Large Volumes Of Meltwater Research Articles

The outburst of dammed lake Maashey (North-Chuya ridge, Central Altai)

The dammed lakes are widespread in mountainous areas and usually occur when river flow is blocked by landslides, rock glaciers, etc. Among such lakes, the most dangerous are those located in the periglacial zone and blocked by rock glaciers. Continued deglaciation of mountainous areas under changing climate conditions contributes to accumulation of large volumes of melt water in lakes, which may increase pressure on the dam, cause its failure and subsequent outburst flood. In this article we describe the development of such a lake before its outburst and the process of its outburst. The object of study was Maashei Lake (North Chuya Ridge, Central Altai) located in the zone of mountain glaciation and dammed by a rock glacier, where the lake outburst occurred in July 2012. The lake area before the outburst was 259 × 103 m2 and water volume 1.21 × 106 m3. As a result of the outburst, the lake was completely drained. We analyzed the published works on Lake Maashei, materials of our own field studies in the lake basin combined with remote sensing data. We hypothesized that the mechanism of the outburst occurred in 2012 was caused by the water erosion of the filtration channel in the dam body. The mechanism of this outburst was numerically simulated using the method presented in this article. The modeling allowed to reproduce the outburst flood hydrograph, to estimate such characteristics as maximum water discharge, volume of the outburst flood, water flow velocities and the size of the formed breach. Estimated maximum discharge was 694 m3s−1, flow velocities varied from 0.2 to 5-7 m s−1, and the outburst flood period was about 5.5 hours. The breach was formed to the full height of the dam (10 m). Its calculated morphometric characteristics were as follows: average width 47.5 m (measured 41.5 m), скоss-section area 476 m2 (measured 415 m2). The discrepancy between the modeled and measured values was about 15%.

Meltwater sediment transport as the dominating process in mid-latitude trough mouth fan formation

Trough mouth fans comprise the largest sediment deposits along glaciated margins, and record Pleistocene climate changes on a multi-decadal time scale. Here we present a model for the formation of the North Sea Fan derived from detailed horizon and attribute interpretations of high-resolution processed 3D seismic reflection data. The interpretation shows that stacked channel-levee systems form up to 400 m thick sedimentary sequences. The channels are elongated and can be traced from the shelf edge towards the deep basin for distances of >150 km, and document long-distance sediment transport in completely disintegrated water-rich turbidite flows. Downslope sediment transport was a continuous process during shelf-edge glaciations, reaching accumulation rates of 100 m/kyr. Our data highlight that exceptionally large volumes of meltwater may discharge to the slopes of trough mouth fans and trigger erosive turbidite flows. We conclude that freshwater supply is likely an underestimated factor for sedimentary processes during glacial cycles.

Concentration, Composition, and Fluxes of Dispersed Sedimentary Material in the Snow and Ice Cover of the Polar Arctic

Abstract—Dispersed sedimentary material in the snow and ice cover is directly determined near the North Pole. The composition of sedimentary material in the snow and ice cover was studied at the maximum distance from continents in the high latitudes of the Northern Hemisphere, and the vertical fluxes of material from the underice layer were determined. These data were obtained using sediment traps; for snow and ice, using large volumes of melt water. It was found that dispersed aeolian sedimentary material is of primary importance in snow and sea ice.

The North Pole Region: First Data on the Snow–Sea Ice–Ice Water Sedimentation System

The dispersed sedimentary material in the snow–ice cover near the North Pole was analyzed directly for the first time. The composition of sediments in the snow–ice cover and vertical fluxes of the material from the ice water layer were studied at the maximal distance for the Northern Hemisphere from the continents. The data were obtained by sedimentation traps (for water) and in large volumes of melt water (for snow and ice). It has been revealed that the dispersed sedimentary material of aeolian genesis plays the leading role in snow and sea ice.

Ice streams of the Late Wisconsin Cordilleran Ice Sheet in western North America

The Late Wisconsin Cordilleran Ice Sheet (CIS) of western North America is thought to have reached its maximum extent (∼2.5 × 106 km2) as late at c. 14.5 ka. Most (80%) of the ice sheet's bed consists of high mountains but its ‘core zone’ sited on plateaux of the Intermontane Belt of British Columbia and coterminous parts of the USA, shows broad swaths of subglacially-streamlined rock and sediment. Broad scale mapping from new digital imagery data identifies three subglacial bed types: 1) ‘hard beds’ of variably streamlined bedrock; 2) drumlinized ‘soft beds’ of deformation till reworked from antecedent sediment, and 3) ‘mixed beds’ of variably-streamlined bedrock protruding through drumlinized sediment. Drumlins on soft beds appear to be erosional features cut into till and antecedent sediments, and identify the catchment areas of paleo ice streams expressed downglacier as flow sets of megascale glacial lineations (MSGLs). ‘Grooved’ and ‘cloned’ drumlins appear to record the transition from drumlins to MSGLs. The location of paleo ice streams reflects topographic funneling of ice from plateau surfaces through outlet valleys and a soft bed that sustained fast flow; rock-cut MSGLs are also present locally on the floors of outlet valleys. CIS disintegrated in <1000 years shortly after c. 13.0 ka releasing very large volumes of meltwater and sediment to the Pacific coast. Abrupt deglaciation may reflect unsustainable calving of marine-based ice streams along the glacio-isostatically depressed coast; large deep ‘fiord lakes’ in the ice sheet's interior may have played an analogous role. Mapping of the broad scale distribution of bed types across the Cordilleran Ice Sheet provides key information for paleoglaciological modelling and also for understanding the beds of modern ice masses such as the Greenland Ice Sheet which is of a comparable topographic setting.

Assemblage of glacial and related landforms in the fjords of southern Chile

At 42–55° S (Fig. 1a), the fjords of southern Chile are one of the lowest-latitude and mildest regions in which glaciers reach the sea today (Dowdeswell & Vasquez 2013). The Andean ice caps and glaciers of the Darwin Cordillera in Tierra del Fuego are of high mass throughput with precipitation often metres per year and, to balance this, very high rates of surface melting. These ice masses either reach the sea at fjord heads or feed braided-river systems that flow into the fjords. Large volumes of meltwater and glacial sediment are therefore delivered to Chilean fjords either directly from subglacial streams beneath tidewater glaciers or indirectly by glacifluvial processes. At the Last Glacial Maximum (LGM) the Patagonian Ice Cap expanded to fill these fjords, which were re-occupied by ocean waters as deglaciation proceeded. Fig. 1. Sun-illuminated multibeam-bathymetric images of submarine landforms in the fjords of Chilean Patagonia. Acquisition system Atlas Fansweep. Frequency 200 kHz. Grid-cell size 20 m. ( a ) Location of study area (red box; map from GEBCO_08). ( b ) Terminal moraine ridge and other transverse ridges produced by Tempano Glacier, inner Iceberg Fjord. S, streamlined lineations. ( c ) Hummocky but otherwise largely flat seafloor beyond Pio XI Glacier in Eyre Fjord. H, hummocky glacial debris. ( d ) Swath-bathymetric image of 100 m high recessional moraine in Europa Fjord. ( e ) Glacifluvial delta in Iceberg Fjord fed from an associated braided river. ( f ) Glacifluvial delta in Bernardo Fjord, showing a braided river and the adjacent Bernardo Glacier. ( g ) Small fluvial delta in Eyre Fjord. Images modified after Dowdeswell & Vasquez (2013). We thank the Servicio Hidrografico y Oceanografico de la Armada de Chile (SHOA) for allowing use of their swath-bathymetric data. Many Chilean fjords have experienced tidewater-glacier advance during the cool Little Ice Age (approximately sixteenth–nineteenth centuries), followed by retreat over the past century …

Regional deglaciation and postglacial lake development as reflected in a 74 m sedimentary record from Lake Vättern, southern Sweden

The withdrawal of the Late Weichselian ice sheet and rapid isostatic uplift in southern Scandinavia led to the entrainment of large volumes of melt water within the proglacial Baltic Ice Lake (BIL). The eventual western outpost of BIL, Lake Vättern, has been a focal point for studying the dynamic retreat history of the Late Weichselian ice sheet in south central Sweden. This part of the deglacial history is described from an abundance of terrestrial studies, but, to date, no complimentary long sediment cores from Lake Vättern have been available. Here, we present the results from a unique, 74 m borehole in southern Lake Vättern that recovered a Late Pleistocene to Holocene sedimentary sequence. Physical and chemical analyses of the sediment and pore water, together with geophysical mapping, reveal glacial as well as postglacial imprints implying an oscillating ice sheet margin, evidence for neotectonic activity and one or more marine incursions into the lake during deglaciation. We attribute the glaciotectonic deformation of the sediments at 54 m below the lake floor to an ice readvance that likely occurred at the same time or before the advance that formed the Levene moraine (∼13.8–13.4 cal. ka BP). After this event, potential readvances were likely restricted to a more northerly position in the basin. We identify the final drainage of the BIL, but find evidence for an earlier marine incursion into the Vättern basin (∼13.0 cal. ka BP), indicating water exchange between the North Atlantic and the Baltic Ice Lake during the late Alleröd.

Arctic warming: nonlinear impacts of sea-ice and glacier melt on seabird foraging.

Arctic climate change has profound impacts on the cryosphere, notably via shrinking sea-ice cover and retreating glaciers, and it is essential to evaluate and forecast the ecological consequences of such changes. We studied zooplankton-feeding little auks (Alle alle), a key sentinel species of the Arctic, at their northernmost breeding site in Franz-Josef Land (80°N), Russian Arctic. We tested the hypothesis that little auks still benefit from pristine arctic environmental conditions in this remote area. To this end, we analysed remote sensing data on sea-ice and coastal glacier dynamics collected in our study area across 1979-2013. Further, we recorded little auk foraging behaviour using miniature electronic tags attached to the birds in the summer of 2013, and compared it with similar data collected at three localities across the Atlantic Arctic. We also compared current and historical data on Franz-Josef Land little auk diet, morphometrics and chick growth curves. Our analyses reveal that summer sea-ice retreated markedly during the last decade, leaving the Franz-Josef Land archipelago virtually sea-ice free each summer since 2005. This had a profound impact on little auk foraging, which lost their sea-ice-associated prey. Concomitantly, large coastal glaciers retreated rapidly, releasing large volumes of melt water. Zooplankton is stunned by cold and osmotic shock at the boundary between glacier melt and coastal waters, creating new foraging hotspots for little auks. Birds therefore switched from foraging at distant ice-edge localities, to highly profitable feeding at glacier melt-water fronts within <5km of their breeding site. Through this behavioural plasticity, little auks maintained their chick growth rates, but showed a 4% decrease in adult body mass. Our study demonstrates that arctic cryosphere changes may have antagonistic ecological consequences on coastal trophic flow. Such nonlinear responses complicate modelling exercises of current and future polar ecosystem dynamics.

Seismic detection of an active subglacial magmatic complex in Marie Byrd Land, Antarctica

Numerous volcanoes exist in Marie Byrd Land, a highland region of West Antarctica. High heat flow through the crust in this region may influence the stability of the West Antarctic Ice Sheet 1‐4 . Volcanic activity progressed from north to south in the Executive Committee mountain range between the Miocene and Holocene epochs, but there has been no evidence for recent magmatic activity 5‐7 . Here we use a recently deployed seismic network to show that in 2010 and 2011, two swarms of seismic activity occurred at 25‐40 km depth beneath subglacial topographic and magnetic highs, located 55 km south of the youngest subaerial volcano in the Executive Committee Range. We interpret the swarm events as deep long-period earthquakes based on their unusual frequency content. Such earthquakes occur beneath active volcanoes, are caused by deep magmatic activity and, in some cases, precede eruptions 8‐11 . We also use radar profiles to identify a prominent ash layer in the ice overlying the seismic swarm. Located at 1,400 m depth, the ash layer is about 8,000 years old and was probably sourced from the nearby Mount Waesche volcano. Together, these observations provide strong evidence for ongoing magmatic activity and demonstrate that volcanism continues to migrate southwards along the Executive Committee Range. Eruptions at this site are unlikely to penetrate the 1.2 to 2-km-thick overlying ice, but would generate large volumes of melt water that could significantly affect ice stream flow.

Glacimarine sedimentary processes and depositional environments in an embayment fed by West Greenland ice streams

The extent and behaviour of the central West Greenland sector of the Greenland Ice Sheet (GIS) during the Last Glacial Maximum (LGM) and the following deglaciation remains poorly constrained. To investigate deglacial marine environments and sedimentary processes in an area fed by several LGM ice streams we now report findings from a 3.5kHz sub-bottom profiler survey acquired in and around Disko Bay in 2009. Sediment thicknesses and volumes in three glaciated areas, Disko Bay, southern Vaigat and Egedesminde Dyb, are fully constrained for the first time. Acoustic facies types and distributions were also mapped. The largest sediment thicknesses (256m) and widest variation in acoustic character was observed in Disko Bay adjacent to the mouth of Jakobshavns Isfjord. Significant sediment thicknesses were also observed in isolated basins in the Egedesminde Dyb trough and in a trough in southern Vaigat Strait (up to 110m). Given low modern sedimentation rates, these thick sediment packages are inferred to record the retreat of glaciers from the middle shelf through Disko Bay and into both the Jakobshavns and Torssukatak fjord systems in central West Greenland. Our results highlight similarities in deglacial sedimentary processes across the study area, when the margins of retreating glaciers supplied large volumes of sediment to the marine environment from sediment-laden meltwater plumes and melting icebergs. We estimate the sediment flux for the palaeo-Jakobshavn ice stream while the ice margin was stable at a fjord-entrance sill to be 1.6–3.6×107m3a−1. Assuming a flux at the upper end of our range for the Torssukatak fjord system requires the grounded ice margin to be stable for about 450years during retreat. The sediment fluxes we estimate are within the range of previously calculated fluxes for other Arctic and Antarctic ice streams and suggest that large volumes of meltwater and sediment were available at the base of the outlet glaciers during deglaciation, even during periods of quasi-stability. Retreat of the ice margins into the fjord systems is characterised by a rapid transition to ice-distal sedimentation by rainout of iceberg-rafted detritus (IRD) and hemipelagic material; accumulation rates drop to ~2mma−1. This study demonstrates the variability in glacimarine processes and environments on high-latitude continental margins and highlights the importance of local factors, such as bedrock morphology, as well as glacio-dynamic factors, on sedimentation.

Shed Brook Discontinuity and Little Falls Gravel: Evidence for the Erie interstade in central New York

The Shed Brook Discontinuity in the western Mohawk Valley region of central New York is an unconformity separating lacustrine beds of the Valley Heads drift (Port Bruce stade) from pre–Valley Heads lacustrine deposits (Nissouri stade). The Little Falls Gravel is a fluvial unit that can be found draped by Valley Heads lacustrine deposits in the Mohawk Valley. The discontinuity and gravel represent subaerial erosion and braided river deposition in response to initial late Wisconsinan ice recession and lake drainage in the Mohawk Valley. These events were followed by Valley Heads lake impoundment and glacial readvances. The Shed Brook Discontinuity and Little Falls Gravel have a 14 C age constrained to 17–14.1 ka on the basis of stratigraphic relationships in central New York and the correlation of paleomagnetic declination records from central New York and the 14 C-calibrated New England varve chronology. The Shed Brook Discontinuity and Little Falls Gravel appear to be features equivalent in age to the Erie interstade (about 14.5–16 ka), an interval during which eastward drainage to the Mohawk Valley has been inferred for lakes in the Erie basin. Evidence for a river in the Mohawk Valley (Little Falls Gravel) indicates that it may have served as an eastern outlet for the Erie and Ontario basins, and thus allowed the first eastward diversion of meltwater away from the Mississippi Valley during the last deglaciation. Drainage down the Mohawk Valley entered Lake Albany in the Hudson Valley, which drained into Long Island Sound and not along the present Hudson River course to the New Jersey continental shelf. Meltwater drainage across New York during the latest stages of the Erie interstade may have introduced large volumes of meltwater directly to the western Atlantic, creating a situation that needs to be more fully explored in terms of its possible influence on thermohaline circulation in the North Atlantic and climatic change marked by the Port Bruce stade.

A review of the stratigraphy and sedimentary environments of the Karoo-aged basins of Southern Africa

The Karoo Basin of South Africa was one of several contemporaneous intracratonic basins in southwestern Gondwana that became active in the Permo-Carboniferous (280 Ma) and continued to accumulate sediments until the earliest Jurassic, 100 million years later. At their maximum areal extent, during the early Permian, these basins covered some 4.5 million km 2. The present outcrop area of Karoo rocks in southern Africa is about 300 000 km 2 with a maximum thickness of some 8000 m. The economic importance of these sediments lies in the vast reserves of coal within the Ecca Group rocks of northern and eastern Transvaal and Natal, South Africa. Large reserves of sandstone-hosted uranium and molybdenum have been proven within the Beaufort Group rocks of the southern Karoo trough, although they are not mineable in the present market conditions. Palaeoenvironmental analysis of the major stratigraphic units of the Karoo succession in South Africa demonstrates the changes in depositional style caused by regional and localized tectonism within the basin. These depocentres were influenced by a progressive aridification of climate which was primarily caused by the northward drift of southwestern Gondwana out of a polar climate and accentuated by the meteoric drying effect of the surrounding land masses. Changing palaeoenvironments clearly influenced the rate and direction of vertebrate evolution in southern Gondwana as evidenced by the numerous reptile fossils, including dinosaurs, which are found in the Karoo strata of South Africa, Lesotho, Namibia and Zimbabwe. During the Late Carboniferous the southern part of Gondwana migrated over the South Pole resulting in a major ice sheet over the early Karoo basin and surrounding highlands. Glacial sedimentation in upland valleys and on the lowland shelf resulted in the Dwyka Formation at the base of the Karoo Sequence. After glaciation, an extensive shallow sea covered the gently subsiding shelf, fed by large volumes of meltwater. Marine clays and muds accumulated under cool climatic conditions (Lower Ecca Group) including the distinctive Mesosaurus-bearing carbonaceous shales of the Whitehill Formation. Subduction of the palaeo-Pacific plate reslted in an extensive chain of mountains which deformed and later truncated the southern rim of the main Karoo Basin. Material derived from these “Gondwanide” mountains as well as from the granitic uplands to the north-east, accumulated in large deltas that prograded into the Ecca sea (Upper Ecca Group). The relatively cool and humid climate promoted thick accumulations of peat on the fluvial and delta plains which now constitute the major coal reserves of southern Africa. As the prograding deltas coalesced, fluvio-lacustrine sediments of the Beaufort Group were laid down on broad gently subsiding alluvial plains. The climate by this time (Late Permian) had warmed to become semi-arid with highly seasonal rainfall. Vegetation alongside the meander belts and semi-permanent lakes supported a diverse reptilian fauna dominated by therapsids or “mammal-like reptiles”. Pulses of uplift in the southern source areas combined with possible orographic effects resulted in the progadation of two coarse-grained alluvial fans into the central parts of the basin (Katberg Sandstone Member and Molteno Formation). In the upper Karoo Sequence, progressive aridification and tectonic deformation of the basin through the late Triassic and early Jurassic led to the accumulation, in four separate depositories, of “redbeds” which are interpreted as fluvial and flood-fan, playa and dune complexes (Elliot Formation). This eventually gave way to westerly wind-dominated sedimentation that choked the remaining depositories with fine-grained dune sand. The interdune areas were damp and occasionally flooded and provided a habitat for small dinosaurs and the earliest mammals. During this time (Early Jurassic), basinwide volcanic activity began as a precursor to the break-up of Gondwana in the late Jurassic and continued until the early Cretaceous. This extrusion of extensive flood basalts (Drakensberg Group) onto the Clarens landscape eventually brought Karoo sedimentation to a close.

A review of stratigraphy and sedimentary environments of the Karoo Basin of South Africa

The Karoo Supergroup covers almost two thirds of the present land surface of southern Africa. Its strata record an almost continuous sequence of continental sedimentation that began in the Permo-Carboniferous (280 Ma) and terminated in the early Jurassic 100 million years later. The glacio-marine to terrestrial sequence accumulated in a variety of tectonically controlled depositories under progressively more arid climatic conditions.Numerous vertebrate fossils are preserved in these rocks, including fish, amphibians, primitive aquatic reptiles, primitive land reptiles, more advanced mammal-like reptiles, dinosaurs and even the earliest mammals.Palaeoenvironmental analysis of the major stratigraphic units of the Karoo sequence demonstrates the effects of more localised tectonic basins in influencing depositional style. These are superimposed on a basinwide trend of progressive aridification attributed to the gradual northward migration of southwestern Gondwanaland out of polar climes and accentuated by the meteoric drying effect of the surrounding land masses. Combined with progressive climatic drying was a gradual shrinking of the basin brought about by the northward migration of the subducting palaeo-Pacific margin to the south.Following deposition of the Cape Supergroup in the pre-Karoo basin there was a period of uplift and erosion. At the same time the southern part of Gondwana migrated over the South Pole resulting in a major ice-sheet over the early Karoo basin and surrounding highlands. Glacial sedimentation in both upland valley and shelf depositories resulted in the basal Karoo Dwyka Formation.After glaciation, an extensive shallow sea remained over the gently subsiding shelf fed by large volumes of meltwater. Black clays and muds accumulated under relatively cool climatic conditions (Lower Ecca) with perhaps a warmer “interglacial” during which the distinctive Mesosaurus-bearing, carbonaceous shales of the Whitehill Formation were deposited.Deformation of the southern rim of the basin, caused by the subducting palaeo-Pacific plate, resulted in mountain ranges far to the south. Material derived from this source, as well as granitic uplands to the west and morth-east, was deposited on large deltas that built out into the Ecca sea (Upper Ecca). The relatively cool climate and lowland setting promoted thick accumulations of peat on the coastal and delta plains and which now constitute the major coal reserves of southern Africa.Later the prograding deltas coalesced to fill most of the basin after which fluvial sedimentation of the Beaufort Group dominated. The climate by this time (Late Permian) had warmed to become semi-arid with highly seasonal rainfall. The central parts of the basin were for the most part drained by fine-grained meanderbelts and semi-permanent lakes. Significant stratabound uranium reserves have been delimited in the channel sandstones of the Beaufort Group in the southwestern parts of the basin. Pulses of uplift in the southern source areas combined with a possible orogenic effect resulted in two coarser-grained alluvial fans prograding into the more central parts of the basin (Katberg Sandstone Member and Molteno Formation).In the upper Karoo sequence progressive aridification dominated depositional style with playa lake and wadi-type environments (Elliot Formation) that finally gave way to a dune sand dominated system (Clarens Formation). Basinwide volcanic activity of the early Jurassic Drakensberg Group brought deposition in the Karoo Basin to a close.

THE GLACIAL GEOMORPHOLOGY OF THE AREA AROUND HYDE, CHESHIRE

Summary During the main Weichsel glacial period ice movement around Hyde became impeded by the local Pennine relief to such an extent that lobes of ice were ultimately detached from the main body of the ice sheet and left to stagnate in the valleys of the Mersey headwater streams. Large volumes of meltwater were released in the areas adjoining the hills and the streams flowing at the ice margins constructed a number of fluvio-glacial depositional landforms and filled with sediment the valleys eroded by pre-glacial streams. Local relief exerted a strong influence upon meltwater flow and ice movements and in consequence the mode of sedimentation, the stratigraphy and lithological character of the glacial deposits are frequently a reflection of local environmental conditions. In this area therefore it has not been possible to recognize a simple stratigraphical succession applicable to the whole area and therefore the glacial deposits are described with reference to their morphology and topographical expression. Former ice sheet incursions created a number of modifications in the local drainage network. Most diversions resulted from events that occurred during the Weichsel Glaciation but the analysis of the bedrock topography indicates that some alterations of the drainage pattern occurred earlier in the Pleistocene Epoch. The erosion of several now abandoned channels and of the “post-glacial” gorges is attributed to the work of sub-glacial meltwaters which also deposited some varved deposits on the valley floors. Beyond the former ice margin there is considerable evidence of prolonged periglacial denudation and it is concluded that the glacial incursion was only of short duration and was the climax to a long period of cold, but not glacial, climate which persisted from about 75,000 to 25,000 years B.P.