosphere in ice 4g vm2 was near to 120 km best fits to the scottish data require a lithospheric thickness near to 90 km this reduced value for lithospheric thickness agrees exceedingly well with the latest estimates of this earth property based on the inversion of oceanic geoid and topography data as the asymptotic thickness characteristic of the oldest ocean floor this would appear to be the best possible a priori estimate for the thickness of the cratonic lithospheres upon which the largest ice sheets of the late pleistocene are known to have rested we also demonstrate explicitly that inferences of the shallow viscoelastic structure beneath the british isles are strongly influenced by the details of the history of deglaciation at remote locations at antarctica in particular

the storegga slides evidence from eastern scotland for a possible tsunami abstract the second storegga slide on the continental slope off western norway has been dated at between 8000 and 5000 yrs b p a prominent sand layer in flandrian holocene deposits along the coast of eastern scotland and dated at approximately 7000 yrs b p may have been deposited by a tsunami generated by the slide the altitude and stratigraphy of the layer allow estimates to be made of the magnitude of the earthquake which initiated the slide

geochemical evidence for the melting of subducting oceanic lithosphere at plate edges most island arc magmatism appears to result from the lowering of the melting point of peridotite within the wedge of mantle above subducting slabs owing to the introduction of fluids from the dehydration of subducting oceanic crust1 volcanic rocks interpreted to contain a component of melt not just a fluid from the subducting slab itself are uncommon but possible examples have been recognized in the aleutian islands baja california patagonia and elsewhere2 3 4 the geochemically distinctive rocks from these areas termed adakites are often associated with subducting plates that are young and warm and therefore thought to be more prone to melting5 but the subducting lithosphere in some adakite locations such as the aleutian islands appears to be too old and hence too cold to melt6 7 this implies either that our interpretation of adakite geochemistry is incorrect or that our understanding of the tectonic context of adakites is incomplete here we present geochemical data from the kamchatka peninsula and the aleutian islands that reaffirms the slab melt interpretation of adakites2 but in the tectonic context of the exposure to mantle flow around the edge of a torn subducting plate we conclude that adakites are likely to form whenever the edge of a subducting plate is warmed or ablated by mantle flow the use of adakites as tracers for such plate geometry may improve our understanding of magma genesis and thermal structure in a variety of subduction zone environments

problems encountered with the 14c dating of peat abstract pairs of neighbouring short columns of peat from two sites in northern england were divided into contiguous 1 cm thick slices that were sub sampled for pollen and plant macro fossil analysis for each slice the remaining peat was then split into humic acid humin and fulvic acid fractions and radiocarbon dated this research demonstrates that significant variations can occur in the radiocarbon content of discrete chemically defined fractions of peat a total of 127 radiocarbon dates was obtained the results from the four columns of peat are highly variable and mutually inconsistent the fulvic acid fraction although normally younger than the corresponding humic acid and humin fractions has very little effect on a combined date in these samples however it is removed from all samples prior to dating in order to remove any carbonates which could contaminate samples the variations in the ages obtained for the humic acid and corresponding humin fractions range from the humin fraction being 630 years older than the humic acid srr 4029 to the humic acid being 1210 years older than the humin fraction srr 4007 even when a two sigma confidence is allowed no correlation was apparent between pollen concentration 13 c enrichment degree of humification and the conventional radiocarbon ages

ormen lange an integrated study for the safe development of a deep water gas field within the storegga slide complex ne atlantic continental margin executive summary abstract a great effort has been undertaken to investigate potential geohazards in relation to the development of the ormen lange gas field offshore mid norway the field is located in the scar left after the giant tsunami generating storegga slide which occurred roughly 8150 years ago and the slide risk has consequently received particular focus the studies have been multi disciplinary in character and have involved a number of companies universities and research institutions the results of the project have lead to a significant advance in our understanding of the storegga slide in particular and submarine slope instability in general and played an important role in the approval of field development by norwegian authorities this special issue comprises 26 individual contributions in addition to this representing the wide span of topics addressed in the project and this introductory paper gives a brief summary of their contents

sea level fluctuations imply that the younger dryas ice sheet expansion in western norway commenced during the allerod after the first emergence following deglaciation relative sea level rose by 10 m in western norway and culminated late in the younger dryas yd the relative sea level history reconstructed by dating deposits in isolation basins shows a sea level low stand between 13 640 and 13 080 cal yr bp a 10 m sea level rise between 13 080 and 11 790 cal yr bp and a sea level high stand between 11 790 and 11 550 cal yr bp shortly after the yd holocene boundary sea level fell abruptly by 37 m the shorelines formed during the sea level low stand in the mid allerod and during the sea level high stand in the yd have almost parallel tilts with a gradient of 1 3 m km 1 indicating that hardly any isostatic movement has taken place during this period of sea level rise we conclude that the transgression was caused by the major re advance of the scandinavian ice sheet that took place in western norway during the lateglacial the extra ice load halted the isostatic uplift and elevated the geoid due to the increased gravitational attraction on the sea our results show that the crust responded to the increased load well before the yd starting 12 900 cal yr bp with a sea level low stand at 13 640 cal yr bp and the subsequent yd transgression starting at 13 080 cal yr bp thus we conclude that the so called yd ice sheet advance in western norway started during the allerod possibly more than 600 years before the allerod yd transition r 2007 elsevier ltd all rights reserved

new radiocarbon dates for the vedde ash and the saksunarvatn ash from western norway abstract the vedde ash bed mid younger dryas and the saksunarvatn ash early holocene are important regional stratigraphic event markers in the north atlantic the norwegian sea and the adjacent land area it is thus essential to date them as precisely as possible the occurrence of the saksunarvatn ash is reported for the first time from western norway and both tephras are dated precisely by ams analyses of terrestrial plant material and lake sediment at krakenes the vedde ash has been previously dated at sites in western norway to about 10 600 yr b p it is obvious in the younger dryas sediments at krakenes and its identity is confirmed geochemically the mean of four ams dates of samples ofsalix herbacealeaves adjacent to the tephra is 10 310 50 yr b p the saksunarvatn ash is not visible in the early holocene lake sediment at krakenes after removal of organic material and diatoms the identity of the tephra particles was confirmed geochemically and their stratigraphic concentration was estimated from curve matching of a series of seven ams dates of terrestrial plant macrofossils and whole sediment the radiocarbon age of the ash is 8930 9060 yr b p corresponding to an age of 9930 10 010 cal yr b p 7980 8060 cal yr b c

the case for significant numbers of extraterrestrial impacts through the late holocene when astronomers tell us that there should have been numerous impacts from space during the last five millennia when impact craters exist on land and more impacts can be assumed over the oceans why are historians archaeologists and palaeoecologists not diligently seeking evidence for these impacts and their effects this article reviews just some of the relevant evidence for impacts in turn this suggests that ablation material background material from space and micro tektites should all be present in ocean cores ice cores peat and lake sediments it seems that almost no efforts have been made to find evidence that might link to the known crater fields or to identify and date periods of enhanced cosmic activity the question must be why copyright 2007 john wiley sons ltd

glacial rebound of the british isles i preliminary model results summary observations of sea level change from localities around the british coastline indicate that major spatial and temporal variations have occurred over the past 15000 10000yr these observations provide a valuable data set for testing models of glacial rebound and for estimating the earth s response to surface loading as well as for placing broad constraints on models of the ice sheet over the northern british isles in late devensian time simple models have been developed to examine the criteria required for a high precision rebound model suitable for an inversion of the observations of sea level change for earth and ice model parameters for such a model to have a precision of better than 1 m these requirements include 1 introduction of the fennoscandian and more distant ice sheets into the model both as contributions to the sea level rise and to the crustal deformation of the associated changing ice and water loads 2 an expansion of the ice and meltwater loads to very high spherical harmonic degree including terms up to about 240 for the water load term 3 the development of higher iteration solutions of the sea level equation in order to model accurately the meltwater load contribution to sea level change 4 the introduction of loading cycles before the attainment of the last glacial maximum for both the british ice sheet and the other major but more distant ice sheets and 5 the introduction of time dependent coastlines during the period of rapid global sea level rise the sea level predictions are strongly dependent on both earth model and ice model parameters but because observations are available from a wide range of locations within and beyond the former ice sheet margins some separation of the two types of parameters is possible for example the models exclude the possibility that a substantial ice load occurred over the north sea between scotland and norway in late devensian time and that the maximum ice thickness over northern great britain is unlikely to have exceeded about 1500 m during the last glacial maximum the earth model parameters that can be resolved are the lithospheric thickness and the upper mantle viscosity a high resolution model incorporating the above model criteria and used to infer ice and earth model parameters from the observations of sea level change is developed in the accom panying paper

lithium isotopic composition of central american volcanic arc lavas implications for modification of subarc mantle by slab derived fluids abstract li contents and isotopic compositions were determined for a suite of well characterized basaltic lavas from the central american volcanic arc cava variable li y 0 2 0 5 li sc 0 1 0 4 and 6 li values 2 6 to 7 7 attest to significant compositional heterogeneity in the subarc mantle within specific arc segments these parameters correlate strongly with each other and with a number of other constituents e g k rb ba b la 10 be 9 be 87 sr 86 sr u ce and 230 th 232 th among others these correlations are particularly strong for nicaragua samples coupling of this particular set of constituents is best explained in terms of addition of subduction components to the subarc mantle moreover their selective enrichment with respect to relatively fluid immobile incompatible elements signifies the dominance of fluid vs silicate melt transport of slab components to the subarc mantle several interesting nuances are revealed by the li data first although li and b are strongly correlated in both costa rica and nicaragua there are systematic along strike variations in li b that are consistent with these elements having different fluid release patterns from subducted slab segments for example li b is highest in costa rica where auxiliary evidence indicates higher subduction zone temperatures apparently b is preferentially depleted and li retained in the slab under warmer conditions the same relations are reflected in li 10 be and other subduction tracer systematics all of which point to larger subduction contributions below nicaragua yet even nicaragua lavas vary widely in levels of subduction enrichment high ti basalts from nejapa are the least enriched and have the highest 6 li 1 4 to 2 6 these values are greater than in fresh morb ca 4 and are not easily explained by additions of subducted li because most oceanic crustal rocks and marine sediments have lower 6 li than morb with typical values between 8 and 20 thus it appears the nejapa data may be representative of isotopically light mantle domains relatively light 6 li values in an undepleted spinel lherzolite 11 3 from zabargad is red sea and in primitive backarc basalts 1 6 to 0 5 from lau basin support this conclusion considering representative fluid and mantle endmember compositions the cava data are consistent with limited up to a few percent additions of slab derived fluids to a heterogeneous mantle containing variably depleted and enriched domains to form the respective magma sources in our view the subarc mantle is heterogeneous on a small scale but some arc sectors clearly received greater slab inputs than others

tsunamis as geomorphic crises lessons from the december 26 2004 tsunami in lhok nga west banda aceh sumatra indonesia abstract large tsunamis are major geomorphic crises since they imply extensive erosion sediment transport and deposition in a few minutes and over hundreds of kilometres of coast nevertheless little is known about their geomorphologic imprints the december 26 2004 tsunami in sumatra indonesia was one of the largest and deadliest tsunamis in recorded human history we present a description of the coastal erosion and boulder deposition induced by the 2004 tsunami in the lhok nga bay located to the west of banda aceh northwest sumatra the geomorphological impact of the tsunami is evidenced by beach erosion some beaches have almost disappeared destruction of sand barriers protecting the lagoons or at river mouths numerous erosion escarpments typically in the order of 0 5 1 5 m when capped by soil and more than 2 m in dunes bank erosion in the river beds the retreat along the main river is in the order of 5 15 m with local retreats exceeding 30 m large scars typically 20 50 cm deep on slopes dislodgement of blocks along fractures and structural ramps on cliffs the upper limit of erosion appears as a continuous trimline at 20 30 m a s l locally reaching 50 m the erosional imprints of the tsunami extend to 500 m from the shoreline and exceed 2 km along riverbeds the overall coastal retreat from lampuuk to leupung was 60 m 550 000 m 2 and locally exceeded 150 m over 276 000 m 3 of coastal sediments were eroded by the tsunami along the 9 2 km of sandy coast the mean erosion rate of the beaches was 30 m 3 m of coast and locally exceeded 80 m 3 m the most eroded coasts were tangent to the tsunami wave train which was coming from the southwest the fringing reefs were not efficient in reducing the erosional impact of the tsunami the 220 boulders measured range from 0 3 to 7 2 m large typically 0 7 1 5 m with weights from over 50 kg up to 85 t we found one boulder less than 1 m large at 1 km from the coastline but all the others were transported less than 450 m 30 m and the moderate tsunamis height