scholarly journals New insights into ice accumulation at Galena Creek Rock Glacier from radar imaging of its internal structure

2019 ◽  
Vol 66 (255) ◽  
pp. 1-10
Author(s):  
Eric Ivan Petersen ◽  
Joseph S. Levy ◽  
John W. Holt ◽  
Cassie M. Stuurman

AbstractThe ice-cored Galena Creek Rock Glacier, Wyoming, USA, has been the subject of a number of studies that sought to determine the origin of its ice. We present new observations of the rock glacier's internal structure from ground-penetrating radar to constrain ice and debris distribution and accumulation. We imaged dipping reflectors in the center of the glacier that are weak and discontinuous, in contrast to strong reflectors toward the edge of the cirque beneath large debris-avalanche chutes. These reflectors form a network of concave-up, up-glacier dipping layers. We interpret these as englacial debris bands formed by large debris falls buried by subsequent ice and snow accumulation. They are discontinuous where ice outpaces debris accumulation, but with sufficient debris accumulation an interleaved pattern of ice and debris layers can form. We propose a model in which the ice in these interleaved layers is snowfall preserved by debris-facilitated accumulation. Large debris falls that occur in early spring bury sections of the snowpack, which are then preserved through summer and incorporated into the rock glacier body over time. This study highlights the importance of sequential accumulation of ice and debris for understanding the dynamics of rock glaciers and debris-covered glaciers.

2014 ◽  
Vol 60 (221) ◽  
pp. 453-462 ◽  
Author(s):  
Caitlyn Florentine ◽  
Mark Skidmore ◽  
Marvin Speece ◽  
Curtis Link ◽  
Colin A. Shaw

AbstractRock glaciers are periglacial alpine landforms that are found in many locations worldwide. Whereas well-developed models of deformation are established for traditional alpine glaciers, rock glacier deformation is poorly understood. Geophysical data from Lone Peak Rock Glacier (LPRG), southwest Montana, USA, are paired with lidar bare-earth 1 m digital elevation model (DEM) analysis to explore potential genetic relationships between internal composition, structure and regularly spaced arcuate transverse ridges expressed at the rock glacier surface. The internal composition of LPRG is heterogeneous, with frozen debris and clean ice overlain by an unconsolidated talus mantle. Upslope-dipping, clearly distinguished reflectors in the ground-penetrating radar (GPR) longitudinal survey at LPRG correspond to transverse ridges. The spacing and slope of individual features at the surface and in the subsurface were measured and compared and are found to be similar. The structures observed at LPRG and other rock glaciers are similar to structures detected in glaciotectonically altered sediment, ice-cored moraines and other rock glacier settings. This finding suggests that transverse ridges on rock glaciers may be used as geomorphic indicators of internal deformation. This study contributes to the body of research on the application of GPR to rock glaciers, and is the first to directly pair and analyze individual surface topographic features with internal structures.


2017 ◽  
Vol 11 (2) ◽  
pp. 841-855 ◽  
Author(s):  
Adrian Emmert ◽  
Christof Kneisel

Abstract. Interactions between different formative processes are reflected in the internal structure of rock glaciers. Therefore, the detection of subsurface conditions can help to enhance our understanding of landform development. For an assessment of subsurface conditions, we present an analysis of the spatial variability of active layer thickness, ground ice content and frost table topography for two different rock glaciers in the Eastern Swiss Alps by means of quasi-3-D electrical resistivity imaging (ERI). This approach enables an extensive mapping of subsurface structures and a spatial overlay between site-specific surface and subsurface characteristics. At Nair rock glacier, we discovered a gradual descent of the frost table in a downslope direction and a constant decrease of ice content which follows the observed surface topography. This is attributed to ice formation by refreezing meltwater from an embedded snow bank or from a subsurface ice patch which reshapes the permafrost layer. The heterogeneous ground ice distribution at Uertsch rock glacier indicates that multiple processes on different time domains were involved in the development. Resistivity values which represent frozen conditions vary within a wide range and indicate a successive formation which includes several advances, past glacial overrides and creep processes on the rock glacier surface. In combination with the observed topography, quasi-3-D ERI enables us to delimit areas of extensive and compressive flow in close proximity. Excellent data quality was provided by a good coupling of electrodes to the ground in the pebbly material of the investigated rock glaciers. Results show the value of the quasi-3-D ERI approach but advise the application of complementary geophysical methods for interpreting the results.


2019 ◽  
Vol 9 (4) ◽  
pp. 729-731
Author(s):  
G. S. Dyakova ◽  
A. A. Goreyavcheva ◽  
V. V. Potapov ◽  
A. N. Shein ◽  
D. S. Lobachev ◽  
...  

In 2019, a comprehensive study of the internal structure of the talus rock glacier in the Dzhelo River valley was carried out (North-Chuya Range). The identification of the internal structure was performed using electrical resistivity tomography and GPR sounding. In order to compare the internal structure of the rock glacier with its surface morphology, we carried out aerial photography and constructed a digital terrain model. The study revealed that the depth of the rock-ice core varies from 2.5-3 m to 10 m, and the thickness ranges from 7 m to 30 m. The consolidation cores of the rock-ice material are confined to inter-ridge depressions in the rock glacier body. The potential volume of a rock-ice core is 800 thousand m3, which is 53% of the rock glacier total volume, the ice volume in the rock-ice core can be as much as 400 thousand m3.


2020 ◽  
Author(s):  
Nora Krebs ◽  
Anne Voigtländer ◽  
Matthias Bücker ◽  
Andreas Hördt ◽  
Ruben Schroeckh ◽  
...  

<p>Geophysical methods provide a powerful tool to understand the internal structure of active rock glaciers. We applied Electrical Resistivity Tomography (ERT) to a rock glacier at an elevation of 5500 m a.s.l. in the semi-arid Nyainqêntanglha mountain range on the Tibetan plateau, China.  The investigations comprised three transects across the rock glacier and its catchment, each spanning over a distance of 296 m up to 396 m, equipped with 75 up to 100 electrodes respectively. Our measurements were successful in revealing internal structures of the rock glacier, but were also accompanied by challenges.</p><p>We successfully detected first-order permafrost structures, such as a shallow about 4 m thick active layer of low electrical resistivity values that was underlain by potentially ice rich zones of high resistivity. Further high-resistivity zones were found and interpreted as dense bed rock of adjacent slopes that undergird the loose rock glacier debris.</p><p>Challenges, we faced in the application of ERT, were mainly posed by the morphology and internal structure of the rock glacier itself. Coarse debris created a rough surface that prevented a uniform setup with accurate 4 m spacing. The presence of loosely nested blocks of pebble size up to boulders with large interspaces resulted in high contact resistances. The consequent low injection current densities and possible noisy voltage readings downgraded part of the data, causing low data density and resolution. Coupling was partly improved by attaching salt-watered sponges to the electrodes and adding more conductive fine-grained materials to the electrodes. The detected high resistivity ice layer impeded deep penetration of electrical currents, which caused that the lower limit of the permanently frozen zone could not be defined.</p><p>Despite these challenges, the captured ERT profiles are an indispensable contribution to the sparse field data on the internal structure of rock glaciers on the Tibetan plateau. Our results contribute to a better understanding of the prospective evolution of rock glaciers in dry, high mountain ranges under a changing climate.</p>


2020 ◽  
Vol 32 (4) ◽  
pp. 273-287
Author(s):  
Kelsey Winsor ◽  
Kate M. Swanger ◽  
Esther L. Babcock ◽  
James L. Dickson ◽  
Rachel D. Valletta ◽  
...  

AbstractThe South Fork of Wright Valley contains one of the largest rock glaciers in the McMurdo Dry Valleys, Antarctica, stretching 7 km from the eastern boundary of the Labyrinth and terminating at Don Juan Pond (DJP). Here, we use results from ground-penetrating radar (GPR), qualitative field observations, soil leaching analyses and X-ray diffraction analyses to investigate rock glacier development. The absence of significant clean ice in GPR data, paired with observations of talus and interstitial ice influx from the valley walls, support rock glacier formation via talus accumulation. A quartz-dominated subsurface composition and discontinuous, well-developed desert pavements suggest initial rock glacier formation occurred before the late Quaternary. Major ion data from soil leaching analyses show higher salt concentrations in the rock glacier and talus samples that are close to hypersaline DJP. These observations suggest that DJP acts as a local salt source to the rock glacier, as well as the surrounding talus slopes that host water track systems that deliver solutes back into the lake, suggesting a local feedback system. Finally, the lack of lacustrine sedimentation on the rock glacier is inconsistent with the advance of a glacially dammed lake into South Fork during the Last Glacial Maximum.


2013 ◽  
Vol 54 (64) ◽  
pp. 61-72 ◽  
Author(s):  
Sébastien Monnier ◽  
Christophe Kinnard

Abstract This study uses boreholes, ground temperature monitoring and ground-penetrating radar (GPR) in order to understand the internal structure and composition of a rock glacier in the upper Choapa valley, northern Chile. The rock glacier is a small valley-side feature, 200 m long and ranging between 3710 and 3780 ma.s.l. Two boreholes were drilled down to depths of 20 and 25 m, respectively, using the diamond drillhole technique. An ice-rock mixture was encountered in the boreholes, with heterogeneous ice content averaging 15-30%. Data from common-midpoint (CMP) and constant-offset (CO) GPR surveys acquired, respectively, near the boreholes and across the whole rock glacier were processed to highlight the internal stratigraphy and variations in the radar-wave velocity. The GPR profiles depict a rock glacier constituted of stacked and generally concordant layers, with a thickness ranging from 10 m in its upper part to ∼30m towards its terminus. The CMP analysis highlights radar-wave velocities of 0.13-0.16 m ns–1 in the first 20 m of the structure. Larger vertical and lateral velocity variations are highlighted from CO data, reflecting the heterogeneous composition of the rock glacier and the likely presence of unfrozen water in the structure. Given the average air temperature registered at the site (+0.5°C), the near-melting-point temperature registered in the boreholes over more than a year and the presence of locally high water content inferred from GPR data, it is thought that the permafrost in the rock glacier is currently degrading.


1970 ◽  
Vol 6 (1) ◽  
pp. 202-214
Author(s):  
Олена Савченко

У статті розглядається рефлексивна компетентність як інтегративне особистісне утворення, що формується в ході набуття суб’єктом рефлексивного досвіду при застосуванні різних форм рефлексивної активності, спрямованих на розв’язання визначених рефлексивних задач. У структурі рефлексивної компетентності оцінно-мотиваційний компонент виконує наступні функції: оцінку форм рефлексивної активності та її результатів, прогнозування можливих змін у процесі розв’язування проблемно-конфліктних ситуацій, визначення пріоритетних завдань подальшого розвитку себе як суб’єкта рефлексивної активності. На когнітивному рівні функціонує система критеріїв оцінювання власних форм рефлексивної активності, яка характеризується ступенем когнітивної складності, що відображає рівень диференціації та інтеграції системи. Функціонування оцінно-мотиваційного компонента на метакогнітивному рівні забезпечує система здібностей до прогнозування власної активності. Особистісний рівень представлений системою життєвих задач на саморозвиток, які стимулюють суб’єкта докладати зусилля щодо розвитку в себе певних якостей, формування певних вмінь та знань. Розрізненість елементів компонента є індикатором незавершеності процесу формування його внутрішньої структури, низький рівень інтеграції окремих складових не дозволяє системі ефективно компенсувати недорозвинені елементи. Найбільшу вагу у внутрішній структурі оцінно-мотиваційного компонента має показник сформованості системи здібностей до прогнозування власної активності, що підтверджує системотвірну функцію структур метакогнітивного рівня. In the article the reflective competence is seen as an integrative personal formation which develops in the process of acquiring of the reflective experience, when the subject is using various forms of the reflective activity for the solving of specific reflective tasks. In the structure of the reflective competence the value-motivational component performs such functions: an evaluation of forms of the reflective activity and its results, a prediction of the possible changes in the process of solving of the problem-conflict situations, a determining of the priorities for further development of himself as a subject of the reflective activity. The system of the criteria of an evaluating of the reflective activity`s forms functions on the cognitive level of the reflective competence. The level of the cognitive complexity is the basic feature of this system. The predictive abilities` system, that allows to form the expectations of the activity`s results, presents the value-motivational component on the metacognitive level. The system of the life tasks for the self-development, which stimulates the subject to make efforts to develop his own qualities, to form specific skills and knowledge, functions on the personal level. The fragmentation of the elements is an indicator of the incompleteness of the formation of the internal structure of the value-motivational component. The low level of integration of the separate elements does not allow effectively to compensate the functioning of the unformed elements of the system. The index of the formation of the abilities to predict his own activity has the greatest meaning in the internal structure of the value-motivational component. These data confirm the hypothesis about the system-forming function of the metacognitive structures that unite other structures. Thus the development of the predictive abilities will promote the increase of the abilities to the prediction of the others` behavior. An adequate assessment of other people significantly reduces the inconsistency of his own expectations and estimations of others. The development of the predictive abilities creates favorable conditions for the formation of the life tasks for the self-development to increase their value in the system of other tasks


2021 ◽  
pp. 1-13
Author(s):  
E.J. Chamberlain ◽  
A.J. Christ ◽  
R.W. Fulweiler

Abstract Ice-covered lakes in Antarctica preserve records of regional hydroclimate and harbour extreme ecosystems that may serve as terrestrial analogues for exobiotic environments. Here, we examine the impacts of hydroclimate and landscape on the formation history of Lake Eggers, a small ice-sealed lake, located in the coastal polar desert of McMurdo Sound, Antarctica (78°S). Using ground penetrating radar surveys and three lake ice cores we characterize the ice morphology and chemistry. Lake ice geochemistry indicates that Lake Eggers is fed primarily from local snowmelt that accreted onto the lake surface during runoff events. Radiocarbon ages of ice-encased algae suggest basal ice formed at least 735 ± 20 calibrated years before present (1215 C.E.). Persisting through the Late Holocene, Lake Eggers alternated between periods of ice accumulation and sublimation driven by regional climate variability in the western Ross Sea. For example, particulate organic matter displayed varying δ15N ratios with depth, corresponding to sea ice fluctuations in the western Ross Sea during the Late Holocene. These results suggest a strong climatic control on the hydrologic regime shifts shaping ice formation at Lake Eggers.


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