instantaneous end moraine and sediment wedge formation during the 1890 glacier surge of bruarjokull iceland abstract contemporary understanding of the behaviour of surging glaciers and ice streams is hampered by the lack of data on landsystem evolution and sedimentary environments this study concerns the ice marginal environment of the surge type bruarjokull in iceland the sediment distribution in the glacier forefield as well as the morphology sedimentology and tectonic architecture of the 1890 end moraine is investigated for highlighting the interaction between very dynamic ice and sediment landform associations as a result of substrate bedrock decoupling during the 1890 surge subglacial sediment was dislocated across the bedrock surface and deformed compressively leading to gradual substrate thickening and the formation of a sediment wedge in the marginal zone a drop in subglacial porewater pressure at the very end of the surge led to substrate bedrock coupling and a stress transfer up into the sediment sequence causing brittle deformation of the substrate simultaneously the glacier toe ploughed into the topmost part of the marginal sediment wedge initiating the moraine ridge construction fine grained and incompetent sediment deformed in ductile manner resulting in a narrow moraine dominated by rooted folds while coarse grained and competent sediment deformed in brittle fashion resulting in a wider moraine dominated by thrust blocks a new sequential model of subglacial and ice marginal processes operating during a glacier surge is proposed illustrating the stepwise formation of a marginal sediment wedge and an end moraine a twofold inseparable marginal end product that formed during the last days of the 1890 surge

clast shape analysis and clast transport paths in glacial environments a critical review of methods and the role of lithology the reconstruction and tracing of transport paths in glaciated and other environments have a long tradition in the earth sciences we here present a dataset of clast shape samples from a worldwide selection of glaciated mountain environments in order to assess the reliability of this approach overall and the role of lithology on the performance of clast shape measurements in particular our findings demonstrate that the widely used ra c40 co variance approach is applicable to 63 of the 19 catchments investigated while the alternative rwr c40 approach is more widely applicable to 75 of these catchments a systematic assessment of mixing of lithologies at the catchment scale demonstrates that such mixing leads to pronounced overlaps between different control envelopes that had previously been separated thereby removing the discriminatory power of the method mixing of similar lithologies between different catchments shows an even more extreme loss of discriminatory power which strongly suggests that lithology plays a primary role in determining clast shape and that catchment specific processes are superimposed systematic analysis of the dataset also shows that nearly all catchments apart from two can be grouped into two types type i relates to sites in lesser mountain ranges and is characterised by dominantly blocky forms in the subglacial realm highlighting significant reworking processes type ii sites are dominantly in high mountain environments and characterised by a high similarity between subglacial and fluvial control envelopes this indicates that although reworking may be pronounced it is not necessarily effective enough to remove the platy shape that most likely results from extraglacial and supraglacial inputs our study highlights the potential of clast shape analysis as a tool that allows generic processes to be identified between catchments thereby enabling an understanding of debris cascades in glaciated mountain environments we finish with recommendations for ensuring that future clast shape studies are robust reproducible and comparable between different sites

expansion of ice marginal lakes at the vatnajokull ice cap iceland from 1999 to 2009 abstract outlet glaciers from the vatnajokull ice cap in iceland europe s largest ice cap have been retreating since the end of the little ice age only interrupted by short intervals of advances the net mass balance has been negative since 1995 and ice marginal lakes in front of the outlets have been expanding since then the switch from land based glacier termini to lake terminating glaciers is an eye catching environmental change the heat capacity of the ice marginal lakes and the change into calving glacier fronts accelerates ice loss from vatnajokull landsat 7etm satellite imagery from 1999 to 2009 reveals high resolution snapshots of the lake development during the last decade ice marginal lakes are growing at many outlet glaciers draining the southern sector of vatnajokull this is most pronounced at the large brei amerkurjokull glacier where the jokulsarlon lake expanded from 15 km 2 in 2000 to more than 21 km 2 in 2009 the lakes act as traps for sediment that was earlier transported across outwash plains toward the atlantic coast hence the glacier retreat and sediment trapping enhance coastline retreat and river incision in the outwash plains similar changes although at a much larger scale occurred in many past glaciated regions during the last glacial termination thus the lakes in front of vatnajokull provide important modern analogues for processes that likely impacted global climate in the past

is the north atlantic oscillation reflected in scandinavian glacier mass balance records the north atlantic oscillation nao is one of the modes of climate variability in the north atlantic region the atmospheric circulation during the winter season in this region commonly displays a strong meridional north south pressure contrast with low air pressure cyclone centred close to iceland and high air pressure anticyclone near the azores this pressure gradient drives the mean surface winds and the mid latitude winter storms from west to east across the north atlantic bringing mild moist air to northwest europe the nao index is based on the difference of normalised sea level pressures slp between ponta delgada azores and stykkisholmur iceland the slp anomalies at these stations are normalised by division of each monthly pressure by the long term 1865 1984 standard deviation interannual atmospheric climate variability in northwest europe especially over great britain and western scandinavia has during the last decades been attributed mainly to the nao causing variations in the winter weather over the northeast north atlantic and the adjacent land areas a comparison between the nao index and the winter december march precipitation between ad 1864 and 1995 in western norway shows that these are strongly linked correlation coefficient 0 77 variations in the nao index are also reflected in the mass balance records of glaciers in western scandinavia the nao index is best correlated with mass balance data from maritime glaciers in southern norway e g alfotbreen r 2 0 51 the record of holocene last ca 11 500 cal yr glacier variations of maritime glaciers in western scandinavia is thus a proxy of pre instrumental nao variations copyright 2000 john wiley sons ltd

contribution of icelandic ice caps to sea level rise trends and variability since the little ice age 1 in total icelandic ice caps contain 3600 km3 of ice which if melted would raise sea level by 1 cm here we present an overview of mass changes of icelandic ice masses since the end of the 19th century they have both gained and lost mass during this period changes in ice volume have been estimated both through surface mass balance measurements performed annually since 1990 and differencing of digital elevation models derived from various satellite and airborne observations while the glaciers showed little mass loss as the 20th century began losses increased rapidly after 1925 peaked in the 1930s and 1940s and remained significant until the 1960s after being near zero or even positive during the 1980s and early 1990s glacier mass budgets declined considerably and have since the mid 1990s shown an average annual loss of 9 5 1 5 gt a 1 contributing 0 03 mm a 1 to sea level rise since 1995 interannual variability in mass loss is high ranging from 2 7 to 25 3 1 5 gt a 1 corresponding to surface mass balances of 0 2 to 2 2 0 15 m we a 1 this variability is driven by climate fluctuations and also by transient reduction of albedo due to volcanic eruptions

size and shape characteristics of drumlins derived from a large sample and associated scaling laws abstract ice sheets flowing across a sedimentary bed usually produce a landscape of blister like landforms streamlined in the direction of the ice flow and with each bump of the order of 102 to 103 m in length and 101 m in relief such landforms known as drumlins have mystified investigators for over a hundred years a satisfactory explanation for their formation and thus an appreciation of their glaciological significance has remained elusive a recent advance has been in numerical modelling of the land forming process in anticipation of future modelling endeavours this paper is motivated by the requirement for robust data on drumlin size and shape for model testing from a systematic programme of drumlin mapping from digital elevation models and satellite images of britain and ireland we used a geographic information system to compile a range of statistics on length l width w and elongation ratio e where e l w for a large sample mean l is found to be 629 m n 58 983 mean w is 209 m and mean e is 2 9 n 37 043 most drumlins are between 250 and 1000 metres in length between 120 and 300 metres in width and between 1 7 and 4 1 times as long as they are wide analysis of such data and plots of drumlin width against length reveals some new insights all frequency distributions are unimodal from which we infer that the geomorphological label of drumlin is fair in that this is a true single population of landforms rather than an amalgam of different landform types drumlin size shows a clear minimum bound of around 100 m horizontal maybe drumlins are generated at many scales and this is the minimum or this value may be an indication of the fundamental scale of bump generation proto drumlins prior to them growing and elongating a relationship between drumlin width and length is found with r2 0 48 and that is approximately w 7 l 1 2 when measured in metres a surprising and sharply defined line bounds the data cloud plotted in e w l space and records a scale dependent maximum elongation limit approximated by emax l1 3 when l measured in metres for a given length for some reason as yet unknown drumlins do not exceed the elongation ratio defined by this scaling law we also report and compare our statistics to an amalgamated sample 25 907 drumlins of measures derived from around 50 published investigations any theory must be able to explain the drumlin statistics and fundamental scaling properties reported herein and they thus provide powerful tests for drumlin modelling

basal topographic controls on rapid retreat of humboldt glacier northern greenland discharge from marine terminating outlet glaciers accounts for up to half the recent mass loss from the greenland ice sheet yet the causal factors are not fully understood here we assess the factors controlling the behaviour of humboldt glacier hg allowing us to evaluate the influence of basal topography on outlet glacier response to external forcing since part of hg s terminus occupies a large overdeepening hg s retreat accelerated dramatically after 1999 coinciding with summer atmospheric warming of up to 0 19 c a 1 and sea ice decline retreat was an order of magnitude greater in the northern section of the terminus underlain by a major basal trough than in the southern section where the bedrock is comparatively shallow velocity change following retreat was spatially non uniform potentially due to a pinning point near hg s northern lateral margin consistent with observations numerical modelling demonstrates an order of magnitude greater sensitivity to sea ice buttressing and crevasse depth used as a proxy for atmospheric warming in the northern section the trough extends up to 72 km inland so it is likely to facilitate sustained retreat and ice loss from hg during the 21st century

architecture and structural evolution of an early little ice age terminal moraine at the surge type glacier mulajokull iceland the internal architecture and structural evolution of the arnarfellsmular terminal moraine at mulajokull a surge type glacier in central iceland is described in order to demonstrate submarginal and proglacial glaciotectonic processes during glacier surging as well as constraining the age of the maximum extent of the glacier the moraine is 4 7m high 50 100m wide and composed of a highly deformed sequence of loess peat and tephra that is draped by till up to the crest the internal architecture is dominated by steep high amplitude overturned folds and thrusts in the crest zone but open low amplitude folds on the distal slope section balancing suggests a basal detachment decollement depth of 1 4m and a total horizontal shortening of around 59 this implies that the glacier coupled to the foreland about 70m up glacier from its terminal position to initiate the formation of the moraine the structural evolution is polyphase in that the formation commenced with low amplitude open folding of the foreland followed by overfolding and piggyback thrusting radiocarbon dating and analysis of tephra layers along with historical references indicate that the most likely time of moraine formation was between a d 1717 and 1760 which suggests that mulajokull had its little ice age maximum and most extensive surge earlier than many other surge type glaciers in iceland

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

sediment fingerprinting and the mode of formation of singular and composite annual moraine ridges at two glacier margins jotunheimen southern norway sedimentary variation within and between annual moraine ridges formed at storbreen and styggedalsbreen jotunheimen during the 1980s and 1990s is investigated with a focus on processes and mechanisms of moraine ridge formation tops and bottoms of sediment slabs deposited either as single annual moraines or incorporated into composite moraine ridges formed of several annual increments were analysed and compared with possible source sediments with a view to sediment fingerprinting clast roundness and shape indicated mainly subglacial sediment origins while textural variability was mainly inherited from proglacial sediment sources and macrofabrics and micromorphological characteristics revealed overprinting by various glaciofluvial glaciolacustrine and periglacial processes the evidence suggests one dominant mechanism of moraine ridge formation involving the annual freeze on and subsequent melt out of overridden proglacial sediment slabs this mechanism provides the basis of a simple model encompassing both singular and composite annual moraine ridge formation which appears appropriate for temperate glacier snouts characterized by deep seasonally frozen ground close to the lower altitudinal limit of the zone of alpine permafrost

englacial deltaic sediments as evidence for basal freezing and marginal shearing leirbreen southern norway analyse des depots de geles de limons sables et graviers pres du front du glacier leirbreen les structures demontrent une origine deltaique les sediments ayant ete geles avant leur incorporation au glacier et n ayant pas subit de cisaillement pendant le transport glaciaire on en deduit les mecanismes de variation du glacier

controlled moraine development and debris transport pathways in polythermal plateau icefields examples from tungnafellsjokull iceland a modern landsystems analogue for plateau icefield glaciation is presented based upon tungnafellsjokull in the arid cold interior of iceland landform mapping and intensive clast form analysis on three separate forelands occupied during the little ice age reveal variability in the morphology of moraines and the degree of clast modification which is interpreted as a function of the complex interplay between a the efficacy of glacial erosion b passive versus active debris transfer mechanisms and c the volume of debris provision for ice marginal freeze on mechanisms a steep outlet bounded by rockwalls produced a landform assemblage and debris transport signature typical of valley glaciers whereas two unconfined outlets produced a landform sediment imprint typical of polythermal conditions this comprises subglacial bedforms relating to the initiation of warm based ice by strain heating below icefalls at the plateau edge terminating at arcs of ice cored controlled moraine representative of frozen snout conditions patterns in clast form data on the unrestricted forelands reflect the characteristics of glacier dynamics and thermal regimes at the margin of a plateau icefield where bedrock steps of sufficient size to initiate strain heating and bedrock abrasion and plucking are located only a short distance from the marginal freeze on conditions of a snout creating debris rich folia and controlled moraine additional englacial debris may well have been carried to the glacier margin through the development of ogives and englacial thrusting at the base of the icefall thereby explaining the occurrence of striae on clasts that have otherwise been little modified by glacial abrasion copyright 2010 john wiley sons ltd

multi decadal retreat of greenland s marine terminating glaciers many marine terminating glaciers draining the greenland ice sheet have retreated over the past decade yet the extent and magnitude of retreat relative to past variability is unknown we measure changes in front positions of 210 marine terminating glaciers using landsat imagery spanning nearly four decades and compare decadal scale rates of change with earlier observations we find that 90 of the observed glaciers retreated between 2000 and 2010 approaching 100 in the northwest with rapid retreat observed in all sectors of the ice sheet the current retreat is accelerating and likely began between 1992 and 2000 coincident with the onset of warming following glacier stability and minor advance during a mid century cooling period while it is clear an extensive retreat occurred in the early 20th century a period of increasing air temperatures a comparison of our results with historical observations provides evidence that the current retreat is more widespread the onset of rapid retreat with warming relative to the slow and lagged advance with cooling suggests an asymmetry in the response of marine fronts to external forcing

the morphology structural evolution and significance of push moraines abstract push moraines glaciotectonic ice marginal moraines have a restricted distribution at modern glacier margins and consequently are of potential value in reconstructing pleistocene ice sheets providing data both on former glaciodynamics and on the palaeoenvironment of the glacial foreland to the wider earth science community push moraines are of interest as analogues for thin skin tectonics within orogenic belts this paper reviews the morphology structural geology formation and significance of push moraines the morphological and structural characteristics of small seasonal push moraines through to large multi crested examples produced by sustained glacier advances are reported before the primary controls on push moraine formation are examined these controls include the nature of the applied glacial stress field the presence and properties of decollement horizons and the shear strength and rheology of the glacial foreland a conceptual model of push moraine formation is introduced in which the range of observed morphological and structural forms are viewed within a matrix defined by the main variables which control their formation the absence of consensus over which of these variables is of greatest importance currently limits the significance of push moraines in palaeoglaciological research as a consequence this review emphasises the need for future research in order to realise the true potential of push moraine in the reconstruction of pleistocene environments

influence of sea ice decline atmospheric warming and glacier width on marine terminating outlet glacier behavior in northwest greenland at seasonal to interannual timescales 1 discharge from marine terminating outlet glaciers represents a key component of the greenland ice sheet mass budget and observations suggest that mass loss from northwest greenland has recently accelerated despite this the factors controlling outlet glacier dynamics within this region have been comparatively poorly studied here we use remotely sensed data to investigate the influence of atmospheric oceanic and glacier specific controls on the frontal position of alison glacier ag northwest greenland and nine surrounding outlet glaciers ag retreated by 9 7 km between 2001 and 2005 following at least 25 years of minimal change results suggest that sea ice and air temperatures influence glacier frontal position at seasonal and interannual timescales however the response of individual outlet glaciers to forcing was strongly modified by factors specific to each glacier specifically variations in fjord width and terminus type overall our results underscore the need to consider these factors in order to interpret recent rapid changes and predict the dynamic response of marine terminating outlet glaciers to atmospheric and oceanic forcing

glacier fluctuations of jostedalsbreen western norway during the past 20 years the sensitive response of maritime mountain glaciers the steep outlet glaciers of jostedalsbreen western norway are good examples of sensitively reacting maritime mountain glaciers their changes in length frontal position and lower tongue s morphology during the past 20 years have been well documented at first they experienced a strong frontal advance after ad 2000 glacier behaviour was dominated by a strong frontal retreat in some cases causing a separation of the lowermost glacier tongue in this paper the glacier length changes are presented both visually and numerically supplemented by mass balance and meteorological data the glacier behaviour is interpreted and its causes are discussed whereas the factors controlling the advance during the 1990s seem clear the interpretation of the most recent retreat still leaves some uncertainties the actual glacier front behaviour cannot fully be related to the mass balance data terminus response times and relations between individual mass balance and meteorological parameters have changed some hypoth

early holocene glacier fluctuations in krundalen south central norway palaeoglacier dynamics and palaeoclimate krundalen a valley occupied by three eastern outlet glaciers of the jostedalsbre ice cap contains three groups of moraines two of which are outside the dated neoglacial little ice age lia l

rapid climate driven changes in outlet glaciers on the pacific coast of east antarctica multidecadal trends in the terminus position of outlet glaciers along the margin of the east antarctic ice sheet reveal three epochal patterns of glacier retreat or advance consistent with a rapid and coherent response to air temperature and sea ice trends it is widely known that glaciers in west antarctica and greenland have been discharging ice into the oceans in response to warming in recent years and that sea levels have risen as a result by contrast we hear little about the much larger east antarctic ice sheet which has been viewed as being less vulnerable to climate change owing to its location in an extremely cold climate chris stokes and colleagues have used satellite imagery to map a large sample of glaciers along the pacific coast of east antarctica and show that in fact they are responding to decadal climate variability in concert with climate glaciers retreated in the 1970s and 1980s advanced in the 1990s and approximately split between advance and retreat since the 2000s the authors conclude that parts of the world s largest ice sheet may be more responsive to external forcing than previously recognized observations of ocean terminating outlet glaciers in greenland and west antarctica1 2 3 4 5 6 indicate that their contribution to sea level is accelerating as a result of increased velocity thinning and retreat7 8 9 10 11 thinning has also been reported along the margin of the much larger east antarctic ice sheet1 but whether glaciers are advancing or retreating there is largely unknown and there has been no attempt to place such changes in the context of localized mass loss7 9 or climatic or oceanic forcing here we present multidecadal trends in the terminus position of 175 ocean terminating outlet glaciers along 5 400 kilometres of the margin of the east antarctic ice sheet and reveal widespread and synchronous changes despite large fluctuations between glaciers linked to their size three epochal patterns emerged 63 per cent of glaciers retreated from 1974 to 1990 72 per cent advanced from 1990 to 2000 and 58 per cent advanced from 2000 to 2010 these trends were most pronounced along the warmer western south pacific coast whereas glaciers along the cooler ross sea coast experienced no significant changes we find that glacier change along the pacific coast is consistent with a rapid and coherent response to air temperature and sea ice trends linked through the dominant mode of atmospheric variability the southern annular mode we conclude that parts of the world s largest ice sheet may be more vulnerable to external forcing than recognized previously

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

the formation of sawtooth moraine ridges in bodalen western norway abstract the forefield of the bodalsbreen glacier western norway exhibits a prominent set of end moraines the outermost one deposited at the little ice age lia maximum a d 1755 is smooth continuous and arcuate thus reflecting an even ice front in contrast subsequently formed moraines deposited a d 1767 1930 show a striking sawtooth morphology in an attempt to elucidate the formation processes responsible for this complex landform assemblage we have employed several methods of investigation including geomorphological mapping sedimentological studies and ground penetrating radar gpr in general the detailed formation processes of all moraines include bulldozing and thrusting furthermore the sediment composition and structure are similar for all the moraines containing recycled diamicton the remaining major factor influencing the moraine morphology thus seems to be the shape of the glacier front due to the distinctive geometry of the bodalen valley the former glacier underwent strong changes of its transverse stress field in the part where the valley was wider splaying radial crevasses developed further downvalley where the valley again narrowed these crevasses were closed as previous studies have concluded the change in valley morphology to a large extent explains the distinct morphology of the bodalen valley moraines this notion is further corroborated by studying sawtooth or sawtooth like moraines elsewhere where valley geometry also seems to have been a major contributing factor for moraine morphology

sediment deformation beneath glaciers rheology and geological consequences experiments beneath breidamerkurjokull in iceland have led to development of flow laws for the subglacial till relating strain rate to shear stress and effective pressure and assuming either bingham fluid or nonlinearly viscous fluid behavior water pressures in the till are less than ice pressures and it is suggested that this may lead to infiltration of ice into the sediment which inhibits sliding at the ice sediment interface where water pressures are equal or near to ice pressures infiltration does not occur and sliding may result a one dimensional theory of subglacial deformation is developed in which the empirical flow law is coupled with a model of subglacial hydrology and consolidation this predicts stable states in which subglacial sediment either does not deform or a dilatant deforming horizon forms with positive effective pressures at the ice bed interface or unstable states where zero or negative effective pressures are predicted time dependent analyses show that response times following perturbations of the system may be of the order of 103 years and thus that unsteady behavior may be normal on glaciers flowing over unlithified sediment beds it is suggested that the natural variability of material properties in subglacial sediment beds leads to the development of drumlins on the glacier bed it is suggested that unstable deformation at zero or negative effective stress leads to piping in subglacial sediments at the glacier terminus and the growth of sediment floored subglacial tunnels their frequency is that which is sufficient to draw down subglacial water pressures so as to prevent unstable deformation where they discharge large water volumes subglacial sediments flow laterally toward them producing tunnel valleys this sediment is then removed by water flowing along the axial tunnel tunnel valleys can be regarded as the equivalent in soft sediment areas of eskers in bedrock areas

growth rates of rhizocarpon geographicum lichens a review with new data from iceland this paper reviews evidence from previous growth rate studies on lichens of the yellow green species of subgenus rhizocarpon the family most commonly used in lichenometric dating new data are presented from rhizocarpon section rhizocarpon thalli growing on a moraine in southern iceland over a period of 4 33yr measurements of 38 lichen thalli between 2001 and 2005 show that diametral growth rate dgr mmyr 1 is a function of thallus size growth rates increase rapidly in small thalli 50 mm diameter mean dgr in southern iceland between 2001 and 2005 was 0 64 mm yr 1 sd 0 24 the resultant growth rate curve is parabolic and is best described by a third order polynomial function the striking similarity between these findings in iceland and those of armstrong 1983 in wales implies that the shape of the growth rate curve may be characteristic of rhizocarpon geographicum lichens the difference between the absolute growth rate in southern iceland and wales ca 66 faster is probably a function of climate and micro environment between the two sites these findings have implications for previous lichenometric dating studies namely that those studies which assume constant lichen growth rates over many decades are probably unreliable british geological survey natural environment research council copyright 2006

the planar shape of drumlins abstract the asymmetry of the planar shape of drumlins is an established paradigm in the literature and characterizes drumlins as resembling tear drops with a blunt bullet shaped stoss end and a tapering pointed lee end it is widely cited and never been seriously questioned in this paper the planar shape of 44 500 drumlins mapped in various regional settings from drumlin fields in north america and northern europe were objectively analysed by means of geographic information system tools two parameters were considered the first denoted here as as pl focuses on the relative position of the point of intersection between the axes of the maximum length and the maximum width it is defined as the distance between the upstream i e beginning of the drumlin and the intersection point measured along the longitudinal axis divided by the entire length of the long axis results indicate that the intersection point of the majority of drumlins 64 is very close to the longitudinal midpoint 0 33 as pl as pl a is defined as the ratio between the area of the upstream half of the drumlin to that of the entire drumlin results show that for most drumlins 81 the upper half area is almost as large as the down half 0 45 as pl a

characteristics of recessional moraines at a temperate glacier in se iceland insights into patterns rates and drivers of glacier retreat icelandic glaciers are sensitive to climate variability on short term timescales owing to their north atlantic maritime setting and have been undergoing ice marginal retreat since the mid 1990s recent patterns rates and drivers of ice frontal retreat at skalafellsjokull se iceland are examined using small scale recessional moraines as a geomorphological proxy these small scale recessional moraines exhibit distinctive sawtooth planform geometries and are constructed by a range of genetic processes associated with minor ice margin re advance including i combined push squeeze mechanisms ii bulldozing of pre existing proglacial material and iii submarginal freeze on remote sensing investigations and lichenometric dating highlight sequences of annually formed recessional moraines on the northern and central parts of the foreland conversely moraines are forming on a sub annual timescale at the southeastern skalafellsjokull margin using annual moraine spacing as a proxy for annual ice margin retreat rates imrrs we demonstrate that prominent periods of glacier retreat at skalafellsjokull are coincident with those at other icelandic outlet glaciers as well as those identified at greenlandic outlet glaciers analysis of imrrs and climate data suggests summer air temperature sea surface temperature and the north atlantic oscillation have an influence on imrrs at skalafellsjokull with the glacier appearing to be most sensitive to summer air temperature on the basis of further climate data analyses we hypothesise that sea surface temperature may drive air temperature changes in the north atlantic region which in turn forces imrrs the increase in sea surface temperature over recent decades may link to atmospheric driven variations in north atlantic subpolar gyre dynamics

a younger dryas plateau icefield in the monadhliath scotland and implications for regional palaeoclimate a record of younger dryas glaciation in scotland is well established however the role of the monadhliath a significant plateau area extending over 840 km2 in central scotland has never been investigated systematically we present the first systematic glacial geomorphological mapping across the whole region which has led to the identification of hitherto unrecorded glacial and associated landforms the spatial distribution of these landforms indicates that the last phase of glaciation in the area was that of a local plateau icefield in addition a clear morphostratigraphical signature provides a strong indication that the icefield dates to the younger dryas 12 9 11 7 ka which is supported by numerical ages in the southeast of the study area based on the geomorphological evidence and 2d glacier surface profile modelling a 280 km2 icefield is reconstructed a novel approach is introduced to quantify plateau icefield thickness for equilibrium line altitude ela and palaeoprecipitation calculations resulting in greater overall data confidence compared to traditional reconstruction methods the ela for the whole icefield is calculated to be 714 25 m whilst the elas of individual outlet glaciers range from 560 m in the west to 816 m in the east demonstrating a significant w e precipitation gradient across the region during the younger dryas these elas compare well with those calculated for younger dryas ice masses reconstructed in neighbouring regions and are in good agreement with overall precipitation patterns suggested for scotland during this time whilst the total amount of precipitation calculated from these elas is highly dependent on the method used irrespective of this the study suggests a more arid younger dryas climate in the region compared to the present day

the genesis and significance of hummocky moraine evidence from the isle of skye scotland abstract the range of genetic and climatic interpretations of scottish hummocky moraine is reviewed and new data are presented from the isle of skye western scotland which are used as the basis of a genetic classification hummocky moraine on skye is shown to consist of three principal sediment landform associations 1 recessional moraines 2 chaotic ice stagnation moraines and 3 drumlins and fluted moraines the recessional moraines consist of transverse moraine ridges and chains of mounds and were formed by a combination of glaciotectonics and debris accumulation at active ice margins second chaotic moraines consist of randomly distributed hummocks mounds and rim ridges and record deposition in contact with inactive ice finally drumlins and fluted moraines are longitudinally oriented subglacial bedforms formed by a combination of lodgement and sediment deformation individual occurrences of hummocky moraine may comprise one two or all of these associations the detailed study and differentiation of scottish hummocky moraine provides a valuable source of information on former glacier dynamics and landscape change

a simple method of simulating the future frontal position of briksdalsbreen western norway to simulate future mass balance and frontal variations of briksdalsbreen in western norway a degree day model based on temperature and precipitation data from bergen has been used briksdalsbreen is a steep western outlet glacier from jostedalsbreen the calculated relationship between annual glacier front variation and mass balance gives best correlation with a frontal time lag of 3 years which is in accordance with previous studies climate scenarios from the norwegian regclim project have been implemented in the model applying the regclim future climate summer temperature and winter precipitation scenarios our calculations indicate that briksdalsbreen may retreat 2 2 5 km from the 1963 position within the termination of the twenty first century the main icefall may thus disappear and the upper part of the glacier will exist as a plateau glacier the accumulation area may thus consist of a small plateau and the glacier will therefore be sensitive to mass balance changes work is in progress to implement a dynamic glacier model for future studies

origin chronology and climatological significance of annual moraine ridges at myrdalsjokull iceland minor transverse moraine ridges have formed annually at the retreating north margin of myrdalsjokull 550 600 m a s l in south iceland during the period 1928 1981 they are composed of slabs of clast paved lodgement till and their formation at the glacier edge results from subglacial freezing on of sediment slabs during winter and the annual cycle of ice front activity this type of annual moraine ridge is likely to be characteristic of retreating temperate glaciers where the glacier toe is thin and winters are cold the speed of glacier retreat is finely balanced with changes in mean summer temperature suggesting that the short term ice front fluctuations are climatically induced and not a result of surge activity

recent changes on greenland outlet glaciers aircraft laser altimeter surveys during the 1990s showed near coastal parts of the greenland ice sheet to be thinning despite slow thickening at higher elevations the ice sheet lost mass to the ocean many outlet glaciers thinned more rapidly than could be explained by increased melting during the recent warmer summers indicating dynamic imbalance between glacier velocity and upstream snow accumulation results from more recent surveys presented here show that thinning rates have increased in most coastal regions for almost half of the surveys these increases might have resulted from increases in summer melting but rapid thinning on others is indicative of dynamic changes that increased with time in particular thinning rates on the three fastest glaciers increased to tens of m a 1 after 2000 and other observations show an approximate doubling in their velocities the deep beds of these glaciers appear to have a strong influence on rates of grounding line retreat and thickness change with periods of glacier acceleration and rapid thinning initiated by flotation and break up of lightly grounded glacier snouts or break up of floating ice tongues near simultaneous thinning of these widely separated glaciers suggests that warming of deeper ocean waters might be a common cause nearby glaciers without deep beds are thinning far more slowly suggesting that basal lubrication as a result of increased surface melting has only a marginal impact on greenland outlet glacier acceleration

ice melange dynamics and implications for terminus stability jakobshavn isbrae greenland 1 we used time lapse imagery seismic and audio recordings iceberg and glacier velocities ocean wave measurements and simple theoretical considerations to investigate the interactions between jakobshavn isbrae and its proglacial ice melange the melange behaves as a weak granular ice shelf whose rheology varies seasonally sea ice growth in winter stiffens the melange matrix by binding iceberg clasts together ultimately preventing the calving of full glacier thickness icebergs the dominant style of calving and enabling a several kilometer terminus advance each summer the melange weakens and the terminus retreats the melange remains strong enough however to be largely unaffected by ocean currents except during calving events and to influence the timing and sequence of calving events furthermore motion of the melange is highly episodic between calving events including the entire winter it is pushed down fjord by the advancing terminus at 40 m d 1 whereas during calving events it can move in excess of 50 103 m d 1 for more than 10 min by influencing the timing of calving events the melange contributes to the glacier s several kilometer seasonal advance and retreat the associated geometric changes of the terminus area affect glacier flow furthermore a force balance analysis shows that large scale calving is only possible from a terminus that is near floatation especially in the presence of a resistive ice melange the net annual retreat of the glacier is therefore limited by its proximity to floatation potentially providing a physical mechanism for a previously described near floatation criterion for calving

size shape and spatial arrangement of mega scale glacial lineations from a large and diverse dataset mega scale glacial lineations msgls are a characteristic landform on ice stream beds solving the puzzle of their formation is key to understanding how ice interacts with its bed and how this in turn influences the dynamics of ice streams however a comprehensive and detailed characterization of this landform s size shape and spatial arrangement which might serve to test and refine formational theories is largely lacking this paper presents a detailed morphometric analysis and comparison of 4043 msgls from eight palaeo ice stream settings three offshore norway and antarctica four onshore canada and one from under a modern ice stream in west antarctica the length of msgls is lower than previously suggested mode 1000 2000 m median 2892 m and they initiate and terminate at various locations on an ice stream bed their spatial arrangement reveals a pattern that is characterized by an exceptional parallel conformity 80 of all mapped msgls have an azimuth within 5 from the mean values and a fairly constant lateral spacing mode 200 300 m median 330 m which we interpret as an indication that msgls are a spatially self organized phenomenon results show that size shape and spatial arrangement of msgls are consistent both within and also generally between different ice stream beds we suggest this results from a common mechanism of formation which is largely insensitive to local factors although the elongation of msgls mode 6 8 median 12 2 is typically higher than features described as drumlins these values and those of their width mode 100 200 m median 268 m overlap which suggests the two landforms are part of a morphological continuum and may share a similar origin we compare their morphometry with explicit predictions made by the groove ploughing and rilling instability theories of msgl formation although the latter was most compatible neither is fully supported by observations 2014 the authors earth surface processes and landforms published by john wiley sons ltd

the eyjabakkajokull glacial landsystem iceland geomorphic impact of multiple surges abstract a new glacial geomorphological map of the eyjabakkajokull forefield in iceland is presented the map covers c 60 km2 and is based on high resolution aerial photographs recorded in august 2008 as well as field checking landforms are manually registered in a geographical information system arcgis based on inspection of orthorectified imagery and digital elevation models of the area we mapped subglacially streamlined landforms such as flutes and drumlins on the till plain supraglacial landforms such as ice cored moraine pitted outwash and concertina eskers and ice marginal landforms such as the large multi crested 1890 surge end moraine and smaller single crested end moraines the glaciofluvial landforms are represented by outwash plains minor outwash fans and sinuous eskers extramarginal sediments were also registered and consist mainly of old sediments in wetlands or locally weathered bedrock eyjabakkajokull has behaved as a surge type glacier for 2200 years hence the mapped landforms originate from multiple surges landforms such as large glaciotectonic end moraines hummocky moraine long flutes crevasse fill ridges and concertina eskers are characteristic for surge type glaciers the surging glacier landsystem of eyjabakkajokull serves as a modern analog to the landsystems of terrestrial paleo ice streams

north atlantic warming and the retreat of greenland s outlet glaciers mass loss from the greenland ice sheet quadrupled over the past two decades contributing a quarter of the observed global sea level rise increased submarine melting is thought to have triggered the retreat of greenland s outlet glaciers which is partly responsible for the ice loss however the chain of events and physical processes remain elusive recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes multidecadal natural ocean variability and a long term increase in the north atlantic s upper ocean heat content since the 1950s all contributed to a warming of the subpolar north atlantic this led in conjunction with increased runoff to enhanced submarine glacier melting future climate projections raise the potential for continued increases in warming and ice mass loss with implications for sea level and climate

structural evolution triggers a dynamic reduction in active glacier length during rapid retreat evidence from falljokull se iceland over the past two decades iceland s glaciers have been undergoing a phase of accelerated retreat set against a backdrop of warmer summers and milder winters this paper demonstrates how the dynamics of a steep outlet glacier in maritime se iceland have changed as it adjusts to recent significant changes in mass balance geomorphological evidence from falljokull a high mass turnover temperate glacier clearly shows that between 1990 and 2004 the ice front was undergoing active retreat resulting in seasonal oscillations of its margin however in 2004 2006 this glacier crossed an important dynamic threshold and effectively reduced its active length by abandoning its lower reaches to passive retreat processes a combination of ice surface structural measurements with radar lidar and differential global navigation satellite systems data are used to show that the upper active section of falljokull is still flowing forward but has become detached from and is being thrust over its stagnant lower section the reduction in the active length of falljokull over the last several years has allowed it to rapidly reequilibrate to regional snowline rise in se iceland over the past two decades it is possible that other steep mountain glaciers around the world may respond in a similar way to significant changes in their mass balance rapidly adjusting their active length in response to recent atmospheric warming

a revised chronology of key vatnajokull iceland outlet glaciers during the little ice age glacier fluctuations from key vatnajokull outlets have been redated using tephrochronology coupled with two lichenometric techniques to ascertain the timing of the little ice age lia maximum in southeast iceland an updated tephrochronology for southeast iceland both the number of tephra layers present and their geochemical signatures indicates a lia maximum for both glaciers between ad 1755 and 1873 based on a population gradient approach lichenometrically dated moraines along the margins of skalafellsjokull and heinabergsjokull narrow this window to the early to mid 19th century respectively these revised chronologies in addition to emerging evidence from elsewhere in iceland support a late 18th to early 19th century lia glacier maximum in contrast the norwegian lia glacial maximum is strongly centred around ad 1750 this implies differing glaciological responses to secular shifts in the north atlantic oscillation such revisions to the vatnajokull record are crucial as accurately identifying the timing and delimiting the spatial extent of the icelandic lia glacier maximum will allow further light to be shed on glacier climate interactions in the north atlantic

push moraines and glacier contact fans in marine and terrestrial environments the local climatic regime and the mass balance state are important determinants of the dynamics of terrestrial and marine glacier fronts which in turn determine the sediments and landforms produced at the glacier front many modern glaciers undergoing overall retreat in areas of maritime climate produce winter push moraines during a late winter readvance followed by a summer retreat whilst in more continental regions no significant winter readvance occurs and annual push moraines are absent the frontal dynamics which lead to these changes are analysed and the form structure sequence and field relations of both terrestrial and marine push moraines are described from iceland spitsbergen and baffin island long term changes in mass balance leading to major glacier advances or readvances also generate large push moraines in terrestrial environments push moraine formation is accompanied by uplift rejuvenation and down cutting of outwash systems whose sediments become closely associated with glaciotectonic structures which permit pre syn and post tectonic sequences to be identified the development of ice marginal fan moraine complexes is modelled as a function of the relative magnitude of two parameters the velocity of ice movement and the calving rate a high ice velocity just exceeded by the calving rate gives closely spaced push moraines and confluent ice marginal fans a high velocity far exceeded by the calving rate produces closely spaced moraines but separate ice marginal fans a low ice velocity in combination with a high calving rate results in well separated and feebly developed push moraines while a low ice velocity and a low calving rate produces feeble push moraines and coalescent fans

what controls dead ice melting under different climate conditions a discussion abstract in the geological record hummocky dead ice moraines represent the final product of the melt out of dead ice processes and rates of dead ice melting in ice cored moraines and at debris covered glaciers are commonly believed to be governed by climate and debris cover properties here backwasting rates from 14 dead ice areas are assessed in relation to mean annual air temperature mean summer air temperature mean annual precipitation mean summer precipitation and annual sum of positive degree days the highest correlation was found between backwasting rate and mean annual air temperature however the correlation between melt rates and climate parameters is low stressing that processes and topography play a major role in governing the rates of backwasting the rates of backwasting from modern glacial environments should serve as input to de icing models for ancient dead ice areas in order to assess the mode and duration of deposition a challenge for future explorations of dead ice environments is to obtain long term records of field based monitoring of melt progression furthermore many modern satellite borne sensors have high potentials for recordings of multi temporal digital elevation models dems for detection and quantification of changes in dead ice environments in recent years high accuracy dems from airborne laser scanning altimetry lidar are emerging as an additional data source however time series of high resolution aerial photographs remain essential for both visual inspection and high resolution stereographic dem production

younger dryas glacial landsystems in north west scotland an assessment of modern analogues and palaeoclimatic implications abstract by explicitly linking process to form landsystem models developed in modern environments provide powerful tools for the reconstruction of past environments from the sedimentological and geomorphological record some landform characteristics however may originate by more than one process equifinality so although a particular depositional model may fit the data it is not necessarily the correct one here we critically examine the use of modern analogues to interpret glacial landforms focusing on hummocky moraine a distinctive landform association consisting of numerous sharp crested moraine mounds and ridge fragments which occurs on many valley floors in upland britain detailed studies of examples of younger dryas age in the north west highlands of scotland show that they represent ice contact fans which have been affected to varying degrees by ice push and subglacial deformation and that they formed at active oscillating ice margins the sedimentological data are inconsistent with an origin by englacial thrusting as has been proposed for similar moraines elsewhere in upland britain on the basis of morphological criteria comparison with modern glacial landsystems shows that although aspects of hummocky moraines in the study area have close modern counterparts none provides an exact analogue in all respects this may reflect the distinctive climate of western scotland during the younger dryas estimates of mean july temperatures in the younger dryas in scotland based on chironomid assemblages are c 8 c at sea level when combined with reconstructed equilibrium line altitudes for contemporaneous glaciers these estimates indicate mean annual precipitation totals in the range of 2358 337 mm yr 1 at sea level in nw scotland c 26 higher than present day values the implied heavy snowfall suggests that glaciers in western scotland during the younger dryas were of high activity type unlike modern glaciers in svalbard for example high glacier velocities and high winter precipitation would suppress permafrost development despite low mean annual temperatures the climatic environment also favoured rapid oscillations of glacier margins during both glacier build up and retreat phases climatic factors combined with the availability of large quantities of subglacial debris led to the development of distinctive glacial landsystems which may have no direct modern analogue

distributed mass balance and climate sensitivity modelling of engabreen norway department of geosciences university of oslo po box 1047 blindern no 0316 oslo norwayabstract assessing the impact of possible climate change on the water resources of glacierized areasrequires a reliable model of the climate glacier mass balance relationship in this study we simulate themass balance evolution of engabreen norway using a simple mass balance model based on dailytemperature and precipitation data from a nearby climate station ablation is calculated using adistributed temperature index method including potential direct solar radiation while accumulation isdistributed linearly with elevation the model was run for the period 1974 75 2001 02 for whichannual mass balance measurements and meteorological data are available parameter values weredetermined by a multi criteria validation including point measurements of mass balance mass balancegradients and specific mass balance the modelled results fit the observed mass balance well simplesensitivity experiments indicate a high sensitivity of the mass balance to temperature changes asexpected for maritime glaciers the results suggest further that the mass balance of engabreen is moresensitive to warming during summer than during winter while precipitation changes affect almostexclusively the winter balance

active drumlin field revealed at the margin of mulajokull iceland a surge type glacier abstract recent marginal retreat of mulajokull a surge type outlet glacier of hofsjokull iceland has revealed a drumlin fi eld consisting of more than 50 drumlins the drumlins are 90 320 m long 30 105 m wide 5 10 m in relief and composed of multiple beds of till deposited by lodgment and bed deformation the youngest till layer truncates the older units with an erosion surface that parallels the drumlin form thus the drumlins are built up and formed by a combination of subglacial depositional and erosional processes field evidence suggests each till bed to be associated with individual recent surges we consider the fi eld to be active in the sense that the drumlins are shaped by the current glacial regime the mulajokull fi eld is the only known active drumlin fi eld and is therefore a unique analogue to pleistocene drumlin fi elds

glacial landsystems of the southwest laurentide ice sheet modern icelandic analogues landform assemblages and associated stratigraphy sedimentology and structure are used in the reconstruction of palaeo ice sheet dynamics in alberta western canada interpretations are based upon the modern analogues from four outlet glaciers at the margins of vatnajokull and myrdalsjokull iceland in the area between lloydminster and lac la biche central alberta an extensive landform assemblage of megaflutings crevasse squeeze ridges and thrust block moraine arcs document the former surging of part of the margin of the laurentide ice sheet during later stages of recession this landform assemblage including numerous exposures of glacitectonised bedrock and quaternary sediments is comparable to the landsystem of the surging glaciers eyjabakkajokull and bruarjokull in iceland near high river southern alberta the former existence of an ice lobe characterised by active recession is recorded by closely spaced low amplitude recessional push moraines that drape tunnel valleys these are comparable in form and pattern to annual push moraines and fluted till surfaces produced by breidamerkurjokull and sandfellsjokull iceland and also include rimmed depressions produced by the escape of artesian water during ice marginal pushing this study provides interpretations of the regional glacial geomorphology of alberta based upon comparisons of form and stratigraphy with modern glacial analogues and provides an alternative to recent models which invoke large floods of subglacial meltwater to explain many of these same features implications for ice dynamics and regional till stratigraphies are discussed copyright 1999 john wiley sons ltd

geomorphology and the little ice age extent of the drangajokull ice cap nw iceland with focus on its three surge type outlets abstract detailed geomorphological maps from the forefields of three surging outlets of the drangajokull ice cap northwest iceland are presented the maps are based on field studies in 2011 2013 high resolution orthorectified aerial photographs recorded in 2005 2006 and airborne lidar data from 2011 the maps cover an area of about 40 60 km2 each furthermore we present an overview map that covers the area surrounding the drangajokull ice cap landforms and sediments were manually registered in a geographic information system esri arcgis 10 we mapped glacial landforms such as flutes ice sculpted bedrock hummocky moraine kame terraces and moraines fluvial landforms include outwash plains sandur pitted sandur and eskers in addition raised beaches were mapped the little ice age lia maximum extent of drangajokull and its outlet glaciers are fingerprinted by surficial till deposits and freshly glacially scoured bedrock sediments distal to the lia deposits were recorded and consist mainly of late weichselian and early holocene sediments and locally weathered bedrock periglacial activity is demonstrated by patterned ground mainly occurring on the 500 700 m high plateaux and three rock glaciers at least 3 4 surge events are described from each of the outlet glaciers occurring over the last three centuries in contrast to most other surge type outlets from icelandic ice caps the drangajokull outlets are confined within valleys which affect the forefield geomorphology glaciofluvial landforms moraines and a thin sheet of till with numerous boulders are characteristic for the forefields of the drangajokull outlets

till deposition by glacier submarginal incremental thickening macro and micro scale sedimentological analyses of recently deposited tills and complex push squeeze moraines on the forelands of icelandic glaciers and in a stacked till sequence at the former younger dryas margin of the loch lomond glacier lobe in scotland are used to assess the depositional processes involved in glacier submarginal emplacement of sediment where subglacial meltwater is unable to flush out subglacial sediment or construct thick debris rich basal ice by cumulative freeze on processes glacier submarginal processes are dictated by seasonal cycles of refreezing and melt out of tills advected from up ice by a combination of lodgement deformation and ice keel and clast ploughing although individual till layers may display typical a and b horizon deformation characteristics the spatially and temporally variable mosaic of subglacial processes will overprint sedimentary and structural signatures on till sequences to the extent that they would be almost impossible to classify genetically in the ancient sediment record at the macro scale icelandic tills display moderately strong clast fabrics that conform to the ice flow directions documented by surface flutings very strong fabrics typify unequivocally lodged clasts despite previous interpretations of these tills as subglacial deforming layers micro morphological analysis reveals that shearing played only a partial role in the emplacement of till matrixes and water escape and sediment flowage features are widespread a model of submarginal incremental thickening is presented as an explanation of these data involving till slab emplacement over several seasonal cycles each cycle involves 1 late summer subglacial lodgement bedrock and sediment plucking subglacial deformation and ice keel ploughing 2 early winter freeze on of subglacial sediment to the thin outer snout 3 late winter readvance and failure along a decollement plane within the till resulting in the carriage of till onto the proximal side of the previous year s push moraine 4 early summer melt out of the till slab initiating porewater migration water escape and sediment flow and extrusion repeated reworking of the thin end of submarginal till wedges produces overprinted strain signatures and clast pavements

synchronous retreat and acceleration of southeast greenland outlet glaciers 2000 06 ice dynamics and coupling to climate a large portion of the recent increase in the rate of mass loss from the greenland ice sheet is from increased outlet glacier discharge along its southeastern margin while previous investigations of the region s two largest glaciers suggest that acceleration is a dynamic response to thinning and retreat of the calving front it is unknown whether this mechanism can explain regional acceleration and what forcing is responsible for initiating rapid thinning and retreat we examine seasonal and interannual changes in ice front position surface elevation and flow speed for 32 glaciers along the southeastern coast between 2000 and 2006 while substantial seasonality in front position and speed is apparent nearly all the observed glaciers show net retreat thinning and acceleration with speed up corresponding to retreat the ratio of retreat to the along flow stress coupling length is proportional to the relative increase in speed consistent with typical ice flow and sliding laws this affirms that speed up results from loss of resistive stress at the front during retreat which leads to along flow stress transfer large retreats were often preceded by the formation of a flat or reverse sloped surface near the front indicating that subsequent retreats were influenced by the reversed bed slope many retreats began with an increase in thinning rates near the front in the summer of 2003 a year of record high coastal air and sea surface temperatures this anomaly was driven in part by recent warming suggesting that episodes of speed up and retreat may become more common in a warmer climate

correlation of late quaternary moraines impact of climate variability glacier response and chronological resolution abstract the last decade has seen a global surge in the number and resolution of well dated geomorphological reconstructions of mountain glacier fluctuations and former ice sheet extents this has been facilitated by the widespread deployment of large samples of terrestrial cosmogenic nuclide dating tcnd allowing more sophisticated probability analyses for reducing the statistical uncertainty of moraine ages and testing of correlations at local regional and hemispheric scales geochronological advances in the field laboratory and on model calibration have taken place in parallel with modelling of palaeoclimate based on glacier reconstructions and of glacier sensitivity to temperature and precipitation forcing in spite of these advances basic conceptual issues remain this review questions whether the technical leap forward in dating has encouraged us to over reach our interpretive limits particularly in terms of the concept and practice of correlation we propose that to enable reliable correlation glacier chronologies should first be examined for their climatic integrity spatial coherence and chronological robustness even with excellent dating interpretive complexity remains due to complex climate signals and glacier response characteristics and to erosion censoring of the landform record all are issues which must be addressed to avoid either spurious lumping correlation or splitting differentiation of glacier chronologies and thus misinterpretation of the climatic significance of reconstructed glacier advances we suggest that the reliability of correlation is no better than the weakest link in the chain of reasoning which connects climatic fluctuations with dated landforms and sediments improved dating means that poor chronological resolution is less likely to be the limiting factor for correlation but shifts the focus onto other less quantifiable sources of uncertainty these conceptual statements are exemplified with reference to holocene glacial chronologies of contrasting mid latitude environments in southern norway iceland and new zealand

contributions and unrealized potential contributions of cosmogenic nuclide exposure dating to glacier chronology 1990 2010 abstract this paper reviews the application of cosmogenic nuclide exposure dating to glacier chronology exposure dating of glacial landforms has made an outsize impact on this field because the technique filled an obvious need that had already been recognized by glacial geologists by now hundreds of studies have used cosmogenic nuclide exposure dating to date glacial deposits and in fact it is rare to find a study of glacial geology or glacier chronology or any paleoclimate synthesis that makes use of such studies that does not involve exposure dating these developments have resulted in major contributions to glacier chronology and paleoclimate in particular i reconstructing antarctic ice sheet change ii establishing the chronology of late pleistocene and holocene glacier change in mountain regions where it was previously unknown iii establishing the broad chronological outlines of mountain glaciations prior to the last glacial maximum and iv gaining insight into subglacial erosional processes through the observation that many glaciated surfaces preserve cosmogenic nuclide inventories from long past ice free periods as well as the present one an important potential future contribution will be the application of the large data set of exposure dated glacier chronologies to better understand global and regional climate dynamics during lateglacial and holocene millennial scale climate changes however this contribution cannot be realized without significant progress in two areas i understanding and accounting for geologic processes that cause apparent exposure ages on glacial landforms to differ from the true age of the landform and ii minimizing systematic uncertainties in exposure ages that stem from cosmogenic nuclide production rate estimates and scaling schemes at present there exists an enormous data set of exposure ages on glacial deposits but these data cannot be used to their full potential in paleoclimate syntheses due to an inadequate understanding of geologic scatter and production rate uncertainties the intent of this paper is to highlight this situation and suggest some strategies for realizing this potential

hylaeosaurus polacanthus and the systematics and stratigraphy of wealden armoured dinosaurs two genera of armoured dinosaurs ankylosauria are present in the lower cretaceous wealden beds of england polacanthus owencan be distinguished from hylaeosaurus mantell on the basis of significant differences in the pectoral girdle hindlimb and dermal armour a comprehensive review of the dinosaurs from the wealden series of england and contemporary basins of western europe adds further evidence of a biologicalseparation between lower wealden hastings beds containing hylaeosaurusarmatus and upper wealden faunas wealden group of the isle of wight containing polacanthus foxii and nearly equivalent units in belgium france germany and spain

the active temperate glacial landsystem a model based on breiðamerkurjokull and fjallsjokull iceland accurate interpretations of ancient glaciated terrains rely heavily on our knowledge of process form relationships in contemporary glacierized basins a landsystems model for temperate actively receding glaciers is presented based upon brei amerkurjokull and fjallsjokull iceland historical documentation maps and or aerial photography documenting recession since 1903 provide a unique series of snapshots of the evolving glacial geomorphology at these snouts this documentation is employed in association with sedimentological investigations to assess the evolution of sediment landform assemblages at active temperate glacier margins using the wealth of geomorphological and sedimentological information produced during the recent recession of brei amerkurjokull and fjallsjokull three depositional domains are recognized 1 areas of extensive low amplitude marginal dump push and squeeze moraines derived largely from material on the glacier foreland and often recording annual recession of active ice 2 incised and terraced glacifluvial forms such as recessional ice contact fans and hochsandur fans and simple and complex anabranched eskers and small areas of pitted outwash 3 subglacial landform assemblages of flutes drumlins and overridden push moraines located between ice marginal glacifluvial depo centres the lack of supraglacial sediment in active temperate glaciers like brei amerkurjokull and fjallsjokull generally precludes the widespread development of chaotic hummocky moraine the hummocky terrain previously termed kame and kettle topography has mostly evolved by melt out into a complex network of anabranched eskers over the period 1945 1998 or actually comprises pitted or kettled outwash sandar the tills across the foreland were emplaced by subglacial deformation and lodgement and comprise materials derived from pre existing stratified sediments in addition to localized abrasion of rock surfaces and patches of lake sediments till sequences thicker than 2 m have been constructed by the sequential plastering of till layers onto stratified sediments and bedrock because this stacking is a sub marginal process it is suggested that complex till sequences similar to those observed at brei amerkurjokull fjallsjokull may be employed in the reconstruction of ancient glacier margins additionally the geomorphology of the active temperate landsystem at east brei amerkurjokull may contain subtle surge signatures verifying the historical record of small surges by this part of the glacier this illustrates the danger of employing landform sediment associations from restricted study areas e g parts of landsystems as representative process form models for glaciated terrains

the drumlin field and the geomorphology of the mulajokull surge type glacier central iceland article i nfo herewe presenta newgeomorphological mapof the active drumlin field and theforefieldof mulajokull a surge type outlet glacier iceland the map is based on aerial photographs taken in 1995 and lidar data recorded in 2008 mapping was done using arcgis 10 software on orthorectified imagery lidar data and digital elevation models the mapped landforms were initially identified on the aerial imagery and lidar and then ground checked in the field we mapped subglacial supraglacial ice marginal periglacial and glaciofluvial landforms the geomorphology of the mulajokull forefield is similar to that of the forefields of other surge type glaciers in iceland with a highly streamlined forefield crevasse fill ridges and series of glaciotectonic end moraines how ever thelargenumber i e 110 of drumlinsformingthe drumlin fieldisuniqueformodernicelandicsurge type glaciersand as yet unique for contemporary glaciersingeneral also apparent isthat thedrumlins are widerand shorter in the distal part of the drumlin field and narrower and longer in the proximal part hence the mapping reveals a development of the drumlins toward a more streamlined shape of the proximal landforms that have experienced more surges the drumlins in the drumlin field are active i e they form during the modern surges of mulajokull

fluted moraine formation and till genesis below a temperate valley glacier slettmarkbreen jotunheimen southern norway clast fabric and morphological data have been used to determine the origin of fluted subglacial tills exposed by recent retreat of the slettmarkbreen glacier norway a new method for the interpretation of clast fabric data allows aspects of the strain and depositional history of the till to be reconstructed the till formed by a combination of lodgement and subsole deformation by slip along discrete shear planes lodgement was dominant for the larger size fractions 125 mm while the smaller material was more susceptible to deformation the fluted till surface reflects the tendency for the till matrix to deform into regions of low confining pressure in the lee of lodged boulders downglacier components of till flow are thought to have resulted in significant sediment transfer towards the margin

glacial geomorphology of terrestrial terminating fast flow lobes ice stream margins in the southwest laurentide ice sheet glacial geomorphological mapping of southern alberta canada reveals landform assemblages that are diagnostic of terrestrial terminating ice streams fast flowing outlet glaciers with lobate snouts spatial variability in features that comprise the landform assemblages reflects changes in a palaeo ice stream activity switch on off and b snout basal thermal regimes associated with climate sensitive steady state flow palaeo ice stream tracks reveal distinct inset sequences of fan shaped flowsets indicative of receding lobate ice stream margins former ice lobe margins are demarcated by a major often glacially overridden transverse moraine ridges commonly comprising glacitectonically thrust bedrock and b minor closely spaced recessional push moraines and hummocky moraine arcs details of these landform types are well exhibited around the former southern margins of the central alberta ice stream where larger scale more intensive mapping identifies a complex glacial geomorphology comprising minor transverse ridges mtr types 1 3 hummocky terrain ht types 1 3 flutings and meltwater channels spillways the mtr type 1 constitute the summit corrugation patterns of glacitectonic thrust moraines or major transverse ridges and have been glacially overrun and moderately streamlined the mtr type 2 sequences are recessional push moraines similar to those developing at modern active temperate glacier snouts the mtr type 3 document moraine construction by incremental stagnation because they occur in association with hummocky terrain the close association of hummocky terrain with push moraine assemblages indicates that they are the products of supraglacial controlled deposition on a polythermal ice sheet margin where the ht type 3 hummocks represent former ice walled lake plains the ice sheet marginal thermal regime switches indicated by the spatially variable landform assemblages in southern alberta are consistent with palaeoglaciological reconstructions proposed for other ice stream fast flow lobes of the southern laurentide ice sheet where alternate cold polythermal and temperate marginal conditions associated with climate sensitive steady state flow sequentially gave way to more dynamic streaming and surging activity

annual push moraines as climate proxy 1 we reconstruct the terminus position of a mountain glacier in british columbia canada from annual push moraines formed between 1959 and 2007 our reconstruction represents the longest annually resolved record of length change for a north american glacier comparison of annual recession with climate records indicates that glacier recession is controlled by air temperatures during the ablation season and accumulation season precipitation during the previous decade analysis among records of glacier frontal variation and mass balance in western north america similarly reveals an immediate terminus reaction to summer and net balance and a delayed reaction to winter and net balance other mountain ranges may contain long series of push moraines that could be exploited as climate proxies and to improve understanding of glacier response to climate

decline of subpolar north atlantic circulation during the 1990s observations of sea surface height reveal that substantial changes have occurred over the past decade in the mid to high latitude north atlantic ocean topex poseidon altimeter data show that subpolar sea surface height increased during the 1990s and the geostrophic velocity derived from altimeter data exhibits declining subpolar gyre circulation combining the data from earlier satellites we find that subpolar circulation may have been weaker in the late 1990s than in the late 1970s and 1980s direct current meter observations in the boundary current of the labrador sea support the weakening circulation trend of the 1990s and together with hydrographic data show that the mid to late 1990s decline extends deep in the water column analysis of the local surface forcing suggests that the 1990s buoyancy forcing has a dynamic effect consistent with altimetric and hydrographic observations a weak thermohaline forcing allows the decay of the domed structure of subpolar isopycnals and weakening of circulation

probability of moraine survival in a succession of glacial advances emplacement of glacial moraines normally results in obliteration of any older moraines deposited by less extensive glacial advances a process we call obliterative overlap a probability analysis of the likely impact of obliterative overlap on the completeness of the glacial record assumes that moraines were deposited at various distances from their glacial source areas randomly over time assuming randomness and obliterative overlap after 10 glacial episodes the most likely number of surviving moraines is only three the record of the pleistocene is in agreement with the probability analysis the 10 glaciations during the past 0 9 m y inferred from the deep sea record resulted in moraine sequences in which only two or three different aged moraine belts can generally be distinguished

heat budget in the north atlantic subpolar gyre impacts of atmospheric weather regimes on the 1995 warming event abstract in the mid 1990s the north atlantic subpolar gyre has shown a dramatic warming event that has been thoroughly investigated from observations and numerical simulations some studies suggest that it was due to an interannual wind driven weakening and shrinking of the gyre that facilitated the penetration of warm atlantic water the weakening of the gyre being attributed to changes in the north atlantic oscillation nao and in the east atlantic pattern which are the two dominant modes of atmospheric variability in the north atlantic however other studies suggest that the warming event was due to a decadal buoyancy driven strengthening of the meridional overturning circulation and subsequent intensification of the poleward heat transport in response to the positive nao conditions of 1988 1995 to reconcile this discrepancy the heat budget in the north atlantic subpolar gyre is reconstructed from four ocean hindcast simulations sharing the same modelling platform but using different settings the novelty of this work is the decomposition of the subpolar gyre into a western and an eastern subregion which is motivated by water mass distribution around reykjanes ridge and by the fact that deep convection only occurs in the western subpolar gyre in the western subpolar gyre the 1995 warming event is the decadal baroclinic ocean response to positive nao conditions from 1988 to 1995 the latter induced increased surface heat loss in the labrador sea that intensified deep convection hence strengthened the meridional overturning circulation and the associated poleward heat transport in the eastern subregion a concomittant warming is induced by an interannual barotropic adjustment of the gyre circulation to an abrupt switch from positive nao conditions in winter 1995 to negative nao conditions in winter 1996 indeed the gyre response to negative nao conditions is a cyclonic intergyre gyre that increases northward volume and heat transports at the southeastern limit of the subpolar gyre therefore the discrepancies found in the literature about the 1995 warming event of the north atlantic subpolar gyre are reconciled in the present work which suggests that the atmospheric drivers the mechanisms at stake and the associated timescales are different to the east and to the west of reykjanes ridge

a revised approach to discriminating sediment transport histories in glacigenic sediments in a temperate alpine environment a case study from fox glacier new zealand clast shape measurements have developed into a standard method for reconstructing the transport histories of sediments in glacial environments the majority of studies use the ra c40 covariance approach with some researchers routinely including clasts of varying lithologies within their samples the corollary is that variable lithological properties may control clast form and roundness rather than debris transport mechanisms despite this the role of lithology on clast shape in glacial environments has rarely been analysed furthermore some studies have reported difficulties in using the ra c40 co variance plot in discriminating clasts that have undergone subglacial transport and clasts that have been modified by fluvial activity results from a glacierized valley in a temperate alpine setting indicate that detailed analysis of clast shape where samples are of uniform lithology although time consuming is a useful tool in the investigation of deposits in glaciated environments copyright 2012 john wiley sons ltd

simulation of the evolution of breidamerkurjokull in the late holocene 1 we have simulated the advance and retreat of breidamerkurjokull a tidewater glacier in iceland by means of a one dimensional numerical ice flow model the calculations were done with two different schemes for iceberg calving the flotation model and the water depth model the model simulates the glacier history by an advance into a lake filled by unlithified sediments without the occurrence of calving followed by a retreat with calving into the excavated lake the results indicate that the flotation model is not capable of producing the observed glacier retreat into deep water well whereas the water depth model provides a glacier evolution similar to the observed retreat the water depth model predicts that breidamerkurjokull will retreat out of the lake after approximately 100 years under the present climatic conditions

lateglacial surface exposure dating in the monadhliath mountains central highlands scotland we constrain the deglaciation history of the monadhliath mountains since the last glacial maximum using glacial geomorphology and surface exposure dating collectively these data clarify the glacial history of the monadhliath mountains at the close of the devensian cold period 10be exposure ages indicate deglaciation of the last devensian ice sheet at 15 1 1 4 ka at ca 640 m od the exposure ages are consistent with basal radiocarbon ages from nearby loch etteridge 5 km to the south east 15 3 0 2 kcal bp1 boulders from moraines in three monadhliath corries yielded exposure ages between 11 8 ka and 9 8 ka 470 600 m od suggesting that a lateglacial advance occurred during the younger dryas stadial the limited extent of these younger dryas glaciers in the monadhliath mountains results from the combined effect of a drier climate experienced in the eastern part of the central highlands ice cap and topographical factors our reconstruction largely supports the deglaciation model of golledge et al 2008 and confirms that a sw to ne precipitation gradient dominated scotland during the younger dryas

influence of the atlantic subpolar gyre on the thermohaline circulation during the past decade record high salinities have been observed in the atlantic inflow to the nordic seas and the arctic ocean which feeds the north atlantic thermohaline circulation thc this may counteract the observed long term increase in freshwater supply to the area and tend to stabilize the north atlantic thc here we show that the salinity of the atlantic inflow is tightly linked to the dynamics of the north atlantic subpolar gyre circulation therefore when assessing the future of the north atlantic thc it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account

lichenometric dating science or pseudo science the popular technique of estimating ages of deposits from sizes of lichens continues despite valid criticism and without agreement on range of utility treatment of error and methods of measurement sampling and data handling a major source of error is the assumption that the largest lichen s colonized soon after deposition and will survive indefinitely recent studies on lichen mortality suggest that this assumption is untenable meanwhile the use of growth curves constructed from independently dated substrates is problematic for many reasons but this has not prevented the publication of baseless claims of accuracy and ages that are extrapolated well beyond data experiments indicate that numeric lichenometric ages are not reliable and in general do not advance the cause of quaternary science there are a few studies suggesting reliability and indeed there may be cases where lichens and growth curves actually provide realistic numerical ages but it cannot be foretold which lichen assemblages will provide good ages and which bad ages the logical conclusion is that no assumption of good ages can be made and that it is folly to assign numerical ages to a deposit on the basis of lichen sizes

sorted circles relative age dating and palaeoenvironmental reconstruction in an alpine periglacial environment eastern jotunheimen norway lichenometric and weathering based approaches lichenometric and weathering based techniques are employed in an investigation of the chronology of large scale sorted circles in jotunheimen southern norway comparison of diameter measurements of rhizocarpon geographicum agg with local growth curves and size frequency analysis of lichen population data indicate that all the sorted circles originated prior to the mid eighteenth century little ice age maximum parts of the circle borders appear to have been stable since before the twelfth century although minor disturbances to border clasts were widespread between about ad 1640 and 1740 large proportions of the smaller surface clasts in circle centres have stabilized only since the little ice age maximum the thickness of surface weathering rinds and measurements of rock surface hardness r values obtained using a schmidt hammer indicate long periods of clast exposure in circle borders at least 1500 years at some sites and shorter exposure times for central clasts despite difficulties in inf

a review of the holocene environmental history of iceland abstract the purpose of this paper is to review the present knowledge of the holocene environmental history of iceland focusing on glacier fluctuations the ideas of the holocene being a relatively flat epoch in terms of environmental changes have been superseded by new studies reflecting active fluctuations the present paper promotes a revised model of the holocene glacier fluctuation history of iceland and recognises a long period of neoglaciation present data suggests an onset of glacier expansion in iceland around 5 ka bp which can be roughly correlated between different parts of the country and coincides with wider environmental changes specific glacier advances have been bracketed to 5 4 5 ka bp ca 4 2 ka bp ca 3 ka bp 2 ka bp and 1 5 1 2 ka bp during the little ice age lia glaciers in iceland begun to advance in the late 18th century and were biggest in the late 19th century

holocene and latest pleistocene climate and glacier fluctuations in iceland abstract multiproxy climate records from iceland document complex changes in terrestrial climate and glacier fluctuations through the holocene revealing some coherent patterns of change as well as significant spatial variability most studies on the last glacial maximum and subsequent deglaciation reveal a dynamic iceland ice sheet iis that responded abruptly to changes in ocean currents and sea level the iis broke up catastrophically around 15 ka as the polar front migrated northward and sea level rose indications of regional advance or halt of the glaciers are seen in late allerod early younger dryas time and again in preboreal time due to the apparent rise of relative sea level in iceland during this time most sites contain evidence for fluctuating tidewater glacier termini occupying paleo fjords and bays the time between the end of the younger dryas and the preboreal was characterized by repeated jokulhlaups that eroded glacial deposits by 10 3 ka the main ice sheet was in rapid retreat across the highlands of iceland the holocene thermal maximum htm was reached after 8 ka with land temperatures estimated to be 3 c higher than the 1961 1990 reference and net precipitation similar to modern such temperatures imply largely ice free conditions across iceland in the early to mid holocene several marine and lacustrine sediment climate proxies record substantial summer temperature depression between 8 5 and 8 ka but no moraines have been detected from that time termination of the htm and onset of neoglacial cooling took place sometime after 6 ka with increased glacier activity between 4 5 and 4 0 ka intensifying between 3 0 and 2 5 ka although a distinct warming during the medieval warm period is not dramatically apparent in icelandic records the interval from ca ad 0 to 1200 is commonly characterized by relative stability with slow rates of change the literature most commonly describes little ice age moraines ca ad 1250 1900 as representing the most extensive ice margins since early holocene deglaciation with temperature depressions of 1 2 c compared to the ad 1961 1990 average steep north south and west east temperature gradients are reconstructed in the holocene records of iceland suggesting a strong maritime influence on the terrestrial climate of iceland

sedimentary and tectonic architecture of a large push moraine a case study from hagafellsjokull eystri iceland original article can be found at http www sciencedirect com science journal 00370738 copyright elsevier b v full text of this article is not available in the uhra

a comparison of the lichenometric and schmidt hammer dating techniques based on data from the proglacial areas of some icelandic glaciers abstract measurements of rhizocarpon section and schmidt hammer r values are reported from the proglacial geomorphic features on the forelands of the icelandic glaciers of kviarjokull holarjokull and heinabergsjokull oraefi and south vatnajokull sandfellsjokull and oldufellsjokull east m rdalsjokull and bruarjokull eyjabakkajokull and west snaefell north vatnajokull these data are used in reconstructions of patterns of glacier recession since the little ice age maximum and the geomorphic signals of climatic versus non climatic events are discussed age control was obtained from various dated substrates by utilizing historical accounts aerial photographs and grave stones three lichen growth rates are calculated a 0 51 mm a 1 corrected to 0 50 mm a 1 with a colonization lag time of

the 1890 surge end moraine at eyjabakkajokull iceland a re assessment of a classic glaciotectonic locality abstract the glaciotectonic architecture and sequential evolution of the eyjabakkajokull 1890 surge end moraines in iceland were studied for understanding better the formation and evolution of glaciotectonic end moraines and their relation to glacier dynamics based on morphological geological and geophysical data from terrain cross profiles cross sections and ground penetrating radar profiles we demonstrate that three different qualitative and conceptual models are required to explain the genesis of the eyjabakkajokull moraines firstly a narrow single crested moraine ridge at the distal end of a marginal sediment wedge formed in response to decoupling of the subglacial sediment from the bedrock and associated downglacier sediment transport secondly large lobate end moraine ridges with multiple closely spaced narrow asymmetric crests formed by proglacial piggy back thrusting thirdly a new model shows that moraine ridges with different morphologies may reflect different members of an end moraine continuum this is true for the eastern and western parts of the eyjabakkajokull moraines as they show similar morphological and structural styles which developed to different degrees the former represents an intermediate member with decollement at 4 5 m depth and 27 33 shortening through multiple open anticlines that are reflected as moderately spaced symmetric crests on the surface the latter represents an end member with decollement at about 27 m depth and 39 horizontal shortening through multiple high amplitude overturned and overthrusted anticlines appearing as broadly spaced symmetric crests we propose that the opposite end member would be a moraine of multiple symmetric wide open anticlinal crests of low amplitude our data suggest that the glacier coupled to the foreland to initiate the end moraine formation when it had surged to within 70 190 m of its terminal position this indicates a time frame of 2 6 days for the formation of the end moraines

sediment deformation beneath glaciers and its coupling to the subglacial hydraulic system abstract the extent and style of shear deformation in sediments beneath modern glaciers and the geological evidence for such deformation in deposited sediments are reviewed new evidence is presented from beneath a modern glacier of the spatial and temporal patterns of water pressure fluctuation and of time dependent patterns of deformation in sediments it is concluded that in most experimental sites beneath soft bedded modern glaciers deformation is a significant or major contributor to glacier movement and the resultant discharge of till is large enough to make sediment deformation a major till forming process particular modes of deformation facilitate incorporation of underlying material into the till whilst the capacity of a deforming till to absorb strain can protect the underlying strata from deformation leading to the commonly found relationship where till overlies other strata with a sharp planar interface it is argued that the almost ubiquitous occurrence of drumlins on the beds of former ice sheets is a reflection of the widespread occurrence of sediment deformation beneath them with important implications for the coupling of ice sheet flow and bed properties it is argued that the mechanical behaviour of the subglacial system is not simply determined by till properties but largely controlled by the subglacial water pressure regime determined by the nature of subglacial drainage results of field experiments show how the nature of the basal hydraulic system can play a vital role in controlling the coupling between the glacier and till deformation processes they show that rapid glacier advances can produce undrained loading of sediments that effective pressure may increase either upwards or downwards in a till according to the direction of drainage and that interstitial water pressures in subglacial sediments can show large and rapid variations producing strong variations in the rate and distribution of strain and in the partitioning of basal movement between sliding and deformation

in situ cosmogenic exposure ages from the isle of skye northwest scotland implications for the timing of deglaciation and readvance from 15 to 11 ka we present 10 in situ cosmogenic exposure ages from two moraines on the isle of skye the strollamus medial moraine was deposited during deglaciation of the devensian ice sheet and yields a mean exposure age from five samples of 14 3 0 9 ka the moraine age indicates that a significant ice mass existed on skye at the time of a regional readvance recorded in wester ross northwest scotland taken at face value the ages suggest that deglaciation did not occur until well into greenland interstade 1 the slapin moraine represents the local limit of the loch lomond readvance llr and yields a mean exposure age from five samples of 11 5 0 7 ka which is consistent with deposition relating to the llr these ages suggest that the maximum extent may have been reached late in the stadial and that some glaciers may have remained active until after the climatic amelioration that marks its end this scenario is considered unlikely given the nature of the climate during this period which leads us to call for a locally calibrated production rate copyright 2011 john wiley sons ltd

formation of mega scale glacial lineations on the dubawnt lake ice stream bed 1 size shape and spacing from a large remote sensing dataset abstract mega scale glacial lineations msgls are the largest flow parallel bedforms produced by ice sheets and are formed beneath rapidly flowing ice streams knowledge of their characteristics and genesis is likely to result in an improved understanding of the rate at which ice and sediment are discharged by ice sheets but there is little consensus as to how they are formed and there are few quantitative datasets of their characteristics with which to formulate or test hypotheses this paper presents the results of a remote sensing survey of 46 000 bedforms on the dubawnt lake palaeo ice stream bed focussing on a central transect of 17 038 that includes highly elongate bedforms previously described as msgls within this transect lineations exceed 10 km in length max 20 km and 23 have elongation ratios 10 1 max 149 1 highly elongate features are interspersed with much shorter drumlin like features but longer bedforms are typically narrower suggesting that their length develops more quickly than or at the expense of their width bedforms are broadly symmetrical in plan form and have a preferred lateral spacing of 50 250 m which implies a regular rather than random pattern of corrugations comparison with drumlins reveals that the more attenuated msgls simply extend the tail of the distribution of data rather than plotting as a separate population taken together this supports the idea of a subglacial bedform continuum primarily controlled by ice velocity but existing hypotheses of msgl formation are either not supported or are insufficiently developed to explain our observations rather we conclude that under conditions of rapid ice flow msgls attain their great length relatively quickly decades through a probable combination of subglacial deformation which attenuates ridges and erosional processes that removes material from between them

de icing progression of ice cored moraines in a humid subpolar climate kotlujokull iceland modes and rates of de icing ice cored moraines under humid subpolar conditions have been determ ined for two dead ice fields of different age representing a mature and a final stage of collapse in the kotlujokull terminus region south iceland the melting processes considered are backwasting defined as the lateral retreat of near vertical ice walls or steep ice cored slopes and downwasting defined as the thinning of the ice core by melting along the top and bottom surfaces in the mature stage of collapse where there is less than 1 m of sediment cover major faces of ice exposed for rapid melting are ordinarily significant and long lived due to intense precipitation in this fully ice cored terrain the predominating processes are backwasting of exposed ice walls and downwasting by bottom melt each contributing to the annual surface lowering of about 0 5 m or 35 the total annual surface lowering melt rate due to all processes averages 1 4 m in those parts of the fully ice cored dead ice field

subglacial till formation sedimentary characteristics and classification we review the major subglacial till forming processes as presently understood by glacial researchers and define the parameters within which tills are produced and reconcile them with sedimentary end members processes of deformation flow sliding lodgement and ploughing coexist at the base of temperate glacier ice and act to mobilize and transport sediment and deposit it as various end members ranging from glacitectonically folded and faulted stratified material to texturally homogeneous diamicton the dominance of any one subglacial process varies both spatially and temporally giving rise to the possibility that a till or complex till sequence contains a superimposed signature of former transportation deposition at the ice bed interface we recommend that while glacial geologists and geomorphologists should be able to recognize the sedimentary imprints of various subglacial processes genetic fingerprinting of subglacial tills should be less process specific and till classification must reflect the range of products encompassed by the subglacial till production continuum glacial geologists can presently unequivocally identify a glacitectonite rock or sediment that has been deformed by subglacial shearing deformation but retains some of the structural characteristics of the parent material b subglacial traction till sediment deposited by a glacier sole either sliding over and or deforming its bed the sediment having been released directly from the ice by pressure melting and or liberated from the substrate and then disaggregated and completely or largely homogenised by shearing and support the theoretical case for c melt out till sediment released by the melting of stagnant or slowly moving debris rich glacier ice and directly deposited without subsequent transport or deformation because observations on contemporary glaciers reveal that their beds are most likely to be mosaics of deformation and sliding and warm based and cold based conditions the patterns of which change temporally and spatially it is extremely unlikely that subglacial till end members in the geological record will be anything but hybrids produced by the range of processes operative in the subglacial traction zone

a review of topographic controls on moraine distribution ice marginal moraines are often used to reconstruct the dimensions of former ice masses which are then used as proxies for palaeoclimate this approach relies on the assumption that the distribution of moraines in the modern landscape is an accurate reflection of former ice margin positions during climatically controlled periods of ice margin stability however the validity of this assumption is open to question as a number of additional nonclimatic factors are known to influence moraine distribution this review considers the role played by topography in this process with specific focus on moraine formation preservation and ease of identification topoclimatic controls are not considered published literature indicates that the importance of topography in regulating moraine distribution varies spatially temporally and as a function of the ice mass type responsible for moraine deposition in particular in the case of ice sheets and ice caps 1000 km2 one potentially important topographic control on where in a landscape moraines are deposited is erosional feedback whereby subglacial erosion causes ice masses to become less extensive over successive glacial cycles for the marine terminating outlets of such ice masses fjord geometry also exerts a strong control on where moraines are deposited promoting their deposition in proximity to valley narrowings bends bifurcations where basins are shallow and or in the vicinity of topographic bumps moraines formed at the margins of ice sheets and ice caps are likely to be large and readily identifiable in the modern landscape in the case of icefields and valley glaciers 10 1000 km2 erosional feedback may well play some role in regulating where moraines are deposited but other factors including variations in accumulation area topography and the propensity for moraines to form at topographic pinning points are also likely to be important this is particularly relevant where land terminating glaciers extend into piedmont zones unconfined plains adjacent to mountain ranges where large and readily identifiable moraines can be deposited in the case of cirque glaciers 10 km2 erosional feedback is less important but factors such as topographic controls on the accumulation of redistributed snow and ice and the availability of surface debris regulate glacier dimensions and thereby determine where moraines are deposited in such cases moraines are likely to be small and particularly susceptible to post depositional modification sometimes making them difficult to identify in the modern landscape based on this review we suggest that despite often being difficult to identify quantify and mitigate topographic controls on moraine distribution should be explicitly considered when reconstructing the dimensions of palaeoglaciers and that moraines should be judiciously chosen before being used as indirect proxies for palaeoclimate i e palaeoclimatic inferences should only be drawn from moraines when topographic controls on moraine distribution are considered insignificant

reconstructing the transport history of glacigenic sediments a new approach based on the co variance of clast form indices abstract two indices are used to describe the aggregate shape and roundness characteristics of glacially transported clasts the c40 index the percentage of clasts with c a ratios 0 4 and the ra index the percentage of very angular and angular clasts in a sample analysis of the between and within sample co variance of these indices provides a powerful tool for discriminating actively and passively transported clasts in glacigenic deposits use of these indices is illustrated in an analysis of the form characteristics of clasts from lateral and frontal moraines at storbreen jotunheimen these fall between those of actively transported clasts in basal till low c40 and ra values and those of unmodified frost weathered clasts high c40 and ra values both indices decline down moraine within sample analyses of clast shape demonstrates that these aggregate clast form gradients reflect changes in the relative proportions of actively and passively transported debris on the moraines rather than progressive modification of actively transported clasts these analyses also indicate that actively transported clasts form the dominant component of the moraines particularly near the former glacier terminus further applications of the approach developed here are suggested

an aerial view of 80 years of climate related glacier fluctuations in southeast greenland both marine and land terminating glaciers in southeast greenland have experienced dramatic recent retreat an 80 year record of historical aerial photographs and satellite imagery shows that many land terminating glaciers in this region retreated more rapidly in the 1930s than today whereas marine terminating glaciers have retreated faster in the 2000s

response of the north atlantic subpolar gyre to persistent north atlantic oscillation like forcing the response of the north atlantic subpolar gyre spg to a persistent positive or negative phase of the north atlantic oscillation nao is investigated using an ocean general circulation model forced with idealized atmospheric reanalysis fields the integrations are analyzed with reference to a base line integration for which the model is forced with idealized fields representing a neutral state of the nao in the positive nao case the results suggest that the well known cooling and strengthening of the spg are after about 10 years replaced by a warming and subsequent weakening of the spg the latter changes are caused by the advection of warm water from the subtropical gyre stg region driven by a spin up of the atlantic meridional overturning circulation amoc and the effect of an anomalous wind stress curl in the northeastern north atlantic which counteracts the local buoyancy forcing of the spg in the negative nao case however the spg response does not involve a sign reversal but rather shows a gradual weakening throughout the integration the asymmetric spg response to the sign of persistent nao like forcing and the different time scales involved demonstrate strong non linearity in the north atlantic ocean circulation response to atmospheric forcing the latter finding indicates that analysis based on the arithmetic difference between the two nao states e g nao minus nao may hide important aspects of the ocean response to atmospheric forcing