three dimensional deformation measured in an alaskan glacier measurements of movement along 28 boreholes reveal the three dimensional flow field in a 6 million cubic meter reach of worthington glacier a temperate valley glacier located in alaska sliding at the bed accounted for 60 to 70 percent of the glacier s surface motion strain rates in the ice were low from the surface to a depth of about 120 meters but then increased rapidly toward the bed ice deformation was not affected by temporal changes in the sliding rate the three dimensional pattern of motion indicates that plane strain which is often assumed by models is a poor approximation of this viscous flow

relating the occurrence of crevasses to surface strain rates the presence of crevasses on the surface of ice masses indicates that a fracture criterion has been met understanding how crevasses form will provide information about the stress and strain rate fields in the ice this study derives a relationship between measurements of strain rate and observations of crevassing on the surface of ice masses a literature search yielded 17 polar and alpine locations where strain rates had been measured and crevassing recorded by plotting strain rates converted to stresses using a creep law using axes representing the surface parallel principal stresses failure envelopes were derived by enclosing measurements where surface crevassing was absent the derived failure envelopes were found to conform well to theoretical ones predicted by the coulomb and the maximum octahedral shear stress von mises theories of failure the derived failure envelopes were scaled by the tensile strength which was found to vary from 90 to 320 kpa there was no systematic variation of tensile strength with either temperature at 10 m depth or the method used to locate the crevasses the observed variation in tensile strength could result from variations in ice properties e g crystal size impurity content or density or could be related to uncertainty in the constitutive relation creep flow and fracture share a very similar temperature dependence suggesting similar crystal scale processes are responsible for both the observed relationship will provide a supplementary tool with which to verify and test models of ice dynamics against remotely sensed imagery the study also indicates that a temperature rise of a few degrees throughout the ice column will not result directly in any increase in calving rates from the large antarctic ice shelves such as the filchner ronne or ross ice shelves

spatially integrated geodetic glacier mass balance and its uncertainty based on geostatistical analysis application to the western svartisen ice cap norway estimates of glacier mass balance using geodetic methods can differ significantly from estimates using direct glaciological field based measurements to determine if such differences are real or methodological there is a need to improve uncertainty estimates in both methods in this paper we focus on the uncertainty of geodetic methods and describe a geostatistical technique that takes into account the spatial correlation of the elevation differences when calculating spatially averaged elevation changes we apply this method to the western svartisen ice cap norway using elevation differences from the surrounding bedrock derived from stereophotogrammetry we show that the uncertainty is not only dependent on the standard error of the individual elevation differences but is also dependent on the size of the averaging area and the scale of the spatial correlation to assess if the geostatistical analysis made over bedrock is applicable to glacier surfaces we use concurrent photogrammetrical and laser scanning data from bedrock and a range of glacier surfaces to evaluate the dependency of the geostatistical analysis on the surface type the estimated geodetic mass balance and its uncertainty is 2 6 0 9 m w e for the period 1968 85 and 2 0 2 2 m w e for 1985 2002

using lidar data to map gullies and headwater streams under forest canopy south carolina usa abstract the southeastern piedmont of the usa was severely gullied during the early 20th century a thick canopy established by reforestation in many areas now inhibits the identification or mapping of gullies by aerial photography or other conventional remote sensing methods an airborne laser scanning als or lidar mapping mission flown for the u s forest service in april 2004 acquired bare earth topographic data this paper tests the ability of the als topographic data to identify headwater channels and gullies for two branching gully systems in forested areas and to extract gully morphologic information comparisons are made with field traverses using differential gps and reference cross sections measured by leveling surveys at the gully network scale lidar data provide accurate maps the best available with robust detection of small gullies except where they are narrow or parallel and closely spaced errors in mapping channel location and network topological connectivity under forest canopy increase with attempts to identify smaller features such as large rills the ability of lidar data to map gullies and channels in a forested landscape should improve channel network maps and topological models at the gully reach scale attempts to use lidar data to extract gully cross section morphologic information under forest canopy were less successful due to systematic underestimation of gully depths and overestimation of gully top widths limited morphologic accuracy of the data set at this scale may be due to low bare earth point densities shadowing of gully bottoms and filtering of topographic discontinuities during post processing the als data used in this study are not suitable for detailed morphometric analysis or subtle change detection to monitor gullies or develop sediment budgets data collection may be improved by orienting flights over gullies and with increased point densities through improved scanner technology or better filtering and software capabilities to differentiate between vegetation and ground surfaces

temperature and vapour trajectory controls on the stable isotope signal in canadian rocky mountain snowpacks the effects of temperature and seasonal air mass trajectories on stable water isotopes in alpine snowpacks are investigated using meteorological and snow pit data at two alpine field sites in the canadian rocky mountains haig glacier alberta and opabin glacier british columbia snow pits were sampled through three accumulation seasons october june 2004 05 2005 06 and 2006 07 for 18 o d temperature and density the isotopic characteristics of precipitation over these time periods including the local meteoric waterline and average 18 o d and deuterium excess were defined using this dataset individual snowfall events over the three seasons were identified in the accumulation records from both sites and then fit to snow pit stratigraphies to determine their mean isotopic characteristics a trajectory classification was produced for all events and the key meteorological characteristics of each trajectory class were investigated using data from alpine field sites and a suite of meteorological records from the region an analysis of the relative influences of temperature and air mass trajectory on snow isotope ratios reveals some separation in mean 18 o between storm classes however the separation appears to be driven primarily by the mean temperature of each class rather then being a direct effect of vapour pathway

two orogenies in the grenville belt the age of the grenvillian event is commonly taken to be 1 000 myr but depending on the isotopic systems used and the rocks examined dates vary from 1 100 myr or more1 to 700 myr ref 2 k ar mineral dates and 40ar 39ar dates reflect blocking temperatures that correspond to regional cooling they should therefore be younger than the true age of a thermal event that would be more accurately dated by rb sr whole rock isochrons or by u pb dating of zircons however because blocking temperature for argon is estimated to be 550 600 c in hornblende3 hornblende dates should at least correspond to the time at which medium to high grade metamorphism was last reached in the rock if systems have remained closed ever since in the grenville province the discrepancy between 1 100 and 950 myr dates recorded by different radiometric clocks has commonly been attributed to a progressive and slow cooling of the region4 i suggest here that the presence of at least two distinct thermal events in that time interval is a plausible explanation

40ar 39ar incremental heating studies on the tudor gabbro grenville province ontario its bearing on the north american apparent polar wander path in late proterozoic times summary 40 ar 39 ar incremental heating studies have been carried out on samples taken from the tudor gabbro grenville province ontario in an earlier k ar study these rocks have yielded an isochron age of 700ma together with very high initial argon ratios age spectrum plots on whole rock samples in general display a saddle shaped character with two of them exhibiting minima close to 700 ma no clear plateaus are observed for these rocks a hornblende separate records the time 1110 ma at which the stock finally cooled through the 590 c isotherm the tudor gabbro was prob ably intruded into an area undergoing middle amphibolite facies meta morphism about 1180 ma ago the age spectra of two whole rock samples together with that of their plagioclase separates suggest that the stock cooled to 200 250 c at about 720 ma slow cooling averaging about 1 o c ma 1 is indicated for this section of the grenville province for the period 1100 700 ma if the age of the tudor gabbro s palaeomagnetic pole position is taken to be 720 ma the hadrynian track hypothesis leads to very high polar wander rates of 20 em a 1 for the period 820 720 ma if this hypo thesis is rejected the average drift rate for this period would be 4 em a 1 in much better agreement with published values of 5 em a i for the period 1400 820ma

40ar 39ar dating of the beja gabbro timing of the accretion of southern portugal the sup 40 ar sup 39 ar dating of the amphibole from the beja gabbro southern portugal yields a plateau age at 336 4 plus minus 0 8 ma 2 sigma level the corresponding calculated isotopic closure temperature is around 800c the comparison of this temperature with the magnetic blocking temperature approximately 570c allows an estimation of a probable thermoremanent acquisition age for the characteristic magnetization component of the beja gabbro between 335ma and 315ma assuming cooling rates between 10c ma and 100c ma these results combined wtih paleomagnetic results from the beja gabbro and late paleozoic rocks from southern portugal perroud et al 1985 suggest that the southermost part of spain and portugal was separated from northern iberia in early carboniferous times and was accreted to europe during the late carboniferous

glacier crevasses observations models and mass balance implications we review the findings of approximately 60 years of in situ and remote sensing studies of glacier crevasses as well as the three broad classes of numerical models now employed to simulate crevasse fracture the relatively new insight that mixed mode fracture in local stress equilibrium rather than downstream advection alone can introduce nontrivial curvature to crevasse geometry may merit the reinterpretation of some key historical observation studies in the past three decades there have been tremendous advances in the spatial resolution of satellite imagery as well as fully automated algorithms capable of tracking crevasse displacements between repeat images despite considerable advances in developing fully transient three dimensional ice flow models over the past two decades both the zero stress and linear elastic fracture mechanics crevasse models have remained fundamentally unchanged over this time in the past decade however multidimensional and transient formulations of the continuum damage mechanics approach to simulating ice fracture have emerged the combination of employing damage mechanics to represent slow upstream deterioration of ice strength and fracture mechanics to represent rapid failure at downstream termini holds promise for implementation in large scale ice sheet models finally given the broad interest in the sea level rise implications of recent and future cryospheric change we provide a synthesis of 10 mechanisms by which crevasses can influence glacier mass balance

the evolution of a submarine landform record following recent and multiple surges of tunabreen glacier svalbard this study focuses on the glacial landform record associated with recent surge events of tunabreen a calving tidewater glacier in tempelfjorden spitsbergen submarine geomorphology and recent te

paleointensity determination on the late precambrian tudor gabbro ontario paleointensity determination by the coe modified thellier method was carried out on the 1100 ma tudor gabbro of southern ontario the tudor has a bivectorial natural remanent magnetization nrm the c nrm is a grenvillian uplift thermoviscous remagnetization which overprints the a nrm the surviving primary thermoremanent magnetization trm of the tudor intrusion a sharp junction at 530 c between the a and c vectors in laboratory thermal demagnetization matches the peak metamorphic reheating temperature of 480 500 c in nature when the difference in time scales is taken into account the unblocking temperature distributions of the a nrm and of laboratory trm also match a is carried by single domain or small pseudo single domain grains probably magnetite rods exsolved in plagioclase or pyroxene at temperatures above 580 c arai plots of nrm versus partial trm are linear from 520 c or 530 c to 580 c for 45 specimens of 19 samples from 9 sites the 45 reliable paleointensity values from these specimens give a virtual axial dipole moment vadm of 4 6 0 8 1022 a m2 around 1100 ma this is about one half of the modern field intensity but is similar to the mean cretaceous cenozoic intensity and to most archean and proterozoic vadms keweenawan rocks whose ages are within 20 myr of the tudor gabbro have a vadm of 11 4 1022 a m2 the difference between the tudor and keweenawan vadms is similar to differences recorded over similar time intervals in the cretaceous and seems to represent normal variation in geomagnetic field strength throughout earth s history

uplift deduced from remanent magnetization of a proterozoic basic dyke and the baked country rock in the hoting area central sweden a palaeomagnetic and 40ar 39ar study remanent magnetization in dyke contact zones in the hoting area of the fennoscandian shield in the central part of sweden has been studied in order to establish the ambient temperature of the host

rock water interactions in hot dry rock geothermal systems field investigations of in situ geochemical behavior abstract two hot dry rock hdr geothermal energy reservoirs have been created by hydraulic fracturing of precambrian granitic rock between two wells on the west flank of the valles caldera in the jemez mountains of northern new mexico heat is extracted by injecting water into one well flowing it through the fractured region and recovering the heated water from the second well the produced fluid is cooled on the surface and reinjected into the system the first reservoir was formed by fracturing the injection well at a depth of 2 75 km where the initial rock temperature was 185 c a heat extraction experiment conducted in this reservoir was run from january 27 to april 13 1978 a second larger reservoir was created after cementing the fracture to wellbore connections at 2 75 km in the injection well and refracturing 180 m deeper this second reservoir was tested from october 23 to november 16 1979 during each of these experiments samples of the geothermal fluids and gases were collected at regular intervals from the injection wellhead the production wellhead and at the make up pump which provided the water from storage ponds to replace the water lost downhole by permeation into the reservoir walls changes in the composition of the produced fluid provide a means for studying the reservoir behaviour under normal recirculating operating conditions certain of the dissolved species appear to be derived by displacement of an indigenous pore fluid while others appear to be derived by dissolving minerals known to be present in the reservoir rock in this paper we describe the results of the chemical analysis of the geothermal fluids and relate the fluid and gas chemistry to geochemical processes that result from the heat extraction experiments in particular the implications of the silica and na k ca geothermometers and the pore fluid displacement theory are examined for insight about the long term effects of fluid geochemistry on heat extraction from hdr reservoirs

an 40ar 39ar geochronological study of the elzevir batholith and its bearing on the tectonothermal history of the southwestern grenville province canada results of 40ar 39ar step heating for muscovite potassium feldspar and plagioclase from the ca 1240 ma elzevir trondhjemite in the central metasedimentary belt of the canadian grenville province have been combined with earlier data and used to deduce a thermal history for the eastern elzevir terrane following the ottawan orogeny 1050 950 ma muscovite yielded precise plateau dates of ca 900 ma whereas the potassium feldspar displayed disturbed age spectra with ca 730 760 ma dates for broad plateau regions this age difference could be explained by slow cooling or by thermal overprinting at 760 800 ma that has updated the microcline the plagioclase spectra provide evidence for a low temperature hydrothermal event ca 380 ma ago that has generated sericite in saussurite and has caused partial argon loss from the microcline this result agrees with the other plagioclase thermochronometry and paleomagnetism on the cordova gabbro 25 km to the west but provides a lower estimate for the upper age brac

calcite graphite isotope thermometry a test for polymetamorphism in marble tudor gabbro aureole ontario canada graphitization and coarsening of organic material in carbonate bearing metasedimentary rocks is accompanied by carbon isotope exchange which is the basis of a refractory pressure independent geothermometer comparison of observed isotopic fractionations between calcite and graphite a13ccal gr with independent petrological thermometers provides the following empirical calibration over the range 400 800 c a13ccal gr 5 81 x lo6 x t k 2 61 this system has its greatest potential in marbles where calcite graphite is a common assemblage and other geothermometers are often unavailable the temperature dependency of this empirical calibration differs from theoretical calibrations reasons for this are unclear but the new empirical calibration yields temperature estimates in better agreement with independent thermometry from several terranes and is preferred for geological applications both calcite graphite isotopic thermometry and calcite dolomite solvus thermometry are applied to marble adjacent to the tudor gabbro in the grenville province of ontario canada the marble has undergone two metamorphic episodes early contact metamorphism and later regional metamorphism values of a13cca gr decrease regularly from c 8 0 in samples over 2 km from the pluton to values of 3 4 within 200m of the contact these samples appear to preserve fractionations from the early thermal aureole with the empirical geothermometer and indicate temperatures of 450 500 c away from the intrusion and 700 750 c near the gabbro this thermal profile around the gabbro is consistent with conductive heat flow models in contrast the distribution of mg between calcite and dolomite has been completely reset during later regional metamorphism and yields uniform temperatures of c 500 c even at the contact graphite textures are important for interpreting the results of the calcite graphite thermometer coarsening of graphite approaching the tudor gabbro correlates with the decrease in isotopic fractionations and provides textural evidence that graphite crystallization took place at the time of intrusion in contrast to isotopic exchange during prograde metamorphism which is facilitated by graphitization retrogressive carbon isotopic exchange appears to require recrystallization of graphite which is sluggish and easily recognized texturally resistance of the calcite graphite system to resetting permits thermometry in polymetamorphic settings to see through later events that have disturbed other systems

transmission electron microscope and rock magnetic investigations of remanence carriers in a precambrian metadolerite a precambrian metadolerite dyke has two distinct types of remanence carriers those with medium high coercivities unblocking fields of 20 120 mt and those with low coercivities unblocking fields of 15 mt optical examination reveals numerous submicron probably opaque inclusions in the plagioclase feldspar and also large opaque grains consisting of coarse oxidation exsolution intergrowths of magnetite and ilmenite all opaque phases have been examined using transmission electron microscopy together with microanalysis and electron diffraction the submicron inclusions in the plagioclase are titanomagnetites 0 x 0 14 with a size range between about 0 01 and 0 5 m and axial ratios between 1 equidimensional and about 0 3 many of these inclusions fall in the single domain field but some are probably pseudo single domain the large opaque grains contain almost pure magnetite and ilmenite and show no fine scale exsolution the magnetite regions of the intergrowths are of multidomain size and reveal multidomain structure under lorentz electron microscopy there are also some primary ilmenites containing very fine exsolved haematite and there are very fine plates of ilmenite and very elongate needles of magnetite within the augite experiments on artificial samples containing very carefully prepared separates of plagioclase and large opaque grains show that the pure plagioclase acquires a remanence with unblocking fields of 20 140 mt and blocking temperatures of 390 590 c and the large opaque grains acquire a remanence with unblocking fields of less than 15 mt but a wide range of blocking temperatures up to about 570 c it is concluded that the medium high coercivity component of remanence in the rock is carried largely or possibly entirely by the submicron magnetites within the plagioclase and that the low coercivity component is carried largely or entirely by the multidomain magnetites in the large opaques the contribution of the magnetite needles in the augite is uncertain as the rock does not contain any detectable component of remanence with the extremely high coercivities expected from their very elongate shape

paleo uplift and cooling rates from various orogenic belts of india as revealed by radiometric ages discussion 1 discussion sur l article de sharma k k bal k d parshad r nard lal nagpaul k k paru dans tectonophysics nld 1980 70 135 158

a structural glaciological analysis of the 2002 larsen b ice shelf collapse this study provides a detailed structural glaciological analysis of changes in surface structures on the larsen b ice shelf on the antarctic peninsula prior to its collapse in february march 2002 mapped features include the ice shelf front rifts crevasses longitudinal linear surface structures and meltwater features we define domains on the ice shelf related to glacier source areas and demonstrate that prior to collapse the central larsen b ice shelf consisted of four sutured flow units fed by crane jorum punchbowl and hektoria green evans glaciers between these flow units were suture zones of thinner ice where the feeder glaciers merged prior to collapse large open rift systems were present offshore of foyn point and cape disappointment these rifts became more pronounced in the years preceding break up and ice blocks in the rifts rotated because of the strong lateral shear in this zone velocity mapping of the suture zones indicates that the major rifts were not present more than about 20 years ago we suggest that the ice shelf was preconditioned to collapse by partial rupturing of the sutures between flow units this we believe was the result of ice shelf front retreat during 1998 2000 reducing the lateral resistive stress on the upstream parts of the shelf and glacier flow units ice shelf thinning and pre shelf break up glacier acceleration

40ar 39ar dating of the thanet gabbro ontario looking through the grenvillian metamorphic veil and implications for paleomagnetism in this first dating study of the thanet gabbro complex from the hastings basin area we have obtained k ar evidence to support the geological contention that this pluton and by inference others nearby has escaped the severity of the grenvillian metamorphic overprint specifically a reliable date of 1200 ma for a hornblende demonstrates that this body was emplaced at least 100 ma earlier than the peak of metamorphism in the adjacent haliburton highlands from considerations of possible cooling histories and a proposed grenville apparent polar wander apw curve we deduce that only the thanet magnetization component with the lowest laboratory blocking temperatures th3 was likely acquired as a thermoremanent magnetization whereas the other two components were probably acquired as low temperature chemical remanent magnetizations furthermore the th3 component was likely set before 1 0 ga consistent with our earlier proposed grenville loop

40ar 39ar dating of a late proterozoic palaeomagnetic pole for the armorican massif france summary part of a combined geochronologic and palaeomagnetic study of the trcgor area armorican massif we have attempted to obtain a reliable age for a late proterozoic palaeopole from experiments carried out on the keralain and petit taurel diorites a heterogeneous population of amphiboles analysed by the 40ar 39ar stepheating method gave a flat saddle shaped age spectrum characteristic of excess argon with a minimum age of 604 9f 1 2 ma which represents a maximum estimate of the age of the mineral the isochron calculation gives an initial 40ar xar ratio sensibly higher than the atmospheric ratio this indicates that the isochron age 583 f 2 ma is a better estimate of the age of the keralain diorite laser single step fusion and step heating experiments performed on single grains representative of the different components of this heterogeneous population of amphiboles show that the excess argon affects it in its entirety the minimum age of 590 8 f 2 3 ma of the flat saddle shaped age spectrum displayed by the core of a crystal of hornblende is concordant at the 20 level with the isochron age the isotopic closure temperature calculated from the step heating results is 556 f 43 c the palaeomagnetic study has shown using a thermal demagnetization procedure that the samples have a multicomponent magnetization two characteristic components a and b have been recognized respectively at keralain and the petit taurel a careful rock magnetic study has established that the magnetic carrier of the primary component a isolated at keralain is magnetite with a magnetic blocking temperature of 575 c the similarity of this temperature with the calculated isotopic closure temperature allows us to assign an age of c 583 ma to the corresponding well defined palaeopole dka located at 33 n 256 e the demagnetization experiments have also clearly shown that component b well isolated at the petit taurel is a remagnetization probably related to magmatic events at around 550 ma furthermore its magnetic behaviour as observed at keralain indicates a possible thermochemical origin the well dated dka palaeopole allows us to refine the late proterozoic polar wander path for armorica and seems to confirm that the armorican massif and southern united kingdom were linked together at that period

an increase in crevasse extent west greenland hydrologic implications 1 we compare high resolution 1985 and 2009 imagery to assess changes in crevasse extent in the sermeq avannarleq ablation zone west greenland the area occupied by crevasses 2 m wide significantly increased 13 4 over the 24 year period this increase consists of an expansion of existing crevasse fields and is accompanied by widespread changes in crevasse orientation up to 45 we suggest that a combination of ice sheet thinning and steepening are responsible for the increase in crevasse extent we examine the potential impact of this change on the hydrology of the ice sheet we provide a first order demonstration that moulin type drainage is more efficient in transferring meltwater fluctuations to the subglacial system than crevasse type drainage as enhanced basal sliding is associated with meltwater pulses an increase in crevasse extent can therefore be expected to result in a net decrease in basal sliding sensitivity an increase in crevasse extent may also accelerate cryo hydrologic warming and enhance surface ablation

palaeomagnetism of the tudor gabbro ontario evidence for divergence between grenvillia and interior laurentia summary after thermal and alternating field af cleaning the characteristic high blocking temperature a component of natural remanent magnetization nrm of the tudor gabbro of southern ontario has a mean direction d 326 i 46 k 132 95 4 8 n 8 sites the corresponding palaeopole 133 e 12 n dp 4 dm 6 confirms the palaeopole 137 e 17 n 95 8 4 reported earlier by palmer carmichael based on af cleaning only the a nrm has unblocking temperatures 515 525 c which exceed the estimated 500 c peak temperature reached locally during 1050 ma grenvillian regional metamorphism the a nrm therefore predates metamorphism and is probably a primary thermoremanence trm the age of the tudor nrm has previously been taken to be about 675 ma but recent 40ar 39ar dating by baksi has shown that this is the time of post metamorphic cooling to 200 250 c hornblendes record initial cooling of the intrusion to 590 20 c at 1110 ma and this is the best estimate of the age of the a remanence successful thellier type palaeointensity determinations on 11 tudor samples confirm that the a nrm is a trm and indicate a palaeofield at this time of 18 27 t about 50 70 per cent of the present field intensity at 27 magnetic latitude the anomalous tudor a palaeopole which lies well to the west of both 1000 800 ma grenvillian palaeopoles and 1100 1050 ma poles from interior laurentia is interpreted as recording divergence between grenvillia and interior laurentia just before the grenvillian orogeny rather than a post metamorphic extension of the apparent polar wander path as previously assumed

40ar 39ar incremental heating study of mineral separates from the early archean east indian craton implications for the thermal history of a section of the singbhum granite batholithic complex 40ar 39ar incremental heating studies on mineral separates from three sets of rocks in the singbhum craton in eastern india have helped unravel the thermochronometric history of the terrane and explain an earlier discrepancy between sm nd 3800 ma and rb sr 3100 ma whole rock ages for the older metamorphic tonalitic gneiss omtg high precision plateau ages for hornblende separates from the older metamorphic group of rocks omg suggest that this unit is older than 3300 ma and that enclaves of both the omtg and omg within the batholithic complex cooled to 500 c at 3300 15 ma following engulfment in magma forming the singbhum granite sg results from a biotite separate from the omtg imply that slow cooling continued to a temperature of 300 c at 3160 ma study of a feldspar separate from the singbhum granite suggests final cooling uplift through the 150 c isotherm 660 ma ago we suggest that an earlier rb sr whole rock age of 3130 85 ma on the omtg did not yield the crystallisation a

neural networks applied to estimating subglacial topography and glacier volume abstract to predict the rate and consequences of shrinkage of the earth s mountain glaciers and ice caps it is necessary to have improved regional scale models of mountain glaciation and better knowledge of the subglacial topography upon which these models must operate the problem of estimating glacier ice thickness is addressed by developing an artificial neural network ann approach that uses calculations performed on a digital elevation model dem and on a mask of the present day ice cover because suitable data from real glaciers are lacking the ann is trained by substituting the known topography of ice denuded regions adjacent to the ice covered regions of interest and this known topography is hidden by imagining it to be ice covered for this training it is assumed that the topography is flooded to various levels by horizontal lake like glaciers the validity of this assumption and the estimation skill of the trained ann is tested by predicting ice thickness for four 50 km 50 km regions that

quantitative analysis of land surface topography land surface topography significantly affects the processes of runoff and erosion a system which determines slope aspect and curvature in both the down slope and across slope directions is developed for an altitude matrix also the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix a fortran 66 program performs the analysis

lidar derived slopes for headwater channel network analysis abstract slope is one of the most important distinguishing features for channel morphology variations in the computation of slope from a digital elevation model can affect a wide range of hydrogeomorphically derived applications we compare different methods for computing channel slope using lidar derived digital terrain models dtms with varying resolutions we chose a headwater basin of the eastern italian alps characterized by a dense ephemeral colluvial network and a main alluvial channel as our study area the identified alluvial morphologies are characteristic of steep mountain streams namely cascades and step pools field surveys were carried out along the main channel and in some small tributaries results indicate that a single method for slope calculation cannot estimate channel slope at the hydrographic network scale the differential geometry approach for slope calculation tends to overestimate field surveyed channel slope values for all the dtm resolutions 1 2 5 m when a trigonometric approach for slope calculation is applied 2 and 5 m dtm resolutions give more consistent results nevertheless a reliable channel slope can be derived from a dtm with an appropriate resolution by choosing a suitable method only after considering the channel width