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Existing methods of evaluating the hazard posed by moraine-dammed lakes are unsystematic, subjective, and depend on the expertise and biases of the geoscientist. In this paper, we provide a framework for making objective preliminary assessments of outburst flood hazard in southwestern British Columbia. Our procedure relies on remote sensing methods and requires only limited knowledge of glacial processes so that evaluations of outburst flood hazard can be incorporated into routine hazard assessments of glaciated regions. We describe objective approaches, which incorporate existing empirical relations applicable to the study region, for estimating outburst peak discharge, maximum volume, maximum travel distance, maximum area of inundation, and probability. Outburst flood hazard is greatest for moderately large lakes that are impounded by large, narrow, ice-free moraine dams composed of sedimentary rock debris and drain into steep, sediment-filled gullies above major river valleys. We demonstrate the application of the procedure using three case studies and show that flood hazard varies, especially with major changes in lake level. Our assessment scheme yields reproducible results and enables engineers and geoscientists to prioritize potentially hazardous lakes for more detailed field investigation.

At least one large, late Pleistocene flood traveled into the Owyhee River as a result of a rise and subsequent outburst from pluvial Lake Alvord in southeastern Oregon. Lake Alvord breached Big Sand Gap in its eastern rim after reaching an elevation of 1292 m, releasing 11.3 km 3 of water into the adjacent Coyote Basin as it eroded the Big Sand Gap outlet channel to an elevation of about 1280 m. The outflow filled and then spilled out of Coyote Basin through two outlets at 1278 m and into Crooked Creek drainage, ultimately flowing into the Owyhee and Snake Rivers. Along Crooked Creek, the resulting flood eroded canyons, stripped bedrock surfaces, and deposited numerous boulder bars containing imbricated clasts up to 4.1 m in diameter, some of which are located over 30 m above the present-day channel. Critical depth calculations at Big Sand Gap show that maximum outflow from a 1292- to 1280-m drop in Lake Alvord was ∼ 10,000 m 3 s − 1 . Flooding became confined to a single channel approximately 40 km downstream of Big Sand Gap, where step-backwater calculations show that a much larger peak discharge of 40,000 m 3 s − 1 is required to match the highest geologic evidence of the flood in this channel. This inconsistency can be explained by (1) a single 10,000 m 3 s − 1 flood that caused at least 13 m of vertical incision in the channel (hence enlarging the channel cross-section); (2) multiple floods of 10,000 m 3 s − 1 or less, each producing some incision of the channel; or (3) an earlier flood of 40,000 m 3 s − 1 creating the highest flood deposits and crossed drainage divides observed along Crooked Creek drainage, followed by a later 10,000 m 3 s − 1 flood associated with the most recent shorelines in Alvord and Coyote Basins. Well-developed shorelines of Lake Alvord at 1280 m and in Coyote Basin at 1278 m suggest that after the initial flood, postflood overflow persisted for an extended period, connecting Alvord and Coyote Basins with the Owyhee River of the Columbia River drainage. Surficial weathering characteristics and planktonic freshwater diatoms in Lake Alvord sediment stratigraphically below Mt. St. Helens set Sg tephra, suggest deep open-basin conditions at ∼ 13–14 ka ( 14 C yr) and that the flood and prominent shorelines date to about this time. But geomorphic and sedimentological evidence also show that Alvord and Coyote Basins held older, higher-elevation lakes that may have released earlier floods down Crooked Creek.

Outburst flooding from subglacial reservoirs and associated surging of ice-streams are caused by processes following climatic cooling that produce ice-shelf grounding on proglacial sills trapping subglacial water, according to an hypothesis presented here. Glaciers often advance into proglacial water bodies. Cooling may allow ice-shelf formation and advance causing grounding on a proglacial sill, trapping subglacial water. Ice-shelf freeze-on to the sill and development of a local reversal in ice–air surface slope over the sill then are likely, allowing ice thickening and water overpressurization. If basal thawing then occurs, as is likely, an outburst flood and a surge may be triggered. These processes may have been involved in Heinrich events, generation of Antarctic subglacial lakes, and meltwater scouring of some regions.

Jokulhlaups (glacial outburst floods) are common hazards in many glaciated environments. However, research on the controls on the sedimentological and geomorphological impact of jokulhlaups is rare...

At 00:30 (local time) on the 10th September 2003 a joint and foliation defined wedge of material with an estimated volume of 7–12×106 m3 slid into the narrow Tsatichhu River Valley, in Jarrey Geog, Lhuentse, eastern Bhutan. The Tsatichhu River, a north–easterly flowing tributary of the Kurichuu River, was completely blocked by the landslide. During its movement, the landslide transitioned into a rock avalanche that travelled 580 m across the valley before colliding with the opposite valley wall. The flow then moved down valley, travelling a total distance of some 700 m. The rock avalanche was accompanied by an intense wind blast that caused substantial damage to the heavily forested valley slopes. The resulting geomorphologically-typical rock-avalanche dam deposit created a dam that impounded a water volume of 4–7×106 m3 at lake full level. This lake was released by catastrophic collapse of the landslide, which occurred at 16:20 (local time) on 10th July 2004, after reported smaller failures of the saturated downstream face. The dam failure released a flood wave that had a peak discharge of 5900 m3 s−1 at the Kurichhu Hydropower Plant 35 km downstream.

Geomorphic evidence and stratigraphic information from boreholes suggest that the oversized Central Kalamazoo River Valley (CKRV) in southwest Michigan resulted from a catastrophic outburst flood emanating from subglacial channels under the Saginaw lobe of the Laurentide Ice Sheet. The CKRV occurs as a deeply incised trench over 2 km wide and in excess of 50 m deep situated in a reentrant formed by the Lake Michigan, Saginaw and Huron-Erie lobes. The course of the CKRV follows an irregular flow path that bisects the Kalamazoo Moraine of the Lake Michigan lobe. Erosional terraces near the mouth of the channel indicate that Lake Michigan lobe meltwater drained eastward prior to the westward Saginaw outburst. Prior to valley formation the Lake Michigan lobe had retreated westward to at least the Lake Border Moraine. With the Lake Michigan lobe absent to impede flow, drainage from the CKRV proceeded southwesterly until draining into glacial Lake Chicago near St. Joseph, Michigan. The outburst originated from a system of Saginaw tunnel channels that display convex-up flow profiles and contain eskers. Meltwater drainage transitioned from subglacial-to-ice marginal and proglacial environments. During the interval represented by the outburst, the Saginaw Lobe appears to have been in a relatively stationary position.

Quantitative assessments of landslide hazard usually employ empirical, heuristic, deterministic, or statistical methods to derive estimates of magnitude–frequency distributions of landsliding. The formation and failure of landslide dams are common geomorphic processes in mountain regions throughout the world, causing a series of consequential off-site hazards such as catastrophic outburst floods, debris flows, backwater ponding, up- and downstream aggradation, and channel instability. Conceptual and methodological problems of quantifying geomorphic hazard from landslide dams result from (a) aspects of defining “landslide-dam magnitude”, (b) scaling effects, i.e. the geomorphic long-range and long-term implications of river blockage, and (c) paucity of empirical data. Geomorphic hazard from a landslide dam-break flood on the basis of conditional probabilities is being analysed for the alpine South Westland region of New Zealand, where formation and failure of landslide dams is frequent. Quantification of the annual probability of landsliding and subsequent dam formation in the area is limited by historical and only partially representative empirical data on slope instability. Since landslide-dam stability is a major control governing the potential of catastrophic outburst flooding, the ensuing hazard is best assessed on a recurring basis. GIS-based modelling of virtual landslide dams is a simple and cost-effective approach to approximate site-specific landslide dam and lake dimensions, reservoir infill times, and scaled magnitude of potential outburst floods. Although crude, these order-of-magnitude results provide information critical to natural hazard planning, mitigation, or emergency management decisions.

In July 2003 an ice-dammed lake was suddenly drained in an outburst flood at Qorlortorssup tasia in south Greenland, the site of a projected hydropower station. The lake developed during the first decades of the 20th century as a result of the recession of the ice cap in this area. It used to drain over a shallow rock spillway towards Sermeq kangigdleq, the adjacent outlet glacier to the north. In order to assess the hazard potential and the additional water contribution from the enlarged catchment, the glacial lake and its surroundings were investigated. Based on the analysis of available historical data, field investigations and model results, the history of lake generation and the sudden outbreak were reconstructed. With the lake formation the ice dam lost its connection to the ice cap. The flood was initiated after the ice surface became low enough for the lake water to overflow the glacier towards Qorlortorssup tasia basin, creating a gully through the glacier which drained approximately 55 × 106 m3 of water over a period of 8-10 days. Thanks to the stability of the dam and the downstream damping of the flood, there was no serious threat to a farm that is situated close to the planned power-station site. In the future, we expect much smaller floods, as a result of partial closure of the gully by ice movement or snowdrift in the winter. The new drainage pattern into Qorlortorssup tasia basin, however, will be a permanent situation. The amount of this new water contribution can only be roughly estimated since the exact size of the drainage basin is not well known.

Glacier sliding is commonly linked with elevated water pressure at the glacier bed. Ice surface motion during a 3 week period encompassing an outburst of ice-dammed Hidden Creek Lake (HCL) at Kennicott Glacier, Alaska, USA, showed enhanced sliding during the flood. Two stakes, 1.2 km from HCL, revealed increased speed in two episodes, both associated with uplift of the ice surface relative to the trajectory of bed-parallel motion. Uplift of the surface began 12 days before the flood, initially stabilizing at a value of 0.25 m. Two days after lake drainage began, further uplift (reaching 0.4 m) occurred while surface speed peaked at 1.2 md–1. Maximum surface uplift coincided with peak discharge from HCL, high water level in a down-glacier ice-marginal basin, and low solute concentrations in the Kennicott River. Each of these records is consistent with high subglacial water pressure. We interpret the ice surface motion as arising from sliding up backs of bumps on the bed, which enlarges cavities and produces bed separation. The outburst increased water pressure over a broad region, promoting sliding, inhibiting cavity closure, and blocking drainage of solute-rich water from the distributed system. Pressure drop upon termination of the outburst drained water from and depressurized the distributed system, reducing sliding speeds. Expanded cavities then collapsed with a 1 day time-scale set by the local ice thickness.

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.

An ice-dammed lake at the margin of the glacier Salkaglaciaren, in the Kebnekaise Mountains in northern Sweden, drained suddenly in July 2003 producing a flood with a measured peak discharge of 9.5±0.25 m3s-1. The total lake volume of 4.55×105 million3 drained within two days. The hydrograph of this event is characteristic of a jokulhlaup controlled by a single basal ice tunnel that enlarges due to melting. The jokulhlaup had an exponential rise to a peak discharge, and following the peak, a very steep fall in discharge as the water supply to the drainage system ceased. A similar jokulhlaup was observed in August 1990 with an estimated release of 8.05×105 m3 water. Jokulhlaups at Salkaglaciaren are recurring events and have been indirectly observed since the 1950s.

During the last deglaciation of North America, huge proglacial lakes formed along the southern margin of the Laurentide Ice Sheet. The largest of these was glacial Lake Agassiz, which formed about 11.7 14 C kyr and drained into Hudson Bay about 7.7 14 C kyr (8.45 cal kyr ) . Overflow from these lakes was variably directed to the Mississippi, St. Lawrence and Mackenzie drainage systems and it is thought that switches in routing were accompanied by a response in ocean circulation that produced abrupt climate events. When the ice dam across Hudson Bay finally was breached, a massive flood drained Lake Agassiz, which was routed through Hudson Strait to the Labrador Sea. In terms of stored water volume the largest reservoir was associated with the Kinojevis level of Lake Agassiz. For this maximum filling, the impounded water volume available to produce floods is estimated as 40,000– 151,000 km 3 , depending on the location of the ice margin and route used. The timing of this rapid release of stored freshwater just precedes the early Holocene cooling event at 8.2 cal kyr BP . We use the Spring–Hutter theory to simulate flood hydrographs for floods that originate in subglacial drainage conduits and find that flood magnitude and duration are ∼5 Sv and ∼0.5 yr . Multiple fillings and floods are possible as are single floods having a complex multipulse structure. Modelling results suggest that the outburst flood from Lake Agassiz may have terminated before the lake surface elevation dropped to sea level and that the flood ended when a stable drainage channel was established, connecting Lake Agassiz to the Tyrrell Sea.

Pleistocene basaltic lava dams and outburst‐flood deposits in the western Grand Canyon, Arizona, have been correlated by means of cosmogenic 3He (3Hec) ages and concentrations of SiO2, Na2O, K2O, and rare earth elements. These data indicate that basalt clasts and vitroclasts in a given outburst‐flood deposit came from a common source, a lava dam. With these data, it is possible to distinguish individual dam‐flood events and improve our understanding of the interrelations of volcanism and river processes. At least five lava dams on the Colorado River failed catastrophically between 100 and 525 ka; subsequent outburst floods emplaced basalt‐rich deposits preserved on benches as high as 200 m above the current river and up to 53 km downstream of dam sites. Chemical data also distinguishes individual lava flows that were collectively mapped in the past as large long‐lasting dam complexes. These chemical data, in combination with age constraints, increase our ability to correlate lava dams and outburs...

Water bodies impounded by glaciers, moraines, and ice jams on rivers can drain suddenly, with disastrous downstream consequences. Lakes can form at the margins of an alpine glacier or ice cap, on its surface, or at its base. Smaller pockets of water may also be present within some glaciers. In all cases, these water bodies might drain by enlarging subglacial tunnels or by mechanical collapse of the glacier dam. Many formerly stable glacier lakes have failed over the past century, in some cases repeatedly, as Earth’s atmosphere has warmed and glaciers thinned and receded. The peak discharge, duration, and volume of a subglacial outburst flood depend mainly on (1) the geometry and rate of development of the tunnel at the base of the glacier and (2) the size and geometry of the impounded water body. Discharge commonly increases exponentially during the outburst, but ends quickly when the lake empties or when the drainage tunnel is plugged by collapse of the tunnel roof or closes due to plastic ice flow. Some glacier outburst floods result from the mechanical collapse of the ice dam. In such cases, the peak flow is achieved rapidly during the collapse. Outburst floods from glacier lakes attenuate due to temporary storage of floodwaters in channels and on valley floors. Many hazardous lakes are dammed by lateral and end moraines that formed in the past two centuries when valley and cirque glaciers retreated from advanced positions reached during the Little Ice Age. Moraine dams are susceptible to failure because they are steep and relatively narrow, because they comprise loose poorly sorted sediment, and because they may contain ice cores or interstitial ice. These dams generally fail by overtopping and incision. The triggering event may be a heavy rainstorm, strong winds, or an ice avalanche or landslide into the lake that generates waves that overtop the dam. Melting of moraine ice cores and piping are other possible failure mechanisms. Outflow from a moraine-dammed lake increases as the breach enlarges and then decreases as the level of the lake falls. The moraine breach may become armored, preventing further incision, or the hydraulic gradient at the breach may decrease to a point that erosion ceases. Outburst floods from glacier- and moraine-dammed lakes typically entrain, transport, and deposit large amounts of sediment. If the channel is steeper than about 0.10-0.15 and contains abundant loose sediment, the flood likely will transform into a debris flow. Such flows may be larger and more destructive than the flood from which they formed. A period of protracted warming is required to trap lakes behind moraines and create conditions that lead to dam failure. The warming also forces glaciers to retreat, prompting ice avalanches, and landslides that have destroyed many moraine dams.

This study deals with Siberian rivers dominated by outburst flood within a continuous and deep permafrost zone. The Lena basin rivers (Lena, Aldan and Vilioui) present specific fluvial forms: they consist of multiple wide channels separated by sandy bars and vegetated allu- vial islands; sinuous and narrow branches can be observed in the floodplain and on the islands. The objective of this preliminary study is to understand the dynamics of these hydro- systems on the basis of a sedimentary processes analysis. Firstly, the study of the channels deposits reveals that the thickness of sediments remobilised during the annual flood is more important in the case of the anastomosed branches than in the main channels. Furthermore, Passega's method (1957) allows the determination of depositional mechanisms for the active fluvial units. Secondly, the analysis of sections located at the interface between active channels and stabilised units provide information about the channels' sedimentary processes. Specific deposits bordering the channels, that could be associated with log-jams and ice-jams, are also identified as major sedimentation processes. Finally, the effect of thermal and mechanical erosion on the banks is examined. It appears that the narrowly graded sediments deposited in the river bars derive mainly from the remobilisation of ancient aeolian deposits. During the summer low discharge, the dewatered channels are subject to aeolian deflation, building younger dunes on the banks., Cette étude concerne les rivières à régime de débâcle en milieu périglaciaire à pergélisol épais et continu. La Léna et ses principaux affluents (Aldan, Vilioui) présentent des formes fluviales spécifiques : on distingue dans le lit mineur des chenaux larges et peu profonds, qui enserrent des bancs sableux et des îles boisées, tandis que dans la plaine et les îles se développent des bras anastomosés plus sinueux et plus étroits. L'objectif de cette étude préliminaire est la compréhension du fonctionnement de ces hydrosystèmes, en se fondant sur une analyse des processus sédimentaires. En premier lieu, l'étude des dépôts dans les chenaux révèle des épaisseurs remobilisées à l'occasion de la crue annuelle, plus fortes dans le cas des bras anastomosés que dans les chenaux principaux. De plus, la méthode de Passega (1957) permet la détermination des modes de dépôt des particules pour chacune des unités fluviales fonctionnelles. En second lieu, l'analyse de coupes situées à l'interface de chenaux actifs et d'unités stabilisées apporte des informations sur les modes de remblaiement des chenaux et met également en évidence des dépôts spécifiques que l'on peut interpréter comme étant liés à des ruptures d'embâcles de glace et de débris ligneux. Enfin, le rôle de l'érosion thermique et mécanique que les cours d'eau exercent localement sur les berges est examiné. Le recul des berges apporte au système une charge abon- dante très homométrique issue en grande partie de dunes éoliennes anciennes. Au cours de l'étiage d'été, les dépôts des chenaux asséchés sont repris partiellement en charge par la déflation éolienne et contribuent ainsi à l'édification de nouvelles dunes sur les berges., Diese Studie betrifft Flüsse mit Eis- gang in periglazialem Milieu mit tiefem kontinuierlichem Permafrostboden. Die Lena und ihre wichtigsten Zuflüsse (Aldan, Vilioui) weisen spezifische Flussformen auf: Man erkennt im Normalbett breite Gerinne mit geringer Tiefe, welche sandige Bänke und bewaldete Inseln umschließen; in der Ebene und den Inseln dagegen entwickeln sich gewundene und engere verwilderte Flussarme. Das Ziel dieser vorbereitenden Studie ist das Funktionieren dieser Wassersysteme zu verstehen und dies ausgehend von der Analyse der Ablagerungprozesse. Als erstes lässt die Untersuchung der Ablagerungen in den Gerinnen erkennen, dass die Dicke der während der jährlichen Überflutung wiedermobilisierten Ablagerungen in den verwilderten Armen stärker als in den Hauptgerinnen ist. Darüberhinaus erlaubt die Methode von Passega (1957) den Ablagerungsmodus für jede aktive Flusseinheit zu bestimmen. Zweitens liefert die Analyse von Abschnitten am Berührungspunkt von aktiven Gerinnen und stabilisierten Einheiten Informationen über den Aufschüttungsmodus der Gerinne und macht spezifische Ablagerungen deutlich, welche man auf Durchbrüche der Eis- und Holztrümmeranhäufung zurückführen kann. Schließlich wird die Rolle der thermischen und mechanischen Erosion untersucht, welche die Wasserläufe örtlich auf die Flussufer ausüben. Der Rückzug der Uferträgt dem System eine starke, sehr homometrische Schuttlast zu, zum großen Teil aus den alten, durch den Wind gebildeten Dünen stammend. Während des Niedrigwassers im Sommer werden die Ablagerungen der ausgetrockneten Gerinne teilweise durch die Windabnahme wieder angela- gert und tragen so zur Errichtung neuer Dünen an den Ufern bei.

More than a decade has passed since the publication of the benchmark paper of Costa and Schuster (Costa, J.E. and Schuster, R.L. 1988: The formation and failure of natural dams. Geological Society of America Bulletin 100, 1054-68) on the formation and failure of natural dams. This review takes a critical look at recent trends and developments in international and New Zealand-based research on landslide dams. Temporary or permanent stream blockages by mass movements commonly occur in steep terrain, and gradually receive more attention and awareness with increasing population and land use pressure in upland regions. Different approaches in methodology and their relevance and application potential for engineering and mitigative measures are reviewed and several shortcomings outlined, with a view towards possible future research directions. A high percentage of previous work on landslide dams has been mainly descriptive in character, and has produced a multitude of documented case studies. Recent attempts to redress the balance have included the establishment of global and nationwide databases (inventories) of landslide dams, progress in predictive, quantitative and GIS-based modelling. Furthermore, interpretative approaches towards the reconstruction of former stream blockages and their spatio-temporal distribution patterns have been pursued, which may assist assessments of present and future geomorphic hazards. Both such appraisals as well as management strategies in mountainous regions in general, will have to rely on key data efficiently extracted from a plethora of case examples. Further work includes consideration of temporal and permanent landslide-triggered stream impoundments within Quaternary landscape evolution, quantification of sediment budgets and palaeoenvironmental reconstruction. Overall, there is still a considerable lack of understanding of geomorphic forms and processes involved with landslide-dam formation, stability and failure, part of which is inherent in the often ephemeral nature of stream blockages in coupled hillslope-valley systems.

A distributed temperature index melt model including potential clear-sky solar radiation was applied to Unteraargletscher, Bernese Alps, Switzerland, to quantify water input to the glacial hydrological system during the ablation season 1999. Model parameters were determined by calibrating calculated melt with ablation measurements. Discharge was measured in the proglacial stream for 18 days until the station was destroyed by an outburst flood. Comparison of modeled melt and measured discharge reveals that routing processes of water through the glacier vary with time as the water is transferred through a dynamic drainage system. Furthermore, an imbalance of water input and output suggests that water was stored in or beneath the glacier during this period. The culminating outburst flood presumably released this en– or subglacially stored water and may be related to a change in the configuration of the glacial drainage system as inferred from measurements of subglacial water pressure.

Glacial lakes in the Nepal Himalaya can threaten downstream communities and have large socio-economic consequences if an outburst flood occurs. This study identified 131 glacial lakes in Nepal in 2015 that are greater than 0.1 km ²and performed a first-pass hazard and risk assessment for each lake. The hazard assessment included mass entering the lake, the moraine stability, and how lake expansion will alter the lake’s hazard in the next 15–30 years. A geometric flood model was used to quantify potential hydropower systems, buildings, agricultural land, and bridges that could be affected by a glacial lake outburst flood. The hazard and downstream impacts were combined to classify the risk associated with each lake. 11 lakes were classified as very high risk and 31 as high risk. The potential flood volume was also estimated and used to prioritize the glacial lakes that are the highest risk, which included Phoksundo Tal, Tsho Rolpa, Chamlang North Tsho, Chamlang South Tsho, and Lumding Tsho. These results are intended to assist stakeholders and decision makers in making well-informed decisions with respect to the glacial lakes that should be the focus of future field studies, modeling efforts, and risk-mitigation actions.

Global warming causes rapid shrinking of mountain glaciers. New lakes can, thus, form in the future where overdeepenings in the beds of still-existing glaciers are becoming exposed. Such new lakes can be amplifiers of natural hazards to downstream populations, but also constitute tourist attractions, offer new potential for hydropower, and may be of interest for water management. Identification of sites where future lakes will possibly form is, therefore, an essential step to initiate early planning of measures for risk reduction and sustainable use as part of adaptation strategies with respect to impacts from climate change. In order to establish a corresponding knowledge base, a systematic inventory of glacier-bed overdeepenings and possible future lakes was compiled for the still glacierized parts of the Peruvian Andes using the 2003–2010 glacier outlines from the national glacier inventory and the SRTM DEM from the year 2000. The resulting inventory contains 201 sites with overdeepened glacier beds >1 ha (104 m2) where notable future lakes could form, representing a total volume of about 260 million m3. A rough classification was assigned for the most likely formation time of the possible new lakes. Such inventory information sets the stage for analyzing sustainable use and hazard/risk for specific basins or regions.

Wu et al ., Han, and Huang et al . question our reconstruction of a large outburst flood and its possible relationship to China’s Great Flood and the Xia dynasty. Here, we clarify misconceptions concerning geologic evidence of the flood, its timing and magnitude, and the complex social-cultural response. We also further discuss how this flood may be related to ancient accounts of the Great Flood and origins of the Xia dynasty.

By analyzing the data and methodology of Wu et al . (Reports, 5 August 2016, p. 579), I find that their conclusions about the scale of the dammed lake, the dating of the lake, and the peak discharge at the point of dam failure and at the Lajia site cannot be validated. The conjecture of the supposed Great Flood and its impact on the formation of the early Chinese dynasty is not substantiated.

Natural damming of upland river systems, such as landslide or lava damming, occurs worldwide. Many dams fail shortly after their creation, while other dams are long-lived and therefore have a long-term impact on fluvial and landscape evolution. This long-term impact is still poorly understood and landscape evolution modelling (LEM) can increase our understanding of different aspects of this response. Our objective was to simulate fluvial response to damming, by monitoring sediment redistribution and river profile evolution for a range of geomorphic settings. We used LEM LAPSUS, which calculates runoff erosion and deposition and can deal with non-spurious sinks, such as dam-impounded areas. Because fluvial dynamics under detachment-limited and transport-limited conditions are different, we mimicked these conditions using low and high erodibility settings, respectively. To compare the relative impact of different dam types, we evaluated five scenarios for each landscape condition: one scenario without a dam and four scenarios with dams of increasing erodibility. Results showed that dam-related sediment storage persisted at least until 15 000years for all dam scenarios. Incision and knickpoint retreat occurred faster in the detachment-limited landscape than in the transport-limited landscape. Furthermore, in the transport-limited landscape, knickpoint persistence decreased with increasing dam erodibility. Stream capture occurred only in the transport-limited landscape due to a persisting floodplain behind the dam and headward erosion of adjacent channels. Changes in sediment yield variation due to stream captures did occur but cannot be distinguished from other changes in variation of sediment yield. Comparison of the model results with field examples indicates that the model reproduces several key phenomena of damming response in both transport-limited and detachment-limited landscapes. We conclude that a damming event which occurred 15 000years ago can influence present-day sediment yield, profile evolution and stream patterns. Copyright (c) 2014 John Wiley & Sons, Ltd.

The 2,360 BP eruption of Mount Meager, British Columbia began as an explosive, dacitic sub-Plinian eruption that waned rapidly to a sustained period of Vulcanian, eruption-triggered dome collapse events producing voluminous block and ash flow (BAF) deposits. The earliest BAF deposits accumulated rapidly enough immediately downslope of the vent to retain heat and weld; using the deposit as a paleoviscometer determines an effective viscosity of 109–1010 Pa s during welding. This prolific production of hot lava and block and ash flows, in a steep mountainous terrain, created a ∼110 m high, largely impermeable dam capped by permeable, non-welded BAF deposits and unconsolidated avalanche deposits that blocked the flow of the Lillooet River and created a temporary lake. The welded pyroclastic dam was compromised and overtopped at least once before the peak dam height was reached. Renewed eruption caused buildup of the dam to a maximum of 780 m above sea level (asl) and grew the temporary lake to an elevation of 740 m asl and a minimum volume of 0.55 km3. The rise of lake level led to catastrophic failure of the top of the dam, generating an outburst flood that carved a canyon through most of the dam and resulted in a voluminous lahar that is traced at least 65 km downstream. Based on current flow rates of the Lillooet River, the lake would have overtopped the final dam at a minimum of 39–65 days after its formation. The peak deluge lasted approximately 8 h and eroded a 2.5-km long canyon into the still-hot dam core before returning to background flow rates.

Surface deposits of the Tuttle Canyon alluvial fan, eastern Sierra Nevada piedmont, California, mainly accumulated during a catastrophic outburst flood probably triggered by the failure of a moraine-dammed lake in the steep (16.4°), high-relief (2361 m), and high-elevation (to 4275 m) catchment. Moraines of the catchment and upper fan (Facies A) comprise unsorted sand to blocks derived from the granitic bedrock. The main flood facies (B) is texturally like the moraine, consisting of unsorted, matrix-supported, sandy pebbly cobbly blocky boulder gravel in a single unit 3 to 8+ m thick distributed across most of the 10.5 km long and 28.1 km2 fan. Facies B was deposited during the initial outburst-flood phase as a high-volume, noncohesive sediment gravity flow (NCSGF) instigated by water rapidly descending over moraine. It differs from the moraine by a planar unit geometry and a slope-transverse long-axis alignment of boulders. NCSGF deposition was followed by a water-flood phase caused by continued lake drainage subsequent to removal of loose sediment in the flood path. This discharge carved channels 2-22 m deep and 5-60 m wide around and across fan NCSGF deposits, with channels departing from various points along Tuttle Creek. Horseshoe separation scours also formed around bedrock spurs, and laminated pebbly sand accumulated on the channel beds (Facies D). Flood discharge expanded on the distal fan into a sheetflood that first deposited a boulder unit (Facies E), and then 4+ m of cobbly sandy pebble gravel in planar beds 5-20 cm thick (Facies F). The final flood phase entailed incision of Tuttle Creek, wherein bouldery cobble gravel (Facies C) was concentrated. Post-flood modification of these deposits has been limited to secondary processes such as eolian deposition (Facies G) and bioturbation. Outburst floods on fans of the Sierra Nevada piedmont ultimately are caused by the glacial transfer of colluvium from the upper catchment slopes into moraines on the valley floors that dam drainage to form lakes. Outburst floods differ from meteorological floods in the valley by the high water and sediment discharge achieved during a single event, by deposition of massive NCSGF beds, and by causing major changes to the landscape such as the carving of channels. These differences produce fans with distinctive facies and hazards, the former allowing their recognition in either modern or ancient settings.

Sedimentary deposits from the Smith Canyon dune field, south-central Columbia Basin, Washington, U.S.A. document climatically-influenced Late Pleistocene and Holocene aeolian and fluvial deposition in a region impacted by glacial outburst floods and tephra falls. The depositional history is summarized by five environmentally distinctive and climatically sensitive sedimentary units (temporal limits estimated): Unit 1 ( c. 15·5–8 ka), pedogenically altered glacial outburst flood and minor aeolian silt and clay; Unit 2 ( c. 8–6·9 ka), fluvial and minor aeolian sand; Unit 3 ( c. 6·9–6·8 ka), flood-induced fluvial sand with gravel-sized tephra clasts; Unit 4 ( c. 6·8–3·9 ka), aeolian dune sand; Unit 5 ( c. 3·9 ka to present), pedogenically altered, stabilized dune sand. Estimated age ranges are based on stratigraphic position, tephrochronology, and correlation with temporally constrained strata from elsewhere in the region.

Several fluvial terraces and other flat surfaces are well developed in Wangdi Phodrang District along Chang Chhu (Puna Tshan Chhu) in central Bhutan.The low terrace of 5 m to 18 m in relative height is widely distributed, preserving the river flat reliefs on the surface. The middle terrace of 20 m to 50 m in relative height is well developed from Wangdi Phodrang to the upper reaches. The high surfaces of 110 m in relative height are distributed only in Wangdi Phodrang Town and Bajo Monastery Hill, which is 2 km upstream from the former.Geology of the middle terrace is mainly composed of a well rounded and imbricated boulder bed with several sand beds of lesser amount.Geology of the high surface in Wangdi Phodrang Town is composed of two members : the underlying 50 m-thick massive huge boulder bed and the 60 m-thick mudflow deposits overlying the former horizontally. The huge boulder bed continues to the imbricated boulder bed of the middle terrace, suggesting that the mudflow forming the high surface is younger than the middle terrace.On the opposite bank of Wangdi Phodrang Town, there are huge mudflow deposits, which have flowed down towards Wangdi Phodrang Town. Judging from the stratigraphic relation with middle terrace deposits, flow direction, elevation, size, and lithology, the mudflow can be safely correlated with the mudflow at Wangdi Phodrang Town.Then, the mudflow may once have formed natural dam by covering the river flat gravel bed of the middle terrace. Estimated height of the dam is 1310 m a.s.l., and the crest was almost 1000 m wide.While Bajo Monastery Hill is composed of two geological members, the northern major portion of the hill is brown-colored massive sand of over 20 m thick, which are delta fan deposits of a tributary named Limte Chhu, while massive white sand distributed locally at southern downstream side of the hill is abutting on the former. Groundwater drilling on the middle terrace revealed that the well rounded boulder bed is thinly overlaid by white silty sand, which continues to the massive white sand at Bajo Monastery Hill. This evidently suggests that the massive white sand bed is younger than the middle terrace boulder bed.Judging from massive appearance without stratification and mixed occurrence with blocks and fragments of varved clay, the genesis of the massive white sand at Bajo Monastry Hill without doubt resulted from turbidity current of the Glacier Lake Outburst Flood (GLOF).When the GLOF flowed into the deep lake formed by the mudflow dam, the suspended sand, as well as transported blocks of varved clay, may have been settled in the lake. Concurrently, the GLOF may have destroyed the natural dam and drained the lake. Only a small portion of the GLOF sediments remained at the riverside stagnate concavity in the Bajo monastery area.The above-mentioned Quaternary geo-history constructed from field evidence is identical to the legend of the Wangdi Phodrang district.The legend is that an ancient lake was drained in one night by God, who was angry with the impious inhabitants. The upper reach of the lake in the legend is Punakha Town, which is at an elevation of 1340 m. Therefore, the size of the lake in the legend is as same as the size estimated by geology.The legend may suggest that the GLOF event was observed by ancient inhabitants settled in this area.

Moraine-dammed lakes are common in the high mountains of British Columbia. Most of these lakes formed when valley and cirque glaciers retreated from advanced positions achieved during the Little Ice Age. Many moraine dams in British Columbia are susceptible to failure because they are steep-sided, have relatively low width-to-height ratios, comprise loose, poorly sorted sediment, and may contain ice cores or interstitial ice. In addition, the lakes commonly are bordered by steep slopes that are prone to snow and ice avalanches and rockfalls. Moraine dams generally fail by overtopping and incision. The triggering event may be a heavy rainstorm, or an avalanche or rockfall that generates waves that overtop the dam. The dam can also be overtopped by an influx of water caused by sudden drainage of an upstream ice-dammed lake (jokulhlaup). Melting of moraine ice cores and piping are other possible failure mechanisms. Failures of moraine dams in British Columbia produce destructive floods orders of magnitude larger than normal streamflows. Most outburst floods are characterized by an exponential increase in discharge, followed by an abrupt drop to background levels when the water supply is exhausted. Peak discharges are controlled by dam characteristics, the volume of water in the reservoir, failure mechanisms, and downstream topography and sediment availability. For the same potential energy at the dam site, floods from moraine-dammed lakes have higher peak discharges than floods from glacier-dammed lakes. The floodwaters may mobilize large amounts of sediment as they travel down steep valleys, producing highly mobile debris flows. Such flows have larger discharges and greater destructive impact than the floods from which they form. Moraine dam failures in British Columbia and elsewhere are most frequent following extended periods of cool climate when large lateral and end moraines are built. A period of protracted warming is required to trap lakes behind moraines and create conditions that lead to dam failure. This sequence of events occurred only a few times during the Holocene Epoch, most notably during the last several centuries. Glaciers built large moraines during the Little Ice Age, mainly during the 1700s and 1800s, and lakes formed behind these moraines when climate warmed in the 1900s. Twentieth-century climate warming is also responsible for recent moraine dam failures in mountains throughout the world. Warming from the late 1800s until about 1940 and again from 1965 to today destabilized moraine dams with interstitial or core ice. The warming also forced glaciers to retreat, prompting ice avalanches, landslides, and jokulhlaups that have destroyed some moraine dams.

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.

Glaciers and snowfields can form potential hazards in the Himalayas, and in similarly glacierised regions of the world. Some glaciological phenomena can have significant impacts upon society over a short time scale (minutes–days), such as ice/snow avalanches and glacial floods. Other related hazards can be equally serious but less obvious when considered on a much longer time scale (months–years–decades), such as glacier volume fluctuations leading to water resource problems. Only when humans and their activities become vulnerable to glacier-related processes is there considered to be a hazard risk. As glaciers recede in response to climatic warming, the number and volume of potentially hazardous moraine-dammed lakes in the Himalayas is increasing. These lakes develop behind unstable ice-cored moraines, and have the potential to burst catastrophically, producing devastating Glacial Lake Outburst Floods (GLOFs). Discharge rates of 30,000 m 3 s −1 and run-out distances in excess of 200 km have been recorded. Despite the scale of the risk, it is possible to assess and mitigate hazardous lakes successfully. Hazard assessment using satellite images has been effective for remote areas of Bhutan, and remediation techniques successfully developed in the Peruvian Andes are now being deployed for the first time in Nepal.

In the winter of 1911, a massive earthquake-induced landslide in the Pamir Mountains of eastern Tajikistan completely blocked the valley of the Bartang (Murgab) River, a headwater tributary to the Amu Darya River basin. A lake began to grow behind this natural dam and has now reached a length of 60 km. In a worst-case scenario that assumes collapse of the dam, a catastrophic outburst flood from Lake Sarez would destroy the villages and infrastructure in the Amu Darya basin between the lake and the Aral Sea, affecting an area inhabited by more than five million people across a distance of over 2000 km. But local populations in the mountain valleys face further, more immediate and pressing hazards; the annual cycle of rockfalls, debris flows, avalanches, and flooding constantly impinges on human activities. Development assistance is thus needed on a small, participatory scale in the form of enhancing existing local emergency response infrastructure. Moreover, monitoring Lake Sarez and designing an ...

A large outburst flood from a glacial terminal moraine lake can cause severe damage to downstream communities. This paper presents a study on the outbursts of glacial terminal moraine lakes in the upper Nainchu River basin of Tibet. This study includes an investigation of the number, size, and distribution of glacial terminal moraine lakes; analysis of climatic and geographic factors that contribute to glacial lake outbursts; investigations of the outburst potential of the three largest lakes in the Nainchu River basin; simulations of floods that might occur from the glacial lakes; and a description of the monitoring and flood warning system setup.

Sudden releases of impounded water from lakes in volcanic regions constitute a major and frequently repeated hazard. An outburst flood from Taupo caldera, New Zealand, released ∼20 km 3 of water, within decades following an ignimbrite-emplacing eruption, ca. 1.8 ka. Paleohydrologic reconstruction of the Taupo flood provides estimates of peak discharge at the outlet in the range 17 000–35 000 m 3 /s. Dimensionless analysis demonstrates that (1) failure of the barrier was essentially instantaneous, (2) the event may be treated hydraulically as a dam break, and (3) the peak discharge was a function of outlet geometry rather than lake volume or breach formation rate. Paleohydraulic reconstructions based on empirical relations derived from historic dam breaches yield only order of magnitude estimates of peak discharge. Calculations based on the physical dimensions of the outlet channel and hydraulic principles are likely to be more accurate and are in close agreement with computer-implemented dynamic-flow–routing models. The latter give peak discharges and maximum stage levels similar to constraints imposed by field evidence and estimates of flow depth and velocity. The long duration of the Taupo flood and the relatively narrow, confined flood route resulted in minimal attenuation of the flood wave compared with modern dam breach events, and flood deposits can be traced as far as 232 km downstream. Caldera lake breakout floods may be among the most far-reaching hazards associated with volcanism.

This paper presents new evidence of coarse-grained deposition from a turbulent suspension within a low-energy `slack-water' location during a recent well-documented, volcanically related, high-magnitude glacier outburst flood or jokulhlaup, Skeiðararjokull, Iceland. This study uses established spatial and temporal constraints on processes observed during the November 1996 jokulhlaup to interpret resultant flood sediments. Coarse-grained sediments were deposited within flood slack-water conditions from suspension load by repeated turbulent flow pulses with durations of seconds–minutes. Depositional processes are thought to be analogous to turbidity currents. A minimum thickness of 15 m of rhythmites record suspended sediment dynamics at a conduit mouth during the late rising and early falling stages of the jokulhlaup. The morphology and sedimentology of deposits in a large ice-walled chamber are consistent with previous models proposed for bar deposition during cataclysmic floods. Flood flows within subglacial conduits and ice-walled open channels were sufficiently powerful to carry material up to boulder size in suspension. Macro-turbulent flows carried huge quantities of suspended sediment to high levels within the main outlet channel. High-frequency, short-duration flow pulses entering a complex ice-walled channel geometry generated highly unsteady and non-uniform flows capable of both erosional and depositional work. This study lends support to the deposition of multiple rhythmites per flood under main flow slack-water conditions. Identification of high-magnitude jokulhlaups in the ice-marginal sedimentary record will depend on the identification and correct interpretation of feeder channel and slack-water turbidite sediments. The results described here may also have application to rhythmic deposits formed by large turbulent flows in other environmental settings.

Measurements made at John Evans Glacier, eastern Ellesmere Island, Nunavut, Canada in 1994 and 1996 provide new insight into the internal hydrology of polythermal glaciers. During the early part of each melt season, supraglacial waters enter the glacier via a crevasse field about 4 km from the terminus and are stored in a subglacial reservoir. Release of the water from the reservoir occurs initially via an artesian fountain on the glacier surface and by upwelling of waters through subglacial sediments at the terminus (event1). Channelization of the subglacial waters then occurs and water is discharged as an outburst flood (event 2), which releases a considerably larger volume of water than event 1. Thus, drainage of the subglacial reservoir follows a cyclical pattern in which discharge oscillations increase in amplitude over time. The cycle may end with complete reservoir drainage. The total volume of water released was much greater in 1994 than in 1996, primarily because the 1994 melt season was longer and warmer than the 1996 season. Interannual differences in the form of the outflow hydrographs, and in the extent and timing of connections between the subglacial reservoir and marginal melt streams, are linked to variations in the size and rate of growth of the subglacial reservoir. This hydrological behaviour may have important implications for the dynamics of polythermal glaciers.

While the paper by Alley et al. (Alley, R.B., Dupont, T.K., Parizek, B.R., Anandakrishnan, S., Lawson, D.E., Larson, G.J., Evenson, E.B., 2006. Outburst flooding and the initiation of ice-stream surges in response to climatic cooling: A hypothesis. Geomorphology 75, 76–89) is a welcome contribution as it presents some new arguments and expands the discussion, it unfortunately overlooked the literature on the captured ice shelf (CIS) hypothesis. Considering all recent results, the hypothesis has the potential for drastically altering our understanding of sudden climate change during the Quaternary period. Also, the interpretation of macrogeomorphology in land-ice covered continents and seas, including the Hudson Bay and the Baltic Sea, is affected.

The International Summer School on Rockslides and Related Phenomena in the Kokomeren River valley, Tien Shan, Kyrgyzstan is the annual field training course focused on identification and study of large-scale bedrock landslides. These phenomena pose a threat to communities living in mountainous regions all over the world and are characterised by the enormous amount of material involved, and its high mobility and ability to create natural dams. Since 2006 more than 50 students and young landslide researchers from 17 countries have been introduced to rockslides and rock avalanches of different morphological types, some of which have formed deeply eroded rockslide dams that allow study of their internal structure, as well as evidence of inundation and of catastrophic outburst floods, and impressive manifestations of recent tectonic phenomena.

Due to global climate change and ongoing deglaciation, research on Glacial Lake Outburst Floods (GLOFs) is of great importance. The idea of a glacial lake outburst floods database project arose from our effort to identify regional specifics of these events in our region of research interest—the highest Peruvian mountain range, Cordillera Blanca. The project is designed under the International Programme on Landslides (IPL) for 3 years (2013–2015) and then we suppose it will be continued. The main goal of this project is the creation of a widely available online database of GLOFs that have occurred worldwide since the end of the “Little Ice Age”. An important step will be the initiation of international cooperation between individual scientific departments. We would like to complete and share information about each event, such as probable cause, flood volume, and socioeconomic impacts downstream. Our preliminary results showed important regional differences in the representation and proportion of various causes in different high mountainous regions worldwide. The most frequent causes are various types of dynamic slope movements into lakes (icefalls, rockfalls or other landslides). This cause is dominant in all of the studied regions. On the other hand, some causes are regionally specific—e.g., dam failure following a large earthquake was recorded in only one region, the Cordillera Blanca. Taking these differences into account is a crucial step in creating an optimal regionally focused method of GLOF hazard assessment.

The climate across Alaska is changing, as are the melting and other dynamics of glaciers and their lengths, widths, thicknesses, and masses. One may reasonably expect that terminus and surface ablation of Alaskan glaciers would impact the occurrence and sizes of glacier-dammed lakes (GDLs) impounded by many of these glaciers. An individual lake and its damming glacier may have unique dynamics, exhibiting chaotic variations not directly attributable to climate change. Statistical analysis of a large GDL population, however, indicates that changes may be linked directly to shifting climatic conditions, thus providing an empirical basis for quantitative numerical models of future behavior. In this chapter we show that the rapidly changing distribution of glacier-dammed lakes is neither simple nor homogeneous, but that lake changes may be amenable to modeling. These lakes, their impounding glaciers, and their changes through time can be detected in satellite imagery. Presented here is research enabled by the GLIMS initiative, and the Terra/ASTER and Landsat programs. Archived imagery facilitated review and change analysis of 538 previously mapped GDLs across Alaska, U.S.A. All glacier perimeters within the study area were also reviewed for additional lakes forming since the prior survey in 1971. Change analyses of the combined lake population over time found nonuniform distributions of lake losses and gains from 1971 to 2000 across Alaska. Detected changes appear less related to elevation, latitude, or maritime influence than to the complexity, origin and terminus types of damming glaciers, the aspects of their ice dams, possibly the topographic gradient below and near the lake, and possibly the rate of recent temperature increases. The Copper River Basin (CRB), for example, has recorded low rates of atmospheric warming relative to adjoining areas over the past 50 years, and it has retained and developed the greatest proportion of GDLs. A concurrent detailed remote-sensing and field observation study of the CRB highlighted the dynamics of individual GDLs and their damming glaciers. Whereas there is no single typical or representative lake, Iceberg Lake, in the far eastern Chugach Mountains, provides an example showing how a climatic shift to warmer conditions may result in diminishment and even disappearance of these lakes. Iceberg Lake was comparatively stable for at least 1,500 years, but responded to > 100 years of thinning of its damming glacier with the initiation of episodic glacier lake outburst flood (GLOF) drainages every year or two, starting in 1999. The thinning of the damming glacier, in turn, is partly a response to a moraine-dammed lake that has formed since the 1970s at the terminus of the trunk (Tana) glacier, catalyzing disarticulation of that terminus and causing a furtherance of thinning of Iceberg Lake’s damming glacier. The entire system including the Bagley Icefield, outlet glaciers, multiple GDLs (Iceberg Lake among them), and oraine-dammed lakes, is dynamically complex; some parts appear to be responding to climate shifts, and other parts may be displaying intrinsic unsteadiness of flow (including a surge/waste cycle of Bering Glacier). At the same time as known lakes have been diminishing or disappearing, in recent decades at lower elevations, GDLs tended to form and persist at higher elevations.

Flash floods are the important events of the hydrological regime of rivers in arid areas. In the Tarim River, northwestern China, flash floods are being monitored. The observed data and investigation demonstrate the difference in time, place, frequency and intensity of their occurrences. In this paper two main flash floods are put forward, they are rainstorm flash flood (RFF) and glacier lake outburst flood (GLOF). Two cases of flash flood in the two tributaries of the Tarim River presented in this paper. It analyses and compares the causes and the development of the two kinds of flash floods. Through further discussion about influence of flash floods on the main channel of the Tarim River, conclusion can be drawn that the greatest flood in record of the main channel come from the GLOF of the upper reaches of the Kunmalik River, especially augmented by great ablation flood. Finally the advantages and disadvantages from flash floods to the environment of the catchment are demonstrated in the paper.

Effects of climate change are particularly strong in high-mountain regions. Most visibly, glaciers are shrinking at a rapid pace, and as a consequence, glacier lakes are forming or growing. At the same time the stability of mountain slopes is reduced by glacier retreat, permafrost thaw and other factors, resulting in an increasing risk of landslides which can potentially impact lakes and therewith trigger far reaching and devastating outburst floods. To manage risks from existing or future lakes, strategies need to be developed to plan in time for adequate risk reduction measures at a local level. However, methods to assess risks from future lake outbursts are not available. It is actually a challenge to develop methods to evaluate both, future hazard potential and future damage potential. Here we present an analysis of future risks related to glacier lake outbursts for a local site in southern Switzerland (Naters, Valais). To estimate two hazard scenarios, we used glacier shrinkage and lake formation modelling, simple flood modelling and field work. Further we developed a land-use model to quantify and allocate land-use changes based on local-to-regional storylines and three scenarios of land-use driving forces. Results are conceptualized in a matrix of three land-use and two hazard scenarios for a time period of 2045, and show the distribution of risk in the community of Naters, including high and very high risk areas. The study corroborates the importance of land-use planning to effectively reduce future risks related to lake outburst floods.

At Solheimajokull glacier in southern Iceland, field evidence has been collected of a Tenth Century jokulhlaup (or glacial outburst flood). It was an exceptional event in terms of generation, scale, magnitude and geomorphic impact. Although now fragmented and piecemeal, many of its direct (and indirect) geomorphological and sedimentary markers have been identified, mapped and dated to unravel the sequence of events played out during this significant episode in the glacial history. 'VolcVis', an innovative, customised visualisation platform using computer gaming technology is developed and applied for the first time in coalescing and displaying field results from Solheimajokull, creating an interactive, multi-perspective, three-dimensional (3D) prototype model. A visual simulation of Solheimajokull's Tenth Century physical environment places the flood into geomorphic and topographic context. This ability to dynamically display and interpret field data presents new possibilities for testing hypotheses, and for data sharing with Icelandic hazard mitigation authorities and the general public.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE; International audience; Tete Rousse is a small polythermal glacier located in the Mont Blanc area (French Alps) at an altitude of 3100 to 3300 m. In 1892, an outburst flood from this glacier released about 200 000m(3) of water mixed with ice, causing much damage. A new accumulation of melt water in the glacier was not excluded. The uncertainty related to such glacier conditions initiated an extensive geophysical study for evaluating the hazard. Using three-dimensional surface nuclear magnetic resonance imaging (3-D-SNMR), we showed that the temperate part of the Tete Rousse glacier contains two separate water-filled caverns (central and upper caverns). In 2009, the central cavern contained about 55 000m(3) of water. Since 2010, the cavern is drained every year. We monitored the changes caused by this pumping in the water distribution within the glacier body. Twice a year, we carried out magnetic resonance imaging of the entire glacier and estimated the volume of water accumulated in the central cavern. Our results show changes in cavern geometry and recharge rate: in two years, the central cavern lost about 73% of its initial volume, but 65% was lost in one year after the first pumping. We also observed that, after being drained, the cavern was recharged at an average rate of 20 to 25m(3) d(-1) during the winter months and 120 to 180m(3) d(-1) in summer. These observations illustrate how ice, water and air may refill englacial volume being emptied by artificial draining. Comparison of the 3-D-SNMR results with those obtained by drilling and pumping showed a very good correspondence, confirming the high reliability of 3-D-SNMR imaging.

The period in the Upper Mississippi Valley (UMV) from about 25 000 years B.P. until the time of strong human influence on the landscape beginning about 150–200 years ago can be characterized by three distinctly different alluvial episodes. The first episode is dominated by the direct and indirect effects of Late Wisconsin glacial ice in the basin headwaters. This period, which lasted until about 14 000 years B.P., was generally a time of progressive valley aggradation by a braided river system transporting large quantities of bedload sediment. An island braided system evolved during the second episode, which extended from about 14 000 to 9000 years B.P. The second episode is associated with major environmental changes of deglaciation when occurrences of major floods and sustained flows of low sediment concentration from drainage of proglacial lakes produced major downcutting. By the time of the beginning of the third episode about 9000 years B.P., most vegetation communities had established their approximate average Holocene locations. The change of climate and establishment of good vegetation cover caused upland landscapes of the UMV to become relatively stable during the Holocene in comparison to their relative instability during the Late Wisconsin. However, Holocene remobilization of Late Wisconsin age sediment stored in tributary valleys resulted in a return to long-term upper Mississippi River aggradation. The dominance of Holocene deposition over transportation reflects the abundance of sandy bedload sediment introduced from tributaries and the situation that energy conditions for floods and the hydraulic gradient of the upper Mississippi River are much less for the Holocene than they were for the Late Wisconsin and deglaciation periods. Outburst floods from glacial lakes appear to have been common in the UMV during the Late Wisconsin and especially during deglaciation. Magnitudes for the Late Wisconsin floods are generally poorly understood, but an estimate of 10 000–15 000 m3 s−1 was determined for one of the largest events in the northern UMV based on heights of paleo-foreset beds in a flood unit deposited in the Savanna Terrace. For comparison, the great flood of 1993 on the upper Mississippi River was about 12 000 m3 s−1 at Keokuk, Iowa, near the Des Moines River confluence where it represented the 500-year event in relation to modem flood series. Exceptionally large outburst floods derived from the rapid drainage of pro-glacial Lake Michigan and adjacent smaller proglacial lakes between about 16 000 and 15 500 years B.P. are a likely cause of the final diversion of the Mississippi River through the Bell City-Oran Gap at the upstream end of the Lower Mississippi Valley (LMV). The largest outburst flood from northern extremities of the UMV appears to have occurred between about 11700 and 10 800 years B.P. when the southern outlet of Lake Agassiz was incised. Based on the probable maximum capacity of the Agassiz flood channel 600 km downstream near the junction of the Wisconsin and Mississippi Rivers, the Agassiz flood discharge apparently did not exceed 30 000 m3 s−1. However, if the Agassiz flood channel here is expanded to include an incised component, then the flood discharge maximum could have been as large as 100,000 to 125 000 m3 s−1. The larger flood is presently viewed as unlikely, however, because field evidence suggests that the incised component of the cross-section probably developed after the main Agassiz flood event. Nevertheless, the large Agassiz flood between about 11 700 and 10 800 years B.P. produced major erosional downcutting and removal of Late Wisconsin sediment in the UMV. This flood also appears to be mainly responsible for the final diversion of the Mississippi River through Thebes Gap in extreme southwestern Illinois and the formation of the Charleston alluvial fan at the head of the LMV. After about 9000 years B.P. prairie-forest ecotones with associated steep seasonal climatic boundaries were established across the northern and southern regions of the UMV. The general presence of these steep climatically sensitive boundaries throughout the Holocene, in concert with the natural tendency for grasslands to be especially sensitive to climatic change, may partially explain why widespread synchroneity of Holocene alluvial episodes is recognized across the upper Mississippi River and Missouri River drainage systems. Comparison of estimated beginning ages of Holocene flood episodes and alluvial chronologies for upper Mississippi River and Missouri River systems with beginning ages for LMV meander belts and delta lobes shows a relatively strong correlation. At present, dating controls are not sufficiently adequate and confidence intervals associated with the identified ages representing system changes are too large to establish firm causal connections. Although the limitations of the existing data are numerous, the implicit causal connections suggested from existing information suggest that further exploration would be beneficial to improving the understanding of how upper valley hydrological and geomorphic events are influencing hydrological and geomorphic activity in the LMV. Since nearly 80% of the Mississippi River drainage system lies upstream of the confluence of the Mississippi and Ohio Rivers, there is a strong basis for supporting the idea that UMV fluvial activity should be having a strong influence on LMV fluvial activity. If this assertion is correct, then the traditional assignment of strong to dominant control by eustatic sea level variations for explaining channel avulsions, delta lobes, and meander belts in the LMV needs re-examination. A stronger role for upper valley fluvial activity as a factor influencing lower valley fluvial activity does not disregard the role of eustatic sea level, tectonic processes or other factors. Rather, upper valley fluvial episodes or specific events such as extreme floods may commonly serve as a “triggering mechanism” that causes a threshold of instability to be exceeded in a system that was poised for change due to sea level rise, tectonic uplift, or other environmental factors. In other situations, the upper valley fluvial activity may exert a more dominant control over many LMV fluvial processes and landforms as frequently was the case during times of glacial climatic conditions.