submarine landforms and shallow acoustic stratigraphy of a 400 km long fjord shelf slope transect kangerlussuaq margin east greenland kangerlussuaq fjord is a relatively uniform steep walled basin whose floor has an almost smooth surface debris is supplied mainly from icebergs from the fast flowing kangerlussuaq glacier sedimentation after iceberg release from multi year sea ice is mainly by rain out of fine grained englacial debris streamlined glacial lineations and drumlins were produced at the sedimentary bed of an ice sheet that expanded into kangerlussuaq trough at the last glacial maximum lgm bedrock channels and crescentic overdeepenings indicate warm based ice and free water beneath parts of the former ice sheet cross cutting iceberg scour marks which characterise outer kangerlussuaq shelf were produced not only during deglaciation but also occasionally through the holocene by deep keeled icebergs from further north in east greenland the outward convex contours of the shelf edge and slope beyond kangerlussuaq trough and debris flows on the slope suggest a glacier influenced high latitude fan the distribution of streamlined subglacial landforms demonstrates that the greenland ice sheet extended throughout kangerlussuaq fjord and reached at least 200 km across the shelf in kangerlussuaq trough at the lgm streamlined landform orientation indicates ice flow from the interior of greenland down the axis of kangerlussuaq trough there is little evidence for discrete sedimentary depocentres in the trough implying that ice probably retreated rapidly from the outer and mid shelf during deglaciation

seismic evidence for shallow gas escape features associated with a retreating gas hydrate zone offshore west svalbard active gas venting occurs on the uppermost continental slope off west svalbard close to and upslope from the present day intersection of the base of methane hydrate stability bmhs with the seabed in about 400 m water depth in the inter fan region between the kongsfjorden and isfjorden cross shelf troughs from an integrated analysis of high resolution two dimensional pre stack migrated seismic reflection profiles and multibeam bathymetric data we map out a bottom simulating reflector bsr in the inter fan region and analyze the subsurface gas migration and accumulation gas seeps mostly occur in the zone from which the bmhs at the seabed has retreated over the recent past 1975 2008 as a consequence of a bottom water temperature rise of 1 c the overall margin parallel alignment of the gas seeps is not related to fault controlled gas migration as seismic evidence of faults is absent there is no evidence for a bsr close to the gas flare region in the upper slope but numerous gas pockets exist directly below the predicted bmhs while the contour following trend of the gas seeps could be a consequence of retreat of the landward limit of the bmhs and gas hydrate dissociation the scattered distribution of seeps within the probable hydrate dissociation corridor and the occurrence of a cluster of seeps outside the predicted bmhs limit and near the shelf break indicate the role of lithological heterogeneity in focusing gas migration

ice stream dynamics of the sw barents sea revealed by high resolution 3d seismic imaging of glacial deposits in the hoop area abstract recent developments in seismic acquisition systems and seismic data visualization have contributed to improve the imaging of seismic geomorphologies over a broad range of topics this study focuses on a new high resolution p cable 3d seismic cube located in the hoop area in the sw barents sea the scientific motivations of the study are 1 to document glacial landforms on a meter scale 2 to study the link of these landforms with the subsurface and 3 to understand ice stream dynamics by detailed interpretation of main horizons including the seabed intra glacial horizons and upper regional unconformity uru the horizons are assessed using the concept of seismic geomorphology and compared with interpretations derived from conventional 3d seismic and state of the art multibeam echosounder technologies to discuss the benefits and limitations of the different geophysical technologies a well defined intra glacial seismic reflection is imaged in the eastern part of the p cable cube this reflection has an overall ne trending ridge shaped morphology which is up to 50 m high and 5 10 km wide and interpreted as a shear margin moraine the top of the moraine displays well defined iceberg ploughmarks and clear slope failure events along its eastern flank the seabed geomorphology which has been directly shaped by glacial processes related to multiple phases of ice streaming appears to be influenced by the buried shear margin moraine mega scale glacial lineations msgls indicative of fast flowing ice streams characterize the seabed west of the moraine infilled msgls and different sets of iceberg ploughmarks with large berms dominate the seabed geomorphology above the moraine the seabed east of the moraine characterized by a smooth morphology and few pockmarks is inferred to reflect more slowly moving ice not resolved by other geophysical techniques seismic attribute maps of p cable 3d allowed the identification of smaller ploughmarks and corrugated ridges related to paleo tides eroded by the larger iceberg ploughmarks these small ploughmarks are suggested to be linked to an earlier rapid disintegration of the barents sea ice stream the new high resolution 3d seismic data have led to the development of a revised ice stream model of the barents sea linking the glacial deposits to different ice stream events

catastrophic fluid escape venting tunnels and related features associated with large submarine slides on the continental rise off vesteralen troms north norway abstract video inspection of the seabed on the continental rise ca 2200 m water depth off vesteralen troms north norway has revealed several remarkable features including large tunnels small tunnels chimney tunnels carbonate crusts and bacterial mats the structures occur in landslide areas with slide blocks up to 2 km long 1 km wide and 100 m high we hypothesize that the large seabed tunnels in and between slide blocks and with opening diameters up to 1 m and apparent inner diameters of 10 20 cm are formed by dewatering of fine grained sediments buried by the slide masses and possibly venting of underground gas reservoirs related to sliding and loading this process probably occurred instantaneously after sliding numerous small tunnels with diameters up to a few centimetres in slide blocks of compacted sediments may have formed by dewatering following sudden pressure release or by decomposition of gas hydrates following off loading of sediments due to sliding bacterial mats and carbonate crusts indicate active leakage of subsurface fluids and methane through the seabed and the gas hydrate stability zone either from thermogenic sources or from shallow reservoirs cemented chimney tunnels up to 15 cm tall and with inner diameters up to a few centimetres occur both on slide blocks and on flat and even seabed the presence of apparently both inactive and active chimney tunnels indicates that gas and fluid release is a process that has been periodically active possibly from before sliding up to the present

the marine based nw fennoscandian ice sheet glacial and deglacial dynamics as reconstructed from submarine landforms abstract the configuration of the marine based nw fennoscandian ice sheet during the last glacial maximum lgm and deglaciation is reconstructed using detailed swath bathymetry and high resolution seismic data the investigated area covers about 10 000 km 2 of the continental shelf off troms northern norway large scale morphology is characterized by cross shelf troughs coast parallel troughs and banks based on mega scale glacial lineations msgl lateral and shear zone moraines and grounding zone systems the extent and dynamics of the ice sheet during the lgm are deduced msgl indicate fast flowing ice streams in the cross shelf troughs while the glacial morphology on the banks indicates more sluggish ice here the marine based part of the fennoscandian ice sheet was sourced from ice domes in the east via fjord and valley systems inshore using a balance flux approach we estimate palaeo ice stream velocities during the lgm to be approximately 350 m year three deglaciation events have been reconstructed i during the torsken 1 event the ice sheet halted or readvanced to form groundings zone wedges gzw and the torsken moraine ii several still stands or readvances characterized the ice behaviour on the shallower banks during the torsken 2 event iii during the flesen event prominent end moraines in the inner parts of the troughs and banks were deposited the locations of the end moraines and gzw in the troughs indicate that the retreat of marine based ice streams in areas of reverse bed slope was episodic probably mainly due to the variation in widths of the cross shelf troughs

late quaternary lithofacies provenance and depositional environments 12 30 cal ka north and south of the denmark strait this paper describes the lithofacies and chronology of cores from north and south of the denmark strait for a period when ice sheets flanked both sides of the strait a wide range of sediments have been recovered indicating a complex of depositional processes jm96 1229ggc1 1047 m water depth is from the base of the nw iceland slope at the southern edge of the blosseville basin whereas jm96 1226ggc4 retrieved sediments south of the sill in 1519 m of water additional information is based on jm96 1220ggc2 and 1221ggc2 which were recovered from the upper w iceland slope at 500 m water depth below the latra moraine of possible last glacial maximum age and upslope of jm96 1226 ams 14c dates indicate that jm96 1226 and 1229 span the last 10 to 27 32 ka bp whereas jm96 1220 and 1221 recovered sediments dated between ca 8 and 18 ka bp closely spaced radiocarbon dates on jm96 1229 indicate an erosional hiatus of 7 ky between 12 and 19 cal ka lithofacies descriptions are based on visual descriptions and x radiographs jm96 1229 consists of fine grained sediments sometimes graded with scattered ice rafted debris whereas jm96 1226 consists largely of beds of matrix supported diamicton provenance indicators mass magnetic susceptibility and geochemistry for jm96 1229 support the delivery of sediments from nw iceland but there is a substantial difference in these properties between sediments from the w iceland upper slope and the sediments in jm96 1226 south of the denmark strait this indicates that the diamictons on the floor of the strait did not derive entirely from the iceland ice sheet and adjacent upper slope the general absence of sediments 12 cal ka on the slopes and floor of the denmark strait indicates that denmark strait overflow waters inhibited sediment accumulation during the holocene between ca 12 and 30 cal ka however a combination of more proximal sediment sources ice sheets and reduced thermohaline activity resulted in the accumulation of sediments on the slopes and basin floors

late quaternary stratigraphy and sedimentology of orphan basin implications for meltwater dispersal in the southern labrador sea abstract orphan basin is a deep water basin on the continental margin off newfoundland which throughout the late quaternary received proglacial sediment from local ice that crossed the continental shelf sediment from more distant sources was transported southward in the labrador current as proglacial plumes and in icebergs five sedimentary facies related to glacial processes are distinguished in cores recovered from orphan basin hemipelagic sediment nepheloid layer deposits layered mud beds rich in ice rafted detritus ird sand and mud turbidites and glaciogenic debris flow deposits ird rich beds correspond to periods of intensified iceberg calving and layered mud turbidites and glaciogenic debris flow deposits with glacial meltwater discharge in the late wisconsinan eight periods of meltwater discharge and iceberg calving from the newfoundland ice sheet are interpreted from the sediment facies in orphan basin these discharges coincide with the terminations of the colder periods of the d o cycles recorded in greenland ice cores the oldest minor meltwater event 27 5 28 5 cal ka corresponds to the first late wisconsinan ice advance across the grand banks and ne newfoundland shelf the following three meltwater discharges 23 23 5 23 8 24 5 and 25 27 cal ka deposited sand turbidites and glaciogenic debris flow deposits seaward of trinity trough which was occupied by an ice stream at this time and mud turbidites in the southern part of the basin derived from a mid shelf ice margin on the grand banks four periods of meltwater discharge occurred during the deglaciation and are centered at 15 18 5 19 75 and 20 75 cal ka the youngest is correlated to heinrich event 1 in the literature the 18 5 and 20 75 cal ka events have been recorded in multiple glacial settings in the north atlantic and therefore are interpreted as large scale events of meltwater discharge and iceberg calving but in orphan basin the 19 75 cal ka event is also of similar scale

the norwegian greenland sea continental margins morphology and late quaternary sedimentary processes and environment the continental margins surrounding the norwegian greenland sea are to a large degree shaped by processes during the late quaternary the paper gives an overview of the morphology and the processes responsible for the formation of three main groups of morphological features slides trough mouth fans and channels several large late quaternary slides have been identified on the eastern norwegian greenland sea continental margin the origin of the slides may be due to high sedimentation rates leading to a build up of excess pore water pressure perhaps with additional pressure caused by gas bubbles triggering might have been prompted by earthquakes or by decomposition of gas hydrates trough mouth fans tmf are fans at the mouths of transverse troughs on presently or formerly glaciated continental shelves in the norwegian greenland sea seven tmfs have been identified varying in area from 2700 km2 to 215 000 km2 the trough mouth fans are depocentres of sediments which have accumulated in front of ice streams draining the large northwest european ice sheets the sediments deposited at the shelf break upper slope by the ice stream were remobilized and transported downslope mostly as debris flows the trough mouth fans hold the potential for giving information about the various ice streams feeding them with regard to velocity and ice discharge two large deep sea channel systems have been observed along the norwegian continental margin the lofoten basin channel and the inbis channel along the east greenland margin several channel systems have been identified the deep sea channels may have been formed by dense water originating from cooling sea ice formation and brine rejection close to the glacier margin or they may originate from small slides on the upper slope transforming into debris flows and turbidity currents

seafloor geomorphology of the sw barents sea and its glaci dynamic implications abstract three dimensional 3d reflection seismic imaging techniques provide a unique means of identifying large scale submarine geomorphic features produced by former ice sheets we have used such techniques to image the geomorphology of the sw barents sea but using a dense grid of 2d seismic covering a 240 000 2 km large study area supplemented with 3d seismic from selected areas the study area is located at the convergence of ice flow from the former fennoscandian barents sea and svalbard ice sheets the morphology of the major cross shelf troughs is characterized by elongated ridge groove features interpreted to be glacial bedforms produced by fast flowing grounded glaciers mega scale glacial lineations have been grouped into distinct flow sets related to three specific ice flow events these events document the last glacial maximum lgm and two readvances during deglaciation of specific interest is a detailed and well preserved set of seafloor imprints in the bjornoyrenna trough which acted as the main pathway for ice streams draining the surrounding ice sheets the geomorphic features indicate that bjornoyrenna hosted six separate ice stream lobes that diverged fan like at their margins but were not all active simultaneously an end moraine zone 68 km wide up to 85 m high and 300 km long filled the whole width of this major glacial trough as a result of high sediment flux within sub ice stream deformable beds the imprint of this ice stream system can be followed on our seabed images for 500 km however detailed geomorphologic elements demonstrate that these imprints reflect time transgressive behaviour and do not indicate the length or width of single ice streams the seismic derived seafloor geomorphology demonstrates that the barents sea ice behaved in a much more dynamic way during the last glaciation than previously assumed with major shifts between ice originating from the fennoscandian spitsbergen and barents sea ice sheets

a combined spectrophotometric and morphometric study of the lunar mare dome fields near cauchy arago hortensius and milichius in this study we examine the spectral and morphometric properties of the four important lunar mare dome fields near cauchy arago hortensius and milichius we utilize clementine uv vis mulfispectral data to examine the soil composition of the mare domes while employing telescopic ccd imagery to compute digital elevation maps in order to determine their morphometric properties especially flank slope height and edifice volume after reviewing previous attempts to determine topographic data for lunar domes we propose an image based 3d reconstruction approach which is based on a combination of photoclinometry and shape from shading accordingly we devise a classification scheme for lunar marc domes which is based on a principal component analysis of the determined spectral and morphometric features for the effusive mare domes of the examined fields we establish four classes two of which are further divided into two subclasses respectively where each class represents distinct combinations of spectral and morphometric dome properties as a general trend shallow and steep domes formed out of low tio2 basalts are observed in the hortensius and milichius dome fields while the domes near cauchy and arago that consist of high tio2 basalts are all very shallow the intrusive domes of our data set cover a wide continuous range of spectral and morphometric quantities generally characterized by larger diameters and shallower flank slopes than effusive domes a comparison to effusive and intrusive mare domes in other lunar regions highland domes and lunar cones has shown that the examined four mare dome fields display such a richness in spectral properties and 3d dome shape that the established representation remains valid in a more global context furthermore we estimate the physical parameters of dome formation for the examined domes based on a rheologic model each class of effusive domes defined in terms of spectral and morphometric properties is characterized by its specific range of values for lava viscosity effusion rate and duration of the effusion process for our data set we report lava viscosities between about 10 2 and 10 8 pas effusion rates between 25 and 600 m 3 s 1 and durations of the effusion process between three weeks and 18 years lava viscosity decreases with increasing r 415 r 750 spectral ratio and thus tio2 content however the correlation is not strong implying an important influence of further parameters like effusion temperature on lava viscosity

climatic dependence of the organic matter contributions in the north eastern norwegian sea over the last 15 000 years abstract lipids are used for the evaluation of the different organic matter contributions in the north eastern norwegian sea m23258 site 75 n 14 e over the last 15 000 years development of a mass balance model based on the down core quantification of the c 37 alkenones the odd carbon numbered n alkanes a odd and the unresolved complex mixture of hydrocarbons ucm has allowed three main organic matter inputs involving marine continental and ancient reworked organic matter to be recognized the model shows good agreement between measured and reconstructed toc values similarly a strong parallelism is observed between predicted components such as marine toc and carbonate content which was determined independently representation of the model results within a time scale based on 15 ams 14 c measurements shows that the main changes in organic matter constituents are coincident with the major climatic events of the last 15 000 years thus the predominance of reworked organic matter is characteristic of termination ia up to 70 continental organic matter was dominant during the bolling allerod b a and younger dryas yd periods about 85 and a strong increase of marine organic matter occurred in the holocene between 50 and 75 this agreement reflects the main hydrographic changes that determined the deposition of sedimentary materials between 0 and 15 cal ka ice rafted detritus from the barents continental platform ice melting waters from the arctic fluvial system discharging into the barents sea and dominance of north atlantic currents respectively in this respect the high resolution down core record resulting from the mass balance and lipid measurements allows for the identification of millennial scale events such as the increase of reworked organic matter at the final retreat of the barents ice sheet at the end of the deglaciation period termination ib

physical models of rock avalanche spreading behaviour with dynamic fragmentation the dynamic fragmentation of rock during avalanche motion has been postulated as a mechanism explaining the long runout of large rock avalanches or sturzstrome this paper investigates whether test

canyons and late quaternary sedimentation on the north norwegian margin the presence of erosive canyons on high latitude passive margins is unusual such margins are more normally dominated by subsidence and glacially influenced deposition however ten canyons are identified at the edge of the narrow shelf on the north norwegian margin off the lofoten islands between the traenadjupet and andoya slides on the basis of gloria long range side scan sonar and contemporaneous 3 5 khz profiler data combined with a detailed bathymetry the canyons are located down stream of sediments transported through the lofoten drift and the margin is characterized by an absence of cross shelf troughs canyons are up to 420 m deep u shaped display steep gradients in their upper parts and sediments derived from them have short runout distances onto the continental rise the canyons are estimated to be 20 30 ma old being incised into only thinly covered lithified pre miocene sediments as a response to cenozoic uplift late quaternary sedimentation processes associated with the canyons are inferred to occur during both glacials and interglacials glacial sedimentation is probably in the form of direct subglacial debris input in addition to turbid subglacial meltwater plumes interglacial sedimentation processes are probably dominated by the along shelf transport of sediments by strong ocean currents canyon heads capture sediment from the shelf the remobilization of this coarse material and erosion of the canyons occurs through debris flows and turbidity currents canyon preservation and continued development can be attributed directly to the comparatively low sedimentation rates during full glacial conditions as ice streams located to the north and south produce regional depocentres away from this area of relatively slow flowing ice

variable history of quaternary ice sheet advance across the beaufort sea margin arctic ocean the seismic stratigraphy and architecture of the beaufort sea shelf and slope are investigated using a comprehensive grid of high resolution two dimensional seismic reflection data three cross shelf troughs representing locations of former ice streams draining a 1000 km long section of the laurentide ice sheet lis are examined the mackenzie amundsen gulf and m clure strait systems dynamics of these paleo ice streams influenced ice sheet configuration and may have forced abrupt climatic change through delivery of ice and freshwater to the arctic ocean a comprehensive understanding of their geometry and dynamics is crucial for constraining numerical models of the lis evidence for two quaternary ice advances to the shelf break is interpreted from the mackenzie trough by contrast seismic stratigraphy of the amundsen gulf trough 400 km east of the mackenzie trough records at least nine quaternary ice advances here the outer shelf consists of stacked till sheets extending to the shelf break and forming a trough mouth fan the contrasting glacial histories of these neighboring ice streams are explained by their positions within the lis the mackenzie trough ice stream was situated at the extreme northwest ice sheet margin whereas the amundsen gulf ice stream had a more central location and larger drainage basin supplying significant quantities of ice and sediment to the arctic ocean through much of the quaternary the m clure strait trough probably possesses a similar architecture to the amundsen gulf trough and an even larger trough mouth fan

geophysical investigations of a high latitude submarine channel system and associated channel mouth lobe in the lofoten basin polar north atlantic the lofoten basin channel forms one of two major submarine channels on the norwegian margin of the polar north atlantic the channel system connects upslope with the andoya canyon which is the only canyon to cut back across the continental shelf in this region high resolution geophysical records including multibeam swath bathymetric and tobi side scan sonar data show that the distal part of the channel system is braided and connects to a low gradient 0 01 channel mouth lobe on the abyssal plain of the lofoten basin geophysical data indicate that the channel floor is composed of sandy material deposited by turbidity currents these turbidity currents spilled out over the channel sides to deposit acoustically stratified sediment in the channel levees side scan sonar data supplemented by sediment cores indicate that the channel mouth lobe is sandy in composition the lofoten channel and its associated channel mouth lobe is therefore related to turbidity current activity and formation of the system appears to pre date the holocene morphological variation between the upper reaches of the andoya canyon lofoten channel system and the submarine channels of the greenland basin is proposed to relate to differences in the nature of the flows feeding both systems the andoya canyon lofoten channel system bears strong similarities to some mid and low latitude submarine fans with respect to its morphology and architecture

characterization of a stratigraphically constrained gas hydrate system along the western continental margin of svalbard from ocean bottom seismometer data the ongoing warming of bottom water in the arctic region is anticipated to destabilize some of the gas hydrate present in shallow seafloor sediment potentially causing the release of methane from dissociating hydrate into the ocean and the atmosphere ocean bottom seismometer obs experiments were conducted along the continental margin of western svalbard to quantify the amount of methane present as hydrate or gas beneath the seabed p and s wave velocities were modeled for five sites along the continental margin using ray trace forward modeling two southern sites were located in the vicinity of a 30 km long zone where methane gas bubbles escaping from the seafloor were observed during the cruise the three remaining sites were located along an e w orientated line in the north of the margin at the deepest northern site vp anomalies indicate the presence of hydrate in the sediment immediately overlying a zone containing free gas up to 100 m thick the acoustic impedance contrast between the two zones forms a bottom simulating reflector bsr at approximately 195 m below the seabed the two other sites within the gas hydrate stability zone ghsz do not show the clear presence of a bsr or of gas hydrate however anomalously low vp indicating the presence of free gas was modeled for both sites the hydrate content was estimated from vp and vs using effective medium theory at the deepest northern site modeling suggests a pore space hydrate concentration of 7 12 if hydrate forms as part of a connected framework and about 22 if it is pore filling at the two other northern sites located between the deepest site and the landward limit of the ghsz we suggest that hydrate is present in the sediment as inclusions hydrate may be present in small quantities at these two sites 4 5 of the pore space the variation in lithology for the three sites indicated by high resolution seismic profiles may control the distribution concentration and formation of hydrate and free gas

provinciality of ice rafting in the north atlantic application of 40ar 39ar dating of individual ice rafted hornblende grains the history of the northern hemisphere ice sheets is an important aspect of the paleoclimate system the layered record of ice rafted detritus ird and other climate indicators preserved in deep sea sediment cores provides the potential to unravel the sequences of events surrounding important intervals during the last glacial cycle the work presented here is a first step in the goal to characterize the composition of glacially derived detritus in proximal locations near the laurentide greenland and scandinavian ice sheets the intent of this paper is to highlight the potential for using provenance studies of ird in marine sediments in particular 40 ar 39 ar ages of hornblende grains in this case to trace the history of ice sheets in the past published work on land and at the glacial marine margins has mapped the margins of important ice sheets including the locations where glacial ice extended to the shelf slope break at these shelf slope break locations large glacial marine fans termed trough mouth fans tmf are known to occur in about 25 locations around the north atlantic nordic arctic oceans by characterizing the sediment sources in these tmfs the major ird components for deposition in deep sea sediment cores are documented although there is substantial overlapin the geological histories of the continental sources around the north atlantic there are also some systematic variations that will allow distinction of different sources realization of the full potential awaits characterizing the sources with multiple tracers as well as sedimentological studies and documenting the geographic pattern of dispersal in marine sediments within small time windows r 2002 published by elsevier science ltd

relationship between continental rise development and palaeo ice sheet dynamics northern antarctic peninsula pacific margin abstract acquisition of swath bathymetry data west of the north antarctic peninsula nap between 63 s and 66 s and its integration with the predicted seafloor topography of smith and sandwell global seafloor topography from satellite altimetry and ship depth soundings science 277 1956 1962 reveal the links between the continental rise depositional systems and the nap palaeo ice sheet dynamics the nap pacific margin consists of a wide continental shelf dissected by several troughs tens of kilometres wide and long the biscoe trough which has been almost entirely surveyed with multibeam sonar shows spectacular fan shaped streamlining sea floor morphologies revealing the presence of ice streams during the last glacial maximum in the study area the continental rise comprises the six northernmost sediment mounds of the nap pacific margin and the canyon channel systems between them these giant sediment mounds have developed since the early neogene by southwest flowing bottom currents which have redistributed along the margin the fine grained component of the turbiditic currents flowing down canyon channel systems the widespread evidence of shallow slope instability within the sediment mounds has been identified from both swath bathymetry and topographic parametric sonar seismic reflection profiles bathymetric data show that the heads of all the rise canyon channel systems coincide geographically with the mouths of the major glacial troughs on the continental shelf edge this suggests a close genetic link between these morphological features and allows considering a glacio sedimentary model for the western nap outer margin seascape development this model considers the availability of depositional space on the continental rise as the limiting factor for mound development the depositional space in turn is controlled by the spacing between glacial maxima shelf edge reaching ice streams this model takes into account both glacial and interglacial scenarios and gives new insights on evaluating the palaeoenvironmental record of the continental rise sediment mounds

controls on the formation and stability of gas hydrate related bottom simulating reflectors bsrs a case study from the west svalbard continental slope 1 the growth and stability of the free gas zone fgz beneath gas hydrate related bottom simulating seismic reflectors bsrs is investigated using analytical and numerical analyses to understand the factors controlling the formation and depletion of free gas for a model based on the continental slope west of svalbard a continental margin of north atlantic type we find that the fgz is inherently unstable under a wide range of conditions because upward flow of under saturated liquid depletes free gas faster than it is produced by hydrate recycling in these scenarios the 150 m thick fgz that presently exists there would deplete within 105 106 years we suggest the fgz is in a stable state however that is formed by a diffusion dominated mechanism that produces low concentrations of gas in a fgz of steady state thickness gas forms across a thick zone because the upward fluid flux is relatively low and because the gas water solubility decreases to a minimum several hundred meters below the seabed this newly understood solubility curvature effect is complementary to hydrate recycling but becomes the most important factor controlling the presence and properties of the bsr in environments where the rate of upward fluid flow and the rate of hydrate recycling are both relatively low i e rifted continental margins if the present day fgz is in steady state we estimate that the upward fluid flux in the west svalbard site must be less than 0 15 mm a 1

late cenozoic evolution of high gradient trough mouth fans and canyons on the glaciated continental margin offshore troms northern norway paleoclimatic implications and sediment yield trough mouth fans contain information about the evolution of high latitude continental margins including rates of glacial sedimentation and hinterland erosion here the late cenozoic evolution of high gradient trough mouth fans and canyons on the troms margin northern norway is reconstructed paleocanyons were active prior to the quaternary glaciations glaciomarine and glaciofluvial conditions prevailed between ca 2 7 ma and ca 1 5 ma and ice sheets possibly reached the paleo shelf break at least once the minimum average sedimentation rate of this period was 0 22 m k y from ca 1 5 ma to ca 0 7 ma the glaciations intensified and fast flowing ice streams reaching the shelf break were established in the cross shelf troughs subglacial deformation till was deposited at the outer shelf and later reworked by debris flows and turbidity currents the fennoscandian ice sheet started to route much of its ice mass to the north and south of the study area and so the troms margin possibly was a low ice flow sector from this time with a minimum average sedimentation rate of 0 15 m k y during the last ca 0 7 m y ice streams continued to traverse the troughs while sluggish flowing ice prevailed on the banks a minimum average sedimentation rate of 0 14 m k y is estimated for this period the minimum total erosion and erosion rate for the quaternary are 50 140 m and 0 02 0 05 m k y respectively compared with previous studies from other areas this implies up to one order of magnitude variation in average glacial erosion rates along the western sector of the fennoscandian barents sea ice sheets this is interpreted to be due to the size and bedrock composition of the catchment areas and the timing of ice growth and ice sheet dynamics in addition the steep preglacial continental slope promoted high sediment flow velocity for the glacigenic sediments causing much of the debris flows to transform into turbidity currents which efficiently transported sediments across the slope and thereby maintained its steep gradient

late quaternary palaeoenvironment and chronology in the traenadjupet slide area offshore norway the northern mid norwegian continental slope was studied based on high resolution side scan sonar data multibeam bathymetry high resolution and multichannel seismics together with gravity cores sedimentary provinces identified include a partly buried slide on the eastern inner voring plateau an area dominated by glacigenic debris flows south west of the traenadjupet slide the traenadjupet slide and an area of glacimarine sedimentation and a slide scar north east of the traenadjupet slide the traenadjupet slide affected an area of about 14100 km2 and mobilised about 900 km3 of sediments little is known about the areal extent and volume of the older events the glacigenic debris flows and glacimarine sediments were deposited while the fennoscandian ice sheet was at the shelf break during the late weichselian glacial maximum prior to 13 2 14c kyr bp hemipelagic and or contouritic sedimentation prevailed during the holocene period two large slide scars were probably formed sometime prior to or during the late weichselian glacial maximum inner voring plateau and north east of the traenadjupet slide and another during the mid holocene interglacial period immediately prior to 4000 14c kyr bp the traenadjupet slide the two older scars may represent one event or two separate events deposition of poorly permeable glacigenic sediments over high water content fine grained hemipelagic and or contourites may have prevented water escape and increased failure potential thus continental slope areas of episodically high sediment input of glacigenic sediments are prone to failure as illustrated by this study which has identified at least two large slope failures failures have occurred both during glacial maxima periods of climate deterioration and low global eustatic sea level and during interglacials as today with improved climatic conditions and a high global eustatic sea level

hydrate occurrence in europe a review of available evidence abstract large national programs in the united states and several asian countries have defined and characterised their marine methane hydrate occurrences in some detail but european hydrate occurrence has received less attention the european union funded project marine gas hydrate an indigenous resource of natural gas for europe migrate aimed to determine the european potential inventory of exploitable gas hydrate to assess current technologies for their production and to evaluate the associated risks we present a synthesis of results from a migrate working group that focused on the definition and assessment of hydrate in europe our review includes the western and eastern margins of greenland the barents sea and onshore and offshore svalbard the atlantic margin of europe extending south to the northwestern margin of morocco the mediterranean sea the sea of marmara and the western and southern margins of the black sea we have not attempted to cover the high arctic the russian ukrainian and georgian sectors of the black sea or overseas territories of european nations following a formalised process we defined a range of indicators of hydrate presence based on geophysical geochemical and geological data our study was framed by the constraint of the hydrate stability field in european seas direct hydrate indicators included sampling of hydrate the presence of bottom simulating reflectors in seismic reflection profiles gas seepage into the ocean and chlorinity anomalies in sediment cores indirect indicators included geophysical survey evidence for seismic velocity and or resistivity anomalies seismic reflectivity anomalies or subsurface gas escape structures various seabed features associated with gas escape and the presence of an underlying conventional petroleum system we used these indicators to develop a database of hydrate occurrence across europe we identified a series of regions where there is substantial evidence for hydrate occurrence some areas offshore greenland offshore west svalbard the barents sea the mid norwegian margin the gulf of cadiz parts of the eastern mediterranean the sea of marmara and the black sea and regions where the evidence is more tenuous other areas offshore greenland and of the eastern mediterranean onshore svalbard offshore ireland and offshore northwest iberia we provide an overview of the evidence for hydrate occurrence in each of these regions we conclude that around europe areas with strong evidence for the presence of hydrate commonly coincide with conventional thermogenic hydrocarbon provinces

ice sheets viewed from the ocean the contribution of marine science to understanding modern and past ice sheets over the last two decades marine science aided by technological advances in sediment coring geophysical imaging and remotely operated submersibles has played a major role in the investigation o

granular flow simulation in a centrifugal acceleration field the use of the geotechnical centrifuge to obtain scaled physical models is a useful tool in geomechanics when dealing with granular flows however the traditional scaling principles are challenge

ice stream retreat dynamics inferred from an assemblage of landforms in the northern barents sea abstract palaeo records of rapid ice stream retreat are important as they can be used to identify the processes involved and inform investigations of present day ice masses here we document a previously unknown retreat stage in northernmost bjornoyrenna bear island trough in the northern barents sea representing the youngest stage in a stepwise retreat of the bjornoyrenna ice stream we present a descriptive landsystem model for retreat of a marine based ice stream which provides new insights into the glacial dynamics of the episodic retreat stages this model captures the landforms produced during a cycle of 1 fast ice stream flow 2 intense calving of large icebergs locked in a dense matrix of smaller icebergs probably from a collapsed ice shelf 3 ice stream stagnation 4 ice stream floating off forming an ice shelf as the grounding line retreats and eventually 5 ice shelf disintegration we hypothesize that the presented ice stream retreat model reflects glacial surging the formation of corrugated furrows in the study area is consistent with interpretation of similar features in pine island bay west antarctica which are interpreted to have been formed during a massive ice shelf break up and associated grounding line retreat two directions of past ice flow are indicated from streamlined glacial landforms in the study area ice flow from north north east is indicated for the last glacial maximum and an early phase of deglaciation whereas a shift to flow from north north west from an ice dome located over hinlopenstretet svalbard is indicated for the latest deglaciation phases of the bjornoyrenna ice stream

late weichselian iceberg surface melt and sediment production from the eurasian ice sheet results from numerical ice sheet modelling abstract results from a numerical ice sheet model were matched with geological evidence detailing the extent and timing of the late weichselian ice sheet in the eurasian arctic through simple adjustments in the model s environmental inputs the numerical model predicts the spatial and temporal variation in 1 subglacial sediment transport and deposition 2 rates of iceberg calving and 3 rates of supraglacial melting over the past 30 000 yr the ice sheet is characterised by a series of ice streams occupying bathymetric troughs in the barents sea and west of norway which act as sources for glacial sediment build up and iceberg production our model indicates that significant volumes of sediment are deposited over the bear island fan 3000 km 3 in 12 000 yr franz victoria trough fan 500 km 3 in 8000 yr and a series of smaller fans west of norway which combine to yield 4000 km 3 in 12 000 yr the norwegian channel ice stream operated for only 4000 yr during which time 400 km 3 of sediments were deposited on the adjacent fan the ice sheet experienced two major periods of iceberg production where the rate of calving increased by 50 at about 15 000 and 12 500 yr ago however the time dependent response of iceberg calving to sea level rise for individual ice streams is shown to be more complicated than the generalised ice sheet response the marine portions of the ice sheet decayed after 15 000 yr ago resulting in several embayments at the mouths of bathymetric troughs a second pulse of enhanced iceberg calving at 12 500 yr ago caused further decay of the marine ice sheet and the ice margin retreated back to the shorelines of island archipelagos in the northern barents sea ice loss through surface melting was restricted mostly to the southern margin of the ice sheet

asynchronous deposition of ice rafted layers in the nordic seas and north atlantic ocean instabilities in ice stream flow within the north american laurentide ice sheet leading to the periodic release of armadas of icebergs into the north atlantic ocean over the past 60 000 years have produced extensive layers of coarse grained iceberg rafted debris heinrich layers in north atlantic sediments1 2 correlation of these layers with iceberg discharge events from the ice sheets on greenland iceland and scandinavia suggested in previous studies for some heinrich layers and in some areas3 4 5 would imply that ice sheet instability had been synchronous across the north atlantic presumably in response to a common environmental cause here we show a lack of widespread systematic correlations both between ice rafted debris layers in different sediment cores from the nordic seas and between the nordic layers and the north atlantic heinrich layers this suggests that the full glacial nordic ice sheets did not exhibit unstable behaviour coincident with iceberg discharge from the vast hudson bay drainage basin of the laurentide ice sheet6 7 off the hudson strait significant ice sheet discharge of melt water is indicated by size sorted sandy and muddy turbidite sediments different from the poorly sorted debris flows which dominate sedimentation on the margins of the nordic seas8 9 10 together these results suggest that the dynamics of quaternary ice sheets surrounding the nordic seas were different from the outlet glacier draining the hudson bay basin and they provide evidence against a common circum north atlantic mechanism driving the discharge of icebergs

glacio seismotectonics ice sheets crustal deformation and seismicity abstract the last decade has witnessed a significant growth in our understanding of the past and continuing effects of ice sheets and glaciers on contemporary crustal deformation and seismicity this growth has been driven largely by the emergence of postglacial rebound models pgm constrained by new field observations that incorporate increasingly realistic rheological mechanical and glacial parameters in this paper we highlight some of these recent field based investigations and new pgms and examine their implications for understanding crustal deformation and seismicity during glaciation and following deglaciation the emerging glacial rebound models outlined in the paper support the view that both tectonic stresses and glacial rebound stresses are needed to explain the distribution and style of contemporary earthquake activity in former glaciated shields of eastern canada and fennoscandia however many of these models neglect important parameters such as topography lateral variations in lithospheric strength and tectonic strain built up during glaciation in glaciated mountainous terrains glacial erosion may directly modulate tectonic deformation by resetting the orogenic topography and thereby providing an additional compensatory uplift mechanism such effects are likely to be important both in tectonically active orogens and in the mountainous regions of glaciated shields in general the short term response to ice fluctuations is similar to the earth s response to fluctuations in water reservoirs with the subsequent increase or decrease in seismicity which depends on the pre existing stress state when the ice fluctuations occur on the spatial scale and magnitude of the late pleistocene glaciation and deglaciation however the viscoelastic response of the earth especially the mantle causes significant changes in crustal deformation and earthquake activity that is spatially extensive and temporally complex the regions of greatest ice thickness and the regions marginal to the late pleistocene ice sheets indicate the most dramatic evidence of earthquake faulting the mantle response to these large ice mass fluctuations and the change in mass between the oceans and land caused and continues to cause measureable crustal deformation at hundreds of kilometres from the ice margins for both tectonically active and cratonic regions palaeoseismic investigations of late pleistocene and holocene faults are an important tool in evaluating earthquake hazard the predicted response of the earth over this time however is very dependent on the model assumed for most regions far more carefully designed field observations are needed to constrain the existing rheological and ice models

shock waves dead zones and particle free regions in rapid granular free surface flows shock waves dead zones and particle free regions form when a thin surface avalanche of granular material flows around an obstacle or over a change in the bed topography understanding and modelling these flows is of considerable practical interest for industrial processes as well as for the design of defences to protect buildings structures and people from snow avalanches debris flows and rockfalls these flow phenomena also yield useful constitutive information that can be used to improve existing avalanche models in this paper a simple hydraulic theory first suggested in the russian literature is generalized to model quasi two dimensional flows around obstacles exact and numerical solutions are then compared with laboratory experiments these indicate that the theory is adequate to quantitatively describe the formation of normal shocks oblique shocks dead zones and granular vacua such features are generated by the flow around a pyramidal obstacle which is typical of some of the defensive structures in use today

the seismic architecture and geometry of grounding zone wedges formed at the marine margins of past ice sheets grounding zone wedges form where halts of decades to centuries during ice sheet retreat across polar shelves allow sediment buildup at the grounding zone through delivery of deforming basal debris from fast flowing ice streams thirty grounding zone wedges were identified on two dimensional seismic reflection profiles across the continental shelves of ne and nw greenland grounding zone wedges close to the seafloor are probably of late weichselian age others are on paleoshelves buried beneath thick prograding glacial sediments several greenland shelf grounding zone wedges occur on topographic highs that provide stabilizing pinning points in relatively shallow water grounding zone wedges are asymmetric in the ice flow direction with steeper ice distal sides typical grounding zone wedges are approximately 5 20 km long and 50 100 m thick with a lateral width of several tens of kilometers forty grounding zone wedges from the greenland norwegian and antarctica margins show considerable variability about these values grounding zone wedge dimensions are controlled by sediment flux the duration of halts in ice retreat subice cavity shape and ice stream width low angle ice shelf cavity roofs immediately beyond the grounding zone probably restrict vertical accommodation space preventing formation of high amplitude ridges grounding zone wedges are mainly transparent or chaotic on seismic profiles probably resulting from delivery of diamictic debris offlapping reflectors represent progradation into an ice roofed cavity reflector truncations of grounding zone wedge bases indicate erosion during initiation channels are present within some grounding zone wedges meltwater flow is under high pressure and v shaped incisions suggest high energy flow channels are not ubiquitous within greenland grounding zone wedges and may represent nonsteady meltwater release perhaps through lake drainage where ice sheet mass loss is dominated by meltwater runoff grounding zone wedges probably contain more sorted sediment than those from greenland simple models of grounding zone wedge architecture are presented grounding zone wedges indicate episodic rather than catastrophic ice sheet retreat and are a mechanism for ice shelf stabilization because wedge growth counteracts collapse induced by ice sheet thinning and sea level rise

antarctic palaeo ice streams we review the geomorphological sedimentological and chronological evidence for palaeo ice streams on the continental shelf of antarctica and use this information to investigate basal conditions and processes and to identify factors controlling grounding line retreat a comprehensive circum antarctic inventory of known palaeo ice streams their basal characteristics and minimum ages for their retreat following the last glacial maximum lgm is also provided antarctic palaeo ice streams are identified by a set of diagnostic landforms that nonetheless display considerable spatial variability due to the influence of substrate flow velocity and subglacial processes during the lgm palaeo ice streams extended via bathymetric troughs to the shelf edge of the antarctic peninsula and west antarctica and typically to the mid outer shelf of east antarctica the retreat history of the antarctic ice sheet since the lgm is characterised by considerable asynchroneity with individual ice streams exhibiting different retreat histories this variability allows antarctic palaeo ice streams to be classified into discrete retreat styles and the controls on grounding line retreat to be investigated such analysis highlights the important impact of internal factors on ice stream dynamics such as bed characteristics and slope and drainage basin size whilst grounding line retreat may be triggered and to some extent paced by external atmospheric and oceanic forcing the individual characteristics of each ice stream will modulate the precise timing and rate of retreat through time

submarine slope stability on high latitude glaciated svalbard barents sea margin abstract slope stability is evaluated at two locations on high latitude deep sea fans along the svalbard barents sea margin based on available samples and using an infinite slope analysis the stability evaluation uses the mohr coulomb failure criterion and a semi analytical approach based on gibson s formulation for determining the excess pore pressure build up due to sedimentation the main results are presented in the form of contour plots of slope safety factors in a diagram with axes of time and thickness of deposit the results show that during rapid sedimentation which mostly takes place during periods of maximum glaciation with the ice front located along the shelf edge slope failure will occur with a frequency varying between 95 and 170 years only part of the upper sedimented layer will be mobilised 10 30 m while the remaining thickness 40 70 m will remain at the initial sedimentation site these results may explain why the continental slope is characterised by relatively uniform sediment thickness from upper to lower slope

modelling the influence of glacial isostasy on late weichselian ice sheet growth in the barents sea a fully integrated ice sheet and glacio isostatic numerical model was run in order to investigate the crustal response to ice loading during the late weichselian glaciation of the barents sea the model was used to examine the hypothesis that relative reductions in water depth caused by glacio isostatic uplift may have aided ice growth from scandinavia and high arctic island archipelagos into the barents sea during the last glacial two experiments were designed in which the bedrock response to ice loading was examined i complete and rapid glaciation of the barents sea when iceberg calving is curtailed except at the continental margin and ii staged growth of ice in which ice sheets are allowed to ground at different water depths model results predict that glacially generated isostatic uplift caused by an isostatic forebulge from loads on scandinavia svalbard and other island archipelagos affected the central barents sea during the early phase of glaciation isostatic uplift combined with global sea level fall is predicted to have reduced sea level in parts of the central barents sea by up to 200 m this reduction would have been sufficient to raise the sea floor of the central bank into a subaerial position such sea floor emergence is conducive to the initiation of grounded ice growth in the central barents sea the model indicates that prior to its glaciation the depth of the central deep would have been reduced from around 400 m to 200 m such uplift aided the migration of grounded ice from the central barents sea and scandinavia into the central deep we conclude that ice loading over scandinavia and arctic island archipelagos during the first stages of the late weichselian may have caused uplift within the central barents sea and aided the growth of ice across the entire barents shelf copyright 2000 john wiley sons ltd

contour current driven continental slope situated sandwaves with effects from secondary current processes on the barents sea margin offshore norway abstract seabed data acquired from the southern barents sea continental margin offshore norway reveal detailed morphology of large sandwave fields multibeam echosounder bathymetry and backscatter shallow seismic sediment samples and seabed video data collected by the mareano program have been used to describe and interpret the morphology distribution and transport of the sandwaves the bedforms lie on a slope dominated by relict glacial forms and muddy sandy gravelly sediments sandwave migration across small gravity mass failures of the glacial mud constrains the field initiation as early post glacial or later the contour parallel nature of the fields and crestlines normal to the bathymetry contours and the geostrophic norwegian atlantic current nwac demonstrate that the nnw flowing oceanographic circulation is the primary driving current the fields coincide with the depth range at which a transition between warm saline and underlying cooler less saline waters fluctuate across the seabed statistically rigorous measurements of height width and various parameters of slope and symmetry confirm a tendency to downstream nnw sandwave migration but with significant exceptions anomalous bedform symmetry domains within the fields are tuned to meso scale topography along relict glacial debris flow chutes indicating current focusing upstream and upper slope derived winnowed sand transport eroded from the glacial sediments is the supposed source sandwave flank slope values are comparable to the regional slope such that the gravitational vector would have a cumulative downslope migration affect unless balanced by upslope drivers perpendicular cross cutting of stoss face 3 d ripples by linear 2 d ripples in the sandwave troughs and lee faces is evidence for non synchronous episodic current variations though deep ekman transport and internal wave action are unproven here these could explain chute related tuning of bedform symmetry through funneling in the debris flow chutes and favor sand recycling thus contributing to long term maintenance of the sandwave field

geometry and genesis of glacigenic debris flows on the north sea fan tobi imagery and deep tow boomer evidence abstract acoustic data have been used to study the upper sequence of glacigenic debris flows gdfs deposited during the last glacial maximum on the north sea fan the presumed gdf release area at the shelf break 450 m water depth exhibits a sequence up to 90 m thick thinning to less than 45 m basinward at approx 750 800 m depth on a low slope 0 6 0 8 a seismically featureless sequence at the shelf break changes distinctly the first kilometers basinward showing a significant occurrence of features interpreted as infilled transport chutes the straight or sinuous chutes feed into well defined relief building gdf lobes 10 40 km from the shelf break a lack of failure scarps at the shelf break suggests that the gdfs have been sourced by a relatively continuous release of material flow lines concentrated along the chutes and center of the gdfs suggest a laminar movement pattern in the gdf core supported by passive flanks based on the flow morphology high pore pressure and low sediment strength within a central core of the flow is assumed to have contributed to the mobility of the gdfs dissipation of pore pressure along the margins of the flow may have caused the margins freeze while the sediment in the core remained mobile

north atlantic ocean deep water processes and depositional environments a study of the cenozoic norway basin abstract despite the enormous areas deep water basins occupy in modern oceans our knowledge about them remains poor at depths of greater than 2000 m the cenozoic norway basin in the northernmost part of the atlantic ocean is one such basin interpretation of 2d multichannel seismic data suggests a three stage evolution for the norway basin 1 eocene pliocene this time period is characterised by deposition of ooze rich sediments in a widening and deepening basin 2 early middle pleistocene a significant shift in sedimentary processes and depositional environments took place in the early pleistocene mass failures initiated on the norwegian continental slope and three early and middle pleistocene slide debrites with maximum thicknesses of 600 m and sediment volumes of up to 25 10 3 km 3 were deposited with ages estimated at c 2 7 1 7 ma 1 7 1 1 ma and 0 5 ma these slide deposits are among the largest identified worldwide and among the oldest mapped along the entire ne atlantic continental margin 3 late pleistocene present since c 0 5 ma the norway basin has been effected by glacigenic debris flows the storegga slide and hemipelagic glacimarine sedimentation these sedimentary processes were active during a time of repeated shelf edge ice advances along the ne atlantic continental margin this study shows that deep water basins represent dynamic depositional environments reflecting regional tectonic and climatic changes trough time

a neoproterozoic ice advance sequence sperry wash california the kingston peak formation is an archetypal cryogenian succession that crops out across the death valley region of eastern california above pre glacial strata kp1 two distinct glacial phases have been recognized and are interpreted to be allied to the panglacial sturtian kp2 and kp3 and marinoan kp4 icehouse events the thickest and most extensive unit kp3 forms the entire exposed section at sperry wash at this locality ice distal turbidites are succeeded in turn by ice medial and ice proximal facies comprising a spectrum of ice rafted debris bearing turbidites debrites and shales these are overlain by ice marginal grounding line fan deposits interbedded with glacitectonically deformed heterolithics supporting local advance to an ice contact position the succession records accumulation within a glacier fed subaqueous shelf wherein the clear progradational signature is driven by ice advance towards the south east evolution of the subaqueous complex is five fold comprising i ice distal outwash ii build out of ice medial depositional lobes iii ice proximal deposition and increased calving iv resumed ice margin advance and v growth of ice contact grounding line fan this sequence is unique in the death valley region for recording the first evidence of advance to ice marginal and ice contact settings thereby enabling the location of the glacier terminus to be documented for the first time

scaling and design of landslide and debris flow experiments abstract scaling plays a crucial role in designing experiments aimed at understanding the behavior of landslides debris flows and other geomorphic phenomena involving grain fluid mixtures scaling can be addressed by using dimensional analysis or more rigorously by normalizing differential equations that describe the evolving dynamics of the system both of these approaches show that relative to full scale natural events miniaturized landslides and debris flows exhibit disproportionately large effects of viscous shear resistance and cohesion as well as disproportionately small effects of excess pore fluid pressure that is generated by debris dilation or contraction this behavioral divergence grows in proportion to h3 where h is the thickness of a moving mass therefore to maximize geomorphological relevance experiments with wet landslides and debris flows must be conducted at the largest feasible scales another important consideration is that unlike stream flows landslides and debris flows accelerate from statically balanced initial states thus no characteristic macroscopic velocity exists to guide experiment scaling and design on the other hand macroscopic gravity driven motion of landslides and debris flows evolves over a characteristic time scale l g 1 2 where g is the magnitude of gravitational acceleration and l is the characteristic length of the moving mass grain scale stress generation within the mass occurs on a shorter time scale h gl 1 2 which is inversely proportional to the depth averaged material shear rate a separation of these two time scales exists if the criterion h l

the timing of initiation of fast flowing ice streams during a glacial cycle inferred from glacimarine sedimentation fast flowing ice streams drain huge basins within modern ice sheets and are a mechanism for rapid iceberg production and mass loss some ice streams are known to be unstable and to switch between fast flow and stagnation numerical ice sheet models and geophysical observations of large scale streamlined glacial landforms and large glacier derived sedimentary fans along high latitude continental margins indicate the presence of ice streams in quaternary ice sheets high resolution ams dated sedimentary records from an inter fan area on the svalbard continental margin yield evidence on the timing of initiation of fast glacier flow during a glacial cycle of ice sheet growth and decay sedimentation rates and iceberg rafted debris influx show that debris delivery to the svalbard margin was relatively high during the period of late weichselian ice sheet growth from about 30 000 18 000 yr bp both parameters fell dramatically in inter fan areas when full glacial conditions with ice at the continental shelf edge were established at about 18 000 yr bp this shift is interpreted to mark the initiation of a fast flowing ice stream the convergence of flow from the surrounding ice sheet into this ice stream and the consequent slowing of ice flow and sediment delivery to the inter fan area beyond the ice stream margins this provides a constraint on the timing of icestream initiation during the cycle of ice sheet growth and decay 4 2002 elsevier science b v all rights reserved

the role of grounding line sediment supply in ice sheet advances and growth on continental shelves an example from the mid norwegian sector of the fennoscandian ice sheet during the saalian and weichselian abstract we discuss the consequence of sediment accumulation at the grounding line of glaciers advancing across continental shelves sediment transfer through a deformable till bed and deposition at the grounding line act to decrease the water depth and adds support to the termini both are mechanisms that act to lower the calving rate and hence reduce mass losses during an advance of a grounded glacier we use the geological record of the saalian and weichselian advances of the fennoscandian ice sheet across the mid norwegian continental shelf to elucidate the consequence of this process based on seismic investigations and published maps we infer that the development of a morainal bank fed and sustained through the advance s by means of a deformable bed was indeed important this allowed the ice sheet to advance across a wide seaward dipping shelf depositing thick diamicton in places of more than 200 m thick and a terminal morainal bank complex we relate the reasons for this depositional mode i e shelf and shelf edge accumulation rather than deposition of glacial debris flows on the continental slope to slow and fast glacier flow regimes

physical and numerical modelling of dry granular flows under coriolis conditions in this paper quantitative observations of dry granular flows subject to varying magnitude and direction of coriolis acceleration are presented in order to assess the robustness of the savage hutt

gas hydrates free gas distribution and fault pattern on the west svalbard continental margin summary a 3 d tomographic analysis of seismic velocity and attenuation fields is presented with the purpose to analyse the intimate relation of gas hydrates and free gas distribution with the fault pattern the 3 d four component seismic data have been acquired offshore western svalbard the analysis of the subbottom topography of the base of the stability field of gas hydrates indicated by the bottom simulating reflector and the thickness of the underlying free gas bearing zone suggest a fault induced compartmentalization of the gas reservoir the proposed fluid and gas circulation scheme assumes deep sourced warm fluids moving upwards mainly along high permeability faults and fractures below the gas hydrate stability zone faults change from being a pathway of fluid flow to being barriers to fluid flow in the hydrate stability zone consequently below the hydrate stability zone free gas is transferred from the permeable faults to non faulted but fault bounded sediments where it accumulates below the base of the hydrate stability zone producing a significantly thicker free gas layer the tomographic approach is therefore proposed as an effective procedure to provide detailed information on 3 d p and s wave velocity and attenuation distribution in marine sediments and specifically to examine the details of the distribution of the gas hydrates and of the free gas for which the dependence on the vp vs and qp is now fairly well known

pleistocene iceberg dynamics on the west svalbard margin evidence from bathymetric and sub bottom profiler data large icebergs leave evidence of their drift via ploughing of the seabed thereby providing a geological record of episodes of calving from thick ice sheets we interpret large scale curvilinear depressions on the western svalbard margin as ploughmarks produced by the keels of icebergs that grounded on the seafloor as they drifted through this area iceberg ploughmarks were identified at modern water depths between 300 m and 1000 m and in two distinct stratigraphic units combining data from sediment cores with seismic stratigraphy from sub bottom profiler data suggests that the ploughmarks developed in two phases 1 during marine isotope stage mis 6 and 2 during mis 2 indicating the presence of large drifting icebergs on the western svalbard margin during both the late saalian and late weichselian glaciations sediment core data along the western svalbard margin indicate a sharp increase in mass transported sediments dated at 23 7 0 2 ka consistent with the mis 2 age of the younger iceberg ploughed surface the ploughmarks are oriented in two main directions sw ne and s n s n oriented ploughmarks which shallow to the north indicate iceberg drift from the south with a sw ne component marking the zone of splitting of the west spitsbergen current wsc into the yermak slope current ysc and north spitsbergen current nsc large mis 6 and mis 2 icebergs most likely had an arctic ocean source we suggest that these icebergs probably left the arctic ocean southward through fram strait and circulated within the norwegian greenland sea before being transported northwards along the svalbard margin by the wsc an additional likely source of icebergs to the western svalbard margin during mis 2 was the ice sheet terminating in the western barents sea from which icebergs drifted northward

morphology sedimentary infill and depositional environments of the early quaternary north sea basin 56 62 n abstract the north sea basin has been subsiding during the quaternary and contains hundreds of metres of fill seismic surveys 170 000 km2 provide new evidence on early quaternary sedimentation from about 2 75 ma to around the brunhes matuyama boundary 0 78 ma we present an informal seismic stratigraphy for the early quaternary of the north sea and calculate sediment volumes for major units early quaternary sediment thickness is 1000 m in the northern basin and 700 m in the central basin total about 40 000 km3 northern north sea basin fill comprises several clinoform units prograding westward over 60 000 km2 architecture of the central basin also comprises clinoforms building from the southeast to the west an acoustically layered and mounded unit unit z was deposited remaining accommodation space was filled with fine grained sediments of two central basin units above these units an upper regional unconformity equivalent uru records a conformable surface with flat lying units that indicate stronger direct glacial influence than on the sediments below on the north sea plateau north of 59 n the upper regional unconformity uru is defined by a shift from westward to eastward dipping seismic reflectors recording a major change in sedimentation with the shetland platform becoming a significant source a model of early quaternary sediment delivery to the north sea shows sources from the scandinavian ice sheet and major european rivers clinoforms prograding west in the northern north sea basin representing glacigenic debris flows indicate an ice sheet on the western scandinavian margin in the central basin sediments are generally fine grained suggesting a distal fluvial or glacifluvial origin from european rivers ploughmarks also demonstrate that icebergs derived from an ice sheet to the north drifted into the central north sea basin by contrast sediments and glacial landforms above the uru provide evidence for the later presence of a grounded ice sheet

lateral shear moraines and lateral marginal moraines of palaeo ice streams abstract an understanding of the nature of sedimentation at ice stream lateral margins is important in reconstructing the dynamics of former ice sheets and modelling the mechanisms by which sediment is transported beneath contemporary ice streams theories of the formation of ice stream lateral moraines islms have hitherto been based on a relatively limited number of terrestrial and marine examples here an inventory of islms is compiled from available studies together with independent analysis of seismic reflection and bathymetric datasets the locations and dimensions of 70 islms alongside a synthesis of their key architectural and geomorphic characteristics are presented two different types of islms are identified type 1 islms are up to 3 5 km wide and 60 m thick they maintain a constant width thickness and cross sectional shape along their length type 1 islms are interpreted and referred to as ice stream lateral shear moraines that form subglacially in the shear zone between ice streams and slower flowing regions of an ice sheet in contrast type 2 islms are up to 50 km wide and 300 m thick they are only identified close to the shelf break in the marine environment type 2 islms exhibit an increase in width and thickness along their length and their distal slopes become steeper in a seaward direction they contain internal dipping reflections that indicate sediment progradation away from the former ice stream type 2 islms are interpreted and referred to as ice stream lateral marginal moraines that were formed at the lateral boundary between ice streams and seafloor terrain that was free of grounded ice we suggest that using bathymetric images and acoustic profiles it is possible to differentiate between ice stream lateral shear moraines and lateral marginal moraines in the geological record this distinction is important for understanding the mechanisms of sediment transfer beneath ice streams and for making inferences about the conditions that existed beyond the lateral ice stream margin at the time of lateral moraine formation slow moving ice beyond lateral shear moraines and ocean water rather than ice beyond lateral marginal moraines

neoproterozoic ice sheets and olistoliths multiple glacial cycles in the kingston peak formation california the kingston peak formation is a diamictite bearing succession that crops out in the death valley region california usa an exceptionally thick 1 5 km outcrop belt in its type area the kingston range provides clear insights into the dynamics of mid cryogenian sturtian ice sheets in laurentia seven detailed logs allow the lateral and vertical distribution of facies associations to be assessed we recognize 1 diamictite facies association ice proximal glacigenic debris flows 2 lonestone bearing facies association ice marginal hemipelagic deposits and low density gravity flows with iceberg rafting 3 pebble to boulder conglomerate facies association ice proximal cogenetic glacigenic debris flows and high density turbidites 4 megaclast facies association olistostrome and hemipelagic sediments subject to ice rafting and 5 interbedded heterolithics facies association low density turbidites and hemipelagic deposits the stratigraphic motif allows three glacial cycles to be inferred across the range ice minimum conditions interrupting the kingston peak succession are associated with the development of an olistostrome complex succeeded by a thick accumulation of boulder conglomerates deposited during ice readvance the data testify to a strong glacial influence on sedimentation within this ancient subaqueous succession and to highly dynamic ice sheet behaviour with clear glacial cycles during the sturtian glaciation

holocene sedimentary processes in the andoya canyon system north norway abstract the andoya canyon system is the most pronounced of the ten canyon systems identified on the norwegian continental margin none of these canyon systems is linked to any present active drainage area and are interpreted to have been basically non active since the last glacial maximum and the deglaciation period our knowledge on these canyon systems is however still limited as no high resolution stratigraphical or acoustic data sets are available from these areas the main target for analysing the long term history of the andoya canyon has been to study the distal accumulation part of this system in the lofoten basin the lofoten basin area is characterized by repeated stacks of extensive turbidite units where the details of the stratigraphical succession can be studied in undisturbed settings about 3000 km 2 of high resolution multibeam data em300 along with three gravity cores have been collected from the lofoten basin area the analyses carried out on the cores revealed that the predominant process results in single turbidite units interbedded with thin units of hemipelagic sedimentation the radiocarbon dating revealed that turbidites have been transported through this channel system at least twice during the holocene the two uppermost dated turbidite sequences give a maximum age of 7 9 ka 14 c bp for the lower sequence and an age of ca 4 0 ka 14 c bp for the upper sequence the upper sequence is of a similar age as the traenadjupet slide failure whereas the lower sequence indicates an age close to the storegga slide failure event taking into consideration the erosive lower boundary of that sequence the location of the investigated cores which are far away from both the traenadjupet slide and the storegga slide indicate that the instability in these canyon systems during the holocene period has most probably been influenced by these large scale failure events what triggered the release of these turbidites is still not understood but earthquakes or tsunami waves associated with the mega scale traenadjupet slide and the storegga slide events are considered to be the most likely mechanism at least during the holocene interglacial period

arctic ocean glacial history while there are numerous hypotheses concerning glacial interglacial environmental and climatic regime shifts in the arctic ocean a holistic view on the northern hemisphere s late quaternary ice sh

pleistocene development of the se nordic seas margin abstract throughout the pleistocene the sedimentary environment on the se nordic seas continental slope outer shelf off western norway has been strongly controlled by variability in the norwegian atlantic current nwac glaciations of the shelf areas and sea level changes acoustic and core data from the southern voring plateau show a pleistocene sequence characterised by hemipelagic sediments interfingered by diamictons on the upper slope the area of the 7 25 14 c ka bp storegga slide shows evidence of a long history of pleistocene mega slides during the last interglacial and most likely also during previous interglacials the slide region has been the locus of rapid deposition between water depths of 800 and 1200 m as a result of nwac winnowing along the upper slope the north sea fan region is strongly influenced by glacigenic debris flows gdfs deposited during glacial advances reaching the shelf edge when the norwegian channel was occupied by the norwegian channel ice stream it appears that gdf activity was initiated at ca marine isotope stage 12 interbedded between the debris flow sequences mega slide events such as the more and tampen slides have been identified during glaciations when the entire se nordic seas continental shelf was covered by extensive grounded ice sheets basal till were transported to the shelf edge from where subsequent mass movement occurred during late glaciation early deglaciation meltwater plumes were released at the time of disintegration of ice streams in the norwegian channel as is evidenced from the last deglaciation of the margin at ca 15 14 c ka bp the plume material was transported northwards by currents before rapidly deposited as a thick package within the storegga slide area and on the south voring plateau based on identification and dating of iceberg scourings glacial erosion surfaces and delta deposits on the shelf subsidence rates between 0 7 and 1 2 m ky have been calculated for the last ca 250 ka

late quaternary ice flow and sediment delivery through hinlopen trough northern svalbard margin submarine landforms and depositional fan abstract the morphology and distribution of submarine landforms in hinlopen trough northern svalbard margin and the upper continental slope beyond are investigated using swath bathymetric data together with side scan sonar acoustic profiler records and sediment cores sun illuminated images reveal a number of landform assemblages on the sea floor of hinlopen trough and confirm that this depression was occupied by an ice stream during the late weichselian glaciation around 20 ka before present the geomorphology of the inner shelf is characterised by bedrock drumlins and ice sculpted bedrock there is a middle shelf transition from a rock bed to an unconsolidated sedimentary bed that contains highly attenuated drumlins and megaflutes formed within a dark grey matrix supported diamict interpreted as subglacial till outer shelf landforms are mainly iceberg ploughmarks the geomorphological imprint identified from hinlopen trough is similar to that of many former ice streams the trough is dominated by elongate landforms orientated parallel to the inferred flow direction and is lacking in transverse features indicative of inter ice stream locations a characteristic down flow progression in landform elongation is also observed suggesting an increase in ice velocity across the continental shelf the lack of grounding zone features imaged from swath bathymetric data implies that deglaciation was probably rapid within the trough a large depositional fan exists on the upper continental slope beyond the trough characterised by debris flow deposits relating to the down slope transport of glacigenic sediment order of magnitude calculations of the volume of glacigenic sediment on the continental slope indicate that the ice stream provided high rates of debris delivery of around 5 7 5 m ka this suggests that hinlopen trough ice stream represented a major route for the transfer of ice and debris to the hinlopen fan on the northern continental margin of svalbard during the late weichselian glaciation

dry granular flow interaction with dual barrier systems multiple barriers are commonly installed along predicted geophysical flow paths to intercept large flow volumes the main criterion for multiple barrier design is volume retained the velocity of t

morphology and origin of smaller scale mass movements on the continental slope off northern norway abstract little attention has been paid to smaller scale mass movements on continental slopes even though they occur much more frequently than their large scale counterparts swath bathymetry side scan sonar sub bottom profiler and seismic data from the continental slope offshore the lofoten islands northern norway reveal evidence of repetitive smaller scale translational sliding involving spreading and multi phase retrogression in water depths between 1100 and 2500 m three styles of failure have been identified occurring in close proximity style 1 is characterized by a 4 7 km wide and up to 100 m deep amphitheater shaped headwall a relatively deep glide plane 130 mbsf detached sediment ridges and a run out area with rafted sediment blocks style 2 consists of a staircase pattern of secondary escarpments caused by the activation of several glide planes between 30 and 110 mbsf headwalls and secondary escarpments have a height of up to 30 and 70 m respectively the run out area shows an almost complete sediment evacuation style 3 is more subtle as it is only identified on the side scan sonar data due to its higher spatial resolution this style shows different phases of on going evolution illustrating the gradual disintegration of a slab of sediments moving over a shallow glide plane at 13 mbsf zones with sediment slabs are up to several hundreds of meters wide and are sharply delineated by shear margins or escarpments the spatial variation in the failure style is inferred to have been caused by the activation of different glide planes which is probably a result of the thinning of contouritic sediments towards the south west in the north east the mounded contouritic sediments contain more potential glide planes and higher slope angles the smaller scale mass movements are suggested to have been triggered by undercutting and removal of support at the foot of the slope due to large scale mass movements that have occurred immediately south of the study area such as the traenadjupet or nyk slides the geophysical data indicate that relatively recent mass movement processes have taken place in this area through the formation of shallow cracks and graben structures by the movement of 13 m thick slabs of sediments style 3 which could have severe implications for offshore infrastructure

glaciogenic debris flow deposits of orphan basin offshore eastern canada sedimentological and rheological properties origin and relationship to meltwater discharge abstract glaciogenic debris flow deposits gdfs have been recognized in the last decade seaward of many shelf crossing ice streams the rheology of gdfs remains poorly understood ultra high resolution sparker seismic profiles and 25 long piston cores were used to define the architecture age and sediment properties of the gdf deposits in trinity trough mouth fan tmf offshore northeast newfoundland and hence understand their origin and emplacement the gdf deposits comprise poorly sorted gravelly mud individual gdf lenses are 5 30 m thick 2 10 km wide and up to 250 km long shear strength measurements and grain size analysis indicate that gdfs have a different more fluid rheology at their margins and tops exhibiting a surging flow behavior on the upper slope the transition from hard over consolidated till to thin proximal gdf deposits is exposed in a mid holocene landslide scar the transition between the two lithotypes appears gradual and no pre holocene failure scarps were detected a process involving the continuous release of subglacial flowing material with high pore pressure and low shear strength is invoked for the production of gdfs five stacked gdf units a e were deposited during the last glacial maximum 20 5 28 cal ka and can be correlated into a regional lithostratigraphy based on the presence of heinrich beds and 8 local meltwater events r1 8 represented by red plumite deposits south of the trinity tmf this correlation indicates that the timing of major gdf pulses corresponds to the early part of five meltwater discharge events 20 5 21 23 23 5 23 8 24 5 25 27 and 27 5 28 5 cal ka so that gdf deposits represent only a small period of time during a major glacial advance three meltwater events 19 2 20 23 23 5 and 25 27 cal ka produced hyperpycnal flows that resulted in the formation of channel systems and distal sand turbidites the presence of such erosional features in tmfs on the continental margins of the norwegian greenland sea suggests that this novel relationship between gdfs and hyperpycnal turbidites may be widespread and thus important for understanding the glaciological processes involved

late glacial holocene clay minerals elucidating glacial history in the sw barents sea abstract detailed investigations of the distribution of clay minerals of late glacial holocene sediments from the sw barents sea provide important new information about the provenance and transport paths of the sediments this information leads to better understanding of the onset of the last deglaciation and subsequent advances retreats of the barents sea and fennoscandian ice sheets the results show interaction and changes in the fennoscandian ice sheet and bjornoyrenna ice stream during the last deglaciation high illite content and maximum kaolinite content 18 700 cal yr b p indicate glacial erosion from both the fennoscandian ice sheet and bjornoyrenna ice stream lgm ii the occurrence of a c reniforme dominated benthic foraminiferal assemblage 18 700 cal yr b p indicates that the northern most cores site in ingoydjupet had already been deglaciated and was probably situated in a glacier distal environment in addition smectite content reaching its highest level concurrent with the presence of neogloboquadrina pachyderma sin dominated planktic foraminifera can be related to the strengthening of the atlantic current the inflow of the atlantic water may have triggered deglaciation of the fennoscandian ice sheet bolling interstadial a rapid increase in illite content reflecting strong melting of the fennoscandian ice sheet 15 000 cal yr b p indicates the onset of deglaciation in a core closer to the continent decrease of illite and ird content together with the deposition of laminated sediments during the older dryas stadial 15 000 14 000 cal yr b p indicates colder conditions and formation of at least seasonal sea ice in addition increased kaolinite content indicates increased glacial erosion of the bjornoyrenna ice stream the highest values of illite content and increased ird content 14 000 13 000 cal yr b p can be related to strong melting of the fennoscandian ice sheet a slight indication of the younger dryas cold period is given by the decrease in illite and ird contents all clay contents are more stable during holocene compared to lgm and the last deglaciation

architecture and sedimentary processes on the mid norwegian continental slope a 2 7 myr record from extensive seismic evidence abstract quaternary architectural evolution and sedimentary processes on the mid norwegian continental slope are investigated using margin wide three and two dimensional seismic datasets of 100 000 km3 sediments delivered to the mid norwegian shelf and slope over the quaternary 75 000 km3 comprise the slope succession the structural high of the voring plateau characterised by initially low 1 2 slope gradients and reduced accommodation space exerted a strong control over the long term architectural evolution of the margin slope sediment fluxes were higher on the voring plateau area increasing up to 32 km3 ka 1 during the middle pleistocene when fast flowing ice streams advanced to the palaeo shelf edge resulted in a more rapid slope progradation on the voring plateau these rates of sediment delivery are high compared to the maximum of 7 km3 ka 1 in the adjacent sectors of the slope characterised by steeper slope 3 5 more available accommodation space and smaller or no palaeo ice streams on the adjacent shelves in addition to the broad scale architectural evolution identification of more than 300 buried slope landforms provides an unprecedented level of detailed process based palaeoenvironmental reconstruction channels dominate the early pleistocene record 2 7 0 8 ma during which glacimarine sedimentation on the slope was influenced by dense bottom water flow and turbidity currents morphologic signature of glacigenic debris flows appear within the middle late pleistocene 0 8 0 ma succession their abundance increases towards late pleistocene marking a decreasing role for channelized turbidity currents and dense water flows this broad scale palaeo environmental shift coincides with the intensification of northern hemispheric glaciations highlighting first order climate control on the sedimentary processes in high latitude continental slopes

ordovician proglacial sediments in algeria insights into the controls on hydrocarbon reservoirs in the in amenas field illizi basin abstract ordovician proglacial deposits form gas reservoirs in the in amenas field illizi basin algeria depositional models were developed to understand the context and disposition of the main reservoirs through an evaluation of core and analogous outcrops from the tassili n9ajjer tunnel valleys initially accumulated sandstones with tractional structures subsequent failures of subaqueous grounding line sediment deposited proglacial debrites comprising poorly sorted argillaceous sandstone with granules these were interbedded with high density turbidity sandstones their fine grain size indicates they were dynamically disconnected from the lithologically varied debrites a lobate geometry has been defined for one subsurface composite turbidite periodic catastrophic outflows possibly evacuating subglacial lakes incised the network of subglacial tunnels and in the process delivered sand to the turbidite outwashes bedforms indicate high energy transcritical to supercritical outflows that were stable for extended periods during ice retreat a period of ice margin stability may have occurred due to grounding over the in amenas granitic palaeohighs outwash fan apices were located along this grounding line with feeder channels developing where the substrate was more easily eroded such as between the palaeohighs following further ice retreat deposition evolved to variably sinuous channels and thence to pelagic fines with dropstones

aligned glaciotectonic rafts on the central barents sea seafloor revealing extensive glacitectonic erosion during the last deglaciation 1 erosion rates on glaciated continental shelves are remarkably high especially within ice stream troughs although glaciotectonic erosion may have considerably contributed to enhanced glacial erosion of these landscapes entrainment mechanisms of glaciotectonically emplaced megablocks and rafts remain little understood here we report a northeast southwest trending chain of over 1300 glacial rafts observed on the seafloor in bjornoyrenna a paleo ice stream trough with particularly high erosion rates the landform assemblage adjacent to the glacial rafts includes streamlined bedforms and crevasse squeeze ridges and may represent a lateral shear zone where a paleo ice stream met cold stagnant ice during the last deglaciation individual glacial rafts along the chain are up to 30 m high tend to be elongated with lengths and widths on the order of tens of meters and are oriented from northeast southwest to north south the north southern rearrangement of rafts may reflect a compressional strain regime along the ice stream margin