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Rock Glaciers (rock + glacier)
Kinds of Rock Glaciers Selected AbstractsDebris-covered Glaciers and Rock Glaciers in the Nanga Parbat Himalaya, PakistanGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2000John F. Shroder The origin and mobilization of the extensive debris cover associated with the glaciers of the Nanga Parbat Himalaya is complex. In this paper we propose a mechanism by which glaciers can form rock glaciers through inefficiency of sediment transfer from glacier ice to meltwater. Inefficient transfer is caused by various processes that promote plentiful sediment supply and decrease sediment transfer potential. Most debris-covered glaciers on Nanga Parbat with higher velocities of movement and/ or efficient debris transfer mechanisms do not form rock glaciers, perhaps because debris is mobilized quickly and removed from such glacier systems. Those whose ice movement activity is lower and those where inefficient sediment transfer mechanisms allow plentiful debris to accumulate, can form classic rock glaciers. We document here with maps, satellite images, and field observations the probable evolution of part of a slow and inefficient ice glacier into a rock glacier at the margins of Sachen Glacier in c. 50 years, as well as several other examples that formed in a longer period of time. Sachen Glacier receives all of its nourishment from ice and snow avalanches from surrounding areas of high relief, but has low ice velocities and no efficient system of debris removal. Consequently it has a pronounced digitate terminus with four lobes that have moved outward from the lateral moraines as rock glaciers with prounced transverse ridges and furrows and steep fronts at the angle of repose. Raikot Glacier has a velocity five times higher than Sachen Glacier and a thick cover of rock debris at its terminus that is efficienctly removed. During the advance stage of the glacier since 1994, ice cliffs were exposed at the terminus, and an outbreak flood swept away much debris from its margins and terminus. Like the Sachen Glacier that it resembles, Shaigiri Glacier receives all its nourishment from ice and snow avalanches and has an extensive debris cover with steep margins close to the angle of repose. It has a high velocity similar to Raikot Glacier and catastrophic breakout floods have removed debris from its terminus twice in the recent past. In addition, the Shaigiri terminus blocked the Rupal River during the Little Ice Age and is presently being undercut and steepened by the river. With higher velocities and more efficient sediment transfer systems, neither the Raikot nor the Shaigiri form classic rock-glacier morphologies. [source] Modeling past and future alpine permafrost distribution in the Colorado Front RangeEARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2005Jason R. Janke Abstract Rock glaciers, a feature associated with at least discontinuous permafrost, provide important topoclimatic information. Active and inactive rock glaciers can be used to model current permafrost distribution. Relict rock glacier locations provide paleoclimatic information to infer past conditions. Future warmer climates could cause permafrost zones to shrink and initiate slope instability hazards such as debris flows or rockslides, thus modeling change remains imperative. This research examines potential past and future permafrost distribution in the Colorado Front Range by calibrating an existing permafrost model using a standard adiabatic rate for mountains (0·5 °C per 100 m) for a 4 °C range of cooler and warmer temperatures. According to the model, permafrost currently covers about 12 per cent (326·1 km2) of the entire study area (2721·5 km2). In a 4 °C cooler climate 73·7 per cent (2004·4 km2) of the study area could be covered by permafrost, whereas in a 4°C warmer climate almost no permafrost would be found. Permafrost would be reduced severely by 93·9 per cent (a loss of 306·2 km2) in a 2·0 °C warmer climate; however, permafrost will likely respond slowly to change. Relict rock glacier distribution indicates that mean annual air temperature (MAAT) was once at least some 3·0 to 4·0 °C cooler during the Pleistocene, with permafrost extending some 600,700 m lower than today. The model is effective at identifying temperature sensitive areas for future monitoring; however, other feedback mechanisms such as precipitation are neglected. Copyright © 2005 John Wiley & Sons, Ltd. [source] Flow velocities of active rock glaciers in the Austrian AlpsGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2006Karl Krainer ABSTRACT. High surface flow velocities of up to 3 m a,1 were measured near the front of three active rock glaciers in the western Stubai Alps (Rei-chenkar) and Ötztal Alps (Kaiserberg and Ölgrube) in Tyrol (Austria) using differential GPS technology. Flow velocities have increased since about 1990. The highest velocities were recorded in 2003 and 2004, but showed a slight decrease in 2005. At the Reichenkar rock glacier, flow rates are constant throughout the year, indicating that meltwater has no significant influence on the flow mechanism. At Ölgrube rock glacier, flow velocities vary seasonally with considerably higher velocities during the melt season. Meltwater is likely to influence the flow of Ölgrube rock glacier as evident by several springs near the base of the steep front. Because the high surface velocities cannot be explained by internal deformation alone on Reichenkar rock glacier, we assume that horizontal deformation must also occur along a well defined shear zone within a water-saturated, fine-grained layer at the base of the frozen body. The increased surface flow velocities since about 1990 are probably caused by slightly increased ice temperature and greater amounts of meltwater discharge during the summer, a product of global warming. [source] Topography of a composite relict rock glacier, ,l,,a Massif, SW PolandGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2003Dorota Borowicz Abstract A detailed geodetic survey and, additionally, a map of slope covers have been carried out for a composite relict rock glacier on the slopes of Mt ,l,,a (718 m a.s.l.), Sudetic Foreland, SW Poland. The survey allows one to distinguish the mobilisation, transition and accumulation zones and to define geomorphic features diagnostic for relict rock glaciers such as lateral ridges standing above a central depression, steep margins of the landforms in the transition and accumulation zones, as well as absence of distinct head scarps above. Furthermore, it indicates that the present-day hydrographic pattern on the surface of relict rock glaciers has been superimposed on the relief inherited from the active landforms. The topography indicates that tension prevailed rather than compression during the development of the rock glaciers. Some of the features, such as small lateral lobes, developed probably as a result of the compressive flow, however. The pattern of the slope cover shows that it developed during activity of the rock glaciers and been modified afterwards due to solifluction. [source] Debris-covered Glaciers and Rock Glaciers in the Nanga Parbat Himalaya, PakistanGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2000John F. Shroder The origin and mobilization of the extensive debris cover associated with the glaciers of the Nanga Parbat Himalaya is complex. In this paper we propose a mechanism by which glaciers can form rock glaciers through inefficiency of sediment transfer from glacier ice to meltwater. Inefficient transfer is caused by various processes that promote plentiful sediment supply and decrease sediment transfer potential. Most debris-covered glaciers on Nanga Parbat with higher velocities of movement and/ or efficient debris transfer mechanisms do not form rock glaciers, perhaps because debris is mobilized quickly and removed from such glacier systems. Those whose ice movement activity is lower and those where inefficient sediment transfer mechanisms allow plentiful debris to accumulate, can form classic rock glaciers. We document here with maps, satellite images, and field observations the probable evolution of part of a slow and inefficient ice glacier into a rock glacier at the margins of Sachen Glacier in c. 50 years, as well as several other examples that formed in a longer period of time. Sachen Glacier receives all of its nourishment from ice and snow avalanches from surrounding areas of high relief, but has low ice velocities and no efficient system of debris removal. Consequently it has a pronounced digitate terminus with four lobes that have moved outward from the lateral moraines as rock glaciers with prounced transverse ridges and furrows and steep fronts at the angle of repose. Raikot Glacier has a velocity five times higher than Sachen Glacier and a thick cover of rock debris at its terminus that is efficienctly removed. During the advance stage of the glacier since 1994, ice cliffs were exposed at the terminus, and an outbreak flood swept away much debris from its margins and terminus. Like the Sachen Glacier that it resembles, Shaigiri Glacier receives all its nourishment from ice and snow avalanches and has an extensive debris cover with steep margins close to the angle of repose. It has a high velocity similar to Raikot Glacier and catastrophic breakout floods have removed debris from its terminus twice in the recent past. In addition, the Shaigiri terminus blocked the Rupal River during the Little Ice Age and is presently being undercut and steepened by the river. With higher velocities and more efficient sediment transfer systems, neither the Raikot nor the Shaigiri form classic rock-glacier morphologies. [source] Internal structure of an alpine rock glacier based on crosshole georadar traveltimes and amplitudesGEOPHYSICAL PROSPECTING, Issue 3 2006Martin Musil ABSTRACT Rapid melting of permafrost in many alpine areas has increased the probability of catastrophic rock slides. In an attempt to provide critical structural information needed for the design and implementation of suitable mitigation procedures, we have acquired low frequency (22 MHz) cross-hole radar data from within a fast-moving rock glacier, an important form of alpine permafrost. Since the ice, rock and pockets of water and air found in the underground of high alpine areas have very different dielectric permittivities and electrical conductivities, the radar method was well-suited for investigating the structure and state of the rock glacier. Our interpretation of the radar velocities and attenuations was constrained by geomorphological observations, borehole lithological logs and the results of a surface seismic survey. The radar data revealed the existence of a discontinuous 7,11 m thick ice-rich zone distinguished by high velocities (0.14,0.17 m/ns) and low attenuations (0.04,0.09 m,1) and a thin underlying ice-free zone characterized by moderate velocities (0.11,0.12 m/ns) and low attenuations (0.04,0.09 m,1). Beneath these two zones, we observed a prominent band of high velocities (0.14,0.17 m/ns) and moderately high attenuations (0.10,0.20 m,1) associated with unconsolidated glacial sediments and numerous large air-filled voids, which in the past were probably filled with ice. At greater depths, the variably dry to water-saturated sediments were represented by generally lower velocities (0.08,0.10 m/ns) and higher attenuations (0.16,0.24 m,1). The bedrock surface was represented by an abrupt ,0.03 m/ns velocity increase. We speculate that the disappearance of ice, both laterally and with depth, occurred during the past one to two decades. [source] Using DC resistivity tomography to detect and characterize mountain permafrostGEOPHYSICAL PROSPECTING, Issue 4 2003Christian Hauck ABSTRACT Direct-current (DC) resistivity tomography has been applied to different mountain permafrost regions. Despite problems with the very high resistivities of the frozen material, plausible results were obtained. Inversions with synthetic data revealed that an appropriate choice of regularization constraints was important, and that a joint analysis of several tomograms computed with different constraints was required to judge the reliability of individual features. The theoretical results were verified with three field experiments conducted in the Swiss and the Italian Alps. At the first site, near Zermatt, Switzerland, the location and the approximate lateral and vertical extent of an ice core within a moraine could be delineated. On the Murtel rock glacier, eastern Swiss Alps, a steeply dipping boundary at its frontal part was observed, and extremely high resistivities of several M, indicated a high ice content. The base of the rock glacier remained unresolved by the DC resistivity measurements, but it could be constrained with transient EM soundings. On another rock glacier near the Stelvio Pass, eastern Italian Alps, DC resistivity tomography allowed delineation of the rock glacier base, and the only moderately high resistivities within the rock glacier body indicated that the ice content must be lower compared with the Murtel rock glacier. [source] Two decades of responses (1986,2006) to climate by the Laurichard rock glacier, French AlpsPERMAFROST AND PERIGLACIAL PROCESSES, Issue 4 2009Xavier Bodin Abstract The Laurichard active rock glacier is the permafrost-related landform with the longest record of monitoring in France, including an annual geodetic survey, repeated geoelectrical campaigns from 1979 onwards and continuous recording of ground temperature since 2003. These data were used to examine changes in creep rates and internal structure from 1986 to 2006. The control that climatic variables exert on rock glacier kinematics was investigated over three time scales. Between the 1980s and the early 2000s, the main observed changes were a general increase in surface velocity and a decrease in internal resistivity. At a multi-year scale, the high correlation between surface movement and snow thickness in the preceding December appears to confirm the importance of snow cover conditions in early winter through their influence on the ground thermal regime. A comparison of surface velocities, regional climatic datasets and ground sub-surface temperatures over six years suggests a strong relation between rock glacier deformation and ground temperature, as well as a role for liquid water due to melt of thick snow cover. Finally, unusual surface lowering that accompanied peak velocities in 2004 may be due to a general thaw of the top of the permafrost, probably caused both by two successive snowy winters and by high energy inputs during the warm summer of 2003. Copyright © 2009 John Wiley & Sons, Ltd. [source] The lower limit of mountain permafrost in the Russian Altai MountainsPERMAFROST AND PERIGLACIAL PROCESSES, Issue 2 2007Kotaro Fukui Abstract Permafrost-indicator features, such as rock glaciers, pingos and ice-wedge polygons, exist at many locations in and around the South Chuyskiy Range of the Russian Altai Mountains (,50°N). The distribution of these features suggests that the altitudinal range of the sporadic/patchy permafrost zones and the widespread discontinuous/continuous permafrost zones are 1800,2000,m ASL and above 2000,m ASL, respectively. The lower limit of discontinuous permafrost is approximately 200,m lower than in the Mongolian Altai, which are at a similar latitude. Cold air drainage and/or temperature inversions during winter within U-shaped valleys together with a thin snow cover because of low precipitation during the same season likely cause the lower permafrost limit in the study area. The calibrated 14C ages of tree remnants found in a rock glacier front in the lower Akkol valley were 293,±,21 years BP and 548,±,21 years BP. Given the time of emergence from beneath the Sofiyskiy glacier, this rock glacier developed between 3800,2600 and 550 years BP. Copyright © 2007 John Wiley & Sons, Ltd. [source] Geochemistry and source waters of rock glacier outflow, Colorado Front RangePERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2006M. W. Williams Abstract We characterize the seasonal variation in the geochemical and isotopic content of the outflow of the Green Lake 5 rock glacier (RG5), located in the Green Lakes Valley of the Colorado Front Range, USA. Between June and August, the geochemical content of rock glacier outflow does not appear to differ substantially from that of other surface waters in the Green Lakes Valley. Thus, for this alpine ecosystem at this time of year there does not appear to be large differences in water quality among rock glacier outflow, glacier and blockslope discharge, and discharge from small alpine catchments. However, in September concentrations of Mg2+ in the outflow of the rock glacier increased to more than 900,µeq,L,1 compared to values of less than 40,µeq,L,1 at all the other sites, concentrations of Ca2+ were greater than 4,000,µeq,L,1 compared to maximum values of less than 200,µeq,L,1 at all other sites, and concentrations of SO reached 7,000,µeq,L,1, compared to maximum concentrations below 120,µeq,L,1 at the other sites. Inverse geochemical modelling suggests that dissolution of pyrite, epidote, chlorite and minor calcite as well as the precipitation of silica and goethite best explain these elevated concentrations of solutes in the outflow of the rock glacier. Three component hydrograph separation using end,member mixing analysis shows that melted snow comprised an average of 30% of RG5 outflow, soil water 32%, and base flow 38%. Snow was the dominant source water in June, soil water was the dominant water source in July, and base flow was the dominant source in September. Enrichment of ,18O from ,10, in the outflow of the rock glacier compared to ,20, in snow and enrichment of deuterium excess from +,17.5, in rock glacier outflow compared to +,11, in snow, suggests that melt of internal ice that had undergone multiple melt/freeze episodes was the dominant source of base flow. Copyright © 2005 John Wiley & Sons, Ltd. [source] Borehole deformation measurements and internal structure of some rock glaciers in SwitzerlandPERMAFROST AND PERIGLACIAL PROCESSES, Issue 2 2002Lukas Arenson Abstract In order to understand the mechanical processes that influence the deformation patterns of active rock glaciers, information about local horizontal and vertical deformations as well as knowledge of the internal structure and the temperature distribution is necessary. Results from borehole deformation measurements of three sites in the Swiss Alps show that despite different internal structures, similar phenomena can be observed. In contrast to temperate glaciers, permafrost within rock glaciers has distinct shear zones where horizontal and vertical differential movements are concentrated. In addition, a reduction in volume can be caused by compressive flow due to the presence of air voids within the permafrost. The flow velocity depends on the temperature, the surface and bedrock slopes of the rock glacier, and the composition of the ice-rich frozen ground. Within degrading permafrost, the ice content decreases, the creep velocity increases and the shear zone rises towards the surface, where seasonal temperature changes and the presence of liquid water might also influence deformation. Copyright © 2002 John Wiley & Sons, Ltd. [source] Internal Structure of a relict rock glacier, ,l,,a Massif, Southwest PolandPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2002Roman, urawek Abstract The sediments of a large accumulation landform, interpreted as one of six Pleistocene rock glaciers occurring in the ,l,,a Massif, southwest Poland, are described. The sediments have been subject to strong compression and the main deformation mechanism is that of shearing. The similar angle of shear in sediments of extremely different lithology is inferred from the geometry of failure surfaces and indicates that ice was necessary for the debris transport. Because the geomorphological setting excludes a glacigenic origin, the sediments are interpreted to result from the creep of permafrost, i.e. the landform is a relict rock glacier. The movement of the rock glacier, at least in its terminal stage, is associated with a dense pattern of shear planes and would have occurred even in the presence of a small amount of interstitial ice. Copyright © 2002 John Wiley & Sons, Ltd. [source] Genetic differences of rock glaciers and the discontinuous mountain permafrost zone in Kanchanjunga Himal, Eastern NepalPERMAFROST AND PERIGLACIAL PROCESSES, Issue 3 2001Mamoru Ishikawa Abstract A number of rock glaciers, including glacier-derived and talus-derived rock glaciers, were identified in Kanchanjunga Himal, easternmost Nepal. DC resistivity imagings were applied to representative rock glaciers of both types. The distribution of resistivity values in the subsurface within these rock glaciers was significantly different. A massive glacial ice body was found within the glacier-derived rock glacier, suggesting this rock glacier originated from glacial dead ice (ice-cored rock glacier). The lower limits of discontinuous mountain permafrost zone in Kanchanjunga Himal were inferred from the distribution of talus-derived rock glaciers (ice-cemented rock glaciers) and the estimated mean annual air temperature. The lower limit of the discontinuous mountain permafrost zone is 4800 m ASL on the north-facing slopes, while 5300 m ASL on the south- to east-facing slopes. These altitudes were considerably higher than those of the western Himalaya, which are under dry continental climatic conditions. Copyright © 2001 John Wiley & Sons, Ltd. RÉSUMÉ Plusieurs glaciers rocheux comprenant à la fois des formes dérivéees de vrais glaciers et des formes provenant de la mise en mouvement de talus, ont été identifiés dans le Kanchanjunga Himal, dans le Népal le plus oriental. Des images par résistivité DC ont été obtenues pour des glaciers représentatifs des deux catégories. La distribution des valeurs de résistivité en profondeur dans ces glaciers rocheux a été significativement différente. Un corps de glace massif a été trouvé dans le glacier rocheux provenant d'un vrai glacier suggérant qu'il s'agissait de glace morte glaciaire (glacier rocheux à noyau de glace). Les limites inférieures de la zone du pergélisol discontinu dans le Kanchanjungga Himal ont été déduites de la distribution des glaciers rocheux provenant de talus (glaciers rocheux avec de la glace ciment) et d'une estimation de la température moyenne annuelle de l'air. La limite inférieure de la zone du pergélisol discontinu de montagne est de 4800 m d'altitude sur les pentes exposées au nord, tandis que la limite est de 5300 m sur les pentes exposées au sud. Ces altitudes sont considérablement plus élevées que celles de l'ouest de l'Himalaya exposé à des conditions climatiques continentales sèches. Copyright © 2001 John Wiley & Sons, Ltd. [source] Quantifying sediment storage in a high alpine valley (Turtmanntal, Switzerland)EARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2009Jan-Christoph Otto Abstract The determination of sediment storage is a critical parameter in sediment budget analyses. But, in many sediment budget studies the quantification of magnitude and time-scale of sediment storage is still the weakest part and often relies on crude estimations only, especially in large drainage basins (>100,km2). We present a new approach to storage quantification in a meso-scale alpine catchment of the Swiss Alps (Turtmann Valley, 110,km2). The quantification of depositional volumes was performed by combining geophysical surveys and geographic information system (GIS) modelling techniques. Mean thickness values of each landform type calculated from these data was used to estimate the sediment volume in the hanging valleys and the trough slopes. Sediment volume of the remaining subsystems was determined by modelling an assumed parabolic bedrock surface using digital elevation model (DEM) data. A total sediment volume of 781·3×106,1005·7×106,m3 is deposited in the Turtmann Valley. Over 60% of this volume is stored in the 13 hanging valleys. Moraine landforms contain over 60% of the deposits in the hanging valleys followed by sediment stored on slopes (20%) and rock glaciers (15%). For the first time, a detailed quantification of different storage types was achieved in a catchment of this size. Sediment volumes have been used to calculate mean denudation rates for the different processes ranging from 0·1 to 2·6,mm/a based on a time span of 10,ka. As the quantification approach includes a number of assumptions and various sources of error the values given represent the order of magnitude of sediment storage that has to be expected in a catchment of this size. Copyright © 2009 John Wiley & Sons, Ltd. [source] Modeling past and future alpine permafrost distribution in the Colorado Front RangeEARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2005Jason R. Janke Abstract Rock glaciers, a feature associated with at least discontinuous permafrost, provide important topoclimatic information. Active and inactive rock glaciers can be used to model current permafrost distribution. Relict rock glacier locations provide paleoclimatic information to infer past conditions. Future warmer climates could cause permafrost zones to shrink and initiate slope instability hazards such as debris flows or rockslides, thus modeling change remains imperative. This research examines potential past and future permafrost distribution in the Colorado Front Range by calibrating an existing permafrost model using a standard adiabatic rate for mountains (0·5 °C per 100 m) for a 4 °C range of cooler and warmer temperatures. According to the model, permafrost currently covers about 12 per cent (326·1 km2) of the entire study area (2721·5 km2). In a 4 °C cooler climate 73·7 per cent (2004·4 km2) of the study area could be covered by permafrost, whereas in a 4°C warmer climate almost no permafrost would be found. Permafrost would be reduced severely by 93·9 per cent (a loss of 306·2 km2) in a 2·0 °C warmer climate; however, permafrost will likely respond slowly to change. Relict rock glacier distribution indicates that mean annual air temperature (MAAT) was once at least some 3·0 to 4·0 °C cooler during the Pleistocene, with permafrost extending some 600,700 m lower than today. The model is effective at identifying temperature sensitive areas for future monitoring; however, other feedback mechanisms such as precipitation are neglected. Copyright © 2005 John Wiley & Sons, Ltd. [source] Flow velocities of active rock glaciers in the Austrian AlpsGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2006Karl Krainer ABSTRACT. High surface flow velocities of up to 3 m a,1 were measured near the front of three active rock glaciers in the western Stubai Alps (Rei-chenkar) and Ötztal Alps (Kaiserberg and Ölgrube) in Tyrol (Austria) using differential GPS technology. Flow velocities have increased since about 1990. The highest velocities were recorded in 2003 and 2004, but showed a slight decrease in 2005. At the Reichenkar rock glacier, flow rates are constant throughout the year, indicating that meltwater has no significant influence on the flow mechanism. At Ölgrube rock glacier, flow velocities vary seasonally with considerably higher velocities during the melt season. Meltwater is likely to influence the flow of Ölgrube rock glacier as evident by several springs near the base of the steep front. Because the high surface velocities cannot be explained by internal deformation alone on Reichenkar rock glacier, we assume that horizontal deformation must also occur along a well defined shear zone within a water-saturated, fine-grained layer at the base of the frozen body. The increased surface flow velocities since about 1990 are probably caused by slightly increased ice temperature and greater amounts of meltwater discharge during the summer, a product of global warming. [source] Photogrammetric Analysis of Front Range Rock Glacier Flow RatesGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2005Jason Ronald Janke Abstract Flow rates for rock glaciers in the European Alps have been monitored using photogrammetric techniques; however, a program has not been initiated for similar Front Range, USA, rock glaciers. Horizontal rock glacier displacements were measured by tracking large surficial rocks on temporal orthophotos from 1978, 1990, and 1999. Vertical change was measured by creating digital elevation models (DEMs) from digital stereopairs, then subtracting elevations to detect change. Long-term horizontal velocities ranged from 14 to 20 cm/yr on average, although uncertainty ranged from 4 to 5 cm/yr. On average, vertical elevation changes were negligible with most rock glaciers exhibiting a slight growth or thinning (1,2 cm/yr). Over shorter time scales (c. 10-year periods), horizontal velocities have only increased by about 2 cm/yr. Because horizontal and vertical change is minimal, Front Range rock glaciers appear to be adjusted with current climate, unlike some rock glaciers in the European Alps that have shown increasing subsidence rates or significant increasing or decreasing horizontal velocities. [source] Topography of a composite relict rock glacier, ,l,,a Massif, SW PolandGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2003Dorota Borowicz Abstract A detailed geodetic survey and, additionally, a map of slope covers have been carried out for a composite relict rock glacier on the slopes of Mt ,l,,a (718 m a.s.l.), Sudetic Foreland, SW Poland. The survey allows one to distinguish the mobilisation, transition and accumulation zones and to define geomorphic features diagnostic for relict rock glaciers such as lateral ridges standing above a central depression, steep margins of the landforms in the transition and accumulation zones, as well as absence of distinct head scarps above. Furthermore, it indicates that the present-day hydrographic pattern on the surface of relict rock glaciers has been superimposed on the relief inherited from the active landforms. The topography indicates that tension prevailed rather than compression during the development of the rock glaciers. Some of the features, such as small lateral lobes, developed probably as a result of the compressive flow, however. The pattern of the slope cover shows that it developed during activity of the rock glaciers and been modified afterwards due to solifluction. [source] Debris-covered Glaciers and Rock Glaciers in the Nanga Parbat Himalaya, PakistanGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2000John F. Shroder The origin and mobilization of the extensive debris cover associated with the glaciers of the Nanga Parbat Himalaya is complex. In this paper we propose a mechanism by which glaciers can form rock glaciers through inefficiency of sediment transfer from glacier ice to meltwater. Inefficient transfer is caused by various processes that promote plentiful sediment supply and decrease sediment transfer potential. Most debris-covered glaciers on Nanga Parbat with higher velocities of movement and/ or efficient debris transfer mechanisms do not form rock glaciers, perhaps because debris is mobilized quickly and removed from such glacier systems. Those whose ice movement activity is lower and those where inefficient sediment transfer mechanisms allow plentiful debris to accumulate, can form classic rock glaciers. We document here with maps, satellite images, and field observations the probable evolution of part of a slow and inefficient ice glacier into a rock glacier at the margins of Sachen Glacier in c. 50 years, as well as several other examples that formed in a longer period of time. Sachen Glacier receives all of its nourishment from ice and snow avalanches from surrounding areas of high relief, but has low ice velocities and no efficient system of debris removal. Consequently it has a pronounced digitate terminus with four lobes that have moved outward from the lateral moraines as rock glaciers with prounced transverse ridges and furrows and steep fronts at the angle of repose. Raikot Glacier has a velocity five times higher than Sachen Glacier and a thick cover of rock debris at its terminus that is efficienctly removed. During the advance stage of the glacier since 1994, ice cliffs were exposed at the terminus, and an outbreak flood swept away much debris from its margins and terminus. Like the Sachen Glacier that it resembles, Shaigiri Glacier receives all its nourishment from ice and snow avalanches and has an extensive debris cover with steep margins close to the angle of repose. It has a high velocity similar to Raikot Glacier and catastrophic breakout floods have removed debris from its terminus twice in the recent past. In addition, the Shaigiri terminus blocked the Rupal River during the Little Ice Age and is presently being undercut and steepened by the river. With higher velocities and more efficient sediment transfer systems, neither the Raikot nor the Shaigiri form classic rock-glacier morphologies. [source] Ground penetrating radar survey and stratigraphic interpretation of the Plan du Lac rock glaciers, Vanoise Massif, northern French AlpsPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2008Sébastien Monnier Abstract Internal boundaries of the Plan du Lac rock glaciers in the northern French Alps were investigated using ground-penetrating radar (GPR) and were correlated with the surface morphology. Data collected using 50,MHz antennae along three profiles were processed in a novel manner by applying modulated automatic gain control to discriminate reflection events according to coherence and continuity patterns. Based on the GPR and morphological analyses, the stratigraphy appears complex, with prominent internal boundaries dividing the features into several depositional units, interpreted as sequential creeping or thrusting events. Copyright © 2008 John Wiley & Sons, Ltd. [source] The lower limit of mountain permafrost in the Russian Altai MountainsPERMAFROST AND PERIGLACIAL PROCESSES, Issue 2 2007Kotaro Fukui Abstract Permafrost-indicator features, such as rock glaciers, pingos and ice-wedge polygons, exist at many locations in and around the South Chuyskiy Range of the Russian Altai Mountains (,50°N). The distribution of these features suggests that the altitudinal range of the sporadic/patchy permafrost zones and the widespread discontinuous/continuous permafrost zones are 1800,2000,m ASL and above 2000,m ASL, respectively. The lower limit of discontinuous permafrost is approximately 200,m lower than in the Mongolian Altai, which are at a similar latitude. Cold air drainage and/or temperature inversions during winter within U-shaped valleys together with a thin snow cover because of low precipitation during the same season likely cause the lower permafrost limit in the study area. The calibrated 14C ages of tree remnants found in a rock glacier front in the lower Akkol valley were 293,±,21 years BP and 548,±,21 years BP. Given the time of emergence from beneath the Sofiyskiy glacier, this rock glacier developed between 3800,2600 and 550 years BP. Copyright © 2007 John Wiley & Sons, Ltd. [source] Permafrost and Little Ice Age glacier relationships, Posets Massif, Central Pyrenees, SpainPERMAFROST AND PERIGLACIAL PROCESSES, Issue 3 2004Ralph Lugon Abstract This paper contributes to the study of permafrost in the Pyrenees by reporting geoelectrical investigations and thermal measurement on the Little Ice Age (LIA) forefields of two glaciers. The aim was to assess the internal composition of sedimentary bodies (debris rock glaciers and moraine deposits) located in this proglacial environment. Ground ice was prospected using two DC resistivity techniques: vertical electrical soundings and resistivity mapping at a fixed pseudo-depth. Extreme specific resistivities ranging between 1 and 25,M,,m were detected under a thin (1,2,m) unfrozen layer, indicating the presence of a massive ice layer, certainly buried glacier ice. This ice of glacial origin probably covers former permafrost bodies, i.e. a much thicker layer of perennially frozen sediments. Low subsurface temperatures measured on the deposits indicate that buried glacier ice could have been preserved on top of permafrost since the end of the LIA or earlier Holocene glacier advances. This stratigraphy demonstrates that glaciers and pre-existing perennially frozen sediments (permafrost) were in contact during the LIA. Copyright © 2004 John Wiley & Sons, Ltd. [source] Borehole deformation measurements and internal structure of some rock glaciers in SwitzerlandPERMAFROST AND PERIGLACIAL PROCESSES, Issue 2 2002Lukas Arenson Abstract In order to understand the mechanical processes that influence the deformation patterns of active rock glaciers, information about local horizontal and vertical deformations as well as knowledge of the internal structure and the temperature distribution is necessary. Results from borehole deformation measurements of three sites in the Swiss Alps show that despite different internal structures, similar phenomena can be observed. In contrast to temperate glaciers, permafrost within rock glaciers has distinct shear zones where horizontal and vertical differential movements are concentrated. In addition, a reduction in volume can be caused by compressive flow due to the presence of air voids within the permafrost. The flow velocity depends on the temperature, the surface and bedrock slopes of the rock glacier, and the composition of the ice-rich frozen ground. Within degrading permafrost, the ice content decreases, the creep velocity increases and the shear zone rises towards the surface, where seasonal temperature changes and the presence of liquid water might also influence deformation. Copyright © 2002 John Wiley & Sons, Ltd. [source] Internal Structure of a relict rock glacier, ,l,,a Massif, Southwest PolandPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2002Roman, urawek Abstract The sediments of a large accumulation landform, interpreted as one of six Pleistocene rock glaciers occurring in the ,l,,a Massif, southwest Poland, are described. The sediments have been subject to strong compression and the main deformation mechanism is that of shearing. The similar angle of shear in sediments of extremely different lithology is inferred from the geometry of failure surfaces and indicates that ice was necessary for the debris transport. Because the geomorphological setting excludes a glacigenic origin, the sediments are interpreted to result from the creep of permafrost, i.e. the landform is a relict rock glacier. The movement of the rock glacier, at least in its terminal stage, is associated with a dense pattern of shear planes and would have occurred even in the presence of a small amount of interstitial ice. Copyright © 2002 John Wiley & Sons, Ltd. [source] Genetic differences of rock glaciers and the discontinuous mountain permafrost zone in Kanchanjunga Himal, Eastern NepalPERMAFROST AND PERIGLACIAL PROCESSES, Issue 3 2001Mamoru Ishikawa Abstract A number of rock glaciers, including glacier-derived and talus-derived rock glaciers, were identified in Kanchanjunga Himal, easternmost Nepal. DC resistivity imagings were applied to representative rock glaciers of both types. The distribution of resistivity values in the subsurface within these rock glaciers was significantly different. A massive glacial ice body was found within the glacier-derived rock glacier, suggesting this rock glacier originated from glacial dead ice (ice-cored rock glacier). The lower limits of discontinuous mountain permafrost zone in Kanchanjunga Himal were inferred from the distribution of talus-derived rock glaciers (ice-cemented rock glaciers) and the estimated mean annual air temperature. The lower limit of the discontinuous mountain permafrost zone is 4800 m ASL on the north-facing slopes, while 5300 m ASL on the south- to east-facing slopes. These altitudes were considerably higher than those of the western Himalaya, which are under dry continental climatic conditions. Copyright © 2001 John Wiley & Sons, Ltd. RÉSUMÉ Plusieurs glaciers rocheux comprenant à la fois des formes dérivéees de vrais glaciers et des formes provenant de la mise en mouvement de talus, ont été identifiés dans le Kanchanjunga Himal, dans le Népal le plus oriental. Des images par résistivité DC ont été obtenues pour des glaciers représentatifs des deux catégories. La distribution des valeurs de résistivité en profondeur dans ces glaciers rocheux a été significativement différente. Un corps de glace massif a été trouvé dans le glacier rocheux provenant d'un vrai glacier suggérant qu'il s'agissait de glace morte glaciaire (glacier rocheux à noyau de glace). Les limites inférieures de la zone du pergélisol discontinu dans le Kanchanjungga Himal ont été déduites de la distribution des glaciers rocheux provenant de talus (glaciers rocheux avec de la glace ciment) et d'une estimation de la température moyenne annuelle de l'air. La limite inférieure de la zone du pergélisol discontinu de montagne est de 4800 m d'altitude sur les pentes exposées au nord, tandis que la limite est de 5300 m sur les pentes exposées au sud. Ces altitudes sont considérablement plus élevées que celles de l'ouest de l'Himalaya exposé à des conditions climatiques continentales sèches. Copyright © 2001 John Wiley & Sons, Ltd. [source] | |||||||||||||