the response of black rapids glacier alaska to the denali earthquake rock avalanches 1 we describe the impact of three simultaneous earthquake triggered rock avalanches on the dynamics of black rapids glacier alaska by using spaceborne radar imagery and numerical modeling we determined the velocities of the glacier before and after landslide deposition in 2002 by using a combination of ers 1 ers 2 tandem radarsat 1 and alos palsar synthetic aperture radar data ice velocity above the debris covered area of the glacier increased up to 14 after the earthquake but then decreased 20 by 2005 within the area of the debris sheets mean glacier surface velocity increased 44 within 2 years of the landslides at the downglacier end of the lowest landslide where strong differential ablation produced a steep ice cliff velocities increased by 109 over the same period by 2007 ice velocity throughout the debris area had become more uniform consistent with a constant ice flux resulting from drastically reduced ablation at the base of the debris without further analysis we cannot prove that these changes resulted from the landslides because black rapids glacier displays large seasonal and interannual variations in velocity however a full stokes numerical ice flow model of a simplified glacier geometry produced a reversal of the velocity gradient from compressional to extensional flow after 5 years which supports our interpretation that the recent changes in the velocity field of the glacier are related to landslide induced mass balance changes

change in surface debris cover on mont blanc massif glaciers after the little ice age termination because of insulation by supraglacial debris the dynamics of debris covered glaciers differ from those of clean glaciers thus changes in debris cover have to be taken into account when interpreting glacier fluctuations in terms of climate forcing three large glaciers in the mont blanc massif were investigated for the period since the termination of the little ice age lia using historical and scientific documents of the eighteenth and nineteenth centuries although debris cover was limited to its frontal area until the 1840s miage glacier exhibited a continuous debris cover in the first decades after the lia increasing to its present extent by the 1930s on the mer de glace a partial debris cover formed by coalescence of two of the four medial moraines at the close of the lia until 1890 these moraines have formed the present veine noire black vein in contrast brenva glacier had a continuous debris cover at the end of the eighteenth century possibly following a rock avalanche in 1767 fo

glacier changes in the central and northern tien shan during the last 140 years based on surface and remote sensing data this research presents a precise evaluation of the recession of akshiirak and ala archa glaciers tien shan central asia based on data of geodetic surveys from 1861 69 aerial photographs from 1943 1963 1977 and 1981 1 25 000 scale topographic maps and srtm and aster data from 2000 03 the akshiirak glacierized massif in the central tien shan contains 178 glaciers covering 371 6 km 2 and the ala archa glacier basin in the northern tien shan contains 48 glaciers covering 36 31 km 2 the tien shan glaciers retreated as much as 3 km from the 1860s to 2003 area shrinkage of akshiirak and ala archa was 4 2 and 5 1 respectively from 1943 to 1977 and 8 7 and 10 6 respectively from 1977 to 2003 the volume of the akshiirak glaciers was reduced by 3 566 km 3 from 1943 to 1977 and 6 145 km 3 from 1977 to 2000 the total reduction of the tien shan glaciers is 14 2 during the last 60 years 1943 2003 the northern and central tien shan have not experienced a significant precipitation increase during the last 100 years but they have experienced an increase in summer air temperatures especially observable since the 1970s which accelerated the recession of the tien shan glaciers

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

glacial advance and stagnation caused by rock avalanches abstract new model results show that a glacier advance caused by deposition of a rock avalanche on the ice will be followed by stagnation of the advanced ice lobe producing distributed hummocky deposits quite different from the single moraine ridges typically dated in paleoclimatic reconstructions we obtain these results using a numerical flow line glacier model with superimposed rock debris in particular our results imply that the single moraine ridge known as the waiho loop of the franz josef glacier new zealand is not the result of an advance triggered by a rock avalanche else there would be a widespread hummocky glacial stagnation deposit associated with it

rapid advance of two mountain glaciers in response to mine related debris loading rapid glacier advance is known to occur by a range of mechanisms however although large scale debris loading has been proposed as a process for causing rapid terminus advance it has rarely been observed we use satellite remote sensing data to observe accelerated glacier terminus advance in response to massive supraglacial loading on two glaciers in kyrgyzstan over a 15 year period mining activity has led to the dumping of spoil of up to 180 m thick on large parts of these valley glaciers we find that the termini of these glaciers advance by 1 2 and 3 2 km respectively at a rate of up to 350 m yr 1 our analysis suggests that although enhanced basal sliding could be an important process massive supraglacial loads have also caused enhanced internal ice deformation that would account for most or all of the glacier terminus advance in addition narrowing of the glacier valley and mining and dumping of ice alter the mass balance and flow regime of the glaciers although the scale of supraglacial loading is massive this full scale experiment provides insight into glacier flow acceleration response where small valley glaciers are impacted by very large volumes of landslide debris

geomorphology and sedimentology of surging glaciers a land systems approach the identification of surging glaciers and ice streams in glaciated landscapes is of major importance to the understanding of ice sheet dynamics and for reconstructing ice sheets and climate no single landform or diagnostic criterion has yet been found with which to identify surging glaciers a surging glacier land system model is constructed using observations and measurements from contemporary surging glacier snouts in iceland svalbard u s a and canada for differentiating ancient surging margins from other non surging palaeoglaciers this integrates the suite of landforms sediments and stratigraphy produced at surging glacier margins landforms produced during surging include thrust moraines concertina eskers and subglacial crevasse squeeze ridges sedimentary sequences are usually characterized by multiple stacked diamictons and stratified interbeds which display severe glaciotectonic contortion and faulting hummocky moraine comprising interbedded stratified sediments and mass flow diamictons has also been associated with surge margins where large quantities of supraglacial and englacial debris entrained during the surge event have melted out in situ an example of the application of the land system model is presented for east central alberta canada a surging palaeo ice stream is identified within this part of the southwestern laurentide ice sheet where thrust block moraines crevasse squeeze ridges flutings hummocky moraine and glaciotectonized sediments are juxtaposed

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

how do glaciers surge a review the quasi periodic oscillations between normal and fast motion exhibited by surge type glaciers provide the best observational opportunity to determine limiting conditions that allow fast motion the measurements from variegated glacier prove that its surge motion is caused by rapid sliding induced by high water pressure this arises from a major restructuring of the basal hydraulic system which impedes water discharge prior to and during surge although the evolving glacier geometry and stress distribution play a principal enabling role the seasonal timing of two distinct surge pulses each initiated in winter and terminated in summer indicates a major influence from variable external water inputs this influence is not considered in existing surge models and should promote caution in the use of data from temperate and subpolar surge type glaciers to deduce surge potential in polar ice masses the spatial spreading of surge motion from a zone of local initiation occurs by stress redistribution which may spread the surging zone rapidly upglacier or downglacier inside a region of active ice and by mass redistribution with compressional thickening at the surge front which enables down glacier propagation into less active ice the data from other surge type glaciers including the extensive data from medvezhiy glacier are not inconsistent with the above processes but are inadequate to establish whether completely different mechanisms operate in some surges the way by which water accumulates and produces fast sliding is not established in detail for any surge type glacier and may be different on different glaciers depending for example on the presence or absence of unconsolidated debris between the ice and rock

how much do we really know about glacier surging some of the ideas about glacier surging are considered mainly but not entirely in the light of observations of temperate glaciers in alaska u s a made within the last 15 years climate has an influence on surge recurrence interval climate and weather also affect surge initiation termination and magnitude regional studies lead to the speculation that subglacial till plays a key role in surging and it has been found under all surge type glaciers studied so far including black rapids and variegated glaciers alaska in most of the glaciers studied till deformation processes dominate the motion in quiescence the linked cavity model of surge triggering and rapid motion is not consistent with these observations but the limited coverage of the observations does not rule it out under parts of the glaciers studied the till observations in alaska raise old questions about the interaction between till and the hydraulic systems of temperate glaciers the role of stored water which observations show to be active even in winter on black rapids glacier is noted

mass balance and equilibrium line altitudes of glaciers in high mountain environments abstract the mass balance characteristics of glaciers in high mountain environments complicate the relationship between glacier equilibrium line altitudes elas and climatic variables such as precipitation and air temperature therefore methods of ela reconstruction employed in low relief environments are commonly not applicable in high mountains or require some modification we review the concept of the ela with reference to the mass balance of a range of glacier types found in high mountain regions we examine the applicability of several commonly used methods of ela reconstruction for different glacier types and propose some general principles to guide the choice of appropriate methods

slow surge of trapridge glacier yukon territory canada 1 trapridge glacier a polythermal surge type glacier located in the st elias mountains yukon territory canada passed through a complete surge cycle between 1951 and 2005 air photos 1951 1981 and ground based optical surveys 1969 2005 are used to quantify the modifications in flow and geometry that occurred over this period yearly averaged flow records suggest that the active phase began 1980 and lasted until 2000 the average velocity in the central area of the glacier went from 16 m yr 1 in 1974 to 39 m yr 1 in 1980 it peaked at 42 m yr 1 in 1984 and remained above 25 m yr 1 until 2001 over that interval the flow decelerated by steps in 4 year pulses after a particularly vigorous acceleration in 1997 1999 the glacier gradually slowed to presurge velocities in 2005 the flow was less than 9 m yr 1 digital elevation models are generated by stereographic analysis of air photos for 1951 1970 1972 1977 and 1981 these models are updated annually using ground based survey data and a novel implementation of bayesian kriging over the course of the surge the front of active ice advanced 450 m and the glacier area increased by 10 with an associated thinning of the ice the previous surge of trapridge glacier starting before 1939 and ending before 1951 led to a terminus advance of 1 km comparison of the two surges suggests that the 1930s surge started with a slow progression similar to what we observed in the 1980s and 1990s and switched to a faster flow mode after 1941 this second phase was never attained in the recent surge probably owing to a lack of mass

effects of debris on ice surface melting rates an experimental study here we report a laboratory study of the effects of debris thickness diurnally cyclic radiation and rainfall on melt rates beneath rock avalanche debris and sand representing typical highly permeable supraglacial debris under continuous steady state radiation sand cover 50mm thick delays the onset of ice surface melting by 12 hours but subsequent melting matches melt rates of a bare ice surface only when diurnal cycles of radiation are imposed does the debris reduce the longterm rate of ice melt beneath it this is because debris 50 mm thick never reaches a steady state heat flux and heat acquired during the light part of the cycle is partially dissipated to the atmosphere during the nocturnal part of the cycle thereby continuously reducing total heat flux to the ice surface underneath the thicker the debris the greater this effect rain advects heat from high permeability supraglacial debris to the ice surface thereby increasing ablation where thin highly porous material covers the ice in contrast low permeability rock avalanche material slows water percolation and heat transfer through the debris can cease when interstitial water freezes during the cold night part of the cycle this frozen interstitial water blocks heat advection to the ice debris contact during the warm day part of the cycle thereby reducing overall ablation the presence of metre deep rock avalanche debris over much of the ablation zone of a glacier can significantly affect the mass balance and thus the motion of a glacier the length and thermal intensity of the diurnal cycle are important controls on ablation and thus both geographical location and altitude significantly affect the impact of debris on glacial melting rates the effect of debris cover is magnified at high altitude and in lower latitudes copyright 2010 elsevier b v all rights reserved

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

catastrophic landslides glacier behaviour and moraine formation a view from an active plate margin the influence of large bedrock landslides rock avalanches on the behaviour of glaciers is incompletely recognised here we present an example from an active tectonic margin in south island new zealand where large earthquakes leave a significant imprint on glacial records we demonstrate that terminal moraines on the western side of the southern alps record both ordinary i e climate driven and landslide initiated glacial advances following consideration of the processes involved in rock avalanche initiated moraine construction we suggest ways of determining the nature of the advance that built the terminal moraine the implications of these observations are important in breaking the conventional linkage of individual terminal moraines with climate forcing

the formation of beaches on shore platforms in microtidal environments beaches are common features of many rocky shorelines and can be considered to be constrained by the underlying geology in mesotidal to macrotidal areas the slope of the substrate and sediment supply are the primary factors in constraining the size and development of beaches on shore platforms in microtidal settings it is not known if these factors are wholly responsible for determining the presence of beaches on shore platforms nor the contribution of other factors such as hydrodynamics the microtidal coast of victoria australia is surveyed in this study in order to quantify the morphological boundary conditions that constrain beach development on semi horizontal shore platforms an ample sediment supply indicates that the underlying geology is controlling the presence and absence of beaches where beaches occur they always overlie a rock ramp which is the steepest part of the platform the two most important morphological constraints were platform width and height both of which significantly correlated with beach volume an elevational threshold exists at just over 1 0 m where beaches cannot accumulate below this threshold platform width appears to be the principle constraining factor in beach accumulation an evolutionary model is inferred which suggests that dissipation of wave energy associated with platform widening plays an important role in allowing beaches to accumulate the model suggests beaches on platforms will be particularly sensitive to sea level rise copyright 2014 john wiley sons ltd

combined measurements of subglacial water pressure and surface velocity of findelengletscher switzerland conclusions about drainage system and sliding mechanism interpretation des mesures de pression dans les forages et des vitesses superficielles la comparaison avec les modeles suggere que l on a neglige le frottement du aux debris dans les modeles et qu il n existe jamais de chenaux cylindriques rectilignes

late quaternary glaciation in the kyrgyz tien shan the tien shan of kyrgyzstan contains multiple moraines and drift from late quaternary glaciations the spatial temporal distribution of the glaciers inferred from the moraines suggests that the main factor controlling glacier advance here was the availability of moisture the dominant modern climatic signatures in northern central asia include orographic thunderstorms in summer cold and dry siberian high pressure cells in winter and westerly cyclonic storms from the north atlantic and eastern mediterranean in spring and fall changes in any of these systems during the late quaternary would have varied precipitation delivery to and glacier growth in the kyrgyz tien shan geomorphic mapping and reconnaissance level 10be cosmic ray exposure dating of moraine sequences in six drainages indicate that there were multiple maximum advances of similar extents and equilibrium line depressions across the range glaciers in the north and east of the kyrgyz tien shan last advanced to their maximum positions during marine oxygen isotope stage mis 5 and again during mis 4 while in the south and west of the range advance occurred during mis 3 in contrast to maritime europe and north america there is no evidence of a major glacial advance during mis 2 glacier advances during mis 2 and since were restricted to the vicinity of modern glaciers allowing the older glacial record to be preserved well