geomorphological evidence for jokulhlaups from kverkfjoll volcano iceland abstract jokulhlaups glacial outburst floods are known to have drained along the jokulsa a fjollum river in iceland during the holocene however little is known about their number age source and flow characteristics this paper provides detailed geomorphological evidence for jokulhlaups that have routed from the kverkfjoll ice margin and hence into the jokulsa a fjollum erosional evidence of jokulhlaups from kverkfjoll includes gorges cataracts spillways subaerial lava steps and valley wide scoured surfaces depositional evidence includes wash limits boulder bars cataract fill mounds terraces slackwater deposits and outwash fans some of these landforms have been documented previously in association with jokulhlaups however subaerial lava surfaces that have been scoured of the upper clinker gorges within pillow hyaloclastite ridges gorges between pillow hyaloclastite ridges and subaerial lava flows subaerial lava lobe steps cataract fill mounds and boulder run ups are previously undocumented in the literature these landforms may therefore be diagnostic of jokulhlaups within an active volcanic rifting landscape the nature and spatial distribution of these landforms and their stratigraphic association with other landforms suggest that there have been at least two jokulhlaups through kverkfjallarani the biskupsfell eruption occurred between these two jokulhlaups kverkfjallarani jokulhlaups were very strongly influenced by topography geology and interevent processes that together determined the quantity and nature of sediment availability such controls have resulted in jokulhlaups that were probably fluidal turbulent and supercritical over large areas of the anastomosing channel bed kverkfjallarani jokulhlaups would have had highly variable hydraulic properties both spatially and temporally the knowledge of flow characteristics that can be gained from jokulhlaup impacts has implications for recognising jokulhlaups in the rock record and for hazard analysis and mitigation within similar landscapes and upon other glaciated volcanoes

precise analysis of icesat altimetry data and assessment of the hydrostatic equilibrium for subglacial lake vostok east antarctica summary based on the ice cloud and land elevation satellite icesat laser altimetry data the hydrostatic equilibrium he condition for the subglacial lake vostok east antarctica is evaluated a digital elevation model dem of the ice surface is derived by a regional crossover adjustment the analysis of the dem and its comparison with gps derived ice surface elevations and an ice surface dem based on radar altimetry data reveal an overall accuracy of better than 0 7 m for the lake area the dem is combined with an ice thickness model and a regional geoid model to determine the deviation of the local ice surface height from he for large parts of the lake the ice sheet fulfils the he our results reveal a strong positive deviation of about 10 m along the lake shoreline in addition positive deviations are found in the northern part of the lake which coincide with ice rumples detected by radio echo sounding in the southern part of the lake we find a linear negative deviation 4 0 m which coincides with the convoy route from vostok station to mirny base in addition to the dem relative biases for the icesat laser operational periods are determined in the regional crossover adjustment

integrated electrical resistivity tomography ert and self potential sp techniques for assessing hydrological processes within glacial lake moraine dams moraine dams can be inherently unstable but effective assessment strategies remain poorly identified we integrate electrical resistivity tomography ert with electrical self potential sp and lake level measurements to investigate the structure of and hydrological processes within a moraine dam complex adjacent to miage glacier italy this complex separates two meltwater lakes characterized by an efficient subterranean hydraulic connection our ert data reveal a continuous free surface within the complex whose morphology reflects the topography of the moraine complex akin to unconfined groundwater aquifers sp data were corrected for spatial changes in the thickness of the upper unsaturated layer using principles of electrography the residual streaming potential map is consistent with darcian flow of lake waters through the moraine complex characterized by a negative to positive potential change from 70 mv these electrical signatures are consistent with those generated by water seepage through earth dams in various non glacial settings integrated electrical geophysical methods thus provided an inexpensive and unobtrusive evaluation of the hydrological properties of and processes within the moraine complex since spatio temporal patterns of subsurface water flow critically affect the strengths of moraine sediments such methods promise to be powerful in assessing the long term stability of moraine dammed glacial lakes

comparative lahar hazard mapping at volcan citlaltepetl mexico using srtm aster and dted 1 digital topographic data abstract in this study we evaluated and compared the utility of spaceborne srtm and aster dems with baseline dted 1 bald earth topography for mapping lahar inundation hazards from volcan citlaltepetl mexico a volcano which has had a history of producing debris flows of various extents in particular we tested the utility of these topographic datasets for resolving ancient valley filling deposits exposed around the flanks of the volcano for determining their magnitude using paleohydrologic methods and for forecasting their inundation limits in the future we also use the three datasets as inputs to a gis stream inundation flow model laharz and compare the results in general all three datasets with spatial resolution of 90 m or better were capable of resolving debris flow and lahar deposits at least 3 106 m3 in volume or larger canopy and slope related height errors in the aster and srtm dems limit their utility for measuring valley filling cross sectional area and deriving flow magnitude for the smallest deposits using a cross sectional area to volume scaling equation height errors in the aster and srtm dems also causes problems in resolving stream valley hydrography which controls lahar flow paths and stream valley morphology which controls lahar filling capacity however both of the two spaceborne dem datasets are better than dted 1 at resolving fine details in stream hydrography and erosional morphologies of volcaniclastics preserved in the valleys around the more humid eastern flanks of the volcanic range the results of laharz flow inundation modeling using all three dems as inputs are remarkably similar and co validate one another for example at citlaltepetl all lahar simulations show that the city of orizaba is the most vulnerable to flows similar in magnitude to or larger than one that occurred in 1920 many of the other cities and towns illustrated are built higher up on terrace deposits of older debris flows and are safe from all but the largest flows which occur less frequently finally asters 60 km swath width and 8 duty cycle presents a challenge for mapping lahar inundation hazards at e w oriented stream valleys in low latitude areas with persistent cloud cover however its continued operations enhances its utility as a means for updating the continuous but one time coverage of srtm and for filling voids in the srtm dataset such as those that occur along steep sided valleys prone to hazards from future lahars

characteristics and evolution of supraglacial ponds on debris covered tasman glacier new zealand supraglacial ponds on tasman glacier new zealand initiated the development of the large tasman lake during the 1980s and still play an important role for ice loss and further terminus disintegration limnological and glaciological measurements between 2001 and 2003 reveal distinct differences between ponds the hydraulic connection of a pond to the englacial water level exerts a key control on whether the pond contributes to longer term terminus disintegration in the earlier stages of pond development ice loss occurs predominantly in the horizontal dimension by subaerial melt subaqueous calving at later stages plays a major role for ice loss during the capture of a pond by the lake substantial limnological changes lead to changes in relative significance and rates of ice loss processes the most important being the change from melting to predominantly calving as a result ice loss accelerated from around 11 m a 1 of melt under partial debris cover to a retreat by calving and melting of 34 m a 1 ice loss at the ponds accounted for only 10 of the surface loss in the lower terminus area but is likely to increase in the future with enlargement and coalescence of ponds

gravity field determination and characteristics retrospective and prospective gravimetry has had a long history using pendulums torsion balances and static spring gravimeters relative accuracy adequate for many geophysical problems was already attained by 1900 but it took another half century to build readily portable gravimeters calibration and datum definition remained problems until the 1970s when free fall absolute gravimeters were developed that now have a precision of 10 3 mgal the problems of geographic inaccessibility and field party costs notably in areas of greatest tectonic interest are now being overcome by airborne gravimetry that has already achieved accuracies of 1 3 mgal with resolutions of 10 to 20 km satellite techniques are the best way to determine the long wavelength variations of the gravity field the resolution of the models has steadily improved with the number of satellites and the precision of the observations the best current model includes tracking data from more than 30 satellites satellite altimetry and surface gravimetry and has a resolution of about 290 km harmonic degree 70 with the most recent improvements coming from doppler orbitography and radiopositioning integrated by satellite doris tracking of the spot 2 satellite and satellite laser ranging slr doris and global positioning system gps tracking of the topex poseidon satellite meanwhile radar altimetry has become the dominant technique to infer the marine geoid with a resolution of tens of kilometers or shorter similarly the gravity fields of the moon venus and mars have been determined to harmonic degrees 70 75 and 50 respectively although tracking limitations result in variations of spatial resolution modeling earth s gravity field from the abundance of precise data has become an increasingly complex task with which the development of computer capacity has kept pace contemporary solutions now entail about 10 000 parameters half of them for effects other than the fixed gravity field of earth temporal variations arising from tides have long been well modeled and nontidal changes are now being identified the improvement in gravitational models engendered corresponding advances in geophysical interpretation isostatic models were refined and expanded to account for regional thermal and tectonic histories interpretation of the long wavelength gravity field determined by satellite techniques has been mainly in terms of plate tectonics as a manifestation of mantle convection gravity has been significant in inferring that there must be a large increase in viscosity with depth most strongly from the apparent slow sinking of subducted slabs the prospects for increasing accuracy and resolution in the determination of earth s gravity field rest primarily with the development of new measurement systems airborne gravimetry is taking promising new steps using gps but significant global model improvement awaits a dedicated satellite gravimetry system and future satellite altimeter missions will do more for ocean dynamics studies than geoid improvement advances in interpretation will occur through the development of other data such as seismic tomography and larger scale computer modeling of tectonics and convection

the use of one and two dimensional hydraulic modelling to reconstruct a glacial outburst flood in a steep alpine valley the hydrologic characteristics of the 1943 outburst flood from the glacier du mont mine switzerland are herein reconstructed using field evidence palaeostage indicators in conjunction with shallow water modelling techniques these techniques rely on accurately characterising the hydraulic roughness of the channel the water height established as boundary conditions and the main flow path during the former flood but the selection of appropriate parameter values can be problematic and hence there is uncertainty in the estimated discharge in this study minimal flow discharge estimates derived from one dimensional modelling were found to vary between 429 and 557 m3 s 1 as the hydraulic roughness ks and water height at the inlet were varied over a realistic range of values 0 8 1 4 m and 3 31 6 m respectively whereas flow rates derived via two dimensional modelling were confined in a narrower lower range of 358 454 m3 s 1 this degree of sensitivity to bed roughness ks boundary conditions and the spatial dimensions of the modelling approach is for the one dimensional modelling higher than reported in previous studies but the precision of flow discharge values reconstructed using the two dimensional modelling approach appears to be acceptable even for floods in the very steep valley 0 1 m m that is subject of this study

expansion of a moraine dammed glacial lake tsho rolpa in rolwaling himal nepal himalaya across the surface of debris covered glaciers in the nepal himalayas there are many lakes on the order of 1 km in scale some of the lakes dammed by the end lateral moraine have been expanded from ponds on the order of 100 m in length tsho rolpa glacier lake in the headwater region of the rolwaling valley eastern nepal was probably a small pond in the early 1950s the present expansion rate of the glacial lake is unknown from our investigation of the hydrological and meteorological conditions in 1993 1994 the calculated heat balance in the lake showed a deepening rate of about 1 2 m yr 21 all through the year this is comparable to the mean deepening rate of the bottom basin since 1952 the vertical expansion thus is still continuing annual volume expansion including the calving ice horizontal expansion volume was 3 of the present total volume of the lake

comparing a 1d hydraulic model with a 2d hydraulic model for the simulation of extreme glacial outburst floods glacial outburst floods jokulhlaups destroy a significant amount of infrastructure in proglacial areas nevertheless few studies have simulated extreme jokulhlaup inundation using hydraulic modelling in this study we demonstrate the capability of one dimensional jokulhlaup simulation hec ras modelling software and compare simulation results with those from a two dimensional finite element model telemac 2d modelling software to determine the potential and limitations of one dimensional modelling for jokulhlaup simulations in both models a pre defined hydrograph was used as an upstream boundary condition for the jokulhlaup which was simulated on the mo rudalur floodplain northeast iceland an unsteady flow simulation of the rising stage of the flood 5 h 15 min was undertaken with both models to produce maps of flood inundation and flow depth the study shows that simulations had a 200 m horizontal difference in inundated area at the peak discharge stage additional differences were also detected in the rising stage of the hydrograph the most significant differences between the models was found at the time when the front of the jokulhlaup inundated a new area through a sinuous gorge or when inundation took place through a complex flow route maximum difference 1800 m this study demonstrates that one dimensional modelling of jokulhlaup propagation provides results broadly comparable to data derived from more complex simulations copyright 2007 john wiley sons ltd

ice avalanches some empirical information about their formation and reach evaluation d apres l etude d environ 100 avalanches de glace des zones de rupture et des distances d arret

aster measurement of supraglacial lakes in the mount everest region of the himalaya we demonstrate an application of advanced spaceborne thermal emission and reflection radiometer aster images to detect and monitor supraglacial lakes on glaciers in the mount everest region in tibet xizang and nepal aster offers powerful capabilities to monitor supraglacial lakes in terms of 1 surface area growth and disappearance spatial resolution 15m 2 turbidity 15m resolution and 3 temperature 90m resolution preliminary results show an overall similarity of supraglacial lakes on three glaciers lakes have widely varying turbidity as indicated by color in visible near infrared bands 1 3 the largest lakes being bright blue highly turbid cold near 0 c and hydraulically connected with other lakes and supraglacial streams while small lakes are mostly darkblue relatively clear water warmer 4 c and appear hydraulically isolated high levels of turbidity in supraglacial lakes indicate high rates of meltwater input from streams or erosion of ice cliffs and thus are an indirect measure relating to the activity and hydraulic integration of the lake with respect to other lakes and streams in the glacier

very high spatial resolution imagery for channel bathymetry and topography from an unmanned mapping controlled platform the increasing availability of aerial photography and satellite imagery offers new possibilities for characterizing river morphology the precision of new very high resolution vhr images allows smaller scale objects within river corridors to be studied high survey frequencies provide increased opportunities for the monitoring of river restoration following this evolution in platform technology a small radio controlled motorized vehicle flying at low altitude was used to study both channel water depth and gravel bar geometry the vhr imagery provided by this equipment allowed both channel bathymetry and a high accuracy photogrammetric digital elevation model dem to be realized using case studies from the ain and the drome rivers in france the accuracy of the results is presented and the various challenges associated with the new platform are discussed one significant issue is that due to the low elevation of the survey the coverage of a target area is usually based on several photographs which leads to variations in illumination conditions that stem from atmospheric changes the images were processed to minimize this source of error but a number of issues have yet to be resolved bathymetric models with r2 values between 0 59 and 0 90 were created in spite of the lack of channel bed homogeneity at the various sites the gravel bar was also effectively mapped and the photogrammetrically predicted dem provided a 5 10 cm pixel resolution with a vertical precision between 2 and 40 cm according to the position within the image this paper shows that despite unstable image acquisition unmanned radio controlled platforms provide significant advantages for the study of river processes offering a flexible very high resolution data source for both channel bathymetry and gravel bar topography copyright 2007 john wiley sons ltd

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

late pleistocene earthquake triggered moraine dam failure and outburst of lake zurich switzerland 1 lakes impounded by moraines may be considered hazardous in glaciated areas throughout the world because dams can fail suddenly producing destructive floods with peak discharges far in excess of normal flows here we present a comprehensive case study in the zurich switzerland area that reveals several independent lines of evidences for the occurrence of a late pleistocene 13 760 calibrated years b p moraine breach and subsequent lake zurich outburst discharge volume 2 5 km3 we use seismic and core data in order to track and date the geological fingerprint of this event data from areas downstream of the lake show coarse grained massive 25 m thick reworked morainic deposits behind four breached zones in lake zurich sedimentary structures recorded in a paleowater depth of 36 m indicate strong outburst induced currents hydrodynamic calculations reconstructing the sediment transport capacity explaining the observed bed forms allow estimating averaged outburst discharge to exceed minimum values of 2400 m3s 1 the potential maximal magnitude of the outburst is inferred from calculations considering critical flow conditions through the breaches revealing estimated peak discharge of 20 600 m3s 1 we also discuss long term causes and short term trigger mechanisms of the dam failure that occurred several thousand years after moraine formation and show that it coincides with a reconstructed strong northern alpine earthquake magnitude 6 5 our data thus suggest that catastrophic drainage of lake zurich was initiated as a consequence of the moraine dam failure that either was triggered by primary earthquake shaking or by secondary effects such as overtopping by landslide generated waves

observations from the large rapid yigong rock slide debris avalanche southeast tibet the yigong rock slide debris avalanche yra which occurred on 9 april 2000 received worldwide attention as one of the largest nonseismic landslides in recent years with a volume of 0 3 109

snow avalanche mass balance calculation and simulation model verification two or three dimensional avalanche simulation models offer a wide range of applications however a challenging model verification process is demanded accompanied by a reliable determination of model input parameters we show that a verification process can be arranged with remote monitoring data from an artificially triggered avalanche leading to the calculation of avalanche mass balance two numerical methods are applied to increase the quality of the parameter fit and to reduce the number of simulations the quality of the parameter fit is verified by comparing measured and simulated run out lengths in addition a cross check is performed using velocities derived from doppler radar measurements

effects of wood on debris flow runout in small mountain watersheds 1 debris flows have typically been viewed as two phase mixtures of sediment and water but in forested mountain landscapes wood can represent a sizable fraction of total flow volume the effects of this third phase on flow behavior are poorly understood to evaluate whether wood can have a significant effect on debris flow runout in small mountainous watersheds we used a landscape scale model combining empirical stochastic and physical submodels of storms fires forest growth tree fall wood decay soil production and diffusion landslide initiation debris flow runout and fluvial sediment transport we examined changes in the cumulative distribution function of debris flow runout lengths in a small 2 km2 watershed in the oregon coast range due to presence or absence of two hypothesized effects of wood 1 velocity reduction due to entrainment of wood in the runout path and 2 velocity reduction due to changes in flow direction angle the model was calibrated such that the distribution for simulations including both effects was similar to that measured in the study basin and amounts of wood in the simulation and the field both fallen in small valleys and incorporated by debris flows were comparable removal of either effect or both significantly shifted runout length distributions to longer lengths simulations and field observations indicate that with wood fluvial transport is a significant source of sediment output few debris flows reach the outlet and debris flow deposits are widely distributed throughout the network simulations indicate that without wood basin sediment yield greatly increases that yield is dominated by longer runout debris flows and that debris flow deposits are concentrated in the low gradient reach near the outlet

the 1786 earthquake triggered landslide dam and subsequent dam break flood on the dadu river southwestern china abstract chinese historic documents recorded that on june 1 1786 a strong m 7 75 earthquake occurred in the kangding luding area sichuan southwestern china resulting in a large landslide that fell into the dadu river as a result a landslide dam blocked the river ten days later the sudden breaching of the dam resulted in catastrophic downstream flooding historic records document over 100 000 deaths by the flood this may be the most disastrous event ever caused by landslide dam failures in the world although a lot of work has been carried out to determine the location magnitude and intensity of the 1786 earthquake relatively little is known about the occurrence and nature of the landslide dam in this paper the dam was reconstructed using historic documents and geomorphic evidence it was found that the landslide dam was about 70 m high and it created a lake with a water volume of about 50 106 m3 and an area of about 1 7 km2 the landslide dam breached suddenly due to a major aftershock on june 10 1786 the peak discharge at the dam breach was estimated using regression equations and a physically based predictive equation the possibility of a future failure of the landslide seems high particularly due to inherent seismic risk and detailed geotechnical investigations are strongly recommended for evaluating the current stability of the landslide

a 10 km resolution synthetic venus gravity field model based on topography a high resolution gravity field model is extremely important in the exploration of venus in this paper we present a 3 dimensional venus gravity field vgm2014 constructed by using the latest gravity and topography models residual terrain model rtm and the airy heiskanen isostatic compensation model the vgm2014 is the first 10 km scale venus gravity field model the final results are representations of the 3 dimensional surface gravity accelerations and gravity disturbances for venus we found that the optimal global compensation depth of venus is about 60 km and the crustal density is potentially less than the commonly accepted value of 2700 2900 kg m 3 this model will be potentially beneficial for the precise orbit determination and landing navigation of spacecraft around venus and may be utilized as a priori model for venus gravity field simulation and inversion studies the vgm2014 does not incorporate direct gravity information beyond degree 70 and it is not recommended for small scale geophysical interpretation

breaching parameters for earth and rockfill dams dam risk analysis is at the heart of dam failure prevention and mitigation in order to assess dam risk it is essential to conduct a quantitative analysis of the process of a dam breach which can be described by such parameters as breach geometry breaching duration and peak outflow rate the main objective of this paper is to develop robust empirical formulas with physical meaning for predicting dam breaching parameters based on past dam failure data a database of 182 earth and rockfill dam failure cases has been compiled among these cases nearly one half are for large dams higher than 15 m a multiparameter nonlinear regression model is recommended to develop empirical relationships between five breaching parameters breach depth breach top width average breach width peak outflow rate and failure time and five selected dam and reservoir control variables dam height reservoir shape coefficient dam type failure mode and dam erodibility the relative importance of each control variable is evaluated the dam erodibility is found to be the most important factor influencing all five breaching parameters the reservoir shape coefficient and the failure mode also play an important role in the prediction models two case studies are presented to show the application of the empirical models developed in this paper

thermo erosional notch development at fresh water calving tasman glacier new zealand controls on glacier calving rates are receiving increased scientific interest at fresh water calving glaciers limnological factors might be more important than glaciological ones measurements of thermo erosional notch development at the calving ice cliff of tasman glacier new zealand suggest that the calving rates at this glacier are directly controlled by the rate of thermal undercutting notch formation rates typically vary between 10 and 30 cm d 1 maximum rate 65 cm d 1 in summer corresponding to an average calving rate of 34 m a 1 notch formation is slower than waterline melt and is controlled by water temperatures and circulation cliff geometry debris supply and water level fluctuations the latter shift the position of undercutting resetting the level of the notch formation process and thereby slowing it the geometry of the notch and the debris supply determine the extent of influence of the lake on notch water temperatures and circulation hence water temperatures in the lake are not necessarily indicative of the rate of notch formation the prediction of rate of notch formation from far field variables is hampered by the complex interaction of the influencing factors the significance of thermal undercutting as a calving rate controlling process decreases with increasing ice velocities calving rates and surface gradients

dynamic topography estimates using geosat data and a gravimetric geoid in the gulf stream region summary a gravimetric geoid undulation on a 3 x 3 grid has been calculated in the gulf stream region 30 5 i 45 278 5 i 5 318 these undulations were calculated using two 360 potential coefficient models land ship and altimeter derived gravity anomalies and bathymetric data least squares collocation and fast fourier transform procedures were used with various data selection and gridding procedures results from five different undulation computations are described with comparisons made with synthetic geoid undulations along geosut tracks in the region the standard deviation of the undulation differences was f14cm when a cubic polynomial was used to model long wavelength errors a point verification of the geoid undulation at the laser tracking station on bermuda was also made with a discrepancy ground truth minus model undulation of 40 cm within the predicted standard deviation the gravimetric geoid undulation was used to compute dynamic topography along geosat tracks for comparison with existing estimates based on hydrographic data in the gulf stream region the agreement between these two estimates is on the order of f15 cm although the discrepancies can reach 60 cm the larger differences are usually associated with a location on a track that passes near a seamount where the gravity data may be inadequate to represent the high frequency variations in the geoid undulations this effect will be represented in the undulation standard deviations that have been calculated using the least squares collocation procedure the average accuracy is fl6cm with the range from f14 to f48cm the dynamic height derived from the gravimetric undulations and altimeter data has been used to calculate characteristics of the gulf stream width velocity centre location height profile using an implied velocity model for the set the results are compared with previous estimates with generally good agreement however the maximum velocities and the jump function are approximately 30 per cent larger than previous studies that used an average of altimeter tracks to define the geoid undulation the dynamic topography was calculated for the entire region using a mean sea surface based on geos 3 seasat and geosat data the results are compared with two hydrographic estimates due to martel wunsch and letraon mercier the agreement is at the f25cm level with the best correlation coefficient reaching 0 72 with the martel wunsch model

the yellowstone hebgen lake geoid obtained through the integrated geodesy approach the 1987 crustal deformation survey of the yellowstone hebgen lake region produced accurate geodetic measurements in an area unique for its rugged topography and volcanic processes using the integrated geodesy approach global positioning system gps baseline vectors geodetic leveling and gravity measurements were combined in a simultaneous least squares adjustment using 30 30 digital terrain data and an airy model isostatically corrected complete bouguer gravity disturbances highlight both the yellowstone caldera and a second gravity low near hebgen lake a linear relationship between these disturbances and the departures of geoid height from the airy isostatic model have been found r 0 84 adjusting the covariance function while incorporating the gps contribution yields a function whose correlation length is significantly longer than that predicted by autocorrelation statistics of the gravity disturbances alone the integrated adjustment produced a geoid whose low frequency components are in good agreement with osu86f formal statistics indicate precision of 2 5 cm gps residuals for 35 leveled points in the adjustment have a root mean square value of 2 9 cm and a standard error estimate of 4 6 cm in comparison a free adjustment of 152 gps vectors yields a differential height standard error of 3 8 cm

growth and drainage of supraglacial lakes on debris mantled ngozumpa glacier khumbu himal nepal ablation of debris mantled glaciers in nepal has resulted in the formation of several potentially unstable moraine dammed lakes some of which constitute serious hazards ngozumpa glacier khumbu himal has undergone significant downwasting in recent decades and is believed to lie close to the threshold for moraine dammed lake formation the debris mantled ablation area of the glacier is studded with numerous supraglacial lakes the majority of which occupy closed basins with no perennial connections to the englacial drainage system perched lakes perched lakes can undergo rapid growth by subaerial and water line melting of exposed ice faces and calving subaerial and subaqueous melting beneath thick 1 m debris mantles is comparatively insignificant although lake expansion can contribute substantially to ablation of the glacier perched lakes cannot continue to grow indefinitely but are subject to rapid drainage once a connection is made to englacial conduits the level of one of the lakes on the ngozumpa however is controlled by the altitude of a spillway through the lateral moraine of the glacier this lake underwent only limited growth in the period 1998 2000 but is likely to experience monotonic growth if glacier mass balance continues to be negative

ephemeral grounding as a signal of ice shelf change interferometric synthetic aperture radar insar observations of ice shelf tidal deformation reveal the wide transition between grounded and floating ice as well as local areas where the ice shelf is only grounded at low tide a condition that we call ephemeral grounding ephemeral grounding creates a subtle local disturbance on the vertical motion field of the ice shelf surface in response to changes in occanic tide which is detected with millimetric precision using insar these ice shelf features are however not expected to produce a noticeable disturbance on the ice shelf velocity field to illustrate the influence of ephemeral grounding on ice shelf creep flow we use a finite element model in which ephemeral grounding is incorporated through a variable basal friction coefficient the results show that while ice rises permanently grounded areas have a pronounced influence on the ice shelf velocity field areas of ephemeral grounding have a vanishingly small influence what is thus of most interest is the capacity for observations of ephemeral grounding to reveal subtle changes in ice shelf thickness over time we discuss an example in the thwaites glacier area west antarctica where multi year data show how ice rises become ephemeral grounding and subsequently disappear this result is consistent with the grounding line retreat and ice thinning of thwaites glacier

flow hydraulics and geomorphic effects of glacial lake outburst floods in the mount everest region nepal glacial lake outburst floods glofs on 3 september 1977 and 4 august 1985 dramatically modified channels and valleys in the mount everest region of nepal by eroding transporting and depositing large quantities of sediment for tens of kilometres along the flood routes the glof discharges were 7 to 60 times greater than normal floods derived from snowmelt runoff glacier meltwater and monsoonal precipitation referred to as seasonal high flow floods shffs specific stream power values ranged from as low as 1900 w m 2 in wide low gradient valley segments to as high as 51 700 w m 2 in narrow high gradient valley segments bounded by bedrock along the upper 16 km of the glof routes the reach averaged specific stream power of the glofs was 3 2 to 8 0 times greater than the reach averaged specific stream power of the shffs the greatest geomorphic change occurred along the upper 10 to 16 km of the glof routes where the ratio between the glof specific stream power and the shff specific stream power was the greatest there was an abundant supply of sediment and channel valley boundaries consisted primarily of unconsolidated sediment below 11 to 16 km from the source area the geomorphic effects of the glofs were reduced because of the lower specific stream power ratio between the glofs and shffs more resistant bedrock flow boundaries reduced sediment supply and the occurrence of past glofs copyright 2003 john wiley sons ltd

application of 2d hydrodynamic modelling to high magnitude outburst floods an example from kverkfjoll iceland abstract high magnitude outburst floods cause rapid landscape change and are a hazard to life property and infrastructure however high magnitude fluvial processes and mechanisms of erosion transport and deposition are very poorly understood and remain largely unquantified this poor understanding is partly because of the inherent difficulty of directly measuring high magnitude outburst floods but also because of the limitations and assumptions of 1d models and other palaeohydrological methods which reconstructions of high magnitude floods have to date relied upon this study therefore applies a 2d hydrodynamic model sobek to reconstructing a high magnitude outburst flood this method offers the first calculations of high magnitude fluvial flow characteristics within an anastomosing network of simultaneously inundated channels including sheet or unconfined flow simultaneous channel and sheet flow flow around islands hydraulic jumps multi directional flow including backwater areas hydraulic ponding and multiple points of flood initiation 2d modelling of outburst floods clearly has the potential to revolutionise understanding of high magnitude spatial and temporal hydraulics and high magnitude flow phenomena geomorphological and sedimentological processes and hence rapid fluvial landscape change this potential for new understanding is because of the now wide availability of high resolution dem data for large and often inaccessible areas and the availability of remotely sensed data that can parameterise outburst flood sources such as glacial lakes for example additionally hydraulic models and computing power are now sufficient to cope with large 5 000 000 grid cells areas of inundation and large 100 000 m3 s 1 peak discharges

volume calculation and analysis of the changes in moraine dammed lakes in the north himalaya a case study of longbasaba lake glacial lake outburst flood hazards in the himalayan region have received considerable attention in recent years accurate volume estimation for glacial lakes is important for calculating outburst flood peak discharge and simulating flood evolution longbasaba lake a potentially dangerous moraine dammed lake is located on the north side of the himalaya its depth was surveyed using the syqwest hydrobox high resolution echo sounder and 6916 measurements were collected in september 2009 the maximum and average depths of the lake were 102 2 and 48 2 m respectively the morphology of the lake basin was modeled by constructing a triangulated irregular network and the lake was found to have a storage capacity of 0 064 0 002 km 3 multi source remote sensing images from landsat mss landsat tm etm and terra aster and a topographic map were digitized to delineate the outlines of the lake between 1977 and 2009 the results indicate that the length and area of the lake have increased during the past 32 years with a drastic expansion occurring since 2000 based on volume and area data of longbasaba lake in different periods we deduced an empirical equation of the lake volume area relationship that can be used to calculate the storage capacity of similar moraine dammed lakes in the himalayan region

prevention of outburst floods from periglacial lakes at grubengletscher valais swiss alps flood and debris flow hazards at grubengletscher near saas balen in the saas valley valais swiss alps result from the formation and growth of several lakes at the glacier margin and within the surrounding permafrost in order to prevent damage related to such hazards systematic investigations were carried out and practical measures taken the evolution of the polythermal glacier the creeping permafrost within the large adjacent rock glacier and the development of the various periglacial lakes were monitored and documented for the last 25 years by photogrammetric analysis of annually flown high resolution aerial photographs seismic refraction d c resistivity and gravimetry soundings were performed together with hydrological tracer experiments to determine the structure and stability of a moraine dam at a proglacial lake the results indicate a maximum moraine thickness of 100 m extremely high porosity and even ground caverns near the surface may have resulted from degradation of sub and periglacial permafrost following 19th 20th century retreat of the partially cold glacier tongue the safety and retention capacity of the proglacial lake were enhanced by deepening and reinforcing the outlet structure on top of the moraine complex the water level of an ice dammed lake was lowered and a thermokarst lake artficially drained

combining airborne and terrestrial laser scanning for quantifying erosion and deposition by a debris flow event abstract we quantified the sediment volume transported by a major debris flow event in the halltal austrian alps using a combination of terrestrial tls and airborne laser scanning als which has rarely been carried out before a digital terrain model dtm derived from als data pre event surface was combined with a dtm derived from tls data post event surface both datasets were aligned and compared in a cut and fill analysis estimating differential volumes the main focus lay on the evaluation and accuracy assessment of the applied method tie point based registration of both datasets proved to be insufficient additional alignment by multi station adjustment was necessary to minimise the averaged height error between both datasets amounting for a volumetric error of less than 10 which is comparable to pure als campaigns larger errors were estimated for complex terrain with low scanning resolutions a particular problem in data processing was the low and dense shrub vegetation in the study area which required a specifically adapted filter algorithm an insufficient ground representation was observed for the als data overestimating ground heights for averaged 70 cm despite these limitations the approach proved to be suitable for accurate extreme event quantification the starting zones of the debris flows lie at the bedrock debris interface where runoff is concentrated volumes of 5000 to 12 000 m3 were assessed volume estimation worked better for the erosional than for the depositional features this is because the erosional gullies are relatively deep and the calculation is not affected by pre event vegetation while erosion and sedimentation are balanced for one of the three catchments investigated the deposited volumes are higher than the detected eroded volumes for the other two the reasons are not fully understood the magnitude of the flows was determined by catchment size topographical characteristics and deforestation by a major wildfire in 1946

modelling outburst floods from moraine dammed glacial lakes in response to climatic change the size and number of moraine dammed supraglacial and proglacial lake systems have increased dramatically in recent decades given an appropriate trigger the natural moraine dams that impound these proglacial lakes are breached producing catastrophic glacial lake outburst floods glofs these floods are highly complex phenomena with flood characteristics controlled in the first instance by the style of breach formation downstream glofs typically exhibit transient often non newtonian fluid dynamics as a result of high rates of sediment entrainment from the dam structure and channel boundaries combined these characteristics introduce numerous modelling challenges in this review the historical contemporary and emerging approaches available to model the individual stages or components of a glof event are introduced and discussed a number of methods exist to model the stages of a glof event dam breach models can be categorised as being empirical analytical or numerical in nature with each method having significant advantages and shortcomings empirical relationships that produce estimates of peak discharge and time to peak are straightforward to implement but the applicability of these models is often limited by the nature of the case study data from which they are derived furthermore empirical models neglect the inclusion of basic hydraulic principles that describe the mechanics of breach formation analytical or parametric models simulate breach development using simplified versions of the physically based equations that describe breach enlargement whilst complex physically based codes represent the state of the art in numerical dam breach modelling to date few of the latter have been applied to investigate the moraine dam failure problem despite significant advances in the physical complexity and availability of higher order hydrodynamic solvers the majority of published accounts that have attempted to reconstruct or predict glof characteristics have been limited often by necessity to the use of relatively simplistic models this is in part attributable to the unavailability of terrain models of many high mountain catchments at the fine spatial resolutions required for the effective application of numerically sophisticated codes and their proprietary and often cost prohibitive nature however advanced models are experiencing increasing use in the glacial hazards literature in particular the suitability of emerging mesh free particle based methods for simulating dam breach and glof routing may represent a solution to many of the challenges associated with modelling this complex phenomenon sources of uncertainty in the glof modelling chain have been identified by various workers however to date their significance for the robustness of reconstructive and predictive modelling efforts have been largely unexplored and quantified in detail these sources include the geometric and material characterisation of moraine dam complexes including lake bathymetry and the presence and extent of buried ice initial conditions freeboard precise spillway dimensions spatial discretisation of the down valley domain hydrodynamic model dimensionality and the dynamic coupling of successive components in the glof model cascade

paleohydraulic reconstruction of flash flood peaks from boulder deposits in the colorado front range nine watersheds in the colorado front range with steep bedrock channels were used to test the accuracy of paleohydraulic reconstruction of large flash floods using boulder deposits the nine basins consist of eight small ungauged basins ranging in size from 1 6 to 29 km2 and the big thompson river at the mouth of the big thompson canyon draining 790 km2 between 1923 and 1976 all nine basins had had one catastrophic flash flood the magnitude of which has been estimated by the conventional slope area method in each basin coarse boulder deposits of the large flash floods were identified and three axes of the five largest boulders were measured along with at least two profiles of the valley cross section a simple arithmetic average of two theoretical and two empirical relationships was used to estimate average flood velocity using boulder size and shape average depth was estimated as the arithmetic average of four values computed from the manning equation a regression equation for boulder size and unit stream power a relative smoothness equation and a modified shields relationship the appropriate flood width for the estimated average depth was found by iteration using the valley cross sections the paleohydraulic discharges thus computed generally underestimate conventional slope area discharge estimates on small streams by as much as 75 although the average amount is only 28 too low and the reconstructed discharge in one stream was 31 too large the big thompson river flood of 1976 was overestimated by 76 reasons for discrepancy in reconstructed peaks could include 1 the possibility that floods may have been able to move boulders larger than those available to be moved 2 overestimation of the slope area discharge because high water marks were set prior to erosion of the channel 3 underestimation of original roughness coefficients and 4 macroturbulent effects during fast deep flows the paleohydraulic technique is applied to two other streams in colorado with sedimentological evidence of large flash floods but no conventional indirect discharge estimates a small tributary to the big thompson river draining 1 8 km2 has a paleohydraulic reconstructed flood peak of about 60 m3 s from a flood in 1976 using boulders excavated from a foundation site in holocene alluvium along boulder creek in boulder colorado a paleohydraulic reconstructed flood peak of between 860 and 1 512 m3 s is calculated this is 1 4 to 2 4 times the magnitude of the estimated 500 yr flood

reconstruction of the largest holocene jokulhlaup within jokulsa a fjollum ne iceland abstract glacial outburst floods jokulhlaups have a significant role for landscape evolution in ne iceland a number of jokulhlaups have routed from the northern margin of vatnajokull during the holocene in this study reconstruction of the largest holocene jokulhlaup along jokulsa a fjollum ne iceland was undertaken using the hec ras hydraulic modelling and hec georas flood mapping techniques with a digital elevation model dem derived from ers insar data and field based wash limit evidence the largest jokulhlaup produced extensive erosional and depositional landforms across an inundated area of 1390 km2 and is calculated to have had a peak discharge of 0 9 106 m3 s 1 power per unit area within this jokulhlaup varied from 6 to 46 000 w m 2 jokulhlaup hydraulics are related to geomorphogical evidence at three key sites in va alda upptyppingar and mo rudalur sub areas in order to explain the abrupt spatial variation of the flood characteristics on a regional scale and to relate erosional and depositional features to spatial variations in jokulhlaup hydraulics these process form relationships of the largest jokulhlaup along the jokulsa a fjollum are compared with large outburst floods elsewhere the largest jokulsa a fjollum jokulhlaup had a factor of 20 times smaller discharge and a factor of 20 times lower power per unit area than altai palaeoflood the largest known flood on the earth

himalayan glacial sedimentary environments a framework for reconstructing and dating the former extent of glaciers in high mountains abstract reconstructing paleoenvironmental change from glacial geologic evidence in the himalayas has been difficult because of the lack of organic material for radiocarbon dating and the problems of correctly identifying the origin of highly dissected landforms studies of the contemporary glacial depositional environments and ancient landforms and sediments in the hunza valley karakoram mountains the lahul and garhwal himalaya and the khumbu himalaya illustrate the variability in processes landforms and sediment types these studies can be used to interpret ancient landforms and sediments for paleoenvironmental reconstructions and aid in forming strategies for sampling sediments and rocks for the developing techniques of cosmogenic radionuclide crn surface exposure and optically stimulated luminescence osl dating many himalayan glaciers have thick covers of supraglacial debris derived from valley sides and such debris mantled glaciers exhibit important differences from clean glaciers both in terms of debris transport processes and the depositional landforms that they produce analysis of sediment landform associations can be used to reconstruct processes of sediment transport and deposition and the relationship between moraines and other landforms and climatic forcing cycles such analysis is of fundamental importance in guiding sampling and interpretation in crn and osl dating work

a 1 5km resolution gravity field model of the moon we present a high resolution lunar gravity field model lgm2011 that provides gravity accelerations free air gravity anomalies selenoid undulations and vertical deflections over the entire moon s surface lgm2011 is based on the japanese selene mission that provides the low and medium frequency constituents of the gravity field down to spatial scales of 78 km at spatial scales between 78 km and 1 5 km lgm2011 uses highfrequency topographic information derived from lola laser altimetry to approximate the gravity field signatures of many medium and small size impact craters for the first time for the topography based gravity approximation we use newtonian forward modelling under the key assumptions that the selene and lola data are consistent the high frequency lunar topography is uncompensated and the topographic mass density is constant the short scale component of lgm2011 should not be relied upon in geophysical interpretations lgm2011 can be used as an a priori model for lunar gravity field simulation and inversion studies evaluation of past and future lunar gravity field missions improved topographic mapping

gravity field mapping from satellite altimetry sea gravimetry and bathymetry in the eastern mediterranean summary using data from the eastern mediterranean it has been shown how different data types may improve the quality of a gravity field approximation and a detailed geoid has been computed for the area the following data types were available a bias adjusted satellite altimetry b sea gravimetry c bathymetry and heights and d the spherical harmonic coefficient set osu81 complete to degree 180 a comparison of the satellite altimetry with geoid heights computed from the osu81 coefficients with and without the additional use of gravity data revealed substantial errors due to unmodelled orbit tilts a trend analysis of the altimeter data showed a tilt of 0 0026 m km 1 in eastern direction and 0 0067 m km 1 in northern direction the standard deviation s d of observed altimeter values minus osu81 geoid heights decreased from 1 53 m to 1 07 m after a correction for the tilt least squares collocation was then used to predict subsets of the data types a and or b from subsets of the same data types the results given here are in terms of the s d of observed minus computed values using every third value of the corrected altimeter data for gravity prediction a s d of 17 mgal was found when gravity values spaced 10 apart were used to predict 1 gravity values in a grid with the same mesh width shifted 5 and 2 altimeter observations a s d of 10 mgal and 0 42 m respectively were found a combination of gravity and altimeter data made the first s d of 10 mgal decrease to 7 mgal showing the impact of combining the two data types the use of topographic information to smooth the locally strongly varying gravity field gave substantial improvements in the gravity values predicted from either altimeter observations or gravity data error estimates of geoid heights predicted in between the altimeter tracks showed that a 65 per cent improvement had been achieved

1d finite volume model of unsteady flow over mobile bed summary a one dimensional 1d finite volume method fvm model was developed for simulating unsteady flow such as dam break flow and flood routing over mobile alluvium the governing equation is the modified 1d shallow water equation and the exner equation that take both bed load and suspended load transport into account the non equilibrium sediment transport algorithm was adopted in the model and the van rijn method was employed to calculate the bed load transport rate and the concentration of suspended sediment at the reference level flux terms in the governing equations were discretised using the upwind flux scheme harten et al 1983 hll and hllc schemes roe s scheme and the weighted average flux waf schemes with the double minmod and minmod flux limiters the model was tested under a fixed bed condition to evaluate the performance of several different numerical schemes and then applied to an experimental case of dam break flow over a mobile bed and a flood event in the rillito river tucson arizona for dam break flow over movable bed all tested schemes were proved to be capable of reasonably simulating water surface profiles but failed to accurately capture the hydraulic jump the waf schemes produced slight spurious oscillations at the water surface and bed profiles and over estimated the scour depth when applying the model to the rillito river the simulated results generally agreed well with the field measurements of flow discharges and bed elevation changes modeling results of bed elevation changes were sensitive to the suspended load recovery coefficient and the bed load adaptation length which require further theoretical and experimental investigations

new ultrahigh resolution picture of earth s gravity field 9 10 abstract 11 we provide an unprecedented ultra high resolution picture of earth s gravity over all continents 12 and numerous islands within 60 degree latitude this is achieved through augmentation of new 13 satellite and terrestrial gravity with topography data and use of massive parallel computation 14 techniques delivering local detail at 200 m spatial resolution as such our work is the first of 15 its kind to model gravity at unprecedented fine scales yet with near global coverage the new 16 picture of earth s gravity encompasses a suite of gridded estimates of gravity accelerations 17 radial and horizontal field components and quasigeoid heights at over 3 billion points covering 18 80 of earth s land masses we identify new candidate locations of extreme gravity signals 19 suggesting that the codata standard for peak to peak variations in free fall gravity is too low 20 by about 40 the new models are beneficial for a wide range of scientific and engineering 21 applications and freely available to the public 22 23 keywords 24

impact of a rock avalanche on a moraine dammed proglacial lake laguna safuna alta cordillera blanca peru hubbard bryn heald a reynolds j quincey d 2005 impact of a rock avalanche on a moraine dammed proglacial lake laguna safuna alta cordillera blanca peru earth surface processes and landforms 30 10 pp 1251 1264 rae2008

hydrologic and geomorphic effects of temporary ice dammed lake formation during jokulhlaups glacial outburst oods jokulhlaups occur frequently in glaciated environments and the resultant ooding causes geomorphic change and in some instances damage to local infrastructure during some jokulhlaups oodwater is stored temporarily in ice marginal locations in july 1999 a linearly rising jokulhlaup burst from solheimajokull iceland during this remarkable event subglacial oodwater pooled transiently in two relict ice dammed lake basins before draining suddenly back into solheimajokull the signi cance of such rapid formation and attendant drainage of temporary ice dammed lakes during jokulhlaups has not been addressed consequently this paper i assesses the hydrologic and geomorphic effects of temporary ice dammed lake formation caused by lake basin retro lling and ii discusses the impact and signi cance of transient retro lling under jokulhlaup conditions pre and post ood eldwork at solheimajokull enabled the impact and signi cance of lake basin retro lling to be assessed field evidence demonstrates that the july 1999 jokulhlaup had an unusually rapid rise to peak discharge resulting in subglacial oodwater being purged to ice marginal locations the propensity for temporary retro lling was controlled by rapid expulsion of oodwater from solheimajokull coincident with locations suitable for oodwater storage floodwater inundated both ice marginal lake basins permitting signi cant volumes of sediment deposition coarse grained deltas prograding from the ice margin and boulders perched on scoured bedrock provide geomorphic records of sudden retro lling the depositional characteristics of lake basin deposits at solheimajokull are similar to jokulhlaup sediments documented in proglacial settings elsewhere however their depositional setting and association with ice marginal landforms is distinctive findings suggest that temporary ice dammed lake formation and drainage has the capacity to alter the shape of the ood hydrograph especially if drainage of a temporary lake is superimposed on the original jokulhlaup deposits associated with lake basin retro lling have a long term preservation potential that could help to identify temporary ice dammed lake formation in modern and ancient glacial environments copyright 2003 john wiley sons ltd

assessment of egm2008 in europe using accurate astrogeodetic vertical deflections and omission error estimates from srtm dtm2006 0 residual terrain model data 1 we assess the new egm2008 earth gravitational model using a set of 1056 astrogeodetic vertical deflections over parts of continental europe our astrogeodetic vertical deflection data set originates from zenith camera observations performed during 1983 2008 this set which is completely independent from egm2008 covers e g switzerland germany portugal and greece and samples a variety of topography level terrain medium elevated and rugged alpine areas we describe how egm2008 is used to compute vertical deflections according to helmert s surface definition particular attention is paid to estimating the egm2008 signal omission error from residual terrain model rtm data the rtm data is obtained from the shuttle radar topography mission srtm elevation model and the dtm2006 0 high degree spherical harmonic reference surface the comparisons between the astrogeodetic and egm2008 vertical deflections show an agreement of about 3 arc seconds root mean square rms adding omission error estimates from rtm to egm2008 significantly reduces the discrepancies from the complete european set of astrogeodetic deflections to 1 arc second rms depending on the region the rms errors vary between 0 4 and 1 5 arc seconds these values not only reflect egm2008 commission errors but also short scale mass density anomalies not modelled from the rtm data given 1 formally stated egm2008 commission error estimates of about 0 6 0 8 arc seconds for vertical deflections and 2 that short scale mass density anomalies may affect vertical deflections by about 1 arc second the agreement between egm2008 and our astrogeodetic deflection data set is very good further focus is placed on the investigation of the high degree spectral bands of egm2008 as a general conclusion egm2008 enhanced by rtm data is capable of predicting helmert vertical deflections at the 1 arc second accuracy level over europe

frequency and characteristics of glacier floods in the swiss alps damage due to glacier floods in the swiss alps occurs about once every two years at present despite the pronounced retreat of glaciers during the twentieth century and the installation of many water reservoirs which act as flood retention basins over half 60 to 70 of the observed floods are caused by outbursts of marginal glacier lakes or sudden breaks of ice dams and 30 to 40 by ruptures of water pockets in a glacierized mountain region as densely populated as the swiss alps even debris flows triggered by outbursts of very small water masses may be dangerous historical information about glacier floods in the swiss alps although incomplete and heterogeneous is used as an empirical basis for an attempt to recognize potential hazards at an early stage by considering outburst processes volumes of water involved potential peak discharge values lithology and inclination within the reach of glacier streams

physical scale modelling of jokulhlaups glacial outburst floods with contrasting hydrograph shapes jokulhlaups glacial outburst floods are hazards in many glaciated environments jokulhlaups generated by different trigger mechanisms have different hydrograph shapes field evidence indicates that jokulhlaups with different hydrograph shapes produce different impacts however little attention has been paid to understanding the controls on jokulhlaups with differing hydrograph shapes and their subsequent impacts historically flume studies have been used to investigate fluvial processes under controlled laboratory conditions nevertheless few flume studies have replicated scaled hydrographs and none have attempted to model field jokulhlaups this study documents the technical procedure by which field prototype jokulhlaups were replicated using physical scale modelling techniques an exponentially rising jokulhlaup characterized by a prolonged rising stage and a rapid falling stage and a linearly rising jokulhlaup characterized by a rapid rising stage and a prolonged falling stage the parameters of water discharge time discharge acceleration and deceleration rate sediment size and sediment discharge were scaled to a 1 20 ratio better sorted sediment more uniform downstream sediment thickness and more gradual aggradation and deposition rates resulted from the prolonged rising stage of the exponentially rising hydrograph more time was available during the prolonged rising stage of the exponentially rising hydrograph for bedload sheets to migrate and for sand ripples to develop rapid rising stage deposition during the linearly rising hydrograph produced thick proximal deposits limited bedload sheet migration massive sand sheets and structureless and poorly sorted sediments during the prolonged falling of the linearly rising hydrograph sufficient time was available to support sand ripple development the study highlights that jokulhlaup hydrograph shape is important for controlling rates of sediment acquisition transport deposition erosion and bedform development the outcomes of these experimental investigations indicate that modelling of high magnitude floods is feasible in a laboratory flume this technical approach has proved very beneficial for developing a greater understanding of flood impacts and the processes that operate during jokulhlaups copyright 2006 john wiley sons ltd

recent high arctic glacial sediment redistribution a process perspective using airborne lidar abstract progressive glacier thinning retreat and mass loss in the high arctic is increasingly exposing forefield sediments to processes of mobilisation and redistribution in this paper we quantify forefield sediment redistribution at midtre lovenbreen svalbard using repeat light detection and ranging lidar surveys conducted in 2003 and 2005 in combination with field based observations average surface lowering of the forefield over the observation period identified from lidar surveys is 0 05 ma 1 and two primary areas of sediment reworking are identified active fluvial incision of proglacial streams by 2 m and lateral moraine downwasting of similar magnitude multivariate analysis of fluvial and climatological field data indicates that observed forefield sediment mobilisation is driven primarily by discharge forcing but with contributions from thermoerosive processes and stochastic autogenic sediment supply during the period of observation disparity between sediment loss in forefield fluvial systems as calculated from lidar data 3000 4000 103 kg and monitoring of fluvial sediment load 1600 3500 103 kg suggests the likely presence of significant quantities of buried ice beneath a thick debris mantle as evidenced by field observations relatively uniform lowering of the moraine crest identified from our repeat lidar surveys indicates thermoerosion of an ice core however simple debris layer thickness modelling indicates an increase in variation of debris layer thickness at lower elevations providing support for the assertion that moraine disintegration is driven by complex combinations of both thermal and mechanical processes this study demonstrates the viability of using lidar in conjunction with field monitoring to better understand sedimentary deglaciation dynamics and processes and also highlights the significance of forefield areas in controlling the sediment yield from deglaciating catchments

sedimentological geomorphological and dynamic context of debris mantled glaciers mount everest sagarmatha region nepal abstract this paper presents the sediment landform and dynamic context of four avalanche fed valley glaciers khumbu imja lhotse and chukhung in the mount everest sagarmatha region of nepal all four glaciers have a mantle of debris dominated by sandy boulder gravel that suppresses melting to an increasing degree towards the snout leading to a progressive reduction in the overall slope of their longitudinal profile prominent lateral terminal moraine complexes also comprising sandy bouldergravel enclose the glaciers these terminal moraines originally grew by accretion of multiple sedimentary facies of basal glacial and supraglacial origin probably by folding and thrusting when the glaciers were more dynamic during the little ice age the four glaciers are in various stages of recession and demonstrate a range of scenarios from down wasting of the glacier tongue through morainedammed lake development to post moraine dam breaching khumbu glacier is at the earliest stage of supraglacial pond formation and shows no sign yet of developing a major lake although one is likely to develop behind its 250 m high composite terminal moraine imja glacier terminates in a substantial body of water behind a partially ice cored moraine dam as determined from geophysical surveys but morphologically appears unlikely to be an immediate threat chukhung glacier already has a breached moraine and a connected debris fan and therefore no longer poses a threat lhotse glacier has an inclined free draining tongue that precludes hazardous lake development from the data assembled a conceptual model applicable to other himalayan glaciers is proposed to explain the development of large lateral terminal moraine complexes and associated potentially hazardous moraine dams 2008 elsevier ltd all rights reserved

dam breaking by wave induced erosional incision 1 we present an experimental and theoretical study of whether a large displacement wave can lead to catastrophic erosional incision of a moraine damming a glacial lake the laboratory experiments consist of reservoirs held by barriers of granular materials in a glass tank the theoretical model combines the saint venant equations of hydraulic engineering with an empirical prescription for erosion the results of both the laboratory experiments and the numerical simulations indicate that a single wave is generally unable to break the dam but a sufficiently large disturbance in an almost filled reservoir creates a seiche that can repeatedly overtop the dam in such a case the combined effect of the multiple erosion events ultimately breaks the dam

changes in jokulhlaup sizes in grimsvotn vatnajokull iceland 1934 91 deduced from in situ measurements of subglacial lake volume a record of volumes of jokulhlaups from the subglacial grimsvotn lake vatnajokull iceland has been derived for the period 1934 91 the change in lake volume during jokulhlaups is estimated from the lake area ice cover thickness and the drop in lake level the jokulhlaup volumes have decreased gradually during this period of low volcanic activity and declining geothermal power the two jokulhlaups in the 1930s each discharged about 4 5 km peak discharge 25 30 10 3 m 3 s 1 in the 1980s jokulhlaup volumes were 0 6 1 2 km 3 peak discharge 2 10 3 m 3 s 1 the lake level required to trigger a jokulhlaup has risen as an ice dam east of the lake has thickened water flow in a jokulhlaup ceases when the base of a floating ice shelf covering grimsvotn settles to about 1160 m a s l apparently the jokulhlaups are cut off when the base of the ice shelf collapses on to a subglacial ridge bordering the lake on its eastern side the decline in melting rates has resulted in a positive mass balance of the 160 170 km grimsvotn ice drainage basin comparison of maps shows that the average positive mass balance rate was 0 12 km 3 a 1 25 of the total accumulation in the period 1946 87 a gradually increasing positive mass balance has prevailed since 1954 reaching 0 23 km 3 a 1 in 1976 86 48 of total accumulation

dam break outburst flood propagation and transient hydraulics a geosciences perspective summary dam break outburst floods are sudden short lived and high magnitude discharges of water and sediment propagating over an initially dry terrain both field observations by geoscientists and experimental measurements by engineers have produced understanding of outburst floods but neither approach has satisfactorily supplied data that is directly of use to hazard managers this study draws together those two literature groups and provides new experimental data to test hypotheses concerning the effect of a series of external controls on resultant longitudinal flow propagation and transitory hydraulics these external controls form experimental treatments and are i the height of the lock gate raise as a surrogate for dam breach evolution and initial hydrograph ii bed roughness and iii suspended sediment concentration these control both horizontal and vertical fluid motion the latter of which is a key property for controlling aeration bed shear stress and turbulence intensity the experimental treatments show that outburst floods on horizontal beds can be identified to possess three longitudinal flow regimes firstly there is a short acceleration due to the reservoir pressure level i e the depth of impounded water secondly channel flow quickly converges to an inertial regime the third flow regime is viscous and dominated by channel bed friction flow depth increases in the inertial regime then decreases in the viscous regime experiments herein show that the timing of the peaks at a point down channel of each hydraulic quantity varies most notably peak bed shear stress precedes flow velocity which precedes peak flow depth a point of inflexion occurs with distance down channel that is a manifestation of the transition from accelerating to decelerating flows these external controls and the effects of them on longitudinal and vertical motion are analysed statistically and quantitative relationships are derived to underpin the resultant conceptual model this conceptual model should serve as a platform for future probabilistic and process based modelling of outburst floods

topographic isostatic evaluation of new generation goce gravity field models 1 we use gravity implied by the earth s rock equivalent topography ret and modeled isostatic compensation masses to evaluate the new global gravity field models ggms from european space agency esa s gravity field and steady state ocean circulation explorer goce satellite gravimetry mission the topography is now reasonably well known over most of the earth s landmasses and also where conventional ggm evaluation is prohibitive due to the lack or unavailability of ground truth gravity data we construct a spherical harmonic representation of earth s ret to derive band limited topography implied gravity and test the somewhat simplistic airy heiskanen and pratt hayford hypotheses of isostatic compensation but which did not improve the agreement between gravity from the uncompensated ret and goce the third generation goce ggms based on 12 months of space gravimetry resolve the earth s gravity field effectively up to spherical harmonic degree 200 220 90 100 km resolution such scales could not be resolved from satellites before goce from the three different goce processing philosophies currently in use by esa the time wise and direct approaches exhibit the highest sensitivity to short scale gravity recovery being better than the space wise approach our topography implied gravity comparisons bring evidence of improvements from goce to gravity field knowledge over the himalayas africa the andes papua new guinea and antarctic regions in attenuated form goce captures topography implied gravity signals up to degree 250 80 km resolution suggesting that other signals originating e g from the crust mantle boundary and buried loads are captured as well which might now improve our knowledge on the earth s lithosphere structure at previously unresolved spatial scales

oceanwide gravity anomalies from geos 3 seasat and geosat altimeter data three kinds of satellite altimeter data have been combined along with 5 5 bathymetric data to calculate a 0 125 ocean wide gridded set of 2 3 106 free air gravity anomalies the procedure used was least squares collocation that yields the predicted anomaly and standard deviation the value of including the bathymetric data was shown in a test around the dowd seamount where the root mean square rms difference between ship gravity measurements decreased from 40 mgal to 20 mgal when the bathymetry was included comparisons between the predicted anomalies and ship gravity data is described in three cases in the banda sea the rms differences were 20 mgal for two lines in the south atlantic rms differences over lines of 2000 km in length were 7 mgal for cruise data in the antarctica region the discrepancies were 12 mgal comparisons of anomalies derived from the geosat geodetic mission data by marks and mcadoo 1992 with ship data gave differences of 6 mgal showing the value of the much denser geosat geodetic mission altimeter data

hydrodynamic characteristics of the tam pokhari glacial lake outburst flood in the mt everest region nepal the tam pokhari glacial lake outburst flood glof which occurred in 1998 in the mt everest region of nepal was evaluated using hydrodynamic models to gain a better understanding of the flow behaviour the flood wave was analysed separately under rigid and erodible boundary conditions in both cases the calculated dam breach hydrograph which had a peak discharge of about 10 000 m3 s was routed through the inkhu river which originates from the lake the morphologic changes along the river were also analysed and the results were compared with satellite images field observations and recorded data in the case of rigid boundaries the routing procedure gradually attenuated the peaks of the hydrographs to account for hydraulic pooling in narrow gorges and storage in the channel in the case of erodible boundaries such effects were minimized due to the increment in channel capacity associated with erosion by debris flow the study revealed that the glof event produced a large scale debris flow additionally the results revealed that erosion and deposition took place intermittently but that approximately 440 000 m3 of sediment was deposited about 14 km downstream from the lake mouth the calculated peak of the water and sediment mixture at 14 4 km was found to be 30 000 m3 s which is almost 6 times as large as that observed when the rigid boundary conditions were used further the increase in the peaks of the hydrographs due to sediment transport was the primary reason for the destruction associated with the glof these findings suggest that the local sedimentology and topography as well as other geo hazard conditions in the area should be carefully evaluated before recommending any control measures against glofs in the himalayan region copyright 2009 john wiley sons ltd

a smoothed particle hydrodynamic automaton of landform degradation by overland flow abstract a novel model for calculating hillslope degradation by overland flow is based on a coupling of the cellular automaton and smoothed particle hydrodynamics theories simulated debris laden floods were initiated on digital elevation models dems the flows were created by solving equations for diffusion routing and erosion and deposition we separated advection and diffusion terms using operator splitting then solved the advection term via automaton and the diffusion term via smoothed particle hydrodynamics the technique was tested on geometrically simple synthetic slopes against data for erosion and deposition by debris laden flows in a gully developing on a scoria cone arizona and against data on a recent moderate sized debris laden flood generated by possible partial glacier melting at popocatepetl volcano mexico the flow and erosion deposition patterns on the simple synthetic slopes appear intuitively reasonable on the synthetic scoria cone slope the model reproduced some of the observed spatial patterns of event scale erosion and deposition reasonable flow speeds runup heights and runout lengths were produced for the debris laden flood at popocatepetl the coupled cellular automaton smoothed particle hydrodynamics technique represents some advance in the modeling of landform degradation and channel development by cellular automata ca use of the technique may aid our understanding of the link between hillslope scale and landform scale degradation patterns

catastrophic lake drainage within the homathko river basin british columbia three distinct phenomena related to sudden lake drainage which occurred in a restricted area within the southern coast mountains of british columbia are described i moraine breaching by solita

structure from motion photogrammetry a low cost effective tool for geoscience applications abstract high resolution topographic surveying is traditionally associated with high capital and logistical costs so that data acquisition is often passed on to specialist third party organisations the high costs of data collection are for many applications in the earth sciences exacerbated by the remoteness and inaccessibility of many field sites rendering cheaper more portable surveying platforms i e terrestrial laser scanning or gps impractical this paper outlines a revolutionary low cost user friendly photogrammetric technique for obtaining high resolution datasets at a range of scales termed structure from motion sfm traditional softcopy photogrammetric methods require the 3 d location and pose of the camera s or the 3 d location of ground control points to be known to facilitate scene triangulation and reconstruction in contrast the sfm method solves the camera pose and scene geometry simultaneously and automatically using a highly redundant bundle adjustment based on matching features in multiple overlapping offset images a comprehensive introduction to the technique is presented followed by an outline of the methods used to create high resolution digital elevation models dems from extensive photosets obtained using a consumer grade digital camera as an initial appraisal of the technique an sfm derived dem is compared directly with a similar model obtained using terrestrial laser scanning this intercomparison reveals that decimetre scale vertical accuracy can be achieved using sfm even for sites with complex topography and a range of land covers example applications of sfm are presented for three contrasting landforms across a range of scales including an exposed rocky coastal cliff a breached moraine dam complex and a glacially sculpted bedrock ridge the sfm technique represents a major advancement in the field of photogrammetry for geoscience applications our results and experiences indicate sfm is an inexpensive effective and flexible approach to capturing complex topography

an unusual jokulhlaup resulting from subglacial volcanism solheimajokull iceland jokulhlaups glacial outburst floods are frequent in glaciated terrain jokulhlaups exhibiting a sudden rise to peak discharge have not been subject to detailed investigation a volcanically generated flood burst from solheimajokull iceland in july 1999 this paper accounts for the causes characteristics and impacts of this flood pre and post flood fieldwork was carried out at solheimajokull allowing the reconstruction of mean flow velocities and peak discharge flood onset was rapid rising to a peak discharge of 4 4 x 103 m3s 1 1 2 x 103 m3s 1 within one hour high basal water pressures resulted in floodwater bursting through the glacier surface ice rip up clasts containing glacial diamict provided evidence of floodwater contact with the glacier bed within the glacier jokulhlaup sedimentation occurred within hydrofractures and conduits generating complex hydrofracture fills and esker ridges in the proglacial zone regions of flow expansion associated with rapid reductions in sediment transport capacity controlled the locations of major jokulhlaup sedimentation a large fan composed of material of up to boulder size was deposited at the glacier snout two ice marginal basins filled and drained during the jokulhlaup one of the basins jokulsargil emptied rapidly during the flood via ice dam flotation accentuating peak jokulhlaup discharge high rates of downstream peak discharge attenuation during the july 1999 jokulhlaup provides an analogy with flash flood hydrographs in semi arid regions and the catastrophic failure of man made dams the july 1999 jokulhlaup was initially triggered by the subglacial volcanic eruption but the characteristics of the flood were accentuated by within event meltwater storage and release this unusual jokulhlaup provides an important addition to our understanding of the spectrum of distinctive jokulhlaup characteristics

a debris flow triggered by the breaching of a moraine dammed lake klattasine creek british columbia a very large debris flow of unusual origin occurred in the basin of klattasine creek southern coast mountains british columbia between june 1971 and september 1973 the flow was triggered by the sudden release of up to 1 7 106 m3 of water from a moraine dammed lake at the head of a tributary of klattasine creek water escaping from the lake mobilized large quantities of unconsolidated sediment in the valley below and thus produced a debris flow that travelled in one or more likely several surges 8 km downvalley on an average gradient of 10 to the mouth of the stream here the flow deposited a sheet of coarse bouldery debris up to about 20 m thick which temporarily blocked homathko river slumps slides and debris avalanches occurred on the walls of the valley both during and in years following the debris flow several secondary debris flows of relatively small size have swept down klattasine creek in the 12 14 years since klattasine lake drained

the use of height data in gravity field approximation by collocation the accuracy of a gravity field model depends on the amount of available data and on the variation of the gravity field when topographic height data are available for example in the form of a digital terrain model it is possible to smooth the gravity field on a local scale by removing the gravitational effects calculated from models of the topographic masses in this way significant improvements of the prediction results are obtained in mountainous areas in this paper we describe methods for the calculation of such gravitational terrain effects applicable in collocation approximation of the gravity field the terrain effects on gravity field quantities such as gravity anomalies deflections of the vertical and geoid undulations are calculated using a system of rectangular prisms representing either a quasi traditional model of the topography and the isostatic compensation or a residual terrain model where only the deviation of the topography from a mean elevation surface is considered to test the terrain reduction methods numerical prediction experiments have been conducted in the mountainous white sands area new mexico from gravity anomalies spaced approximately 6 arc min apart other known gravity anomalies and deflections of the vertical were predicted using collocation when using terrain effects calculated on the basis of 0 5 0 5 arc min point heights the rms errors decreased by a factor of nearly 3 to 1 arc sec for the deflections and 3 4 mgal for the gravity anomalies quite insensitive to the actual type of terrain reduction used the feasibility of using topographic reductions in collocation is thus effectively demonstrated

numerical simulation of a dam break for an actual river terrain environment a two dimensional 2d finite difference shallow water model based on a second order hybrid type of total variation diminishing tvd approximate solver with a muscl limiter function was developed to model flooding and inundation problems where the evolution of the drying and wetting interface is numerically challenging both a minimum positive depth mpd scheme and a non mpd scheme were employed to handle the advancement of drying and wetting fronts we used several model problems to verify the model including a dam break in a slope channel a dam break flooding over a triangular obstacle an idealized circular dam break and a tide flow over a mound computed results agreed well with the experiment data and other numerical results available the model was then applied to simulate the dam breaking and flooding of hsindien creek taiwan with the detailed river basin topography computed flooding scenarios show reasonable flow characteristics though the average speed of flooding is 6 7 m s 1 which corresponds to the subcritical flow condition fr 1 the local maximum speed of flooding is 14 12 m s 1 which corresponds to the supercritical flow condition fr 1 31 it is necessary to conduct some kind of comparison of the numerical results with measurements experiments in further studies nevertheless the model exhibits its capability to capture the essential features of dam break flows with drying and wetting fronts it also exhibits the potential to provide the basis for computationally efficient flood routing and warning information copyright 2006 john wiley sons ltd

analytical solutions for gradual dam breaching and downstream river flooding 1 an analytical model is proposed to describe lake drainage and downstream flooding due to the gradual breaching of natural and manmade earthen dams erodible triangular dams are considered undergoing gradual incision by a breaching channel of constant effective width adopting a simple stream power law for dam material transport the long profile evolution of the breaching channel is governed by a diffusion equation with variable diffusion rate proportional to the water discharge the resulting flood is routed downstream using the kinematic wave equation moving boundary problems are obtained due to retrogression of the breach crest and to the downstream propagation of the flood wavefront for both the dam breaching and flood routing problems explicit analytical solutions are derived they depict a breaching process that is at first self accelerating then becomes self limiting results include boundary paths long profiles and stage and discharge hydrographs in particular the breaching solution yields a discharge hydrograph of simple analytical shape that turns out to be ideally suited for kinematic wave routing the model is applied to the well documented breaching of the tangjiashan landslide dam sichuan in june 2008 calculated results for this and other cases are in reasonably good agreement with the measured data as the model is simple to apply with minimal computational and data requirements it could prove useful as a tool for rapid risk assessment the proposed analytical approach also complements numerical models by providing more transparent links between solution outcomes and the problem data