hydraulics of subglacial supercooling theory and simulations for clear water flows 1 glaciohydraulic supercooling is a mechanism for accreting ice and sediment to the base of glaciers we extend existing models by reworking the spring hutter model for subglacial water flow in tubular conduits to allow for distributed water sheets our goal is to determine diagnostic features of supercooling relative to controlling variables results focus on along path water flow under time varying conditions with attention to ice accretion in and along subglacial overdeepenings we contrast simulations with constant recharge to diurnally varying recharge and expose behavior that cannot be inferred from simple models for example locations of simulated ice accretion differ from those found for steady state models even though total ice accretion remains comparable to field estimates downstream accretion influences upstream effective pressures that then modify the hydraulic gradient that drives water flow this modified gradient tends to inhibit additional accretion by increasing velocity and heat production via viscous dissipation during diurnal cycles accretion varies considerably in daytime viscous dissipation dominates the heat balance and ice melts in morning and evening when flow is rising or falling viscous dissipation is lower and accretion can proceed over nighttime the largest temperature depressions occur in the subglacial system but water flux is lowest and accretion rates are negligible we conclude by inferring that overdeepened glaciers with only clear water flows evolve toward stronger supercooling regimes rather than toward a dynamic equilibrium stabilizing feedbacks are unlikely to occur through glacier hydrology alone and other processes such as erosion sedimentation and sliding must play an important role

thrusting evolution in the southern cordillera oriental northern argentine andes constraints from growth strata abstract growth strata and unconformities in the cenozoic synorogenic sediments in the southern cordillera oriental of the northern argentine andes provide new evidence for the eastward migration of the andean deformation from the puna to the santa barbara system the growth sequences and unconformities allow us to constrain the age of the structures with greater precision and to determine the distribution of this deformation in the thrust and fold wedge over time thrust evolution was mainly controlled by the reactivation of earlier extensional faults of the cretaceous salta rift basin the geometry of the inverted structures together with the general forward migration of the deformation gave rise to different thrust sequences the foreland dipping imbricate stack of the western cordillera oriental developed forwards during middle late miocene resulting in a break back thrusting sequence thrust propagation rate increased in late miocene early pliocene times when the eastern part of the cordillera oriental developed at that time a widespread deformation and synchronous thrusting occurred in the cordillera oriental subsequently deformation was mainly confined to the eastern part of the cordillera oriental finally during the pleistocene holocene deformation affected a wider zone including the cordillera oriental and the santa barbara system giving rise to the reactivation of previously developed thrusts

forces controlling the present day state of stress in the andes the present day state of stress in the andes is expected to be controlled primarily by two different types of forces 1 the resistive force exerted on the western overriding margin of the south american plate and 2 forces that arise from the thickened crust of the andes i e the effect of topography and its compensating crustal root we have studied these forces on the basis of a model for the dynamics of the entire south american plate in which the andes are embedded in this model a given set of forces is constrained by the criterion that the net torque on the plate should vanish a thin elastic shell representation is used to calculate the intra plate stress field associated with the various force distributions we define a reference model for the present study that incorporates a uniform magnitude for the resistance associated with convergence along the western plate margin fpcr plate contact resistance and does not include the effects of topography subsequently we investigate the effect of lateral variation in the magnitude of fpcr and add the topography related forces the main results are 1 a uniform magnitude of fpcr leads to a better match with the observations than a magnitude that is a function of the dip of the lithosphere subducting below the western plate margin 2 the amount of horizontal compression across the andes found in the case that ridge push is considered to be the only force driving the south american plate is small compared to the value required to sustain the andes

gravity anomalies and flexure of the brazilian shield beneath the bolivian andes abstract seismological and geological data suggest that the brazilian shield is now underthrusting beneath the sub andes in order to constrain the minimum amount of shortening that results from this underthrusting we analyzed bouguer gravity anomalies over the shield and the bolivian andes assuming that they are due primarily to variations in crustal thickness that in turn are due to the flexure of an effectively elastic plate brazilian shield loaded by the weight of the andean mountain range gravity anomalies show that airy type isostatic equilibrium does not exist the sub andes are overcompensated and the chaco plain to the east is undercompensated the flexure of the plate can help explain both the overcompensation and the undercompensation if the brazilian shield behaves as an essentially elastic plate that extends at least 150 km and probably 200 km beneath the sub andes and the cordillera oriental and if the flexural rigidity of the plate is between 0 1 and 2 10 24 n m the fit of observed and calculated anomalies however is far from perfect and additional sources of short wavelength anomalies appear to be present assuming that the sediments and sedimentary rocks in the sub andes and cordillera oriental were deposited on the brazilian shield and that later they were overthrust eastward onto one another causing the present topography and the deflection of the plate we computed a family of estimates for the minimum amount of crustal shortening these estimates depend strongly on the amount of sedimentary rock deposited before deformation which does not seem to be well constrained by published geologic mapping nevertheless the calculations suggest that at least 100 km of crustal shortening have occurred and probably more implying that the andes may have been built mostly by crustal shortening

estimating glacier bed overdeepenings as possible sites of future lakes in the de glaciating mont blanc massif western european alps de glaciating high mountain areas result in new landscapes of bedrock and debris where permafrost can degrade persist or even newly form in cases and of new lakes in glacier bed overdeepenings gbos becoming ice free these landscapes with new lakes in close neighborhood to over steepened and perennially frozen slopes are prone to chain reaction processes e g rock ice avalanches into lakes triggering impact waves dam breach or overtopping and debris flows with potentially far reaching run out distances causing valley floors devastation the frequency magnitude and zonation of hazards are shifting requiring integrative approaches combining comprehensive information about landscape evolution and related processes to support stakeholders in their adaptation strategies in this study we intend to setup an essential baseline for such an integrative approach in the mont blanc massif mbm which is a typical high mountain range affected by de glaciation processes we first i predict and ii detect potential gbos by combining the glabtop model with a visual analysis based on morphological indications of glacier flow through over deepened bed parts we then iii determine the level of confidence concerning the resulting information and iv estimate the approximate time range under which potential lakes could form the location of the predicted gbos and the shape of glacier beds are evaluated against currently forming water bodies at retreating glacier snouts and seismic and ice penetrating radar measurements on the argentiere glacier this comparison shows that the location of predicted gbos is quite robust whereas their morphometric characteristics depth volume are highly uncertain and tend to be underestimated in total 48 80 of the predicted or detected gbos have a high level of confidence in addition to five recently formed water bodies at glacier snouts one of the high confidence gbos talefre glacier which is also the most voluminous one could form imminently during coming years if not partially or totally drained through deeply incised gorges at the rock threshold twelve other lakes could form within the first half of the century under a constant or accelerated scenario of continued glacier retreat some of them are located below high and permanently frozen rock walls prone to destabilization and high energy mass movements hinting at possible hot spots in terms of hazards in the coming decades where more detailed analysis would be required

hypocentral trend surface analysis probing the geometry of benioff zones a hypocentral trend surface is a continuous function of latitude and longtitude fitted by least squares to a set of hypocenters so that it predicts depth to the middle of a benioff zone in this paper we take a relatively simple approach to hypocentral trend surface analysis the hypocentral trend surface is constructed from a spherical surface harmonic expansion whose coefficients are selected so as to minimize the standard vertical deviation between hypocenters and trend surface the vertical deviation of a hypocenter from the hypocentral trend surface is called its residual consideration of a hypocentral trend surface cannot be divorced from consideration of the associated residuals and their spatial distribution any analysis of benioff zone geometry trades off presumed thickness of the zone with its presumed shape this trade off can be investigated by examining suites of candidate hypocentral trend surfaces together with their associated residual distributions generated by varying the number of degrees of freedom available to the trend surface hypocentral trend surfaces are generated for three high quality sets of hypocenters obtained by local seismic networks in honshu japan cook inlet alaska and south peru hypocenters beneath honshu generate a bimodal distribution of residuals about their trend surface the vertical separation of the upper and lower sheets of this double benioff zone averages about 33 km no double benioff zone configuration is discovered below cook inlet or south peru regional trend surfaces are established for intermediate depth teleseismic data from south and middle america in south america 0 40 s teleseismic data suggest that along strike transitions between flat and moderately steeply dipping sections of the benioff zone are achieved by flexure of a coherent slab rather than by fragmentation of the slab into tear bound flaps or separate tongues of lithosphere hypocentral trend surface analysis of teleseismic data from south peru suggests a geometry similar to that indicated by hypocentral trend surface analysis of the local data of hasegawa and sacks an eastward shallowing benioff zone beneath southwest mexico is closely associated with the geometry of the trans mexican volcanic arc the benioff zone beneath central america is more steeply dipping the flat slab steep slab transition near 96 w may relate to the difference in age of oceanic lithosphere on either side of the tehuantepec ridge while the strong flexure of the subducted nazca plate beneath ecuador is closely associated with the carnegie ridge the nazca ridge extropolates slightly north of the flexure in subducted lithosphere beneath south peru the flexure appears instead more closely associated with the pronounced inflection in the map view shape of the leading edge of the overriding south american plate

on the morphological characteristics of overdeepenings in high mountain glacier beds overdeepenings i e closed topographic depressions with adverse slopes in the direction of flow are characteristic for glacier beds and glacially sculpted landscapes quantitative information about their morphological characteristics however has so far hardly been available the present study provides such information by combining the analysis of a numerous bed overdeepenings below still existing glaciers of the swiss alps and the himalaya karakoram region modelled with a robust shear stress approximation and b detailed bathymetries from recently exposed lakes in the peruvian andes the investigated overdeepenings exist where glacier surface slopes are low 5 10 occur in bedrock or morainic material and are most commonly a fraction of a kilometre squared in surface area hundreds of metres long about half the length in width and tens of meters deep they form under conditions of low to high basal shear stresses at cirque confluence trunk valley and terminus positions the most striking phenomenon however is the high variability of their geometries depths surface areas lengths and widths of the overdeepenings vary over orders of magnitude and are only weakly if at all interrelated inclinations of adverse slopes do not differ significantly from those of forward slopes and are in many cases higher than so far assumed theoretical limits for supercooling of ascending water and corresponding closure of sub glacial channels such steep adverse slopes are a robust observation and in support of recently developed new concepts concerning the question about where supercooling of sub glacial water and closure of ice channels can or must occur however the question of when and under what climatic topographic and ice conditions the overdeepenings had formed remains unanswered this open question constitutes a key problem concerning the interpretation of observed overdeepenings the understanding of the involved glacio hydraulic processes and the possibility of realistic predictive modelling of overdeepening formation

glacial lake evolution and glacier lake interactions in the poiqu river basin central himalaya 1964 2017 despite previous studies glacier lake interactions and future lake development in the poiqu river basin central himalaya are still not well understood we mapped glacial lakes glaciers their frontal positions and ice flow from optical remote sensing data and calculated glacier surface elevation change from digital terrain models during 1964 2017 the total glacial lake area increased by 110 glaciers retreated with an average rate of 1 4 km 2 a 1 between 1975 and 2015 based on rapid area expansion 150 and information from previous studies eight lakes were considered to be potentially dangerous glacial lakes corresponding lake terminating glaciers showed an overall retreat of 6 0 1 4 to 26 6 1 1 m a 1 and accompanying lake expansion the regional mean glacier elevation change was 0 39 0 13 m a 1 while the glaciers associated with the eight potentially dangerous lakes lowered by 0 71 0 05 m a 1 from 1974 to 2017 the mean ice flow speed of these glaciers was 10 m a 1 from 2013 to 2017 about double the mean for the entire study area analysis of these data along with climate observations suggests that ice melting and calving processes play the dominant role in driving lake enlargement modelling of future lake development shows where new lakes might emerge and existing lakes could expand with projected glacial recession

tephrochronologic constraints on temporal distribution of large landslides in northwest argentina abstract two morphologic settings in the northwestern argentine prone to giant mountain front collapse deeply incised narrow valleys and steep range fronts bordering broad piedmonts were analyzed through detailed investigations of fossil landslides and related fluvio lacustrine sediments nine different rhyodactic tephra layers were defined by geochemical fingerprinting of glass morphology of pumice stratigraphic relationships and mineralogy the age of three tephra could be determined either directly by 40ar 39ar dating or relatively by 14c dating of associated sediments paranilla ash documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont decl

cenozoic stratigraphy and basin tectonics of the andes mountains 20 28 south latitude clastic sedimentary basins have evolved during the past 40 m y in the central andes lat 20 28 s in response to shifting patterns of magmatism and deformation the distribution of these basins and their genetic relations to uplifted areas are analogous to the basins and mountain belts of the north american rocky mountains during the late cretaceous and early cenozoic petroleum exploration has focused on zones underlying the upper cenozoic strata along the eastern margin of the andes mountain belt between about 40 and 25 ma a nonmarine basin extended across the region that is now the andes mountains between about 25 and 10 ma the western part of the former basin became the site of a volcanic arc sediment accumulation continued in the east where marine intercalations demonstrate the low elevation of the basin after 10 ma the volcanic arc remained active and locally widened and crustal shortening caused regionally important thrust and reverse faulted ranges during the past 10 m y up to 4 000 m of coarse clastic debris accumulated in a foreland basin on the eastern flank of the mountains meanwhile in the interior of the mountains over 4 000 m of fine grained strata and evaporites accumulated in local depocenters

accurate source depths and focal mechanisms of shallow earthquakes in western south america and in the new hebrides island arc synthetic seismograms are matched to long period p waveforms in order to obtain accurate depths of shallow earthquakes with known focal mechanisms accurate depths are obtained for a large sample of moderate sized 6 ms 7 events which produced relatively simple p waveforms and do not require intensive analysis the estimated error in the determination of depth is about 5 km or less for most of the events considered the procedure is applied to two suites of events one in south america 83 events and one in the new hebrides 61 events in these two areas of contrasting styles of subduction the accurate depths provide new information on the bending of descending plates near trenches the seismicity and tectonics of the upper plate and the geometry and structure of the zone of contact between the upper and descending plates depths of suboceanic earthquakes which occurred near the trench and which have either tensional and compressional horizontal stress axes agree well with chapple and forsyth s 1979 preferred model of a bending elastic perfectly plastic plate however an unusually deep event occurred beneath the fiji plateau in an area of young ocean floor supposed to have been formed by sea floor spreading processes only since late miocene time the calculated depth of the event 48 km places it below the lithosphere asthenosphere boundary derived from thermal models vertical cross sections through the shallow parts of the subduction zones show that most of the earthquakes with thrust faulting focal mechanisms can be interpreted to be interplate events located in a thin 10 km thick curved zone of contact dipping arcward or landward from the trench axis however a few events with focal mechanisms similar to the interplate events do not fit on the inferred thin zone of contact these events would be accommodated by an interplate zone 15 km thick in both subduction zones interplate events occur at depths between about 15 and 50 km however the downdip width of the south american interplate zone is 2 to 3 times larger than that in the new hebrides most of the intraplate events near the interplate boundary are located in the descending plate in the upper plate seismicity is more pronounced in the back arc regions of the two subduction zones thus our results support the generality of a relatively aseismic zone in the upper plate located trenchward of the magmatic arc depths of shallow earthquakes in the eastern andes and sub andean regions of south america range between about 9 and 36 km indicating that both the upper and middle crust are seismically active about 75 of the events occurred in the upper 25 km furthermore the focal mechanisms indicate that from ecuador to argentina the crust of the eastern side of the andean cordilleran is in a state of east west compression oriented nearly parallel to the direction of convergence between the nazca and south american plates the depths the orientations of the earthquake nodal planes and the close relationships to quaternary tectonics imply basement involved crustal shortening in much of the eastern andes and sub andean zones of peru and argentina

automated mapping of glacial overdeepenings beneath contemporary ice sheets approaches and potential applications awareness is growing on the significance of overdeepenings in ice sheet systems however a complete understanding of overdeepening formation is lacking meaning observations of overdeepening location and morphometry are urgently required to motivate process understanding subject to the development of appropriate mapping approaches high resolution subglacial topography data sets covering the whole of antarctica and greenland offer significant potential to acquire such observations and to relate overdeepening characteristics to ice sheet parameters we explore a possible method for mapping overdeepenings beneath the antarctic and greenland ice sheets and illustrate a potential application of this approach by testing a possible relationship between overdeepening elongation ratio and ice sheet flow velocity we find that hydrological and terrain filtering approaches are unsuited to mapping overdeepenings and develop a novel rule based gis methodology that delineates overdeepening perimeters by analysis of closed contour properties we then develop gis procedures that provide information on overdeepening morphology and topographic context limitations in the accuracy and resolution of bed topography data sets mean that application to glaciological problems requires consideration of quality control criteria to a remove potentially spurious depressions and b reduce uncertainties that arise from the inclusion of depressions of nonglacial origin or those in regions where empirical data are sparse to address the problem of overdeepening elongation potential quality control criteria are introduced and discussion of this example serves to highlight the limitations that mapping approaches and applications of such approaches must confront we predict that improvements in bed data quality will reduce the need for quality control procedures and facilitate increasingly robust insights from empirical data

relative motion of the nazca farallon and south american plates since late cretaceous time by combining reconstructions of the south american and african plates the african and antarctic plates the antarctic and pacific plates and the pacific and nazca plates we calculated the relative positions and history of convergence of the nazca and south american plates despite variations in convergence rates along the andes periods of rapid convergence averaging more than 100 mm a between the times of anomalies 21 49 5 ma and 18 42 ma and since anomaly 7 26 ma coincide with two phases of relatively intense tectonic activity in the peruvian andes known as the late eocene incaic and mio pliocene quechua phases the periods of relatively slow convergence 50 to 55 30 mm a at the latitude of peru and less farther south between the times of anomalies 30 31 68 5 ma and 21 and between those of anomalies 13 36 ma and 7 correlate with periods during which tectonic activity was relatively quiescent thus these reconstructions provide quantitative evidence for a correlation of the intensity of tectonic activity in the overriding plate at subduction zones with variations in the convergence rate

paleogeography and andean structural geometry northwest argentina neogene tectonic segmentation of the andean cordillera in northwestern argentina is a function of both the dip of the subducted plate and of major paleogeographic structures and sedimentary basins vergence fault dip and lateral continuity of neogene structures can be related to the character and pre existing geometries and structures of the materials in which they form south of 27 s the thick skinned sierras pampeanas which occur mostly over a flat segment of the subducted nazca plate formed where little sedimentary cover overlay crystalline basement north of 24 s the thin skinned subandean belt overlying an inclined slab segment formed within a thick elongate eastward tapering trough of paleozoic and mesozoic sediments that may represent a complex of pre andean foreland basin deposits the transitional region between 24 27 s the santa barbara system and cordillera oriental is characterized paleogeographically by complex cross trending structures and irregular basin geometries and the neogene structures are equally complex and variable the paleogeographic features of nw argentina are a product of compressional tectonism during much of the paleozoic that resulted in an orogenic belt oriented obliquely to the modern andes this earlier orogen was disrupted by several zones of transverse structures and by cretaceous extensional or pull apart basins these features clearly influence the geometry of the superposed andean structures more intriguing however is the possibility that preexisting structures of the continental lithosphere may in some way help to modify the geometry of the subducted plate

late cenozoic tectonism and landscape development in the foreland of the andes northern sierras pampeanas 26 28 s argentina the argentine sierras pampeanas are reverse fault bounded mountain blocks of precambrian to paleozoic basement rocks in the foreland of the central andes uplift in the northernmost sierras pampeanas fault blocks of sierra de quilmes sierra cumbres calchaquies and sierra aconquija started about 7 ma and became pronounced between 4 and 3 4 ma the movements culminated after 2 9 ma when the conformable mio pliocene santa maria group was overthrusted faulted and folded in the course of principal basement uplift these movements created climate and base level conditions that resulted in the formation of five pediment levels in the deformed basin strata between 2 5 and 0 3 ma tectonically induced base level changes in the piedmont resulted in three tectonism related pediment surfaces between 2 5 and 0 6 ma which attest to the neotectonic activity in the andean foreland the chronology of young tectonic uplift contradicts models in which early uplift between 20 and 13 ma is due to the interaction between high topography on the subducting nazca plate and the south american craton in conjunction with the principal uplift of the adjacent puna plateau the northernmost sierras pampeanas are better explained by e w compressional stresses superposed on a thinned lithosphere and inherited zones of structural weakness that facilitated uplift

remote sensing based assessment of hazards from glacier lake outbursts a case study in the swiss alps glacier lakes are a common phenomenon in high mountain areas outbursts from glacier lakes have repeatedly caused the loss of human lives as well as severe damage to local infrastructure in several high mountain ranges around the world a grave uncertainty about the hazard potential of glacier lakes still exists especially with respect to the effects of accelerating rates of glacier retreat as a consequence of atmospheric warming area wide detection and modeling of glacier lake hazard potentials is therefore a major challenge in this study an approach integrating three scale levels allows for the progressive focus on critical glacier lakes remote sensing methods for application in glacier lake hazard assessment are presented and include channel indexing data fusion and change detection each method matches the requirements of a certain scale level for estimating potential disaster amplitudes assessments must be made of maximum discharge and runout distance of outbursts floods and debris flows existing empirical relations are evaluated and complementary ones as derived from available data are proposed tests with observations from a recent outburst event from a moraine dammed lake in the swiss alps show the basic applicability of the proposed techniques and the usefulness of empirical relations for first hazard assessments in particular the observed runout distance of the debris flow resulting from the outburst does not exceed the empirically estimated maximum runout distance a list of decision criteria and related remote sensing techniques are discussed in conclusion such a list is an essential tool for evaluating the hazard potential of a lake a systematic application of remote sensing based methods for glacier lake hazard assessment is recommended

andean age structure of eastern cordillera province of la paz bolivia a moho root beneath the bolivian andes 40 km deep is consistent with 230 km of overlap of neogene age on a single trenchward dipping transcrustal thrust fault with 10 of finite ramp cutoff main andean thrust mat only 10 of the andean crustal volume is ascribable to magmatic addition the mat is located within south american crust of full thickness it intersects the basement top 450 km inland from the neogene crustal margin it is not a collision suture as shown by persistent pre neogene facies continuity thrusting is not accompanied by terrane accretion the present bilaterally symmetrical thrust belt responds to elastic line loading and to coulomb rheology in the hanging wall of the mat a deep high stress wedge base builds a steep critical slope in the footwall the foredeep response is fast subcritical growth by progradation and blind thrusting on a low stress decollement interaction is maintained by out of sequence renewal of movement on the mat

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

tectonic inversion in the santa barbara system of the central andean foreland thrust belt northwestern argentina 1 the santa barbara system sbs of northern argentina is a 400 km long segment of the subandean foreland thrust belt it is characterized by predominantly west verging relatively high angle thrust faults many of these faults are reactivated normal faults from one branch of a complex cretaceous to paleogene rift system heteroaxial folding in parts of the sbs is probably due to a slight component of range parallel dextral strike slip motion acting on preexisting faults striking north and ne during inversion regional balanced cross sections along two transects across the northern sbs indicate that the major faults flatten into a detachment in the basement at about 10 km depth neogene e w contraction in the sbs is of the order of 21 26 km rift extension is not very well constrained but was probably less than 10 km the structural style of the sbs differs from the thin skinned subandean thrust belt to the north and from the large wavelength sierras pampeanas basement uplifts to the south the changes between the different styles are sharp and coincide with the northern and southern boundaries of the rift in the foreland suggesting that crustal or lithospheric heterogeneities exert an overriding control on foreland structural style

modeling glacier thickness distribution and bed topography over entire mountain ranges with glabtop application of a fast and robust approach 1 the combination of glacier outlines with digital elevation models dems opens new dimensions for research on climate change impacts over entire mountain chains of particular interest is the modeling of glacier thickness distribution where several new approaches were proposed recently the tool applied herein glabtop glacier bed topography is a fast and robust approach to model thickness distribution and bed topography for large glacier samples using a geographic information system gis the method is based on an empirical relation between average basal shear stress and elevation range of individual glaciers calibrated with geometric information from paleoglaciers and validated with radio echo soundings on contemporary glaciers it represents an alternative and independent test possibility for approaches based on mass conservation and flow as an example for using glabtop in entire mountain ranges we here present the modeled ice thickness distribution and bed topography for all swiss glaciers along with a geomorphometric analysis of glacier characteristics and the overdeepenings found in the modeled glacier bed these overdeepenings can be seen as potential sites for future lake formation and are thus highly relevant in connection with hydropower production and natural hazards the thickest ice of the largest glaciers rests on weakly inclined bedrock at comparably low elevations resulting in a limited potential for a terminus retreat to higher elevations the calculated total glacier volume for all swiss glaciers is 75 22 km3 for 1973 and 65 20 km3 in 1999 considering an uncertainty range of 30 these results are in good agreement with estimates from other approaches

seismotectonics of the himalayan collision zone geometry of the underthrusting indian plate beneath the himalaya fault plane solutions and well determined focal depths of medium sized earthquakes topography and landsat imagery in conjunction with seismicity maps cross sections and available geological information are used to investigate the present tectonics of the himalayan continental collision zone most of the accurately located epicenters of events along the himalayan arc 78 e 95 e that occurred between 1961 and 1981 are concentrated in a narrow zone about 50 km wide lying between the northerly dipping main boundary mbt and main central mct thrusts most of these events are located just south of the mct though the epicenters of the events are in general well located their depths as determined by teleseismic travel time data are very unreliable events with accurately determined depths obtained from identification of surface reflected phases define a simple planar zone from about 10 km and 20 km depth with an apparent dip of about 15 this result is all the more remarkable considering that the events used were located along about an 1800 km length of the himalyan arc except for one all available focal mechanisms of events within this zone indicate shallow 30 north dipping thrusts this shallow north dipping zone apparently defines a part of the detachment that separates the underthrusting indian plate from the lesser himalayan crustal block the spatial extent and the geometry of this interplate thrust zone strongly indicate that the mbt and nearby subsidiary surface and blind thrusts rather than the mct are currently the most active structures of the himalayan arc we suggest that the great himalayan earthquakes m 8 occur along the same detachment surface as defined by the thrust type medium sized events events located to the south of the mbt and beneath the ganges foredeep show normal faulting with t axes perpendicular to the himalayan trend the above results suggest that the indian continental plate is underthrusting the himalayan crustal blocks in a relatively coherent and simple geometry and that this geometry is not much different from that observed along oceanic subduction zones the november 19 1980 earthquake that occurred near the mct near 88 5 e shows a predominantly strike slip focal mechanism one of the nodal planes of this mechanism is transverse to the himalayan structural grain and moreover this plane has a trend similar to that of the recently mapped yadong gulu rift in the tethyan himalaya and in southern tibet just northeast of the earthquake we interpret this predominantly left lateral strike slip mechanism to indicate a possible genetic relationship between transverse structural features in the underthrusting indian plate the kishangang basement fault and the upper himalayan blocks and tibet

uplift of the central andean plateau and bending of the bolivian orocline the topography of the central andes can be considered the primary tectonic signal of late cenozoic mountain building in an arid region where the effects of uplift and magmatism are little obscured by denudation the spatial coverage of the topographic signal is more complete than that for sparsely sampled geological and geophysical data a color coded image of digitized topography between 12 s and 37 s highlights the altiplano puna one of the world s most remarkable plateaus and reveals important physiographic clues about the formation of that major feature the topographic data combined with information on structure magmatism seismicity and paleomagnetism support a simple kinematical model for the late cenozoic evolution of the central andes the model does not require collisional effects or enormous volumes of intrusive additions to the crust but instead calls upon plausible amounts of crustal shortening and lithospheric thinning the model interrelates andean uplift a changing geometry of the subducted nazca plate and a changing outline in map view of the leading edge of the south american plate crustal shortening has accommodated convergence between the chilean peruvian forearc and the south american foreland the altiplano puna plateau can be constructed by a combination of crustal shortening and thickening and lithospheric thinning above a shallow dipping 20 30 subducted plate the seawardly concave bend of western south america the bolivian orocline was enhanced but not completely produced by an along strike variation in the amount of late cenozoic shortening maximum shortening in bolivia both produced the widest part of the plateau and increased the seaward concavity of the bolivian orocline the along strike variations of shortening are hypothesized to result from corresponding along strike variations in the width of a weakened zone in the overriding plate weakening occurs above the wedge of asthenosphere located between the subducted and overriding plates hence the width of the zone of weakening depends upon the dip of the subducted plate two types of shortening are recognized 1 a widespread basin and range laramide like shortening that characterizes modem activity in the sierras pampeanas and late miocene deformation of the altiplano puna and 2 on the eastern side of the cordilleras and plateau an east verging foreland fold thrust belt in which the underthrust foreland compresses and thickens the ductile lower crust and produces a plateau uplift of the upper crust the second type of shortening can be applied to plio quaternary deformations throughout the central andes but with a substantial narrowing of the region of plateau uplift in peru and south of 28 s a proposed monoclinal flexure of the upper crust on the western side of the plateau uplift explains the remarkably simple and regular morphology of the main western slope of the central andes the monocline is located above the tip of the asthenospheric wedge between the converging plates it is postulated to occur above the western limit of lower crustal thickening in the regions of horizontal subduction the monocline can be associated with a late miocene asthenospheric wedge tip

seismotectonics of thin and thick skinned deformation in the andean foreland from local network data evidence for a seismogenic lower crust local network data from san juan argentina provides new information about crustal seismicity in the andean foreland above a horizontal segment of the subducted nazca plate the authors find two areas of foreland seismicity one associated with the sierras pampeanas basement uplifts and the other beneath but not within the precordillera foreland fold thrust belt the precordillera seismicity provides direct evidence for basement deformation beneath the sediments of the thrust belt and supports the idea that its eastern part is significantly modified by underlying basement deformation in both areas events are concentrated between 15 and 35 km depth and have volumetric rather than planar fault like distributions the depth distribution is usually deep for intraplate earthquakes and suggests a brittle ductile transition near 30 35 km it also suggests the upper plate may have a geotherm similar to stable cratonic regions rather than a steeper one that may be expected due to a lithospheric thinning implied by the location of the subducted plate this can be understood as a transient effect of a neogene flattening of the dip of the subducted plate where a rapid thinning of the upper plate was followed with underplating by the cool subducted plate leaving the upper plate geothermmore unchanged while producing a thinned mechanically weaker lithosphere finally a spatial correlation of upper plate seismicity and structures with subducted plate seismicity raises the possibility that a major lithospheric structure cutting across the strike of the foreland near 31 degree s may be related to subduction of the juan fernandez ridge less

the role of inherited structures in a foreland basin evolution the metan basin in nw argentina the foreland basin of the central andes in nw argentina is formed by partially unconnected basins limited by uneven high ranges the metan basin is located in the foothills of the central andes in nw argentina between the eastern cordillera the sierras pampeanas and the santa barbara system this basin resulted from a cretaceous to paleogene rifting event and from two neogene to quaternary foreland basin stages for this study field data log well seismic reflection and satellite images have been interpreted the propagation of deformation in this sector of the andes is influenced by inherited structures e g cretaceous extensional faults which have been reactivated during andean compression as high angle and oblique reverse faults deformation does not advance regularly throughout the foreland in a normal forward sequence but jumps across inherited faults fault reactivation has resulted in uplift of basement cored ranges and hanging wall anticlines that divided the foreland into small basins e g the metan basin

space time variations of stresses in the miocene quaternary along the calama olacapato el toro fault zone central andes abstract we describe the temporal and spatial changes in the tectonic state of stress occurred during the miocene quaternary in the trans orogen area of the calama olacapato el toro cot fault zone in the central andes at about 24 s within the northern portion of the puna plateau this work sheds new light on the complexity of stress pattern distribution in general and contributes to the analysis of the relationships between tectonics and volcanism and of the seismic hazard of the area field geological surveys along with kinematic analysis and numerical inversion of 140 new fault slip measurements have revealed that this portion of the cot zone previously considered a continuous long lived lineament in reality has been subjected to three different kinematic regimes 1 a miocene transpressional phase with the maximum principal stress 1 chiefly trending nne ssw 2 an extensional phase that started by 9 ma with a horizontal nw se trending minimum principal stress 3 and 3 a left lateral strike slip phase with a horizontal e w 1 and n s 3 dating to the late pliocene quaternary which decreases toward the westernmost part of the studied zone where it transitions to extension producing a n s trending graben structure hence even if transcurrence is still active in the eastern portion of the cot as focal mechanisms of crustal earthquakes indicate our study demonstrates that extension is becoming the predominant structural style of deformation at least in the western region the major changes in the tectonic regimes are attributed to changes in the magnitude of the boundary forces due to subduction processes whereas gravitational effect of a thickened crust might be responsible for the overall orogen perpendicular extension

multivariate geostatistical modeling of the spatial sediment distribution in a large scale drainage basin upper rhone switzerland abstract there is a notable discrepancy between detailed sediment budget studies in small headwater catchments 103 km2 in higher order catchments applying modeling and or remote sensing based approaches for major sediment storage delineation to bridge the gap between these scales we compiled an inventory of sediment and bedrock coverage from field mapping remote sensing analysis and published data for five key sites in the upper rhone basin val d illiez val de la liene turtmanntal lotschental goms 360 3 km2 equivalent to 6 7 of the upper rhone basin this inventory was used as training and testing data for the classification of sediment and bedrock cover from a digital elevation model 2 2 m ground resolution and landsat imagery we derived 22 parameters characterizing local morphometry topography and position contributing area and climatic and biotic factors on different spatial scales which were used as inputs for different statistical models logistic regression principal component logistic regression generalized additive model best prediction results with an excellent performance mean auroc 0 8721 0 0012 and both a high spatial and non spatial transferability were achieved applying a generalized additive model since the model has a high thematic consistency the independent input variables chosen based on their geomorphic relevance are suitable to model the spatial distribution of sediment our high resolution classification shows that 53 5 21 7 of the upper rhone basin are covered with sediment these are by no means evenly distributed small headwaters

cenozoic plate kinematics subduction and magmatism south american andes revised plate reconstructions and enlarged isotopic age data sets strongly support three mechanisms for controlling the configuration and associated volcanism and tectonism of the andean subduction zone these include age of subducted plate convergence rate and interaction with hotspot traces from 50 to 25 ma in the andes the age of oceanic plate subducted progressively decreased apparently resulting in a9gradual decrease in subduction angle and consequent eastward shift in the loci of magmatic activity a major reorganization of plate motions at 25 ma resulted in an increased convergence rate normal to the chilean andes and was accompanied by subsequent broadening of the locus of magmatic activity into adjacent portions of bolivia and argentina convergence rates changed only slightly across the peruvian margin and no clear effect on subsequent magmatism is indicated interaction of the andean subduction zone with the juan fernandez and easter nazca hotspot traces apparently resulted in lower angle subduction and consequent gaps in magmatic activity as predicted continuations of the traces correspond with regions lacking dated volcanic rocks the current gaps in igneous activity correspond with contemporary subduction of the two traces and this association apparently occurred in the past as well

stress and the direction of slip on fault planes the shear stress direction on a fault plane depends only on four of the six components of the stress tensor assuming only that the slip direction marks the shear stress direction on any fault plane and that stress is homogeneous it is possible to estimate these four stress parameters from populations of fault planes with known slip directions as several workers have observed different formulations of the problem may yield varying best fitting stresses and estimates of uncertainty in the simplest case no assumptions are made regarding the orientations of fault planes relative to the stress tensor thus the technique allows for the possibility that the fault planes may be very weak here we present simple analytical and graphical descriptions of the field of admissible fault geometries relative to any four parameter stress model which can be used to illustrate the significance of various inverse strategies in particular this paper explores the effects of using two alternative measures of misfit between an observed fault datum and stress model 1 the pole rotation the angle between the observed and predicted slip direction on the observed fault plane and 2 the minimum rotation the smallest angle between the observed fault geometry and any fault geometry which is consistent with the model by allowing for variation of the fault plane as well as the slip vector the minimum rotation procedure generally achieves a more stable and presumably realistic estimate of the actual discrepancy between a fault observation and stress model than the pole rotation procedure in a test case using 17 earthquake focal mechanisms from the yuii region of eastern taiwan separate inversions based on the two misfit criteria yield different optimum stress models and uncertainty estimates additional constraints on the stress tensor such as the effect of friction can be superimposed on the ones used here

application of inventory data for estimating characteristics of and regional climate change effects on mountain glaciers a pilot study with the european alps a parameterization scheme using simple algorithms for unmeasured glaciers is being applied to glacier inventory data to estimate the basic glaciological characteristics of the inventoried ice bodies and simulate potential climate change effects on mountain glaciers for past and potential climate scenarios glacier changes for assumed mass balance changes are calculated as step functions between steady state conditions for time intervals that approximately correspond to the characteristic dynamic response time a few decades of the glaciers in order to test the procedure a pilot study was carried out in the european alps where detailed glacier inventories had been compiled around the mid 1970s total glacier volume in the alps is estimated at about 130 km3 for the mid 1970s strongly negative mass balances are likely to have caused a loss of about 10 20 of this total volume during the decade 1980 90 backward calculation of glacier length changes using a mean annual mass balance of 0 25m w e a 1 since the end of the little ice age around 1850 ad gives considerable scatter but satisfactory overall results as compared with long term observations the total loss of alpine surface ice mass since 1850 can be estimated at about half the original value an acceleration of this development with annual mass losses of around 1 m a 1 or more as anticipated from ipcc scenario a for the coming century could eliminate major parts of the presently existing alpine ice volume within decades

subglacial basins their origin and importance in glacial systems and landscapes closed topographic basins are found beneath contemporary ice masses and within the footprint of former ice masses in all glaciated regions we present the first integrated review of subglacial basin occurrence and formation and the implications of such basins for glaciological processes and the evolution of landscape our purpose is to motivate research in areas where understanding of basin origin and process significance is weak basins on the order of 10 102 m deep and 102 103 m long are produced by glacial erosion of subglacial rock and or sediment and are known as overdeepenings outlet and valley glaciers can overdeepen their beds far below sea level or local fluviatile base level larger basins typically in ice sheet contexts may have a pre glacial usually tectonic origin subglacial basins are important glaciologically because they require ice water and sediment to ascend an adverse subglacial slope in order to exit the glacial system the efficiency of which is dependent upon the gradient of the adverse slope and that of the ice surface basins thus influence subglacial drainage system morphology and transmissivity the thickness and distribution of basal ice and sediment layers and the mechanisms and dynamics of ice flow adverse gradients that exceed 11 times that of the ice surface may even permit the formation of subglacial lakes we speculate that in comparison to ice masses with few or no subglacial basins those with numerous or very large basins may respond to climatic changes with unexpected vigour in addition erosion rates and transport pathways of water and sediment through the glacial system and the expression of these processes in the sediment and landform record may be unexpectedly complex further our review shows that in a warming climate ice masses resting on adverse slopes will be vulnerable to rapid and potentially catastrophic retreat new lakes in subglacial basins exposed by mountain glacier retreat will present an increasing hazard and subglacial lakes may drain catastrophically on even longer time scales we speculate that the glacial excavation and post glacial filling of basins in mountainous regions should contribute importantly to climate related changes in isostasy and relief although the controls on overdeepening and their influence on other glacial and landscape processes remain uncertain we hypothesise that overdeepened glacial systems reflect an equilibrium ice bed geometry that maximises the efficiency of ice discharge improved understanding of overdeepening processes especially overdeepened bed hydrology is therefore necessary to understand fully the dynamic behaviour of valley and outlet glaciers and thus the fate of earth s largest ice masses

increasing risks related to landslides from degrading permafrost into new lakes in de glaciating mountain ranges abstract while glacier volumes in most cold mountain ranges rapidly decrease due to continued global warming degradation of permafrost at altitudes above and below glaciers is much slower as a consequence many still existing glacier and permafrost landscapes probably transform within decades into new landscapes of bare bedrock loose debris sparse vegetation numerous new lakes and steep slopes with slowly degrading permafrost these new landscapes are likely to persist for centuries if not millennia to come during variable but mostly extended future time periods such new landscapes will be characterized by pronounced disequilibria within their geo and ecosystems this especially involves long term stability reduction of steep icy mountain slopes as a slow and delayed reaction to stress redistribution following de buttressing by vanishing glaciers and to changes in mechanical strength and hydraulic permeability caused by permafrost degradation thereby the probability of far reaching flood waves from large mass movements into lakes systematically increases with the formation of many new lakes and systems of lakes in close neighborhood to or even directly at the foot of so affected slopes results of recent studies in the swiss alps are reviewed and complemented with examples from the cordillera blanca in peru and the mount everest region in nepal hot spots of future hazards from potential flood waves caused by large rock falls into new lakes can already now be recognized to this end integrated spatial information on glacier permafrost evolution and lake formation can be used together with scenario based models for rapid mass movements impact waves and flood propagation the resulting information must then be combined with exposure and vulnerability considerations related to settlements and infrastructure this enables timely planning of risk reduction options such risk reduction options consist of two components mitigation of hazards which in the present context are due to effects from climate change and reduction in consequences which result from societal conditions and changes hazard mitigation may include artificial lake drainage or lake level lowering and flood retention optimally in connection with multipurpose structures for hydropower production and or irrigation reduction in damage potential exposure vulnerability can be accomplished by installing early warning systems adapting spatial planning and or by improving preparedness of local people and institutions

ice volume and subglacial topography for western canadian glaciers from mass balance fields thinning rates and a bed stress model abstracta method is described to estimate the thickness of glacier ice using information derived from the measured ice extent surface topography surface mass balance and rate of thinning or thickening of the ice column shear stress beneath an ice column is assumed to be simply related to ice thickness and surface slope as for an inclined slab but this calculation is cast as a linear optimization problem so that a smoothness regularization can be applied assignment of bed stress is based on the flow law for ice and a mass balance calculation but must be preceded by delineation of the ice flow drainage basin validation of the method is accomplished by comparing thickness estimates to the known thickness generated by a numerical ice dynamics model once validated the method is used to estimate the subglacial topography for all glaciers in western canada that lie south of 60 n adding the present ice volume of each glacier gives the estimated total volume as 2320 km3 equivalent to 5 8 mm of sea leve

glacial overdeepenings in the swiss alps and foreland spatial distribution and morphometrics abstract overdeepenings ods are erosional features that have been excavated below the regional sea fluvial base level to produce closed topographic basins accessing bedrock topography and od volume is often challenging hence despite constituting major landscape features and being widespread in paleo glaciated regions ods have been overlooked and the subglacial processes involved in their evolution have remained debated in the swiss alpine foreland and valleys ods are commonly found filled with water or large volumes of sediment using a gis matlab approach based on topographic datasets and bedrock contour curves we mapped the spatial distribution of ods in switzerland and adjacent areas in the ice free alpine areas the majority of the mapped ods occurs in very low bedrock erosional resistance where ods are larger wider and shallower than in medium to high bedrock erosional resistance domains evidencing a strong lithological control on od geometry longitudinal asymmetry and hypsometric integral suggest a dominance of quarrying during od evolution and for selected glacial catchments headward erosion propagation or high sediment evacuation efficiency od surface data surface and length can be tentatively used for extracting od subsurface metrics depths nested valleys and first order volume estimates our data seem to indicate that ods may initiate as multiple small nested valleys and progress to a single and connected depression transversal cross sections also suggest a negative feedback between the erosion potential for deep carving and the presence of low resistance bedrock where subglacial meltwater infiltration could have played a key role in od evolution although insightful relationships have been evidenced for ods in the swiss alps and foreland we have also observed a high spatial variability in key od metrics such as surface area and depth this results in general first order interpretations at regional scale but currently prevent to quantitatively constrain physical subglacial processes at their origin comparisons with existing od datasets under present day ice greenland antarctica and modern swiss glaciers place our results in a broader context and allow a step forward in our understanding of the complex patterns and mechanisms of sub glacial erosion and resulting landforms

rapid geodetic shortening across the eastern cordillera of nw argentina observed by the puna andes gps array exxonmobil through the convergent orogenic systems analysis achievement rewards for college scientists foundation peter j coney fellowship

modelling glacier bed overdeepenings and possible future lakes for the glaciers in the himalaya karakoram region surface digital elevation models dems and slope related estimates of glacier thickness enable modelling of glacier bed topographies over large ice covered areas due to the erosive power of glaciers such bed topographies can contain numerous overdeepenings which when exposed following glacier retreat may fill with water and form new lakes in this study the bed overdeepenings for 28 000 glaciers 40 775 km 2 of the himalaya karakoram region are modelled using glabtop2 glacier bed topography model version 2 in which ice thickness is inferred from surface slope by parameterizing basal shear stress as a function of elevation range for each glacier the modelled ice thicknesses are uncertain 30 but spatial patterns of ice thickness and bed elevation primarily depend on surface slopes as derived from the dem and hence are more robust about 16 000 overdeepenings larger than 10 4 m 2 were detected in the modelled glacier beds covering an area of 2200 km 2 and having a volume of 120km 3 3 4 of present day glacier volume about 5000 of these overdeepenings 1800 km 2 have a volume larger than 10 6 m 3 the results presented here are useful for anticipating landscape evolution and potential future lake formation with associated opportunities tourism hydropower and risks lake outbursts

potential future lakes from continued glacier shrinkage in the aosta valley region western alps italy abstract aosta valley western alps italy is the region with the largest glacierized area of italy like other high mountain regions it has shown a significant glacier retreat starting from the end of the little ice age that is expected to continue in the future as a direct consequence of glacier shrinkage glacier bed overdeepenings become exposed offering suitable geomorphological conditions for glacier lakes formation in such a densely populated and developed region opportunities and risks connected to lakes may arise 1 economic exploitation for hydropower production tourism and water supply 2 environmental relevance for high mountain biodiversity and geodiversity 3 potential risks due to outbursts and consequent floods in this study the locations of potential future glacier lakes over large glacierized areas 183 glaciers covering 163 1 km2 of aosta valley were assessed by using the glabtop2 model 46 overdeepenings larger than 10 800 m2 were identified covering an area of 3 1 0 9 km2 and having a volume of 0 06 0 02 km3 the majority of the overdeepenings are located in the monte rosa cervino massif and a mean depth thanks to the validation by the proposed backward approach and gpr ground penetrating radar data we can confirm that the location of the overdeepenings is robust while their actual dimensions are subject to considerable uncertainties almost all of large lakes area 10 000 m2 potentially the most dangerous are modelled finally we suggest choosing medium pixel size about 60 m of the dem in order to obtain at least the location of the largest lakes and to avoid overestimations of ice thickness and thus a great number of false positive overdeepenings the results presented here can be useful for understanding how the alpine environment will look in the future and can help the management of water resources and risks related to glacier lakes

evolution of subglacial overdeepenings in response to sediment redistribution and glaciohydraulic supercooling received 16 august 2012 revised 18 december 2012 accepted 15 january 2013 1 glaciers erode bedrock rapidly but evacuation of sediments requires efficient subglacial drainage networks if glaciers erode more rapidly than evacuation proceeds a protective subglacial till layer can form to armor the bed where glaciers cross overdeepenings local closed depressions the bed slope opposes the ice surface and lowers the hydraulic potential gradient that drives water flow here we present results of a dynamic distributed model of coupled basal water flow and sediment transport to show how overdeepenings evolve over the course of a melt season we use steady state calculations as well as numerical simulations to understand how alluvial bed erosion alters overdeepenings numerical results from a modified form of the spring hutter equations show behaviors that cannot be inferred from either local or steady state calculations in general opposition of surface and bed slopes lessens sediment transport regardless of ice accretion from glaciohydraulic supercooling drainage efficiency strongly affects erosion and deposition rates results show characteristic behaviors of flow through overdeepenings such as overpressured water systems and accretion rates compatible with field measurements simulations that start with overdeepened glacier configurations progress out of a freezing regime where glaciohydraulic supercooling occurs this progression indicates that glacier hydrology is more strongly affected by erosion and deposition than by freezing from glaciohydraulic supercooling we discuss how this outcome affects glacier erosion and sediment transport under modern and past ice sheets

cold firn and ice of high altitude glaciers in the alps measurements and distribution modelling the thermal regime of high altitude accumulation areas in the swiss alps was systematically investigated on the jungfraufirn bernese alps on the breithornplateau valais alps and on grenzgletscher valais alps in 1991 1992 and 1994 temperatures were measured in a deep hole 120 m deep and in several shallow holes 14 30 m deep whereas the wide neve of the jungfraufirn at 3400 3600 m a s l and the 3800 m high breithorn plateau seems to be predominantly temperate cold firn and ice temperatures were measured throughout on grenzgletscher 3900 4450 m a s l mean firn temperatures on grenzgletscher vary strongly and range between 3 and 14 c a comparison between the measured temperature profiles and a one dimensional heat conduction calculation shows that the release of latent heat by penetrating and refreezing meltwater decisively influences the thermal pattern of the firn pack a multiple linear regression model based on measured firn temperatures from the european alps and the parameters altitude and aspect yields aspect dependent lower boundaries for the occurrence of cold firn ranging between 3400 northerly aspects and 4150 m a s l southerly aspects a total of 120 glaciers with cold firn areas are found when applying the model to glacier inventory data from the european alps

the glacially overdeepened trough of the salzach valley austria bedrock geometry and sedimentary fill of a major alpine subglacial basin abstract overdeepened valleys are unambiguous features of glacially sculpted landscapes they result from erosion at the bed of the glacier and their size and shape is determined by ice dynamics and the characteristics of the underlying bedrock major overdeepened valleys representing vertical bedrock erosion of several hundreds of meters are characteristic features of many trunk valleys in the formerly glaciated parts of the alpine mountain belt the thick sedimentary fill usually hinders attempts to unravel bedrock geometry formation history and fill characteristics based on reflection seismic data and core logs from multiple deep drillings we construct a detailed bedrock model of the lower salzach valley trough one of the largest overdeepened valleys in the european alps the analysed overdeepened structure characterized by a strongly undulating topography two reaches of enhanced erosion can be identified and are suggested to be related to variations in bedrock erodibility and a triple glacier confluence the sedimentary fill shows clear characteristics of rapid infilling and subaqueous fan delta deposits indicate a strong influence of tributary streams associated surface lowering of the valley floor had a major impact on tributary stream incision but also on the available ice accumulation area at subsequent glaciations the extent to which fills of earlier glaciations have been preserved from erosion during the last glacial maximum remains ambiguous and demands further exploration to our knowledge the presented bedrock model is one of the best defined of any major overdeepened trunk valley

three dimensional p and s wave velocity structures beneath taiwan deep structure beneath an arc continent collision the island of taiwan is a byproduct of one of the few active collisions between a continent represented by the eurasian continental shelf and an island arc represented by the northern extension of the luzon arc on the philippine sea plate to understand better the evolution and current tectonics of this collision we selected 1260 well recorded earthquakes from an initial set of 50 000 located by the taiwan telemetered seismograph network for the determination of one and three dimensional p and s wave velocity structures beneath the island the results for both structures and earthquake relocations reveal that the island is divided tectonically into three distinct zones in the east the philippine oceanic plate is underthrusting the eurasian plate east of a north south boundary that is well defined by both seismic activity and a region of high velocity in the south the eurasian continental plate is underthrusting the philippine sea plate south of an east west boundary at about 23 n that is sharply defined by both subcrustal seismicity and a zone of relatively low velocities the dip of the subducted continent is shallow until it reaches the luzon island arc 50 km east of the main island structure under the main part of the island north of 230n reveals a shallow dipping zone of low velocities in the west above 25 km depth that narrows and steepens below that depth to at least 50 km beneath the central range the dip of this low velocity region is outlined by a narrow zone of seismicity that extends to depths of 100 km this seismic zone lies in a velocity saddle and marks an apparent offset in the central low velocity region at 24 n evidence for the subduction of the eurasian continent beneath taiwan therefore exists everywhere beneath the island and the low velocity regions in the mantle support but do not require the subduction of some 6 16 km of lower continental crust to depths of at least 50 km the distinct change in both the velocity structure and the seismic activity at 23 n and the offset of the low velocity regions at 24 n argue for abrupt changes in the nature of subduction across these latitudes these changes may be caused by an interaction of the luzon island arc with the subducted continental shelf that mimics a similar interaction evident at the surface finally the velocity structure of the subducting philippine sea plate suggests that the earthquakes beneath 70 km depth are not occurring within the highest velocity regions of the plate but are probably located near the upper edge of the plate there is also evidence from earthquake locations and velocity structure that suggests that the subducting plate is segmented and that subduction is presently occurring as far south as 22 n

gps derived deformation of the central andes including the 1995 antofagasta mw 8 0 earthquake in order to study both the interplate seismic loading cycle and the distribution of intraplate deformation of the andes a 215 site gps network covering chile and the western part of argentina was selected monumented and observed in 1993 and 1994 a dense part of the network in northern chile and northwest argentina comprising some 70 sites was re observed after two years in october november 1995 the m w 8 0 antofagasta north chile earthquake of 30th july 1995 took place between the two observations the city of antofagasta shifted 80 cm westwards by this event and the displacement still reached 10 cm at locations 300 km from the trench three different deformation processes have been considered for modeling the measured displacements 1 interseismic accumulation of elastic strain due to subduction coupling 2 coseismic strain release during the antofagasta earthquake and 3 crustal shortening in the sub andes eastward displacement of the sites to the north and to the south of the area affected by the earthquake is due to the interseismic accumulation of elastic deformation assuming a uniform slip model of interseismic coupling the observed displacements at the coast require a fully locked subduction interface and a depth of seismic coupling of 50 km the geodetically derived fault plane parameters of the antofagasta earthquake are consistent with results derived from wave form modeling of seismolog ical data the coseismic slip predicted by the variable slip model reaches values of 3 2 m in the dip slip and 1 4 m in the strike slip directions the derived rake is 66 our geodetic results suggest that the oblique nazca south american plate convergence is accommodated by oblique earthquake slip with no slip partitioning the observed displacements in the back arc indicate a present day crustal shortening rate of 3 4 mm year which is significantly slower than the average of 10 mm year experienced during the evolution of the andean plateau

a continuum model of continental deformation above subduction zones application to the andes and the aegean large scale continental tectonics of back arc extensional and andean type compressional environments are investigated by using the thin viscous sheet model to calculate the deformation within continental lithosphere that is subjected to horizontal forces on its plate boundaries and to basal drag from the asthenospheric flow beneath the shear tractions acting on the base of a deformable lithosphere are derived from a corner flow model that assumes a rigid subducting plate and a deformable overlying plate because the calculated shear tractions and the deformation within the overlying plate are interdependent the corner flow and the thin viscous sheet models are solved simultaneously we use a perturbation method to obtain analytical solutions for the velocity and strain rate fields within the overlying continental lithosphere the solutions depend on the angle of subduction the dimensionless thickness of the lithosphere and the ratio of asthenospheric to lithospheric viscosities which governs the viscous coupling between the asthenosphere and the lithosphere calculations are compared with observations from the andes and the aegean our results explain some of the features of the deformation in these regions that have heretofore not been explained by other models our model predicts that in a compressional environment a broad region of uplifted topography will tend to develop above a more steeply dipping slab 30o rather than above a shallower slab 10o 15o this is in accord with observations in the various segments of the central andes for an extensional environment the model predicts that a zone of compression can develop near the trench and that extensional strain rate can increase with distance from the trench as is observed in the aegean we also estimate the effective viscosities of 102o pa s for the asthenosphere 2x 1021 pa s for the aegean lithosphere and 1022 pa s for the andean lithosphere

tectonic and magmatic evolution of the andes of northern argentina and chile abstract two orogenic cycles both with different evolution are developed in the western margin of the south american continent in northern argentina and chile the paleozoic hercynic cycle and the meso cenozoic andean cycle the hercynic cycle a wide marine basin extending westward of the cordillera oriental which developed in cambrian ordovician times marks the beginning of this cycle in contrast to peru and bolivia where this basin developed between two precambrian blocks the western margin of this basin in northern argentina and chile is still unknown the ordovician sedimentation and accompanied volcanism ends with the ocloyic deformation phase and its synkinematic granitic plutonism two basins were developed in the silurian devonian separated by the puna arc uplifted during this ocloyic phase the shallow water marine terrigeneous sediments which were deposited in them were deformed by a new tectono magmatic associated phase chanic phase carboniferous to lower permian marine carbonates were deposited west of the puna arc and red beds east of it later on during the permian to triassic a magmatic belt was developed along the cordillera occidental the rhyolites ignimbrites and the granitic to granodioritic related intrusives are well represented in chile although the overall geologic history of this period is known many problems concerning its origin and relations to plate tectonics are still unsolved the andean cycle during this cycle a series of magmatic arc systems related to the subduction of the pacific crust was built up along the western margin of south america huge volumes of calc alkaline lavas and related plutons were emplaced since the jurassic along belts parallel to the present coastline showing a general eastward migration trend up to the lower cretaceous an ensialic back arc basin was formed east of this magmatic arc thousands of meters of marine and continental sediments were deposited in it this basin disappeared during the middle cretaceous probably as a result of the final opening of the atlantic and the active westward movement of the south american plate since middle cretaceous times the magmatic arc has been the fundamental paleogeographic element the arc progressively migrated stepwise eastward each step marked by a tectonic phase subduction related crustal erosion could explain the lack of fore arc petrotectonic assemblages the eastward magmatic polarity which characterizes this section of the andes could also be explained by such a mechanism

distributed ice thickness and volume of all glaciers around the globe 1 a new physically based approach for calculating glacier ice thickness distribution and volume is presented and applied to all glaciers and ice caps worldwide combining glacier outlines of the globally complete randolph glacier inventory with terrain elevation models shuttle radar topography mission advanced spaceborne thermal emission and reflection radiometer we use a simple dynamic model to obtain spatially distributed thickness of individual glaciers by inverting their surface topography results are validated against a comprehensive set of thickness observations for 300 glaciers from most glacierized regions of the world for all mountain glaciers and ice caps outside of the antarctic and greenland ice sheets we find a total ice volume of 170 103 21 103 km3 or 0 43 0 06 m of potential sea level rise

seismicity and average velocities beneath the argentine puna plateau a network of 60 seismographs was deployed across the andes at 23 5 s the array was centered in the backarc atop the puna high plateau in nw argentina p and s arrival times of 426 intermediate depth earthquakes were inverted for 1 d velocity structure and hypocentral coordinates average velocities and v p v s in the crust are low average mantle velocities are high but difficult to interpret because of the presence of a fast velocity slab at depth although the hypocenters sharply define a 35 dipping benioff zone seismicity in the slab is not continuous the spatial clustering of earthquakes is thought to reflect inherited heterogeneties of the subducted oceanic lithosphere additionally 57 crustal earthquakes were located seismicity concentrates in the fold and thrust belt of the foreland and eastern cordillera and along and south of the el toro olacapato calama lineament tocl focal mechanisms of two earthquakes at this structure exhibit left lateral strike slip mechanisms similar to the suggested kinematics of the tocl we believe that the puna north of the tocl behaves like a rigid block with little internal deformation whereas the area south of the tocl is weaker and currently deforming

glacial hydrology and erosion patterns a mechanism for carving glacial valleys article i nfo article history most glacial erosion models assume that erosion rates are proportional to ice sliding velocity while recent studies have shown that water plays a major role in modulating sliding velocities the impact it might have on erosion rates is still unclear here we incorporate subglacial hydrology into a glacial erosion model that is based on a sliding rule our results explicitly highlight that adding subglacial hydrology has profound impacts on the temporal and spatial patterns of glacial erosion first it suggests that erosion might mainly occur during melting seasons when subglacial water pressure is large and effective pressure is low i e before the channels fully develop and reduce the water pressure at the ice bedrock interface which promotes sliding and erosion second the distribution of erosion is bimodal with a peak at the equilibrium line altitude and as we demonstrate enhanced erosion at much lower altitudes within the ablation area where water due to melting abounds this has important implications because it explains why glacial erosion can simultaneously

coupling the flow of ice water and sediment in a glacial landscape evolution model abstract the processes of subglacial erosion depend not only on the sliding motion of glaciers over bedrock but also on the presence of meltwater and sediment in the subglacial environment in particular theoretical models for subglacial quarrying and abrasion as well as hypothesized erosion thresholds associated with subglacial sediment transport include both positive and negative effects of subglacial water and sediment on the rate of erosion in order to incorporate the existing theoretical models for subglacial erosion by quarrying and abrasion in a long term glacial landscape evolution model we here present a coupled computational framework for simulating the simultaneous flow processes of ice water and sediment we supplement a higher order ice sheet model with simple long term models for glacial hydrology and subglacial sediment transport as well as fluvial and hillslope related erosion processes an important strength of the modeling framework presented relates to the morphological detail of the landscapes produced which facilitates direct comparison with existing landforms this improves the connection between glacial landscape evolution models geomorphological observations and the existing knowledge of the physical processes that operate under glaciers we demonstrate with model examples how increased basal meltwater pressure and transport limited subglacial erosion lead to both positive and negative feedbacks related to glacial erosion and the formation of overdeepenings

the randolph glacier inventory a globally complete inventory of glaciers the randolph glacier inventory rgi is a globally complete collection of digital outlines of glaciers excluding the ice sheets developed to meet the needs of the fifth assessment of the intergovernmental panel on climate change for estimates of past and future mass balance the rgi was created with limited resources in a short period priority was given to completeness of coverage but a limited uniform set of attributes is attached to each of the 198 000 glaciers in its latest version 3 2 satellite imagery from 1999 2010 provided most of the outlines their total extent is estimated as 726 800 34 000 km 2 the uncertainty about 5 is derived from careful single glacier and basin scale uncertainty estimates and comparisons with inventories that were not sources for the rgi the main contributors to uncertainty are probably misinterpretation of seasonal snow cover and debris cover these errors appear not to be normally distributed and quantifying them reliably is an unsolved problem combined with digital elevation models the rgi glacier outlines yield hypsometries that can be com bined with atmospheric data or model outputs for analysis of the impacts of climatic change on glaciers the rgi has already proved its value in the generation of significantly improved aggregate estimates of glacier mass changes and total volume and thus actual and potential contributions to sea level rise

a method to estimate the ice volume and ice thickness distribution of alpine glaciers sound knowledge of the ice volume and ice thickness distribution of a glacier is essential for many glaciological applications however direct measurements of ice thickness are laborious not feasible everywhere and necessarily restricted to a small number of glaciers in this paper we present a method to estimate the ice thickness distribution and the total ice volume of alpine glaciers this method is based on glacier mass turnover and principles of ice flow mechanics the required input data are the glacier surface topography the glacier outline and a set of borders delineating different ice flow catchments three parameters describe the distribution of the apparent mass balance which is defined as the difference between the glacier surface mass balance and the rate of ice thickness change and two parameters define the ice flow dynamics the method was developed and validated on four alpine glaciers located in switzerland for which the bedrock topography is partially known from radio echo soundings the ice thickness along 82 cross profiles can be reproduced with an average deviation of about 25 between the calculated and the measured ice thickness the cross sectional areas differ by less than 20 on average this shows the potential of the method for estimating the ice thickness distribution of alpine glaciers without the use of direct measurements

distribution and characteristics of overdeepenings beneath the greenland and antarctic ice sheets implications for overdeepening origin and evolution das thanks the national cooperative for the disposal of radioactive waste nagra switzerland for their role in stimulating new research on the topic of focused glacial erosion and das and hp further thank nagra for funding the quantitative study of overdeepening morphology on which this paper is based grant 11 716 fcu bys hp also acknowledges support by the research council of norway through its centres of excellence funding scheme grant 223259 and the petromaks project glaciations in the barents sea area glacibar grant 200672 j

andean tectonics related to geometry of subducted nazca plate seismological and geological data show that tectonic segmentation of the andes coincides with segmentation of the subducted nazca plate which has nearly horizontal segments and 30 east dipping segments andean tectonics above a flat subducting segment between 28 s to 33 s are characterized by from west to east 1 a steady topographic rise from the coast to the crest of the andes 2 no significant quaternary and possibly neogene magmatism 3 a narrow belt of eastward migrating apparently thin skinned neogene to quaternary shortening of the andes and 4 plio pleistocene uplift of the crystalline basement on reverse faults in the pampeanas ranges from about 15 to 24 s over a 30 dipping subducted plate a west to east andes cross section includes 1 a longitudinal valley east of coastal mountains 2 an active neogene and holocene andesitic volcanic axis 3 the altiplano puna high plateau 4 a high neogene but inactive thrust belt eastern cordillera and 5 an active eastward migrating subandean thin skinned thrust belt tectonics above a steeply subducting segment south of 33 s are similar west of the volcanic axis but quite different to the east early cenozoic tectonics of western north america were quite similar to the neogene andes however duration of segmentation was longer and the width of deformation was greater in the western united states patterns of crustal seismicity are systematically related to plio quaternary structural provinces implying that current deformational processes have persisted since at least the pliocene horizontal compression parallel to the plate convergence direction is indicated to a distance of 800 km from the trench above flat subducting segments crustal seismicity occurs over a broad region whereas over steep segments it is confined to the narrow thrust belt strain patterns in the forearc region are complex and perhaps extensional and a broad region of the altiplano puna and eastern cordillera appears to be aseismic

transition from basement involved to thin skinned thrusting in the cordillera oriental of southern bolivia the eastern flank of the central andes in southern bolivia and northern argentina is underlain by a fold and thrust belt of neogene age it comprises an external thin skinned segment with basal detachment in silurian shales subandean ranges and an internal segment where units as deep as precambrian metasedimentary and igneous rocks are involved in thrusting eastern cordillera oriental between the cordillera oriental and the subandean ranges an intermediate segment interandean zone intervenes north of the argentinian bolivian border 22 s the structure of the interandean zone is characterized by folded and thrust faulted cambrian to triassic strata balanced cross sections across the western subandean ranges the interandean zone and the eastern cordillera oriental are based on previously available data and recent field work they suggest that the geological structure can be interpreted in terms of two major basement involved thrusts here referred to as interandean and subandean thrusts the more internal interandean thrust caused the development of broad basement anticlines in the eastern cordillera oriental however at shallower levels its displacement was accommodated by thin skinned folding and thrusting in the interandean zone in sequence activation of the subandean thrust uplifted the interandean zone on top of an imbricate basement sheet and caused the development of the thinskinned subandean ranges farther east published radiometric data and subsidence history of the subandean foreland basin suggest that the interandean thrust was active between about 10 ma and 5 ma the subandean thrust is still active southward displacement transfer from the subandean thrust onto the interandean thrust and a southward dipping lateral ramp of the interandean thrust result in the gradual transition from the interandean zone north of 22 s to the cordillera oriental of northern argentina a similar but larger scale transfer may be involved in the southern termination of the thin skinned subandean ranges of argentina at 23 s shortening in the western part of the thrust belt is of the order of 80 90 km total shortening in the eastern andean thrust belt from the undeformed foreland to the eastern margin of the cordillera oriental is 140 150 km

the footwall ramp of the subandean decollement northernmost argentina from extended correlation of seismic reflection data abstract the link between thin skinned foreland shortening and thickening of the lower crust beneath the hinterlands of mountain belts has seldom been observed we have reprocessed yacimientos petroliferos fiscales ypf s a seismic reflection data from the eastern cordillera of the central andes at 22 s latitude using vibroseis extended correlation the result we tentatively interpret as an image of the crustal scale footwall ramp of the subandean belt decollement three crossing lines extended from 5 to 15 s 45 km provide excellent 3d control a band of strong mid crustal reflections between 4 5 and 6 s 9 to 13 km displays imbricate thrust geometry it may be a shallow zone of decollement but is 5 10 km too shallow for the subandean belt decollement at 7 8 s 16 to 20 km a band of reflections dips steeply nw at about 35 migrated and strikes parallel to the andean structure underlying the camargo syncline the dipping band correlates closely with the westward projection of the subandean decollement east of the dipping event scattered horizontal reflections are present to 12 s 32 km reflections above the dipping event have geometries similar to hanging wall anticlines and may truncate against it west of the band reflections occur to 15 s 41 km none of these lines have sufficient penetration to image moho the footwall ramp of the subandean belt apparently extends to near the base of the crust and would mark the western limit of under thrusting of undeformed craton beneath the orogen based on lateral variation in surface geology existing balanced cross sections and the geometry imaged on the reprocessed seismic lines we suggest that the subandean belt decollement steepens its ramp from north to south as shortening dies out southward at 24 s foreland structures are locally compensated and have seismicity to 25 km

pure and simple shear plateau uplift altiplano puna argentina and bolivia abstract the concepts of pure and simple shear strain provide a meaningful way of discussing the alternative modes of lithospheric shortening which produced uplift of the central andean plateau since 10 ma discrete segments of the plateau exemplify pure or simple shear modes characteristics of the simple shear mode are a flanking thin skinned thrust belt and subdued relief and lack of significant late miocene to recent deformation within the plateau the pure shear mode is characterized by more rugged internal relief and active neotectonic deformation within the plateau and thick skinned foreland deformation involving seismic deformation of the crust to 30 km or more these modes of crustal thickening correlate with changes in lithosphere thickness modes of isostatic compensation broad wavelength topography and back arc magmatism the correlation of the boundary between pure and simple shear segments with major changes in pre existing anisotropies in the foreland of the orogen suggests that events which long pre date the andean orogeny indirectly controlled the along strike variation in the magnitude and style of shortening in the central andes and may have influenced the development of flat subduction

seismotectonics of a newly formed transform zone near a hotspot earthquake mechanisms and regional stress in the south iceland seismic zone abstract we carry out mass inversion of focal mechanisms of earthquakes from 1991 to 2004 along the south iceland seismic zone within a quadrangle about 37 km wide and 65 km long with 33 878 earthquakes illuminating a crust volume of nearly 35 000 km3 our inversion aims at identifying the seismotectonic stress regimes that best account for the whole set of data not at examining local variations and stress perturbations in space and time regardless of magnitude selection the inversion reveals consistent orientations for both a primary regime with ne sw compression and nw se extension accounting for about three fourths of the data and a secondary regime with nw se compression and ne sw extension the corresponding earthquakes are highly intricate in space and time suggesting that the secondary regime which shows larger dispersion and slightly lower magnitudes as compared with the primary regime mainly results from the effects of elastic rebound stress drop and fluid migration because the data acquisition and our inversion technique are independent this analysis provides confirmation that even the negative magnitude earthquakes recorded by the icelandic seismic network sil are reliable our analysis reveals high levels of consistency between the seismotectonic stress pattern and the transform kinematics of the south iceland seismic zone the proximity of the icelandic mantle plume with a positive thermal anomaly modified the rheology of the upper lithosphere and hence influenced structural development simple shear probably prevails within a 20 km wide corridor in the underlying viscous layer inducing particular block faulting at the surface both the fault distribution and the effective block dimensions are consistent with a simple structural evolution model

seismicity fault plane solutions depth of faulting and active tectonics of the andes of peru ecuador and southern colombia the intracontinental seismicity of the andes of peru ecuador and southern colombia is concentrated along the easternmost flank of the cordillera beneath the western margin of the sub andes the focal depths and fault plane solutions of the largest events were constrained by comparing the observed long period p waves with synthetic waveforms in general the fault plane solutions show reverse faulting on steeply dipping nodal planes striking northwest southeast and reflect crustal shortening perpendicular to the range probably in response to the subduction of the nazca plate to the west earthquakes in the sub andes occur at depths of between 8 and 38 km indicating that much of the crust deforms in a brittle manner the seismicity seems to reflect antithetic underthrusting of the brazilian shield beneath the eastern margin of the andes however the earthquakes are too deep and their nodal planes are too steep to be associated with the thin skinned decollement of the sedimentary cover instead they appear to reflect the tectonic deformation of the underthrust basement west of the zone of active deformation at the surface in the sub andes hence the earthquakes on the east side of the andes may reflect the style of deformation in the hinterland of fold and thrust belts such as in the canadian rockies while much of the decollement farther east occurs aseismically in contrast normal faulting occurs in the high andes on planes parallel to the strike of the mountain belt thus there is a delicate balance between the compressive stress applied to the andes in the direction of subduction which causes thrust faulting in the sub andes and the gravitational body forces acting on the topographically higher parts and the crustal root of the andes which may cause normal faulting at high elevation

velocity structure of the pamir hindu kush region possible evidence of subducted crust the arrival times of compressional p and shear s waves from approximately 580 microearthquakes recorded by a temporary array in the pamir hindu kush region in central asia are used to deduce one and three dimensional velocity structures of this region the results for one dimensional structures imply that the moho is at 70 5 depth also there is a velocity reversal near 160 km depth which is inferred to be the beginning of the low velocity zone this reversal continues to depths of approximately 230 km below 230 km velocities are somewhat higher than those of normal mantle at similar depths 9 3 km s versus 8 4 km s for p waves the outstanding feature of the results for three dimensional velocity structures is a broad 40 km centrally located region with 8 to 10 lower velocities than those in the surrounding regions this low velocity region envelopes the seismic zone at depths between 70 and 150 km the region may actually extend beyond these depths but the results for shallower and deeper structure lack sufficient resolution to decide several tests using both hypothetical and real data were performed to estimate the reliability of the three dimensional solutions the results of these tests suggest that the inferred velocities are reasonably accurate representations of the average velocities in the blocks although one must be cautious of the effects of averaging in interpreting the solution the low velocity region is inferred to be a manifestation of substantial quantities of subducted continental crust therefore while subduction has occurred in the pamir hindu kush the results of the three dimensional inversions suggest that continental rather than only oceanic lithosphere has been subducted to depths of at least 150 km appendices are available with the entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j81 013 1 00 payment must accompany order

seismicity and tectonics in jujuy province northwestern argentina the portable array for numerical digital analysis panda network a digitally recorded seismic array operated for nine months in jujuy province of northwestern argentina the network was deployed along the eastern edge of the altiplano puna plateau in a major n s thrust belt that is transitional in style between the thin skinned deformation of the bolivian foreland to the north and basement involved deformation of the pampean region to the south teleseismic locations of crustal earthquakes in the region indicate that seismicity is associated with compressional structures found near the eastern deformation front no crustal seismicity was detected beneath the puna plateau to the west peak seismicity levels beneath the foreland occurred between 20 and 25 km depth a sharp decrease in seismicity was observed below 25 km an estimate of 42 km for the thickness of the jujuy foreland crust was inferred from wide angle moho reflections observed on the digital seismograms the highest concentration of crustal seismicity was located beneath sierra de zapla a broad anticline immediately east of san salvador de jujuy many of the earthquakes in the 20 25 km depth range have a shallow west dipping nodal plane as does the focal mechanism solution for a moderately large 1973 earthquake inversion of focal mechanism data for the orientation of principal stresses shows that maximum compression is oriented at azimuth 74 closely paralleling both the current nazca south america convergence direction and the shortening direction derived from regional quaternary fault slip data we interpret the earthquakes as occurring on planes of weakness first produced during cretaceous rifting and later reactivated by neogene compressive stresses crustal seismicity patterns and fault plane solutions suggest the presence of a midcrustal detachment along which significant late cenozoic e w shortening has occurred

response of intracontinental deformation in the central andes to late cenozoic reorganization of south american plate motions new stratigraphic chronologic and fault kinematic data from the quebrada del toro in northwestern argentina provide a detailed view of late cenozoic kinematic reorganization in the southern central andes the quebrada del toro is a thrust bounded basin filled with 2 km of synorogenic clastic deposits ranging in age from early miocene to holocene as observed elsewhere in northwestern argentina faults in the quebrada del toro record an early phase of horizontal nw se contraction beginning between early and late miocene and ending after 0 98 ma and a later phase of horizontal ne sw contraction beginning between late miocene and 4 17 ma and still active these results require both kinematic regimes to have been active between 4 17 and 0 98 ma compatible with timing and kinematic data from the adjacent central andes and best explained by a temporal pattern of serial recurrence of the kinematic regimes a hypothesis that intraplate deformation in the central andes is driven by the absolute motion of the south american plate with respect to the hotspot reference frame is tested by comparing quebrada del toro kinematics to plate reconstructions and space based geodetic results nazca south america relative motion and absolute nazca plate motion show consistent azimuths throughout the past 20 5 myr in contrast absolute south american plate motion azimuths mimic the changing contraction directions determined from intraplate andean faults although the timing of the south american plate motion change is poorly resolved by current data it is compatible with the quebrada del toro data absolute upper plate motion might control intraplate kinematics along many of the earth s convergent margins

sediment glaciohydraulic supercooling and fast glacier flow glaciers often advance over proglacial sediments which then may enhance basal motion forglaciers with abundant meltwater thermodynamic considera tions indicate that the sediment ice contact in the direction of ice flow tends toward an angle opposed to and somewhat steeper than the surface slope by slightly more than 50 a simple model basedonthis hypothesisyieldstheextentof over ridden sediments as a function of sediment thickness and strength a result that may be useful in guiding additional fieldwork forhypothesistesting sediment floored as wellasrock floored over deepenings are common features along glacier flow paths and are expected based on theories of glacier erosion entrainment transport and deposition