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Glacial lake outburst floods (GLOFs) are a natural hazard that affects a number of communities around the world. GLOFs affect a number of downstream communities directly in Alaska, with a variety o...

The Tam Pokhari glacial lake outburst flood (GLOF), which occurred in 1998 in the Mt. Everest region of Nepal, was evaluated using hydrodynamic models to gain a better understanding of the flow behaviour. The flood wave was analysed separately under rigid and erodible boundary conditions. In both cases, the calculated dam-breach hydrograph, which had a peak discharge of about 10 000 m3/s, was routed through the Inkhu River, which originates from the lake. The morphologic changes along the river were also analysed and the results were compared with satellite images, field observations and recorded data. In the case of rigid boundaries, the routing procedure gradually attenuated the peaks of the hydrographs to account for hydraulic pooling in narrow gorges and storage in the channel. In the case of erodible boundaries, such effects were minimized due to the increment in channel capacity associated with erosion by debris flow. The study revealed that the GLOF event produced a large-scale debris flow. Additionally, the results revealed that erosion and deposition took place intermittently, but that approximately 440 000 m3 of sediment was deposited about 14 km downstream from the lake mouth. The calculated peak of the water and sediment mixture at 14·4 km was found to be 30 000 m3/s, which is almost 6 times as large as that observed when the rigid boundary conditions were used. Further, the increase in the peaks of the hydrographs due to sediment transport was the primary reason for the destruction associated with the GLOF. These findings suggest that the local sedimentology and topography, as well as other geo-hazard conditions in the area, should be carefully evaluated before recommending any control measures against GLOFs in the Himalayan region. Copyright © 2009 John Wiley & Sons, Ltd.

The resolution and accuracy of digital elevation models (DEMs) can affect the hydraulic simulation results for predicting the effects of glacial lake outburst floods (GLOFs). However, for the Tibetan Plateau, high-quality DEM data are often not available, leaving researchers with near-global, freely available DEMs, such as the Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM) and the Shuttle Radar Topography Mission data (SRTM) for hydraulic modelling. This study explores the suitability of these two freely available DEMs for hydraulic modelling of GLOFs. Our study focused on the flood plain of a potentially dangerous glacial lake in southeastern Tibet, to evaluate the elevation accuracy of ASTER GDEM and SRTM, and their suitability for hydraulic modelling of GLOFs. The elevation accuracies of ASTER GDEM and SRTM were first validated against field global position system (GPS) survey points, and then evaluated with reference to the relatively high precision of 1:50 000 scale DEM (DEM5) constructed from aerial photography. Moreover, the DEM5, ASTER GDEM and SRTM were used as basic topographic data to simulate peak discharge propagation, as well as flood inundation extent and depth in the Hydrologic Engineering Center's River Analysis System one-dimensional hydraulic model. Results of the three DEM predictions were compared to evaluate the suitability of ASTER GDEM and SRTM for GLOF hydraulic modelling. Comparisons of ASTER GDEM and SRTM each with DEM5 in the flood plain area show root-mean-square errors between the former two as ± 15·4 m and between the latter two as ± 13·5 m. Although SRTM overestimates and ASTER GDEM underestimates valley floor elevations, both DEMs can be used to extract the elevations of required geometric data, i.e. stream centre lines, bank lines and cross sections, for flood modelling. However, small errors still exist in the cross sections that may influence the propagation of peak discharge. The flood inundation extent and mean water depths derived from ASTER GDEM predictions are only 2·2% larger and 2·3-m deeper than that of the DEM5 predictions, whereas the SRTM yields a flood zone extent 6·8% larger than the DEM5 prediction and a mean water depth 2·4-m shallower than the DEM5 prediction. The modelling shows that, in the absence of high-precision DEM data, ASTER GDEM or SRTM DEM can be relied on for simulating extreme GLOFs in southeast Tibet. Copyright © 2011 John Wiley & Sons, Ltd.

The effects of glacier ice block grounding on the morphology and sedimentology of proglacial fluvial outwash were examined during a glacier outburst flood or jokulhlaup, near Sondre Stromfjord, west Greenland. Observations made during and after the 1987 jokulhlaup both on the surface of an ice contact delta and within a confined valley sandur plain provided information about the formation of ice block obstacle marks and the significance of these bedforms for sandur morphology and sedimentology. Flow directions determined from obstacle mark morphology have been used successfully to chart flow direction changes on the falling limb of the jokulhlaup. Maximum flow depths for scour around stranded ice blocks may be given by 0·5–0·9 times the diameter of the ice block, as estimated from the depth of scour, the height of the obstacle shadow or the extent of ice block meltout sediments. Minimum flow depths can be represented by the height of the obstacle shadow above the mean bed level. The internal composition of the shadow indicates the ability of the flow to transport various sizes of material into the lee of obstacles. Ice block obstacle marks within the distal portion of the sandur initiated waning stage channel change. Proximal and lateral erosion around stranded ice blocks extended downstream from the ice block, forming chute channels which then captured waning stage flows, resulting in significant bar incision with associated deposition of lobate or deltaic deposits. It is suggested that ice block obstacle marks are important in terms of channel morphology, channel morphological change and their usefulness as palaeohydrological indicators.

Upper-flow-regime bedforms, including upper-stage-plane beds, antidunes, chutes-and-pools and cyclic steps, are ubiquitous in glacigenic depositional environments characterized by abundant meltwater discharge and sediment supply. In this study, the depositional record of Froude near-critical and supercritical flows in glacigenic settings is reviewed, and similarities and differences between different depositional environments are discussed. Upper-flow-regime bedforms may occur in subglacial, subaerial and subaqueous environments, recording deposition by free-surface flows and submerged density flows. Although individual bedform types are generally not indicative of any specific depositional environment, some observed trends are similar to those documented in non-glacigenic settings. Important parameters for bedform evolution that differ between depositional environments include flow confinement, bed slope, aggradation rate and grain size. Cyclic-step deposits are more common in confined settings, like channels or incised valleys, or steep slopes of coarse-grained deltas. Antidune deposits prevail in unconfined settings and on more gentle slopes, like glacifluvial fans, sand-rich delta slopes or subaqueous (ice-contact) fans. At low aggradation rates, only the basal portions of bedforms are preserved, such as scour fills related to the hydraulic-jump zone of cyclic steps or antidune-wave breaking, which are common in glacifluvial systems and during glacial lake-outburst floods and (related) lake-level falls. Higher aggradation rates result in increased preservation potential, possibly leading to the preservation of complete bedforms. Such conditions are met in sediment-laden jökulhlaups and subaqueous proglacial environments characterized by expanding density flows. Coarser-grained sediment leads to steeper bedform profiles and highly scoured facies architectures, while finer-grained deposits display less steep bedform architectures. Such differences are in part related to stronger flows, faster settling of coarse clasts, and more rapid breaking of antidune waves or hydraulic-jump formation over hydraulically rough beds. © 2020 The Authors. Sedimentology published by John Wiley & Sons Ltd on behalf of International Association of Sedimentologists

During the Middle Pleistocene late Saalian glaciation of northern central Europe numerous pro-glacial lakes formed along the southwestern margin of the Scandinavian Ice Sheet. Little is known about the drainage history of these lakes, the pathways of glacial lake outburst floods and their impacts on erosion, sedimentation and landscape evolution. This study investigated the impact of the late Saalian Weser and Munsterland Lake (Germany) outburst floods. In particular, we reconstructed the routing and flow dynamics of the lake outburst flood and analysed the flood related sediments. We employed one-dimensional hydraulic modelling to calculate glacial lake outburst flood hydrographs. We modelled the flow pathway and local flow conditions along the pathway based on the boundary conditions of two different hydrographs and two different ice-margin positions. The modelling results were compared with geomorphological and sedimentological field data in order to estimate the magnitude and impact of the flood on erosion and sedimentation. Two major lake drainage events are reconstructed for the study area, during which approximately 90–50 km3 of water was released. Modelling results indicate that the lake outburst floods created a high-energy flood wave with a height of 35–50 m in confined valley areas that rapidly spread out into the Lower Rhine Embayment eventually flowing into the North Sea basin. The sedimentary record of the outburst floods comprises poorly sorted coarse-grained gravel bars, long-wavelength bedforms and sandy bedforms deposited by supercritical and subcritical flows. Some parts of the sandy flood deposits are rich in reworked mammoth bones or mammoth and horse teeth, pointing to reworking of older fluvial sediments, hydraulic concentration and subsequent re-sedimentation of vertebrate remains. These deposits are preserved in sheltered areas or at high elevations, well above the influence of postglacial fluvial erosion. The flood-related erosional features include up to 80-m-deep scour pools, alluvial channels and streamlined hills.

Decay of the last Cordilleran Ice Sheet (CIS) near its geographical centre has been conceptualized as being dominated by passive downwasting (stagnation), in part because of the lack of large recessional moraines. Yet, multiple lines of evidence, including reconstructions of glacio-isostatic rebound from palaeoglacial lake shoreline deformation suggest a sloping ice surface and a more systematic pattern of ice-margin retreat. Here we reconstructed ice-marginal lake evolution across the subdued topography of the southern Fraser Plateau in order to elucidate the pattern and style of lateglacial CIS decay. Lake stage extent was reconstructed using primary and secondary palaeo-water-plane indicators: deltas, spillways, ice-marginal channels, subaqueous fans and lake-bottom sediments identified from aerial photograph and digital elevation model interpretation combined with field observations of geomorphology and sedimentology, and ground-penetrating radar surveys. Ice-contact indicators, such as ice-marginal channels, and grounding-line moraines were used to refine and constrain ice-margin positions. The results show that ice-dammed lakes were extensive (average 27 km2; max. 116 km2) and relatively shallow (average 18 m). Within basins successive lake stages appear to have evolved by expansion, decanting or drainage (glacial lake outburst flood, outburst flood or lake maintenance) from southeast to northwest, implicating a systematic northwestward retreating ice margin (rather than chaotic stagnation) back toward the Coast Mountains, similar in style and pattern to that proposed for the Fennoscandian Ice Sheet. This pattern is confirmed by cross-cutting drainage networks between lake basins and is in agreement with numerical models of North American ice-sheet retreat and recent hypotheses on lateglacial CIS reorganization during decay. Reconstructed lake systems are dynamic and transitory and probably had significant effects on the dynamics of ice-marginal retreat, the importance of which is currently being recognized in the modern context of the Greenland Ice Sheet, where >35% of meltwater streams from land-terminating portions of the ice sheet end in ice-contact lakes.

On 3 September 1998, a glacial lake outburst flood (GLOF) that originated from Tam Pokhari occurred in the Hinku valley of the eastern Nepal Himalaya. This study analyses the lake's geomorphic and hydrologic conditions prior to the outburst, and evaluates the conditions that could contribute to a future flood through photogrammetric techniques. We processed high-resolution Corona KH-4A (2.7 m) and ALOS PRISM (2.5 m) stereo-images taken before and after the GLOF event, and produced detailed topographic maps (2-m contour interval) and DEMs (5 m × 5 m). We (re-) constructed lake water surfaces before (4410 ± 5 m) and after (4356 ± 5 m) the outburst, and reliably estimated the lake water surface lowering (54 ± 5 m) and the water volume released (19.5 ± 2.2 × 106 m3) from the lake, showing good agreement with the results obtained from ground-based measurements. The most relevant conditions that may have influenced the catastrophic drainage of Tam Pokhari in 1998 include the presence of: (i) a narrow (75 ± 6 m), steep (up to 50°) and high (120 ± 5 m) moraine dam; (ii) high lake level (8 ± 5 m of freeboard) and (iii) a steep overhanging glacier (>40°). The lake outburst substantially altered the immediate area, creating a low and wide (>500 m) outwash plain below the lake, a wide lake outlet channel (~50 m) and a gentle channel slope (~3–5°). Our new data suggest that the likelihood of a future lake outburst is low. Our results demonstrate that the datasets produced by photogrammetric techniques provide an excellent representation of micro-landform features on moraine dams, lake water surfaces and the changes in both over time, thereby allowing highly accurate pre- and post-GLOF (volumetric) change analysis of glacial lakes. Furthermore, it enables precise measurement of several predictive variables of GLOFs that can be useful for identifying potentially dangerous glacial lakes or prioritizing them for detailed field investigations. Copyright © 2015 John Wiley & Sons, Ltd.

High resolution DEMs obtained from LiDAR topographic data have led to improved landform inventories (e.g. landslides and fault scarps) and understanding of geomorphic event frequency. Here we use airborne LiDAR mapping to investigate meltwater pathways associated with the Tweed Valley palaeo ice-stream (UK). In particular we focus on a gorge downstream of Palaeolake Milfield, previously mapped as a sub-glacial meltwater channel, where the identification of abandoned headcut channels, run-up bars, rock-cut terrace surfaces and eddy flow features attest to formation by a sub-aerial glacial lake outburst flood (GLOF) caused by breaching of a sediment dam, likely an esker ridge. Mapping of these landforms combined with analysis of the gorge rim elevations and cross-section variability revealed a two phase event with another breach site downstream following flow blockage by higher elevation drumlin topography. We estimate the magnitude of peak flow to be 1–3 × 103 m3/s, duration of the event to range from 16–155 days, and a specific sediment yield of 107–109 m3/km2/yr. We identified other outburst pathways in the lower Tweed basin that help delineate an ice margin position of the retreating Tweed Valley ice stream. The results suggest that low magnitude outburst floods are under-represented in Quaternary geomorphological maps. We therefore recommend regional LiDAR mapping of meltwater pathways to identify other GLOFs in order to better quantify the pattern of freshwater and sediment fluxes from melting ice sheets to oceans. Despite the relatively low magnitude of the Till outburst event, it had a significant impact on the landscape development of the lower Tweed Valley through the creation of a new tributary pathway and triggering of rapid knickpoint retreat encouraging new regional models of post-glacial fluvial landscape response. Copyright © 2015 John Wiley & Sons, Ltd.

The Northern Patagonia Icefield (NPI) is the primary glaciated terrain worldwide at its latitude (46.5–47.5°S), and constraining its glacial history provides unique information for reconstructing Southern Hemisphere paleoclimate. The Colonia Glacier is the largest outlet glacier draining the eastern NPI. Ages were determined using dendrochronology, lichenometry, radiocarbon, cosmogenic 10Be and optically stimulated luminescence. Dated moraines in the Colonia valley defined advances at 13.2 ± 0.95, 11.0 ± 0.47 and 4.96 ± 0.21 ka, with the last being the first constraint on the onset of Neoglaciation for the eastern NPI from a directly dated landform. Dating in the tributary Cachet valley, which contains an ice‐dammed lake during periods of Colonia Glacier expansion, defined an advance at ca. 2.95 ± 0.21 ka, periods of advancement at 810 ± 49 cal a BP and 245 ± 13 cal a BP, and retreat during the intervening periods. Recent Colonia Glacier thinning, which began in the late 1800s, opened a lower‐elevation outlet channel for Lago Cachet Dos in ca. 1960. Our data provide the most comprehensive set of Latest Pleistocene and Holocene ages for a single NPI outlet glacier and expand previously developed NPI glacial chronologies.

Glacier and permafrost hazards such as glacial-lake outburst floods and rock–ice avalanches cause significant socio-economic damages worldwide, and these processes may increase in frequency and magnitude if the atmospheric temperature rises. In the extratropical Andes nearly 200 human deaths were linked to these processes during the twentieth century. We analysed bibliographical sources and satellite images to document the glacier and permafrost dynamics that have caused socio-economic damages in this region in historic time (including glacial lake outburst floods, ice and rock–ice avalanches and lahars) to unravel their causes and geomorphological impacts. In the extratropical Andes, at least 15 ice-dammed lakes and 16 moraine-dammed lakes have failed since the eighteenth century, causing dozens of floods. Some floods rank amongst the largest events ever recorded (5000 × 106 m3 and 229 × 106 m3, respectively). Outburst flood frequency has increased in the last three decades, partially as a consequence of long-term (decades to centuries) climatic changes, glaciers shrinkage, and lake growth. Short-term (days to weeks) meteorological conditions (i.e. intense and/or prolonged rainfall and high temperature that increased meltwater production) have also triggered outburst floods and mass movements. Enormous mass failures of glaciers and permafrost (> 10 × 106 m3) have impacted lakes, glaciers, and snow-covered valleys, initiating chain reactions that have ultimately resulted in lake tsunamis and far-reaching (> 50 km) flows. The eruption of ice-covered volcanoes has also caused dozens of damaging lahars with volumes up to 45 × 106 m3. Despite the importance of these events, basic information about their occurrence (e.g. date, causes, and geomorphological impact), which is well established in other mountain ranges, is absent in the extratropical Andes. A better knowledge of the processes involved can help to forecast and mitigate these events. Copyright © 2014 John Wiley & Sons, Ltd.

Damage, destruction and casualties related to landslide and debris flow are common phenomena in the Himalaya, especially during the summer monsoon. This fact was tragically illustrated on 22 July 1996, when Larcha, situated at the 109-km mark of the Arniko Highway, upper Bhotekoshi Valley, central Nepal, experienced a catastrophic debris flow powered by the Bhairab Kunda Stream. Of the 22 houses in Larcha, 16 were swept away, two were partially damaged and 54 people were killed in a matter of a few minutes. The event attracted attention when media linked it to a glacial lake outburst flood as a result of the fact that the source of the stream is a glacial lake. To understand the cause, initiation mechanism and deposition process, the basin area was studied from geological, geomorphologic and engineering geological points of view and the role of precipitation was evaluated. A combination of rainfall, runoff from cliff faces and stream undercutting triggered failure of the bedrock and colluvium, both on the dip and counter-dip slopes, 500 m upstream from the highway. The landslide debris dammed the channel, which was eventually breached, and deposited approximately 104 000 m3 of coarse debris, dominated by the metasediments of the Lesser Himalayan origin, and overwhelmed the village of Larcha. The debris deposit was studied for clast size, composition, texture and dimensions. Lack of sorting and the presence of abundant silt and clay in the source area helped in the initiation of debris flow. The abundance of the Lesser Himalayan metasediment clasts together with the absence of debris traces upstream from the landslide site ruled out the possibility of a glacial lake outburst flood. The disaster was a result of landslide damming triggered by precipitation and stream undercutting and sudden bursting.

Glacial lake outburst floods (GLOF) often have a significant impact on downstream users. Including their effects in hydrological models, identifying past occurrences and assessing their potential impacts are challenges for hydrologists working in mountainous catchments. The regularly outbursting Merzbacher Lake is located in the headwaters of the Aksu River, the most important source of water discharge to the Tarim River, northwest China. Modelling its water resources and the evaluation of potential climate change impacts on river discharge are indispensable for projecting future water availability for the intensively cultivated river oases downstream of the Merzbacher Lake and along the Tarim River. The semi-distributed hydrological model SWIM was calibrated to the outlet station Xiehela on the Kumarik River, by discharge the largest tributary to the Aksu River. The glacial lake outburst floods add to the difficulties of modelling this high-mountain, heavily glaciated catchment with poor data coverage and quality. The aims of the study are to investigate the glacier lake outburst floods using a modelling tool. Results include a two-step model calibration of the Kumarik catchment, an approach for the identification of the outburst floods using the measured gauge data and the modelling results and estimations of the outburst flood volumes. Results show that a catchment model can inform GLOF investigations by providing ‘normal’ (i.e. without the outburst floods) catchment discharge. The comparison of the simulated and observed discharge proves the occurrence of GLOFs and highlights the influences of the GLOFs on the downstream water balance. © 2013 The Authors. Hydrological Processes Published by John Wiley & Sons Ltd.

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.

Large subglacial cavities in basal ice. the presumed precursors of depositional drumlins, can be created by corrasion from suspended sediment during a large water sheet outburst flood. The cavities are primarily the result of vortex action. For a given flood discharge the corrasion rate of the ice roof increases with water sheet velocity, V, to a power greater than V16/3, Because of ice displacment during a flood, V can vary spatially along a flow line by up to an order of magnitude. The highest velocities normally occur downstream from major bed depressions or near the ice margin. Fields of large drumlins frequently occur at such sites. The process of formation of large subglacial cavities is predicted to be more velocity-sensitive than the erosion of bedrock. No accurate estimate of water sheet flood volumes can be made at this time but they could be at least an order of magnitude less than the 80 000 km3, which was previously estimated.

Outwash plains, such as Skeiaararsandur, serve as prototypes for braided river facies and analogs for the Mars Pathfinder and Viking 1 landing sites on the margins of the Chryse Basin. Glacier outburst floods (jokulhlaups) have generated some of the largest known terrestrial freshwater flows and recent studies suggest that the stratigraphy of outwash plains (sandur) is dominated by sedimentary sequences laid down during jokulhlaups, rather than by braided river facies produced by an ablation-related flow regime. The modern point-source drainage configuration on Skeiaararsandur evolved from a diffuse, multipoint distributary system during glacier retreat, when meltwater began to be routed parallel to the ice front. The contemporary pattern of water and sediment dispersal across Skeiaararsandur differs from the conditions that prevailed when the ice front was coupled to the sandur, and the November 5–6 1996 outburst flood from Skeiaararjokull had little impact on the proximal surface of Skeiaararsandur beyond the confines of the entrenched channels that traverse it. Thus, the point-source dispersal system on Skeiaararsandur may not provide an exact analogue for the pattern of meltwater dispersal responsible for the sediment assemblage laid down during past jokulhlaups, and caution may be required when comparing conditions on Skeiaararsandur to those presumed to have been experienced during massive outburst floods elsewhere.

An unpredicted sudden outburst flood from Solheimajokull, Southern Iceland, in July 1999 may herald a major subglacial volcanic eruption beneath Mýrdalsjokull ice cap.

We present evidence that suggests a new risk scenario for the Valdivia basin in south Chile, located in the area of the magnitude 9.5 1960 earthquake. In 1960, three mass movements, triggered by the earthquake shaking, dammed the upper course of the San Pedro River and threatened Valdivia City until it was opened in a controlled manner by its inhabitants. Published historical accounts indicate that the 1575 earthquake, predecessor of the 1960 event, also triggered a mass movement that dammed the upper course of the river. However, here we reinterpret the published account and present new historical records, which we combined with satellite imagery and field surveys to show that the volume of the landslide in 1575 was smaller than the smallest of those of 1960, yet its outburst flood killed thousands of natives located downstream. Additionally, we characterized different mass movement deposits in the upper course of the San Pedro River, including both ancient and those formed in 1960, and we evaluated the mechanisms that could contribute to their generation at present (e.g. land use). Our results suggest that in the present-day conditions a moderately-sized (Mw ~8) earthquake can be sufficient to cause damming the San Pedro River, which challenges the previous assumption that such phenomena are exclusively related to giant 1960-like earthquakes.

Holocene glaciers have contributed to an abundance of unstable sediments in mountainous environments. In permafrost environments, these sediments can contain ground ice and are subject to rapid geomorphic activity and evolution under condition of a warming climate. To understand the influence of ground ice distribution on this activity since the Little Ice Age (LIA), we have investigated the Pierre Ronde and Rognes proglacial areas, two cirque glacier systems located in the periglacial belt of the Mont Blanc massif. For the first time, electrical resistivity tomography, temperature data loggers and differential global positioning systems (dGPS) are combined with historical documents and glaciological data analysis to produce a complete study of evolution in time and space of these small landsystems since the LIA. This approach allows to explain spatial heterogeneity of current internal structure and dynamics. The studied sites are a complex assemblage of debris-covered glacier, ice-rich frozen debris and unfrozen debris. Ground ice distribution is related to former glacier thermal regime, isolating effect of debris cover, water supply to specific zones, and topography. In relation with this internal structure, present dynamics are dominated by rapid ice melt in the debriscovered upper slopes, slow creep processes in marginal glacigenic rock glaciers, and weak, superficial reworking in deglaciated moraines. Since the LIA, geomorphic activity is mainly spatially restricted within the proglacial areas. Sediment exportation has occurred in a limited part of the former Rognes Glacier and through water pocket outburst flood and debris flows in Pierre Ronde. Both sites contributed little sediment supply to the downslope geomorphic system, rather by episodic events than by constant supply. In that way, during Holocene and even in a paraglacial context as the recent deglaciation, proglacial areas of cirque glaciers act mostly as sediment sinks, when active geomorphic processes are unable to evacuate sediment downslope, especially because of the slope angle weakness.

A robust Godunov-type numerical scheme solver is proposed for solving 2D SWEs and is applied to simulate flow over complex topography with wetting and drying. In reality, the topography is usually complex and irregular; therefore, to avoid the numerical errors generated by such features, a Homogenous Flux Method is used to handle the bed slope term in the SWEs. The method treats the bed slope term as a flux to be incorporated into the flux gradient and so maintains the balance between the two in a Godunov-type shock-capturing scheme. The main advantages of the method are: first, it is simple and easy to implement; second, numerical experiments demonstrate that it can handle discontinuous or vertical bed topography without any special treatment and third, it is applicable to both steady and unsteady flows. It is demonstrated how the approach set out here can be applied to the nonlinear hyperbolic system of the SWEs. The two-dimensional hyperbolic system is then solved by use of a second-order total-variation-diminishing version of the weighted average flux method in conjunction with a Harten-Lax-van Leer-Contract approximate Riemann solver incorporating the new flux gradient term. Several benchmark tests are presented to validate the model and the approach is verified against experimental measurements from the European Union Concerted Action on Dam Break Modelling project. These show very good agreement. Finally, the method is applied to a volcano-induced outburst flood over an initially dry channel with complex irregular topography to demonstrate the technique's capability in simulating a real flood.

The rheology of debris flows is difficult to characterize owing to the varied composition and to the uneven distribution of the components that may range from clay to large boulders, in addition to water. Few studies have addressed debris flow rheology from observational, experimental, and theoretical viewpoints in conjunction. We present a coupled rheological-numerical model to characterize the debris flows in which cohesive and frictional materials are both present. As a first step, we consider small-scale artificial debris flows in a flume with variable percentages of clay versus sand, and measure separately the rheological properties of sand–clay mixtures. A comparison with the predictions of a modified version of the numerical model BING shows a reasonable agreement between measurements and simulations. As application to a field case, we analyse a recent debris flow that occurred in Fjaerland (Western Norway) for which much information is now available. The event was caused by a glacial lake outburst flood (GLOF) originating from the failure of a moraine ridge. In a previous contribution (Breien et al., Landslides, 2008, 5: 271–280) we focused on the hydrological and geomorphological aspects. In particular we documented the marked erosion and reported the change in sediment transport during the event. In contrast to the laboratory debris flows, the presence of large boulders and the higher normal pressure inside the natural debris flow requires the introduction of a novel rheological model that distinguishes between mud-to–clast supported material. We present simulations with a modified BING model with the new cohesive-frictional rheology. To account for the severe erosion operated by the debris flow on the colluvial deposits of Fjaerland, we also suggest a simple model for erosion and bulking along the slope path. Numerical simulations suggest that a self-sustaining mechanism could partly explain the extreme growth of debris flows running on a soft terrain.

The 1918 eruption of the glacially capped Katla volcano, southern Iceland, generated a violent jokulhlaup, or glacial outburst flood, inundating a large area of Mýrdalssandur, the proglacial outwash plain, where it deposited ca 1 km3 of volcaniclastic sediment. The character of the 1918 jokulhlaup is contentious, having been variously categorized as a turbulent water flow, a hyperconcentrated flow or as a debris flow, based on localized outcrop analysis. In this study, outcrop-based architectural analyses of the 1918 deposits reveal the presence of lenticular and tabular bedsets associated with deposition from quasi-stationary antidunes and down-current migrating antidunes, and from regular based bedsets, associated with transient chute-and-pool bedforms, all of which are associated with turbulent, transcritical to supercritical water flow conditions. Antidune wavelengths range from 24 to 96 m, corresponding to flow velocities of 6 to 12 m sec−1 and average flow depths of 5 to 19 m. This range of calculated flow velocities is in good agreement with estimates made from eyewitness accounts. Architectural analysis of the 1918 jokulhlaup deposits has led to an improved estimation of flow parameters and flow hydraulics associated with the 1918 jokulhlaup that could not have been achieved through localized outcrop analysis. The observations presented here provide additional sedimentological and architectural criteria for the recognition of deposits associated with transcritical and supercritical water flow conditions. The physical scale of sedimentary architectures associated with the migration of bedforms is largely dependent on the magnitude of the formative flow events or processes; sedimentary analyses must therefore be undertaken at the appropriate physical scale if reliable interpretations, regarding modes of deposition and formative flow hydraulics, are to be made.