geomorphological evidence for jokulhlaups from kverkfjoll volcano iceland abstract jokulhlaups glacial outburst floods are known to have drained along the jokulsa a fjollum river in iceland during the holocene however little is known about their number age source and flow characteristics this paper provides detailed geomorphological evidence for jokulhlaups that have routed from the kverkfjoll ice margin and hence into the jokulsa a fjollum erosional evidence of jokulhlaups from kverkfjoll includes gorges cataracts spillways subaerial lava steps and valley wide scoured surfaces depositional evidence includes wash limits boulder bars cataract fill mounds terraces slackwater deposits and outwash fans some of these landforms have been documented previously in association with jokulhlaups however subaerial lava surfaces that have been scoured of the upper clinker gorges within pillow hyaloclastite ridges gorges between pillow hyaloclastite ridges and subaerial lava flows subaerial lava lobe steps cataract fill mounds and boulder run ups are previously undocumented in the literature these landforms may therefore be diagnostic of jokulhlaups within an active volcanic rifting landscape the nature and spatial distribution of these landforms and their stratigraphic association with other landforms suggest that there have been at least two jokulhlaups through kverkfjallarani the biskupsfell eruption occurred between these two jokulhlaups kverkfjallarani jokulhlaups were very strongly influenced by topography geology and interevent processes that together determined the quantity and nature of sediment availability such controls have resulted in jokulhlaups that were probably fluidal turbulent and supercritical over large areas of the anastomosing channel bed kverkfjallarani jokulhlaups would have had highly variable hydraulic properties both spatially and temporally the knowledge of flow characteristics that can be gained from jokulhlaup impacts has implications for recognising jokulhlaups in the rock record and for hazard analysis and mitigation within similar landscapes and upon other glaciated volcanoes

sedimentology paleoflow dynamics and flood history of jokulhlaup deposits paleohydrology of holocene sediment sequences in southern iceland sandur deposits abstract this paper examines the sedimentology of a series of deposits associated with catastrophic floods caused by subglacial volcanic eruptions in southern iceland a simple model is proposed for the interpretation of the sediments in terms of changes in flow characteristics of the fluid sediment mix a range of sediment types characteristic of these flood flows is identified the predominant one being thick massive homogeneous poorly structured black pumice fine gravels with 65 p rcent silt clay type e and single lithology boulder deposits type f these flood deposits alternate with or are channeled into more normal sandur deposits comprising heterogeneous poorly sorted clast supported imbricated rounded cobble and pebble gravels type g the dominant sediment sequences are interpreted as representing hyperconcentrated fluid sediment mixtures with dispersive stresses acting to create massive poorly sorted nongraded or inversely graded sediments the latter characterized by large surface boulders the vertical changes in sediment type reflect significant changes in flow conditions during transport and subsequent deposition with an initial massive flood surge followed by flow deceleration sediment freezing and dewatering producing a more fluid series of flows the more fluid phases were associated with extensive erosion and channelization cutting deep scour channels marked by residual streamlined hummocks boulder lags and fields of megaripples leading downstream to a washed sandur plain the paper examines some of the problems associated with the application of paleoflow models for determining former flow dynamics the models adopted suggest that most of the flows occurred as relatively mobile low viscosity flows with little internal resistance to shear while sediment concentrations are estimated to have reached about 50 percent by weight with maximum yield strengths between 2 9 103 and 4 2 105 dn cm 2 maximum viscosities ranged between only about 2 and 8 102 poises a range of paleovelocity models applied to the flood sediment indicates flow rates of between abo t 4 and 13 ms 1 with peak discharges reaching a maximum of 3 3 105 m3 s 1 dating of the deposits by 14c dating and tephrochronology indicates that at least 8 major sediment producing jokulhlaups occurred over a 4 000 year period between c 4500 yr bp and 1357 ad hence although relatively rare the effects of these floods still dominate the proglacial landscape probably producing 85 percent of the total thickness of proglacial sandur sediments

architecture and sedimentation of outwash fans in front of the mýrdalsjokull ice cap iceland in this study we introduce the architecture and style of sedimentation of two outwash fans in front of the myrdalsjokull ice cap central south iceland that broaden different types of ice marginal sedimentation at kotlujokull a southeastern outlet of the ice cap fan formation was monitored from the late 1970s to 2002 thus the style of sedimentation is well understood and the relationship to the depositional architecture easily established in front of slettjokull a northern lobate extension of the ice cap a fan from the 10th century ad is capped by neoglacial till sheets at both sites the fan surfaces were reconstructed in three dimensions ground penetrating radar gpr provided the thickness and internal structure of sediment bodies geological exposures and excavations were used for detailed sedimentological documentation of the outwash deposits in proximal to distal transects the outwash deposits at both kotlujokull and slettjokull are considered to be alluvial fans of the hochsander type i e supraglacially fed as they show all the architectural characteristics of alluvial fans with a semiconical shape a restricted radial length of ca 0 5 1 5 km a plano convex cross profile and a slope gradient ranging between 1 and 5 fan deposits are dominated by planar or low angle cross bedded sand facies interbedded with thin laminae of fine gravel occasionally draped by mud sedimentation occurs during upper flow regime sheetflows associated with antidune migration within an aggrading shallow braided stream network hochsanders are intimately linked to advancing or stationary glaciers with steep ice cored frontal slopes that favor supraglacial over subglacial drainage most important hochsander fans lack any proximal to distal transition in the grain size distribution sediment facies or facies associations because much classification of glacial outwash sediments is based on proximal to distal distinctions it is crucial to consider the depositional model for hochsanders this study also indicates a strong dependence between the altitudes of the buried fan surface and the present day terrain in the forefield of slettjokull illustrating that subsequent to fan formation subglacial landforms merely mask many of the pre existing morphological features less

jokulhlaup deposits in proglacial areas abstract this paper discusses the main causes and characteristics of jokulhlaup glacier burst floods and explores the extent to which they generate depositional landform and sediment assemblages that are distinct from those of normal braided river outwash type i outwash two main jokulhlaup outwash environments are identified type ii outwash produced by sudden drainage of ice dammed lakes and type iii associated with drainage during subglacial geothermal activity and distinguished by deposits resulting from high sediment concentrations and hyperconcentrated flows in fluid flows especially ones yielding type ii outwash the most common deposits are large scale expansion bars and locally eddy and pendant bars and mega ripples or dunes both forms normally composed of large scale gravel cobble cross bedding often capped by an imbricated boulder lag a type b2 lithofacies sequence the armour is absent only where runoff decreased too rapidly to allow surface winnowing other jokulhlaup facies include extensive boulder beds type c inverse normally graded cobble beds type ds ice proximal debris flow deposits and deformed bedding containing diamicton clasts types g and h and slack water sediments type a type iii outwash is dominated by massive homogeneous flood surge granules underlain by pre surge gravels and capped by post surge fluid bedforms reflecting deposition during both the rising and falling limbs of the flood hydrograph type e4 the paper demonstrates that jokulhlaups do generate distinctive assemblages of depositional landforms and sediments and concludes with a model of the dominant lithofacies sequences and associated landforms in proglacial environments subject to jokulhlaup drainage

a parameterization of the ice ocean drag coefficient 1 a parameterization of the ice ocean drag coefficient cw was developed through partitioning the oceanic drag force into three components 1 form drag on the floe edge 2 form drag on the ridge keel and 3 skin friction on the ice bottom through these quantities cw was expressed as a function of observable sea ice geometric parameters sensitivity studies were carried out to investigate the influence of varying sea ice conditions on cw the results revealed that cw increases first and then decreases with increasing ice concentration a similar to the observations of the air ice drag coefficient and which is mainly attributed to the nonmonotonic variation of the form drag on the floe edge with ice concentration moreover the form drag on the floe edge is always the dominant component having a proportion of more than 60 in sea ice with a large aspect ratio draft length 1 100 indicating the necessity of including this term in sea ice dynamic models particularly for the marginal ice zone miz the form drag on the ridge keel becomes dominant only when the ridging intensity is extremely high depth spacing 1 20 additionally a large value of cw cannot be caused only by the inclusion of form drag terms but also by large skin friction over rough ice bottoms finally for typical situations in the miz with moderate ridging intensity the parameterization will underestimate cw by approximately 30 for a rough ice bottom and by over 80 for a smooth ice bottom if no form drags are considered

ice growth and oceanic heat flux models and measurements heat fluxes at the ice ocean interface and ice thickness are investigated by comparing field data from the coordinated eastern arctic experiment cearex drift phase with model calculations the calculations are based on two types of models the first one is a one dimensional ice ocean model with high vertical resolution this model is based on the conservation equations for heat salt and momentum and uses turbulence models to achieve closure a discrete element approach is also introduced to explicitly parameterize the ice roughness the second model is a simple one dimensional bulk heat transfer model in this version the interfacial salinity is modelled on the basis of salt conservation at the ice ocean interface the bulk heat transfer model is then calibrated using the former model the two models predict ocean heat fluxes that are quite variable in time owing to short term variations in the ice drift both models calculate realistic ice thicknesses it is demonstrated that the observed time variation in ice thickness from eight different experimental sites with varying initial thicknesses and bottom topographies can be reproduced by applying bulk heat transfer coefficients in the range 2 8 1 10 4 horizontal variation of the thermal state within a single pack ice floe results in simultaneous freezing and melting over relatively small spatial scales when modeling or averaging ice data in space these aspects need to be considered

fluvial lacustrine interaction on skeiðararsandur iceland implications for sandur evolution abstract a complex assemblage of fluvial and lacustrine sediments is identified in a major section through proglacial sediments on skei ararsandur south iceland high magnitude low frequency events are identified in both the fluvial and lacustrine sediments however much of the sedimentary succession is composed of normal low magnitude high frequency sediments retreat of skei ararjokull following a surge event created a topographic basin occupied at various times by both fluvial and lacustrine depositional systems and also subjected to a high magnitude jokulhlaup previous studies have examined the processes and events occurring on skei ararjokull in isolation this paper improves the understanding of the way in which processes with varying magnitude and frequency regimes interact and contribute to the sedimentary record of proglacial environments

three dimensional architecture and hydrostratigraphy of cross cutting buried valleys using airborne electromagnetics glaciated central lowlands nebraska usa buried valleys are characteristic features of glaciated landscapes and their deposits host important aquifers worldwide understanding the stratigraphic architecture of these deposits is essential for protecting groundwater and interpreting sedimentary processes in subglacial and ice marginal environments the relationships between depositional architecture topography and hydrostratigraphy in dissected pre illinoian till sheets is poorly understood boreholes alone are inadequate to characterize the complex geology of buried valleys but airborne electromagnetic surveys have proven useful for this purpose a key question is whether the sedimentary architecture of buried valleys can be interpreted from airborne electromagnetic profiles this study employs airborne electromagnetic resistivity profiles to interpret the three dimensional sedimentary architecture of cross cutting buried valleys in a ca 400 km2 area along the western margin of laurentide glaciation in north america a progenitor bedrock valley is succeeded by at least five generations of tunnel valleys that become progressively younger northward tunnel valley infills are highly variable reflecting under filled and over filled conditions under filled tunnel valleys are expressed on the modern landscape and contain fine sediments that act as hydraulic barriers over filled tunnel valleys are not recognized in the modern landscape but where they are present they form hydraulic windows between deep aquifer units and the land surface the interpretation of tunnel valley genesis herein provides evidence of the relationships between depositional processes and glacial landforms in a dissected pre illinoian till sheet and contributes to the understanding of the complex physical hydrology of glacial aquifers in general this article is protected by copyright all rights reserved

turbulent stress at the ice ocean interface and bottom surface hydraulic roughness during the sheba drift 1 upper ocean turbulence and mean current data from the 1997 1998 surface heat budget of the arctic ocean sheba drift in the western arctic ocean were used to estimate turbulent shear stress at the ice ocean interface and hydraulic roughness of the ice undersurface techniques for determining interfacial stress from velocity covariance measurements in the ice ocean boundary layer iobl are complicated by buoyancy flux and the heterogeneity of the ice undersurface where protrusions corresponding to relatively small upper surface features become major obstacles when compared to the scale of the iobl in addition ice deformation forced relocation of the main sheba oceanographic program about midway through the experiment hence there were two different measurement sites to consider three different methods were used to compute the undersurface roughness characterizing the undeformed multiyear floe occupied by the sheba project the first was straightforward naive application of the law of the wall to turbulent stress and mean velocity measurements from the turbulence instrument cluster nearest to the interface assuming a logarithmic velocity profile and constant stress for the second method local turbulence closure was used to model the entire iobl in order to estimate the impact of coriolis stress attenuation and buoyancy forces on stress and shear near the boundary a third method proposed here for the first time estimated mixing length and eddy viscosity from a scale inversely proportional to the wave number at the peak of the weighted vertical velocity spectrum the last method appears most robust in that it shows no overall difference in z0 between the two sites and only minor seasonal and directional differences the best estimate for the undersurface roughness of undeformed multiyear ice at the sheba site is 0 0048 m z0 0 007 i e about 6 mm specification of a regional aggregate under ice roughness requires additional consideration of the added drag from isolated pressure keels and floe edges along with reduced drag from smoother newly frozen ice and open water

discovery of a recurrent lava lake on saunders island south sandwich islands using avhrr imagery abstract monitoring of the remote south sandwich islands volcanic arc using advanced very high resolution radiometer avhrr data has identified a radiant pixel on channels 3 3 55 3 93 m and rarely 4 10 3 11 3 m the position of the pixel is coincident with mount michael saunders island the active summit crater of a snow covered basaltic stratovolcano with a persistent steam plume the radiant pixel was continuously present in successive avhrr images acquired during intervals of several months in the period examined march 1995 february 1998 although apparently disappearing for similar time intervals more than 5000 images were examined during this study the radiant pixel is interpreted to indicate that the crater has contained a lava lake the first to be recorded in the south sandwich islands the lake appears to persist in the crater for several months at a time at least it may have drained completely at times and was probably absent when the crater was viewed briefly during an overflight in january 1997 persistent or recurring lava lakes are very uncommon world wide and that at mount michael is one of only two recorded in the antarctic region

present day sandurs are not representative of the geological record abstract present day sandurs are formed under conditions that are geologically exceptional consequently they show characteristics that differ from those formed under more common conditions we show this on the basis of polish examples formed during the last ice age a good understanding of sandur formation requires models that are not based on the present day situation

geomorphic effectiveness sandur development and the pattern of landscape response during jokulhlaups skeiðararsandur southeastern iceland by contrast with other historical outburst floods on skeitararsandur the 1996 jokulhlaup was unprecedented in its magnitude and duration attaining a peak discharge of f53 000 m 3 s in 17 h using a combination of field sampling and remote sensing techniques landsat tm sar interferometry airphotos and laser altimetry we document the sandur wide geomorphic impacts of this event these impacts varied widely across the skeitararsandur and cannot be singularly attributed to jokulhlaup magnitude because pre jokulhlaup glacial dynamics and the extant setting largely conditioned the spatial pattern type and magnitude of these impacts topographic lowering and asymmetric retreat of the ice front during the late twentieth century has decoupled the ice sheet from the moraine sandur complex along the central and western sandur this glacial control in combination with the convex topography of the proximal sandur promoted a shift from a primarily diffuse source braided outwash system to a more point sourced channelized discharge of water and sediment deposition dominated within the proglacial depression with approximately 3 8 10 7 m 3 of sediment and along channel systems that remained connected to subglacial sediment supplies this shift to a laterally dissimilar channelized routing system creates a more varied depositional pattern that is not explicitly controlled by the concave longitudinal profile down sandur laterally contiguous units therefore may vary greatly in age and sediment character suggesting that current facies models inadequately characterize sediment transfers when the ice front is decoupled from its sandur water was routed onto the sandur in a highly organized fashion and this jokulhlaup generated major geomorphic changes including sandur incision in normally aggradational distal settings and eradication of proximal glacial landforms dating to fa d 1892 d 2002 elsevier science b v all rights reserved

sedimentology and progressive tectonic unconformities of the sheetflood dominated hell s gate alluvial fan death valley california abstract the hell s gate alluvial fan of northern death valley has an area of 49 5 km2 a radius of 11 8 km and a smooth 5 3 sloping surface interrupted by shallow

modeling winter circulation under landfast ice the interaction of winds with landfast ice 1 idealized models and a simple vertically averaged vorticity equation illustrate the effects of an upwelling favorable wind and a spatially variable landfast ice cover on the circulation beneath landfast ice for the case of no along shore variations in ice upwelling favorable winds seaward of the ice edge result in vortex squashing beneath the landfast ice leading to 1 large decreases in coastal and ice edge sea levels 2 cross shore sea level slopes and weak 05 m s 1 under ice currents flowing upwind 3 strong downwind ice edge jets and 4 offshore transport in the under ice and bottom boundary layers of the landfast ice zone the upwind under ice current accelerates quickly within 2 4 days and then slows as cross shore transport gradually decreases the cross shore sea level slope near the ice edge bottom boundary layer convergence produces ice edge upwelling cross ice edge exchanges occur in the surface and above the bottom boundary layer and reduce the under ice shelf volume by 15 in 10 days under ice along shore pressure gradients established by along and cross shore variations in ice width and or under ice friction alter this basic circulation pattern for a landfast ice zone of finite width and length upwelling favorable winds blowing seaward of and transverse to the ice boundaries induce downwind flow beneath the ice and generate vorticity waves that propagate along shore in the kelvin wave direction our results imply that landfast ice dynamics not included explicitly herein can effectively convert the long wavelength forcing of the wind into shorter scale ocean motions beneath the landfast ice

estimation of erosion deposition and net volumetric change caused by the 1996 skeiðararsandur jokulhlaup iceland from synthetic aperture radar interferometry using repeat pass satellite synthetic aperture radar interferometry we develop a methodology to measure flood induced erosion and deposition and apply it to a record 1996 glacier outburst flood jokulhlaup on skei ararsandur iceland the procedures include 1 coregistration of backscatter intensity images to observe morphological differences 2 mapping of interferometric phase correlation to identify preserved and modified surfaces and 3 construction correction and differencing of pre jokulhlaup and post jokulhlaup topography procedures 1 and 2 are robust and should be widely applicable to other fluvial environments while procedure 3 is complicated by uncertainties in phase measurement baseline estimate and atmospheric effects after a correction procedure involving interpolation of digital elevation model elevation differences across low correlation areas we find 4 m of elevation change are required to calculate volumes of erosion or deposition this condition was satisfied for the 40 km2 proglacial zone of skei ararsandur where we estimate 38 106 m3 of net sediment deposition along the ice margin 2 106 m3 of net erosion in channels downstream and a total net balance of 13 106 these estimates are supported by field observations and survey data collected in 1997

development of minor outwash fans at kotlujokull iceland throughout the 1980s the development of minor outwash fans was studied at and beyond a northeastern section of the steep advancing ice front of kotlujokull the largest outlet glacier on the east side of the ice cap myrdalsjokull in central south iceland in contrast to the extensive outwash fans of gravelly and stony material deposited by high energy streams from underneath the glacier the minor fans consist of fine grained material mainly of sand size deposited by low energy streams draining the debris covered glacier surface the vertical alteration in texture of the minor fan deposits results from changing influx of sediments which in turn is coupled to varying activity in the processes working in the supraglacial sediment source area these processes are ablation sudden drainage of pockets of water influx of rainwater and resedimentation of debris by fall slide and flow along with the glacier advance during the 1980s slabs of fan sediments were incorporated in the push moraine ridge being formed the subsequent glacier retreat during the 1990s has largely curtailed the production of minor outwash fans it is concluded that this type of outwash fan is likely to be produced along advancing or stationary glaciers where the frontal slope is steep and covered by debris similar minor outwash fans termed hochsander fans have been identified beyond ice marginal moraine ridges bounding dead ice morainic terrain in pleistocene landscapes

sedimentary architecture of large scale jokulhlaup generated ice block obstacle marks examples from skeiðararsandur se iceland during glacial outburst floods jokulhlaups large ice blocks are often released from the glacier margin ice blocks ground at points of flow deceleration generating distinctive patterns of scour and deposition scaled to the obstacle size the large scale ice block obstacle marks produced within the proglacial zone are diagnostic of jokulhlaups we use ground penetrating radar gpr to investigate the sedimentary architecture of ice block obstacle marks generated by the november 1996 jokulhlaup at skei ararjokull iceland the gpr data reveal a varied sedimentary architecture interpreted to suggest that ice block obstacle mark sedimentology is controlled by flow conditions sediment supply and whether ice blocks are deposited in isolation or as a cluster following ice block grounding deflection of flow down and away from the obstacle develops horseshoe vortices that maintain a non depositional hollow around the obstacle whilst continued outwash deposition away from the obstacle raises the level of the surrounding sandur where ice blocks ground early during the jokulhlaup hollows are infilled with foreset beds at the up flow end and backset beds antidune distally however where ice blocks ground on the waning stage when sediment flux is reduced antidunes are not preserved and the hollow is infilled with low angle foreset beds in both cases the lee side shadow ridge is composed of pseudo anticlinal beds proximal to the obstacle where shed vortices are strong and plane beds distally where flows converge and the shed vortices weaken where flow parallel ice block clusters develop the grounding of smaller ice blocks in the lee of the initial obstacle results in only limited shadow ridge aggradation these data provide improved insight into the controls on ice block obstacle mark sedimentary architecture and allow identification of high magnitude jokulhlaups in the sedimentary record

unconfined alluvial flow processes recognition and interpretation of their deposits and the significance for palaeogeographic reconstruction abstract palaeogeographic interpretation of the sedimentary rock record depends on correct recognition from the preserved evidence of the processes responsible for transporting and depositing the sediment this in turn depends on robust knowledge transfer from previous workers and the successful exchange of ideas between workers requires consistent use of a well defined vocabulary we have identified serious breakdowns in all these interpretation steps in the case of terrestrial unconfined flow and its deposits and these failures are leading to unreliable environmental and climatic interpretation this is significant because such alluvial deposits commonly form a majority of the rock record of continental environments working from the basic principles of geomorphology and fluid dynamics we have undertaken a wide ranging analysis of the nature of out of channel flow and from this make predictions about the characteristics of its deposits we identify the range of possible locations and conditions that lead to the development of unconfined flow review the processes operating in each case and examine the range of lithological features that can be produced by these processes this allows us to evaluate the reliability of the criteria claimed for identification of out of channel flow deposits and examine how our new insights might alter palaeoclimatic and palaeogeographic reconstructions published previously by others the sedimentary record of unconfined flows is much more diverse and complex than usually portrayed the received wisdom that the record of unconfined flow consists solely of upwards fining thin beds produced from shallow waning flows is shown to be flawed a wide range of lithofacies are possible and the variation in both flow steadiness and uniformity needs to be taken into account the previously published criteria for recognition of flows of this type are not diagnostic of process or location unconfined flow deposits cannot reliably be identified from grain size or bed thickness similar lithofacies may develop in a wide range of geomorphic and climatic settings because the deposits solely reflect the local flow conditions and sediment availability we recommend that the terms sandflat and sheetflood should not be used in sedimentological accounts because there is no longer a safe informal usage for either contradictory application of these terms and lack of robust definitions is leading to significant misunderstanding of palaeogeography and process our analysis should improve reconstruction of past terrestrial environments because it reveals more clearly the true variety of possibilities for the occurrence of unconfined flow and the resultant deposits enhanced understanding of the inherent uncertainties and realisation of the wider range of plausible alternative explanations should help resolve apparent contradictions with independent indicators of climate or geographic position

architectural analysis of a volcaniclastic jokulhlaup deposit southern iceland sedimentary evidence for supercritical flow the 1918 eruption of the glacially capped katla volcano southern iceland generated a violent jokulhlaup or glacial outburst flood inundating a large area of m rdalssandur the proglacial outwash plain where it deposited ca 1 km3 of volcaniclastic sediment the character of the 1918 jokulhlaup is contentious having been variously categorized as a turbulent water flow a hyperconcentrated flow or as a debris flow based on localized outcrop analysis in this study outcrop based architectural analyses of the 1918 deposits reveal the presence of lenticular and tabular bedsets associated with deposition from quasi stationary antidunes and down current migrating antidunes and from regular based bedsets associated with transient chute and pool bedforms all of which are associated with turbulent transcritical to supercritical water flow conditions antidune wavelengths range from 24 to 96 m corresponding to flow velocities of 6 to 12 m sec 1 and average flow depths of 5 to 19 m this range of calculated flow velocities is in good agreement with estimates made from eyewitness accounts architectural analysis of the 1918 jokulhlaup deposits has led to an improved estimation of flow parameters and flow hydraulics associated with the 1918 jokulhlaup that could not have been achieved through localized outcrop analysis the observations presented here provide additional sedimentological and architectural criteria for the recognition of deposits associated with transcritical and supercritical water flow conditions the physical scale of sedimentary architectures associated with the migration of bedforms is largely dependent on the magnitude of the formative flow events or processes sedimentary analyses must therefore be undertaken at the appropriate physical scale if reliable interpretations regarding modes of deposition and formative flow hydraulics are to be made

interpreting flash flood palaeoflow parameters from antidunes and gravel lenses an example from montserrat west indies the wavelength of stationary water surface waves and their associated antidune bedforms are related to the mean velocity and depth of formative flow in sand bed flume experiments alexander et al 2001 found that lens structures were preserved during antidune growth and change and the dimension of the lenses were empirically related to antidune wavelength and thus could be used to estimate flow velocity and depth this study is the first to compare observations of formative flow conditions and resulting sedimentary structures in a natural setting testing the alexander et al 2001 relationship at a field scale trains of stationary and upstream migrating water surface waves were prevalent during the flash flood in october 2012 in the belham valley montserrat west indies wave positions and wavelengths were assessed at 900 s intervals through the daylight hours of the event within a monitored reach the wave data indicate flow depths up to 1 3 m and velocity up to 3 6 m s 1 sedimentary structures formed by antidune growth and change were preserved in the event deposit these structures include lenses of clast supported gravel and massive sand with varying internal architecture the lenses and associated low angle strata are comparable to sand bed structures formed from stationary and upstream migrating waves in flume experiments confirming the diagnostic value of these structures using mean lens length in the event deposit underestimated peak flow conditions during the flood and implied that the lenses were preserved during waning flow

geomorphic impact and rapid subsequent recovery from the 1996 skeiðararsandur jokulhlaup iceland measured with multi year airborne lidar the november 1996 jokulhlaup that burst from the vatnajokull ice cap onto skei ararsandur was the highest magnitude flood ever measured on the largest active glacial outwash plain sandur centimeter scale elevation transects measured from repeat pass airborne laser altimetry missions flown in 1996 pre flood 1997 and 2001 show that sediment deposition exceeded erosion across the central skei ararsandur and established an average net elevation gain of 22 cm for the event net elevation gains of 29 and 24 cm occurred in braided channels of the go gjukvo sl and skei ararivers respectively nearly half of these gains however were removed within 4 years and the two rivers contrast strongly in style of erosional depositional impact and subsequent recovery in the go gjukvo sl the 1996 jokulhlaup caused massive sediment deposition up to 12 m near the ice margin and intense bmega formingq of braided channels and bars downstream post jokulhlaup recovery 1997 2001 was characterized by rapid erosion 0 5 m of ice proximal sediments and their transport to downstream reaches and eradication of the mega forms in contrast the skei ara displays minimal post jokulhlaup sediment erosion in its upstream reaches and little change in braided channel relief this contrast between river systems is attributed to the presence of a previously studied 2 km wide ice marginal trench caused by glacier retreat and lowering which contained flows of the go gjukvo sl but not the skei araprior to dispersal onto the outwash plain rapid removal of jokulhlaup deposits from this trench suggests that in terms of long term evolution of the sandur such features only delay downstream migration of jokulhlaup derived sediment these results therefore suggest that the net geomorphic impact of jokulhlaups on surface relief of skei ararsandur while profound in the short term may be eradicated within years to decades d 2005 elsevier b v all rights reserved

genesis of the glacial curvilineation landscape by meltwater processes under the former scandinavian ice sheet poland abstract dobrzyn plateau in central poland contains a suite of enigmatic glacial bedforms termed glacial curvilineations gcl these landforms occur within tunnel valleys forming a complex anabranched network gcl consist of a series of parallel ridges extending for as much as 5 km over their length gcl ridges are parallel to neighboring ridges and to tunnel valley margins internal gcl composition consists of sand gravel and till distributed randomly within ridges and in intervening troughs electric resistivity tomography surveys confirm the sediment distribution seen in field exposures truncated beds near the ridge forms and the heterogeneous nature and distribution of sediments suggest an erosional rather than accretionary origin for gcl in this case internal gcl composition is not related to gcl genesis it records proglacial and subglacial conditions prior to gcl shaping by erosion the terminal zone of the anabranched tunnel valley network is characterized by a broad apron like ice marginal sedimentary complex sand and gravel dominate sedimentary facies within this zone sediments record evidence of meltwater sedimentation associated with supraglacial melting near the ice margin and high energy subglacial outbursts emanating from tunnel valleys this interpretation suggests that the gcl surface is a regional unconformity representing an erosional landscape where sediments within landforms offer limited insights into landform genesis cf sharpe et al 2004 subglacial meltwater erosion is proposed as unifying model of landscape development as it accounts for both erosion of tunnel valleys and gcl and meltwater dominated sedimentation in the ice marginal sedimentary complex

water stress and ocean current measurements under first year sea ice in the canadian arctic ocean current profiles were measured to calculate the ice water drag coefficent for tidal currents under landfast ice at the intersection of lancaster sound and navy board inlet in the canadian arctic under ice current profiles showed 1 3 m of a logarithmic layer with a friction velocity ranging from 0 3 to 1 0 cm s no significant ekman veering was found below the logarithmic layer which suggests a strong modulation of the surface current by tidal currents the ice water drag coefficients at 1 m depth calculated from the mean current profiles ranged from 0 0053 to 0 0093 reflecting a nonhomogeneous rough surface and ridges it was shown that the present estimate of the drag coefficient was consistent with previously measured values of the ice stress

freshwater megaflood sedimentation what can we learn about generic processes abstract there is growing recognition that sedimentary deposits related to high energy large scale freshwater floods are widespread across the continents and in the main can be related to quaternary outbreak flows from ice dammed lakes such deposits may also occur in the neogene and earlier recognition of these megaflood deposits is hindered by the lack of well conditioned stratigraphic models of depositional successions however descriptions of successions from many locations often exhibit commonalities when compared carefully thus the primary purpose of this paper is to examine and condense the published stratigraphic and sedimentological evidence so as to identify the key signatures of megaflood successions the deposits often are the only record of a flood and so the secondary purpose is to interpret the sedimentary sequences in order to recreate the behaviour of floods through single and multiple events finally some pointers are provided as to those areas of sedimentological research that might be profitably explored in more depth to improve understanding of megaflood dynamics a key characteristic of megaflood deposits is the apparent massive appearance of single units which on closer inspection usually are amalgamated layers of similar grain size distribution individual beds and sets of beds are commonly near horizontal planar and laterally extensive successions evidently are not channelized and extensivity is indicative of simultaneous and coherent deposition over large areas localised large scale clinoforms or smaller scale cross beds are common associated with bar front or dune progradation respectively but otherwise extensivity implies that cross cutting erosional contacts notably steeply inclined examples and small scale scours are not common except immediately around large isolated clasts such as dropstones and ice blocks a common vertical stack of sequences in any one succession consists of 1 basal thick coarse parallel bedded units 2 large scale clinoforms 3 horizontally bedded thin laminated units 4 ripple and dune cross beds 5 silt beds and 6 succession capping debris flow deposits in some cases such a succession usually is indicative of a single cycle of waxing and waning flood flow generally dominated by high concentration suspension deposition onto plane beds the high power allows the transport of fine gravel and coarse sand in suspension leading upon deposition to relatively coarse beds from suspension fall out clay and silt is generally sparse or absent being transported further down the system at the scale of the hydrograph the successions indicate that flows initially accelerate and then decelerate with significant shorter period flow pulses also evident in the sedimentary signatures in parallel bedded sequences primarily during waxing flows bedload transport often was ineffective in sorting sediment due to the high rates of deposition from the highly sediment charged waters resulting in diffuse accretion surfaces at each location similar sequence stacks are common leading to the impression of rhythmic deposition from pulsing flow including from repetitive series of floods although often composed of coarse grains many sequence stacks excluding any debris flows are not dissimilar to turbidity flow sequences the bouma sequence in particular although there is limited experimental evidence for turbidity currents associated with high energy freshwater flows theory does not preclude the deposition of similar sedimentary motifs from high concentration flows such that an analogy between some megaflood sedimentary beds and turbidites is not unreasonable despite considerable variation in megaflood sedimentary successions commonalities occur which are indicative of similar processes of deposition from high energy floods at geographically different locations the changes in style of deposition throughout a succession provide clues as to the nature of the flood flows and this information could be used to improve estimates of flood hydrograph behaviour however hypotheses linking deposit characteristics to flow dynamics are currently ill conditioned and often poorly tested the majority of published studies describe the coarser scale stratigraphy with only passing reference to the fine scale structure of individual beds closer attention to lamination styles particle orientation and syn depositional deformation structures for example should provide information on the flow mechanics at the time of bed deposition thus better consideration of the sedimentology of megaflood deposit beds will lead to better understanding of the controlling hydraulics and should result in better models of flood deposition

sea ice melting in the marginal ice zone the heat and salt flux boundary conditions together with the freezing curve relationship are a necessary component of any ice sea water thermodynamic model a neutral two layer oceanic planetary boundary layer model that incorporates these boundary conditions gives the following results the interfacial salinity is within 10 of the far field salinity for conditions commonly encountered in the miz and depends only on the turbulent lewis number and the far field temperature and salinity the predicted melt rates agree with the limited field observations of the order of 1 m day 1 the obukov lengths determined from the predicted interface conditions and melt rates are generally much greater than the ekman layer thicknesses hence the surface buoyancy flux has little effect on the turbulence in the planetary boundary layer

a review of glacier outburst floods in iceland and greenland with a megafloods perspective the very largest glacier outburst floods have been termed megafloods given their volume and peak discharge that definition might be revised because those floods have become understood due to their distinctive and pervasive landscape impacts at least three floods in iceland can be categorized as megafloods since they produced impressive bedrock canyons and giant fluvially transported boulders glacier lake outburst floods glofs in greenland might also have megaflood type attributes given the enormous lake volumes drained we therefore here present the first review of glacier outburst floods in greenland sites isvand russell glacier kuannersuit glacier lake tininnilik two unnamed lakes near amitsulooq ice cap and iluliallup tasersua base camp lake lake hullett qorlortorssup tasia imaersartoq tordenso north midternaes and an outlet glacier of the a p olsen ice cap overall megaflood type landscape impacts in iceland tend to be best preserved and most easily identified inland although there has also been extensive offshore sedimentation there are very few reported impacts of glacier outburst floods in greenland in greenland ice dam failure causes frequent flooding compared to the volcanically triggered floods in iceland and this combined with the proximity of the greenland glacier lakes to the coast means that most proglacial channels in greenland are flood hardened and most landscape impact is likely to be offshore in estuaries and fjords future floods with megaflood type attributes will occur in iceland induced by volcanic activity in greenland they will be induced by extreme weather and rapid ice melt any potential landscape impact of these future floods remains open to question

path averaged measurements of turbulence beneath ice in the arctic two way acoustic propagation measurements obtained along 200 m horizontal paths a few meters below ice in the eastern arctic are used to estimate energy dissipation rate and momentum transfer between the ice and the ocean forward scattered sound propagating through the turbulent fluid of the boundary layer under ice produces characteristic scintillation patterns at the receivers which are interpreted in terms of the refractive index fine structure of the flow reciprocal travel time measurements yield information about the velocity variability along each acoustic path by combining these two types of measurements the contributions of sound speed and water particle velocity fluctuations to forward acoustic scatter can be separated for the particular case of the under ice boundary layer sound speed variability is negligible therefore under the assumptions of a kolmogorov inertial subrange and taylor s frozen field hypothesis the one way and the reciprocal acoustical measurements provide two independent estimates of turbulent kinetic energy dissipation rate averaged over the propagation paths both these methods yield a value of 8 10 8 w kg 1 6 m from the bottom of the ice for a 7 hour period during which the mean ice relative velocity is 0 11 m s 1 surface layer approximations then yield a value of 0 03 n m 2 for turbulent stress near the surface the acoustical measurements also indicate that circulation around ice keels can cause horizontal lift forces of order 104 n

glaciovolcanic hydrothermal environments in iceland and implications for their detection on mars abstract volcanism has been a dominant process on mars along with a pervasive global cryosphere therefore the interaction between these two is considered likely terrestrial glaciovolcanism produces distinctive lithologies and alteration terrains as well as hydrothermal environments that can be inhabited by microorganisms here we provide a framework for identifying evidence of such glaciovolcanic environments during future mars exploration and provide a descriptive reference for active hydrothermal environments to be utilised for future astrobiological studies remote sensing data were combined with field observations and sample analysis that included x ray diffraction raman spectroscopy thin section petrography scanning electron microscopy electron dispersive spectrometer analysis and dissolved water chemistry to characterise samples from two areas of basaltic glaciovolcanism askja and kverkfjoll volcanoes in iceland the glaciovolcanic terrain between these volcanoes is characterised by subglacially erupted fissure swarm ridges which have since been modified by multiple glacial outburst floods active hydrothermal environments at kverkfjoll include hot springs anoxic pools glacial meltwater lakes and sulphur and iron depositing fumaroles all situated within ice bound geothermal fields temperatures range from 0 c 94 4 c and aqueous environments are acidic neutral ph 2 7 5 and sulphate dominated mineralogy of sediments mineral crusts and secondary deposits within basalts suggest two types of hydrothermal alteration a low temperature 120 c assemblage signified by zeolite heulandite and quartz these mineral assemblages are consistent with those identified at the martian surface in situ and laboratory vnir 440 1000 nm reflectance spectra representative of mars rover multispectral imaging show sediment spectral profiles to be influenced by fe2 3 bearing minerals regardless of their dominant bulk mineralogy characterising these terrestrial glaciovolcanic deposits can help identify similar processes on mars as well as identifying palaeoenvironments that may once have supported and preserved life

channel pattern of proglacial rivers topographic forcing due to glacier retreat this is the peer reviewed version of the following article marren p m toomath s c 2014 channel pattern of proglacial rivers topographic forcing due to glacier retreat earth surface processes and landforms 39 7 943 951 doi 10 1002 esp 3545 which has been published in final form at http onlinelibrary wiley com doi 10 1002 esp 3545 abstract this article may be used for non commercial purposes in accordance with wiley terms and conditions for self archiving

sedimentology and flow behavior of a rain triggered lahar mangatoetoenui stream ruapehu volcano new zealand on october 28 1995 heavy rain triggered failure of approximately 3 3 10 5 m 3 of fall deposits on the mangatoetoenui glacier and generated a lahar event that flowed east northeast of ruapehu volcano down the mangatoetoenui stream and eventually entered the tongariro river 19 km downstream the lahar left multiple stacked deposits of at least three major flow surges or pulses which traveled down slope at calculated velocities of as much as 27 m s 1 and calculated maximum peak discharges of as much as 2900 m 3 s 1 the source area of the mangatoetoenui lahar is delineated by a thin furrowed lag of unsorted ash and lapilli margined by steep headwall scarps marking the edges of undisturbed fall deposits failure of fall deposits in the source area triggered debris flows down a north and south branch of the mangatoetoenui stream these two debris flows coalesced and ponded then flowed across seasonal snowpack covering the stream in the proximal zone to 5 km downstream of the source area the deposits of the individual constituent debris flows cannot be distinguished however in the medial zone between 5 and 16 km downstream of the source area and beyond the limit of the snowpack and the junction with perennial streamflow the depositional record of this lahar shows clear evidence for downstream transformation of individual peak flows from debris flow to hyperconcentrated flow transformation began at 5 km from source due to dilution 1 by each peak flow incorporating normal streamflow in the perennial mangatoetoenui stream and tributaries and 2 through deposition of part of each peak flow9s sediment load the hyperconcentrated flow deposits frequently may be subdivided into multiple units which is evidence that the lahar flowed as a series of surges or waves we consider that these were caused by episodic but contemporaneous inputs from a divergent flow from a single source area or by ponding and episodic release of debris within the channel estimated froude numbers for the mangatoetoenui lahar are greater than 3 implying supercritical flow and the development of fluid mechanical instabilities that enhanced these flow surges

glacier outburst floods and outwash plain development skeiaararsandur iceland outwash plains such as skeiaararsandur serve as prototypes for braided river facies and analogs for the mars pathfinder and viking 1 landing sites on the margins of the chryse basin glacier outburst floods jokulhlaups have generated some of the largest known terrestrial freshwater flows and recent studies suggest that the stratigraphy of outwash plains sandur is dominated by sedimentary sequences laid down during jokulhlaups rather than by braided river facies produced by an ablation related flow regime the modern point source drainage configuration on skeiaararsandur evolved from a diffuse multipoint distributary system during glacier retreat when meltwater began to be routed parallel to the ice front the contemporary pattern of water and sediment dispersal across skeiaararsandur differs from the conditions that prevailed when the ice front was coupled to the sandur and the november 5 6 1996 outburst flood from skeiaararjokull had little impact on the proximal surface of skeiaararsandur beyond the confines of the entrenched channels that traverse it thus the point source dispersal system on skeiaararsandur may not provide an exact analogue for the pattern of meltwater dispersal responsible for the sediment assemblage laid down during past jokulhlaups and caution may be required when comparing conditions on skeiaararsandur to those presumed to have been experienced during massive outburst floods elsewhere

dynamical evaluation of the surface circulation using remote sensing of drifting ice floes an analysis of ice drift from consecutive landsat multispectral scanner images of the same area taken at 24 h interval allowed the calculation of the surface circulation using a dynamical approach comparison between calculated and measured values shows that this method leads to a good approximation of the surface circulation in a region where ice floes are free drifting on the other hand the sole use of the floe drift over time to evaluate the currents leads to results that are far from the measured values tests made using various air and ice drag coefficients and wind speeds and directions for different drift distances show that the error associated with these parameters is small although the values obtained using the numerical data involved considerably more effort and expense the results were not significantly better than those found using photographic products a good approximation of the surface circulation can thus be made using a simple digitization of the floe positions on photographic products application of the methodology to a set of four image pairs led to the recognition of two modes of circulation in southeastern hudson bay in spring 1985 this method can thus become a useful tool for rapid evaluations of surface currents in ice covered areas that can hardly be sampled otherwise

reconstruction of the largest holocene jokulhlaup within jokulsa a fjollum ne iceland abstract glacial outburst floods jokulhlaups have a significant role for landscape evolution in ne iceland a number of jokulhlaups have routed from the northern margin of vatnajokull during the holocene in this study reconstruction of the largest holocene jokulhlaup along jokulsa a fjollum ne iceland was undertaken using the hec ras hydraulic modelling and hec georas flood mapping techniques with a digital elevation model dem derived from ers insar data and field based wash limit evidence the largest jokulhlaup produced extensive erosional and depositional landforms across an inundated area of 1390 km2 and is calculated to have had a peak discharge of 0 9 106 m3 s 1 power per unit area within this jokulhlaup varied from 6 to 46 000 w m 2 jokulhlaup hydraulics are related to geomorphogical evidence at three key sites in va alda upptyppingar and mo rudalur sub areas in order to explain the abrupt spatial variation of the flood characteristics on a regional scale and to relate erosional and depositional features to spatial variations in jokulhlaup hydraulics these process form relationships of the largest jokulhlaup along the jokulsa a fjollum are compared with large outburst floods elsewhere the largest jokulsa a fjollum jokulhlaup had a factor of 20 times smaller discharge and a factor of 20 times lower power per unit area than altai palaeoflood the largest known flood on the earth

icelandic jokulhlaup impacts implications for ice sheet hydrology sediment transfer and geomorphology abstract glaciers and ice sheets erode entrain and deposit massive quantities of debris fluxes of subglacial meltwater exert a fundamental control on ice dynamics and sediment transport budgets within many glacial systems outburst floods jokulhlaups constitute high magnitude high frequency fluxes of meltwater relative to normal ablation controlled discharge this paper presents a synthesis of research on recent icelandic jokulhlaups and their geomorphological and sedimentary impact we identify jokulhlaup impacts within subglacial englacial and proglacial settings and discuss their wider significance for ice sheet hydrology sediment transfer and geomorphology because jokulhlaups erode deposit and re work sediment simultaneously they usually cause significant glaciological and sedimentological impacts jokulhlaups that propagate as subglacial flood waves often produce widespread hydromechanical disruption at the glacier base recent icelandic jokulhlaups have been recognised as highly efficient agents of reworking subglacial sediment and glacial sediment entrainment models of jokulhlaup impact therefore need to encompass the sub and englacial environment in addition to the proglacial zone where research has traditionally been focussed most jokulhlaups transport sediment to proglacial sandar and often directly to oceans where preservation potential of the impact is greater proglacial jokulhlaup deposits form distinctive sedimentary assemblages coupled with suites of high energy erosional landforms this study of modern jokulhlaup processes and sedimentary products may be useful for the interpretation of meltwater processes associated with quaternary ice sheets

outburst flood sedimentation on the proglacial tuttle canyon alluvial fan owens valley california u s a abstract surface deposits of the tuttle canyon alluvial fan eastern sierra nevada piedmont california mainly accumulated during a catastrophic outburst flood probably triggered by the failure of a moraine dammed lake in the steep 16 4 high relief 2361 m and high elevation to 4275 m catchment moraines of the catchment and upper fan facies a comprise unsorted sand to blocks derived from the granitic bedrock the main flood facies b is texturally like the moraine consisting of unsorted matrix supported sandy pebbly cobbly blocky boulder gravel in a single unit 3 to 8 m thick distributed across most of the 10 5 km long and 28 1 km2 fan facies b was deposited during the initial outburst flood phase as a high volume noncohesive sediment gravity flow ncsgf instigated by water rapidly descending over moraine it differs from the moraine by a planar unit geometry and a slope transverse long axis alignment of boulders ncsgf deposition was followed by a water flood phase caused by continued lake drainage subsequent to removal of loose sediment in the flood path this discharge carved channels 2 22 m deep and 5 60 m wide around and across fan ncsgf deposits with channels departing from various points along tuttle creek horseshoe separation scours also formed around bedrock spurs and laminated pebbly sand accumulated on the channel beds facies d flood discharge expanded on the distal fan into a sheetflood that first deposited a boulder unit facies e and then 4 m of cobbly sandy pebble gravel in planar beds 5 20 cm thick facies f the final flood phase entailed incision of tuttle creek wherein bouldery cobble gravel facies c was concentrated post flood modification of these deposits has been limited to secondary processes such as eolian deposition facies g and bioturbation outburst floods on fans of the sierra nevada piedmont ultimately are caused by the glacial transfer of colluvium from the upper catchment slopes into moraines on the valley floors that dam drainage to form lakes outburst floods differ from meteorological floods in the valley by the high water and sediment discharge achieved during a single event by deposition of massive ncsgf beds and by causing major changes to the landscape such as the carving of channels these differences produce fans with distinctive facies and hazards the former allowing their recognition in either modern or ancient settings

sedimentology of a sandur formed by multiple jokulhlaups kverkfjoll iceland abstract the kverkfjoll sandur in north iceland is the furthest upstream of a suite of fluvial landforms extending for 200 km along the jokulsa a fjollum river incision of the sandur exposes over 3 km of sedimentary sections up to 15 m in height a sandur wide well bedded succession of matrix rich cobble gravel and pebble granule gravel with individual beds 0 2 to 0 5 m thick indicates that the sandur is primarily the product of sandur wide sheet floods with sediment rich hyperconcentrated flows and also some debris flows and channelised turbulent flows this interpretation is evidenced by bedded hyperconcentrated flow deposits occurring as laterally extensive tabular depositional units that dominate the entire sandur reflecting the unconfined nature of the flow clast supported boulder gravel units interpreted as the product of macroturbulent flow occur in relatively narrow but deep channels the sedimentary succession is interpreted as the product of at least six volcanically generated catastrophic outburst floods jokulhlaups during the little ice age the sedimentology of these little ice age flood deposits on a small high gradient sandur contrasts strongly with the deposits of volcanically generated jokulhlaups on large low gradient coastal sandar and sandar associated with retreating glaciers which have been the basis for most previous models of jokulhlaup sedimentation

drag measurements for first year sea ice over a shallow sea for a free drift case a method is developed for simultaneously determining air ca and water cw drag coefficients by solving the vertically integrated stress balance equation for sea ice the method allows the algebraic determination of ca and cw from measurements of relative wind and relative current at single reference levels from estimates of the densities of all three fluids and ice thickness and from estimates of the accelerations caused by the nonsurface stress terms derived from position measurements the method treats the ice as a natural drag plate and therefore includes contributions from both skin and form drag one shortcoming of the technique is that if the relative wind and current are colinear then only the ratio of ca and cw can be determined another is that the accelerations caused by other forces need to be independently determined an experiment was conducted on a single floe in the eastern bering sea over the continental shelf during march 1981 the site was about 80 km from the ice edge and was occupied for approximately 3 days following the passage of a storm which had broken the pack into 10 20 m diameter floes both profile and slab inversion estimates of drag were made from the current meter and anemometer measurements at the site ca at 3 m was 4 55 10 3 by the profile method compared to 3 63 4 39 10 3 for slab depending on assumptions cw at 1 1 m by profile was 24 2 10 3 compared to 18 3 22 0 10 3 for slab the two methods gave results which were not statistically separable and which were among the highest drags observed for sea ice the instantaneous stress balance on the floe included contributions from material acceleration coriolis force the two surface stresses and sea surface tilt relative to mean current and tide

the kverkfjoll fissure swarm and the eastern boundary of the northern volcanic rift zone iceland rift zones at the divergent plate boundary in iceland consist of central volcanoes with swarms of fractures and fissures extending away from them fissure swarms can display different characteristics in accordance with their locations within the 50 km wide rift zones to better discern the characteristics of fissure swarms we mapped tectonic fractures and volcanic fissures within the kverkfjoll volcanic system which is located in the easternmost part of the northern volcanic rift zone nvz to do this we used aerial photographs and satellite images we find that rifting structures such as tectonic fractures holocene volcanic fissures and hyaloclastite ridges are unevenly distributed in the easternmost part of the nvz the kverkfjoll fissure swarm extends 60 km north of the kverkfjoll central volcano holocene volcanic fissures are only found within 20 km from the volcano the fjallgar ar area extending north of the kverkfjoll fissure swarm is characterized by narrow hyaloclastite ridges indicating subglacial volcanism we suggest that the lack of fractures and holocene volcanic fissures there indicates decreasing activity towards the north in the easternmost part of the nvz due to increasing distance from the long term spreading axis we argue that arcuate hyaloclastite ridges at the eastern boundary of the northern volcanic rift zone are mainly formed during deglaciations when three conditions may occur firstly eruption rate increases due to decompression of the mantle secondly the high tensile stresses accumulated during glaciations due to lack of magma supply may be relieved as magma supply increases during deglaciations thirdly faulting may occur during unloading due to differential movements between the thinner and younger northern volcanic rift zone crust and the thicker and older crust to the east of it

catastrophic impact of extreme flood events on the morphology and evolution of the lower jokulsa a fjollum northeast iceland during the holocene abstract the impact of extreme flood events is rarely considered in studies of long term landscape evolution despite the potential for catastrophic landscape change in a short period of time here we use an integrated approach of geomorphological mapping topographic analysis and geophysical surveys to identify and quantify the impact of extreme flood events jokulhlaups along the jokulsa a fjollum iceland where evidence for the action of such floods is widespread on microspatial to macrospatial scales the apex of the 28 km long jokulsargljufur canyon is characterised by a complex network of palaeo flood channels and large vertical knickpoints such as dettifoss 54 m high and hafragilsfoss 20 m high downstream the forvo valley contains large terraces of boulder rich deposits 50 m thick 3 km long near the outlet of the canyon is asbyrgi a dry canyon 3 km long 1 km wide up to 90 m deep with eroded cataracts and scabland morphology immediately upstream and 90 m above the current river channel topographic analysis and electrical resistivity tomography surveys show that 0 144 km3 of rock was eroded from asbyrgi during its formation 10 000 years ago and just 4 of this eroded volume is currently filled with sediment deposits up to 5 m thick deposited boulders across the canyon floor of asbyrgi demonstrate that the discharge of the jokulhlaup that formed the canyon was at least 39 000 m3 s 1 we present a model for the evolution of the lower jokulsa a fjollum and the jokulsargljufur canyon during various stages of an extreme flood event reconstruction of the early holocene flood event includes the initiation and development of different canyons before the capture of all floodwater within one canyon at the end we tie the evolution of the lower jokulsargljufur canyon to established chronology of flood events during the holocene farther upstream and highlight the dominant impact of extreme flood events over background processes in this landscape

coarse grained nonmarine volcaniclastic sediment terminology and depositional process modern and ancient volcaniclastic sedimentary sequences contain depositional units whose features cannot be attributed to fully turbulent dilute stream flow or viscous debris flow the characteristics of these poorly sorted sediments suggest rapid deposition from high concentration dispersions but not en masse sedimentation thus appears related to high discharge flows intermediate in sediment water ratio between stream flow and debris flow the term hyperconcentrated flood flow is proposed for describing this intermediate condition hyperconcentrated flood flow deposits are distinguished from debris flow deposits by lack of matrix support or reverse grading and instead exhibit distribution normal grading and horizontal stratification these deposits are distinguished from normal dilute stream flow deposits by lack of cross stratification in sand facies and by very poor sorting poor imbrication and numerous clasts with long axes oriented parallel to flow direction in gravel facies the horizontal bedding that dominates sandy hyperconcentrated flood flow deposits consists of sediment too coarse grained and strata too thick to have been produced in the boundary layer of the upper flow regime and should not be confused with the more familiar thin graded laminae of fine to medium grained sand often associated with parting lineation hyperconcentrated flood flow deposits are not unique to volcanic settings they also occur in arid alluvial fan sequences debris flow and hyperconcentrated flood flow deposits however are much thicker and more extensive in volcanic regions than on alluvial fans because explosive volcanism leads to rapid mobilization of large volumes of sediment and water on a scale unparalleled in nonvolcanic settings in volcanic regions therefore these deposits have greater preservation potential show greater lateral variability and are more voluminous transformation of channelized debris flow to hyperconcentrated flood flow by dilution with stream water recently observed at mount st helens is recorded in ancient volcaniclastic sequences and may serve as the primary mechanism for generating hyperconcentrated flood flow

roughness of weddell sea ice and estimates of the air ice drag coefficient the roughness of a sheet of sea ice encodes its deformational history and determines its aerodynamic coupling with the overlying air and underlying water here we report snow surface ice surface and ice underside roughness computed from 47 surface elevation profiles collected during a transect of the weddell sea the roughness for each surface parameterized as the standard deviation of the surface elevation segregates according to whether or not a floe has been deformed deformed ice has greater roughness than undeformed ice regardless of deformational history the underside roughness is almost always greater than the snow surface and ice surface roughnesses which are nearly equal roughness spectra for all three surfaces and for both deformed and undeformed ice roll off roughly as k 1 when the wavenumber k is between 0 1 and 3 rad m 1 the snow surface and underside spectra roll off somewhat faster than k 1 and the ice surface spectra roll off somewhat slower than k 1 both top and underside arctic ice roughness spectra on the other hand have been reported to roll off faster than k 2 we speculate that the excess spectral intensity at high wavenumbers in the antarctic ice surface spectra results from the small scale roughness that the ice sheet had on consolidation this excess high wavenumber spectral intensity persists in the ice surface spectra of second year ice evidently once formed the ice surface remains unchanged on the microscale until the entire ice sheet melts with a remote measurement of roughness we should be able to decide whether an ice floe is deformed or undeformed our spectral analysis hints that remote sensing may also be able to differentiate between first year and second year ice from the snow surface spectra we compute a roughness scale that parameterizes the air ice momentum coupling and lets us estimate the neutral stability drag coefficient referenced to a height of 10 m cdn10 typical cdn10 values are 1 1 1 4 10 3 over undeformed ice and 1 3 1 8 10 3 over deformed ice

sedimentary processes vertical stratification sequences and geomorphology of the roaring river alluvial fan rocky mountain national park colorado abstract the roaring river alluvial fan formed on 15 july 1982 in rocky mountain national park colorado by a catastrophic flood that was generated by a dam failure the fan covers an area of 0 25 square km has a radial length of 0 7 km and is up to 14 m thick sedimentation occurred in three phases each producing a distinct fan lobe initial sedimentation was by a noncohesive sediment gravity flow which deposited two levees on the proximal boundaries of lobe i the levees consist of a poorly sorted mixture of logs sand pebbles cobbles and boulders the first two lobes were built primarily by sheetflooding which deposited imbricated boulders in trains behind obstacles that formed as jams between boulders or logs and upright trees horizontally laminated granule and sand sedimentation took place down fan from the boulders due to deceleration of the expanding sheetflood thin to medium interbedded sand and cobble pebble gravel couplets were deposited by sheetflooding on the third lobe gravel was transported as bedload by supercritical flow and deposited locally where antidunes broke sand was transported as suspended load and deposited where flood velocity locally decreased due to destruction of antidunes increased roughness or flow separation around the low amplitude gravel bed forms the flood rechannelized at the distal end of lobe iii due to constriction between the fan and the valley margin deposits in the upper rechannelized reaches consist of crudely bedded cobble and pebble gravel and interstratified pebble gravel and backset bedded sand deposition was by supercritical flow in the lower reaches planar cross bedded sandy pebble gravel and climbing ripple horizontal trough cross bedded and backset bedded sand were deposited by supercritical and subcritical flow the flood deposit was modified during waning flood stage and during the three years following the flood by noncatastrophic discharge events these events formed braided distributary channels by erosion into the top of the sheet flood deposits fan building took place mostly by catastrophic unconfined discharge whereas much of the present fan surface consists of braided channels that formed by erosion into the sheetflood deposits by noncatastrophic discharge

lateral and vertical facies relationships of bedforms deposited by aggrading supercritical flows from cyclic steps to humpback dunes abstract the preservation of bedforms related to supercritical flows and hydraulic jumps is commonly considered to be rare in the geologic record although these bedforms are known from a variety of depositional environments this field based study presents a detailed analysis of the sedimentary facies and stacking pattern of deposits of cyclic steps chutes and pools antidunes and humpback dunes from three dimensional outcrops the well exposed middle pleistocene successions from northern germany comprise glacilacustrine ice contact subaqueous fan and glacial lake outburst flood deposits the studied successions give new insights into the depositional architecture of bedforms related to supercritical flows and may serve as an analogue for other high energy depositional environments such as fluvial settings coarse grained deltas or turbidite systems deposits of cyclic steps occur within the glacial lake outburst flood succession and are characterised by lenticular scours infilled by gently to steeply dipping backsets cyclic steps formed due to acceleration and flow thinning when the glacial lake outburst flood spilled over a push moraine ridge these bedforms are commonly laterally and vertically truncated and alternate with deposits of chutes and pools and antidunes the subaqueous fan successions are dominated by laterally extensive sinusoidal waveforms which are interpreted as deposits of aggrading stationary antidunes which require quasi steady flows at the lower limit of the supercritical flow stage and high rates of sedimentation humpback dunes are characterised by downflow divergent cross stratification displaying differentiation into topsets foresets and bottomsets and are interpreted as deposited at the transition from subcritical to supercritical flow conditions or vice versa gradual lateral and vertical transitions between humpback dunes and antidune deposits are very common the absence of planar parallel stratification in all studied successions suggests that the formation of these bedforms is suppressed in flows characterised by hydraulic jumps under highly aggradational conditions the large scale lateral and vertical successions of bedforms are interpreted as representing the temporal and spatial evolution of the initial supercritical flows which was strongly affected by the occurrence of hydraulic jumps small scale facies changes and the formation of individual bedforms are interpreted as controlled by fluctuating discharge bed topography and pulsating unstable flows

lithofacies variations within sandur deposits the role of runoff regime flow dynamics and sediment supply characteristics abstract the icelandic sandur plains have for long acted as classic sites for models of braided river behaviour and of associated lithofacies assemblages however many of the icelandic sandurs are subject to repeated catastrophic flood events or jokulhlaups which are likely to have played a significant role in sandur construction established lithofacies models based on the icelandic sandurs have failed to take account of the varying runoff regimes which characterise the different sandur environments in addition sediment inputs to sandur channel systems are highly variable fluctuating in response both to varying runoff patterns and to advance and retreat of the source glacier that affect sediment availability within the proglacial zone this paper describes the main lithofacies types and vertical profiles that characterize the sandurs of south iceland and demonstrates that they can largely be attributed to extreme runoff events with few deposits typical of braided river facies occurring within the sedimentary record a preliminary qualitative model is developed that allows interpretation and prediction of vertical lithofacies profiles derived from glacial outwash in terms of i the drainage mechanism which in turn controls the dominant runoff population ii sediment availability and iii the spatial variability in flow dynamics

hydrodynamics and geomorphic work of jokulhlaups glacial outburst floods from kverkfjoll volcano iceland jokulhlaups glacial outburst floods occur frequently within most glaciated regions of the world and cause rapid landscape change infrastructure damage and human disturbance the largest jokulhlaups known to have occurred during the holocene within iceland drained from the northern margin of vatnajokull and along the jokulsa a fjollum some of these jokulhlaups originated from kverkfjoll volcano and were routed through anastomosing high gradient and hydraulically rough channels landforms and sediments preserved within these channels permit palaeoflow reconstructions kverkfjoll jokulhlaups were reconstructed using palaeocompetence point measurements slope area one dimensional and depth averaged two dimensional 2d hydrodynamic modelling techniques the increasing complexity of 2d modelling required a range of assumptions but produced information on both spatial and temporal variations in jokulhlaup characteristics the jokulhlaups were volcanically triggered had a linear rise hydrograph and a peak discharge of 50 000 100 000 m3 s 1 which attenuated by 50 75 within 25 km frontal flow velocities were 2 m s 1 but as stage increased velocities reached 5 15m s 1 peak instantaneous shear stress and stream power reached 1 104 n m 2 and 1 105 w m 2 respectively hydraulic parameters can be related to landform groups a hierarchy of landforms is proposed ranging from the highest energy zones erosional gorges scoured bedrock cataracts and spillways to the lowest energy zones of valley fills bars and slackwater deposits fluvial erosion of bedrock occurred in kverkfjallarani above 3 m flow depth 7m s 1 flow velocity 1 102 n m 2 shear stress and 3 102 w m 2 stream power fluvial deposition occurred in kverkfjallarani below 8 m flow depth 11 m s 1 flow velocity 5 102 n m 2 shear stress and 3 103 w m 2 stream power hence erosional and depositional envelopes have considerable overlap probably due to transitional flow phenomena and the influence of upstream effects such as hydraulic ponding and topographic constrictions for example holocene kverkfjoll jokulhlaups achieved geomorphic work comparable to that of other late pleistocene megafloods this work was a result of steep channel gradients topographic channel constrictions and high hydraulic roughness rather than to extreme peak discharges the kverkfjoll jokulhlaups have implications for landscape evolution in north central iceland for water sediment inputs into the north atlantic and for recognizing jokulhlaups in the rock record 2d hydrodynamic modelling is likely to be important for hazard mitigation in similar landscapes and upon other glaciated volcanoes because it only requires an input hydrograph and a digital elevation model to run a model rather than suites of geomorphological evidence and field surveyed valley cross sections for example copyright 2006 john wiley sons ltd

late ordovician climbing dune cross stratification a signature of outburst floods in proglacial outwash environments climbing dune scale cross statification is described from late ordovician paraglacial successions of the murzuq basin sw libya this depositional facies is comprised of medium grained to coarse grained sandstones that typically involve 0 3 to 1 m high 3 to 5 m in wavelength asymmetrical laminations most often stoss depositional structures have been generated with preservation of the topographies of formative bedforms climbing dune cross stratification related to the migration of lower flow regime dune trains is thus identified related architecture and facies sequences are described from two case studies i erosion based sandstone sheets and ii a deeply incised channel the former characterized the distal outwash plain and the fluvial subaqueous transition of related deltaic wedges while the latter formed in an ice proximal segment of the outwash plain in erosion based sand sheets climbing dune cross stratification results from unconfined mouth bar deposition related to expanding sediment laden flows entering a water body within incised channels climbing dune cross stratification formed over eddy related side bars reflecting deposition under recirculating flow conditions generated at channel bends associated facies sequences record glacier outburst floods that occurred during early stages of deglaciation and were temporally and spatially linked with subglacial drainage events involving tunnel valleys the primary control on the formation of climbing dune cross stratification is a combination between high magnitude flows and sediment supply limitations which lead to the generation of sediment charged stream flows characterized by a significant relatively coarse grained sand sized suspension load concentration with a virtual absence of very coarse to gravelly bedload the high rate of coarse grained sand fallout in sediment laden flows following flow expansion throughout mouth bars or in eddy related side bars resulted in high rates of transfer of sands from suspension to the bed net deposition on bedform stoss sides and generation of widespread climbing dune cross stratification the later structure has no equivalent in the glacial record either in the ancient or in the quaternary literature but analogues are recognized in some flood dominated depositional systems of foreland basins

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

water drag coefficient of first year sea ice in may 1977 eddy flux measurements of momentum were made with a three component ultrasonic current meter in the oceanic boundary layer under a first year floe of fast sea ice in barrow strait n w t by using eddy correlation methods values of horizontal reynolds stress were computed from each of 20 data runs of about 1 hour duration during which the mean current was reasonably steady a least squares analysis in which water stress was assumed proportional to the square of the mean current yielded a value for the 1 m water drag coefficient of 1 32 10 3 with a standard deviation of 0 06 10 3 the diameter of the floe was greater than 1 km and its mean thickness was 128 cm with a standard deviation of 4 cm and a maximum deviation of 7 cm

sedimentary processes and facies of the waterlaid anvil spring canyon alluvial fan death valley california the anvil spring canyon fan of the panamint range piedmont in central death valley was built entirely by water flow processes as revealed by an analysis of widespread 2 to 12 m high stratigraphic cuts spanning the 9 7 km radial length of this 2 5 5 0 sloping fan two facies deposited from fan sheetfloods dominate the fan from apex to toe the main one 60 95 of cuts consists of sandy granular fine to medium pebble gravel that regularly and sharply alternates with cobbly coarse to very coarse pebble gravel in planar couplets 5 25 cm thick oriented parallel to the fan surface the other facies 0 25 of cuts comprises 10 to 60 cm thick wedge planar and wedge trough beds of pebbly sand and sandy pebble gravel in backsets sloping 3 28 both facies are interpreted as resulting from rare sediment charged flash floods from the catchment and were deposited by supercritical standing waves of expanding sheetfloods on the fan standing waves were repeatedly initiated enlarged migrated and then terminated either by gradually rejoining the flood or by more violent breakage and washout the frequent autocyclic growth and destruction of standing waves during an individual sheetflood resulted in the deposition of multiple coarse and fine couplet and backset sequences 50 250 cm thick across the active depositional lobe of the fan erosional intensity during washout of the standing wave determined whether early phase backset bed deposits or washout phase sheetflood couplet deposits were selectively preserved in a given cycle two minor facies are also found in the anvil fan pebble cobble gravel lags 0 20 of cuts are present above erosional scours into the sheetflood couplet and backset deposits they consist of coarse gravel concentrated through fine fraction winnowing of the host sheetflood facies by sediment deficient water flows this reworking occurred during recessional flood stage or from non catastrophic discharge during the long intervals between major flash floods this facies is common at the surface giving rise to a braided stream appearance however it is stratigraphically limited present as thin continuous to discontinuous beds or lenses that bound 50 to 250 cm thick sheetflood sequences the other minor facies of the anvil fan consists of clast supported and imbricated thickly stratified pebbly cobbly boulder gravel present in narrow radially aligned ribbons nested within sheetflood deposits this facies is interpreted as representing deposition in the incised channel of the fan a subenvironment characterized by greater flow competence resulting from maintained depth from channel wall confinement and by more frequent water flows and winnowing events caused by its direct connection with the catchment feeder channel

magnitude and frequency in proglacial rivers a geomorphological and sedimentological perspective abstract proglacial fluvial sedimentary systems receive water from a variety of sources and have variable discharges with a range of magnitudes and frequencies little attention has been paid to how these various magnitude and frequency regimes interact to produce a distinctive sedimentary record in modern and ancient proglacial environments this paper reviews the concept of magnitude and frequency in relation to proglacial fluvial systems from a geomorphic and sedimentary perspective rather than a hydrological or statistical perspective the nature of the meltwater inputs can be characterised as low magnitude high frequency primarily controlled by ablation inputs from the source glacier or high magnitude low frequency primarily controlled by exceptional inputs the most important high magnitude low frequency inputs are catastrophic outburst floods often referred to by the term jokulhlaup icelandic for glacier burst glacier surges are an additional form of cyclical variation impacting the proglacial environment which briefly alter the volumes and patterns of meltwater input the sedimentary consequences of low magnitude high frequency discharges are related to frequent variations in stage the greater directional variability that sediment will record and the increased significance of channel confluence sedimentation in contrast the most significant characteristics of high magnitude low frequency flooding include the presence of large flood bars and mid channel jokulhlaup bars hyperconcentrated flows large gravel dunes and the formation of ice block kettle hole structures and rip up clasts glacier surges result in a redistribution of low magnitude high frequency processes and products across the glacier margin and small floods may occur at the surge termination criteria for distinguishing magnitude and frequency regimes in the proglacial environment are identified based on these major characteristics studies of quaternary proglacial fluvial sediments are used to determine how the interaction of the various magnitude and frequency regimes might produce a distinctive sedimentary record consideration of sandur architecture and stratigraphy shows that the main controls on the sedimentary record of proglacial regions are the discharge magnitude and frequency regime sediment supply the pattern of glacier advance or retreat and proglacial topography a model of sandur development is suggested which shows how discharge magnitude and frequency in combination with sandur incision and aggradation controlled by glacier advance and retreat can control sandur stratigraphy

sedimentary and structural evolution of a relict subglacial to subaerial drainage system and its hydrogeological implications an example from anglesey north wales uk subglacial drainage systems exert a major control on basal sliding rates and glacier dynamics however comparatively few studies have examined the sedimentary record of subglacial drainage this is due to the paucity of modern analogues the limited recognition and preservation of upper flow regime deposits within the geological record and the difficulty of distinguishing subglacial meltwater deposits from other meltwater sediments e g glacier outburst flood deposits within this study the sedimentological and structural evolution of a subglacial to subaerial ice marginal proglacial drainage system is examined particular emphasis is placed upon the genetic development and preservation of upper flow regime bedforms and specifically recognising them within a subglacial meltwater context facies are attributed to subglacial meltwater activity and record sedimentation within a confined but progressively enlargening subglacial channel system produced under dune to upper flow regime conditions bedforms include rare large scale sinusoidal bedding with syn depositional deformation produced by current induced traction and shearing within the channel margins subglacial sedimentation culminated with the abrupt change to a more ephemeral drainage regime indicating channel abandonment or a seasonal drainage regime retreat of the ice margin led to the establishment of subaerial drainage with phases of sheet flow punctuated by channel incision and anastomosing channel development under diurnal ablation related seasonal discharge the presence of extensive hydrofracture networks demonstrate that proglacial groundwater levels fluctuated markedly and this may have influenced later overriding of the site by an ice stream

dynamic interactions between lahars and stream flow a case study from ruapehu volcano new zealand three lahars were sampled in the whan gaehu river on the eastern flank of ruapehu volcano new zealand at 23 5 and 42 km from the source as they were flowing on september 27 and 29 and october 6 1995 the lahars were generated by water explosively ejected from the highly mineralized crater lake we used the chemical contrast between the lahars and resident stream water in their paths to describe a four phase model of a noncohesive lahar wave in a river channel 1 ambient stream water pushed ahead of the lahar in a process of miscible displacement due to hydrodynamic dispersion 2 a zone of mixing between the stream water and the lahar that increases in length with distance from source 3 a remnant of the original lahar least diluted by stream water that decreases in length and dilutes downstream 4 the tail of the lahar surge peak discharge occurs at the end of phase 1 as water is pushed ahead of the lahar peak sediment concentration occurs at the end of phase 2 where debris entrainment by the flow is at its greatest i e in front of the lahar proper deposits record only phases 2 and 3 of the lahar wave phase 1 flow left only a tide line of organic debris and phase 4 deposits were rapidly eroded by later streamflow downstream dilution by stream water eventually caused transformation of phases 2 and 3 of the lahars from debris flow to hyperconcentrated streamflow and then to normal streamflow as the flows became progressively finer grained and more turbulent

the spreading of a buoyant plume beneath a landfast ice cover abstractidealized numerical simulations using the regional ocean modeling system demonstrate the effects of an immobile landfast ice cover that is frictionally coupled to an underice buoyant plume established by river discharge the discharge rapidly increases and decreases over a 30 day period and has a maximum of 6000 m3 s 1 this study examined the response to a landfast ice cover of 26 km width and one that encompasses the entire shelf width the model setting mimics spring conditions on the alaskan beaufort sea abs shelf in comparison with the ice free case subject to the same discharge scenario underice plumes are broader and deeper and the downwave freshwater flux is substantially decreased and delayed multiple anticyclonic bulges form in the ice free case but only a single large bulge forms when ice is present these differences are because of the frictional coupling between the ice and plume which results in an ekman like underice boundary layer a subsurface velocity maximum and fricti