release fault a variety of cross fault in linked extensional fault systems in the sergipe alagoas basin ne brazil abstract two types of cross faults are herein recognized transfer faults and the newly termed release faults transfer faults form where cross faults connect distinct normal faults and horizontal displacements predominate over vertical ones in contrast release faults form where cross faults associated with individual normal faults die out within the hangingwall before connecting to other normal faults and have predominantly vertical displacements release faults are geometrically required to accommodate variable displacements along the strike of a normal fault thus they form to release the bending stresses in the hangingwall and do not cut normal fault planes nor detachment surfaces at depth release faults have maximum throws adjacent to normal faults and may be nearly perpendicular or obliquely oriented to the strike of the latter such geometry appears not to depend upon pre existing weaknesses but such variable orientation to normal faults is an inherent property of release faults release faults commonly appear as simple normal faults in seismic sections without implying extension along the strike of rift and basins three dimensional strain deformation occurs in the hangingwall only between the terminations of an individual normal fault but regionally release faulting is associated with plane strain deformation in linked extensional fault systems

the influence of debris cover and glacial lakes on the recession of glaciers in sikkim himalaya india we investigated area changes in glaciers covering an area of similar to 200 km 2 in the tista basin sikkim eastern indian himalaya between similar to 1990 and 2010 using landsat thematic mapper tm and indian remote sensing satellite irs images and related the changes to debris cover supraglacial lakes and moraine dam lakes the glaciers lost an area of 3 3 0 8 between 1989 90 and 2010 more detailed analysis revealed an area loss of 2 00 0 82 2 56 0 61 and 2 28 2 01 km 2 for the periods 1989 97 1997 2004 05 and 2004 2009 10 respectively this indicates an accelerated retreat of glaciers after 1997 on further analysis we observed 1 the formation and expansion of supraglacial lakes on many debris covered glaciers and 2 the merging of these lakes over time leading to the development of large moraine dam lakes we also observed that debris covered glaciers with lakes lose a greater area than debris covered glaciers without lakes and debris free glaciers the climatic data for 24 years 1987 2011 measured at the gangtok meteorological station 1812 m a s l showed that the region experienced a 1 0 degrees c rise in the summer minimum temperature and a 2 0 degrees c rise in the winter minimum temperature indicating hotter summers and warmer winters there was no significant trend in the total annual precipitation we find that glacier retreat is caused mainly by a temperature increase and that debris covered glaciers can retreat at a faster rate than debris free glaciers if associated with lakes

glacier changes between 1971 and 2016 in the jankar chhu watershed lahaul himalaya india glacier changes in the jankar chhu watershed jcw of chandrabhaga chenab basin lahaul himalaya were worked out based on corona and sentinel 2a images between 1971 and 2016 the jcw consists of 153 glaciers 0 02 km 2 with a total area of 185 6 3 8 km 2 that include 82 glaciers with debris covered ablation zone comprising 10 9 of the total glacierized area as in 2016 change analysis based on corona 1971 landsat 2000 and sentinel 2a 2016 was restricted to 127 glaciers owing to the presence of cloud cover on 26 glaciers in 1971 a subset of glaciers was also mapped using landsat thematic mapper tm 1989 image the total glacier area decreased by 14 7 4 3 km 2 0 3 0 1 km 2 a the number of glaciers in the jcw increased by four between 1971 and 2016 due to fragmentation more recently 2000 16 recession rate has increased clean ice area decreased by 21 8 3 8 km 2 0 5 0 1 km 2 a while debris covered ice increased by 7 2 0 4 km 2 0 2 0 01 km 2 a field observations of select glaciers also support derived recession trend in the jcw retreat rates in the jcw have been observed to be much lower than previously reported

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

on the accuracy of glacier outlines derived from remote sensing data deriving glacier outlines from satellite data has become increasingly popular in the past decade in particular when glacier outlines are used as a base for change assessment it is important to know how accurate they are calculating the accuracy correctly is challenging as appropriate reference data e g from higher resolution sensors are seldom available moreover after the required manual correction of the raw outlines e g for debris cover such a comparison would only reveal the accuracy of the analyst rather than of the algorithm applied here we compare outlines for clean and debris covered glaciers as derived from single and multiple digitizing by different or the same analysts on very high 1 m and medium resolution 30 m remote sensing data against each other and to glacier outlines derived from automated classification of landsat thematic mapper data results show a high variability in the interpretation of debris covered glacier parts largely independent of the spatial resolution area differences were up to 30 and an overall good agreement for clean ice with sufficient contrast to the surrounding terrain differences 5 the differences of the automatically derived outlines from a reference value are as small as the standard deviation of the manual digitizations from several analysts based on these results we conclude that automated mapping of clean ice is preferable to manual digitization and recommend using the latter method only for required corrections of incorrectly mapped glacier parts e g debris cover shadow

influence of debris cover and altitude on glacier surface melting a case study on dokriani glacier central himalaya india most of the central himalayan glaciers have surface debris layers of variable thickness which greatly affect the ablation rate an attempt has been made to relate debris cover thickness to glacier surface melting thirty stakes were used to calculate ablation for debris covered and clean ice of dokriani glacier 7km 2 from 2009 10 to 2012 13 our study revealed significant altitude wise difference in the rate of clean and debris covered ice melting we found a high correlation r 2 0 92 between mean annual clean ice ablation and altitude and a very low correlation r 2 0 14 between debris covered ice melting and altitude debris covered ice ablation varies with variation in debris thickness from 1 to 40cm ablation was maximum under debris thicknesses of 1 6cm and minimum under 40cm even a small debris cover thickness 1 2cm reduces ice melting as compared to that of clean ice on an annual basis overall debris covered ice ablation during the study period was observed to be 37 less than clean ice ablation strong downwasting was also observed in the dokriani glacier ablation area with average annual ablation of 1 82mw e a 1 in a similar period our study suggests that a thinning glacier rapidly becomes debris covered over the ablation area reducing the rate of ice loss

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

temperature reconstruction from glacier length fluctuations in the himalaya a temperature reconstruction in the glacierized himalaya over the past centuries using glacial length fluctuation records is challenging due to the abundance of debris covered glaciers and a scarcity of glacial length fluctuation data using idealized flowline model simulations we show that supraglacial debris cover significantly alters the length fluctuations only when the debris cover is very thick an expanded database of length fluctuation records for 43 glaciers in the himalaya and karakoram is compiled and a standard linear inversion procedure is applied to a subset of 34 glaciers in this database the reconstructed temperature anomaly during 1860 2010 indicates a continued warming of the region with a total temperature change of 1 6 k a close resemblance of the regional temperature anomaly to global trends is seen

strike slip duplexes abstract strike slip fault systems often contain zones of steep imbricate faults geometrically similar to imbricate fans and duplexes in dip slip thrust and normal fault systems they are evident in map view rather than in vertical sections examples of duplexes are cited from both active and ancient systems and from theoretical and physical models duplexes may form at bends on strike slip faults by a process kinematically analogous to the sequential imbrication of ramps on dip slip faults however some may form and many may initiate as non sequential riedel fractures at fault offsets or on straight fault segments this process is more marked than in dip slip systems where primary anisotropy such as bedding exerts more control on fault geometry strike slip duplexes may be shunted along the fault system parallel to the regional slip vector however duplexes or individual horses will usually also move up or down perpendicular to the slip vector because of the unconstrained upper surface to the fault system these factors mean that no section through a strike slip system should be expected to area balance the faults of strike slip duplexes and imbricate fans may root in kinematically necessary low dip faults or may converge downwards and appear in vertical sections as flower structures

tectonic evolution of the sergipano fold belt ne brazil during the brasiliano orogeny abstract the sergipano fold belt sfb represents the southern segment of a brasiliano age 600 ma continental collision zone which extends over ne brazil and continues into central africa as the north equatorial fold belt major sinistral transcurrent fault shear zones and thrusts separate domains with individual lithological tectonometamorphic and magmatic characteristics the principal steeply dipping strike slip zones trend east west to wnw ese lithological correlations across the shears have not proved possible which suggests that displacements were probably large but as yet are unquantified major folding and thrusting affected all the domains folds have a southerly vergence with nw se to wnw ese trends consistent with a ne sw to nne ssw shortening direction although small differences in shortening trends exist between individual domains the southernmost allochthonous domain of carbonate to clastic shelf slope sediments was subject to a single phase of folding and thrusting onto the sao francisco craton accompanied by greenschist facies metamorphism north of this domain lies the macurure domain which is separated from the southernmost allochthonous domain by the major sao miguel do aleixo transpressive shear zone polyphase deformation amphibolite facies metamorphism and massive granitic intrusion characterize this domain north of the macurure domain lie the migmatites and granites of the poco redondo domain which represent a deeper crustal level they are separated from the macurure domain by the belo monte shear a late tectonic leucogranite in the poco redondo domain yields a 600 ma rb sr isochron finally the poco redondo domain was overthrust from the north by the caninde gabbroic complex associated with carbonates pelites and amphibolites metamorphosed to greenschist and upper amphibolite facies this has previously been interpreted as an ophiolite sequence although the relative movements or absolute ages of the domains are unknown their distinct geological differences suggest that they are separate crustal blocks which underwent large lateral movement during the brasiliano collision

contrasting patterns of early twenty first century glacier mass change in the himalayas glaciers are among the best terrestrial climate indicators an important water resource in mountains1 2 and a major contributor to global sea level rise3 4 in the hindu kush karakoram himalaya region hkkh a paucity of appropriate glacier data has prevented a comprehensive assessment of current regional mass balance5 however there are indirect evidences of a complex pattern of glacial responses5 8 in reaction to heterogeneous climate change signals9 here we provide the first coherent data set of detailed glacier thickness changes over the hkkh during 2003 2009 by combining satellite laser altimetry and a global elevation model in the eastern central and south western parts of the hkkh glacier wastage is widespread with regional thinning rates up to 0 66 0 09 m a 1 in the jammu kashmir region conversely in the karakoram glaciers are close to balance with only a slight thinning of 0 07 0 04 m a 1 regionally averaged thinning rates under debris mantled ice are similar to those of clean ice despite insulation by debris covers the 2003 2008 specific mass balance for our hkkh study region is 0 21 0 05 m a 1 water equivalent we significantly less negative than the global average of 0 7 m a 1 we for glaciers and ice caps4 10 this difference is mainly an effect of the balanced glacier mass budget in the karakoram the corresponding hkkh sea level contribution is 0 035 0 009 mm a 1 amounting to 1 of the present day sea level rise11 our 2003 2008 mass budget of 12 8 3 5 gt a 1 is more negative than recent satellite gravimetry based estimates of 5 6 gt a 1 over 2003 2010 ref 12 for the mountain catchments of the indus and ganges basins13 the glacier imbalance contributes 3 5 and 2 0 respectively to the annual average river discharge13 and up to 10 for the upper indus basin14

effect of precipitation seasonality on climatic sensitivity of glacier mass balance abstract numerical calculations are described aimed at evaluating the influence of precipitation seasonality and seasonality concentration on climatic sensitivity of glacier mass balance equilibrium line altitudes elas are modeled using idealized meteorological variables and then a warming test 1 c is performed which revealed that the effects of latitude and the annual precipitation amount are less than those of precipitation seasonality and its concentration calculation shows higher sensitivities for the glaciers located in a summer precipitation climate than for those located within a winter precipitation climate difference due to seasonality is enhanced with the seasonality concentration the present study suggests that the earlier parameterization of glacier mass balance with annual precipitation amount is insufficient to describe the response of glaciers to climate change distribution of precipitation seasonality and its concentration suggest that many parts of the world have a summer precipitation climate but their seasonality concentration is not significant worldwide on the other hand an extensive region of asia and part of the andes are located in the highly concentrated summer precipitation climate this suggests the high sensitivity of glacier mass balance in these regions to climate change

upb and smn edvidence for eburnian and pan african high grade metamorphism in cratonic rocks of southern cameroon abstract u pb analyses of zircons and sm nd mineral and whole rock analyses of samples from southern cameroon document three distinct rock forming or high grade metamorphic events 2900 ma 2050 ma and 600 ma zircons from the ebolowa charnockite in southern cameroon yield an age of 2896 7 ma consistent with published rb sr total rock data for the region sm nd crustal formation ages for these rocks are 3000 ma indicating that the granitoids and ntem series gneisses in the north end of the congo craton formed 2900 ma ago and do not contain major contributions from older archean crust a second metamorphic event of eburnian age is identified from re equilibration of sm and nd in gneisses and metadolerites of the ntem complex at 2050 ma zircons from the younger nyong series gneisses are a complex mixture of cores and overgrowths the overgrowths in most cases formed during a high grade metamorphic event between 2100 and 2000 ma and clearly postdate the ebolowa charnockite the ages of the cores are not precisely known but we believe most represent detrital zircons from 2900 ma protoliths sm nd crustal formation ages for samples of the nyong series gneisses are generally 2500 to 2900 ma indicating that their precursors were apparently derived mainly from the archean craton with variable amounts of younger component sm nd garnet total rock isochrons for metamorphosed mafic rocks in the nyong series yield ages of 2050 ma and zircons from one of them yield an upper intercept age of 2037 10 ma further documenting the existence of a major event with magmatism and charnockitization at 2000 to 2100 ma we interpret the nyong series metasedimentary gneisses as post 2900 ma cratonic cover that was deformed and metamorphosed during the 2000 to 2100 ma eburnian orogeny we cannot define precise limits on the ages of sedimentation preliminary data on metamorphosed intrusive rocks associated with the yaounde series yield u pb concordant ages around 620 ma consistent with sm nd garnet whole rock ages from the same series this dates the pan african tectono metamorphic activity in the southern end mobile belt the pan african lower intercepts of zircons and sm nd garnet whole rock ages from thnyong series are the consequences of this event which is further represented by a 590 ma zircon age from a late syenitic pluton results from cameroon are consistent with recent results from the western part of the congo craton farther south and from the northeastern part of the sao francisco craton in brazil one interpretation of these results is that the congo and sao francisco cratons were joined during the ebumian trans amazonian orogeny 2100 ma and are bordered to the north by a late mesoproterozoic rift basin that was closed during the pan african brasiliano orogeny 600 ma

the status and decadal change of glaciers in bhutan from the 1980s to 2010 based on satellite data in order to monitor changes in the glaciers in the bhutan himalaya a repeat decadal glacier inventory was carried out from landsat images of 1977 78 1980 1990 2000 and 2010 the base map of glaciers was obtained by the object based image classification method using the multispectral landsat images of 2010 this method is used separately to delineate clean ice and debriscovered glaciers with some manual editing glacier polygons of 2000 1990 and 1980 were obtained by manual editing on 2010 by separately overlaying respective years the 2010 inventory shows 885 glaciers with a total area of 642 16 1 km the glacier area is 1 6 of the total land cover in bhutan the result of a repeat inventory shows 23 3 0 9 glacial area loss between 1980 and 2010 with the highest loss 11 6 1 2 between 1980 and 1990 and the lowest 6 7 0 1 between 2000 and 2010 the trend of glacier area change from the 1980s to 2010 is 6 4 1 6 loss of glacier area was mostly observed below 5600ma s l and was greater for clean ice glaciers the equilibrium line altitude has shifted upward from 5170 110ma s l to 5350 150ma s l in the years 1980 2010

response of debris covered glaciers in the mount everest region to recent warming and implications for outburst flood hazards abstract in areas of high relief many glaciers have extensive covers of supraglacial debris in their ablation zones which alters both rates and spatial patterns of melting with important consequences for glacier response to climate change wastage of debris covered glaciers can be associated with the formation of large moraine dammed lakes posing risk of glacier lake outburst floods glofs in this paper we use observations of glaciers in the mount everest region to present an integrated view of debris covered glacier response to climate change which helps provide a long term perspective on evolving glof risks in recent decades debris covered glaciers in the everest region have been losing mass at a mean rate of 0 32 m yr 1 although in most cases there has been little or no change in terminus position mass loss occurs by 4 main processes 1 melting of clean ice close to glacier elas 2 melting beneath surface debris 3 melting of ice cliffs and calving around the margins of supraglacial ponds and 4 calving into deep proglacial lakes modelling of processes 1 and 2 shows that everest region glaciers typically have an inverted ablation gradient in their lower reaches due to the effects of a down glacier increase in debris thickness mass loss is therefore focused in the mid parts of glacier ablation zones causing localised surface lowering and a reduction in downglacier surface gradient which in turn reduce driving stress and glacier velocity so the lower ablation zones of many glaciers are now stagnant model results also indicate that increased summer temperatures have raised the altitude of the rain snow transition during the summer monsoon period reducing snow accumulation and ice flux to lower elevations as downwasting proceeds formerly efficient supraglacial and englacial drainage networks are broken up and supraglacial lakes form in hollows on the glacier surface ablation rates around supraglacial lakes are typically one or two orders of magnitude greater than sub debris melt rates so extensive lake formation accelerates overall rates of ice loss most supraglacial lakes are perched above hydrological base level and are susceptible to drainage if they become connected to the englacial drainage system speleological surveys of conduits show that large englacial voids can be created by drainage of warm lake waters along pre existing weaknesses in the ice roof collapses can open these voids up to the surface and commonly provide the nuclei of new lakes thus by influencing both lake drainage and formation englacial conduits exert a strong control on surface ablation rates an important threshold is crossed when downwasting glacier surfaces intersect the hydrological base level of the glacier base level lakes formed behind intact moraine dams can grow monotonically and in some cases can pose serious glof hazards glacier termini can evolve in different ways in response to the same climatic forcing so that potentially hazardous lakes will form in some situations but not others additionally the probability of a flood is not simply a function of lake volume but depends on the geometry and structure of the dam and possible trigger mechanisms such as ice or rockfalls into the lake satellite based measurements of glacier surface gradient and ice velocities allow probable future locations of base level lakes to be identified a base level lake has begun to grow rapidly on ngozumpa glacier west of mount everest and could attain a volume of 10 8 m 3 within the next 2 or 3 decades unless mitigation efforts are undertaken this lake could pose considerable glof hazard potential

spatially variable response of himalayan glaciers to climate change affected by debris cover the present state and future evolution of himalayan glaciers has been controversial an analysis of remotely sensed frontal changes and surface velocities from glaciers in the greater himalaya between 2000 and 2008 shows large regional variability in the responses of himalayan glaciers to climate change

hydrology of debris covered glaciers in high mountain asia abstract the hydrological characteristics of debris covered glaciers are known to be fundamentally different from those of clean ice glaciers even within the same climatological geological and geomorphological setting understanding how these characteristics influence the timing and magnitude of meltwater discharge is particularly important for regions where downstream communities rely on this resource for sanitation irrigation and hydropower such as high mountain asia the hydrology of debris covered glaciers is complex rugged surface topographies typically route meltwater through compound supraglacial englacial systems involving both channels and ponds as well as pathways that remain unknown low gradient tongues that extend several kilometres retard water conveyance and promote englacial storage englacial conduits are frequently abandoned and reactivated as water supply changes new lines of permeability are exploited and drainage is captured due to high rates of surface and subsurface change seasonal influences such as the monsoon are superimposed on these distinctive characteristics reorganising surface and subsurface drainage rapidly from one season to the next recent advances in understanding have mostly come from studies aimed at quantifying and describing supraglacial processes little is known about the subsurface hydrology particularly the nature or even existence of subglacial drainage in this review we consider in turn the supraglacial englacial subglacial and proglacial hydrological domains of debris covered glaciers in high mountain asia we summarise different lines of evidence to establish the current state of knowledge and in doing so identify major knowledge gaps finally we use this information to suggest six themes for future hydrological research at high mountain asian debris covered glaciers in order to make timely long term predictions of changes in the water they supply

assessing the status of glaciers in part of the chandra basin himachal himalaya a multiparametric approach this study investigates the change in multiple glacier parameters of three valley type glaciers sakchum sc chhota shigri cs and bara shigri bs located in chandra basin himachal himalaya sharing the same climatic regime and assesses the control of nonclimatic factors on wholesome glacier response multitemporal satellite remote sensing data from landsat tm etm oli 1993 2014 and terra aster 2002 2014 along with an srtm digital elevation model were used for extraction of the glacier parameters results show that while sc and bs retreated sc 10 65 2 52 m y bs 15 51 2 52 m y and lost area sc 0 49 0 0032 km2 bs 1 18 0 0032 km2 the cs remained relatively stable retreat rate 4 06 2 52 m y area loss 0 19 0 0032 km2 during 1993 2014 however results of surface ice velocities siv change sc 24 41 cs 21 60 and bs 28 49 and surface elevation change sc 1 22 m y cs 0 91 m y and bs 1 21 m y suggest a comparable slowing down and surface lowering from 2002 to 2014 debris cover also varied substantially sc 30 25 cs 11 96 bs 19 61 on these glaciers results reveal that higher retreat deglaciation of glaciers was associated with higher altitudinal range slow siv in lower ablation zones laz and glacier hypsometry debris cover on glaciers was found to be controlled by slope higher deglaciation rates higher siv in the upper ablation zone uaz coupled with lower siv in laz and surface lowering glacier siv was primarily governed by slope gradient differential surface lowering and size of accumulation zone acz the siv results confirm the presence of stagnant zones in the lower ablations of sc 1 km upstream and bs 6 km upstream and a major siv dropdown in the uaz sc 34 48 bs 37 35 indicating the expansion of stagnant zones farther up glacier surface lowering seemed to be influenced by ice flux changing spatial distribution of debris cover presence of supraglacial lakes and ice cliffs bordering them melting around supraglacial lakes and backwasting of ice cliffs may be the prime reasons behind intense mass loss observed in the stagnant zone of the bara shigri glacier where surface lowering was 32 higher than glacier wide thinning differential surface lowering in glaciers reduced the surface gradient and hence the siv also rapid surface gradient changes and siv dropdown in the sakchum glacier indicate possible development of supraglacial lakes on it in the future interestingly despite close proximity sc cs and bs demonstrate three distinct ablation patterns reemphasizing the role of nonclimatic factors overall the study states that mutual variation of glacier parameters together with nonclimatic factors exercise a great control on glacier response

glaciers glacial lakes and glacial lake outburst floods in the mount everest region nepal recent climate changes have had a significant impact on the high mountain glacial environment rapid melting of glaciers has resulted in the formation and expansion of moraine dammed lakes creating a potential danger from glacial lake outburst floods glofs most lakes have formed during the second half of the 20th century glaciers in the mount everest sagamartha region nepal are retreating at an average rate of 10 59 m a 1 from 1976 to 2000 lumding and imja glaciers retreated 42 and 34 m a 1 respectively a rate that increased to 74 m a 1 for both glaciers from 2000 to 2007 during the past decade himalayan glaciers have generally been shrinking and retreating faster while moraine dammed lakes have been proliferating although the number of lakes above 3500 m a s l has decreased the overall area of moraine dammed lakes is increasing understanding the behaviour of glaciers and glacial lakes is a vital aspect of glof disaster management

glacier shrinkage across high mountain asia an assessment of glacier shrinkage reductionof area for all of high mountain asia requires a complete compilation of measured rates of change and also a methodology for objective comparison of rates i present a compilation from 155 publications reporting glacier area changes and also a method ology that overcomes the main obstacles hindering comparison glacier areas are not always assigned uncertainties and this problem is addressed with an error model derived from published estimates the problem of discordant survey dates is addressed by interpolating measured areas to fixed dates at pentadal intervals interpolation error depends only incoherently on the time span between measure ments but strongly on glacier size smaller glaciers in addition to changing more rapidly on average exhibit more variable rates of change the overlapping boundaries of study regions are reconciled by mapping all of the information to a 0 5 geographical grid when coupled with glacier area information from the randolph glacier inventory the widely observed inverse dependence of shrinkage rates on glacier size shows promise as a tool for treating incomplete spatial coverage over high mountain asia as a whole from 1960 to 2010 the unweighted average shrinkage rate is 0 57 a 1 but corrections for variable glacier size raise the average to 0 34 a 1 and filling unmeasured gridcells with rates based on size dependence alters the latter estimate to 0 40 a 1 the uncertainties in these rates are large the karakoram anomaly is found to be a zonal feature extending well to the east of the karakoram proper

where are the eburnian transamazonian collisional belts the reconstruction of early proterozoic crustal evolution and geodynamic environments in africa and south america is incomplete if cratonic areas alone are studied if the presence of high grade

u pb dating of granites in the neoproterozoic sergipano belt ne brazil implications for the timing and duration of continental collision and extrusion tectonics in the borborema province abstract the sergipano belt is the outcome of collision between the pernambuco alagoas massif and the sao francisco craton during neoproterozoic assembly of west gondwana field relationships and u pb geochronology of granites intruded in garnet micaschists of the macurure domain are used to constrain the main collisional event d 2 in the belt the granites are divided into two groups the pre collisional granites pre to early d 2 and the syn collisional granites syn to tardi d 2 the latter were emplaced as sheets along the s 2 axial plane foliation or they were collected at the hinge zones of f 2 folds a u pb shrimp zircon age of 628 12 ma was obtained for the pre collisional camara tonalite two u pb tims titanite ages were obtained for the syn collisional granites 584 10 ma for the angico granite and 571 9 ma for the pedra furada granite and these ages are close to the garnet whole rock sm nd isochron of 570 ma found for the peak of metamorphism in the sergipano belt the ages of the camara tonalite 628 ma and the pedra furada granite 571 ma mark respectively the maximum age for beginning of the d 2 event and minimum age for the end in the macurure domain using these ages the main neoproterozoic d 2 collisional event has been in operation in the sergipano belt for at least 57 million years correlation with coeval granitoids farther north in the borborema province indicate that while in the sergipano belt the syn d 2 granites ca 590 570 ma were emplaced under compression in the borborema province they emplaced under extensional conditions related to regional strike slip shear zones these contrasting emplacement settings for contemporaneous neoproterozoic granitoids are explained by a combination of continent continent collision and extrusion tectonics

geospatial observations of topographical control over the glacier retreat miyar basin western himalaya india himalayan glaciers show large spatial variation in glacial retreat and mass loss due to their unique climate setting altitude and topography large variability of glacier response to climate in this region may be due to various factors such as climatic precipitation temperature humidity wind etc and non climatic topography and debris cover in this study an attempt has been made to understand the role of topographical parameters and debris cover for glacier recession in miyar basin western himalaya miyar basin is one of the major contributors of water discharge to indus basin which has significant population dependent upon the glacier runoff a total of 29 glaciers covering an area of 227 km2 were studied the glacier retreat for the period 1989 2014 was estimated using the satellite data of landsat series tm etm and oli topographical features such as size aspect slope and debris cover were extracted from the landsat operational imager scene and aster gdem v2 data these glaciers were classified based on flow direction area covered slope and debris coverage observations revealed almost 9 0 7 km2 recessions in glacier area 4 for studied glaciers of miyar basin during 1989 2014 within the miyar basin glaciers with large size having a steep slope with high debris cover and northward aspect showed low retreat than glaciers of small size gentle slope and low debris cover with southward aspect

correction to divergent t ƒo 2 paths during crystallisation of h 2 o rich and h 2 o poor magmas as recorded by ce and u in zircon with implications for titaniq and titaniz geothermometry in the original article the eq 1 and email address of the co author are published incorrectly the correct eq 1 and email address of the co author are given below

recent expansions of glacial lakes in the bhutan himalayas current conditions and secular changes in ice contact lakes in the bhutan china border region were investigated using satellite imagery more than 50 moraine dammed ice contact or ice proximal lakes were identified of which 14 were evidently growing in debris covered areas of valley glaciers lake growth is characterised by the initial appearance of supraglacial lakes and subsequent upstream expansion by a coalesced lake in small debris free or partially debris covered glaciers lake growth begins from a single lake lake growth has continued over a period ranging from 20 to 70 years with a growth rate of 70 m year in length and 0 04 km2 year in area these values observed at the northern side of the main himalayan range are smaller than those observed at the southern side the initial appearance year estimated from the expansion rate of most of the lakes in the southern and northern sides ranges from the 1950s to the 1970s and before the 1950s respectively

proterozoic links between the borborema province ne brazil and the central african fold belt the congo cc and the sao francisco sfc cratons were joined at about 2 05 ga northern parts of palaeoproterozoic basement subsequently underwent extension at about 1 ga forming intracratonic basins neoproterozoic metasedimentary rocks in these basins yield detrital zircons as young as 630 ma the brasiliano and pan african c 620 580 ma assembly of west gondwana extensively altered this system the sergipano domain occurs north of the sfc and the comparable yaoundedomain occurs north of the cc crust north of the sergipano domain com prises the pernambuco alagoas peal domain the ne sw striking tchollire banyo fault in cameroon may extend southwestwards between the peal and sergipano domains defining northern limits of abundant sfc cc basement the adamawa yadedomain in africa does not appear to extend into brazil the transverse domain of brazil is a collage of palaeoproterozoic crustal blocks the 1 0 ga cariris velhos orogen cvo late neoproterozoic basins and brasi liano granites the cvo extends ene for more than 700 km in brazil but eastern continuation into africa has not been identified north of the transverse domain contiguous c 2 15 ga gneisses comprise basement of rio grande do norte and cearadomains which continue eastwards into western nigeria and western sahara

recent glacier and glacial lake changes and their interactions in the bugyai kangri southeast tibet glaciers in the bugyai kangri are located in a transition zone from southeast tibet where monsoonal temperate glaciers dominate to inner tibet where continental glaciers dominate here we analyze glacier and glacial lake changes in this region using multi year inventories based on landsat images from 1981 2013 results show that the total area of 141 glaciers in the region decreased by 30 44 0 89 km 2 from 198 35 9 54km 2 1980s to 167 93 4 52 km 2 2010s the annual area shrinkage rate 0 48 a 1 is lower than that reported for southeastern tibet but higher than that of inner tibet both the number and total area of glacial lakes increased between 1981 and 2013 among all lakes proglacial lakes contribute most similar to 81 to the expansion the total area of ten proglacial lakes increased by 150 3 13 17 and of these ten lakes the four that expanded most sharply showed increased calving at their upper margins resulting in more rapid retreat of lake terminating glaciers than land terminating glaciers owing to rapid calving several lakes may undergo further growth in the near future increasing the potential risk of glacial lake outburst floods

landsat based inventory of glaciers in western canada 1985 2005 abstract we report on a glacier inventory for the canadian cordillera south of 60 n across the two western provinces of british columbia and alberta containing 30 000 km2 of glacierized terrain our semi automated method extracted glacier extents from landsat thematic mapper tm scenes for 2005 and 2000 using a band ratio tm3 tm5 we compared these extents with glacier cover for the mid 1980s from high altitude aerial photography for british columbia and from landsat tm imagery for alberta a 25 m digital elevation model dem helped to identify debris covered ice and to split the glaciers into their respective drainage basins the estimated mapping errors are 3 4 and arise primarily from seasonal snow cover glaciers in british columbia and alberta respectively lost 10 8 3 8 and 25 4 4 1 of their area over the period 1985 2005 the region wide annual shrinkage rate of 0 55 a 1 is comparable to rates reported for other mountain ranges in the late twentieth century least glacierized mountain ranges with smaller glaciers lost the largest fraction of ice cover the highest relative ice loss in british columbia 24 0 4 6 occurred in the northern interior ranges while glaciers in the northern coast mountains declined least 7 7 3 4

glacier change 1958 1998 in the north cascades national park complex washington usa the spatial characteristics for all glaciers in the north cascades national park complex usa were estimated in 1958 and again in 1998 the total glacier area in 1958 was 117 3 1 1 km 2 by 1998 the glacier area had decreased to 109 1 1 1 km 2 a reduction of 8 2 0 1 km 2 7 estimated volume loss during the 40 year period was 0 8 0 1 km 3 of ice this volume loss contributes up to 6 of the august september stream flow and equals 16 of the august september precipitation no significant correlations were found between magnitude of glacier shrinkage and topographic characteristics of elevation aspect or slope however the smaller glaciers lost proportionally more area than the larger glaciers and had a greater variability in fractional change than larger glaciers most of the well studied alpine glaciers are much larger than the population median so global estimates of glacier shrinkage based on these well studied glaciers probably underestimate the true magnitude of regional glacier change

retreat rates of debris covered and debris free glaciers in the koshi river basin central himalayas from 1975 to 2010 debris covered glaciers are common in the himalayas and play a key role in understanding future regional water availability and management previous studies of regional glacial changes have often neglected debris covered glaciers or have mixed them with debris free glaciers in this study we generated a new glacier data set that includes debris covered and debris free glaciers to study the glacial surface area change in the koshi river basin in the central himalayas long time series landsat data were used to extract the glacier boundaries using automatic and manual classification methods the glacial area decreased by 10 4 from 1975 to 2010 at a rate of 0 30 a 1 with accelerated melting since 2000 0 47 a 1 small glaciers melted faster than large glaciers in terms of distinctive glacier types debris free glaciers shrank at a rate of 0 45 a 1 faster than debris covered glaciers 0 18 a 1 while debris covered glaciers larger than 5 0 km2 retreated at a rate faster than debris free glaciers of the same sized group we also studied the potential interactions between 222 supraglacial lakes and debris covered glaciers debris covered glaciers with glacial lakes melt faster than glaciers without lakes this study can improve our understanding of the differences in the changes between debris covered and debris free glaciers in the central himalayas and help evaluate water resource changes in the himalayas

emplacement petrological and magnetic susceptibility characteristics of diverse magmatic epidote bearing granitoid rocks in brazil argentina and chile abstract magmatic epidote mep bearing granitoids from five neoproterozoic tectonostratigraphic terranes in northeastern ne brazil early palaeozoic calc alkalic granitoids in northwestern nw argentina and from three batholiths in chile have been studied the elongated shape of some of these plutons suggests that magmas filled fractures and that dyking was probably the major mechanism of emplacement textures reveal that in many cases epidote underwent partial dissolution by host magma and in these cases may have survived dissolution by relatively rapid upward transport by the host magma in plutons where such a mechanism is not evident unevenly distributed epidote at outcrop scale is armoured by biotite or near solidus k feldspar aggregates which probably grew much faster than epidote dissolution preventing complete resorption of epidote by the melt al in hornblende barometry indicates that in most cases amphibole crystallized at p 5 kbar kyanite bearing thermal aureoles surrounding plutons that intruded low grade metamorphic rocks in ne brazil support pluton emplacement at intermediate to high pressure mep show overall chemical variation from 20 to 30 mol mole percent pistacite ps and can be grouped into two compositional ranges ps20 24 and ps27 30 the highest ps contents are in epidotes of plutons in which hornblende solidified under p 3 0 10 3 si typical of magnetite series granitoids crystallized under higher oxygen fugacity in ne brazil argentina and chile it seems that mep is more common in precambrian to palaeozoic ilmenite series granitoids while its occurrence in magnetite series granitoids is more restricted to mesozoic to tertiary granitoids

modelling ice cliff backwasting on a debris covered glacier in the nepalese himalaya ice cliffs have been identified as a reason for higher ablation rates on debris covered glaciers than are implied by the insulation effects of the debris this study aims to improve our understanding of cliff backwasting and the role of radiative fluxes in particular an energy balance model is forced with new data gathered in may and october 2013 on lirung glacier nepalese himalaya observations show substantial variability in melt between cliffs between locations on any cliff and between seasons using a high resolution digital elevation model we calculate longwave fluxes incident to the cliff from surrounding terrain and include the effect of local shading on shortwave radiation this is an advance over previous studies that made simplified assumptions on cliff geometry and radiative fluxes measured melt rates varied between 3 25 and 8 6cm d 1 in may and 0 18 and 1 34 cmd 1 in october model results reproduce the strong variability in space and time suggesting considerable differences in radiative fluxes over one cliff in october the model fails to reproduce stake readings probably due to the lack of a refreezing component disregarding local topography can lead to overestimation of melt at the point scale by up to 9

recent recession and potential future lake formation on drang drung glacier zanskar himalaya as assessed with earth observation data and glacier modelling this study assessed the changes in the area snout and proglacial lake formation for drang drung glacier located in zanskar region of jammu and kashmir using earth observation data of 46 years from 1971 to 2017 in addition ice thickness and formation of potential future lakes were modelled using a distributed model glabtop our analysis indicated that drang drung glacier shrunk by 13 84 from 1971 to 2017 meteorological projections of temperature and precipitation over region were used to understand climatic changes over drang drung region the snout of the glacier has retreated by 925 m since 1971 at the rate of 21 11 ma 1 however the snout retreat radically accelerated since 2014 at 60 ma 1 analysis of available satellite data suggested that the proglacial lake formed around 2014 the lake has expanded to 16 62 ha in 2017 amassing a water volume of 2 69 mi m3 with a potential peak discharge of 2667 m3 s 1 based on glabtop simulation the mean thickness of the glacier is 155 m with the highest thickness of 311 m climate projections indicate that the temperatures would rise by over 4 c by the end of this century with insignificant increase in precipitation glabtop simulations indicate formation of two huge lakes with areas of 97 and 47 ha in the lower ablation part of the glacier which could pose a risk to the incidence of glacial lake outburst flood in the near future

spatio temporal and surface elevation change assessment of glaciers of sikkim himalaya india across different size classes using geospatial techniques an assessment of the influence and significance of different topographic and morphometric parameters of glacier catchments such as size average slope median elevation and aspect upon the spatio temporally changing characteristics of glaciers belonging to different size classes in tista river basin of sikkim himalaya has been performed the reference years of 2000 and 2018 were considered and different morphometric techniques showed recessive nature and shape change of the observed main glaciers along with some of the tributary glaciers pearson s correlation coefficient and student s t test were applied to measure the correlation and statistical significance of used parameters to understand the varying morphometric and topographic conditions of the glaciers landsat tm thematic mapper landsat 7 etm enhanced thematic mapper and landsat 8 oli operational land imager imageries and shuttle radar topographic mission srtm digital elevation model dem and different automated and semi automated techniques indicated overall loss of 19 78 over the years 2000 to 2018 of the glaciated area investigated and such decrease in respective years of reference was 2 06 for the year 2000 and 1 65 for the year 2018 respectively of the total geographic area of sikkim tandem x dem 90 m was useful in inferring glacier surface elevation change

major precambrian nappes of the brazilian belt ceara northeast brazil the precambrian of ceara northeast brazil includes the reactivated archean basement and proterozoic metasediments that have gone through one single stage of metamorphism and deformation during the brazilian orogeny that culminated at about 600 ma preliminary petrostructural studies show that crystalline nappes with associated himalayan type reverse metamorphism have been thrust westward to southwestward over more than 150 km geometrical relationships indicate that some steep shear zones could be lateral ramps to the nappes thus this precambrian segment of the brazilian belt has the petrostructural signature of a former overthickened continental crust similar to that generated by himalayan type continent continent collisions

rapid disintegration of alpine glaciers observed with satellite data analyses of multispectral satellite data indicate accelerated glacier decline around the globe since the 1980s by using digitized glacier outlines inferred from the 1973 inventory and landsat thematic mapper tm satellite data from 1985 to 1999 we obtained area changes of about 930 alpine glaciers the 18 area reduction as observed for the period 1985 to 1999 1 3 a corresponds to a seven times higher loss rate compared to the 1850 1973 decadal mean extrapolation of area change rates and cumulative mass balances to all alpine glaciers yields a corresponding volume loss of about 25 km since 1973 highly individual and non uniform changes in glacier geometry disintegration indicate a massive down wasting rather than a dynamic response to a changed climate our results imply stronger ongoing glacier retreat than assumed so far and a probable further enhancement of glacier disintegration by positive feedbacks

radiometric chronology of changme khangpu glacier sikkim the 32 si concentration in a sample of surface ice from the snout of changme khangpu glacier is 0 36 disintegrations per minute tonne compared to the fall out value of 0 7 d p m tonne if this decrease is assumed to be solely due to decay of 32 si an age off c 100 years is estimated for the surface ice of the snout leading to an average flow velocity of c 40 m year for the past century a vertical profile of 210 pb in a core taken at an altitude of 5040 m shows two horizons where this isotope is enriched one between 3 and 4 m and another between 11 and 12 m indicating that the primary concentration of 210 pb can change by physico chemical processes like adsorption on dust none the less a longitudinal profile along the glacier shows a systematic decrease of 210 pb activity with decreasing altitude the surface ice of the snout giving a value of 0 2 d p m l corresponding to an age of 100 years which is concordant with the 32 si age this surface flow rate of the glacier is much larger than the average contemporary flow rate c 13m year the difference can be understood in terms of the past history of advance and recession of the glacier as revealed by the geomorphic evidence

recent changes in glacier area and volume within the southern canadian cordillera net changes in glacier area in the region 50 518 n 116 1258 w which includes the columbia and rocky mountains 1951 52 2001 and the coast mountains 1964 65 2002 were determined through a comparison of historic aerial photography and contemporary landsat 7 etm imagery the volumes of individual glaciers were estimated using an empirical volume area scaling relationship the area of glaciers in the coast mountains decreased by 120 10 km 2 or 5 of the initial ice covered area here the areas of glaciers in the columbia and rocky mountains decreased by 20 and 6k m 2 respectively corresponding to relative changes in total area of 5 and 15 the estimated total ice volume loss from the whole region was 13 3k m 3 in all parts of the study area the relative changes in area of individual glaciers showed considerable variability while the smallest glaciers remained essentially unchanged this suggests that local factors unique to individual glaciers largely determine their sensitivity to climatic change and that the very small glaciers are collectively less sensitive to such change

glacier recession and glacial lake outburst flood studies in zanskar basin western himalaya abstract glacier recession and formation of glacial lakes along with outburst flood hazards are increasing in response to changing climate in the himalayan region this study describes evolution of dalung and padam glaciers and their associated lakes employing multi temporal datasets of landsat mss tm etm indian remote sensing liss iii google earthtm aster gdem and survey of india topographic maps the dalung glacier dg and lake dl are present in suru river catchment whereas the padam glacier pg and lake pl are present in tsarap river catchment of zanskar basin western himalaya from 1962 to 2015 the dg and pg have shrunk at different rates the dg has shrunk by 2 6 0 56 km2 19 2 4 1 at a rate of 0 05 0 01 km2 a 1 whereas the pg has shrunk by 3 4 0 65 km2 12 7 2 4 at a rate of 0 06 0 01 km2 a 1 the frontal recession was recorded as 1 240 0 02 km 15 7 2 0 at a rate of 20 0 4 m a 1 for dg and 2 690 0 5 m 21 3 2 1 at a rate of 50 7 0 1 m a 1 for pg consequently the proglacial glacial lakes have formed indicating an expansion of 20 3 4 dl and 58 4 5 pl during 1990 2015 using integrated criteria of standard indices for the identification of potentially dangerous glacial lakes pdgls the lakes were found to be vulnerable and have a potential to cause breaching in the coming years in order to provide inputs for the emergency action plan one dimensional mike 11 model was used to generate the peak flood hydrographs at the lake and other vulnerable sites downstream highest peak discharge of 3361 7 m3 s 1 dl and 4210 3 m3 s 1 pl were estimated at the lake sites which has reduced to 1520 9 m3 s 1 and 1722 4 m3 s 1 respectively at the outlet sites the reduced discharge at downstream sites still bears the potential to create dangerous flood hazards

interannual flow dynamics driven by frontal retreat of a lake terminating glacier in the chinese central himalaya abstract most lake terminating glaciers in the himalaya retreat rapidly due to periodic frontal ice loss at their terminus but long term observations are still limited regarding their flow dynamics which is crucial for understanding the processes of ice mass loss and proglacial lake growth we present multi decadal surface velocity dynamics of the longbasaba glacier a rapid retreating lake terminating glacier in the chinese himalaya using an image feature tracking method applied on optical satellite images between 1989 and 2018 we show that in companion with rapid retreat 51 7 m a 1 its lower 5 km tongue experienced high interannual fluctuations in velocity comprising periodic acceleration and slowdown in 1989 1995 and 2001 2010 and a recent remarkable acceleration since 2012 the temporal variation of longitudinal velocity distribution indicates an upward propagation of the lake ward acceleration namely a downglacier inversion of strain from compression to extension this propagation is coupled to the retreat of the glacier front and occurs along the lowermost 1 1 5 km lake adjacent section as the proglacial lake expands the most recent acceleration of the near lake section since 2012 has likely facilitated a dynamic thinning on its upper sections where flow acceleration started two years later in 2014 this pattern contrasts markedly with a nearby decelerating land terminating glacier which has experienced a much slower retreat rate 7 8 m a 1 and the same magnitude of mean thinning rate at its lower part since 2000 our results confirm the strong influence of the proglacial lake on ice flow dynamics and suggest that lake ice interactions are important to consider when analyzing interpreting or modeling dynamics of rapidly retreating lake terminating glaciers in the himalayas as well as around the world

c sr isotope and hg chemostratigraphy of neoproterozoic cap carbonates of the sergipano belt northeastern brazil abstract two cap carbonates overlying glaciogenic diamictites crop out extensively in the eastern vaza barris domain of the sergipano belt northeastern brazil they are represented by carbonates of the jacoca formation resting on top of diamictite of the ribeiropolis formation and by the olhos d agua formation carbonates organic rich towards the top which overlies diamictite of the palestina formation these two sequences were deformed and metamorphosed at sub greenschist facies conditions during the brasiliano cycle 650 600 ma in the western vaza barris domain dolostone of the acaua formation rest in sharp contact on diamictites of the juete formation and are much less deformed than the olhos d agua formation values of 13c for the jacoca and acaua formations cluster around 4 to 5 in the olhos d agua formation however negative values around 5 in the shallow marine base of the sequence are replaced up section by values close to zero and abruptly by positive values between 8 and 10 at the top strontium isotope ratios for carbonates of these three formations are within the range of late neoproterozoic seawater 0 7060 0 7090 the acaua formation displays 87sr 86sr ratios from 0 7072 to 0 7073 while the jacoca and olhos d agua formations display values within the range from 0 7077 to 0 7081 strontium isotopes coupled with available c isotopes detrital zircon u pb ages and structural data suggest that the jacoca formation and acaua are probably correlative and mid cryogenian in age and that the olhos d agua formation is lowermost ediacaran marinoan in age mercury concentrations in carbonates of the jacoca olhos d agua and acaua formations are usually much higher than those observed in carbonates deposited not concomitantly with volcanic activities

elevation changes of glaciers revealed by multitemporal digital elevation models calibrated by gps survey in the khumbu region nepal himalaya 1992 2008 due to remoteness and high altitude only a few ground based glacier change studies are available in high mountain areas in the himalaya however digital elevation models based on remotely sensed data rs dems provide feasible opportunities to evaluate how fast himalayan glaciers are changing here we compute elevation changes in glacier surface total area 183 3 km in the khumbu region nepal himalaya for the period 1992 2008 using multitemporal rs dems and a map derived dem calibrated with differential gps survey data in 2007 elevation change is calculated by generating a weighted least squares linear regression model our method enables us to provide the distribution of uncertainty of the elevation change debris covered areas show large lowering rates the spatial distribution of elevation change shows that the different wastage features of the debris covered glaciers depend on their scale slope and the existence of glacial lakes the elevation changes of glaciers in the eastern khumbu region are in line with previous studies the regional average mass balance of 0 40 0 25mw e a for the period 1992 2008 is consistent with a global value of about 0 55mw e a for the period 1996 2005

onset of calving at supraglacial lakes on debris covered glaciers of the nepal himalaya field surveys of supraglacial ponds on debris covered glaciers in the nepal himalaya clarify that ice cliff calving occurs when the fetch exceeds 80 m thermal undercutting is important for calving processes in glacial lakes and subaqueous ice melt rates during the melt and freeze seasons are therefore estimated under simple geomorphologic conditions in particular we focus on the differences between valley wind driven water currents in various fetches during the melt season our results demonstrate that the subaqueous ice melt rate exceeds the ice cliff melt rate when the fetch is 20 m and water temperature is 2 48c calculations suggest the onset of calving due to thermal undercutting is controlled by water currents driven by winds at the surface of the lake which develop with expanding water surface

the west congo orogen a key to pan african thermotectonism the orogenic axis of the west congo orogen is located in a basement complex belt along the west coast of central africa deformation and metamorphism decrease eastwards in the flanking geosynclinal strata of the west congo sequence and westwards in its mirror symmetrical counterpart in east brazil the orogenic axis marks the slowrise of geotherms which is correlated with sedimentary tectonic and metamorphic evolution of the orogen the pan african brazilian network of intraplate thermal welts and adjoining ensialic downwarps is seen in this light

structural control of englacial drainage systems in himalayan debris covered glaciers englacial cave systems were mapped using speleological techniques in three debris covered glaciers in the khumbu himal nepal detailed three dimensional mapping of the cave systems and observations of relationships with structures in the surrounding ice show conduits formed by a mechanism directly analogous to speleogenesis in limestone karst the highest oldest parts of all passages developed along debris filled crevasse traces with hydraulic conductivity in the range 10 4 to 10 5 ms 1 conduits form when these hydraulically efficient pathways bridge between areas with different hydraulic potential they then evolve by grading through head ward migration of nick points and vertical incision to local base level often the surface of supraglacial lakes most supraglacial lakes on himalayan glaciers are perched above the elevation of the terminal stream and exist for a few years before draining through englacial conduits as a result near surface drainage evolution is frequently interrupted by base level fall and conduits may record multiple phases of incision conduits commonly migrate laterally during incision undermining higher levels of the ice and encouraging collapse voids can be created by fluvial processes and collapse of crevassed ice the oft noted resemblance of the surface morphology of debris covered glaciers to karst landscapes thus extends to the subsurface and karst hydrology provides a framework for understanding englacial drainage

northeastern brazilian margin regional tectonic evolution based on integrated analysis of seismic reflection and potential field data and modelling abstract integration of regional seismic reflection and potential field data along the northeastern brazilian margin complemented by crustal scale gravity modelling is used to reveal and illustrate onshore offshore crustal structure correlation the character of the continent ocean boundary and the relationship of crustal structure to regional variation of potential field anomalies the study reveals distinct along margin structural and magmatic changes that are spatially related to a number of conjugate brazil west africa transfer systems governing the margin segmentation and evolution several conceptual tectonic models are invoked to explain the structural evolution of the different margin segments in a conjugate margin context furthermore the constructed transects the observed and modelled moho relief and the potential field anomalies indicate that the reconcavo tucano and jatoba rift system may reflect a polyphase deformation rifting mode associated with a complex time dependent thermal structure of the lithosphere the constructed transects and available seismic reflection profiles indicate that the northern part of the study area lacks major breakup related magmatic activity suggesting a rifted non volcanic margin affinity in contrast the southern part of the study area is characterized by abrupt crustal thinning and evidence for breakup magmatic activity suggesting that this region evolved partially with a rifted volcanic margin affinity and character

snow and glacier cover assessment in the high mountains of sikkim himalaya this study highlights the assessment of snow and glacier cover for possible inferences of global climate change impacts in high mountains like the himalaya the test catchment of the river tista lies in the sikkim state of the indian himalayan region with steep mountains crossing nearly all ecozones from subtropical to glacial river flows are highly fluctuating especially during the peak rainy season and snowmelt periods annual rainfall patterns are non uniform and can cause large floods runoff and discharge downstream are highly dependent upon snow and glacier extent the temporary storage of frozen water brings about a delay in seasonal runoff snow cover built up in the higher regions during the winter months melts in the spring summer autumn cycles and contributes to groundwater recharge a spatial baseline inventory of snow cover glacier the permanent snowline and its short term temporal changes in the remote high mountain areas have been analysed using multidate indian remote sensing satellite data of 1992 to 1997 a geographic information system based overlay has led to inferences on snow cover characteristics and the alignment dimension slope disposition heights of the snout and associated features of each of the glaciers snow and glacier recession are to be monitored in future on a long term basis to derive correlations with climate change parameters copyright 2005 john wiley sons ltd

glacier changes in the garhwal himalaya india from 1968 to 2006 based on remote sensing glacier outlines are mapped for the upper bhagirathi and saraswati alaknanda basins of the garhwal himalaya using corona and advanced spaceborne thermal emission and reflection radiometer aster satellite images acquired in 1968 and 2006 respectively a subset of glaciers was also mapped using landsat tm images acquired in 1990 glacier area decreased from 599 9 15 6 km 2 1968 to 572 5 18 0 km 2 2006 a loss of 4 6 2 8 glaciers in the saraswati alaknanda basin and upper bhagirathi basin lost 18 4 9 0 km 2 5 7 2 7 and 9 0 7 7 km 2 3 3 2 8 respectively from 1968 to 2006 garhwal himalayan glacier retreat rates are lower than previously reported more recently 1990 2006 recession rates have increased the number of glaciers in the study region increased from 82 in 1968 to 88 in 2006 due to fragmentation of glaciers smaller glaciers 2 lost 19 4 2 5 0 51 0 07 a 1 of their ice significantly more than for larger glaciers 50 km 2 which lost 2 8 2 7 0 074 0 071 a 1 from 1968 to 2006 the debris covered glacier area increased by 17 8 3 1 0 46 0 08 a 1 in the saraswati alaknanda basin and 11 8 3 0 0 31 0 08 a 1 in the upper bhagirathi basin climate records from mukhim 1900 m a s l and bhojbasa 3780 m a s l meteorological stations were used to analyze climate conditions and trends but the data are too limited to make firm conclusions regarding glacier climate interactions

ground penetrating radar measurements of debris thickness on lirung glacier nepal m m is funded by nerc dtp grant number ne l002507 1 receives case funding from reynolds international ltd and was provided travel support by the jesus college doctoral research fund i w was funded by the bb roberts fund university travel fund and st catharine s college research fund equipment gpr and dgps was provided under nerc geophysical equipment facility grant number 1014

refined energy balance modelling of a supraglacial pond langtang khola nepal supraglacial ponds on debris covered glaciers present a mechanism of atmosphere glacier energy transfer that is poorly studied and only conceptually included in mass balance studies of debris covered glaciers this research advances previous efforts to develop a model of mass and energy balance for supraglacial ponds by applying a free convection approach to account for energy exchanges at the subaqueous bare ice surfaces we develop the model using field data from a pond on lirung glacier nepal that was monitored during the 2013 and 2014 monsoon periods sensitivity testing is performed for several key parameters and alternative melt algorithms are compared with the model the pond acts as a significant recipient of energy for the glacier system and actively participates in the glacier s hydrologic system during the monsoon melt rates are 2 4 cm d 1 total of 98 5 m3 over the study period for bare ice in contact with the pond and 1 mm d 1 total of 10 6 m3 for the saturated debris zone the majority of absorbed atmospheric energy leaves the pond system through englacial conduits delivering sufficient energy to melt 2612m3 additional ice over the study period 38 4 m3 d 1 such melting might be expected to lead to subsidence of the glacier surface supraglacial ponds efficiently convey atmospheric energy to the glacier s interior and rapidly promote the downwasting process

shrinkage of satopanth and bhagirath kharak glaciers india from 1936 to 2013 we have compiled and analysed available records and data on the shrinkage of satopanth spg and bhagirath kharak bkg glaciers uttarakhand india during the period 1936 2013 we estimate the mean retreat rates of the snouts of spg and bkg for this period at 9 7 0 8m a 1 and 7 0 0 6m a 1 respectively we have also revised the estimates of the area vacated during the period 1956 2013 to be 0 27 0 05 km 2 and 0 17 0 04 km 2 for spg and bkg respectively corresponding to front averaged retreat rates of 5 7 0 6m a 1 and 6 0 0 9m a 1 the study revealed an average thinning of glacial ice in the lower ablation zone of spg of 9 11 m in the past 51 years we observed that while the fronts of spg and bkg depicted in the survey of india topographic map published in 1962 are inconsistent with other available records the elevation contours are consistent with them

decadal changes in glacier parameters in the cordillera blanca peru derived from remote sensing we present spatial patterns of glacier fluctuations from the cordillera blanca peru glacier area terminus elevations median elevations and hypsography at decadal timescales derived from 1970 aerial photography 2003 spot5 satellite data geographic information systems gis and statistical analyses we derived new glacier outlines from the 2003 spot images and ingested them in the global land and ice measurements from space glims glacier database we examined changes in glacier area on the eastern and western side of the cordillera in relation to topographic and climate variables temperature and precipitation results include 1 an estimated glacierized area of 569 6 21 km 2 in 2003 2 an overall loss in glacierized area of 22 4 from 1970 to 2003 3 an average rise in glacier terminus elevations by 113 m and an average rise in the median elevation of glaciers by 66 m showing a shift of ice to higher elevations especially on the eastern side of the cordillera and 4 an increase in the number of glaciers which indicates disintegration of ice bodies annual air temperature showed a significant upward trend in the last 30 years with larger temperature increases at lower elevations there was a slight but not significant decrease in precipitation our results are consistent with glacier retreat and warming trends noted in the last three decades in the tropics

planimetric and volumetric glacier changes in the khumbu himal nepal since 1962 using corona landsat tm and aster data multitemporal space imagery from 1962 corona kh 4 1992 landsat tm 2001 and 2005 terra aster was used to investigate the glacier changes in the khumbu himal nepal the ice coverage in the investigation area decreased by about 5 between 1962 and 2005 with the highest retreat rates occurring between 1992 and 2001 the debris coverage increased concomitantly with the decrease in total glacier area the clean ice area decreased by 10 digital terrain model dtm generation from the early corona kh 4 stereo data in this high relief terrain is time consuming and the results still contain some elevation errors however these are minor in the snow free areas with gentle slopes thus comparison of the surfaces of the debris covered glacier tongues based on the corona dtm and an aster dtm is feasible and shows the downwasting of the debris covered glaciers the highest downwasting rates more than 20 m 0 5 m a 1 can be found near the transition zone between the active and the stagnant glacier parts of the debris covered glacier tongues the downwasting is lower but still evident in the active ice areas and at the snout with thick debris cover all investigated debris covered glaciers in the study area show similar behaviour the estimated volume loss for the investigated debris covered glacier tongues is 0 19 km 3

age origin and cooling history of the coronel joao sa pluton bahia brazil received april 2 2002 accepted august 8 2004advance access publication october 22 2004in north east brazil archean and paleoproterozoic cratonic blocksare enclosed within a network of brasiliano age 0 7 0 55ga metasedimentary foldbelts the unfoliated coronel joa o sa grano diorite pluton which contains magmatic epidote and stronglyresorbed clinopyroxene intrudes the sergipano foldbelt zirconsyield a concordant u pb crystallization age of 625 2ma titanite ages are approximately 621ma discordant zircons suggestinheritance from at least two magma sources of ages 2 2ga model calculations based on diffusion parameters andrb sr isotope data from separated minerals indicate that the plutoncooled ata rate of 36 c myr whole rock element compositionsandinitialsr ndisotopic compositionsthat areheterogeneous onalllength scales suggest magma mixing trace element concentrationsand nd isotope data argue against a contribution from a contem poraneous mantle derived magma values of magmatic e

factors controlling the accelerated expansion of imja lake mount everest region nepal this study explores the link between area increase of imja tsho lake and changes of imja glacier area 25km 2 under the influence of climate change using multitemporal satellite imagery and local climate data between 1962 and 2013 imja lake expanded from 0 03 0 01 to 1 35 0 05 km 2 at a rate of 0 026 0 001 km 2 a 1 the mean glacier wide flow velocity was 37 30ma 1 during 1992 93 and 23 15ma 1 during 2013 14 indicating a decreasing velocity a mean elevation change of 1 29 0 71ma 1 was observed over the lower part of the glacier in the period 2001 14 with a rate of 1 06 0 63ma 1 in 2001 08 and 1 56 0 80ma 1 in 2008 14 we conclude that the decrease in flow velocity is mainly associated with reduced accumulation due to a decrease in precipitation during the last few decades furthermore glacier ablation has increased due to increasing maximum temperatures during the post monsoon months decreased glacier flow velocities and increased mass losses induce the formation and subsequent expansion of glacial lakes under favourable topographic conditions

heterogeneous influence of glacier morphology on the mass balance variability in high mountain asia we investigate the control of the morphological variables on the 2000 2016 glacier wide mass balances of 6 470 individual glaciers of high mountain asia we separate the data set into 12 regions assumed to be climatically homogeneous we find that the slope of the glacier tongue mean glacier elevation percentage of supraglacial debris cover and avalanche contributing area all together explain a maximum of 48 and a minimum of 8 of the glacier wide mass balance variability within a given region the best predictors of the glacier wide mass balance are the slope of the glacier tongue and the mean glacier elevation for most regions with the notable exception of the inner tibetan plateau glacier wide mass balances do not differ significantly between debris free and debris covered glaciers in 7 of the 12 regions analyzed lake terminating glaciers have more negative mass balances than the regional averages the influence of lakes being stronger on small glaciers than on large glaciers

glacier area shrinkage in eastern nepal himalaya since 1992 using high resolution inventories from aerial photographs and alos satellite images to better understand the recent wide scale changes in glacier coverage we created and compared two glacier inventories covering eastern nepal based on aerial photographs 1992 and high resolution advanced land observing satellite alos imagery 2006 10 the alos derived inventory contained 1034 debris free and 256 debris covered glaciers with total and average areas of 440 2 33 3 and 0 42 km 2 and 1074 4 206 4 and 4 19 km 2 respectively we found that the debris free glaciers have lost 11 2 0 7 0 1 a 1 of their area since 1992 whereas the number of glaciers increased by 5 because of fragmentation the area change was significantly correlated by simple linear regression with minimum elevation r 0 30 maximum elevation r 0 18 altitudinal range r 0 50 glacier area r 0 62 and mean slope r 0 16 confirming that larger glaciers tended to lose a larger area but a smaller percentage than smaller glaciers the intra regional analysis of the glacier changes clearly showed higher shrinkage rates in the western massifs compared with the eastern massifs in addition 61 small glaciers covering an area of 2 4 km 2 have completely disappeared since 1992

origin and evolution of the late precambrian high grade yaounde gneisses cameroon abstract the yaounde series is composed of low to high grade garnet bearing schists and gneisses belonging to the pan african north equatorial fold belt the high grade rocks consist of kyanite garnet gneisses and garnet plagioclase gneisses containing layers of calcsilicate rocks marbles quartzites and magnetite rich orthopyroxenites the chemical patterns of these rocks are those of a sedimentary sequence of shales and greywackes and minor dolomite rocks dolomitic marls evaporitic beds quartzites and iron rich sediments some volcanogenic greywackes may have been of alkaline affinity this sequence was probably deposited in shallow water near shore semi barred conditions which can be related either to an intracontinental distensive environment or to a passive margin at the northern edge of the congo craton the yaounde gneisses were deformed during two main tectonic phases the first phase d1 is marked by a layering s0 s1 resulting from tectonic transposition the second one d2 corresponds to tangential tectonics with isoclinal folds and flat lying shear zones associated with a s2 schistosity and a l2 lineation a third phase late d2 is marked by the development of low temperature mylonitic shears scarce wrench faults indicate later e w compression the d1 d2 transition is characterized by the emplacement of mafic and ultramafic rocks and by the development of high pressure granulite facies conditions t 750 800 c p 10 12 kbar these peak metamorphic conditions triggered a widespread migmatization dated at 565 22 ma and coeval with the d2 event the gradual decrease of the metamorphic conditions toward the south and the existence of a syn d2 retrograde inverse metamorphic gradient suggest that the overall structure of the yaounde series is a large tectonic nappe thrust onto the congo craton a geotectonic scheme for the north equatorial fold belt is discussed