bar dynamics in a sandy braided river insights from sediment numerical simulations abstract bar dynamics in sandy braided rivers are keys to better understand the morphological processes of braided rivers and sediment distributions limited by insufficient quantitative information and satellite images that only show the larger scale morphology and do not reveal the sand bars in the deeper channels most previous studies have qualitatively assessed bar dynamics but the ways in which the hydraulic parameters of sandy braided rivers control bar dynamics remains poorly understood here we present sediment numerical simulations on sandy braided rivers to investigate the quantitative controls of river parameters on bar dynamics three bar dynamic forms downstream migration lateral variations and bar tail elongation are observed unit bars are prone to downstream migration following formation and the migration rate shows a deceasing trend during braided river evolution this gradually decreasing migration rate is proven to be strongly connected to the decreasing flow velocity of braided channels that confine bar growth the lateral variation in bar dynamics exhibits narrowing migration and widening of sectional morphologies we suggest that braided channel curvature dominantly controls lateral sediment transportation around the bar and thus results in several lateral variation forms of bars the bar tail elongation difference between the two sides of the bar is associated with bar asymmetry strong bar asymmetry can make apparent differences in bar tail elongation

evolution of the canadas edifice and its implications for the origin of the canadas caldera tenerife canary islands the volcano stratigraphic and geochronologic data presented in this work show that the tenerife central zone has been occupied during the last 3 ma by shield or central composite volcanoes which reached more than 3000 m in height the last volcanic system the presently active teide pico viejo complex began to form approximately 150 ka ago the first canadas edifice ce volcanic activity took place between about 3 5 ma and 2 7 ma the ce i is formed mainly by basalts trachybasalts and trachytes the remains of this phase outcrop in the canadas wall cw sectors of la angostura 3 5 3 0 ma and 3 0 2 7 ma boca de tauce 3 0 ma and in the bottom of some external radial ravines 3 5 ma the position of its main emission center was located in the central part of the cc the volcano could have reached 3000 m in height this edifice underwent a partial destruction by failure and flank collapse forming debris avalanches during the 2 6 2 3 ma period the debris avalanche deposits can be seen in the most distal zones in the n flank of the ce i tigaiga breccia a new volcanic phase whose deposits overlie the remains of ce i and the former debris avalanche deposits constituted a new volcanic edifice the ce ii the dyke directions analysis and the morphological reconstruction suggest that the ce ii center was situated somewhat westward of the ce i reaching some 3200 m in height the ce ii formations are well exposed on the cw especially at the el cedro 2 3 2 00 ma sector they are also frequent in the s flank of the edifice 2 25 1 89 ma in tejina 2 5 1 87 ma as well as in the tigaiga massif to the n 2 23 ma during the last periods of activity of ce ii important explosive eruptions took place forming ignimbrites pyroclastic flows and fall deposits of trachytic composition their ages vary between 1 5 and 1 6 ma adeje ignimbrites to the w in the cw the upper ucanca phonolitic unit 1 4 ma could be the last main episode of the ce ii afterwards the can adas iii phase began it is well represented in the cw sectors of tigaiga 1 1 ma 0 27 ma las pilas 1 03 ma 0 78 ma diego hernandez 0 54 ma 0 17 ma and guajara 1 1 ma 0 7 ma the materials of this edifice are also found in the se flank these materials are trachybasaltic lava flows and abundant phonolitic lava and pyroclastic flows 0 6 ma 0 5 ma associated with abundant plinian falls the ce iii was essentially built between 0 9 and 0 2 ma a period when the volcanic activity was also intense in the dorsal edifice situated in the easterly wing of tenerife the so called valleys of la orotava and gu imar transversals to the ridge axis also formed during this period in the central part of tenerife the ce iii completed its evolution with an explosive deposit resting on the top of the ce for which ages from 0 173 to 0 13 ma have been obtained the cc age must be younger due to the fact that the present caldera scarp cuts these deposits on the controversial origin of the cc central vertical collapse vs repeated flank failure and lateral collapse of mature volcanic edifices the data discussed in this paper favor the second hypothesis clearly several debris avalanche type events exist in the history of the volcano but most of the deposits are now under the sea the caldera wall should represent the proximal scarps of the large slides whose intermediate scarps are covered by the more recent teide pico viejo volcanoes

structure and emplacement of the pliocene roque nublo debris avalanche deposit gran canaria spain abstract collapse of the flanks of the pliocene roque nublo stratocone on gran canaria lead to large debris avalanches that traveled far beyond the coastline with velocities that may have exceeded 100 m s the deposits comprised at least 14 km 3 of debris and covered an area of about 180 km 2 in the southern half of the island the debris filled deep canyons are largely exhumed at present incomplete disintegration poor fluidization and a good preservation of megablocks are thought to be mainly due to the confinement of the debris avalanche within deep canyons the rheological behavior of lithologic domains varies with their size internal strength and relative position within the deposit the deformation structures indicate that distinct components flowed whereas others slid throughout the transport in a relatively dense mode the following factors are believed to have been important in generating the roque nublo debris avalanche deposit 1 unusual abundance of pyroclastic flow and other volcaniclastic deposits making up the upper roque nublo cone 2 highly asymmetric basement beneath the cone with a very high southern ridge and a steep erosional southern slope leading to major instabilities 3 intrusion of dikes and cryptodomes as well as hydrothermal alteration in the crater area further weakening the volcano

the recent deglaciation of kolahoi valley in kashmir himalaya india in response to the changing climate abstract in the present study the retreat of kolahoi glacier was mapped from the satellite observations and historical maps supplemented by the extensive field observations to understand the recent deglaciation of the kolahoi valley kashmir himalaya india the glacier has retreated by 2 85 km during the last 157 years from 1857 to 2014 with an average retreat of about 18 2 m year 1 however the glacier snout has shown higher recession during the last decade the geomorphological evidence reveals glaciation of the kolahoi valley during the quaternary these evidences include glacial till at pahalgam and aru besides terminal and lateral moraines at lidderwat satlanjan and kolahoi gunj in the kolahoi valley the glacier has shrunk by 2 81 km2 during the last 51 years 1962 2013 losing an ice volume of 0 30 km3 the observed glacier changes were correlated with the climate data from pmip3 cmip5 models the temperatures are predicted to increase almost ten times more than that observed during the last glacial maximum lgm the future temperature is predicted to rise between 0 18 c and 0 61 c per decade under rcp 2 6 and rcp 8 5 respectively the projected rise in the temperature if realized will have an adverse effect on the glaciers and would in all likelihood adversely affect the water availability for various sectors in the region

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

volcanic debris avalanche deposits of the upper maronne valley cantal volcano france evidence for contrasted formation and transport mechanisms abstract the deposits of two volcanic debris avalanches vda i and ii that occur in the upper maronne valley northwest sector of cantal volcano france were studied to establish their mechanisms of formation transport and deposition these two volcanic debris avalanches that clearly differ with regard to their structures textures and extensions exemplify the wide spectrum of events associated with large scale sector collapse vda i is voluminous 1 km3 in the upper maronne valley and widespread the deposits comprise two distinct facies the block facies that forms the intermediate and upper part of the unit and the mixed facies that crops out essentially at the base of the unit the block facies consists of more or less brecciated lava block and ash flow breccia and pumice flow tuff megablocks set in breccias resulting from block disaggregation mixing and differential movements are almost absent in this part of the vda the mixed facies consists of breccias rich in fine particles that originate from block disagregation as well as being picked up from the substratum during movement mixing and differential movements are predominant in this zone analysis of fractures on lava megablocks suggests that shear stress during the initial sliding is the principal cause of fracture these data strongly indicate that vda i is purely gravitational and argue for a model in which the initial sliding mass transforms into a flow due to differential in situ fragmentation caused by the shear stress vda ii is restricted to low topography areas its volume in the studied area is about 0 3 km3 the deposits consist of brecciated rounded blocks and megablocks set in a fine grained matrix composed essentially of volcanic glass this unit is stratified with a massive layer that contains all the megablocks at the base and in the intermediate part and in the upper part a normally graded layer that contains only blocks

reactivation of basement faults beneath volcanoes a new model of flank collapse in order to explain the presence of voluminous volcanic debris avalanche deposits around a stratovolcano reactivation of vertical faults beneath a volcanic cone has been tested using analogue models reactivation of a single vertical fault beneath a cone generates a normal fault and an upturning of the layers creating a bulge on the flank the upturning induces a flank collapse characterized by a typical horseshoe shaped scar called an avalanche caldera reactivation of two vertical faults beneath a cone also generates a normal fault and a summit bulge this bulge may result from the movement along a reverse fault a large collapse is generated within the angle created by the two vertical faults the angle of the collapse can be up to 140 whereas this angle is typically 120 for a dome intrusion collapse is instantaneous and is favoured by the presence of ductile layers ash and pumice formations in the example considered in a stratovolcano complex the model may be applicable to volcanoes in a state of dormancy or extinction in regions with active regional tectonism we suggest this mechanism of collapse in the case of the cantal stratovolcano massif central france to explain the presence of voluminous volcanic debris avalanche deposits around this volcano

hasty retreat of glaciers in northern patagonia from 1985 to 2011 mapping changes in glacier extent from repeat optical satellite data has revealed widespread glacier decline in nearly all regions of the world over the past few decades while numerous studies have documented the changes of the outlet glaciers of the northern and southern patagonia icefields npi spi information about glacier changes in the patagonian andes to the north of the npi is much scarcer here we present an assessment of area changes for glaciers mainly located in the palena district of chile based on glacier inventories for 1985 2000 and 2011 that were derived from two consecutive landsat scenes and a digital elevation model the analysis revealed a dramatic area decline for the largest glaciers and total area loss of 25 from 1985 to 2011 the lower parts of several larger glaciers 10 km 2 melted completely area loss below 1000 m elevation was 50 100 in both periods and 374 glaciers out of 1664 disappeared the number of proglacial lakes increased from 223 to 327 and their area expanded by 11 6 km 2 59 between 1985 and 2011 seasonal snow persisting at high elevations in the 2011 scene was a major obstacle to glacier delineation so the obtained area change rate of 1 a 1 over the entire period is a lower bound estimate the observed climate trends e g cooling in puerto montt are in contrast to the observed shrinkage

synergistic approach for mapping debris covered glaciers using optical thermal remote sensing data with inputs from geomorphometric parameters abstract debris cover on glacier boundaries critically impedes the global inventorying of glaciers and confounds most of the techniques developed for semi automated mapping of glaciers debris on the glacier referred as supraglacial debris and that occurring outside the glacier boundaries referred as periglacial debris being derived from a common source i e the valley rock tend to have a similar spectral response in the reflection region which renders them mutually indistinguishable however there exist temperature differences between them this aspect has been considered in this remote sensing based study to distinguish between the supraglacial and periglacial debris in a test area in the chenab basin himalayas by inclusion of thermal infrared tir bands in remote sensing data processing a synergistic multisensor approach for the delineation of debris covered glacier boundaries is used here which integrates the inputs from thermal terra aster sensor and optical irs p6 awifs sensor remote sensing data multispectral classification techniques and the dem derived geomorphometric parameters the results of this study corroborate earlier findings on utilization of temperature differences as one of the parameters in glacial studies the proposed synergistic approach therefore appears useful in accurate mapping of debris covered glaciers in the himalayan region

volcanic and morphological evolution of la gomera canary islands based on new k ar ages and magnetic stratigraphy implications for oceanic island evolution the spatial and chronological evolution of canary islands volcanism is due to eastward progression of the slow moving african plate over a mantle plume la gomera is located between the western shield stage islands 12 ma with 23 k ar ages and palaeomagnetic data we can constrain the timing of the main subaerial volcanic phases of la gomera the shield volcano c 9 4 8 0 ma the postshield peripheral lava flows c 7 4 5 0 ma the postshield horizontal lava flows c 5 4 4 3 ma and late intra canyon lava flows c 1 9 ma the horizontal lava flows fill a 10 km wide depression formed by a giant landslide garajonay the entire structure of la gomera is in relief inversion declining volcanic construction rates from the shield to the postshield stages are correlated with increasing erosion rates whereas the period of volcanic quiescence hiatus has low erosion rates the succession and duration of the hotspot volcanic stages in the canary islands are compared with those in the hawaiian islands thus underlining differences between slow moving and fast moving plate settings

catastrophic collapse at stratovolcanoes induced by gradual volcano spreading unlike ordinary mountains which are formed by slow uplift and erosion volcanoes are constructed rapidly as a consequence many are liable to massive flank failures leading to debris avalanches for example at mount st helens in 1980 such failures occur worldwide about once every 25 years ref 1 and even small ones can present a major hazard in particular if far reaching tsunamis are generated as at mayu yama in 1792 ref 2 previous work has tended to emphasize differences in eruption style associated with flank failure2 but here we focus on the fundamental structural causes of failure most volcanic failures are generated by magmatic intrusion and flank spreading3 we present evidence however that mombacho volcano in nicaragua experienced a previously unrecognized type of failure triggered by sub volcanic basement spreading notably collapses related to basement spreading do not require that the volcano be magma tically active and thus flank failure may pose a significant risk even at inactive volcanoes which are rarely monitored

multiple related flank collapses on volcanic oceanic islands evidence from the debris avalanche deposits in the orotava valley water galleries tenerife canary islands abstract catastrophic flank collapses are common on oceanic islands of volcanic origin and often recognizable from the resulting morphology as large u shaped embayments however post collapse volcanic activity can infill such features thereby obscuring them this study takes advantage of a dense network of long sub horizontal galleries for groundwater extraction in the flank collapse structure of the orotava valley tenerife canary islands this impressive landform is located in the overlapping zone of the ne rift and the canadas edifice of this volcanic island three debris avalanche deposits dads have been identified inside the waterworks bored into the valley s western sector the deeper layer the lower dad l dad was previously described under the local name of mortalon this deposit lies unconformably over older volcanic rocks where a prominent shear zone is developed here interpreted as the detachment plane of a massive rockslide the l dad was therefore produced during the large failure event the orotava landslide ol which carved the depression two younger dads much smaller in volume and not previously described were also identified in the underground strata the intermediate i dad and upper dad u dad both correlate well with the thick breccia deposits cropping out at the base of the marine cliff along the western coast of the valley the i dad and u dad are conformably intercalated between the lava flows and other volcanics infilling the depression and their bases are erosive depositional features without structural deformation zones below them their stratigraphic setting and geometrical reconstruction indicate that both deposits were emplaced after the valley was formed by the ol event in two successive failures here called western orotava landslides wols the younger called wol 2 was dated at 494 22 ka using the 40ar 39ar method these two subaerial failures affected the upper eastern flank of the canadas iii edifice previously destabilized when the ol failure event carved a steep wall at its foot the western lateral escarpment of the orotava valley

using uas optical imagery and sfm photogrammetry to characterize the surface grain size of gravel bars in a braided river veneon river french alps this paper explores the potential of unmanned aerial system uas optical aerial imagery to characterize grain roughness and size distribution in a braided gravel bed river veneon river french alps with this aim in view a wolman field campaign 19 samples and five uas surveys were conducted over the veneon braided channel during summer 2015 the uas consisted of a small quadcopter carrying a gopro camera structure from motion sfm photogrammetry was used to extract dense and accurate three dimensional point clouds roughness descriptors roughness heights standard deviation of elevation were computed from the sfm point clouds and were correlated with the median grain size of the wolman samples a strong relationship was found between uas sfm derived grain roughness and wolman grain size the procedure employed has potential for the rapid and continuous characterization of grain size distribution in exposed bars of gravel bed rivers the workflow described in this paper has been successfully used to produce spatially continuous grain size information on exposed gravel bars and to explore textural changes following flow events c 2017 elsevier b v all rights reserved

field experiment on alternate bar development in a straight sand bed stream alternate bars in rivers and streams develop as a result of differences in length scales involved in the adjustment of flow and sediment transport to irregularities of the bed the amount of field evidence supporting theoretical insights is highly limited here we present results from a large scale field experiment in a 600 m long straight reach over a period of almost 3 years the channel was allowed to evolve autogenously from initially flat bed conditions subject to discharge variation alternate bars developed within 8 months from the start of the experiment the initial stages of bar development included bar growth both in wavelength and amplitude and bar migration the latter was too limited to classify the bars as being migrating bars therefore we classify the bars as nonmigrating bars toward the end of the experiment the regular alternate bar pattern evolved into an irregular pattern and bar amplitude started to decrease from the start of the experiment we observed a declining channel slope from 1 8 m km 1 initially to 0 9 m km 1 halfway the experiment after which it stabilized we applied two bar theories to establish their predictive capacity both bar theories predicted the development of alternate bars under the constructed channel conditions in response to the declining channel slope both theories predicted a decreasing likelihood for the development of alternate bars our study shows that under field conditions the applied bar theories may predict the initial stages of bed development

a new chronostratigraphical and evolutionary model for la gomera implications for the overall evolution of the canarian archipelago a review of the general volcano stratigraphy and geochronology of la gomera one of the lesser known canary islands has led to the establishment of a new evolutionary model the oldest edifice corresponds to the submarine stage built up between 20 and 15 ma the construction of the submarine edifice was followed by an important break in the activity about 4 ma and deep erosion of the edifice about 10 5 ma ago the main present day edifice the old edifice 10 5 6 4 ma emerged which was also submarine in its initial phases two different main stages are distinguishable the first stage was represented by a large some 22 km wide basaltic shield volcano the lower old edifice several lateral collapse events tazo and san marcos avalanches occurred during this time and were responsible for the removal of an important part of its northern flank in the second growth stage the upper old edifice the activity migrated southwards a 25 km wide composite volcano arose covering part of the remaining earlier shield volcano the felsic trachytic to phonolitic activity occurring in two separate episodes formed a significant component of this composite volcano finally one more recent large edifice the young edifice built up from 5 7 to 4 ma the lava flows of this younger edifice covered completely the centre and the south of the island and filled deep ravines in the north more evolved magmas including significant felsic magmas the third and last felsic episode occurred in this phase of activity the growth of la gomera was long lasting separated by an important gap in the activity in the middle miocene with no quaternary activity at all at the same time on tenerife the nearest island east of la gomera three large edifices grew separately roque del conde anaga and teno initially three separated islands from the available data it is inferred that the subaerial activity started earlier in the roque del conde edifice then on la gomera and later in teno in the nw and anaga in ne of tenerife which is the youngest of all these edifices these facts together with the irregular general progress of the volcanic activity support more complex views of the genesis for the canary islands than the simple hotspot model

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

the chimborazo sector collapse and debris avalanche deposit characteristics as evidence of emplacement mechanisms abstract chimborazo is a late pleistocene to holocene stratovolcano located at the southwest end of the main ecuadorian volcanic arc it experienced a large sector collapse and debris avalanche da of the initial edifice ch i this left a 4 km wide scar removing 8 0 0 5 km 3 of the edifice the debris avalanche deposit dad is abundantly exposed throughout the riobamba basin to the rio chambo more than 35 km southeast of the volcano the dad averages a thickness of 40 m covers about 280 km 2 and has a volume of 11 km 3 two main dad facies are recognized block and mixed facies the block facies is derived predominantly from edifice lava and forms 80 vol of the dad with a probable volume increase of 15 25 vol the mixed facies was essentially created by mixing brecciated edifice rock with substratum and is found mainly in distal and marginal areas the dad has clear surface ridges and hummocks and internal structures such as jigsaw cracks injections and shear zone features are widespread structures such as stretched blocks along the base contact indicate high basal shear substratum incorporation is directly observed at the base and is inferred from the presence of substratum derived material in the dad body based on the facies and structural interpretation we propose an emplacement model of a lava rich avalanche strongly cataclased before and or during failure initiation the flow mobilises and incorporates significant substrata 10 14 vol while developing a fine lubricating basal layer the substrata dominated mixed facies is transported to the dad interior and top in dykes invading previously formed fractures

effect of sampling time in the laboratory investigation of braided rivers we focus on the measurement of the bed elevation of braided networks in flume experiments in particular the effect of the survey frequency on the measurement accuracy is studied to this aim an innovative measurement system is adopted it consists of a laser ultrasonic sensor and can survey the bed elevation under owing water this measurement system was used to profile a flume transect with a frequency of 4 minutes without stopping the water discharge by this technique the topography of a single transect was continuously acquired during the evolution of a braided river model twelve braided rivers generated with different experimental conditions were studied the main results are i there exists a threshold survey frequency 4 8 minutes in our analysis which guarantees that the morphological evolution of the braiding channels is fully measured ii if this threshold frequency of survey is exceeded significant errors occur in the balance of the eroded deposited sediments and in the evaluation of the bed elevation dynamics and iii these errors depend on the river stream power

gravel transport and morphological change in braided sunwapta river alberta canada the relation between morphological change and patterns of variation in bedload transport rate in braided streams was observed by repeated daily topographic surveys over a 25 day study period in a 60 m reach of the proglacial sunwapta river alberta canada there are two major periods of morphological change each lasting several days and each involving the complete destruction and reconstruction of bar complexes bar complex destruction was caused by redirection of the flow and by downstream extension of the confluence scour zone upstream reconstruction involved accretion of unit bars on bar head flank and tail and in one case was initiated by disection of a large lobate unit bar high rates of sediment movement measured from net scour and fill of the cross sections coincided with these morphological changes sediment was supplied from both bed and bank erosion and patterns and distances of transfer were highly variable rates of transport estimated by matching upstream erosional volumes with downstream deposition were much greater than those estimated from either a step length approach or a sediment budget measurements of scour and fill and observations of morphological change indicate that step lengths virtual transport distances were typically 40 100m during a diurnal discharge cycle shorter step lengths occurred when transfer was confined to a single anabranch and longer steps involved channel changes at the scale of the entire reach sediment budgeting was used to describe the spatial patterns of sediment transport associated with the morphological changes and to estimate minimum daily reach averaged transport rates mean bedload transport rates correlate with discharge but with considerable scatter the largest deviations from the mean relation can be tied to phases of channel incision bank erosion scour hole migration bar deposition and channel filling apparently controlled by changes and fluctuations in sediment supply from upstream independent of discharge these are interpreted as field evidence of autopulses or macropulses in bedload transport previously observed only in laboratory models of braided streams

fluvial responses to the weichselian ice sheet advances and retreats implications for understanding river paleohydrology and pattern changes in central poland the evolution of the fluvial systems during the weichselian pleniglacial in the torun basin central poland was investigated through sedimentological investigation and paleohydraulic analysis within the basin three fluvial cycles deposited after successive phases of the ice advance which took place 50 28 and 20 ka ago successions of four fluvial lithotypes characterize each fluvial formation that are related to the paleoenvironmental changes e g climate instability and changes in the river regime which affected the channel hydraulics and morphology the successions comprise river style metamorphosis between high energy sand bed meandering rivers lithotype m1 high energy sand bed braided rivers lithotype b1 and medium energy sand bed braided rivers with either unit bars lithotype b2 or compound bars lithotype b3 reflects the maturity stage of sand bed braided river evolution in the basin the assessment of the fluvial sedimentary environments enabled the construction of a quantitative model of the changes in the river channel pattern in relation to the climate oscillation both the paleohydrological controls and their sedimentary consequences are discussed in the article lithotypes m1 and b1 represent riverbed modeled under supercritical flow condition deposition of lithotype b2 corresponded to the river channel pattern transformation and was manifested by decreasing flow velocity energy losses associated with bedform roughness and with the transportation of coarser particles the flow velocity was generally greater in rivers of lithotype b3 and energy of sedimentary environment was more stable than during the deposition of lithotype b2

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

a quantitative three dimensional depositional model of gravelly braided rivers a quantitative three dimensional depositional model of gravelly braided rivers has been developed based largely on the deposits of the sagavanirktok river in northern alaska these deposits were described using cores wireline logs trenches and ground penetrating radar profiles the origin of the deposits was inferred from observations of 1 channel and bar formation and migration and channel filling interpreted from aerial photographs 2 water flow during floods and 3 the topography and texture of the river bed at low flow stage this depositional model quantitatively represents the geometry of the different scales of strataset the spatial relationships among them and their sediment texture distribution porosity and permeability in the model are related to sediment texture the geometry of a particular type and scale of strataset is related to the geometry and migration of the bedform type e g ripples dunes bedload sheets bars associated with deposition of the strataset in particular the length to thickness ratio of stratasets is similar to the wavelength to height ratio of associated bedforms furthermore the wavelength and height of bedforms such as dunes and bars are related to channel depth and width therefore the thickness of a particular scale of strataset i e medium scale cross sets and large scale sets of inclined strata will vary with river dimensions these relationships between the dimensions of stratasets bedforms and channels mean that this depositional model can be applied to other gravelly fluvial deposits the depositional model can be used to interpret the origin of ancient gravelly fluvial deposits and to aid in the characterization of gravelly fluvial aquifers and hydrocarbon reservoirs

analogue models of the effect of long term basement fault movement on volcanic edifices long term fault movement under volcanoes can control the edifice structure and can generate collapse events to study faulting effects we explore a wide range of fault geometries and motions from normal through vertical to reverse and dip slip to strike slip using simple analogue models we explore the effect of cumulative sub volcanic fault motions and find that there is a strong influence on the structural evolution and potential instability of volcanoes the variety of fault types and geometries are tested with realistically scaled displacements demonstrating a general tendency to produce regions of instability parallel to fault strike whatever the fault motion where there is oblique slip faulting the instability is always on the downthrown side and usually in the volcano flank sector facing the strike slip sense of motion different positions of the fault beneath the volcano change the location type and magnitude of the instability produced for example the further the fault is from the central axis the larger the destabilised sector also with greater fault offset from the central axis larger unstable volumes are generated such failures are normal to fault strike using simple geometric dimensionless numbers such as the fault dip degree of oblique motion angle of obliquity and the fault position we graphically display the geometry of structures produced the models are applied to volcanoes with known underlying faults and we demonstrate the importance of these faults in determining volcanic structures and slope instability using the knowledge of fault patterns gained from these experiments geological mapping on volcanoes can locate fault influence and unstable zones and hence monitoring of unstable flanks could be carried out to determine the actual response to faulting in specific cases

k ar chronology of the volcanic eruptions in the canarian archipelago island of la gomera a geochronological study of the island of la gomera canaries has been carried out by the k ar method the 26 new ages obtained together with the 17 previous determinations show that above the main unconformity of the island separating the basal complex from the later volcanic series there is a unit of lower old basalts more than 10 m y old polymictic volcanic breccias were emplaced between 10 and 9 m y ago the upper old basalts above them were formed between 9 and 6 m y ago with a peak of activity around 7 m y after a period of erosion 6 5 m y a thick series of young basalts associated with trachytic and phonolitic domes and flows were rapidly emplaced between 4 5 4 m y ago finally local basaltic activity took place 2 8 m y ago the age of the basal complex is not well known although three ages 14 6 15 5 and 19 3 m y have been obtained for some alkaline intrusives which seem to represent the youngest events in the complex

monitoring and modelling morphological change in a braided gravel bed river using high resolution gps based survey recent research in fluvial geomorphology has emphasized the direct monitoring of channel topography as a useful tool to better understand the interrelationship between river form and process and in particular to estimate bedload transport rates and reach scale sediment budgets until recently however this morphometric approach has been limited to comparison of repeatedly surveyed cross sections with the associated problems of low frequency sampling and an emphasis on cross stream as opposed to downstream morphological dynamics recent advances in analytical photogrammetry have however permitted the acquisition of data at sufficient resolutions to represent macroform 101 m and microform 10 m channel geometry in fully three dimensions while inherently spatially distributed the photogrammetric approach to land surveying is however restricted to observable areas of the channel and is thus of limited use in the subaqueous zone especially if flows are turbid or highly coloured this paper presents an alternative approach to the study of three dimensional morphological dynamics of a divided reach of the gravelly river feshie scotland in which topographic survey of both exposed and submerged areas of the reach was undertaken using the global positioning system gps survey results from two field programmes in 1998 and 1999 are presented in which a geotronics geotracer 2000 real time kinematic gps receiving unit was used to survey a 200 80 m reach rapid radial survey methods were employed permitting the collection of 2000 survey points per day giving a mean density over the 13 ha reach of 1 1 points per square metre a detailed assessment of survey errors and dem quality is presented and a limit of detection of c 10 cm proposed as an upper threshold for the identification of significant change between dems preliminary interpretation of channel dynamics in 1998 99 reveals relatively little change to the overall macroscale reach structure dem differencing techniques however highlight important local changes including the progradation of submerged bar fronts bar head aggradation and scour along major channel thalwegs and the erosion of fines from sloughs copyright 2000 john wiley sons ltd

separating snow clean and debris covered ice in the upper indus basin hindukush karakoram himalayas using landsat images between 1998 and 2002 summary the hindukush karakoram himalayan mountains contain some of the largest glaciers of the world and supply melt water from perennial snow and glaciers to the upper indus basin uib upstream of tarbela dam which constitutes greater than 80 of the annual flows and caters to the needs of millions of people in the indus basin it is therefore important to study the response of perennial snow and glaciers in the uib under changing climatic conditions using improved hydrological modeling glacier mass balance and observations of glacier responses however the available glacier inventories and datasets only provide total perennial snow and glacier cover areas despite the fact that snow clean ice and debris covered ice have different melt rates and densities this distinction is vital for improved hydrological modeling and mass balance studies this study therefore presents a separated perennial snow and glacier inventory perennial snow cover on steep slopes perennial snow covered ice clean and debris covered ice based on a semi automated method that combines landsat images and surface slope information in a supervised maximum likelihood classification to map distinct glacier zones followed by manual post processing the accuracy of the presented inventory falls well within the accuracy limits of available snow and glacier inventory products for the entire uib estimates of perennial and or seasonal snow on steep slopes snow covered ice clean and debris covered ice zones are 7238 724 5226 522 4695 469 and 2126 212 km2 respectively thus total snow and glacier cover is 19 285 1928 km2 out of which 12 075 1207 km2 is glacier cover excluding steep slope snow cover equilibrium line altitude ela estimates based on the snow line elevation sle in various watersheds range between 4800 and 5500 m while the accumulation area ratio aar ranges between 7 and 80 0 c isotherms during peak ablation months july and august range between 5500 and 6200 m in various watersheds these outputs can be used as input to hydrological models to estimate spatially variable degree day factors for hydrological modeling to separate glacier and snow melt contributions in river flows and to study glacier mass balance and glacier responses to changing climate

dike swarms key to the reconstruction of major volcanic edifices the basic dikes of la gomera canary islands the detailed study of the age and distribution of the basic dikes of la gomera canary islands has allowed us to reconstruct the evolution of its main volcanic edifice the dikes of the oldest unit the basal complex have a n70 80 dominant direction at regional scale on the other hand the dikes of the post basal complex subaerial units are the result of local stress fields the oldest swarm is composed of sills dated at 10 2 9 3 ma four younger radial dike swarms have been identified s1 s2 s3 and s4 with ages of 9 1 8 4 ma 8 2 6 7 ma 5 5 4 4 ma and 5 3 4 0 ma respectively the reconstruction of the magmatic focus location using these swarms shows a migration southwards with an average speed of 1 6 mm year this temporal sequence of parallel swarms sills and radial swarms is a pattern frequently repeated during the building of large insular volcanic edifices in the canary islands as well as in other archipelagos

three dimensional sedimentary architecture of a large mid channel sand braid bar jamuna river bangladesh the three dimensional subsurface alluvial architecture of a large approximately 3 km long 1 km wide 12 m high mid channel sand braid bar in the jamuna river bangladesh is described evolution of the bar and its depositional characteristics are assessed from a unique combination of ground penetrating radar surveys vibracoring and trenching that are allied to a series of bathymetric surveys taken during growth of the bar over a 29 month period this methodology permits identification of the formative processes of different packages of braid bar sedimentation and provides a facies model for deposition within the entire bar mid channel bar growth occurred in a region of flow expansion and was probably initiated by the stalling and amalgamation of large dunes these dunes created a bar core that grew by i propagation of a downstream accreting slipface ii vertical accretion through stacking of dunes on both bar stoss and top and iii lateral accretion on the bar margins during recession of the flood hydrograph braid bar sedimentation is dominated by four radar facies 1 large scale predominantly planar dipping reflections interpreted as cross stratification up to 8 m in height and greater than 100 m in width that is produced by the cross channel migration of bar margins 2 medium scale trough shaped and planar discontinuous reflections interpreted as cross stratification up to 4 m in height and 300 m wide that is deposited from large sinuous crested sand dunes 3 discontinuous reflections up to 2 m high and 30 m wide interpreted as small scale trough cross stratification that is the product of smaller sinuous crested dunes and 4 high amplitude undulating reflections interpreted as mud drapes deposited in regions of slow flow often in the bar tail region at low stage dune size decreases vertically within the bar in response to the progressively shallower flows on the emerging bar top later evolution of the bar as one anabranch channel became dominant created a 1 5 km extension to the bar tail with an 8 m high angle of repose bar margin slipface formed by flow transverse to the long axis of the bar seven styles of deposition can be defined that constitute the alluvial architecture bar margin slipface vertical accretion in channel bar top vertical accretion upstream accretion lateral accretion downstream accretion and low stage mud drapes a model of braid bar sedimentation is presented that shares many similarities with previous studies of smaller sand bed braid bars with the dominance of dune scale cross stratification the presence of large scale bar margin cross stratification and the occurrence of lateral vertical upstream and downstream accretion however the contribution of the bar margin facies to the preserved stratigraphy highlighted herein may have been underestimated in previous models of braided rivers in which the braid bars were migrating slowly this study suggests a scale invariance in several aspects of mid channel bar sedimentation in sand bed rivers and proposes a model of braid bar sedimentation that may be applied widely within studies of braided alluvial architecture

morphological evolution and dynamics of a large sand braid bar jamuna river bangladesh the initiation and evolution of a kilometre scale sand braid bar was monitored during a 28 month survey period from 1993 to 1996 in one of the world s largest braided rivers the jamuna river bangladesh repeated bathymetric surveys through two monsoon flood seasons combined with bar top surveys during exposure of the bar at low flow provide the most detailed chronology of braid bar growth yet compiled for a large sand bed river during rising and peak flow of the 1994 monsoon flood a 1 5 km long 0 5 km wide 12 m high symmetrical mid channel bar was deposited in the centre of a major channel downstream of a zone of flow convergence and significant bank erosion initial deposition and growth of the bar core were probably caused by amalgamation of dunes that are present in the jamuna channels at all flow stages bar top aggradation continued through downstream migration of an accretionary dune front a 3 m high angle of repose slipface that was composed of amalgamated 0 5 to 1 m high dunes at waning and low flow the mid channel bar widened by up to 1 km through the lateral accretion of dunes onto the margins of the initial bar core a low velocity zone in the sheltered wake region of the bar tail led to the accumulation of substantial volumes of silts and clays during the rising and peak flows of the next monsoon flood the mid channel bar extended its bar tail by up to 1 5 km as one of the anabranches became dominant and flow was deflected across the bar tail accretion at the bar tail generated a lobate transverse bar front with a 10 m high angle of repose avalanche face emergence of several smaller bars along this depositional front produced an overall reach morphology that more closely resembled an alternate bar rather than several mid channel bars the conversion of a mid channel bar to an alternate bar is contrary to many previous descriptions of the braiding process

deformation of the substratum of a large shield volcano triggering factor for past flank collapses in the old volcanic edifice of la gomera canary islands the basal complex of la gomera canary islands has been analyzed with the aim of deciphering its structural evolution spanning the middle to late miocene detailed structural maps and cross sections and the results of a systematic measurement of dike orientation and fault slip data are presented in this work the main structural features found in the basal complex of la gomera are four dike sets and two large normal faults guillama and montana de alcala faults several extensional episodes have been identified the main deformation phase corresponds to a nnw sse to nw se directed extension that generated first a dense swarm of mafic dikes and then a large scale collapse of the basal complex with displacement along the guillama and montana de alcala faults and associated rotation of large blocks of la gomera basement it is interpreted that the supposed staircase geometry of the guillama fault is responsible for the observed arrangement of rotated dikes due to development of kilometric scale fault bend folds with rounded hinges deformation of the basal complex shows a complete geometric kinematic and chronologic consistency with the large volcanic flank collapses that affected the units belonging to the early growth stages of la gomera subaerial shield volcano the results of this work support the models that invoke the importance of the large scale geodynamic setting on volcano destabilization more attention should be paid to the structural and geophysical characteristics of volcano basements in order to better evaluate the danger of large catastrophic volcanic landslide events

remote sensing science and technology for studying glacier processes in high asia a large number of multispectral and stereo image data are expected to become available as part of the global land ice measurements from space project we investigate digital elevation model extraction anisotropic reflectance correction and selected glacier analysis tasks that must be developed to achieve full utility of these new data results indicate that glaciers in the karakoram and nanga parbat himalaya northern pakistan exhibit unique spectral spatial and geomorphometric patterns that can be exploited by various models and algorithms to produce accurate information regarding glacier extent supraglacial features and glacier geomorphology the integration of spectral spatial and geomorphometric features coupled with approaches for advanced pattern recognition can help geoscientists study glacier mass balance glacier erosion sediment transfer efficiency and landscape evolution

multispectral imaging contributions to global land ice measurements from space global land ice measurements from space glims is an international consortium established to acquire satellite images of the world s glaciers analyse them for glacier extent and changes and assess change data for causes and implications for people and the environment although glims is making use of multiple remote sensing systems aster advanced spaceborne thermal emission and reflection radiometer is optimized for many needed observations including mapping of glacier boundaries and material facies and tracking of surface dynamics such as flow vector fields and supraglacial lake development software development by glims is geared toward mapping clean ice and debris covered glaciers terrain classification emphasizing snow ice water and admixtures of ice with rock debris multitemporal change analysis visualization of images and derived data and interpretation and archiving of derived data a global glacier database has been designed at the national snow and ice data center nsidc boulder colorado parameters are compatible with and expanded from those of the world glacier inventory wgi these technology efforts are summarized here but will be presented in detail elsewhere our presentation here pertains to one broad question how can aster and other satellite multispectral data be used to map monitor and characterize the state and dynamics of glaciers and to understand their responses to 20th and 21st century climate change our sampled results are not yet glaciologically or climatically representative our early results while indicating complexity are generally consistent with the glaciology community s conclusion that climate change is spurring glacier responses around the world mainly retreat whether individual glaciers are advancing or retreating the aggregate average of glacier change must be climatic in origin as nonclimatic variations average out we have discerned regional spatial patterns in glaciological response behavior these patterns are best attributed to climate change variability and to regional differences in glacier size and response times in many cases glacier length changes under represent the magnitude of glacier ablation because thinning sometimes without immediate length changes is also important an expanded systematic uniform analysis of many more glaciers is needed to isolate the glacier response components due to climatic and nonclimatic perturbations to produce quantitative measures of regional variation in glacier changes and to predict future regional glacier trends relevant to water resources glaciological hazards and global sea level this comprehensive assessment to be completed in stages is expected to lend a critically needed filter to identify successful climate models that explain recent glacier changes and change patterns and hence are apt to describe future changes and to eliminate unsuccessful models

nature and origin of toreva remnants and volcaniclastics from la palma canary islands abstract new data pertaining to the origin of volcaniclastic fan delta deposits the el time group and previously unreported toreva remnants intact landslide blocks are presented in terms of their relationships with the quaternary flank destruction of bejenado volcano on la palma canary islands bejenado volcano is the heavily dismantled relic of a stratocone which developed at the confluence of the cumbre nueva embayment and the caldera de taburiente collapse amphitheatre both of these giant landslide structures formed at around 0 55 ma after 0 2 ma of gravitational spreading on the western and eastern flanks of the taburiente cumbre nueva shield volcanic complex evidence is presented on the basis of stratigraphic photogeologic and geographic information system studies that both the toreva remnants and the el time group can be related to the sequential collapses of the north flank and summit region of bejenado inside the caldera de taburiente and the northernmost part of the adjoining cumbre nueva embayment the collapses probably occurred between 0 44 and 0 4 ma and they involved a volume of around 5 km3 the toreva remnants display a deformed volcanic architecture traversed by discontinuities which developed during impact and post collapse dislocation during slip they are composed of layer differentiated scoria with ancillary ankaramite and basanite tephrite lavas and occasional dikes they rest upon a thin veneer of sheared volcaniclastic deposits in relative proximity to the disfigured north flank of bejenado the collapse event s is distinguished by its extremely low mobility due to the deceleration of the debris avalanche mass within the confines of the caldera de taburiente the high friction coefficient h l 0 22 reflects this topographic factor reworking of the avalanche matrix gave rise to the accumulation and offshore progradation of the fan delta deposits at the sw base of bejenado contemporaneous fluvial sediments sourced by the retrogressive erosion of the pre bejenado collapse scarps were fed into the subaerial confines of the cumbre nueva embayment piecemeal scarp failure and the extrusion of substratum from beneath the scarps also contributed to the sediment budget the fluvial sedimentation rates subsequently increased with the onset of cumbre vieja volcanism prior to 0 125 ma these processes have contributed to the development of the flat floored submarine channels which extend onto the volcaniclastic apron west of la palma these new data give a fresh insight into the role of epiclastic processes landsliding and volcanism in the morphology and sediment mass balance of an oceanic island volcano system

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

volcano core collapse triggered by regional faulting it has been proposed recently that large scale caldera like structures may result from the viscous lateral spreading of a hydrothermal system located in the central part of volcanic edifices for this to occur an unbutressed boundary resulting in reduced lateral stresses must exist or be created not far from the hydrothermal system different ways to achieve such a weak lateral confinement may be proposed in this paper we show that regional tectonics may provide an unconfined boundary if a normal fault lowers part of the volcanic edifice a natural example is the island of nuku hiva in the marquesas archipelago french polynesia for which geological data strongly suggest that a regional fault oriented n75 e is responsible for the present day shape of the island i e an ellipse cut in the middle by a straight side along which two nested calderas are breached analogue modelling shows the mechanical consistency of the model and reveals that very low velocity faulting is needed for the formation of a caldera like structure

the cohesive naranjo debris flow deposit 10 km3 a dam breakout flow derived from the pleistocene debris avalanche deposit of nevado de colima volcano mexico abstract mass movement processes on volcanic terrains such as landslides and debris avalanches can cause the obstruction of main drainages producing the formation of temporary dams a good example of this occurred 18 5 ka ago when the eastern flank of the nevado de colima volcano collapsed producing a debris avalanche deposit that was previously described as one of the largest in the world the deposit extended from the volcanic summit as far as the pacific coast 120 km away new stratigraphic sedimentological and componentry data suggest that the volcanic collapse of nevado de colima resulted in a debris avalanche that traveled 20 km southeast to the naranjo river there it crashed against a topographic barrier consisting of cretaceous limestones cerro la carbonera and the flow direction was diverted to the south down the naranjo river channel for another 25 km before the avalanche came to a halt the obstruction of the drainage produced a temporary dam that stored ca 1 km3 of water and deposited fluvial and slack water sediments some time after the damming the accumulated water sediment load was able to overtop the obstructing material and to release a breakout flow with a calculated initial flow discharge of 3 5 million m3 s the resulting flood cohesive debris flow followed the channel of the naranjo river and due to the high erodibility of the channel and introduction of substrate material the debris flow progressively increased its volume up to 10 km3 six times its initial volume this study highlights the relevance of evaluating the potential remobilization of debris avalanche deposits to initiate large magnitude cohesive debris flows therefore the hazard and risk analysis of future potential events of this nature must consider the pre eruption conditions and the topography surrounding a volcano

channel morphology and bedload pulses in braided rivers a laboratory study bedload pulses in gravel bed rivers have been widely reported in recent years and attempts have been made to relate them to channel morphology bedload transport and channel morphology were measured in a small scale generic model of braided gravel bed streams two experiments are described in which braided channels developed in a 14 m 3 m sand tray total bedload output from the tray was weighed every 15 minutes stream bed geometry was surveyed every four hours pulses were observed in the bedload output time series and were qualitatively related to the channel morphology immediately upstream of the measuring section the bagnold 1980 bedload equation generally overpredicts measured bedload transport rates when applied to channels that were in equilibrium or aggrading underprediction occurred when applied to degrading channels aggradation was associated with channel multiplication and bar deposition channel pattern simplification occurred when degradation took place and bars emerged from the water flow development of phases of aggradation and degradation is dependent upon the three dimensional geometry of the stream beds spatial and temporal feedback loops can be identified enabling links between channel morphology and bedload transport rate to be directly identified

splitting rivers at their seams bifurcations and avulsion river bifurcations are critical but poorly understood elements of many geomorphological systems they are integralelements of alluvial fans braided rivers fluvial lowland plains and deltas and control the partitioning of water and sediment throughthese systems bifurcations are commonly unstable but their lifespan varies greatly in braided rivers bars and channels migrate splitand merge at annual or shorter timescales thereby creating and abandoning bifurcations this behaviour has been studied mainly bygeomorphologists and fluid dynamicists bifurcations also exist during avulsion the process of a river changing course on afloodplain or in a delta which may take 102 103years and has been studied mainly by sedimentologists this review synthesizesour current understanding of bifurcations and brings together insights from different research communities and different environmen tal settings we consider the causes and initiation of bifurcations and avulsion the physical mechanisms controlling bifurcation andavulsion evolution mathematical and numerical modelling of these processes and the possibility of stable bifurcations we end thereview with some open questions copyright 2012 john wiley sons ltd

recent glacier retreat in the caucasus mountains russia and associated increase in supraglacial debris cover and supra proglacial lake development this paper reports changes in supraglacial debris cover and supra proglacial lake development associated with recent glacier retreat 1985 2000 in the central caucasus mountains russia satellite imagery landsat tm and etm was used to map the surface area and supraglacial debris cover on six neighbouring glaciers in the adylsu valley through a process of manual digitizing on a false colour composite of bands 5 4 3 red green blue the distribution and surface area of supraglacial and proglacial lakes was digitized for a larger area which extended to the whole landsat scene we also compare our satellite interpretations to field observations in the adylsu valley supraglacial debris cover ranges from 25 on individual glaciers but glacier retreat between 1985 and 2000 resulted in a 3 6 increase in the proportion of each glacier covered by debris the only exception to this trend was a very small glacier where debris cover did not change significantly and remote mapping proved more difficult the increase in debris cover is characterized by a progressive up glacier migration which we suggest is being driven by focused ablation and therefore glacier thinning at the up glacier limit of the debris cover resulting in the progressive exposure of englacial debris glacier retreat has also been accompanied by an increase in the number of proglacial and supraglacial lakes in our study area from 16 in 1985 to 24 in 2000 representing a 57 increase in their cumulative surface area these lakes appear to be impounded by relatively recently lateral and terminal moraines and by debris deposits on the surface of the glacier the changes in glacier surface characteristics reported here are likely to exert a profound influence on glacier mass balance and their future response to climate change they may also increase the likelihood of glacier related hazards lake outbursts debris slides and future monitoring is recommended

length scale of braided river morphology 1 pool bar topography in single channel rivers has a length scale proportional to channel width in braided rivers confluence bifurcation units are analogous to pool bar morphology and in some cases develop from initial alternate bars consequently confluence bifurcation units are expected to have length that scales with the central anabranch width and that constitutes a basic length scale braided channel morphology this idea was tested using measurements from a physical model of a gravel bed braided river and from aerial photographs of braided rivers length distance from confluence to bifurcation anabranch width and confluence angle of confluence bifurcation units were measured a simple length scaling is evident across the range of scales confluence bifurcation length is 4 5 times the channel width this scaling is a fundamental element of braided river morphology and suggests that braided patterns are created by processes and have morphological regularity similar to pool bar units of low sinuosity single thread rivers

sector collapse forming at casita volcano nicaragua catastrophic sector collapse occurs when a volcano becomes structurally unable to support its own load one process particularly capable of weakening the edifice is hydrothermal activity it can produce high pore pressures and alter strong rock to clays alteration can extend progressively over long periods 100 yr allowing deformation to develop slowly before collapse an important finding is that structures produced by such deformation are recognizable and could permit collapse prediction we present the case of casita nicaragua where hydrothermal activity has been weakening the edifice core causing flank spreading altering original constructional shape and steepening flank slopes one side is slumping outward producing a crescentic scar with a basal bulge we identify this feature as the site of a potential sector collapse with conditions ripe for failure

depositional and erosional architectures of gravelly braid bar formed by a flood in the abe river central japan inferred from a three dimensional ground penetrating radar analysis abstract we conducted a ground penetrating radar gpr survey of gravelly braid bars in the abe river central japan to clarify the three dimensional 3d variations in their depositional facies under various geomorphologic conditions in september 2011 a ten year return period flood in the study area reworked and deposited braid bars after the flood we surveyed three bars with different geomorphologies using a gpr system with a 250 mhz antenna and identified seven fundamental radar depositional facies inclined reflections facies ia and ib horizontal to subhorizontal reflections facies iia and iib discontinuous reflections facies iiia and iiib and facies assemblage with a large scale channel shaped lower boundary facies iv combinations of these facies in dicate bar formation processes channel filling lateral aggradation and lateral and downstream accretion in the abe river aerial photographs and airborne laser scanning data were obtained before and after the flood the observed changes of the surface topography are consistent with the subsurface results seen in the gpr sections this study demonstrated that the erosional and depositional architecture observed among bars with different channel styles was related to river width and represented depositional processes for high sediment discharge the quantitative characterizations of the sedimentary architecture will be useful for interpreting gravelly fluvial deposits in the rock record

rift zone reorganization through flank instability in ocean island volcanoes an example from tenerife canary islands the relationship between rift zones and flank instability in ocean island volcanoes is often inferred but rarely documented our field data aerial image analysis and 40ar 39ar chronology from anaga basaltic shield volcano on tenerife canary islands support a rift zone flank instability relationship a single rift zone dominated the early stage of the anaga edifice 6 4 5 ma destabilization of the northern sector led to partial seaward collapse at about 4 5 ma resulting in a giant landslide the remnant highly fractured northern flank is part of the destabilized sector a curved rift zone developed within and around this unstable sector between 4 5 and 3 5 ma induced by the dilatation of the curved rift a further rift arm developed to the south generating a three armed rift system this evolutionary sequence is supported by elastic dislocation models that illustrate how a curved rift zone accelerates flank instability on one side of a rift and facilitates dike intrusions on the opposite side our study demonstrates a feedback relationship between flank instability and intrusive development a scenario probably common in ocean island volcanoes we therefore propose that ocean island rift zones represent geologically unsteady structures that migrate and reorganize in response to volcano flank instability

glacial cover mapping 1987 1996 of the cordillera blanca peru using satellite imagery multitemporal glacier area mapping is a key element in accurately determining fresh water reserves as well as providing an indicator of climate change in peru the first glacier inventory was based on visual interpretation of aerial photos requiring several years of effort landsat thematic mapper satellite imagery on the other hand provides an increasingly employed alternative for the monitoring of changes in glacier area and in other glaciological parameters by means of normalized difference snow index ndsi computations on tm images an estimate of the glacierized area in cordillera blanca peru was carried out for 1987 643 63 km2 and 1996 600 61 km2 compared to an estimate of 721 km2 in 1970 it can be concluded that the glacier area has retreated in this massif by more than 15 in 25 years

transport and emplacement mechanisms of large volcanic debris avalanches evidence from the northwest sector of cantal volcano france abstract large volcanic debris avalanche vda deposits of miocene age occur within the stratigraphic sequence of cantal stratovolcano central france the vda of cantal volcano were initiated by sector collapse of a cone of high elevation up to 4500 m a s l two distinct superimposed vda deposit units breccias i and ii resulted from at least two successive large scale collapse events during the evolution of the volcanic complex breccia i the oldest one is very thick up to 200 m and heterolithologic it is overlain by breccia ii which is thinner up to 50 m and contains more heterometric clasts ranging from hectometer to millimeter size the vda deposits are poorly sorted clasts are angular and highly fractured at different scales often with jigsaw fit in breccia ii jigsaw megaclasts have usually subspheric shapes with size decreasing distally basal deposits commonly display thin inversely graded layers reorientated clasts along ramp structures and cataclasis of the substratum some units have a distal fabric in the form of a poorly developed clast imbrication the clasts are commonly sub rounded thereby indicating abrasion during viscous flow anisotropy of magnetic susceptibility a m s measurements indicate absence of a preferentially oriented matrix fabric magnetic foliation parallel to the bedding suggests that the depositional process is dominated by particle settling the magnetic fabric is better organized in distal deposits where magnetic carriers are imbricated moreover the fragmented clasts and megaclasts are not abraded rather inflation led to isotropic spherical dispersion of clastic material isotropic dispersive inflation which fed the interclast matrix this is also confirmed by the lack of rotation at the individual crystal level all these data strongly suggest transport of vda by liquified non turbulent granular flows distally imbricated deposits suggest more turbulent flow emplacement of the vda results from progressive upward aggradation of the particles by volume reduction and deflation loss the non turbulent liquified stage of the vda disappears the vda behaves as a sliding rigid mass plug flow that exerts strong friction on the basement leading to gouge formation

life of a bifurcation in a gravel bed braided river channel bifurcation is a key element in braided rivers determining the water and sediment distribution and hence controlling the morphological evolution recent theoretical and experimental findings as well as field observations showed that bifurcations in gravel bed braided rivers are often asymmetrical and highly unstable in this paper field data are presented on a bifurcation in the tagliamento river northeast italy the planform configuration of the bifurcation and its temporal evolution was monitored by an automatic digital camera during a series of seven floods with different magnitudes this remote sensing technique allowed a high temporal resolution pictures were acquired every hour that was proved to be essential in a highly dynamic system as the one considered here digitized maps of the channels provided information on the location of the bifurcation the width of the anabranches the angle between them along with the occurrence and migration of sediment bars data were acquired at two different water levels giving the possibility to compare low and high flow conditions the monitored bifurcation is largely unstable and shows sudden changes in the water distribution mainly driven by the bar migrating in the upstream channel and entering the distributaries a relationship between width asymmetry and flood magnitude was observed confirming previous analyses moreover recent theoretical findings were applied in order to test the possibility to estimate general trends in bifurcation evolution the analysis pointed out the relevance of a correct assessment of the characteristic temporal scales as the bifurcation evolves on a timescale similar to that of bar migration and flood duration understanding the interactions between these processes is therefore crucial in order to increase the ability to model and predict the morphological evolution of a braided network copyright 2012 john wiley sons ltd

measurements in a braided river chute and lobe 2 sorting of bed load during entrainment transport and deposition grain size distributions of bed material bed load and bar head deposition were sampled during the evolution of a chute and lobe in the braided gravel bed sunwapta river alberta although bed shear stress and total bed load transport rate varied substantially within the reach and from day to day ferguson et al this issue the median diameter d50 of bed load was remarkably constant the bed initially fined from chute to bar head but became more uniform sediment deposited on the bar head also had a near constant d50 similar to that of the bed load truncated at the same lower size limit both load and deposition were finer on average than the bed suggesting overall selective transport despite little sign of local sorting in contrast to median diameters maximum sizes dmax of sediment in motion and deposited on the bar head varied substantially and showed a weak but significant dependence on shear stress inferring selective entrainment from this evidence alone would be dubious because dmax was also found to increase systematically with the mass of sediment sampled however two different methods of analysis of fractional transport rates throughout the size range also showed size selective entrainment and transport in the marginal transport conditions of this study size sorting appears to occur but only weakly and mainly in the coarser fractions

experimental and numerical findings on the long term evolution of migrating alternate bars in alluvial channels migrating alternate bars form in alluvial channels as a result of morphodynamic instability extensive literature can be found on their origin and short term development but their long term evolution has been poorly studied so far in particular it is not clear whether migrating bars eventually reach a dynamic equilibrium as in previous studies bars were observed to elongate with time we studied the long term evolution of alternate bars by performing two independent long duration laboratory experiments and some numerical tests with a physics based depth averaged model in a straight flume with constant water flow and sediment recirculation migrating bars followed a cyclic variation they became gradually longer and higher for a while then quickly much shorter and lower in one case all migrating bars simultaneously vanished almost completely only to reform soon after at the same time steady bars two to three times as long progressively developed from upstream gradually suppressing the migrating bars we also observed simultaneous vanishing of migrating bars in an annular flume experiment this time at intervals of 6 8 d numerical simulations of long alluvial channels with constant flow rate and fixed banks show periodic vanishing of a few migrating bars at a time occurring at regular spacing under constant flow rates migrating bars appear as a transition phenomenon of alluvial channels having a cyclic character these observations however might hold only for certain morphodynamics conditions which should be further investigated

ductility in fault gouge from a normal fault system death valley california a mechanism for fault zone strengthening and relevance to paleoseismicity fault gouge along the badwater turtleback fault system displays abundant evidence for mesoscopic ductility as foliation isolated and or rotated inclusions and isoclinal folds fault gouge thicknesses also vary dramatically at the outcrop scale gouge thicknesses can range from 0 to 1 m and at the 100 m scale they can range from 0 to 5 m because these variations are closely associated with other ductility related features they probably also formed because of ductile flow ductile flow appears to locally strengthen the fault zone by severe attenuation of the gouge and by transport of inclusions where gouge pinches out to zero thickness hanging wall rock rests directly on footwall rock a condition that produces an overall stronger fault zone as well as stick slip behavior in laboratory tests transport of inclusions within the gouge zone may create local inclusion jams which may also have a strengthening effect the presence of these stronger portions of the fault zone may give indirect evidence for ancient seismicity on the fault

extracting a climate signal from 169 glacier records i constructed a temperature history for different parts of the world from 169 glacier length records using a first order theory of glacier dynamics i related changes in glacier length to changes in temperature the derived temperature histories are fully independent of proxy and instrumental data used in earlier reconstructions moderate global warming started in the middle of the 19th century the reconstructed warming in the first half of the 20th century is 0 5 kelvin this warming was notably coherent over the globe the warming signals from glaciers at low and high elevations appear to be very similar

empirical relationship between river slope and the elongation of bars in braided rivers a potential tool for paleoslope analysis from subsurface data abstract paleoslope of ancient river systems is a fundamental parameter needed to reconstruct paleohydrology and paleoclimate from the fluvial sedimentary record the shape of braid bars in 22 modern rivers yields a relationship between average bar elongation length width and river slope steep rivers display more elongated bars than gently dipping reaches this relationship has potential application to ancient braided systems preserved in the subsurface and imaged by 3d seismic data the average elongation of bars identified on a stratal slice through the dagang river deposits in north east china yields a slope prediction which combined with empirical data on grain size and slope of alluvial rivers predicts a median grain size of between 0 1 and 1 mm for the considered river sediment in agreement with grain size data in an adjacent isochronous belt this study provides an additional approach for paleohydraulics in sedimentary basins and grain size prediction in exploration

morphology and evolution of bars in a wandering gravel bed river lower fraser river british columbia canada a hierarchical typology for the channels and bars within aggradational wandering gravel bed rivers is developed from an examination of a 50 km reach of lower fraser river british columbia canada unit bars built by stacking of gravelly bedload sheets are the key dynamic element of the sediment transfer system linking sediment transport during individual freshets to the creation development and remoulding of compound bar platforms that have either a lateral or medial style primary and secondary unit bars are identified respectively as those that deliver sediment to compound bars from the principal channel and those that redistribute sediment across the compound bar via seasonal anabranches and smaller channels the record of bar accretion evident in ground penetrating radar sequences is consistent with the long term development of bar complexes derived from historical aerial photographs for two compound bars inter annual changes associated with individual sediment transport episodes are measured using detailed topographic surveys and longer term changes are quantified using sediment budgets derived for individual bars from periodic channel surveys annual sediment turnover on the bars is comparable with the bed material transfer rate along the channel indicating that relatively little bed material bypasses the bars bar construction and change are mainly accomplished by lateral accretion since the river has limited capacity to raise bed load onto higher surfaces styles of accretion and erosion and therefore the major bar form morphologies on fraser river are familiar and consistent with those in gravelly braided channels but the wandering style does exhibit some distinctive features for example 65 year histories reveal the potential for long sequences of uninterrupted accretion in relatively stable wandering rivers that are unlikely in braided rivers

quantification of erosion patterns in the brahmaputra jamuna river using geographical information system and remote sensing techniques there is significant evidence of frequent and rapid erosion and fast rates of bank line retreat along the river brahmaputra jamuna within bangladesh this study is aimed at quantifying the actual rates of bank erosion along the river based on time series analysis of satellite images and historical maps analysis shows that the erosion rates in the brahmaputra jamuna river were 160 m year 1 between 1973 and 1992 indicating the severity of erosion hazard along the river this study also revealed the fact that the river has migrated westwards at an average movement rate of 50 m year 1 during the period of 1830 1992 in 1830 the river had an average width of 6 2 km but by 1992 the average width had increased to 10 6 km the channel has widened at an average rate of 27 m year 1 during 1830 1914 after that it has widened at an average rate of 65 m year 1 the average width of the river has increased about 130 m year 1 since 1973 analysis of the landsat images shows that over the whole river riverine islands most often persist from 1 to 7 years but 30 have lasted for 14 years or more accretion has taken place in the middle and lower reaches north of the east bank and in the extreme north of the west bank between 1973 and 1992 the rate of accretion is not comparable with the rate of bank erosion of the brahmaputra jamuna river

rifting recurrent landsliding and miocene structural reorganization on nw tenerife canary islands we studied mechanisms of structural destabilization of ocean island flanks by considering the linkage between volcano construction and volcano destruction exemplified by the composite teno shield volcano on tenerife canary islands during growth tenerife episodically experienced giant landslides genetically associated with rifting and preferentially located between two arms of a three armed rift system the deeply eroded late miocene teno massif allows insights into the rifting processes the failure mechanisms and related structures the semicircular geometry of palaeo scarps and fracture systems breccia deposits and the local dike swarm reconfigurations delineate two clear landslide scarp regions following an earlier collapse of the older los gigantes formation to the north the rocks around the scarp became fractured and intruded by dikes substantial lava infill and enduring dike emplacement increased the load on the weak scarp and forced the flank to creep again finally resulting in the collapse of the younger carrizales formation once more the changing stress field caused deformation of the nearby rocks a fracture belt formed around the scarp and dikes intruded into new concentric directions the outline size and direction of the second failed flank of teno very much resembles the first collapse we suggest structural clues concerning mechanisms of recurrent volcano flank failure verifying the concept that volcano flanks that have failed are prone to collapse again with similar dimensions

deformation structures associated with the tazo landslide la gomera canary islands deformation structures below the basal plane of gravitational slides can provide useful information about the state of stress undergone by rocks prior to the sliding process and about the triggering forces acting at each particular sliding event in the present work we conducted a structural analysis of the rocks below the surface of the gravitational slide of tazo la gomera canary islands and determined the epigenetic processes involved in the filling of the amphitheatre we also inferred the possible triggering phenomena related to the tazo landslide the rocks located below the surface of the gravitational slide of tazo i e the basaltic lava flows sills and dikes of the lower old edifice and the submarine volcanic rocks gabbros pyroxenites and dikes of the basal complex of la gomera are strongly deformed close to this sliding surface the lava flows and dikes of the lower old edifice are folded with fault breccias and gouges and locally foliated defining the sliding surface the dikes of the basal complex are also folded and the gabbros and pyroxenites are affected by a large number of small faults in the basal complex the sliding surface is defined by a foliated granular gouge in the damage zone the basal complex rocks show an incipient fracture cleavage the sliding amphitheatre has been filled by the debris avalanche or cohesive debris flow generated within the slide as well as by later debris flows hyperconcentrated flows sheet flows and by interspersed lava flows from the upper old edifice we suggest here that the collapse of the north western flank of the lower old edifice at tazo could in part have been triggered by continuous magma injection associated with the emplacement of dikes in a rift zone with an ene wsw direction enhanced by the mechanical weakness of the basal complex unit which was affected by hydrothermal metamorphism under greenschist facies conditions and by the displacement along the montana de alcala and guillama normal faults which are deeply entrenched in the altered rocks of the basal complex

estimation of debris cover and its temporal variation using optical satellite sensor data a case study in chenab basin himalaya debris cover over glaciers greatly affects their rate of ablation and is a sensitive indicator of glacier health this study focuses on estimation of debris cover over samudratapu glacier chenab basin himalaya using optical remote sensing data remote sensing image data of irs 1c liss iii september 2001 irs p6 awifs september 2004 and terra aster september 2004 along with survey of india topographical maps 1963 were used in the study supervised classification of topographically corrected reflectance image data was systematically conducted to map six land cover classes in the glacier terrain snow ice mixed ice and debris debris valley rock and water an accuracy assessment of the classification was conducted using the aster visible near infrared data as the reference the overall accuracies of the glacier cover maps were found to range from 83 7 to 89 1 whereas the individual class accuracy of debris cover mapping was found to range from 82 to 95 this shows that supervised classification of topographically corrected reflectance data is effective for the extraction of debris cover in addition a comparative study of glacier cover maps generated from remote sensing data supervised classification of september 2001 and september 2004 and survey of india topographical maps 1963 has highlighted the trends of glacier depletion and recession the glacier snout receded by about 756 m from 1963 to 2004 and the total glacier area was reduced by 13 7 km 2 from 110 km 2 in 1963 further glacier retreat is found to be accompanied by a decrease in mixed ice and debris and a marked increase in debris cover area the area covered by valley rock is found to increase confirming an overall decrease in the glacier area the results from this study demonstrate the applicability of optical remote sensing data in monitoring glacier terrain and particularly mapping debris cover area

dynamics of 30 large channel bars in the lower mississippi river in response to river engineering from 1985 to 2015 abstract channel bars are a major depositional feature in alluvial rivers and their morphodynamics has been investigated intensively in the past several decades however relatively less is known about how channel bars in alluvial rivers respond to river engineering and regulations in this study we assessed 30 yr morphologic changes of 30 large emerged bars located in a 223 km reach of the highly regulated lower mississippi river from vicksburg mississippi to the mississippi atchafalaya river diversion landsat imagery and river stage data between 1985 and 2015 were utilized to characterize bar morphologic features and quantify decadal changes based on bar surface areas estimated with the satellite images at different river stages a rating curve was developed for each of the 30 bars to determine their volumes results from this study show that the highly regulated river reach favored the growth of mid channel and attached bars while more than half of the point bars showed degradation currently the mid channel and attached bars accounted for 38 and 34 of the total volume of the 30 bars the average volume of a single mid channel bar is over two times that of an attached bar and over four times that of a point bar overall in the past three decades the total volume of the studied 30 bars increased by 110 118 000 m 3 41 total dike length in a dike field was found mostly contributing to the bar volume increase currently the emerged volume of the 30 bars was estimated approximately 378 183 000 m 3 the total bar volume is equivalent to 530 million metric tons of coarse sand based on an average measured bulk density of 1 4 t m 3 for the bar sediment the findings show that these bars are large sediment reservoirs

assessing linkages between spatial facies changes and dimensional variations of glaciers in the upper indus basin western himalaya abstract the present study provides an insight into the heterogeneous response of 45 glaciers in the lidder and sindh river basins western himalaya and explores the linkages between glacier facies variability and changing glacier parameters results show that the region has undergone an overall deglaciation of 12 1 5 11 9 1 4 km 2 from 1996 to 2014 fluctuations in the temperature and precipitation patterns seem to be the primary factor controlling the changes in glacier dimensions r 2 0 82 in all cases glacier facies changes suggest depletion in snow ice cover 18 2 3 and an increase in ice mixed debris 4 1 4 supraglacial debris 6 1 5 and periglacial debris 17 1 2 these glacier facies transitions are possibly the result of ice melting however its relative rate and elevation decides the nature of facies conversion an increase in the proportion of supraglacial debris has led to the conversion of 11 clean glaciers to sparsely debris covered glaciers and 5 sparsely debris covered glaciers to debris covered glaciers the size of the glaciers greatly influenced the rate of conversion of glaciers and glaciers 2 dominated the others in this regard the small glaciers also experienced maximum shrinkage further the glaciers with varying supraglacial debris cover respond differently as sparsely debris covered glaciers exhibit the highest rates of retreat 25 7 3 m y followed by clean 23 7 7 3 m y and debris covered glaciers 13 1 7 3 m y thus the findings of this work clearly show that the climate change driven dimensional changes of glaciers and variations in the spatial distribution of glacier facies have strong mutual control on each other

braid scale channel geometry changes in a sand bedded river significance of low stages abstract this study focuses on the importance of different stages of bed formation and transportation processes along the partly managed lowland section of maros river south hungary the role of different stages was determined applying a series of cross sectional data besides major morphological zones of over widened braided sections were defined along with their role and function in sediment storage and transport processes during the rising stage of floods a great volume of sediment is eroded from and transported through the cross sections on the falling stage accumulation will be the dominant process however concerning the total amount of sediment deposited during falling stages braids store overwhelmingly more than straight narrow reaches during long lasting low stage periods the cross sectional area increases which means net erosion and an increase in mean depth therefore braids have a significant role in falling stage sediment storage and low stage release nevertheless the location of accumulation within braids is different influenced by their structure in braids which are characterised by islands the sediment is deposited at their upstream end islands create a transportation zone towards the downstream end of the braid by increasing stream power over widened sections without islands are more likely to experience deposition at their downstream end constant narrowing of the studied reach was also observed braids on unmanaged reaches proved to be the most prominent places in this sense changes in the regime of the river and altered land use help to explain this process as the frequency of floods has decreased while the length of extreme low stages has increased therefore the need for the sediment storing and releasing function of braids is less necessary which leads to their narrowing

combining satellite multispectral image data and a digital elevation model for mapping debris covered glaciers automated glacier mapping from satellite multispectral image data is hampered by debris cover on glacier surfaces supraglacial debris exhibits the same spectral properties as lateral and terminal moraines fluvioglacial deposits and bedrock outside the glacier margin and is thus not detectable by means of multispectral classification alone based on the observation of low slope angles for debris covered glacier tongues we developed a multisource method for mapping supraglacial debris the method combines the advantages of automated multispectral classification for clean glacier ice and vegetation with slope information derived from a digital elevation model dem neighbourhood analysis and change detection is applied for further improvement of the resulting glacier debris map a significant percentage of the processing can be done automatically in order to test the sensitivity of our method against different dem qualities it was also applied to a dem obtained from aster stereo data additionally we compared our multisource approach to an artificial neural network ann classification of debris using only multispectral data while the combination with an aster derived dem revealed promising results the ann classification without dem data does not

detecting himalayan glacial lake outburst floods from landsat time series abstract several thousands of moraine dammed and supraglacial lakes spread over the hindu kush himalayan hkh region and some have grown rapidly in past decades due to glacier retreat the sudden emptying of these lakes releases large volumes of water and sediment in destructive glacial lake outburst floods glofs one of the most publicised natural hazards to the rapidly growing himalayan population despite the growing number and size of glacial lakes the frequency of documented glofs is remarkably constant we explore this possible reporting bias and offer a new processing chain for establishing a more complete himalayan glof inventory we make use of the full seasonal archive of landsat images between 1988 and 2016 and track automatically where glofs left shrinking water bodies and tails of sediment at high elevations we trained a random forest classifier to generate fuzzy land cover maps for 2491 images achieving overall accuracies of 91 we developed a likelihood based change point technique to estimate the timing of glofs at the pixel scale our method objectively detected ten out of eleven documented glofs and another ten lakes that gave rise to previously unreported glofs we thus nearly doubled the existing glof record for a study area covering 10 of the hkh region remaining challenges for automatically detecting glofs include image insufficiently accurate co registration misclassifications in the land cover maps and image noise from clouds shadows or ice yet our processing chain is robust and has the potential for being applied on the greater hkh and mountain ranges elsewhere opening the door for objectively expanding the knowledge base on glof activity over the past three decades

glacial geomorphology and recent glacial recession of the harmukh range nw himalaya abstract a comprehensive description of the glaciation and glacial geomorphology of the harmukh range northwest himalaya is reported first time in this study the geomorphic system of the range is dominated by glaciation and provides an excellent opportunity to assess the glacial fluctuations from the late quaternary to the present using a time series of the satellite data from 1992 to 2018 the glacier area snout and equilibrium line altitude ela changes of the existing glaciers in the harmukh range were estimated the glacier cover has receded from 7 47 0 58 km2 in 1992 to 6 24 0 62 km2 in 2018 a deglaciation of 16 46 0 24 the glaciers showed an upward shift in ela from 47 m to 80 m during the last two and a half decade the observations revealed that other than the climatic factors the ela change and glacier recessions are influenced by the glacier size mean altitude and the aspect of the glaciers further the high resolution google earth images supplemented by field observations were used for mapping various glacial geomorphic landforms the nature of glacial grooves overdeepenings the height of the lateral moraine deposits and trimlines indicated appreciable thickness of the former glaciers the pattern of the glaciated valleys revealed that the area has predominantly experienced alpine type of glaciation with most of the glaciers centred on the harmukh peak based on the shape and the number of lateral moraine ridges present it is suggested that the area has witnessed three major glacial advances by tracing the outer limits of the glacial valleys moraine boulders and ice scoured terrain it was estimated that the glaciers in the range covered 629 km2 during the glacial maxima the presence of numerous rock glaciers and debris free cirque glaciers on the north eastern slopes of the range indicated a strong climatic and topographical control on the pattern situation and extent of glaciers however there is a need for detailed field based mapping of the glacial geomorphology and geochronological study in order to better understand the nature and extent of paleo glaciation the observed glacier recession and the past climatic variations in this hitherto understudied glaciated region of the kashmir himalaya

spectral signature of alpine snow cover from the landsat thematic mapper mapping of snow and estimation of snow characteristics from satellite remote sensing data require that we distinguish snow from other surface cover and from clouds and compensate for the effects of the atmosphere and rugged terrain the spectral signature of the snowpack is calculated from a radiative transfer model accounting for scattering and absorption by the ice grains water inclusions and particulates in interpreting the spectral reflectance measured from the thematic mapper or from any other satellite we need to account for topographic effects without requiring that satellite data be precisely registered to digital elevation data because the poor quality of most digital elevation data introduces considerable noise into calculations of slope and azimuth for a range of snow types atmospheric profiles and topographic illumination conditions i estimate typical spectral signatures for the landsat thematic mapper tm images of the southern sierra nevada are analyzed to distinguish several classes of snow from other surface covers snow can be reliably distinguished from other surfaces and from clouds at all sun angles encountered in the mid latitudes in tm band 1 or 2 snow is brighter than other natural surfaces and in band 5 clouds are usually much more reflective than snow therefore the intersection of the following criteria maps the snow cover planetary reflectance rp in tm band 1 is greater than about 0 16 rp tm5 is less than about 0 2 the normalized band 2 5 difference rp tm2 rp tm5 rp tm2 rp tm5 is greater than about 0 4 large surface grain sizes can be distinguished from areas where the grain size is finer at the snow surface using tm bands 2 4 and 5 because of saturation in tm band 1 estimation of the degree of contamination by absorbing aerosols is not feasible rp tm2 rp tm5 rp tm2 rp tm5 is

dynamics of nonmigrating mid channel bar and superimposed dunes in a sandy gravelly river loire river france abstract a field study was carried out to investigate the dynamics during floods of a nonmigrating mid channel bar of the loire river france forced by a riffle and renewed by fluvial management works interactions between the bar and superimposed dunes developed from an initial flat bed were analyzed during floods using frequent mono and multibeam echosoundings acoustic doppler profiler measurements and sediment grain size analysis when water left the bar terrestrial laser scanning and sediment sampling documented the effect of post flood sediment reworking during floods a significant bar front elongation spreading on margins and swelling was shown whereas a stable area no significant changes was present close to the riffle during low flows and falling limbs of floods intense sediment reworking on the top of the bar and lateral scouring occurred hydrological variations controlled the sediment supply in terms of phasing quantity and grain size delivered by surrounding channels during floods and thus superimposed dune development their development was also linked to the sediment availability armor layers riffle proximity their relatively constant height highlights a preferential adaptation on dune length during floods the role of each morphological forcing parameters riffle vs channel widening and curvature on the bar dynamics and evolution is stage dependent the shape dynamics and long term morphological evolution of the bar and of the river reach surrounding islands channel translation mainly depends on the presence of the natural riffle

assessing ice cliff backwasting and its contribution to total ablation of debris covered miage glacier mont blanc massif italy continuous surface debris cover strongly reduces the ablation of glaciers but high melt rates may occur at ice cliffs that are too steep to hold debris this study assesses the contribution of ice cliff backwasting to total ablation of miage glacier mont blanc massif italy in 2010 and 2011 based on field measurements physical melt models and mapping of ice cliffs using a high resolution 1 m digital elevation model dem short term model calculations closely match the measured melt rates a model sensitivity analysis indicates that the effects of cliff slope and albedo are more important for ablation than enhanced longwave incidence from sun warmed debris or reduced turbulent fluxes at sheltered cliff bases analysis of the dem indicates that ice cliffs account for at most 1 3 of the 1 m pixels in the glacier s debris covered zone but application of a distributed model indicates that ice cliffs account for 7 4 of total ablation we conclude that ice cliffs make an important contribution to the ablation of debris covered glaciers even when their spatial extent is very small

automated mapping of montane snow cover at subpixel resolution from the landsat thematic mapper a fully automated method uses landsat thematic mapper data to map snow cover in the sierra nevada and make quantitative estimates of the fractional snow covered area within each pixel we model winter and spring reference scenes as linear mixtures of image end member spectra to produce the response variables for tree based regression and classification models decision trees identify cloud cover and fractional snow covered area we test the algorithm on a different thematic mapper scene and verify with high resolution large format color aerial photography the accuracy of the automated classification of thematic mapper data equals that obtainable from the aerial photographs but is faster cheaper and covers a vastly larger area the mapping method is insensitive to the choice of lithologic or vegetation end members the water equivalent of the snow pack snow grain size or local illumination angle

the problem of hidden ice in glacier mapping lee can become hidden i e buried by the superimposition of rock debris on a glacier or where rock debris may incorporate interstitial ice because it is obscured problems result from a lack of understanding of the extent and continued activity of such ice landforms may be associated with this phenomenon and can be used as indirect evidence of its existence a rock glacier can contain glacially derived buried ice as well as interstitial ice we show with examples how such rock glaciers can be identified and provide information on the extent and possible volume of hidden ice in marginally glacierized and permafrost areas in most cases recognition of topography is sufficient although time separated aerial photographs may be necessary to locate the extent of ice these are generally preferable to and more cost effective than most detailed on site determinations of ice extent it is possible to incorporate and extend knowledge of hidden ice in glacier mapping and inventory projects

using atmospherically corrected landsat imagery to measure glacier area change in the cordillera blanca peru from 1987 to 2010 abstract the dynamic tropical glaciers of the peruvian cordillera blanca are rapidly changing and these changes are expected to affect water availability especially during the dry season in this study we quantify recent changes to these water reservoirs providing estimates of glacier area in the cordillera blanca and sub watersheds of the rio santa for the following years 1987 1996 2004 and 2010 we explore the effects of atmospheric and topographic corrections by comparing debris free glacier area estimates generated using raw scenes and corrected scenes our results suggest that these corrections can have a significant impact on debris free glacier area estimates when the same threshold is applied debris free glacier area estimates derived from uncorrected scenes are approximately 5 less than debris free glacier area estimates derived from atmospherically corrected scenes we determined that debris free glacier area estimates are most sensitive to the choice of threshold and topographic effects to map glacier area change we used high resolution satellite imagery to calibrate our selection of a single threshold for the normalized difference snow index ndsi this threshold value was applied to all ndsi images which were derived from four carefully selected and atmospherically corrected landsat thematic mapper tm scenes acquired at the end of the dry season in order to calculate total glacier area we manually mapped debris covered glaciers because automated methods were unsuccessful in this region as of august 2010 the cordillera blanca had a total glacier area of 482 km 2 which amounts to a 25 decrease since 1987 glaciers in the southern portions of the cordillera blanca which have lower median elevations on average lost a greater percentage of their area from 1987 to 2010 relative to their northern counterparts overall glacier area change in the cordillera blanca appears to be accelerating between 2004 and 2010 glaciers in the cordillera blanca lost area at a rate that was approximately 3 5 times the average rate of area loss from 1970 to 2003

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

reflectances of glaciers as calculated using landsat 5 thematic mapper data landsat 5 thematic mapper tm data have been used in previous work in order to locate zones of similar spectral reflectance on glaciers in austria and alaska and to relate these zones to the glacier facies which are indicative of glacier mass balance in this paper landsat 5 digital numbers dns have been used to compute the at satellite planetary reflectances p on spectrally similar zones on the meares and schwanda glaciers in alaska and the grossglockner glacier group in austria the patterns of tm derived reflectances in the ablation areas of the grossglockner glacier group and the meares glacier compare favorably with published reflectance curves measured on the surface of glacier ice though the surface reflectance of snow covered ice is higher than the landsat derived reflectance for the glaciers studied the accuracy of the at satellite planetary reflectances is shown to be affected by topographic and atmospheric effects and by the anisotropic nature of snow reflectance use of reflectance values for analysis of snow and ice facilitates scene to scene comparisons of glaciers

debris avalanche deposits of the milo lahar sequence and the opening of the valle del bove on etna volcano italy previously undescribed debris avalanche deposits occur in two locations downslope from the open end of the valle del bove these outcrops comprise unstratified ungraded deposits of metre scale lava blocks in a matrix of weathered and fractured lava clasts the avalanche deposits are unconformably overlain by matrix to clast supported conglomerates representing debris flow and interbedded fluvial deposits that constitute most of the milo lahar sequence we present evidence that the milo lahar sequence which crops out just at the exit of the valle del bove formed during the opening and enlargement of this depression the presence of the avalanche deposits at the base of the milo lahar sequence indicates that catastrophic landslides were involved in the formation of the valle del bove the composition of lavas in the debris avalanche deposits is similar to that of most of the ellittico volcanic sequence exposed along the northern wall of the valle del bove radiocarbon dates of 8400 and 5300 years bp from the base and top respectively of the debris flow sequence indicate that the milo lahars are correlative with the exposed part of the chiancone deposit the basal lahars of the chiancone which contain lava blocks whose compositions partially overlap that of blocks in the avalanche deposits may have formed by water concentration in the distal end of the avalanche causing transformation to debris or alternatively by reworking of the avalanche deposit

spreading and potential instability of teide volcano tenerife canary islands 1 we analyze the role of low strength materials in the potential structural instability related to volcano spreading at the active teide stratovolcano tenerife canary islands to study the low strength materials we took advantage of a network of large tunnels within the volcano excavated for water supply which allows the in situ inspection and reconstruction of both volcano and substratum structure we identified two factors which are potentially important to teide s instability 1 a dipping low strength substratum breccia layer and 2 a hydrothermally altered weak core inside the volcano despite we do not find clear structural evidence for volcano substratum spreading both teide topographic shape and the summit faulting are features similar to those accepted as examples of volcano flank spreading over a weak core the detected asymmetric deformation of the edifice makes the north flank of teide a strong candidate for a potential failure

alternate bars in a sandy gravel bed river generation migration and interactions with superimposed dunes a field study was carried out to investigate the development of alternate bars in a secondary channel of the loire river france as a function of discharge variations we combined frequent bathymetric surveys scour chains and stratigraphical analysis of deposits with measurements and modelling of flow dynamics the channel exhibited migrating bars non migrating bars and superimposed dunes possible mechanisms of bar initiation were found to be chutes associated with changes of bank direction and instability resulting from interactions between existing bars during the fall in water level after floods we propose that the reworking of bar sediments during low flows high width to depth ratio reinforced by high values of the shields mobility parameter can explain the formation or re generation of new alternate migrating bars during a subsequent flood the migration pattern of the bars was found to be cyclic and to depend mainly on i channel layout and ii the dynamics of superimposed dunes with heights and lengths depending on location and discharge value for instance the hysteresis affecting the steepness of dunes influences the flow resistance of the dunes as well as the celerity of migrating bars during flood events we compare the findings from the field with results from theoretical studies on alternate bars this gives insight in the phenomena occurring in the complex setting of real rivers but it also sheds light on the extent to which bar theories based on idealized cases can predict those phenomena copyright 2014 john wiley sons ltd

a super large landslide in tibet in 2000 background occurrence disaster and origin on april 9 2000 a super large landslide 3 x 10 8 m 3 occurred along zhamu creek southeast tibet as a result a landslide dam formed and the yigong river was blocked a channelized diversion was constructed for prevention of overtopping two months later on june 10 a catastrophic flood resulting from the failure of the landslide dam caused a serious loss of property this is the second of landslide occasion dam formation and flooding occurrence at the same site since 1900

volcano spreading controlled by dipping substrata most volcanoes grow on slopes and some tend to fail catastrophically on the downslope side many volcanoes also deform by volcano spreading which may lead to failure we look at the effect of dipping substrata on the potential for spreading and collapse with analogue models the dip is found to strongly control the spreading style rate and direction a distinct change from purely radial spreading occurs even with small 1 substrata tilt structures on the cone and surrounding area are modified according to the underlying dip direction spreading becomes concentrated on downslope sectors where movement is predominantly in the dip direction the degree of structural realignment is a function of the slope angle our models are applied to previously known and new examples of volcano spreading the effect of dipping substrata in confining spreading to sectors increases the potential for deep seated sector collapses this finding provides a mechanism for failure on the downslope side the incorporation of substrata can create very large volume collapses