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

modelling complex flood flow evolution in the middle yellow river basin china summary flood routing processes in the middle yellow river basin are complex since they consist of three types of flood bidirectional convergent and divergent flood flows between the main channel and its tributaries we propose three computation schemes to simulate the complex flood routing a simple scheme for a single main channel with no tributary or backwater an improved schemes for convergent or divergent flow at the confluence and an improved scheme for bidirectional flow the schemes are examined by analyzing seven historical flood events and three scenarios of flood routing in the middle yellow river basin the model was calibrated and validated based on the simulation of three different types of flood as compared with the observed hydrographs the results show that the model is able to simulate flood routing processes efficiently for the study river with nash sutcliffe indices falling in the range 0 75 0 91 the model demonstrates that flood routing during historical flood events 1962 2003 in the middle yellow river was altered under boundary condition changes the shape of the hydrographs changed from high and thin to low and wide which was accompanied by a delayed occurrence and extended duration of peak flow after the 1960s moreover these trends were intensified after the early 1980s backwater resulted from divergent flows and bidirectional flood flows an analysis of combined boundary conditions shows that flood wave volume has the strongest impact on flood duration peak discharge and water level the time of occurrence of peak discharge and the magnitude of backwater river bed slope has the second strongest impact on flood duration and the magnitude of backwater channel roughness has the second strongest impact on peak discharge and water level

orbital forcing of the martian polar layered deposits since the first images of polar regions on mars revealed alternating bright and dark layers there has been speculation that their formation might be tied to the planet s orbital climate forcing1 2 3 4 but uncertainties in the deposition timescale exceed two orders of magnitude estimates based on assumptions of dust deposition ice formation and sublimation and their variations with orbital forcing suggest a deposition rate of 10 3 to 10 2 cm yr 1 refs 5 6 whereas estimates based on cratering rate result in values as high as 0 1 to 0 2 cm yr 1 ref 7 here we use a combination of high resolution images of the polar layered terrains8 high resolution topography9 and revised calculations of the orbital and rotational parameters of mars to show that a correlation exists between ice layer radiance as a function of depth obtained from photometric data of the images of the layered terrains and the insolation variations in summer at the martian north pole similar to what has been shown for palaeoclimate studies of the earth10 11 12 for the best fit between the radiance profile and the simulated insolation parameters we obtain an average deposition rate of 0 05 cm yr 1 for the top 250 m of deposits on the ice cap of the north pole of mars

shuttle imaging radar b sir b weddell sea ice observations a comparison of sir b and scanning multichannel microwave radiometer ice concentrations the october 1984 shuttle imaging radar b sir b flight made three radar passes over the weddell sea ice providing the first high resolution look at the weddell marginal ice zone properties using these data this paper discusses the effect of ocean waves on the radar return at the ice edge and compares ice concentrations derived from the sir b with coincident concentrations from the nimbus 7 scanning multichannel microwave radiometer smmr the comparison of the sir and smmr concentrations is possible because sir cross track width and the diameter of the smmr 37 ghz integrated field of view are both about 30 km the sir ice concentrations are computed in two ways first using a training area classification scheme at the jet propulsion laboratory jpl second using a manual classification method at the scott polar research institute the smmr ice concentrations are calculated using the goddard space flight center algorithm at the ice edge where there were no coincident smmr data and where ice bands predominated to yield an ice concentration of the order of 10 or less comparison of the two different analysis techniques on the same images showed that for the jpl technique to avoid classifying some of the open water as ice two classes of open water must be defined these two classes accounted for the rougher ocean surface upwind of the bands and the smoother downwind surface in the ice interior comparison of the coincident sir and smmr ice concentrations shows that for concentrations greater than 40 which was the smallest concentration jointly observed the mean difference between the two data sets for 12 points is 2 and the standard deviation is 7

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

coupling glacial lake impact dam breach and flood processes a modeling perspective glacial lake outburst floods glofs are highly mobile mixtures of water and sediment that occur suddenly and are capable of traveling tens to hundreds of kilometers with peak discharges and volumes several orders of magnitude larger than those of normal floods they travel along existing river channels in some instances into populated downstream regions and thus pose a risk to people and infrastructure many recent events involve process chains such as mass movements impacting glacial lakes and triggering dam breaches with subsequent outburst floods a concern is that effects of climate change and associated increased instability of high mountain slopes may exacerbate such process chains and associated extreme flows modeling tools can be used to assess the hazard of potential future glofs and process modeling can provide insights into complex processes that are difficult to observe in nature a number of numerical models have been developed and applied to simulate different types of extreme flows but such modeling faces challenges stemming from a lack of process understanding and difficulties in measuring extreme flows for calibration purposes here we review the state of knowledge of key aspects of modeling glofs with a focus on process cascades analysis and simulation of the onset propagation and potential impact of glofs are based on illustrative case studies numerical models are presently available for simulating impact waves in lakes dam failures and flow propagation but have been used only to a limited extent for integrated simulations of process cascades we present a spectrum of case studies from patagonia the european alps central asia and the himalayas in which we simulate single processes and process chains of past and potential future events we conclude that process understanding and process chain modeling need to be strengthened and that research efforts should focus on a more integrative treatment of processes in numerical models

geomorphological impact and morphodynamic effects on flow conveyance of the 1999 jokulhlaup at solheimajokull iceland the 1999 jokulhlaup at solheimajokull was the first major flood to be routed through the proglacial system in over 600 years this study reconstructed the flood using hydrodynamic sediment transport and morphodynamic numerical modelling informed by field surveys aerial photograph and digital elevation model analysis total modelled sediment transport was 469 800 m3 20 maximum erosion of 8 2 m occurred along the ice margin modelled net landscape change was 86 400 m3 40 resulting from 275 400 m3 20 proglacial erosion and 194 400 m3 20 proglacial deposition peak erosion rate and peak deposition rate were 650 m3 s 1 20 and 595 m3 s 1 20 respectively and coincided with peak discharge of water at 1 5 h after flood initiation the pattern of bed elevation change during the rising limb suggested widespread activation of the bed whereas more organisation perhaps primitive bedform development occurred during the falling limb contrary to simplistic conceptual models deposition occurred on the rising stage and erosion occurred on the falling limb comparison of the morphodynamic results with a hydrodynamic simulation illustrated effects of sediment transport and bed elevation change on flow conveyance the morphodynamic model advanced flood arrival and peak discharge timings by 100 and 19 respectively however peak flow depth and peak flow velocity were not significantly affected we suggest that morphodynamic processes not only increase flow mass and momentum but that they also introduce a feedback process whereby flood conveyance becomes more efficient via erosion of minor bed protrusions and deposition that infills or subdues minor bed hollows a major implication of this study is that reconstructions of outburst floods that ignore sediment transport such as those used in interpretation of long term hydrological record and flood risk assessments may need considerable refinement copyright 2015 john wiley sons ltd

jokulhlaup deposits in proglacial areas abstract this paper discusses the main causes and characteristics of jokulhlaup glacier burst floods and explores the extent to which they generate depositional landform and sediment assemblages that are distinct from those of normal braided river outwash type i outwash two main jokulhlaup outwash environments are identified type ii outwash produced by sudden drainage of ice dammed lakes and type iii associated with drainage during subglacial geothermal activity and distinguished by deposits resulting from high sediment concentrations and hyperconcentrated flows in fluid flows especially ones yielding type ii outwash the most common deposits are large scale expansion bars and locally eddy and pendant bars and mega ripples or dunes both forms normally composed of large scale gravel cobble cross bedding often capped by an imbricated boulder lag a type b2 lithofacies sequence the armour is absent only where runoff decreased too rapidly to allow surface winnowing other jokulhlaup facies include extensive boulder beds type c inverse normally graded cobble beds type ds ice proximal debris flow deposits and deformed bedding containing diamicton clasts types g and h and slack water sediments type a type iii outwash is dominated by massive homogeneous flood surge granules underlain by pre surge gravels and capped by post surge fluid bedforms reflecting deposition during both the rising and falling limbs of the flood hydrograph type e4 the paper demonstrates that jokulhlaups do generate distinctive assemblages of depositional landforms and sediments and concludes with a model of the dominant lithofacies sequences and associated landforms in proglacial environments subject to jokulhlaup drainage

north polar region of mars topography of circumpolar deposits from mars orbiter laser altimeter mola data and evidence for asymmetric retreat of the polar cap we have used high resolution mars orbiter laser altimeter mola data to analyze the topography morphology stratigraphy and geologic history of the martian north circumpolar deposits the present polar deposits are offset about toward 0 w from the rotational pole an arc of irregular topography concentric to olympia planitia and the cap consists of polar material remnants depressions which we interpret to be kettles frost covered and residual ice filled craters and frost patches olympia planitia originally thought to be a flat sand covered plain is characterized by a convex upward topography contiguous with the polar cap we interpret olympia planitia to represent a now dune covered extension of the polar materials together olympia planitia and the outlying deposits delineate a former extent of the polar cap topographic data have clarified relationships among the circumpolar deposits contributors to these deposits include local volcanics fluvial and aqueous sediments from outflow channels and a possible standing body of water pyroclastic ash sublimation lag from the olympia lobe and eolian reworked materials significant events in the history of the region include 1 formation of the northern lowlands 2 emplacement of volcanic plains fluvial and aqueous sedimentation and subsequent desiccation forming polygonal patterns which in part underlie the present polar layered deposits 3 formation of the polar cap composed primarily of layered deposits 4 asymmetric retreat of the olympia lobe resulting in sublimation lag deposits polar remnants and kettles and 5 continued collection and reworking of sediments by eolian processes the cause of the asymmetrical retreat of the olympia lobe is unknown

on the icy edge at louth and korolev craters abstract the modern climate of mars has been well characterized from over a decade of orbiting spacecraft in situ measurements via landers rovers and theoretical advances in climate modeling nonetheless important questions remain unanswered including the present day mass balance of the north polar residual cap and its icy outliers exposed water ice mounds are found in craters and extend as far equatorward as 70 2 n due to their southerly location these ice mounds are likely more sensitive to ongoing changes in climate we analyze high resolution images of the louth crater ice mound and employ a coupled 1 d thermal and atmospheric model to estimate annual mass balance of both louth and korolev water ice we incorporate the effects of shallowly sloping surfaces and seasonally dependent water ice albedo no clear trend in the advance or retreat of louth crater water ice is observed in over 4 mars years of repeat high resolution images secular changes are either sufficiently small as to not be detected or the ice is in equilibrium modeled mass balance ranges from 6 to 2 mm of water ice per mars year at both sites with nominal cases being in near equilibrium

the formation and failure of natural dams of the numerous kinds of dams that form by natural processes dams formed from landslides glacial ice and late neoglacial moraines present the greatest threat to people and property landslide dams form in a wide range of physiographic settings the most common types of mass movements that form landslide dams are rock and debris avalanches rock and soil slumps and slides and mud debris and earth flows the most common initiation mechanisms for dam forming landslides are excessive rainfall and snowmelt and earthquakes landslide dams can be classified into six categories based on their relation with the valley floor type i dams 11 of 184 landslide dams from around the world that we were able to classify do not reach from one valley side to the other type ii dams 44 span the entire valley floor in some cases depositing material high on opposite valley sides type iii dams 41 move considerable distances both upstream and downstream from the landslide failure type iv dams 1 are rare and involve the contemporaneous failure of material from both sides of a valley type v dams 1 also are rare and are created when a single landslide sends multiple tongues of debris into a valley and forms two or more landslide dams in the same reach of river type vi dams 3 involve one or more failure surfaces that extend under the stream or valley and emerge on the opposite valley side many landslide dams fail shortly after formation in our sample of 73 documented landslide dam failures 27 of the landslide dams failed less than 1 day after formation and about 50 failed within 10 days over topping is by far the most common cause of failure the timing of failure and the magnitude of the resulting floods are controlled by dam size and geometry material characteristics of the blockage rate of inflow to the impoundment size and depth of the impoundment bedrock control of flow and engineering controls such as artificial spill ways diversions tunnels and planned breaching by blasting or conventional excavation glacial ice dams can produce at least nine kinds of ice dammed lakes the most dangerous are lakes formed in main valleys dammed by tributary glaciers failure can occur by erosion of a drainage tunnel under or through the ice dam or by a channel over the ice dam cold polar ice dams generally drain supraglacially or marginally by downmelting of an outlet channel warmer temperate ice dams tend to fail by sudden englacial or subglacial breaching and drainage late neoglacial moraine dammed lakes are located in steep mountain areas affected by the advances and retreats of valley glaciers in the last several centuries these late neoglacial dams pose hazards because 1 they are sufficiently young that vegetation has not stabilized their slopes 2 many dam faces are steeper than the angle of repose 3 these dams and lakes are immediately downslope from steep crevassed glaciers and near vertical rock slopes and 4 downstream from these dams are steep canyons with easily erodible materials that can be incorporated in the flow and increase flood peaks the most common reported failure mechanism is overtopping and breaching by a wave or series of waves in the lake generated by icefalls rockfalls or snow or rock avalanches melting of ice cores or frozen ground and piping and seepage are other possible failure mechanisms natural dams may cause upstream flooding as the lake rises and downstream flooding as a result of failure of the dam although data are few for the same potential energy at the dam site ownstream flood peaks from the failure of glacier ice dams are smaller than those from landslide moraine and structed earth fill and rock fill dam failures moraine dam failures appear to produce some of the largest downstream flood peaks for potential energy at the dam site greater than 1011 1012 joules differences in flood peaks natural dam failures appear to be controlled by dam characteristics and failure mechanisms

models of climate cycles recorded in martian polar layered deposits abstract layered strata observed in orbital images of polar sedimentary terrains on mars have been hypothesized to contain information about recent variations in the martian climate celestial mechanicians have determined that mars has experienced large amplitude quasi periodic variations in obliquity and eccentricity planetary meteorologists have inferred that the resulting changing patterns of solar heating must have had dramatic effects on martian climate accordingly it might be possible to link the known recent history of orbit axial variations with the physical characteristics of the most recently deposited strate determined from orbital imagery our paper explores that possibility quantitatively for various models of the formation of the polar layered deposits and the layering developed within them we modeled the formation of polar layered deposits during the past 10 my for two general classes of model uniform deposition rate udr models assume that the major constituent of the layered deposits is deposited at a uniform rate and that layering is established by climate induced variations in the concentration of a minor constituent climate modulated deposition rate cmdr models assume that the deposition rate of the major constituent is controlled by climate and that layer boundaries correspond to intervals of nondeposition in both models abrupt changes in deposition regime occur when a function of the orbit axial parameters crosses a threshold value detailed physical mechanisms for the control of sedimentation by orbit axial variations were developed for two specific models of the cmdr type in one model the deposits are assumed to be primarily composed of dust in the other they are assumed to be predominantly water ice we calculated the times at which abrupt changes in deposition regime occur and determined the relative thicknesses of successive layers which can be compared against layer thicknesses made from orbital imagery in all these models obliquity variations exert the dominant influence on the sequential variations in layer thickness although eccentricity and precession index longitude of perihelion may take recognizable contributions as well the layer patterns for the north and south polar deposits are identical for the dust model and only slightly different for the ice model but this is at least partly a consequence of simplifying assumptions the sequential variation in layer thickness is also very sensitive to those model parameters which control the fraction of time for which deposition occurs when the climate threshold for deposition is low deposition occurs a large fraction of the total time and characteristic patterns form with one thick layer and a number of much thinner ones such patterns would be easily recognized in photogeological measurements of layer thickness when the threshold for deposition lies in the mid range with respect to excursions of the climate function deposition occurs approximately half of the time and there is only slight modulation of layer thickness when the threshold for deposition is high deposition occurs only a small fraction of the total time and groups of layers form which are separated form other groups by long periods of nondeposition the stratigraphic unconformities that separate groupings of five to ten layers in the polar deposits may indicate that the martian polar region has experienced such a depositional history the feasibility of using these model results to verify the theory of climate control of polar stratigraphy on mars and to gain additional insights into the significant processes is considered the stratigraphy issues raised here are also explored in the context of recent work on the interpretation of stratigraphy of ocean margins from this comparison there emerge some valuable insights into the stratigraphic effects of periods of nondeposition and the uncertaintiesin interpreting images of exposed polar strata on mars

characterization of sea ice types using synthetic aperture radar the results of an investigation into the use of synthetic aperture radar sar imagery for sea ice type discrimination are presented x and l band dual polarization sar data of beaufort sea ice were examined using manual interpretation techniques to determine which channel provides the most information quantitative methods for ice type discrimination also were explored by statistical parameterization of these data various statistical tests both parametric and nonparametric were applied to evaluate the utility of the parameters for machine interpretation of sar ice data the results obtained indicate that under winter ice conditions x nband is superior to l band for discriminating various ice types also imagery obtained at small incidence angles shows greater tonal variation between ice types than that obtained at larger angles of the quantitative measures evaluated mean and standard deviation appear to be the most valuable examination of quantities involving higher order moments indicates that a better understanding of the sar imaging process is required before these measures can be utilized successfully

stratigraphic relationships within martian polar cap deposits abstract deposits of layered ice and dust accumulate on the smooth and banded terrains of the north and south polar cap deposits while erosion of equator facing slopes of layered terrain expose these layers banded terrain occurs at exposures of irregular layers resulting from slight erosion of the feather edges of layers deposited on pole facing trough walls these deposits unconformably overlap onto adjacent layered terrain stripping of layers occurs in areas of strong multidirectional wind forming striped terrain local wind scour has also produced steep scarps with crescentic planform often associated with dune fields positioned immediately downwind unconformities are common within layered deposits in areas of complex topography at the north pole these indicate that episodes of deposition of 5 10 layers alternate with slight erosion of pole facing trough walls troughs that strike north south alternate between erosional widening and deepening and depositional infilling creating multiple unconformities troughs near the equatorward limit of polar deposits increase in relief by deposition on adjacent smooth terrain and locally by erosional deepening troughs may migrate poleward replacing the relief increase by depositional infilling when they near the poles

three dimensional structure and origin of a 1 8 km thick ice dome within korolev crater mars korolev is an 80 km diameter impact crater located at 72 7 n 164 5 e containing a large domed deposit perennial water ice is thought to be currently unstable there however using a 3 d analysis of the dome s internal radar stratigraphy we estimate that korolev s central mound contains between 1400 and 3500 km3 of water ice that is up to 1 8 km thick furthermore the stratigraphic structure of this ice dome is strikingly similar to the north polar layered deposits npld on planum boreum approximately 600 km to the north additionally our stratigraphic analysis suggests that korolev ice was not previously part of a once larger polar ice sheet but rather it was deposited locally we conclude that korolev crater s ice likely deposited during the same climate regime as planum boreum s npld but independently this implies that the incorporation of circumpolar ice deposits such as korolev may prove useful in reconstructing a unique mars polar climate history

onset and migration of spiral troughs on mars revealed by orbital radar the northern polar cap of mars containing enough water to cover the entire planet to a depth of several metres features two major landforms that stand above all others these are the enormous canyon chasma boreale and a series of spiral troughs the processes leading to their formation have remained unclear now two papers in this issue present detailed histories of both systems john holt and colleagues use penetrating radar imagery from mars reconnaissance orbiter s radar sounder to show that depositional processes rather than a catastrophic event formed the chasma boreale isaac smith and john holt use mars reconnaissance orbiter data to rule out erosional cutting of polar ice as the cause of the central troughs and instead conclude that they too are largely depositional having migrated polewards and upwards in elevation in the past two million years a pinwheel array of deep troughs has been one of the most perplexing features of the north polar layered deposits on mars many ideas have been put forward about how it formed but there is as yet no consensus here penetrating radar has been used to rule out erosional cutting as a mechanism for the formation of the array instead it is concluded that the troughs are largely depositional in origin and have migrated to the poles and upwards in elevation over the past two million years or so the landscape of the north polar layered deposits of mars npld is dominated by a pinwheel array of enigmatic spiral troughs1 the troughs have intrigued planetary scientists since the mariner 9 spacecraft returned the first close up image in 1972 but conclusive evidence of their origin has remained elusive debate continues regarding all aspects of the troughs including the possibility that they have migrated2 3 4 5 their age in relation to the current npld surface6 and whether they are fundamentally erosional6 7 or constructional2 4 features the troughs are probably related to climatic processes2 8 yet the nature of this relationship has remained a mystery previous data characterizing only the exposed nlpd surface were insufficient to test these hypotheses here we show that the central spiral troughs initiated after deposition of three quarters of the npld quickly reached a stable morphology and migrated approximately 65 kilometres poleward and 600 metres in altitude over the past two million years or so our radar stratigraphy rules out hypotheses of erosional incision post dating deposition6 7 9 10 and instead largely validates an early hypothesis for constructional trough migration2 3 4 5 with wind transport and atmospheric deposition as dominant processes these results provide hard constraints for palaeo climate models and a new context for evaluating imagery spectral data and now radar sounding data the better to understand the link between orbital parameters and climate the role of climate in shaping the polar ice of mars and eventually the age of the polar deposits themselves8 11 12 13

an improved method to represent dem uncertainty in glacial lake outburst flood propagation using stochastic simulations modelling glacial lake outburst floods glofs or jokulhlaups necessarily involves the propagation of large and often stochastic uncertainties throughout the source to impact process chain since flood routing is primarily a function of underlying topography communication of digital elevation model dem uncertainty should accompany such modelling efforts here a new stochastic first pass assessment technique was evaluated against an existing gis based model and an existing 1d hydrodynamic model using three dems with different spatial resolution the analysis revealed the effect of dem uncertainty and model choice on several flood parameters and on the prediction of socio economic impacts our new model which we call mc lcp monte carlo least cost path and which is distributed in the supplementary information demonstrated enhanced stability when compared to the two existing methods and this stability was independent of dem choice the mc lcp model outputs an uncertainty continuum within its extent from which relative socio economic risk can be evaluated in a comparison of all dem and model combinations the shuttle radar topography mission srtm dem exhibited fewer artefacts compared to those with the advanced spaceborne thermal emission and reflection radiometer global digital elevation model aster gdem and were comparable to those with a finer resolution advanced land observing satellite panchromatic remote sensing instrument for stereo mapping alos prism derived dem overall we contend that the variability we find between flood routing model results suggests that consideration of dem uncertainty and pre processing methods is important when assessing flow routing and when evaluating potential socio economic implications of a glof event incorporation of a stochastic variable provides an illustration of uncertainty that is important when modelling and communicating assessments of an inherently complex process

river incision into bedrock mechanics and relative efficacy of plucking abrasion and cavitation improved formulation of bedrock erosion laws requires knowledge of the actual processes operative at the bed we present qualitative field evidence from a wide range of settings that the relative efficacy of the various processes of fluvial erosion e g plucking abrasion cavitation solution is a strong function of substrate lithology and that joint spacing fractures and bedding planes exert the most direct control the relative importance of the various processes and the nature of the interplay between them are inferred from detailed observations of the morphology of erosional forms on channel bed and banks and their spatial distributions we find that plucking dominates wherever rocks are well jointed on a submeter scale hydraulic wedging of small clasts into cracks bashing and abrasion by bedload and chemical and physical weathering all contribute to the loosening and removal of joint blocks in more massive rocks abrasion by suspended sand appears to be rate limiting in the systems studied here concentration of erosion on downstream sides of obstacles and tight coupling between fluid flow patterns and fine scale morphology of erosion forms testify to the importance of abrasion by suspended load rather than bedload particles mechanical analyses indicate that erosion by suspended load abrasion is considerably more nonlinear in shear stress than erosion by plucking in addition a new analysis indicates that cavitation is more likely to occur in natural systems than previously argued cavitation must be considered a viable process in many actively incising bedrock channels and may contribute to the fluting and potholing of massive unjointed rocks that is otherwise attributed to suspended load abrasion direct field evidence of cavitation erosion is however lacking in terms of the well known shear stress or stream power erosion law erosion by plucking is consistent with a slope exponent n of 2 3 to 1 whereas erosion by suspended load abrasion is more consistent with a slope exponent of 5 3 given that substrate lithology appears to dictate the dominant erosion process this finding has important implications for long term landscape evolution and the models used to study it

geology and insolation driven climatic history of amazonian north polar materials on mars a wealth of image and topographic data from the mars global surveyor and mars odyssey missions has been combined in a detailed geological map of the north polar region of mars one intriguing finding is a cycle of ice deposition similar in duration to a 1 470 year climate cycle of unknown origin on earth if both are externally driven a mechanism that affects both planets such as variation in solar luminosity must be involved mariner 9 and viking spacecraft images revealed that the polar regions of mars like those of earth record the planet s climate history however fundamental uncertainties regarding the materials features ages and processes constituting the geologic record remained1 2 3 4 5 6 recently acquired mars orbiter laser altimeter data7 and mars orbiter camera high resolution images8 from the mars global surveyor spacecraft and moderately high resolution thermal emission imaging system visible images9 from the mars odyssey spacecraft permit more comprehensive geologic and climatic analyses10 11 12 13 14 15 16 17 here i map and show the history of geologic materials and features in the north polar region that span the amazonian period 3 0 gyr ago to present 18 19 erosion and redeposition of putative circumpolar mud volcano deposits15 formed by eruption of liquefied fine grained material led to the formation of an early amazonian polar plateau consisting of dark layered materials crater ejecta superposed on pedestals indicate that a thin mantle was present during most of the amazonian suggesting generally higher obliquity and insolation conditions at the poles than at present brighter polar layered deposits rest unconformably on the dark layers and formed mainly during lower obliquity over the past 4 5 myr ref 20 finally the uppermost layers post date the latest downtrend in obliquity 20 000 years ago20

mars north polar deposits stratigraphy age and geodynamical response the shallow radar sharad on the mars reconnaissance orbiter has imaged the internal stratigraphy of the north polar layered deposits of mars radar reflections within the deposits reveal a laterally continuous deposition of layers which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice the packet interpacket structure can be explained by approximately million year periodicities in mars obliquity or orbital eccentricity the observed 100 meter maximum deflection of the underlying substrate in response to the ice load implies that the present day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers alternatively the response to the load may be in a transient state controlled by mantle viscosity both scenarios probably require that mars has a subchondritic abundance of heat producing elements

analysis of past and future dam formation and failure in the santa cruz river san juan province argentina abstract around 11 5 106 m3 of rock detached from the eastern slope of the santa cruz valley san juan province argentina in the first fortnight of january 2005 the rockslide debris avalanche blocked the course resulting in the development of a lake with maximum length of around 3 5 km the increase in the inflow rate from 47 000 74 000 m3 d between april and october to 304 000 m3 d between late october and the first fortnight of november accelerated the growing rate of the lake on 12 november 2005 the dam failed releasing 24 6 106 m3 of water the resulting outburst flood caused damages mainly on infrastructure and affected the facilities of a hydropower dam which was under construction 250 km downstream from the source area in this work we describe causes and consequences of the natural dam formation and failure and we dynamically model the 2005 rockslide debris avalanche with dan3d additionally as a volume 24 106 m3of rocks still remain unstable in the slope we use the results of the back analysis to forecast the formation of a future natural dam we analyzed two potential scenarios a partial slope failure of 6 5 106 m3 and a worst case where all the unstable volume remaining in the slope fails the spreading of those potential events shows that a new blockage of the santa cruz river is likely to occur according to their modeled morphometry and the contributing watershed upstream the blockage area as the one of 2005 the dams would also be unstable this study shows the importance of back and forward analysis that can be carried out to obtain critical information for land use planning hazards mitigation and emergency management

high resolution two dimensional spatial modelling of flow processes in a multi thread channel this paper describes application and testing of a two dimensional numerical flow model in a multi thread reach of a proglacial stream the model solves the depth averaged form of the navier stokes equations for open channel flow incorporating a two equation turbulence closure an analytical correction for the effects of secondary circulation and a rigid lid approximation the model requires as input the channel bed topography the water surface bed roughness and inflow discharge information and predicts the spatial distribution of depth averaged velocity and eddy viscosity the results have been subjected to intensive testing using simple assessment of numerical performance e g conservation of mass and momentum numerical convergence distributed sensitivity analysis and comparison of model predictions with field measurements of velocity the results are encouraging particularly given some of the difficulties in obtaining accurate distributed cross stream and downstream velocities distributed sensitivity analysis allowed more detailed consideration of the necessary development of the model this suggested that significant errors in the velocity predictions were largely a result of uncertainty in the specification of both the magnitude and the spatial variation of bed roughness secondly the two equation turbulence closure was observed to have little effect upon model predictions except in the vicinity of the side walls in applications of models of this type to irregular coarse bedded channels improvements in the specification of the topographic boundary condition specification and bed roughness are likely to be more important than a sophisticated turbulence closure scheme thirdly although the secondary circulation correction was observed to reproduce some of the expected streamwise transfer of momentum the effects were seen to be relatively small given the intensity of secondary circulation defined in field contexts the inability of the model to correct effectively for the momentum transfer associated with secondary circulation processes related to topographic discordance and shear generated turbulence suggests that further work is required in this respect 1998 john wiley sons ltd

outburst flood evolution at russell glacier western greenland effects of a bedrock channel cascade with intermediary lakes abstract glacial lake outburst floods have produced a distinctive and widespread quaternary record both onshore and offshore via widespread and intense geomorphological impacts yet these impacts remain poorly understood due to a lack of modern analogues this study therefore makes a systematic quantification of the evolution of a bedrock channelled outburst flood channel topography was obtained from digitised aerial photographs a 5 m grid resolution dem and bathymetric surveys flood inundation was measured in the field from dgps measurements flood evolution was analysed with application of a numerical model novel flood metrics including rate of rise to peak and persistence above a value of hydraulics were calculated the key findings were that outburst floods i that enter intermediary lakes are dramatically attenuated in terms of propagation whilst basin filling proceeds to the outlet level dissipated of energy due to considerable flow recirculation during the rising stage of the flood and after overtopping of the outlet are moderated in terms of peak discharge ii can have kinematic waves that are introduced to a flood via hydraulic ponding iii may develop a partitioning of flow regimes for instantaneous peak discharge bed shear stress and froude number due to time transgressive changes in channel cross section specifically between inner channel and overbank regions furthermore normalised change in cross sectional area and normalised change in channel slope can be used to suggest the relative magnitude of instantaneous peak discharge net erosion along a reach can be related to hydraulic persistence above a marker value and net deposition can be related to a time to peak value reconstructions of quaternary outburst floods should consider the importance of including intermediary lakes modern hazard mitigation studies could usefully note the potential use of reservoirs as an outburst flood alleviation resource

missoula flood dynamics and magnitudes inferred from sedimentology of slack water deposits on the columbia plateau washington sedimentological study of late wisconsin missoula flood slack water sediments deposited along the columbia and tucannon rivers in southern washington reveals important aspects of flood dynamics most flood facies were deposited by energetic flood surges velocities 6 m sec entering protected areas along the flood tract or flowing up and then directly out of tributary valleys true still water facies are less voluminous and restricted to elevations below 230 m high flood stages attended the initial arrival of the flood wave and were not associated with subsequent hydraulic ponding upslope from channel constrictions among 186 flood beds studied in 12 sections 57 have bioturbated tops and about half of these bioturbated beds are separated from overlying flood beds by nonflood sediments a single graded flood bed was deposited at most sites during most floods sequences in which 2 9 graded beds were deposited during a single flood are restricted to low elevations these sequences imply complex multi peaked hydrographs in which the first flood surge was generally the largest and subsequent surges were attenuated by water already present in slack water areas slack water sediment stratigraphy suggests a wide range of flood discharges and volumes of 40 documented late wisconsin floods that inundated the pasco basin only about 20 crossed the palouse snake divide floods younger than the set s tephras from mount st helens were generally smaller than earlier floods of late wisconsin age although most still crossed the palouse snake divide these late floods primarily traversed the cheney palouse scabland because stratigraphy of slack water sediment along the columbia river implies that the largest flood volumes did not enter the pasco basin by way of the columbia river

discussion of field evidence and hydraulic modeling of a large holocene jokulhlaup at jokulsa a fjollum channel iceland by douglas howard sheryl luzzadder beach and timothy beach 2012 this paper discusses howard et al 2012 who reconstruct the peak discharge of a glacial outburst flood or jokulhlaup for part of the jokulsa a fjollum in north central iceland they propose that this flood was the largest on earth weconsider that the magnitude of the jokulhlaup proposed by howard et al 2012 warrants much more robust field evidence and demands more carefully parameterised hydraulic modelling for these reasons we firstly i present their study in the context of previous research ii highlight issues with attributing landforms and sediments to jokulhlaups and iii consider uncertainty regarding the timing and magnitude of jokulhlaups along the jokulsa a fjollum we argue herein that whilst a range of landforms and sediments that are attributable to jokulhlaups can be observed along the jokulsa a fjollum these are not necessarily diagnostic of jokulhlaups secondly we critically discuss iv the major underlying assumptions of their study and v their calculations and subsequent interpretations these assessments lead us to consider that the proposal by howard et al 2012 of the largest flood on earth is highly unrealistic especially when due consideration is given to a possible source area and a trigger mechanism

effect of spatial trends on interpolation of river bathymetry continuous surface of river bathymetry bed topography is typically produced by spatial interpolation of discrete point or cross section data several interpolation methods that do not account for spatial trend in river bathymetry produce inaccurate surfaces thus requiring complex interpolation methods such as anisotropic kriging although isotropic methods are unsuitable for interpolating river bathymetry issues that limit their use remain unaddressed this paper addresses the issue of effect of spatial trend in river bathymetry on isotropic interpolation methods it is hypothesized that if the trend is removed from the data before interpolation the results from isotropic methods should be comparable with anisotropic methods data from six river reaches in the united states are used to i interpolate bathymetry data using seven spatial interpolation methods ii separate trend from bathymetry iii interpolate residuals bathymetry minus trend by using all seven interpolation methods to get residual surfaces iv add the trend back to residual surfaces and v compare resulting surfaces from iv with surfaces created in i quantitative and qualitative comparison of results through root mean square error rmse semi variograms and cross section profiles show that significant improvement as much as 60 in rmse can be accomplished in spatial interpolation of river bathymetry by separating trend from the data although this paper provides a new simple way for interpolating river bathymetry by using otherwise deemed inappropriate isotropic methods the choice of trend function and spatial arrangement of discrete bathymetry data play a vital role in successful implementation of the proposed approach

reconstructing historic glacial lake outburst floods through numerical modelling and geomorphological assessment extreme events in the himalaya westoby m j glasser n f hambrey m j brasington j reynolds j m hassan m a a m 2014 reconstructing historic glacial lake outburst floods through numerical modelling and geomorphological assessment extreme events in the himalaya earth surface processes and landforms 39 12 1675 1692

north polar deposits of mars extreme purity of the water ice 1 the polar layered deposits are the largest reservoir of water on the surface of mars the physical properties of the ice and their spatial distribution are largely unknown 140 000 data points from the sounding radar sharad on the mars reconnaissance orbiter were analyzed over the gemina lingula region one fourth of the north polar layered deposits area maps of the dielectric properties of the bulk ice were drawn up there is no basal melting signature a drop of the dielectric constant in north west of gemina lingula could be explained by an abrupt 250 meter uplift of the base the bulk ice of the studied region has an average dielectric constant of 3 10 0 12 and a loss tangent 0 0026 0 0005 analytic interpretations shown the volume of ice is pure at 95 the impurities have a radial distribution with higher concentrations at margins

a review of glacier outburst floods in iceland and greenland with a megafloods perspective the very largest glacier outburst floods have been termed megafloods given their volume and peak discharge that definition might be revised because those floods have become understood due to their distinctive and pervasive landscape impacts at least three floods in iceland can be categorized as megafloods since they produced impressive bedrock canyons and giant fluvially transported boulders glacier lake outburst floods glofs in greenland might also have megaflood type attributes given the enormous lake volumes drained we therefore here present the first review of glacier outburst floods in greenland sites isvand russell glacier kuannersuit glacier lake tininnilik two unnamed lakes near amitsulooq ice cap and iluliallup tasersua base camp lake lake hullett qorlortorssup tasia imaersartoq tordenso north midternaes and an outlet glacier of the a p olsen ice cap overall megaflood type landscape impacts in iceland tend to be best preserved and most easily identified inland although there has also been extensive offshore sedimentation there are very few reported impacts of glacier outburst floods in greenland in greenland ice dam failure causes frequent flooding compared to the volcanically triggered floods in iceland and this combined with the proximity of the greenland glacier lakes to the coast means that most proglacial channels in greenland are flood hardened and most landscape impact is likely to be offshore in estuaries and fjords future floods with megaflood type attributes will occur in iceland induced by volcanic activity in greenland they will be induced by extreme weather and rapid ice melt any potential landscape impact of these future floods remains open to question

identification of sea ice types in spaceborne synthetic aperture radar data an approach for identification of sea ice types in spaceborne synthetic aperture radar sar image data is presented the unsupervised classification approach involves cluster analysis for segmentation of the image data followed by cluster labeling based on previously defined look up tables containing the expected backscatter signatures of different ice types measured by land based scatterometer the particular look up table used for labeling a segmented image is selected based on the seasonal and meteorological conditions at the time of data acquisition the extensive scatterometer observations and experience accumulated in field campaigns during the last 10 years were used to construct these look up tables these tables are expected to evolve as sea ice observations from the european ers 1 sar become available this paper presents the classification approach its expected performance the dependence of this performance on radar system performance and expected ice scattering characteristics results using both aircraft and simulated ers 1 sar data are presented the results are compared to limited field ice property measurements and coincident passive microwave imagery an algorithm based on this experimental approach has been implemented in the geophysical processor system at the alaska sar facility for classification of sea ice data in ers 1 c band sar data the importance of an integrated postlaunch program for validation and improvement of this approach is discussed

unsteady two dimensional paleohydraulic reconstruction of extreme floods over the last 4000 yr in segura river southeast spain summary floods in the almadenes canyon segura river southeast spain have been reconstructed using unsteady two dimensional shallow water modelling slackwater deposits archaeological age dating and hydraulic modelling allowed us to reconstruct some of the oldest extreme floods reported in spain the paleoreconstruction was performed for the first time in three steps retrodicted flood discharges for the most recent flood ad 900 were quantified comparing the simulated shields and froude numbers with respect to characteristic values for the existence of ripples and upper stage plane bed at a cave that served as a shelter for humans ensuing velocity shields and froude maps were then used as a forward predictor allowing the finding of additional paleostage indicators far from the shelter finally new psis were employed to verify the reliability of the reconstruction in doing so better insight into the paleoflood landscape was derived from consideration of the association of bedforms and modelled hydraulic conditions the present study assuming a stable geometry of the bedrock canyon during the late holocene extends the estimation of flow discharge magnitudes to ca 4000 yr bp ranging from 500 m 3 s in the oldest floods 3700 yr bp up to 700 1000 m 3 s in the most recent ad 900

glaciovolcanic hydrothermal environments in iceland and implications for their detection on mars abstract volcanism has been a dominant process on mars along with a pervasive global cryosphere therefore the interaction between these two is considered likely terrestrial glaciovolcanism produces distinctive lithologies and alteration terrains as well as hydrothermal environments that can be inhabited by microorganisms here we provide a framework for identifying evidence of such glaciovolcanic environments during future mars exploration and provide a descriptive reference for active hydrothermal environments to be utilised for future astrobiological studies remote sensing data were combined with field observations and sample analysis that included x ray diffraction raman spectroscopy thin section petrography scanning electron microscopy electron dispersive spectrometer analysis and dissolved water chemistry to characterise samples from two areas of basaltic glaciovolcanism askja and kverkfjoll volcanoes in iceland the glaciovolcanic terrain between these volcanoes is characterised by subglacially erupted fissure swarm ridges which have since been modified by multiple glacial outburst floods active hydrothermal environments at kverkfjoll include hot springs anoxic pools glacial meltwater lakes and sulphur and iron depositing fumaroles all situated within ice bound geothermal fields temperatures range from 0 c 94 4 c and aqueous environments are acidic neutral ph 2 7 5 and sulphate dominated mineralogy of sediments mineral crusts and secondary deposits within basalts suggest two types of hydrothermal alteration a low temperature 120 c assemblage signified by zeolite heulandite and quartz these mineral assemblages are consistent with those identified at the martian surface in situ and laboratory vnir 440 1000 nm reflectance spectra representative of mars rover multispectral imaging show sediment spectral profiles to be influenced by fe2 3 bearing minerals regardless of their dominant bulk mineralogy characterising these terrestrial glaciovolcanic deposits can help identify similar processes on mars as well as identifying palaeoenvironments that may once have supported and preserved life

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

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

integrating radar stratigraphy with high resolution visible stratigraphy of the north polar layered deposits mars abstract shallow radar sharad on board nasa s mars reconnaissance orbiter has successfully detected tens of reflectors in the subsurface of the north polar layered deposits npld of mars radar reflections are hypothesized to originate from the same material interfaces that result in visible layering as a first step towards verifying this assumption this study uses signal analyses and geometric comparisons to quantitatively examine the relationship between reflectors and visible layers exposed in an npld outcrop to understand subsurface structures and reflector geometry reflector surfaces have been gridded in three dimensions taking into account the influence of surface slopes to obtain accurate subsurface geometries these geometries reveal reflector dips that are consistent with optical layer slopes distance elevation profiling of subsurface reflectors and visible layer boundaries reveals that reflectors and layers demonstrate similar topography verifying that reflectors represent paleosurfaces of the deposit statistical and frequency domain analyses of the separation distances between successive layers and successive reflectors confirms the agreement of radar reflector spacing with characteristic spacing of certain visible layers direct elevation comparisons between individual reflectors and discrete optical layers while necessary for a one to one correlation are complicated by variations in subsurface structure that exist between the outcrop and the sharad observations as inferred from subsurface mapping although these complications have prevented a unique correlation a genetic link between radar reflectors and visible layers has been confirmed validating the assumption that radar reflectors can be used as geometric proxies for visible stratigraphy furthermore the techniques for conducting a stratigraphic integration have been generalized and improved so that the integration can be undertaken at additional locations

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

coupled fluid dynamics sediment transport modelling of a crater lake break out lahar mt ruapehu new zealand summary lahars and other sudden onset floods are highly dynamic with temporally and spatially evolving sediment loads numerical models of sudden onset flood behaviour particularly those applied to real world events have tended to neglect sediment transport processes this is a serious though perhaps understandable shortcoming given a lack of field measurements on flow bed interactions the extra computational complexity required and the problem of iteratively updating plastic channel boundaries this paper applies a fluid dynamics model with suspended sediment and bedload transport to calculate flow conditions and rapid landscape change due to an initially dilute lahar from mt ruapehu new zealand we take advantage of an unprecedented dataset of net topographic changes determined from pre and post lahar airborne lidar surveys and time series of hydrological measurements to run and validate the model a sensitivity analysis of key controls on water surface elevation and final sediment thickness illustrates how the flow was supply limited in the upper reaches it was capable of transporting a greater volume and calibre of material than that available modelled patterns of net erosion and deposition can replicate those observed r 2 0 79 and are dominantly controlled by channel gradient and topographic

evidence for subsurface water ice in korolev crater mars abstract following the work of kieffer and titus 2001 icarus 154 162 180 we present results of thermal ir observations of korolev crater located at 73 latitude in the martian northern polar region similar to techniques employed by titus et al 2003 science 299 1048 1050 we use infrared images from the thermal emission imaging system themis aboard mars odyssey to identify several regions within the crater basin with distinct thermal properties that correlate with topography the themis results show these regions exhibit temperature variations spatially within the crater and throughout the martian year in addition to the variations identified in the themis observations mars global surveyor thermal emission spectrometer tes observations show differences in albedo and temperature of these regions on both daily and seasonal cycles modeling annual temperature variations of the surface we use tes observations to examine the thermal properties of these regions this analysis reveals the crater interior deposits are likely thick layers several meters of high thermal inertia material water ice or extremely ice rich regolith spatial variations of the physical properties of these regions are likely due to topography and possibly variations in the subsurface material itself the nature of these deposits may help constrain polar processes as well as provide context for the polar lander mission phoenix

backscatter characteristics of the winter ice cover in the beaufort sea the microwave backscatter statistics of the sea ice cover in the winter beaufort sea are characterized using c band synthetic aperture radar sar data collected by the european earth resources satellite 1 sea ice backscatter signatures were sampled from sar image data collected during the winter of 1991 1992 and winter of 1992 1993 the spatial and temporal variabilities of the backscatter signatures of different ice types are discussed the results show considerable seasonal stability of the backscatter signature of multiyear ice as well as of first year ice small amplitude regional variations of the multiyear ice backscatter can be observed consistent contrast between multiyear ice and first year ice is maintained throughout the season the highest radiometric variability is observed in sea ice in leads on the basis of these observations the backscatter from the principal ice types multiyear and first year are consistent with scatterometer observations and can be easily identified under winter conditions correlations of the regional variations of multiyear ice signatures to physical processes are suggested

reconstructing flash flood magnitudes using structure from motion a rapid assessment tool summary accurate records of flash flood magnitudes are required to inform flood forecasting and planning however whilst a distributed flood survey is desirable to capture spatial heterogeneity in peak water surface elevation the field time required for a distributed survey often limits the spatial coverage of such reconstructions for the first time we demonstrate the application of structure from motion sfm with multi view stereo mvs to reconstruct the magnitude of a flash flood this approach required only standard digital photographs and ground control points took only 30 min in the field and can be embedded within existing protocols easily we validated the method against a conventional dgps survey in three stages i comparison of topographic data revealed that sfm was accurate to within 0 1 m ii high water marks extracted from the sfm model were within 0 25 m of those surveyed in the field with no consistent over or under estimate iii peak discharge reconstructed from a two dimensional hydraulic model was within the range of more conventional estimates with low uncertainty in our terrain model and our reconstructed flood water surface we highlight the added value of the sfm approach for incorporating reach scale spatial variability into hydraulic reconstructions

sharad sounding radar on the mars reconnaissance orbiter 1 sharad shallow radar is a sounding radar provided by agenzia spaziale italiana asi as a facility instrument on the mars reconnaissance orbiter mission its 20 mhz center frequency and 10 mhz bandwidth complement the lower frequency relatively narrower bandwidth capability of the marsis sounding radar a joint italian u s team has guided the experiment development and is responsible for data analysis and interpretation the radar transmits signals at a 700 hz pulse repetition frequency prf and collects reflections from both the surface and near subsurface of mars vertical and horizontal resolutions are respectively 15 m free space and 3 6 km cross track by 0 3 1 km along track the scientific objective of sharad is to map in selected locales dielectric interfaces to at least several hundred meters depth in the martian subsurface and to interpret these results in terms of the occurrence and distribution of expected materials including competent rock soil water and ice a signal to noise ratio of 50 db for a specular surface return is achieved with 10 w of radiated power by using range and azimuth focusing in ground data processing preprocessed data as well as range and azimuth focused data will be formatted according to planetary data system pds standards and be made available from the asi science data center asdc and from the geosciences node of the planetary data system pds important targets for sharad include the polar layered deposits sedimentary stacks especially in terra meridiani buried channel systems buried impact craters volcanic complexes and shallow ice deposits in equilibrium with the atmosphere

internal structure of planum boreum from mars advanced radar for subsurface and ionospheric sounding data 1 an investigation of the internal structure of the ice rich planum boreum pb deposit at the north pole of mars is presented using 178 orbits of mars advanced radar for subsurface and ionospheric sounding data for each radargram bright laterally extensive surface and subsurface reflectors are identified and the time delay between them is converted to unit thicknesses using a real dielectric constant of 3 results include maps of unit thickness for pb and its two constituent units the stratigraphically older basal unit bu and the stratigraphically younger north polar layered deposits npld maps of the individual units surface elevation are also provided estimates of water ice volume in each unit are 1 3 0 2 106 km3 in pb 7 8 1 2 105 km3 in the npld and 4 5 1 0 105 km3 in the bu no lithospheric deflection is apparent under pb in agreement with previous findings for only the gemina lingula lobe which suggests that a thick elastic lithosphere has existed at the north pole of mars since before the emplacement of the bu the extent of bu material in the olympia planum lobe of pb is directly detected providing a more accurate map of bu extent than previously available from imagery and topography a problematic area for mapping the bu extent and thickness is in the distal portion of the 290 e 300 e region where marsis data show no subsurface reflectors even though the bu is inferred to be present from other lines of evidence

climate driven deposition of water ice and the formation of mounds in craters in mars north polar region this paper explores the origins and evolution of ice rich interior mounds found within craters of the north polar region of mars we present a systematic study of impact craters above 65 n and identify 18 craters that have interior mounds at least 11 of these mounds are composed of water ice and geometric similarities suggest that dune covered mounds may also have a water ice core the mounds are found in the deeper craters in the north polar area and we suggest that these form a specific microclimate favorable for mound initiation and growth it is likely that at least seven of the mounds have evolved as individual outliers rather than conterminous with the main polar cap our observations suggest that the mounds are built up by atmospheric deposition similar to that of the north polar layered deposits using a combination of remote sensing techniques enabling topographic spectral radar and image data analyses we have documented the morphology composition and stratigraphy of selected mounds we advance and test four hypotheses for formation of these mounds artesian outpouring from a deep aquifer hydrothermal activation of ground ice remnants of a more extensive polar cap and atmospheric deposition on ice caps in meteorologically isolated locations we propose that during periods when the perihelion was located in northern summer most recently 10 25 ka before present the microclimate in these craters retarded the sublimation of co2 and water ice in northern spring thus creating a cold trap for volatiles released as the seasonal cap retreated this created a thick enough deposit of water ice to withstand sublimation over the summer and initiate a positive feedback leading to mound building mounds without complete dune cover may be in dynamic equilibrium with the ambient climate and show evidence of both present day and past periods of erosion and aggradation we conclude that the water ice mounds formed in deep impact craters in mars north polar region may contain sensitive records of past polar climate that may enhance our understanding of the co2 h2o system in the polar regions

glacier dammed lakes and geological work of glacial superfloods in the late pleistocene southern siberia altai mountains quaternary glacier dammed lakes ofsouthern siberia produced cataclysmic superfloods floodstreams at the initial and final glacial stages when the ice dams were unstable consequently the initial surface was greatly and geologically instantly transformed morphologic associations ofmountainous scablands developed similar to the diluvial complexes ofthe channeled scabland in north america giant diluvial ramparts and terraces bars diluvial berms and giant current ripple relief diluvial erosional and evorsional forms including spillways outburst and oversplash gorges and dry waterfalls are also present the discharges of the glacial superfloods which have been calculated by independent methods were hundreds ofcubic meters per second at the locations where the giant current ripple marks were formed up to millions of cubic meters per second within the gorges maximum discharges of18 10 6 m 3 s 1 were characteristic ofthe diluvial floods in the runoff channel f rom the chuya kuray system ofthe glacierdammed lakes below the mouth ofthe kuray depression as f as the settlement ofchibit the power ofthose floods reached 10 6 wm 2 these values exceed the hydraulic parameters ofthe jok ulhlaups from late quaternary lake missoula in north america the floods of which previously were considered the most powerful freshwater streams in earth history the last phenomenal glacial superflood with discharges in excess of1 10 6 m 3 s 1 occurred in the chuya and katun valleys no later than 13 000 years ago afterwards the glacier dammed lakes degraded simultaneously with the degradation of the glaciers the glacier dammed lakes ofthe intermontane basins in southern siberia disappeared completely at some time af ter 5000 years ago calculations ofthe hydraulics and the estimates ofthe geological activity ofthe quaternary jok ulhlaups mean that the diluvial processes of relief formation can now be viewed as the most powerful exogenous process r 2001 published by elsevier science ltd

evaluation of second order texture parameters for sea ice classification from radar images with the advent of airborne and spaceborne synthetic aperture radar sar systems sea ice classification from sar images has become an important research subject since gray tone alone has proven to be of limited capability in differentiating ice types texture has naturally become an attractive avenue to explore accordingly performance of texture quantification parameters as related to their ability to discriminate ice types has to be examined sar image appearance depends on radar parameters involved in the image construction procedures from the doppler history record therefore the feasibility of using universal texture ice type relationships that hold for all combinations of radar parameters also has to be investigated to that end imagery data from three different sar systems were used in this study five conventional texture parameters derived from the gray level co occurrence matrix glcm were examined two of them were modified to ensure their invariant character under linear gray tone transformations results indicated that all parameters were highly correlated the parameters did not in general vary with the computational variables used in generating co occurrence matrices ice types can be identified uniquely by the mean value of any texture parameter the relatively high variability of texture parameters however confuses ice discrimination particularly of smoother ice types ice classification was conducted using a per pixel maximum likelihood supervised scheme when texture was combined with gray tone the overall average classification accuracy was improved texture was successful in improving the classification accuracy of multiyear ice but was less promising in discriminating first season ice types the best two glcm texture parameters according to the computed overall average classification accuracies were the inverse difference moment and the entropy a brief description of glcm texture parameters as related to ice s physical characteristics is presented

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

the spiral troughs of mars as cyclic steps we combine observations of stratigraphy morphology and atmospheric processes to relate the spiral troughs on mars polar layered deposits to a class of features known as cyclic steps cyclic steps are quasi stable repeating and upstream migrating bed forms that have been studied in terrestrial and submarine environments the repeating pattern is bounded by hydraulic jumps which act to stabilize the form we use radar stratigraphy from the shallow radar instrument on mars reconnaissance orbiter to examine trough evolution and constrain lateral transport we examine visible images from the thermal emission imaging system and observe low altitude clouds that we interpret to be the result of katabatic jumps i e the aeolian counterpart of hydraulic jumps in open channel flow we then devise a theoretical framework for understanding the origin of the spiral troughs that agree with 10 criteria that should be explained for any scenario to satisfactorily model the spiral troughs finally we use froude and geometrical analysis to estimate the rate of upstream migration caused by katabatic winds for the spiral troughs

a sar for real time ice reconnaissance prior research has shown that open water first year ice and multi year ice can be distinguished on an image obtained by a synthetic aperture radar sar a small lightweight sar star 1 has been built that employs this capability for support of engineering operations for oil exploration in the arctic the sar is a fully focused side looking system capable of mapping either side of the aircraft it has two modes wide swath which covers 45 km and high resolution which covers 22 km the azimuth resolution is 6 m for both modes with a range resolution of 12 m in the wide swath and 6 meters in the high resolution mode the instrument is installed in a cessna 441 conquest capable of flying at high altitudes with minimum fuel consumption an image is produced in real time by a digital image formation processing system aboard the aircraft this image is transmitted to a ground station via a data link where a hardcopy is formed on heat developed film

catastrophic impact of extreme flood events on the morphology and evolution of the lower jokulsa a fjollum northeast iceland during the holocene abstract the impact of extreme flood events is rarely considered in studies of long term landscape evolution despite the potential for catastrophic landscape change in a short period of time here we use an integrated approach of geomorphological mapping topographic analysis and geophysical surveys to identify and quantify the impact of extreme flood events jokulhlaups along the jokulsa a fjollum iceland where evidence for the action of such floods is widespread on microspatial to macrospatial scales the apex of the 28 km long jokulsargljufur canyon is characterised by a complex network of palaeo flood channels and large vertical knickpoints such as dettifoss 54 m high and hafragilsfoss 20 m high downstream the forvo valley contains large terraces of boulder rich deposits 50 m thick 3 km long near the outlet of the canyon is asbyrgi a dry canyon 3 km long 1 km wide up to 90 m deep with eroded cataracts and scabland morphology immediately upstream and 90 m above the current river channel topographic analysis and electrical resistivity tomography surveys show that 0 144 km3 of rock was eroded from asbyrgi during its formation 10 000 years ago and just 4 of this eroded volume is currently filled with sediment deposits up to 5 m thick deposited boulders across the canyon floor of asbyrgi demonstrate that the discharge of the jokulhlaup that formed the canyon was at least 39 000 m3 s 1 we present a model for the evolution of the lower jokulsa a fjollum and the jokulsargljufur canyon during various stages of an extreme flood event reconstruction of the early holocene flood event includes the initiation and development of different canyons before the capture of all floodwater within one canyon at the end we tie the evolution of the lower jokulsargljufur canyon to established chronology of flood events during the holocene farther upstream and highlight the dominant impact of extreme flood events over background processes in this landscape

a single stage megaflood at the termination of the messinian salinity crisis geophysical and modelling evidence from the eastern mediterranean basin abstract the messinian salinity crisis was an extraordinary event that resulted in the deposition of kilometre thick evaporite sequences in the mediterranean sea after the latter became disconnected from the world s oceans the return to fully and stable marine conditions at the end of the crisis is still subject to debate three main hypotheses based on geophysical and borehole data onshore outcrops and climate simulations have been put forward these include a single stage catastrophic flood a two step reflooding scenario and an overspill of paratethyan water followed by atlantic inflow in this study two research questions are addressed i which event marked the termination of the messinian salinity crisis ii what was the sea level in the eastern mediterranean sea during this event geophysical data from the western ionian basin are integrated with numerical simulations to infer that the termination of the crisis consisted of a single stage megaflood following a sea level drawdown of 1900 m this megaflood deposited an extensive sedimentary body with a chaotic to transparent seismic signature at the base of the malta escarpment fine well sorted sediments are predicted to have been deposited within the thicker sections of the flood deposit whereas a more variable distribution of coarser sediments is expected elsewhere the north western ionian basin hosts evidence of episodic post messinian salinity crisis slope instability events in the last 1 8 ma the largest of these emplaced a 200 km3 deposit and is associated with failure of the head of noto canyon offshore se sicily apart from unravelling the final phase of the messinian salinity crisis and the ensuing stratigraphic evolution of the western ionian basin our results are also relevant to better understand megafloods which are some of the most catastrophic geological processes on earth and mars

north polar region craterforms on mars geometric characteristics from the mars orbiter laser altimeter abstract this study focuses on topographic characterization of ice associated north polar region impact craters and several enigmatic polar craterforms using new information from the mars orbiter laser altimeter mola an instrument aboard the mars global surveyor mgs orbiter we find that for ice associated craters the topography reveals several surprising results not previously apparent from orbital images alone first geometric properties for several impact craters associated with ice and frost deposits suggest that cavity infill is as high as 80 of reconstructed preerosion levels second craters associated with ice also demonstrate unique cavity geometries relative to their nonpolar counterparts finally in some cases ice associated impact features are anomalously deep on the basis of depths modeled from the best available scaling laws we suggest that burial of these impact features by either episodic advance of the polar cap margin or by continuous deposition at the highest rates previously estimated for the north polar region of mars has occurred subsequent stripping has exhumed the features leaving behind cavity infill deposits and a few of these display topographic levels above the surrounding preimpact surface in at least one case cavity interior deposits show layering with a typical thickness of 10 m suggesting episodic deposition and ablation of materials as in the polar layered terrain in addition to ice associated craters we investigated the topography of several enigmatic polar craterforms in particular a few craterforms within 150 km of the permanent north polar cap appear to resemble simple effusive lava shield volcanoes found on earth their geometric properties cannot be reconciled with previous suggestions that they were manifestations of martian hydromagmatic processes i e maar volcanism mola s initial measurements of impact craters and other craterforms in the north polar latitudes of mars support the concept of a geologically recent surface with evidence of effusive volcanism and enhanced sedimentation in addition the measured impact crater depths for ice associated craters suggest at least a few cases of enhanced excavation and thus a possibly weaker target relative to the typical northern hemisphere plains

extracting sea ice data from satellite sar imagery with the prospect of operational satellite sar s by the end of the decade there is a clear need to develop automated algorithms for the extraction of geophysical data about sea ice from highresolution radar imagery to this end we have developed techniques for distinguishing ice from open water and for resolving the details of deformation within areas 100 km square imaged by seasat sar the classification of ice and open water is based on the creation of a second band of image data consisting of the local variance of the original brightness the first band being a local average brightness in the space of these two variables ice and open water are separated into two distinct clusters the deformation is found on a 3 4 km mesh by local cross correlations of the brightness the strategy is to find a coarse displacement field with a highly averaged image and to proceed through a hierarchy of images with increasing resolution improving the accuracy of the displacements at each step comparison with manually determined displacement shows room for improvement in regions of high deformation by using smaller areas for cross correlation the concentration and deformation data are used together to determine localized regions of the scene where open water is produced or lost

amazonian northern mid latitude glaciation on mars a proposed climate scenario recent geological observations in the northern mid latitudes of mars show evidence for past glacial activity during the late amazonian similar to the integrated glacial landsystems in the dry valleys of antarctica the large accumulation of ice many hundreds of meters required to create the observed glacial deposits points to significant atmospheric precipitation snow and ice accumulation and glacial flow in order to understand the climate scenario required for these conditions we used the lmd laboratoire de meteorologie dynamique mars gcm general circulation model which is able to reproduce the present day water cycle and to predict past deposition of ice consistent with geological observations in many cases prior to this analysis however significant mid latitude glaciation had not been simulated by the model run under a range of parameters in this analysis we studied the response of the gcm to a wider range of orbital configurations and water ice reservoirs and show that during periods of moderate obliquity 25 35 and high dust opacity sdust 1 5 2 5 broad scale glaciation in the northern mid latitudes occurs if water ice deposited on the flanks of the tharsis volcanoes at higher obliquity is available for sublimation we find that high dust contents of the atmosphere increase its water vapor holding capacity thereby moving the saturation region to the northern mid latitudes precipitation events are then controlled by topographic forcing of stationary planetary waves and transient weather systems producing surface ice distribution and amounts that are consistent with the geological record ice accumulation rates of 10 mm yr

the construction of chasma boreale on mars the northern polar cap of mars containing enough water to cover the entire planet to a depth of several metres features two major landforms that stand above all others these are the enormous canyon chasma boreale and a series of spiral troughs the processes leading to their formation have remained unclear now two papers in this issue present detailed histories of both systems john holt and colleagues use penetrating radar imagery from mars reconnaissance orbiter s radar sounder to show that depositional processes rather than a catastrophic event formed the chasma boreale isaac smith and john holt use mars reconnaissance orbiter data to rule out erosional cutting of polar ice as the cause of the central troughs and instead conclude that they too are largely depositional having migrated polewards and upwards in elevation in the past two million years the chasma boreale is a large canyon 500 km long up to 100 km wide and nearly 2 km deep that cuts into the north polar layered deposits on mars quite how it formed has been unclear however new penetrating radar imagery has now been used to show that depositional processes rather than catastrophic events were responsible the polar layered deposits of mars contain the planet s largest known reservoir of water ice1 2 and the prospect of revealing a detailed martian palaeoclimate record3 4 but the mechanisms responsible for the formation of the dominant features of the north polar layered deposits npld are unclear despite decades of debate stratigraphic analyses of the exposed portions of chasma boreale a large canyon 500 km long up to 100 km wide and nearly 2 km deep have led most researchers to favour an erosional process for its formation following initial npld accumulation candidate mechanisms include the catastrophic outburst of water5 protracted basal melting6 erosional undercutting7 aeolian downcutting7 8 9 and a combination of these processes10 here we use new data from the mars reconnaissance orbiter to show that chasma boreale is instead a long lived complex feature resulting primarily from non uniform accumulation of the npld the initial valley that later became chasma boreale was matched by a second equally large valley that was completely filled in by subsequent deposition leaving no evidence on the surface to indicate its former presence we further demonstrate that topography existing before the npld began accumulating influenced successive episodes of deposition and erosion resulting in most of the present day topography long term and large scale patterns of mass balance achieved through sedimentary processes rather than catastrophic events ice flow or highly focused erosion have produced the largest geomorphic anomaly in the north polar ice of mars

recent ice rich deposits formed at high latitudes on mars by sublimation of unstable equatorial ice during low obliquity observations from the gamma ray spectrometer instrument suite on the mars odyssey spacecraft have been interpreted as indicating the presence of vast reservoirs of near surface ice in high latitudes of both martian hemispheres1 2 3 4 5 ice concentrations are estimated to range from 70 per cent at 60 latitude to 100 per cent near the poles possibly overlain by a few centimetres of ice free material in most places4 this result is supported by morphological evidence of metres thick layered deposits that are rich in water ice6 7 8 9 and periglacial like features10 11 found only at high latitudes diffusive exchange of water between the pore space of the regolith and the atmosphere has been proposed to explain this distribution12 but such a degree of concentration is difficult to accommodate with such processes9 13 14 alternatively there are suggestions that ice rich deposits form by transport of ice from polar reservoirs and direct redeposition in high latitudes during periods of higher obliquity9 13 but these results have been difficult to reproduce with other models here we propose instead that during periods of low obliquity less than 25 high latitude ice deposits form in both hemispheres by direct deposition of ice as a result of sublimation from an equatorial ice reservoir that formed earlier during a prolonged high obliquity excursion using the ice accumulation rates estimated from global climate model simulations we show that over the past ten million years large variations of mars obliquity have allowed the formation of such metres thick sedimentary layered deposits in high latitude and polar regions

planum boreum basal unit topography mars irregularities and insights from sharad shallow radar investigations of planum boreum mars basal unit bu deposit have revealed multiple reentrants morphologic irregularities and thickness trends that differ from those of the overlying north polar layered deposits we present detailed subsurface maps for these features and offer explanation for genesis of the deposit s morphologic asymmetry expressed in different erosional characteristics between 0 e 180 e and 180 e 360 e additionally this work revealed a depression in the basal unit that may have provided a site for spiral trough initiation interpretations of the findings suggest that antecedent bu topography has a marked impact on modern morphology and that aeolian forces have been the dominant driver of polar deposit accumulation since at least the end of rupes unit emplacement we find no results requiring explanation beyond common martian surface processes including aeolian erosion and impact armoring to add to the detailed morphologic study of the bu we mapped the variability of the bu radar reflection character combining generalized katabatic wind flow with the radar mapping results suggests that rupes unit material sourced the younger cavi we present clear evidence that while compositionally distinct from the overlying layered deposits the bu and its morphology are intimately linked to the morphology of the north polar layered deposits combining geologic evidence with paleoclimate modeling the deposits contain evidence for a long history of aeolian emplacement and modification

reassessing the 2006 guerrero slow slip event mexico implications for large earthquakes in the guerrero gap in guerrero mexico slow slip events have been observed in a seismic gap where no earthquakes have occurred since 1911 a rupture of the entire gap today could result in a mw 8 2 8 4 earthquake however it remains unclear how slow slip events change the stress field in the guerrero seismic region and what their implications are for devastating earthquakes most earlier studies have relied on a sparse network of global navigation satellite systems measurements here we show that interferometric synthetic aperture radar can be used to improve the spatial resolution we find that slip due to the 2006 slow slip event enters the seismogenic zone and the guerrero gap with 5 cm slip reaching depths as shallow as 12 km we show that slow slip is correlated with a highly coupled region and estimate that slow slip events have decreased the total accumulated moment since the end of the 2001 2002 slow slip event 4 7 years by 50 nevertheless even accounting for slow slip the moment deficit in the guerrero gap increases each year by mw 6 8 the guerrero gap therefore still has the potential for a large earthquake with a slip deficit equivalent to mw 8 15 accumulated over the last century correlation between the slow slip region and nonvolcanic tremor and between slow slip and an ultraslow velocity layer supports the hypothesis of a common source potentially related to high pore pressures

kinematic wave solutions for dam break floods in non uniform valleys abstract in non uniform valleys dam break flood waves can be significantly affected by downstream variations in river width slope and roughness to model these effects we derive new analytical solutions to the kinematic wave equation applicable to rating curves in the power law form and hydrographs of generic shape as long as they produce a single shock at the wave front new results are first obtained for uniform channels using the gauss green theorem applied to characteristic bounded regions of the x t plane the results are then extended to non uniform valleys using a change of variable that homogenizes river properties by rescaling the distance coordinate the solutions are illustrated and validated for idealized cases then applied to three historical dam failures the 2008 breaching failure of the tangjiashan landslide dam the 1976 piping failure of teton dam and the 1959 sudden failure of malpasset dam in spite of the much reduced computational cost and data requirements the results agree well with the field data and with more elaborate simulations they also clarify how both river and hydrograph properties affect flood propagation and attenuation

revisiting the dynamics of catastrophic late pleistocene glacial lake drainage altai mountains central asia abstract in this work we present a whole system model of megafloods from catastrophic ice dam failure in the late pleistocene that comprises the study of the dynamics of the glacial lake the propagation of the flood wave downstream of the dam and an approximation to the ice breach process the ice dam incision rate was simply considered an unknown constant which was varied systematically to best fit the maximum altitude of the simulated water surface and the paleostage indicators in the downstream valley during the transient megaflood hence the hydrograph resulting from the breach of the ice dam was not prescribed but was an output of the paleohydraulic reconstruction by considering two possible configurations of the breach in the ice dam i e full or partial removal of the ice we constrained the incision rate in the narrow range of 28 42 m h 1 two connected glacial lakes kuray and chuja released 95 of the stored water volume i e 564 km3 in 33 8 hours a peak discharge of 10 5 m m3 s 1 was required to form numerous giant bars and run up deposits in the chuja and katun valleys the peak streamflow occurred after 11 h when 45 of the available lake volume had been evacuated from the kuray and chuja basins further verification of the reconstructed megaflood was achieved by studying the computed hydraulic conditions during the lake draining that justify the existence and orientation of several fields of subaqueous gravel dunes in the glacial lake complex spatiotemporal patterns during the recession stage of the flood built most of the fields of bedforms in terms of nondimensional parameters the froude and shields numbers that formed the dune fields were similar to those observed in large sandy rivers but the flow was undoubtedly unsteady and two dimensional we conclude by noting that the extensions of the simulated area cannot be cropped or analysed by independent parts in order to predict the formation of the most relevant geological records due to the unsteady two dimensional nature of the flow motion and the development of backwater effects in the drainage network lastly the paleohydrological reconstruction of a megaflood has helped not only to infer the dynamics of the event but also to retrodict the mean parameters of the ice dam failure mechanism

modelling the bulk flow of a bedrock constrained multi channel reach of the mekong river siphandone southern laos the general nature of bulk flow within bedrock single channel reaches has been considered by several studies recently however the flow structure of a bedrock constrained large river with a multiple channel network has not been investigated previously the multiple channel network of the siphandone wetlands in laos a section of the mekong river was modelled using a steady one dimensional hydraulic model the river network is characterized by a spatially varying channel form leading to significant changes in the bulk flow properties between and along the channels the challenge to model the bulk flow in such a remote region was the lack of ideal boundary conditions the flow models considered both low flow high inbank and overbank flows and were calibrated using spot satellite sensor imagery and limited field data concerning water levels the application of the model highlighted flow characteristics of a large multi channel network and also further indicated the field data that would be required to properly characterize the flow field empirically important results included the observation that adjacent channels within the network had different water surface slopes for the same moments in time thus calibration data for modelling similar systems needs to account for these significant local differences further the in channel hydraulic roughness coefficient strongly varied from one cross section to the next manning s n range 0 01 to 0 10 these differences were amplified during low flow but persisted in muted form during high discharges

subsurface structure of planum boreum from mars reconnaissance orbiter shallow radar soundings abstract we map the subsurface structure of planum boreum using sounding data from the shallow radar sharad instrument onboard the mars reconnaissance orbiter radar coverage throughout the 1 000 000 km2 area reveals widespread reflections from basal and internal interfaces of the north polar layered deposits npld a dome shaped zone of diffuse reflectivity up to 12 s 1 km thick underlies two thirds of the npld predominantly in the main lobe but also extending into the gemina lingula lobe across chasma boreale we equate this zone with a basal unit identified in image data as amazonian sand rich layered deposits byrne s murray b c 2002 j geophys res 107 5044 12 pp doi 10 1029 2001je001615 fishbaugh k e head j w 2005 icarus 174 444 474 tanaka k l rodriguez j a p skinner j a bourke m c fortezzo c m herkenhoff k e kolb e j okubo c h 2008 icarus 196 318 358 elsewhere the npld base is remarkably flat lying and co planar with the exposed surface of the surrounding vastitas borealis materials within the npld we delineate and map four units based on the radar layer packets of phillips et al phillips r j and 26 colleagues 2008 science 320 1182 1185 that extend throughout the deposits and a fifth unit confined to eastern gemina lingula we estimate the volume of each internal unit and of the entire npld stack 821 000 km3 exclusive of the basal unit correlation of these units to models of insolation cycles and polar deposition laskar j levrard b mustard j f 2002 nature 419 375 377 levrard b forget f montmessin f laskar j 2007 j geophys res 112 e06012 18 pp doi 10 1029 2006je002772 is consistent with the 4 2 ma age of the oldest preserved npld obtained by levrard et al levrard b forget f montmessin f laskar j 2007 j geophys res 112 e06012 18 pp doi 10 1029 2006je002772 we suggest a dominant layering mechanism of dust content variation during accumulation rather than one of lag production during periods of sublimation

winter sea ice mapping from multi parameter synthetic aperture radar data this paper presents examples of quantitative improvements in classification accuracy of six winter ice conditions using sar data resulting from the combination of multiple polarizations and frequencies

energy expenditure and geomorphic work of the cataclysmic missoula flooding in the columbia river ggorge usa cataclysmic releases from the glacially dammed lake missoula producing exceptionally large floods have resulted in significant erosional processes occurring over relatively short time spans erosional landforms produced by the cataclysmic missoula floods appear to follow a temporal sequence in many areas of eastern washington state this study has focused on the sequence observed between celilo and the john day river where the erosional features can be physically quantified in terms of stream power and geomorphic work the step backwater calculations in conjunction with the geologic evidence of maximum flow stages indicate a peak discharge for the largest missoula flood of 10 10 6 m 3 s 1 the analysis of local flow hydraulics and its spatial variation were obtained calculating the hydrodynamic variables within the different segments of a cross section the nature and patterns of erosional features left by the floods are controlled by the local hydraulic variations therefore the association of local hydraulic parameters with erosional and depositional flood features was critical in understanding landform development and geomorphic processes the critical stream power required to initiate erosion varied for the different landforms of the erosional sequence ranging from 500 w m 2 for the streamlined hills up to 4500 w m 2 to initiate processes producing inner channels erosion is possible only during catastrophic floods exceeding those thresholds of stream power below which no work is expended in erosion in fact despite the multiple outbursts which occurred during the late pleistocene only a few of them had the required magnitude to overcome the threshold conditions and accomplish significant geomorphic work 1997 by john wiley sons ltd

recent formation and evolution of northern martian polar layered deposits as inferred from a global climate model 1 we present a time marching model which simulates the exchange of water ice between the martian northern cap the tropics and a high latitude surface reservoir net annual exchange rates of water and their sensitivity to variations in orbital rotational parameters are examined using the martian water cycle modeled by the lmd three dimensional global climate model these rates are propagated over the last 10 myr to follow the thickness of the reservoirs the effect of a sublimation dust lag is taken account to test simple models of layer formation periods of high mean polar summer insolation 5 10 ma ago lead to a rapid exhaustion of a northern polar cap and a prolonged formation of tropical glaciers the formation of a northern cap and of a high latitude icy mantle may have started 4 ma ago with the average decrease of polar insolation tropical ice may have disappeared around 2 7 ma ago but small glaciers could have formed during the last peaks of polar summer insolation over the last 4 myr most of the present cap may have formed at the expense of tropical and high latitude reservoirs forming distinct layers at almost each 51 kyr 120 kyr insolation cycle layers thickness ranges from 10 to 80 m variations being produced by the modulation of the obliquity with 2 4 and 1 3 myr periods because only 30 insolation cycles have occurred since 4 ma ago we found an inconsistency between the recent astronomical forcing the observed number of layers and simple astronomically based scenarios of layers formation

orbital radar imagery and atmospheric modeling reveal an aeolian origin for abalos mensa mars 1 icy deposits surrounding planum boreum mars contain crucial information for deciphering paleoclimate and past geologic processes at the martian north pole one such deposit abalos mensa is an enigmatic wedge of material located near the 1 km high rupes tenuis its unique location and lobate morphology have fostered formation hypotheses that assume either fluvial or aeolian erosion of a once larger ice deposit the aeolian scenario posed previously requires impact shielding of ancient basal unit material to provide an erosional remnant which seeds later deposition while the fluvial hypotheses invoke cryovolcanism beneath the younger north polar layered deposits npld and associated outflow to erode the adjacent chasmata here we combine newly available radar sounding data high resolution imagery digital elevation models and atmospheric modeling to examine internal structure and infer both the mechanisms for and timing of abalos mensa formation from this integrative approach we conclude that abalos mensa formed as a distinct feature via atmospheric deposition following erosion of rupes tenuis and grew concurrently with the rest of planum boreum as the npld accumulated the required processes are consistent with those observed today no exotic phenomena cryovolcanism fluvial activity or impact shielding appear necessary to explain the formation of abalos mensa

information states in radar imagery of sea ice it is shown empirically that information in an image of sea ice exists in two forms textural and structural it is shown that such information can be extracted from the conditional probability of intensity differences between neighboring pixels there exists a relationship between the two forms of information called the information curve which has identifiable subsections each related to an ice type the overall state of the sea ice image composed as it is of a mixture of ice types can therefore be given by the location of phase transition points that mark the end points of the subsections on the information curve composed of the two types of information this result leads to a segmentation of the image by ice type the properties of the information within the image are examined it is shown that the textural information associated with individual ice pieces is scale invariant whereas the structural information associated with the size and shape of these pieces which dominates the image has a scaling or fractal property these results led to the examination of similarity sets describing scaled intensity differences and separation jointly significantly a multifractal relationship for these sets holds at all intensities at least for ice types associated with brittle fracture another result inspired by the need to identify paths of least resistance through an ice field is the existence of a distinct change in the connectivity of these similarity sets at a critical value of the index parameter of the set such a critical value is in turn related to that of the local textural information which is related to the phase transitions associated with the relationship between textural and structural information

a subsurface depocenter in the south polar layered deposits of mars the south polar layered deposits spld are one of the largest water ice reservoirs on mars and their accumulation is driven by variations in the climate primarily controlled by orbital forcings patterns of subsurface layering in the spld provide important information about past atmospheric dust content periods of substantial erosion and variations in local or regional deposition here we analyze the spld using shallow radar sharad sounder data to gain a unique perspective on the interior structure of the deposits and to determine what subsurface layers indicate about the preserved climate history sharad data reveal a major deviation from the gently domical layering typical of the spld a subsurface elongate dome the dome most likely formed due to variations in the accumulation of ice and snow across the cap with a higher rate occurring in this region over a prolonged period this spld depositional center provides an important marker of south polar climate patterns

radar sounding evidence for buried glaciers in the southern mid latitudes of mars lobate features abutting massifs and escarpments in the middle latitudes of mars have been recognized in images for decades but their true nature has been controversial with hypotheses of origin such as ice lubricated debris flows or glaciers covered by a layer of surface debris these models imply an ice content ranging from minor and interstitial to massive and relatively pure soundings of these deposits in the eastern hellas region by the shallow radar on the mars reconnaissance orbiter reveal radar properties entirely consistent with massive water ice supporting the debris covered glacier hypothesis the results imply that these glaciers formed in a previous climate conducive to glaciation at middle latitudes such features may collectively represent the most extensive nonpolar ice yet recognized on mars

a fluid dynamics approach to modelling the 18th march 2007 lahar at mt ruapehu new zealand lahars are water sediment mass flows from a volcanic source they can be triggered by a variety of mechanisms and span a continuum of flow rheology and hydraulic properties even within the same event lahars are extremely powerful landscaping agents and represent a considerable hazard potential however this highly dynamic character and a lack of direct measurements has made modelling lahars difficult this study therefore applies a fluid dynamics model delft3d to analyse the 18th march 2007 dam break lahar at mount ruapehu new zealand the modelled lahar routed through the whangaehu gorge in 30 min crossed the whangaehu fan in 60 min and then over a further 3 h travelled an additional 22 km distance along the whangaehu river to the tangiwai bridge the modelled mean frontal velocity was 6 5 m s 1 along the gorge although peak velocity reached up to 19 6 m s 1 the modelled lahar flow front progressively slowed across the fan but along the river it accelerated from 2 1 3 3 m s 1 calculated peak velocity along the river was 4 5 m s 1 these results generally compare well with gauged records with historical records and with other modelling approaches however discrepancies in frontal velocity and time to peak stage arise due to 1 specifying roughness which arises from slope variations between adjacent computational nodes and which is stage dependant and 2 due to rapid topographic changes that produce frequent hydraulic jumps which are inadequately accommodated in the numerical scheme the overall pattern of discharge attenuation and of relationships between topographic and hydraulic variables is similar to that calculated for lahars on other volcanoes this modelling method could be applied at other similar sites where a likely source hydrograph and high resolution topographic data are available these results have important implications for hazard management at ruapehu and for examining geomorphic and sedimentary impacts of this lahar

the fascination of a shallow water theory for the formation of megaflood scale dunes and antidunes abstract exceptional megaflood scale bedforms on earth are commonly associated with the catastrophic draining of glacial lakes in the late pleistocene the widest studied events have been the missoula and altai floods with 300 700 m flow depth 1 20 m bedform height and 10 300 m wavelength nowadays the saint venant equations have succeeded at simulating the catastrophic glacial lake drainage process numerically but we still lack a depth averaged morphodynamic theory able to predict the growth of dunes and antidunes the disparity of spatial scales in megafloods prevents the use of non depth averaged rotational flow equations motivating the present shallow water theory for the formation of megaflood scale bedforms we adopt a non equilibrium sediment transport equation rooted in einstein s pioneering work here we prove that the bed instability triggers to form dunes and antidunes simply by lagging the entrainment term for sediment mass conservation or the bottom shear stress with respect to the depth averaged flow velocity we formalise this result using a linear stability theory that captures the existence regions of dune and antidune in addition to the roll wave instability furthermore in the spirit of kennedy annu rev fluid mech vol 1 1969 pp 147 168 we derive a closed form solution of growth rate and wave speed of the bedform the nondimensional groups controlling the linear instabilities are the froude number r the shields parameter sh and the grain roughness relative to flow depth d subsequently we simulate the drainage of the largest missoula flood numerically to explain the formation of giant antidunes in the camas prairie montana us during the late stage of the megaflood also considered are large fields of gravel dunes in the kuray chuja lake basin altai mountains siberia the simulated hydraulic conditions over bedforms in both basins yield values of the nondimensional parameters that lie in the theoretical region of dunes and antidunes according to the proposed theory and in situ measurements in sandy rivers and flume experiments

response of glacial lake outburst floods to climate change in the yarkant river basin on northern slope of karakoram mountains china based on the glacial flood events and climate change in the yarkant river basin during the past 50 years the study investigated the long term change of temperature and precipitation the characteristics of glacial floods the origin of sudden flood release the suggested flood mechanism of glacial lakes and the relationship between glacial floods and climate change results showed that there was an obvious increase in the temperature of the basin since 1987 specifically in the mountainous area the significantly increasing temperature in the summer and autumn seasons accelerated the melting rate of glaciers and caused glacial lake burst sudden flood release occurred frequently the frequency of glacial lake outburst floods was 0 4 times a during the period 1959 1986 and increased to 0 7 times a during 1997 2006 peak discharge also increased there were seven floods with peak discharge over 4000 m 3 s from 1959 2006 and three occurred after 1997 the increasing frequency and magnitude of glacial outburst floods mirrored the effect of climate warming on glaciers c 2010 elsevier ltd and inqua all rights reserved