the instability theory of drumlin formation and its explanation of their varied composition and internal structure despite their importance in understanding glaciological processes and constraining large scale flow patterns in palaeo glaciology there is little consensus as to how drumlins are formed attempts to solve the drumlin problem often fail to address how they are created from an initially flat surface in the absence of obvious cores or obstacles this is a key strength of the instability theory which has been described in a suite of physically based mathematical models and proposes that the coupled flow of ice and till causes spontaneous formation of relief in the till surface encouragingly model predictions of bedform height and length are consistent with observations and furthermore the theory has been applied to a range of subglacial bedforms and not just drumlins however it has yet to confront the myriad observations relating to the composition and internal structure of drumlins and this could be seen as a major deficiency this paper is a first attempt to assess whether the instability theory is compatible with the incredible diversity of sediments and structures found within drumlins we summarise the underlying principles of the theory and then describe and attempt to explain the main types of drumlin composition e g bedrock till glaciofluvial sediments and combinations thereof contrary to a view which suggests that the presence of some sedimentary sequences e g horizontally stratified cores is inconsistent with the theory we suggest that one would actually expect a diverse range of constituents depending on the inheritance of sediments that pre date drumlin formation the duration and variability of ice flow and the balance between erosion and deposition till continuity at the ice bed interface we conclude that the instability theory is compatible with and potentially strengthened by what is known about drumlin composition and as such offers the most complete and promising solution to the drumlin problem to date

identifying palaeo ice stream tributaries on hard beds mapping glacial bedforms and erosion zones in nw scotland ice streams are fed by tributaries that can extend deep into the heart of ice sheets these tributaries are born at onset zones the abrupt transitions from slow sheet flow to fast streaming flow that often occur at significant topographic steps on hard beds bedrock dominated beds for this reason tributary onset zones leave only a subtle erosional geomorphic signature in the landscape record that is rarely studied this paper examines in detail the geomorphic signature of ice sheet flow on a hard bed at the head of a palaeo ice stream we use field survey techniques to map glacial bedforms within an 200 km2 area of hard crystalline bedrock in a landscape of areal scour around loch laxford in nw scotland the bedrock bedforms range from plastically moulded p forms and wholly abraded forms to stoss lee forms and plucked surfaces all on an outcrop scale 1 100 m we devise a five zone classification system to map in a gis the presence absence and abundance of glacial erosional forms within 619 500 m square grid cells we go on to use these erosional bedform zones along with known glaciological relationships to interpret the spatial and altitudinal pattern of palaeo ice sheet processes and glacier dynamics in this part of nw scotland our interpretation highlights the strong vertical thermal zonation on mountains and the spatial variations in ice rheology softness ice temperature and by inference ice velocity in troughs intimately associated with the onset of ice streaming in tributaries consequently we define the laxfjord palaeo ice stream tributary a feeder to the minch palaeo ice stream in nw scotland finally we suggest that this new mapping approach could be performed in other deglaciated hard bed terrain to examine more widely the subtle erosional signatures preserved in areas traditionally thought to represent ice sheet areal scour

comprehensive chemical analyses of natural cordierites implications for exchange mechanisms abstract cordierite samples from pegmatites and metamorphic rocks have been analysed for major electron microprobe analysis empa and trace elements inductively coupled plasma mass spectrometry icp ms secondary ion mass spectrometry analyses sims as well as for h 2 o and co 2 coulometric titration and the results evaluated in conjunction with published data in order to determine which exchange mechanisms are significant apart from the homovalent substitutions femg 1 and mnmg 1 on the octahedral site some minor kna 1 on the ch0 channel site and fe 3 al 1 on the t 1 1 tetrahedral site the three most important substitution mechanisms are those for the incorporation of li on the octahedral sites nali 1 mg 1 and of be and other divalent cations on the tetrahedral t 1 1 site nabe 1 al 1 and na mg fe 2 1 al 1 the dominant role of the last vector is clearly demonstrated we propose a new generalized formula for cordierite ch na k 0 1 vi mg fe 2 mn li 2 iv si 5 iv al 3 iv al be mg fe 2 fe 3 o 18 x ch h 2 o co 2 our results show that the population of mg fe 2 on the t 1 1 site is limited to about 0 08 a p f u other exchange mechanisms that were encountered in experiments operate only under p t conditions or in bulk compositions that are rarely realized in nature routine analyses by electron microprobe in which li and be are not determined can be plotted as mg fe mn versus si al to assess whether significant amounts of li and be could be present these amounts can be calculated as li a p f u al na 4 and be a p f u 10 2al m 2 na

cordierite as a sensor of fluid conditions in high grade metamorphism and crustal anatexis cordierite h2o and co2 volatile saturation surfaces derived from recent experimental studies are presented for p t conditions relevant to high grade metamorphism and used to evaluate fluid conditions attending partial melting and granulite formation the volatile saturation surfaces and saturation isopleths for both h2o and co2 in cordierite are strongly pressure dependent in contrast the uptake of h2o by cordierite in equilibrium with melts formed through biotite dehydration melting controlled by the distribution of h2o between granitic melt and cordierite dw dw wt h2o melt wt h2o crd is mainly temperature dependent dw 2 5 6 0 for the h2o contents 0 4 1 6 wt percentage typical of cordierite formed through biotite dehydration melting at 3 7 kbar and 725 900 c this range in dw causes a 15 30 relative decrease in the total wt of melt produced from pelites cordierite in s type granites are h2o rich 1 3 1 9 wt and close to or saturated in total volatiles signifying equilibration with crystallizing melts that achieved saturation in h2o in contrast the lower h2o contents 0 6 1 2 wt percentage preserved in cordierite from many granulite and contact migmatite terranes are consistent with fluid absent conditions during anatexis in several cases including the cooma migmatites and broken hill granulites the cordierite volatile compositions yield ah2o values 0 15 0 4 and melt h2o contents 2 2 4 4 wt compatible with model dehydration melting reactions in contrast h2o leakage is indicated for cordierite from prydz bay antarctica that preserve h2o contents 0 5 0 3 wt which are significantly less than those required 1 0 0 8 wt for equilibrium with melt at conditions of 6 kbar and 860 c the co2 contents of cordierite in migmatites range from negligible 0 1 wt to high 0 5 1 0 wt and bear no simple relationship to preserved cordierite h2o contents and ah2o in most cases the cordierite volatile contents yield total calculated fluid activities ah2o aco2 that are significantly less than those required for fluid saturation at the p t conditions of their formation whether this reflects fluid absence dilution of h2o and co2 by other components or leakage of h2o from cordierite is an issue that must be evaluated on a case by case basis

maximum and minimum water contents of granitic melts implications for chemical and physical properties of ascending magmas new results obtained by the investigation of liquidus and solidus phase relations in the system qz ab or and by the determination of h2o solubility in haplogranitic melts are used to discuss the evolution of granitic quartzo feldspathic magmas during their ascent in the crust particular attention is given to the role of h2o and its effect on physical properties of ascending magmas the evolution of melt fraction h2o content of the melt and viscosity of melt and magma during ascent are discussed for several examples adiabatic ascent ascent with cooling ascent with crystal fractionation it is shown that decompression melting processes may be very important significant increase of the melt proportion especially at low pressure in magmas ascending along adiabats or with slow cooling rates the comparison of the discussed examples shows that melts formed at low t are significantly less viscous than at high t although the degree of melting may remain very low in the case of dehydration melting at low temperature the low viscosity of the generated melts may enhance the extraction of these melts from the source area to produce leucogranites

coupled ice till dynamics and the seeding of drumlins and bedrock forms the geomorphological effects of ice sliding over till internal deformation of till and till sliding over bedrock are considered two questions are examined 1 is the till sheet flow unstable i e is a layer of uniform thickness maintained or not and 2 does the slip of till over bedrock cause amplification of relief of the bedrock such instabilities seem to be necessary to explain such features as drumlins and whaleback forms it is found that the answer to 1 and 2 depends on the position of the system in a parameter space defined by the till rheology and applied shear stress the effective pressure at the ice till interface the thickness of ice and till and the wavelength of the instability two configurations are considered one where the wavelength of the perturbation is much less than the the ice thickness which is related to the classical nye kamb solution for flow over bumps and one where the wavelength is much greater than the ice thickness where the mechanics are described by the shallow ice approximation in both cases substantial areas of parameter space where till sheet and bedrock modes are unstable are found the conceptually related smalley unwin bifurcation is re examined the physical mechanisms by which ice and till flows couple are examined at very short wavelengths 10 m the ice is so rigid that it forces till waves to move at the ice velocity while at long wavelengths 1000 m the flows become essentially uncoupled and till waves move at the kinematic velocity at intermediate wavelengths 100 m high growth rates occur this is postulated to be the scale of drumlin seeding

regional reconstruction of subglacial hydrology and glaciodynamic behaviour along the southern margin of the cordilleran ice sheet in british columbia canada and northern washington state usa abstract subglacial landsystems in and around okanagan valley british columbia canada are investigated in order to evaluate landscape development subglacial hydrology and cordilleran ice sheet dynamics along its southern margin major landscape elements include drumlin swarms and tunnel valleys drumlins are composed of bedrock diamicton and glaciofluvial sediments their form truncates the substrate tunnel valleys of various scales km to 100s km length incised into bedrock and sediment exhibit convex longitudinal profiles and truncate drumlin swarms okanagan valley is the largest tunnel valley in the area and is eroded 300 m below sea level over 600 m of late wisconsin age sediments consisting of a fining up sequence of cobble gravel sand and silt fill okanagan valley landform substrate relationships landform associations and sedimentary sequences are incompatible with prevailing explanations of landsystem development centred mainly on deforming beds they are best explained by meltwater erosion and deposition during ice sheet underbursts during the late wisconsin glaciation okanagan valley functioned as part of a subglacial lake spanning multiple connected valleys few 100s km of southern british columbia subglacial lake development started either as glaciers advanced over a pre existing sub aerial lake catch lake or by incremental production and storage of basal meltwater high geothermal heat flux geothermal springs and or subglacial volcanic eruptions contributed to ice melt and may have triggered along with priming from supraglacial lakes subglacial lake drainage during the underburst s sheetflows eroded drumlins in corridors and channelized flows eroded tunnel valleys progressive flow channelization focused flows toward major bedrock valleys in okanagan valley most of the pre glacial and early glacial sediment fill was removed a fining up sequence of boulder gravel and sand was deposited during waning stages of the underburst s and bedrock drumlins in okanagan valley were enhanced or wholly formed by this underburst s subglacial lake development and drainage had an impact on ice sheet geometry and ice volumes the prevailing conceptual model for growth and decay of the cis suggests significantly thicker ice in valleys compared to plateaus subglacial lake development created a reversal of this ice sheet geometry where grounded ice on plateaus thickened while floating valley ice remained thinner due to melting and enhanced sliding with significant transfer of ice toward the ice sheet margin subglacial lake drainage may have hastened deglaciation by melting ice lowering ice surface elevations and causing lid fracture this paper highlights the importance of ice sheet hydrology its control on ice flow dynamics distribution and volume in continental ice masses

the composition and internal structure of drumlins complexity commonality and implications for a unifying theory of their formation investigation of drumlins is significant to both glaciology and palaeoglaciology but the sheer diversity of their composition and internal structure is often cited as a major obstacle towards a satisfactory unifying explanation of their formation this paper presents the first systematic survey of the vast literature on this subject with the aim of concisely summarising observations and identifying any emergent patterns or commonality that theories of drumlin formation should be able to explain results confirm that investigations are often limited by availability of suitable sediment exposures 40 of studies report data from 5 drumlins and 44 do not specify sample size although borehole data and geophysical techniques can alleviate this problem however it is clear that the constituents of drumlins are incredibly diverse in terms of their composition e g a range of lithologies clast shapes sizes and fabrics structure e g sediments that are sorted homogeneous surface conformable unconformable and evidence of deformation e g ranging from pervasive to non pervasive limited to absent despite this diversity our review leads us to suggest that drumlin composition can be simplified to five basic types i mainly bedrock ii part bedrock part till iii mainly till iv part till part sorted sediments and v mainly sorted sediments this is a potentially significant step in that it reduces the oft cited complexity of drumlin composition and provides a more realistic goal for theories or numerical models of drumlin formation to target the various types can occur within the same drumlin field which leaves us with two possible implications for drumlin formation 1 different types of drumlin are formed seeded by different processes despite being morphologically similar equifinality investigation of drumlin composition may therefore reveal diagnostic processes explanations for these different types of drumlin and we argue that bedrock drumlins are an example 2 a single process occurs across large parts of the ice bed interface to create drumlinised terrain in a variety of sediments investigation of drumlin composition may in this case simply reflect pre existing sediments but importantly the way in which the drumlin forming mechanism modifies is modified by them we argue that the latter simpler explanation applies to all other types of drumlin excluding purely bedrock forms and conclude that the diversity in drumlin composition is no obstacle to a single unifying theory

palaeo ice streams abstract the location and behaviour of ice streams is one of the most important controls on ice sheet configuration and stability in order to reconstruct former ice sheets we need to know ice stream location and timing once identified the beds of palaeo ice streams provide an unprecedented opportunity to glean information about their basal environment something that remains very difficult under contemporary ice streams this paper represents the first synthesis and discussion of palaeo ice stream research from a variety of former ice sheets and includes new insights relating their configuration and activity to the evidence they leave behind the ambiguous use of the term ice stream is addressed and four possible configurations for ice streams are presented diagnostic landforms and landform assemblages that we would expect an ice stream to produce are discussed and the temporal context of bedform generation is described as either a rubber stamped or smudged bedform imprint resulting from isochronous or time transgressive landform generation in particular we focus on the configuration of terrestrially terminating ice streams for which there are no modern analogues technological advances in marine geophysics are helping to generate a convergence of interest between antarctic glaciology and palaeo glaciology it is suggested that investigations around the fringes of contemporary ice sheets i e west antarctica can provide evidence that directly links the geomorphological record of palaeo ice streams with their contemporary counterparts in addition computational advances and modelling adaptations have permitted the incorporation of ice streams within ice sheet models we argue that data from palaeo ice stream beds are invaluable to ice sheet stream modelling experiments and will help us understand ice stream operation and the linkages between climate perturbations and both palaeo and contemporary ice sheets

glacial erosion and bedrock properties in nw scotland abrasion and plucking hardness and joint spacing subglacial erosion beneath glaciers occurs predominantly by abrasion and plucking producing distinct erosional forms the controls on the relative importance of abrasion vs plucking are poorly understood on the one hand glacial conditions that favour or suppress cavity formation ice velocity ice thickness and water pressure are thought to favour plucking or abrasion respectively conversely bedrock properties are also known to control landforms but this has rarely been analysed quantitatively in this study we compare landforms and bedrock properties of sandstone and quartzite at the bed of a palaeo ice stream near ullapool in nw scotland the boundary between the rock types is at right angles to the westward palaeo ice flow and palaeoglacial conditions on both rock types were similar we report quantitative parameters for bedrock properties schmidt hammer hardness and joint spacing and use morphometric parameters to analyse the landforms torridon sandstone is soft but thick bedded and with a wide joint spacing erosional bedforms include roche moutonnees with smoothed tops and concave stoss sides whalebacks and elongate p forms indicating a high proportion of abrasion over plucking cambrian quartzite is hard but thin bedded with narrow joint spacing erosional landforms are angular to subangular with abundant plucked lee faces suggesting a high proportion of plucking over abrasion hardness and joint spacing thus exert a strong control on subglacial erosional landforms and the mechanisms that formed them thus glacial conditions ice velocity ice thickness can only be inferred from glacial erosional landforms if the effects of bedrock properties of the substrate are considered

positive feedbacks associated with erosion of glacial cirques and overdeepenings the principal points of water input to a glacier are the bergschrund in cirques and crevasse fields lower on the glacier crevasse fields commonly occur over convexities at the heads of overdeepenings in glacier beds the amplitude of subglacial water pressure fluctuations is large just down glacier from these points of water input erosion by quarrying is likely in such areas erosion is thus inferred to be localized on the headwalls of cirques and overdeepenings in the case of overdeepenings this leads to a positive feedback process in which a perturbation in the bed causes crevassing at the surface resulting in erosional forces that accentuate the perturbation when subglacial water flows up an adverse bed slope leading out of a cirque or overdeepening much of the viscous energy dissipated is used to warm the water to keep it at the pressure melting temperature as the ice thins and the pressure decreases in such situations subglacial conduits are maintained by high water pressures rather than by melting of conduit walls in the limit water pressures apparently become so high that water is forced out along the ice bed interface and the conduits collapse the products of erosion are then no longer flushed out and a protective till layer accumulates by limiting erosion on such adverse bed slopes this till layer controls the geometry of these overdeepened basins

a new surface processes model combining glacial and fluvial erosion we have developed a new surface processes model incorporating large scale fluvial processes local hill slope processes and glacial erosion ice thickness and velocity are calculated under a shallow ice approximation simulation experiments in fast growing orogens comparing the efficiencies of fluvial and glacial erosion where the two are operating simultaneously over several glacial cycles show that glacial landscapes can support greater ice masses than fluvial landscapes glacial valley and lake shapes create a disequilibrium between landform and land forming process that leads to pulses of high erosion at the end of glacial periods glacial erosion rates can reach a constant value in a uniformly growing orogen and glacial erosion is capable of eroding drainage divides when the ice is moderately thick

flow of the west antarctic ice sheet on the continental margin of the bellingshausen sea at the last glacial maximum geophysical data show that during the last glaciation the west antarctic ice sheet wais drained to the continental shelf edge of the bellingshausen sea through a cross shelf bathymetric trough belgica trough as a grounded fast flowing ice stream the drainage basin feeding this ice stream probably encompassed southwestern palmer land parts of southern alexander island and the bryan coast of ellsworth land with an area exceeding 200 000 km2 on the inner continental shelf streamlined bedrock and drumlins mapped by swath bathymetry show that the ice stream was fed by convergent ice flow draining from eltanin bay and bays to the east as well as by ice draining the southern part of the antarctic peninsula ice sheet through the ronne entrance the presence of a paleoice stream in belgica trough is indicated by megascale glacial lineations formed in soft till and a trough mouth fan on the continental margin grounding zone wedges on the inner and midshelf record ice marginal stillstands during deglaciation and imply a staggered pattern of ice sheet retreat these new data indicate an extensive wais at the last glacial maximum lgm on the bellingshausen sea continental margin which advanced to the shelf edge in conjunction with ice sheet reconstructions from the antarctic peninsula and pine island bay this implies a regionally extensive ice sheet configuration during the lgm along the antarctic peninsula bellingshausen sea and amundsen sea margins with fast flowing ice streams draining the wais and antarctic peninsula ice sheet to the continental shelf edge

surficial glaciology of jakobshavns isbrae west greenland part i surface morphology jakobshavns isbrae is a large fast moving ice stream outlet glacier in west greenland which ends at a floating calving front it drains about 6 5 of the area of the greenland ice sheet studies of its surface morphology are described in this paper the surface is relatively steep 0 01 0 03 and the thickness is large up to 2600 m along the center line clarke and echelmeyer 1989 indicating very high driving stresses 200 300 kpa the ice stream is about 6 km wide and 85 90 km long all of which is in an area of surface melting the base of the ice stream and of much of the drainage area is below sea level marginal crevasse zones have a width on the order of the width of the ice stream itself unique surficial features are ice blisters and lakes the latter have a sequence of ogive like features on their floating ice cover which can be used to determine velocity there is a pinning point near the terminus which may act as a stabilizing influence possibly playing a role in halting at least temporarily a recent retreat of the terminus ice thickness estimates at the terminus lead to a flux which is less than previously assumed by others e g bindschadler 1984 pelto and others 1989 when estimating jakobshavns isbrae s drainage basin to be nearly in balance the driving stresses on jakobshavns isbrae are an order of magnitude higher than those of the ice streams of west antarctica its crevasse patterns are much less localized its relatively unconfined terminus is more comparable to that of relatively unbuttressed ice streams such as pine island and thwaites glaciers than it is to other west antarctic ice streams which terminate in large confined ice shelves

fast glacier flow ice streams surging and tidewater glaciers fast flowing glaciers are unusual but important jakobshavns glacier in western greenland illustrates this point figure 1 considered to be the world s fastest glacier its maximum observed flow rate measured in midsummer near the floating terminus is 8360 m yr 1 lingle et al 1981 except for a tidal influence near the terminus the flow is believed to be fairly steady bindschadler 1984

ftir microspectroscopy and sims study of water poor cordierite from el hoyazo spain application to mineral and melt devolatilization abstract this paper reports the microchemical and microspectroscopic ftir study of cordierite from a partially melted graphite bearing granulitic enclave within the dacitic lava dome of el hoyazo se spain optically transparent single crystals hand picked from the rock were oriented using x ray diffraction and studied by fourier transform infrared ftir single crystal ftir spectroscopy shows that the examined cordierite is co2 rich and almost h2o free two weak and sharp peaks are observed at 3708 and 3595 cm 1 respectively which are strongly polarised for e a these peaks are assigned to combination modes of co2 very weak bands due to h2o molecules oriented with the h h vector c type i water are occasionally observed in certain zones of the grains associated with absorptions due to hydrated inclusions of alteration products the very intense bands observed in the 2600 2000 cm 1 region are assigned to co2 molecules oriented a the spectra also show the presence of 13c and 18o and weak amounts of co in the sample microspectrometric mapping shows that the distribution of c is relatively homogeneous whereas that of h2o is complicated by a very broad absorption extending from 3700 to 3100 cm 1 high resolution ftir imaging done using a focal plane array of detectors shows that this broad absorption is associated with microfractures sims analyses give an average concentration of h2o 0 033 0 007 wt and co2 0 21 0 07 wt on the basis of these data molar absorption coefficients can be calibrated for co2 eico2 integrated 11 000 4000 l mol cm 2 and elco2 linear 800 250 l mol cm 1 due to the extremely low amount of h2o and its inhomogeneous distribution calibration of absorption eh2o coefficients is unreliable the very low h2o contents in the el hoyazo cordierite indicate continued mineral melt volatile exchange during decompression from 5 kbar to significantly shallower levels

geomorphological criteria for identifying pleistocene ice streams ice streams are critical regulatory mechanisms in contemporary ice sheets it has been inferred that they also had a significant effect on the dynamics of former ice sheets subsequently many people have invoked their widespread occurrence from a variety of formerly glaciated areas hypothesised locations however have often outweighed meaningful evidence this paper addresses the problem using the characteristics of contemporary ice streams as a basis for their identification from former ice sheet beds a convergence of knowledge gained from contemporary ice stream research coupled with theories of glacial geomorphology allows several geomorphological criteria to be identified as suggestive signatures of ice stream activity it is envisaged that the geomorphological criteria developed here will introduce a more objective approach to the study of former ice streams the criteria are used to construct conceptual land system models of the beds of former ice streams and it is hoped such models can provide an observational template upon which hypotheses of former ice streams can be better based

a major ice drainage pathway of the last british irish ice sheet the tyne gap northern england the tyne gap is a wide pass situated between the scottish southern uplands and the english pennines that connects western and eastern england it was a major ice flow drainage pathway of the last british irish ice sheet this study presents new glacial geomorphological and sedimentological data from the tyne gap region that has allowed detailed reconstructions of palaeo ice flow dynamics during the late devensian marine isotope stage 2 mapped lineations reveal a complex palimpsest pattern which shows that ice flow was subject to multiple switches in direction these are summarised into three major ice flow phases stage i was characterised by convergent lake district and scottish ice that flowed east through the tyne gap as a topographically controlled ice stream this ice stream was identified from glacial geomorphological evidence in the form of convergent bedforms streamlined subglacial bedforms and evidence for deformable bed conditions stage ii involved northerly migration of the solway firth ice divide back into the southern uplands causing the easterly flow of ice to be weakened and resulting in southeasterly flow of ice down the north tyne valley and stage iii was characterised by strong drawdown of ice into the irish sea ice basin thus starving the tyne gap of ice and causing progressive ice sheet retreat westwards back across the watershed prior to ice stagnation copyright 2009 john wiley sons ltd

streamlined hard beds formed by palaeo ice streams a review fast flowing ice streams occur within modern ice sheets and also operated in pleistocene ice sheets the reconstruction of palaeo ice streams normally relies on the mapping of mega scale glacial lineations msgls and drumlins composed of soft sediment mainly till analysis of new satellite imagery and digital terrain models demonstrates the presence of large fields of kilometre scale glacial lineations comprising rock drumlins megagrooves and megaridges in this paper we describe and analyse a number of such hard bed landform systems from the former laurentide and british irish ice sheets occurring in a variety of palaeo ice stream settings these are attributed to erosion of crystalline and sedimentary rock below fast flowing ice streams bedrock properties such as hardness fracture spacing and bedding and their orientation with respect to ice flow have a profound effect on the occurrence and character of elongate rock bedforms elongate streamlined forms on hard crystalline rock as on the canadian shield only form under special circumstances in contrast sedimentary strata are highly susceptible to form streamlined hard beds specifically if bedrock strike is parallel to ice flow large scale elongate rock bedforms are erosional in origin formed by preferentially focused abrasion or by lateral plucking depending on bedrock type many palaeo ice stream footprints previously mapped in the laurentide ice sheet on the basis of soft bed bedforms are shown to be significantly larger extending up ice across sedimentary strata and onto precambrian crystalline rocks hard bed streamlined forms further show that ice streaming does not necessitate a deformable bed but can equally occur on smooth hard beds

an infrared spectroscopic ir and light element li be na study of cordierites from the bamble sector south norway abstract infrared absorption spectra and light element contents of several natural cordierites across the arendal amphibolite granulite facies transition bamble sector south norway are presented the infrared spectra record h2o both type i and type ii and co2 as fluid constituents in the channels co and hydrocarbons were not detected type ii water and ca na k are correlated and show a 2 1 molar ratio the infrared and light element data indicate a decrease of na type ii h2o co2 and li with metamorphic grade while type i h2o and be are variable the decrease of these volatiles and alkalies and the low total volatile contents of the granulite facies cordierites are best explained by progressive dehydration and decarbonation processes possibly related to partial melting a progressive change of the x h 2 o h 2 o h 2 o co 2 ratio in the cordierites across the transition as suggested by previous studies is not observed greenschist to low amphibolite facies re equilibrated cordierites show a significant increase in either co2 or h2o co2 na is introduced at some localities the retrograde fluid phase is calculated to be co2 rich

ice stream influence on west greenland ice sheet dynamics during the last glacial maximum this paper investigates the processes governing bedrock bedform evolution in ice sheet and ice stream areas in central west greenland and explores the evidence for a cross shelf ice stream at the last glacial maximum lgm to the east of sisimiut the formation of streamlined bedforms with high elongation ratios and high bedform density has been controlled by geological structure and topography in slow flowing ice sheet areas at the coast the effects of regional flow convergence caused by coastal fjord orientation routed ice into the sisimiut itilleq area where it formed an ice stream onset zone this funnelled ice into an offshore trough holsteinsborg dyb resulting in a southwesterly regional ice flow direction and the formation of a topographically routed ice stream holsteinsborg isbrae to the south of this striae and bedform evidence show that local valley glaciers initially flowed east to west across the coast but were later redirected by the itilleq fjord ice which turned southwestward due to diffluent flow and deflection by holsteinsborg isbrae roches moutonnees in this area have low elongation ratios and high bedform density but do not provide unequivocal support for ice streaming as they are a product of both bedrock structure and changes in ice flow direction rather than enhanced flow velocities cosmogenic surface exposure ages limit maximum ice sheet surface elevation to ca 755 810 m above sea level in this region such ice thickness enabled holsteinsborg isbrae to reach the mid outer continental shelf during the lgm and to contribute to the formation of a trough mouth fan and the outer hellefisk moraines initial deglaciation across this region was driven by rising sea level and increasing air temperatures prior to the bolling interstadial at ca 14 5 cal ka bp between 12 and 10 cal ka bp both increased air and ocean temperatures post the younger dryas and peak sea level rise up to the marine limit caused accelerated thinning and marginal retreat through calving although dating evidence suggests ice streams remained along the inner shelf coast boundary until at least ca 10 cal ka bp their longevity maintained by increased ice thickness and ice discharge copyright 2009 john wiley sons ltd

exhumed subglacial landscape in uruguay erosional landforms depositional environments and paleo ice flow in the context of the late paleozoic gondwanan glaciation abstract a well exposed glacial surface sculpted on precambrian crystalline basement rocks occurs below the glacial succession of the san gregorio formation on the eastern border of the chaco parana basin in uruguay and was formed in the context of the late paleozoic gondwana ice age on the glacial surface are asymmetric parallel streamlined bedrock landforms interpreted as whalebacks the downglacier lee side faces of the whalebacks have gentle slopes dipping nnw with striated and sometimes polished surfaces on crystalline rocks these landforms are covered by 10 100 cm thick layers of tillites and shear laminated siltstones suggesting glacial abrasion produced mainly by subglacial till sliding the subglacial facies are ice molded and exhibit meso scale glacial lineations such as ridges and grooves up to 30 m long and 30 cm deep the subglacial association is directly overlain by proglacial fine grained facies rhythmites with dropstones indicating a subaqueous depositional environment following ice margin retreat the fine grained facies are erosively cut by a succession of sandstones with wave generated stratification resting on a basal conglomerate intraformational striated surfaces nne oriented were found on four distinct bedding planes within the sandstone package and interpreted as ice keel scour marks produced by floating ice the san gregorio deposits are partially confined in a wide and shallow subglacial trough and the stratigraphic succession is interpreted as the record of a glacial advance retreat cycle comparable to deglacial sequences from other late paleozoic localities the paleo ice flow to the nnw indicated by subglacial lineations is parallel to that verified in the southernmost parana basin located north of the study area suggesting a paleogeographic scenario in which glaciers advanced northward into a glaciomarine environment the proposed palaeogeography does not confirm the previous hypothesis of an ice center on the sul riograndense shield but instead it corroborates a south derived uruguayan ice lobe advancing to the north probably with provenance far afield in terranes of the present day southern african

fluid present anatexis of metapelites at el joyazo se spain constraints from raman spectroscopy of graphite the garnet biotite sillimanite anatectic xenoliths in the neogene dacite dome of el joyazo also called cerro de hoyazo se spain contain four types of graphite i to iv distinguished on the basis of grain size and texture structural characterization of graphite by laser raman spectroscopy lrs shows systematic differences in the degree of ordering among the four types only type iii is fully consistent with the granulite facies conditions reached by the xenoliths during partial melting the others indicate metamorphic temperatures covering amphibolite facies conditions with only a few examples of granulite grade crystallinity all graphite crystallized before or during the anatectic event indicating that a large fraction of the graphite did not equilibrate at peak temperatures the mm scale coexistence of different types and degrees of ordering in the graphite suggests different origins i e of biogenic derivation and fluid deposited and is explained in terms of fluid melt graphite interaction during the anatectic event disequilibrium behaviour during high temperature metamorphism and anatexis is typical of types i ii and particularly of iv and is attributed to sluggish kinetics of solid state graphitization mainly owing to the limited time of the process and carbon saturation of the intergranular fluid the coexisting well ordered type iii graphite is the product of melting in the presence of a graphite saturated fluid a process that would account for the deposition of new graphite the lrs results together with petrologic observations suggest that it is possible that high melt fractions can be generated by fluid present melting of a metasedimentary protolith also in a closed system although this contradicts the commonly accepted hypothesis that due to limited rock porosities extensive fluid present melting is precluded unless infiltration occurs it is a possible end member model in anatectic settings characterized by rapid heating rates and low grade source rocks

submarine geomorphology and glacial history of the sea of the hebrides uk the sea of the hebrides is an island studded region of complex bathymetry on the uk continental shelf west of the scottish mainland an extensive area 2200 km2 of recently collected multibeam bathymetry data combined with seismic reflection profiles reveal this part of the shelf to have been extensively modified by both glacial and modern processes our new geomorphological evidence strongly supports the contention that an ice stream drained ice from western scotland and the inner hebrides towards the barra fan at the continental shelf break at the height of the last glaciation marine isotope stage 2 3 convergent seabed glacial lineations and other subglacially streamlined features eroded in bedrock around the islands of canna and rum preserve the direction of ice sheet movement and strongly suggest the onset of ice streaming in a southwesterly direction on the continental shelf in the sea of the hebrides region this fast flow zone formed part of a larger convergent ice stream system draining much of western scotland and the north of ireland the southern part of which has been postulated already a number of rock basins linear troughs and deeps west and south of muck kept sediment free by the dominant modern tidal regime are interpreted as being at least partly subglacial in origin similarly a large complex of buried deeps between eigg and arisaig are interpreted as an overdeepened glacial drainage network it is suggested that intense bedrock erosion by focused subglacial abrasion and subglacial meltwater discharge over multiple glacial advance and decay cycles led to significant modifications of the pre quaternary bedrock surface other features such as moraines are only found in shallower water typically 50 m west of canna west of rum and south of skye their relative paucity indicates that the modern tidally dominated environment of the area may have removed much of the localised geomorphological evidence of offshore glacial limits within the sea of the hebrides or alternatively that the ice sheet margin was floating and retreated predominantly by calving leaving little geomorphological evidence of its retreat

cordierite as a monitor of fluid and melt h2o contents in the lower crust an experimental calibration cordierite can contain variable amounts of h 2 o and co 2 and the total amount and relative proportions of these volatiles reflect the environment in which the cordierite was formed in this study cordierite has been experimentally equilibrated with a peraluminous granite melt and the h 2 o contents of the phases have been determined by secondary ion mass spectrometry sims the results show that cordierite can have a range of h 2 o contents at a single pressure and temperature in this case 900 c 5 0 kbar the maximum h 2 o contents occur at saturation when h 2 o vapor is also present at which point cordierite contains 1 69 0 05 wt and the melt contains 10 0 0 42 wt however as the system becomes progressively more water undersaturated the phases contain less h 2 o and the partitioning coefficient d w h 2 o melt h 2 o cordierite in wt decreases from 5 9 0 3 to 4 4 0 6 the experiments show that equilibration with a volatile undersaturated melt provides an alternative to leakage as a mechanism for producing volatile poor cordierites application of this experimental calibration to cordierites from granulite migmatites predicts that the melts with which they last equilibrated contained only 2 7 3 8 wt h 2 o

the dynamics of ice sheet outlets a comparison of data from aircraft altimetry landsat imagery and radia echo sounding has shown characteristic surface topographies associated with sheet and stream flow the transition between the two is abrupt and occurs at a step in the subglacial topography this marks the onset of basal sliding and high velocities caused by subglacial water it results in crevassed amphitheatre like basins round the head of outlet glaciers it is also the zone of maximum driving stress beyond which values decline rapidly as velocities increase this abrupt transition appears to be topographically controlled since basal temperatures are at the pressure melting point well inland of the change in regime the marie byrd land ice streams exhibit qualitative differences from other ice sheet outlets however the change to lower driving stresses is much more gradual and occurs several hundred kilometres inland such ice streams have particularly low surface slopes and appear in form and flow regime to resemble confined ice shelves rather than grounded ice the repeated association of the transition to rapid sliding with a distinct subglacial feature implies a stabilizing effect on discharge through outlet glaciers acceleration of the ice is pinned to a subglacial step and propagation of high velocities inland of this feature seems improbable rapid ice flow through subglacial trenches may also ensure a relatively permanent trough through accentuation of the feature by erosion this is concentrated towards the heads of outlet glaciers up stream of the region where significant basal decoupling occurs this may be a mechanism for the overdeepening of fjords at their inland ends and the development of very steep fjord headwalls

the significance of rock structure lithology and pre glacial deep weathering for the shape of intermediate scale glacial erosional landforms the main landforms within the glacially scoured precambrian rocks of the swedish west coast are closely connected to the principal structural pattern and have lately been explained as mainly a result of etch processes probably during the mesozoic and with a possible second period of etching during the neogene to explore the effect of multiple glacial erosion on the rock surfaces an island with two different lithologies and with striae from different directions was selected for a detailed study focusing on the shape of roches moutonnees air photo interpretation of bedrock lineaments and roches moutonnees combined with detailed field mapping and striae measurements are used to interpret the structural and lithological control on the resulting shape the study reveals a significant difference in shape between roches moutonnees in augen granite and orthogneiss low elongated and streamlined roches moutonnees occur in the gneiss area striated by a late weichselian ice flow from the ne this ice flow is subparallel with both the local dominant trend of topographically well expressed joints and the schistosity of the gneiss frequently there are no signs of quarrying on the lee sides of the gneiss roches moutonnees and hence they resemble the shape of whalebacks or ruwares as typically associated with the exposed basal weathering surface found in tropical areas the granite roches moutonnees were formed by an older ice flow from the ese which closely followed the etched wnw ese joint system of the granite late weichselian ice flow from the ne caused only minor changes of the landforms on the contrary marks of the early ese ice flow are poorly preserved in the gneiss area where it probably never had any large effect as the flow was perpendicular to both schistosity and structures and accordingly also to the pre glacial relief the study demonstrates that coincidence between ice flow direction and pre glacially etched structures is most likely to determine the effects of glacial erosion copyright 2002 john wiley sons ltd

glacial erosion and geomorphology in the northwest sierra nevada ca pleistocene glacial erosion left a strong topographic imprint in the northwestern sierra nevada at many scales yet the specific landforms and the processes that created them have not been previously documented in the region in contrast glaciation in the southern and central sierra was extensively studied and by the end of the 19th century was among the best understood examples of alpine glaciation outside of the european alps this study describes glacially eroded features in the northwest sierra and presents inferred linkages between erosional forms and pleistocene glacial processes many relationships corroborate theoretical geomorphic principles these include the occurrence of whalebacks in deep ice positions roches moutonnees under thin ice and occurrence of p forms in low topographic positions where high subglacial meltwater pressures were likely some of the landforms described here have not previously been noted in the sierra including a large crag and tail eroded by shallow ice and erosional benches high on valley walls thought to be cut by ice marginal channels

modification of bedrock surfaces by glacial abrasion and quarrying evidence from north wales abstract abrasion and quarrying are significant processes of subglacial erosion for ice masses in direct contact with hard substrates yet their relative efficacy and spatio temporal variability is unclear here we investigate the glacial impact of these processes on a 70 m by 60 m bedrock surface at moel ysgyfarnogod in the rhinog mountains wales using a combination of high resolution digital photographs analysis of a digital terrain model derived from an unmanned aerial vehicle survey and regional ice sheet modelling we map and analyze the distribution of grooved and striated surfaces abraded surfaces quarried blocks and open fractures in addition to the orientation of pre existing bedrock fractures and joints the grooves and striations are orientated in a single consistent direction across the bedrock surfaces related to regional ice flow during the late pleistocene abraded and smoothed bedrock dominates the proximal edges of the bedrock outcrop and quarrying prevails on the distal edges of the bedrock outcrop which are dominated by detached and partially detached blocks we propose these blocks were removed during the final stages of the last glacial cycle when subglacial meltwater was plentiful in this otherwise predominantly frozen subglacial setting a minimum estimate of 2000 m3 displaced material at this site implies that subglacial quarrying would have been an important erosional process during final stages of deglaciation

microstructures and composition of melt inclusions in a crustal anatectic environment represented by metapelitic enclaves within el hoyazo dacites se spain abstract this article reports microstructures and compositions of melt inclusions in anatectic metapelites found as enclaves within el hoyazo dacites in the neogene volcanic province of southeastern spain the enclaves represent fragments of continental crust partially melted at 800 850 c and 5 7 kbar and brought to surface rapidly within the host volcanics while they still were in a molten state rapid cooling produced the solidification of silicate melt to glass in the rock matrix and in inclusions within minerals melt inclusions mi are present within nearly all mineral phases in the enclaves and their associated microstructures indicate a primary or pseudo secondary origin the entrapment mechanisms of mi within plagioclase were associated with 1 the presence of micron sized solids mostly graphite on the surface of growing crystals 2 partial resorption of crystals generation of embayments and later growth in the presence of melt and 3 entrapment of melt during crystal growth within crystallographic controlled planar structures e g on crystal faces melt inclusions in garnet are commonly associated with regularly oriented planar discontinuities filled with glass interpreted either as spaces left between adjacent mineral growth spirals or as crystallographic controlled cracks generated in between stages of mineral growth melt was trapped or percolated along these microstructures and later on necking down phenomena individualized inclusions with negative crystal shape melt inclusions in biotite are abundant show negative crystal shape and parallel cleavage planes melt inclusions in cordierite alkali feldspar and ilmenite are isolated sparse and sometimes rather large the composition of glass from all mi is leucogranitic and peraluminous with small differences among glasses in each mineral host there is some variation in glass composition within each textural location as well compositional heterogeneity can be partially explained by a combination of processes such as generation of boundary layers during mineral growth crystallization of daughter phases and hydrogen loss via diffusion through the host mean glass compositions in the several textural locations however can be tentatively interpreted as reflecting the evolution of melt chemistry during the prograde low to medium pressure anatexis of quartz poor metapelites

immiscibility between carbonic fluids and granitic melts during crustal anatexis a fluid and melt inclusion study in the enclaves of the neogene volcanic province of se spain in the restitic crustal enclaves in the neogene volcanics of el hoyazo and mazarron se spain associations of fluid and silicate melt inclusions indicative of immiscibility are frequently observed in the bt poor crd rich graphitic metapelites these occurrences extremely rare for anatectic crustal rocks have been studied by microthermometry micro raman spectroscopy and emp analysis both at el hoyazo and mazarron the immiscible fi and mi are hosted in plagioclase and cordierite with microstructures that suggest primary trapping the fi hosted in cordierite are monophase whereas they may contain crystals of calcite when hosted in plagioclase indicating fluid host reaction during cooling decrepitation microstructures have not been observed the mi contain fresh glass of peraluminous felsic rhyolitic composition typical of anatectic s type melts in all samples the fluids are co2 dominated n85 mol with minor amounts of n2 and ch4 and traces of co and h2 the nucleation of graphite induced by the laser beam in some inclusions demonstrates that the fluids are graphite saturated large scatter in microthermometric behaviour of fi indicates significant density variations only in one sample from el hoyazo are fluid densities compatible with the estimated p tconditions of trapping 5 7 kbar 850 50 c whereas in the remaining samples the extremely low densities suggesting trapping pressures b1 kbar are in contrast with the microstructural indications of primary entrapment and little evidence of decrepitation in addition although some measured compositions are compatible with c o h n fluid speciation at the estimated p t conditions of anatexis the lack of h2o in all fi is inconsistent with the slightly hydrated character of coexisting glasses the possible mechanisms accounting for departure of densities and compositions of fi from expected values are discussed and leakage of h2o suggested as the most plausible

megagrooves and streamlined bedrock in nw scotland the role of ice streams in landscape evolution abstract new multibeam bathymetry data onshore high resolution elevation data nextmap and fieldwork in the ullapool area of nw scotland reveal large scale megagrooves and streamlined bedrock forms in a well defined 20 km wide zone the landsystem is typical of a coherent flow corridor within a grounded ice sheet on bedrock dominated terrain we describe the morphology of the large scale features discuss their likely formation and consider the wider implications for ice sheet dynamics based on the strongly convergent bedform distribution the presence of megagrooves and highly elongate bedrock forms we interpret the erosional landscape to be the signature of a fast flowing tributary that once fed the the minch palaeo ice stream a major artery of the last british irish ice sheet the exact genesis of bedrock megagrooves remains uncertain although focused subglacial abrasion is likely to have carved most of the shallow strongly parallel features whilst glacial meltwater may have carved or modified others bedform morphometry is used to discriminate zones reflecting the degree of glacial streamlining elongation ratios 5 1 we interpret these zones to represent the transition from potentially cold based slow ice sheet flow to warm based fast flow based on these results and the presence of ribbed moraines we suggest a bedform continuum model for onset zones of palaeo ice streams on rigid beds rapid spatial bedform evolution is suggested to reflect an increase in subglacial erosive power that may be diagnostic of palaeo ice sheet thermal boundaries i e from cold to warm based and is also consistent with the expected downstream increase in ice velocity within an ice stream onset zone finally this study speculates on the role played by basal meltwater in ice stream initiation and the role of ice streams and their tributaries in landscape evolution

controls on bedrock bedform development beneath the uummannaq ice stream onset zone west greenland this paper investigates the controls on the formation of subglacially eroded bedrock bedforms beneath the topographically confined region upstream of the uummannaq ice stream uis during the last glacial cycle palaeoglaciological conditions are believed to have been similar for all sites in the study characterised by thick fast flowing ice moving over a rigid bedrock bed classic bedrock bedforms indicative of glacially eroded terrain were mapped including p forms roches moutonnees and whalebacks bedform long axes and plucked face orientations display close correlation parallel and perpendicular to palaeo ice flow directions inferred from striae measurements across all sites elongation ratios length to width varied by an order of magnitude between 0 8 1 and 8 4 1 bedform properties length height width and long axis orientation from four subsample areas form morphometrically distinct populations despite their close proximity and hypothesised similarity in palaeoglaciological conditions variations in lithology and geological structures e g joint frequency joint dip joint orientation bedding plane thickness and bedding plane dip provide lines of geological weakness which focus the glacial erosion in turn controlling bedform geometries determining the relationship s between bedding plane dip relative to palaeo ice flow and bedform shape relative length amplitude and wavelength has important ramifications for understanding subglacial bed roughness cavity formation and likely erosion style quarrying and or abrasion at the ice bed interface this paper demonstrates a direct link between bedrock bedform geometries and geological structure and emphasises the need to understand bedrock bedform characteristics when reconstructing palaeoglaciological conditions

the distribution of h2o co2 between cordierite and granitic melt under fluid saturated conditions at 5 kbar and 900 c experiments to determine the distribution of h2o and co2 between synthetic peraluminous granitic melt and natural fe mg cordierite have been conducted at 5 kbar and 900 c under fluid saturated conditions up to seven charges saturated with a range of h2o co2 fluid compositions were run simultaneously the h2o and co2 contents of the cordierites and the h2o contents of the melts were determined using secondary ion mass spectrometry as the co2 content of the fluid increases the h2o content of both the cordierite and the melt decrease in a similar manner to fluid undersaturated experiments in the h2o only system the cordierite h2o contents in the experiments range from 0 5 to 1 7 wt h2o the distribution coefficients dw wt h2o melt wt h2o cordierite are in the range 3 5 5 9 and agree with the model of harley and carrington for 5 kbar and 900 c the co2 content of the cordierite increases from 0 to 1 wt co2 in the most co2 rich experiment as the cordierite and melt h2o contents decrease our h2o co2 cordierite data allow us to model and predict the maximum co2 content in cordierite to be 0 16 0 01 molecules per formula unit i e 1 16 wt co2 at 5 kbar and 900 c this value and the channel co2 contents of cordierite in equilibrium with h2o co2 fluids at high xco2 are significantly lower than predicted using previous models on the basis of these experiments cordierites that are saturated in h2o co2 and have channel xco2 0 25 require aco2 of over 0 75

new radiocarbon dates for early deglaciation from the southeastern coast mountains of british columbia basal dates obtained on organic material from postglacial lacustrine sediments from four lakes in the kwoiek creek watershed southern coast mountains of british columbia provide minimum dates of deglaciation the dates obtained 12 255 770 11 485 185 10 385 595 and 9640 380 bp at elevations 835 1120 m suggest that extensive areas of the mountains of southern british columbia were ice free prior to 11 500 years ago this has implications for models of the regional deglaciation of the southern portion of the province

structural analysis of mylonitic rocks in the cougar creek complex oregon idaho using the porphyroclast hyperbolic distribution method and potential use of sc type extensional shear bands as quantitative vorticity indicators abstract mylonitic rocks of the cougar creek complex of northeastern oregon and west central idaho provide an opportunity to document the deformational structures produced during general non coaxial shear within quartz feldspar mylonites and to explore the potential role of sc type extensional shear bands in vorticity analysis well developed feldspar porphyroclasts within six mylonite zones were utilized to estimate bulk kinematic vorticity w k using the porphyroclast hyperbolic distribution phd method w k values for the cougar creek mylonites range from w k 0 26 to w k 0 37 synthetic and antithetic shear band inclinations were measured relative to observed shear zone boundaries within five mylonite zones with estimated w k values and compared to the non coaxial flow field geometries and eigenvector orientations in each mylonite zone synthetic sc type shear band populations exhibit a range of inclination with maximum inclination lying approximately parallel to the acute bisector ab of the eigenvectors similarly antithetic shear band populations show a range of inclination near the obtuse bisector ob of the eigenvectors we infer that sc type extensional shear bands form initially parallel to ab and ob and rotate towards the flow plane with progressive deformation decreasing their inclination relative to the shear zone boundary ab and ob have significance in the strain field in that they represent orientations of maximum angular strain rate thus planes perpendicular to ab and ob are mechanically favorable for small zones of localized simple shear shear bands within the heterogeneous bulk strain of the mylonite orientation analysis of populations of sc type shear bands may provide a direct quantitative means of estimating w k

ice streams of the late wisconsin cordilleran ice sheet in western north america abstract the late wisconsin cordilleran ice sheet cis of western north america is thought to have reached its maximum extent 2 5 106 km2 as late at c 14 5 ka most 80 of the ice sheet s bed consists of high mountains but its core zone sited on plateaux of the intermontane belt of british columbia and coterminous parts of the usa shows broad swaths of subglacially streamlined rock and sediment broad scale mapping from new digital imagery data identifies three subglacial bed types 1 hard beds of variably streamlined bedrock 2 drumlinized soft beds of deformation till reworked from antecedent sediment and 3 mixed beds of variably streamlined bedrock protruding through drumlinized sediment drumlins on soft beds appear to be erosional features cut into till and antecedent sediments and identify the catchment areas of paleo ice streams expressed downglacier as flow sets of megascale glacial lineations msgls grooved and cloned drumlins appear to record the transition from drumlins to msgls the location of paleo ice streams reflects topographic funneling of ice from plateau surfaces through outlet valleys and a soft bed that sustained fast flow rock cut msgls are also present locally on the floors of outlet valleys cis disintegrated in

palaeoglaciology of the welsh sector of the british irish ice sheet this palaeoglaciological reconstruction based on the distribution of glacial lineations interpreted from satellite imagery considers the extent thickness and dynamics of the welsh ice cap and its interaction with the british irish ice sheet two major ice flow events were identified the oldest phase of ice flow event i is characterized by ice flowing from an ice dispersal centre situated over the higher terrain in north central wales and by ice thick enough to cover the mountain summits at this time the interior of the ice cap is inferred to have been dominated by cold based ice during the growth of the welsh ice cap it became confluent with the british irish ice sheet the welsh ice cap at this time was again sufficiently thick to submerge the highest mountain summits the youngest detected phase of ice flow event ii was marked by an abrupt change in the dynamics of the welsh ice cap during event ii the welsh ice cap was drained by at least four ice streams which followed major troughs in northern and eastern wales

variations in fluid activity across the etive thermal aureole scotland evidence from cordierite volatile contents the h2o and co2 content of cordierite was analysed in 34 samples from successive contact metamorphic zones of the etive thermal aureole scotland using fourier transform infrared spectroscopy ftir the measured volatile contents were used to calculate peak metamorphic h2o and co2 activities total volatile contents are compared with recently modelled cordierite volatile saturation surfaces in order to assess the extent of fluid present v fluid absent conditions across the thermal aureole in the middle aureole prior to the onset of partial melting calculated ah2o values are high close to unity and measured volatile contents intersect modelled h2o co2 saturation curves at the temperature of interest suggesting that fluid present conditions prevailed total volatile contents and ah2o steadily decrease beyond the onset of partial melting consistent with the notion of ah2o being buffered to lower values as melting progresses once free hydrous fluid is exhausted all sillimanite zone samples record total volatile contents that are significantly lower than modelled h2o co2 saturation surfaces implying that fluid absent conditions prevailed the lowest recorded ah2o values lie entirely within part of the section where fluid absent melting reactions are thought to have dominated samples within 30 m of the igneous contact appear to be re saturated possibly via a magmatically derived fluid in fluid absent parts of the aureole cordierite h2o contents yield melt h2o contents that are compatible with independently determined melt h2o contents the internally consistent cordierite volatile data and melt h2o data support the conclusion that the independent p t estimates applied to the etive rocks were valid and that measured cordierite volatile contents are representative of peak metamorphic values the etive thermal aureole provides the most compelling evidence suggesting that the cordierite fluid monitor can be used to accurately assess the fluid conditions during metamorphism and partial melting in a thermal aureole

abraded rock landforms whalebacks developed under ice streams in mountain areas like many mountain ranges the coast mountains of british columbia canada have undergone both local and ice sheet glaciation effects of ice sheets are concentrated along major valleys and on adjacent spurs and passes which carried strong flows of diffluent ice the major valleys are broad glacial troughs with frequent rock basins their slopes are broken into rounded steep sided bosses whalebacks abraded on all sides they are of the order of 100 m to 1 km long and 10 m high in the southern coast mountains the distribution of these whalebacks is consistent with a proposed pattern of former ice streams 1 0 2 1 km thick within the cordilleran ice sheet they are best developed where geological structures parallel the valley and thus the former ice flow direction but they are found on a range of lithologies and some are transverse to structure the whalebacks provide an impression of glacial streamlining and occasionally grade into rock drumlins roches moutonnees are rare in the major troughs it is hypothesised that these whalebacks and rock drumlins develop under ice streams of greenland or east antarctic type sliding rapidly over bedrock and exploiting rock weaknesses to produce streamlined features lee slopes are abraded when thick ice suppresses bed separation even with rapid flow basal ice of low viscosity would aid this suppression water pressures under the ice streams may have remained high so that lee side plucking was rare such plucking is most likely where pressure fluctuates dramatically and especially when lee cavities under active ice reach atmospheric pressure

subglacial observations from oksfjordjokelen north norway stepped bedrock topography at the snout of a small outlet glacier from oksfjordjokelen north norway produces an extensive subglacial cavity system which stretches some 70m across and 100m up glacier giving access beneath ice 50 m thick inside the cavity regelation ice clean glacier ice and deforming basal ice have been observed samples were taken and basal debris concentrations at the glacier sole were found to vary between 0 005 and 15 38 per cent by volume the basal ice velocity has been determined using a linear variable differential transformer attached to an analogue recorder and also by means of measured displacements of ice crews and clasts embedded in the basal ice velocities were found to differ both spatially and temporally from a maximum of 2 55 mm h1 to a minimum of 0 3 mm h 1 the measurements and observations which have been related to present theory show how spatially averaged values for a number of variables could lead to inaccuracies in predicted erosion values certainly at a local scale on the exposed foreland jointcontrolled lee side faces provide evidence for extensive subglacial plucking here taken to mean the removal of preloosened bed material and or material resulting from bed failure indeed in the cavity the early stages of removal of joint controlled blocks by ice deformation along joints have been observed the importance of debris rich basal ice is shown in the formation of large striations up to 500cm 16cm 2cm present on the foreland

rock drumlins and megaflutes of the niagara escarpment ontario canada a hard bed landform assemblage cut by the saginaw huron ice stream abstract the late wisconsin c 18 000 ybp saginaw huron ice stream shis of the laurentide ice sheet was as much as 800 km long and 250 km wide in the great lakes basin of mid continent north america in its onset zone in the upper lake huron basin of ontario canada it flowed south from the high standing canadian shield to move over gently dipping ordovician and silurian dolostones devoid of glacial sediment cover the onset zone is recorded by a distinct hard bed landform assemblage across 3000 km2 of north facing escarpments niagara fossil hill and kagawong and dip slope pavements on the bruce peninsula and manitoulin island and the adjacent floor of lake huron a wide range of glacially streamlined rock landforms were carved into dolostones below fast flowing ice the largest are 30 km wide bullet shaped escarpment promontories that face upglacier superposed on these are swarms of rock drumlins up to 5 km wide with downglacier lengths of as much as 10 km promontories and drumlins record streaming of dirty basal ice around escarpment highs and create a distinct zig zag planform to the escarpments in turn down dip trailing edge dolostone pavements are corrugated by kilometre long megagrooves and megaflutes cut by basal ice flowing around resistant high standing bioherm mounds on dolostone bedding planes the geomorphology of the niagara escarpment does not primarily reflect a lengthy history of preglacial cenozoic fluvial erosion as classically argued but geologically brief episodes of accelerated abrasion and quarrying below ice streams within successive pleistocene ice sheets

potential effects of subglacial water pressure fluctuations on quarrying water pressure fluctuations beneath glaciers may accelerate rock fracture by redistributing stresses on subglacial bedrock and changing the pressure of water in bedrock cracks to study the potential influence of water pressure fluctuations on the fracture of subglacial bedrock ice flow over a small bedrock step with a water filled cavity in its lee is numerically modeled and stresses on the bedrock surface are calculated as a function of transient water pressures in the cavity stresses on the bed are then used to calculate principal stress differences within the step rapid reductions in cavity water pressure increase principal stress differences in the bed increasing the likelihood of crack growth in the step and the formation of predominantly vertical fractures relatively impermeable bedrock may be most susceptible to fracturing during water pressure reductions because high water pressure in cracks within the rock can be maintained as water pressure decreases in cavities these results when considered in conjunction with the strong likelihood that increases in water pressure accelerate the removal of rock fragments loosened from the bed suggest that in zones of ice bed separation where water pressure fluctuations typically are large rates of quarrying may be higher than along other parts of glacier beds

antarctic ice streams a review an ice stream is a part of an inland ice sheet that flows rapidly through the surrounding ice the distinction between an ice sheet and an outlet glacier is clear in principle but muddy in practice many antarctic glaciers are intermediate in character the ross ice streams which flow through the west antarctic inland ice into the ross ice shelf are distinct in character differing even from other ice streams in the marine ice sheet of west antarctica their surface elevation profiles are low their bed slopes are low and smooth and their driving stresses diminish monotonically downglacier in transverse profile they are broader in relation to ice thickness and exhibit shallower subglacial troughs than other ice streams many models for the fast sliding of glaciers have been applied to the ross ice streams most have included in some form a reduction in basal drag resulting from a lesser effective than glaciostatic pressure at the bed most models are only semi physical at best so need to be tuned by fitting to assumed parameters at some place or places in the real ice sheet the recent discovery of a very small effective pressure beneath one ice stream consequently has led to some gross errors in the velocities predicted by the models the difficulty may be resolved if it is true as recent experiments suggest that ice stream b and by extrapolation other ross ice streams as well slide on a deforming bed that absorbs most or all of the differential motion between the ice and the bedrock