evolution of a surge type glacier in its quiescent phase kongsvegen spitsbergen 1964 95 kongsyegen is a 102 km 2 sub polar polythermal surge type glacier in northwest spitsbergen svalbard it surged just before 1948 and is currently in its quiescent phase measurements of surface geometry since 1966 show a retreat of the front and strong thinning of up to 75 m in the ablation area and a build up of up to 32 m in the accumulation area present day annual velocities along the glacier are low from 1 4 up to 3 6 m a 1 the measured mean net balance for the period 1987 94 and the balance reconstructed back to 1967 show a weak positive balance of about 0 1 m w e the measured actual ice flux is low and the mass transfer down glacier at the ela is only about 3 20 of that required for steady state thus the glacier is building up towards a new surge the total thickening rate on kongsvegen is somewhat higher than in other cases from svalbard but it is small compared with other well studied surge type glaciers in alaska and he pamirs this relatively low rate of change is a function of the low accumulation rate and the relatively cold climate compared to other areas and is common for surge type glaciers in svalbard

late surge glacial conditions on bakaninbreen svalbard and implications for surge termination 1 bakaninbreen is a polythermal glacier in southern spitsbergen svalbard that last surged between 1985 and 1995 seismic reflection data were acquired during early quiescence in spring 1998 just upstream of the surge front the results were combined with complementary ground penetrating radar data to investigate the glacial structure and basal conditions we find no difference between the ice thickness values determined from the seismic and radar methods suggesting that any layer of basal ice cannot be greater than 5 m thick interpretation of the amplitude of the seismic reflections indicates the presence of permafrost close to the glacier base a thin layer of thawed deforming sediment separates the glacier from this underlying permafrost in an area just upstream of the surge front the permafrost becomes discontinuous and may even be absent the ice being underlain by 10 15 m of thawed sediments overlying deeper bedrock high pressure water is believed to have been required to maintain the propagation of the surge and this area of thawed sediment is interpreted as a route for that water to escape from the basal system when the surge front passed over this thawed bed the escaping water reduced the pressure in the subglacial hydraulic system initiating the termination of the surge surge termination was therefore primarily controlled by the presurge permafrost distribution beneath the glacier rather than any feature of the surge itself this termination mechanism is probably limited to surges in polythermal glaciers but the techniques used may have wider glaciological applications

lower and middle ordovician chitinozoans from honghuayuan south china biodiversity patterns and response to environmental changes abstract a complete chitinozoan succession through the uppermost tremadocian to lower darriwilian lower and middle ordovician at honghuayuan northern guizhou province in south china was systematically studied and 47 species of 14 genera were identified two chitinozoan biodiversity acmes were recognized which occur in the lower part of the acrograptus filiformis uppermost hunghuayuan formation and middle part of the azygograptus suecicus middle member of the meitan formation graptolite biozones in the upper dapingian and lower darriwilian uppermost part of the meitan formation chitinozoan diversity was relatively high after a less conspicuous peak in the upper dapingian comparisons between diversity trends of chitinozoans acritarchs and brachiopods and the environmental changes revealed both similarities and differences in the floian the chitinozoan biodiversity curve at honghuayuan shows good correlation with sea level changes the group temporarily disappeared when the sea level was at the highest then reappeared and reached a biodiversity acme when sea level was low furthermore a large organic carbon isotope excursion is coincident with the absence of chitinozoans and a highstand period after the sea level rise in the lower and middle floian diversity curves show fewer connections with the sea level and organic c isotope undulations during the dapingian and early darriwilian new data suggest that the environmental changes played a significant role in the early stage of ordovician chitinozoan radiation roughly corresponding to the floian at the honghuayuan section in the dapingian and early darriwilian the intrinsic factors seem to have played a more important role in shaping biodiversity patterns of chitinozoans in south china

semiautomated georadar data acquisition in three dimensions under favorable conditions georadar techniques can provide vivid images of the shallow subsurface 10 50 m although the significant advantages of 3 d georadar surveying strategies are well documented they generally require much greater expenditures than traditional 2 d approaches we introduce an efficient semiautomated 3 d georadar acquisition and processing scheme that does not jeopardize data quality a standard georadar acquisition unit is integrated with an innovative self tracking laser theodolite with automatic target recognition capabilities georadar and coordinate data are recorded simultaneously as the georadar antennae are transported steadily across a survey area while tracking a target prism mounted between the antennae the theodolite provides real time coordinate information with high accuracy in all directions at 1 m s moderate walking speed the coordinates are determined to better than 0 04 m and at 3 m s they are better than 0 07 m subsequent to acquisition semiautomati

glacier surge propagation by thermal evolution at the bed bakaninbreen southern svalbard began a prolonged surge during 1985 in 1986 an internal reflecting horizon on radio echo sounding data was interpreted to show that the position of the surge front coincided with a transition between areas of warm unfrozen and cold frozen bed ground penetrating radar lines run in 1996 and 1998 during early quiescence show that the basal region of the glacier is characterized by a strong reflection interpreted as the top of a thick layer of sediment rich basal ice down glacier of the present surge front features imaged beneath the basal reflection are interpreted as the bottom of the basal ice layer the base of a permafrost layer and local ice lenses this indicates that this region of the bed is cold up glacier of the surge front a scattering zone above the basal reflection is interpreted as warm ice there is no evidence for this warm zone down glacier of the surge front nor do we see basal permafrost up glacier of it thus as in early surge phase the location of the surge front is now at the transition between warm and cold ice at the glacier bed we suggest that the propagation of the front is associated with this basal thermal transition throughout the surge because propagation of the front occurs rapidly and generates only limited heat basal motion during fast flow must have been restricted to a thin layer at the bed and occurred by sliding or deformation localized at the ice bed interface

glacier motion dominated by processes deep in underlying till black rapids glacier is a 40 km long surge type glacier in the central alaska range in spring 1997 a wireline drill rig was set up at a location where the measured surface velocities are high and seasonal and annual velocity variations are large the drilling revealed a layer of subglacial till up to 7 m thick that is believed to be water saturated at one location a string of instruments containing three dual axis tiltmeters and one piezometer was successfully introduced into the till the tiltmeters monitored the inclination of the borehole at the ice till interface and at 1 and 2 m into the till for 410 days they showed that no significant deformation occurred in the upper 2 m of the till layer and no significant amount of the basal motion was due to sliding of the ice over the till the measured surface velocity at the drill site is about 60 m a 1 of which 20 30 m a can be accounted for by ice deformation almost the entire amount of basal motion 30 40 m a 1 was taken up at a depth of 2 m in the till possibly in discrete shear layers or as sliding of till over the underlying bedrock we propose that the large scale mobilization of such till layers is a key factor in initiating glacier surges

the structural glaciology of kongsvegen svalbard and its role in landform genesis mapping of the structural glaciology of kongsvegen svalbard reveals evidence for four main deformational structures these are stratification longitudinal foliation thrusts and crevasse traces these structures are considered in terms of their contribution to debris entrainment transport and subsequent landform development stratification is associated with small amounts of supraglacial debris that has been folded with flow parallel axes longitudinal foliation in places incorporates basal glacial sediments along folds with flow parallel axes and thrusts transport basal debris to the glacier surface crevasse traces are not significant in terms of debris entrainment the entrainment of basal debris along longitudinal foliation is not a universally recognised process at kongsvegen this process is attributed to the development of a transposition foliation in combination with incorporation of debris rich basal ice or soft basal sediment in the fold complex mapping of the landforms in the proglacial area shows that debris incorporated along longitudinal foliation is released as foliation parallel ridges and that transverse ridges mark debris bearing thrusts the role of longitudinal foliation in landform development has never been documented in this manner although the preservation potential of such ridges may be limited recognition of foliation parallel ridges in the pleistocene landform record has important implications for the interpretation of the dynamics of former ire masses

a sedimentological and isotopic study of the origin of supraglacial debris bands kongsfjorden svalbard hubbard b glasser n f hambrey m j etienne j l 2004 a sedimentological and isotopic study of the origin of supraglacial debris bands kongsfjorden svalbard journal of glaciology 50 169 157 170 rae2008

thermally controlled glacier surging bakaninbreen in svalbard and trapridge glacier in yukon territory canada are two prominent examples of surging glaciers which are thought to be controlled by their thermal regime both glaciers have developed large bulges which have propagated forward as travelling wave fronts and which are thought to divide relatively stagnant downstream cold based ice from faster moving warm based upstream ice additionally both glaciers are underlain by a wet metres thick layer of deforming till we develop a simple model for the cyclic surging behaviour of these glaciers which interrelates the motion of the ice and till through a description of the subglacial hydrology we find that oscillations surges can occur if the subglacial hydrological transmissivity is sufficiently low and the till layer is sufficiently thin and we suggest that these oscillations are associated with the development and propagation of a travelling wave front down the glacier we therefore interpret the travelling wave fronts on both trapridge glacier and bakaninbreen as manifestations of surges in addition we find that the violence of the surge in the model is associated with the resistance to ice flow offered by undulations in the bed and the efficiency with which occasional hydrological events can release water accumulated at the glacier sole

in situ measurements of till deformation and water pressure a newly developed hammer was used to insert two autonomous probes 0 8 m and 2 1 m into clast rich subglacial till under black rapids glacier alaska usa both probes were instrumented with a dual axis tilt sensor and a pore water pressure transducer the data are compared to a 75 day record of surface velocities till deformation at depth was found to be highly seasonal it is significant during an early season speed up event but during long periods thereafter measured till deformation rates are negligible both tilt records show rotation around the probe axis which indicates a change in tilt direction of about 30 the tilt records are very similar suggesting spatial homogeneity on the scale of the probe separation 4 m horizontal and 3 3 m vertical there is evidence that during much of the year sliding of ice over till or deformation of a thin till layer 20 cm accounts for at least two thirds of total basal motion basal motion accounts for 50 70 of the total surface motion the inferred amount of ice till sliding is larger than that found at the same location in a previous study when surface velocities were about 10 lower we suggest that variations in ice till coupling account for the observed variations in mean annual speed

is there a single surge mechanism contrasts in dynamics between glacier surges in svalbard and other regions 1 during the 1990s monacobreen a 40 km long tidewater glacier in svalbard underwent a major surge we mapped the surge dynamics using ers synthetic aperture radar images differential dual azimuth interferometry and intensity correlation tracking a series of 11 three dimensional 3 d velocity maps covering the period 1991 1997 show a months long initiation and years long termination to the surge with no indication of a surge front travelling downglacier during the surge the front of the glacier advanced 2 km the velocity and derived strain rate increased by more than an order of magnitude and maximum ice flow rates measured during 1994 were 5 m d 1 the spatial pattern of both velocity and strain rate was remarkably consistent and must therefore be controlled by spatially fixed processes operating at the glacier bed we combine these results with those published in the literature to construct a typical svalbard glacier surge cycle and compare this to surge dynamics of glaciers from other cluster regions especially those of variegated glacier in alaska the strong contrast in dynamics suggests that there exist at least two distinct surge mechanisms

the formation of a geometrical ridge network by the surge type glacier kongsvegen svalbard traditionally geometrical ridge networks are interpreted as the product of the flow of subglacial sediment into open basal crevasses at the cessation of a glacier surge crevasse fill ridges they are widely regarded as a characteristic landform of glacier surges understanding the range of processes by which these ridge networks form is therefore of importance in the recognition of palaeosurges within the landform record the geometrical ridge network at the surge type glacier kongsvegen in svalbard does not form by crevasse filling the networks consist of transverse and longitudinal ridges that can be seen forming at the current ice margin the transverse ridges form as a result of the incorporation of basal debris along thrust planes within the ice the thrusts were apparently formed during a glacier surge in 1948 longitudinal ridges form through the meltout of elongated pods of debris which on the glacier surface are subparallel to the ice foliation and pre date the surge this work adds to the range of landforms associated with glacier surges

controls on the distribution of surge type glaciers in svalbard we analyzed the possible controls on the distribution of surge type glaciers in svalbard using multivariate logit models including 504 glaciers and a large number of glacial and geological attributes specifically we examined the potential effect of geological boundaries mass balance conditions and thermal regime on surging it was found that long glaciers with relatively steep slopes overlying young fine grained sedimentary lithologies with orientations in a broad arc clockwise from northwest to southeast are most likely to be of surge type no relation between lithological boundaries and surge potential could be established possible explanations for length being conducive to surging are transport distance related substrate properties distance related attenuation of longitudinal stresses and the possible relation between thermal regime and glacier size analysis of glaciers with recorded radioecho sounding reveals that a polythermal regime accumulation area ratios close to balance and a large elevation span increase the surge potential the logit models also enabled us to detect 19 new surge type glaciers to reclassify six glaciers as normal and to identify unusual surge type glaciers our model results suggest that a polythermal regime and fine grained potentially deformable beds are conducive to the surge potential of svalbard glaciers

debris entrainment and transfer in polythermal valley glaciers hambrey mj bennett mr dowdeswell ja et al 1999 debris entrainment and transfer in polythermal valley glaciers journal of glaciology 45 149 69 86 published 1999

glacier surge mechanisms inferred from ground penetrating radar kongsvegen svalbard deformational structures at the surge type glacier kongsvegen sval bard are displayed at the glacier surface and on a grounded cliff section at the terminus a 300 m665 m grid of 200 mhz ground penetrating radar gpr profiles has been col lected adjacent to the cliff section in order to identify englacial structure two sub horizon tal reflectors have been imaged the upper is interpreted as the glacier bed and represents a transition between glacier ice and frozen subglacial sediments while the lower is inter preted as a transition between frozen and unfrozen subglacial sediment dipping reflec tors corresponding to sediment filled features on the cliff and glacier surface do not cross the glacier bed a small number of reflectors interpreted as thrust faults are visible below the bed reflector a model is developed for structural development which suggests that ice built up in a reservoir zone during quiescence during the surge ice propagated rapidly from this reservoir creating a zone of compression which resulted in thrusting subse quently an extensional flow regime resulted in extensive fracture of the ice we suggest dilated sediment was evacuated into these extensional crevasses from the glacier bed accelerating surge termination

ice marginal dynamics during surge activity kuannersuit glacier disko island west greenland the kuannersuit glacier surged 11 km between 1995 and 1998 the surge resulted in the formation of an ice cored thrust moraine complex constructed by subglacial and proglacial glaciotectonic processes four main thrust zones are evident in the glacier snout area with phases of compressional folding and thrusting followed by hydrofracture in response to the build up of compressional stresses and the aquicludal nature of submarginal permafrost and naled various types of stratified debris rich ice facies occur within the marginal zone the first facies i comprises laterally continuous strata of ice with sorted sediment accumulations and is reworked and thrust naled ice the second is laterally discontinuous stratified debris rich ice with distinct tectonic structures and is derived through subglacial extensional deformation and localised regelation facies ii whilst the third type is characterised by reworked and brecciated ice associated with the reworking and entrainment of meteoric ice facies iii hydrofracture dykes and sills facies iv cross cut the marginal ice cored thrust moraines with their sub vertically frozen internal contact boundaries and sedimentary structures suggesting supercooling operated as high pressure evacuation of water occurred during thrusting but this is not related to the formation of basal stratified debris rich ice linear distributions of sorted fines transverse to ice flow and small stratified sediment ridges that vertically cross cut the ice surface up ice of the thrust zone relate to sediment migration along crevasse traces and fluvial infilling of crevasses from a palaeoglaciological viewpoint marginal glacier tectonics ice sediment content and sediment delivery mechanisms combine to control the development of this polythermal surge valley landsystem the bulldozing of proglacial sediments and the folding and thrusting of naled leads to the initial development of the outer zone of the moraine complex this becomes buried in bulldozed outwash sediment and well sorted fines through surface ablation of naled up ice of this the heavily thrust margin becomes buried in sediment melted out from basal debris rich ice and subglacial diamicts routed along thrusts these mechanisms combine to deliver sediment to supraglacial localities and promote the initial preservation of structurally controlled moraines through insulation and the later development of kettled dead ice terrain

reply formation and reorientation of structure in the surge type glacier kongsvegen svalbard we welcome the development of the debate about structures at the surge type glacier kongsvegen svalbard our paper woodward et al 2002 tested a number of hypotheses proposed in the literature by glasser et al 1998 and bennett et al 1996 for sediment entrainment in glacier ice we feel that after testing sufficient evidence exists to reject these hypotheses and as a result we have proposed alternative mechanisms for the formation of these features we wish to reply to the issues raised in the above comment by glasser et al

genesis of hummocky moraines by thrusting in glacier ice evidence from svalbard and britain irregular mounds of glacial debris commonly referred to as 9hummocky moraine9 until recently were linked to ice stagnation during rapid climatic amelioration however recent work in scotland has demonstrated that some hummocky moraine dating from the younger dryas event c 10 000 years bp was the product of deposition at active ice margins observations at modern high arctic glacier margins in svalbard 76 80 n indicate that some moraines of this type form under a dynamic glaciological regime mainly by thrusting in active polythermal ice undergoing strong longitudinal compression this situation is particularly common where there is a transition from warm based ice in the interior of a glacier to cold based ice at the margins or snout from their morphological similarity rectilinear slopes facing up glacier and irregular downglacier faces and apparent stacking of slabs of sediment of subglacial derivation it is concluded that some assemblages of british moraines are also the product of thrusting this process appears to be most dominant in polythermal glaciers rather than in temperate glaciers on this basis it is tentatively suggested that the younger dryas in britain was characterized by a climatic regime similar to that in svalbard today mean annual temperature 5 c 400 1000 mm precipitation and that the associated glaciers may have been of polythermal character

sedimentation and stratigraphy at eyjabakkajokull an icelandic surging glacier a model for sedimentation by surging glaciers is developed from analysis of the debris load sedimentary processes and proglacial stratigraphy observed at the icelandic surging glacier eyjabakkajokull three aspects of the behavior of surging glaciers explain the distinctive landformsediment associations which they may produce a sudden loading of proglacial sediments during rapid glacier advances results in the buildup of excess pore pressures failure and glacitectonic deformation of the overridden sediments b reactivation of stagnant marginal ice by the downglacier propagation of surges is associated with large longitudinal compressive stresses these induce intense folding and thrusting during which basal debris rich ice is elevated into an englacial position in a narrow marginal zone as the terminal area of the glacier stagnates between surges debris from this ice is released supraglacially and deposited by meltout and sediment flows c local variations in overburden pressure beneath stagnant crevassed ice cause subglacial lodgement tills which are sheared during surges to flow into open crevasses and form crevasse fill ridges

full resolution 3d gpr imaging noninvasive 3d ground penetrating radar gpr imaging with submeter resolution in all directions delineates the internal architecture and processes of the shallow subsurface full resolution imaging requires unaliased recording of reflections and diffractions coupled with 3d migration processing the gpr practitioner can easily determine necessary acquisition trace spacing on a frequency wavenumber f k plot of a representative 2d gpr test profile quarter wavelength spatial sampling is a minimum requirement for full resolution gpr recording an intensely fractured limestone quarry serves as a test site for a 100 mhz 3d gpr survey with 0 1 m 0 2 m trace spacing this example clearly defines the geometry of fractures in four different orientations including vertical dips to a depth of 20 m decimation to commonly used half wavelength spatial sampling or only 2d migration processing makes most fractures invisible the extra data acquisition effort results in image volumes with submeter resolution both

imaging glacial sediment inclusions in 3 d using ground penetrating radar at kongsvegen svalbard the quiescent phase surge type glacier kongsvegen flows confluent with the continuously fast flowing kronebreen in northwestern spitsbergen the lower regions of kongsvegen overlie glaciomarine sediments which have been incorporated into the ice during multiple surge events the resulting englacial structures are exposed at the surface and on a cliff section these structures have variously been interpreted as thrusts formed by compression or sediment filled crevasses formed by extension we collected a grid of closely spaced ground penetrating radar profiles in the area adjacent to the cliff section several structures were imaged in 3 d including a strong subhorizontal basal reflector which was underlain by a second weaker subhorizontal reflector the basal reflector was occasionally reverse faulted suggesting compression clear englacial features extended upwards from it dipping up glacier at angles of 40 and steepening towards the glacier surface they had complex geometries that changed rapidly cross glacier the structures were orientated at 30 to ice flow suggesting modification by lateral compression from kronebreen some of these englacial structures clearly crossed the basal reflector we conclude that the englacial features imaged are not likely to be derived from crevasse filling and were probably formed by thrusting the results contribute to our understanding of surge initiation and termination processes and interpretation of features in the palaeorecord copyright 2009 john wiley sons ltd

structure and changing dynamics of a polythermal valley glacier on a centennial timescale midre lovenbreen svalbard hambrey michael murray t glasser n f hubbard a 2005 structure and changing dynamics of a polythermal valley glacier on a centennial timescale midre lovenbreen svalbard journal of geophysical research 110 pp 1 19 rae2008