scholarly journals Numerical Simulation of Supraglacial Debris Mobility: Implications for Ablation and Landform Genesis

2021 ◽  
Vol 9 ◽  
Author(s):  
Peter L. Moore
Keyword(s):  
Conceptual Models ◽  
Slope Angle ◽  
Passive Movement ◽  
Coupled Processes ◽  
Glacier Surface ◽  
Ice Surface ◽  
Debris Transport ◽  
Hillslope Scale ◽  
Genesis Model ◽  
The Relationship

Supraglacial debris does not remain fixed atop ablating ice, but can move across the ice surface as supraglacial topography evolves. This active debris movement (distinct from passive movement due to underlying ice motion) affects landform genesis as well as the rate and spatial distribution of ablation. While observations of debris transport across evolving supraglacial topography are abundant, models of these coupled processes over timescales of decades and longer are few. Here I adapt a numerical model of coupled ablation and downslope debris transport to simulate the evolution of an idealized debris-covered glacier on the timescale of complete de-icing. The model includes ablation that depends on supraglacial debris thickness and a hillslope-scale debris transport function that scales non-linearly with slope angle. Ice thickness and debris distribution evolve with model time, allowing complete simulation of de-icing and landform construction in an idealized glacier test-section. The model produces supraglacial relief that leads to topographic inversions consistent with conceptual models of hummocky landform genesis. Model results indicate that the relief of the glacier surface and postglacial hummocks depend on the relationship between characteristic timescales for ablation and debris transport, which is defined as an index of debris mobility. When debris mobility is high, topographic inversions are rapid and supraglacial and postglacial relief are subdued. When debris mobility is low, more pronounced supraglacial relief is produced, but postglacial relief remains subdued. An intermediate mobility appears to optimize both postglacial relief and the rate of de-icingcompared with both highly-mobile and immobile debris. This enhancement of de-icing due to debris mobility could contribute to the observed anomalous rates of ablation in some debris-covered glaciers.

scholarly journals Modeling Surface Processes on Debris-Covered Glaciers: A Review with Reference to the High Mountain Asia

Water ◽  
2021 ◽  
Vol 13 (1) ◽  
pp. 101
Author(s):  
Da Huo ◽  
Zhaohui Chi ◽  
Andong Ma
Keyword(s):  
Hydrological Cycle ◽  
Current Knowledge ◽  
Numerical Models ◽  
Mass Movement ◽  
Surface Processes ◽  
Coupled Processes ◽  
High Mountain ◽  
Glacier Surface ◽  
In Situ Data ◽  
Debris Transport

Surface processes on debris-covered glaciers are governed by a variety of controlling factors including climate, debris load, water bodies, and topography. Currently, we have not achieved a general consensus on the role of supraglacial processes in regulating climate–glacier sensitivity in High Mountain Asia, which is mainly due to a lack of an integrated understanding of glacier surface dynamics as a function of debris properties, mass movement, and ponding. Therefore, further investigations on supraglacial processes is needed in order to provide more accurate assessments of the hydrological cycle, water resources, and natural hazards in the region. Given the scarcity of long-term in situ data and the difficulty of conducting fieldwork on these glaciers, many numerical models have been developed by recent studies. This review summarizes our current knowledge of surface processes on debris-covered glaciers with an emphasis on the related modeling efforts. We present an integrated view on how numerical modeling provide insights into glacier surface ablation, supraglacial debris transport, morphological variation, pond dynamics, and ice-cliff evolution. We also highlight the remote sensing approaches that facilitate modeling, and discuss the limitations of existing models regarding their capabilities to address coupled processes on debris-covered glaciers and suggest research directions.

scholarly journals Application of a mass-balance model to a Himalayan glacier

1999 ◽  
Vol 45 (151) ◽  
pp. 559-567 ◽  
Author(s):  
Rijan Bhakta Kayastha ◽  
Tetsuo Ohata ◽  
Yutaka Ageta
Keyword(s):  
Mass Balance ◽  
Surface Albedo ◽  
Balance Model ◽  
Mass Balance Model ◽  
Mass Balances ◽  
Climatic Parameters ◽  
Glacier Surface ◽  
Temperature And Precipitation ◽  
Ice Surface ◽  
Good Agreement

AbstractA mass-balance model based on the energy balance at the snow or ice surface is formulated, with particular attention paid to processes affecting absorption of radiation. The model is applied to a small glacier, Glacier AX010 in the Nepalese Himalaya, and tests of its mass-balance sensitivity to input and climatic parameters are carried out. Calculated and observed area-averaged mass balances of the glacier during summer 1978 (June-September) show good agreement, namely -0.44 and -0.46 m w.e., respectively.Results show the mass balance is strongly sensitive to snow or ice albedo, to the effects of screening by surrounding mountain walls, to areal variations in multiple reflection between clouds and the glacier surface, and to thin snow covers which alter the surface albedo. In tests of the sensitivity of the mass balance to seasonal values of climatic parameters, the mass balance is found to be strongly sensitive to summer air temperature and precipitation but only weakly sensitive to relative humidity.

scholarly journals Current glacier recession causes significant rockfall increase: The immediate paraglacial response of deglaciating cirque walls

2020 ◽  
Author(s):  
Ingo Hartmeyer ◽  
Robert Delleske ◽  
Markus Keuschnig ◽  
Michael Krautblatter ◽  
Andreas Lang ◽  
...  
Keyword(s):  
Minor Effect ◽  
European Alps ◽  
Atmospheric Conditions ◽  
Glacier Surface ◽  
Terrestrial Lidar ◽  
Physical Weathering ◽  
Ice Surface ◽  
Recent Climate ◽  
Ample Supply ◽  
A Minor

Abstract. In the European Alps almost half the glacier volume disappeared over the past 150 years. The loss is reflected in glacier retreat and ice surface lowering even at high altitude. In steep glacial cirques surface lowering exposes rock to atmospheric conditions for the very first time in many millennia. Instability of rockwalls has long been identified as one of the direct consequences of deglaciation, but so far cirque-wide quantification of rockfall at high-resolution is missing. Based on terrestrial LiDAR a rockfall inventory for the permafrost-affected rockwalls of two rapidly deglaciating cirques in the Central Alps of Austria (Kitzsteinhorn) is established. Over six-years (2011–2017) 78 rockwall scans were acquired to generate data of high spatial and temporal resolution. 632 rockfalls were registered ranging from 0.003 to 879.4 m³, mainly originating from pre-existing structural rock weaknesses. 60 % of the rockfall volume detached from less than ten vertical meters above the glacier surface, indicating enhanced rockfall activity over tens of years following deglaciation. Debuttressing seems to play a minor effect only. Rather, preconditioning is assumed to start inside the Randkluft (gap between cirque wall and glacier) where sustained freezing and ample supply of liquid water likely cause enhanced physical weathering and high plucking stresses. Following deglaciation, pronounced thermomechanical strain is induced and an active layer penetrates into the formerly perennially frozen bedrock. These factors likely cause the observed paraglacial rockfall increase close to the glacier surface. This paper presents the most extensive dataset of high-alpine rockfall to date and the first systematic documentation of a cirque-wide erosion response of glaciated rockwalls to recent climate warming.

scholarly journals Application of nonlinear colour enhancement on transparencies for interpretation of glacier surface characteristics

1992 ◽  
Vol 16 ◽  
pp. 190-192
Author(s):  
Cao Meisheng ◽  
Mi Desheng ◽  
Pu Yinbin ◽  
Liu Jinghaung
Keyword(s):  
Surface Characteristics ◽  
False Colour Composite ◽  
High Contrast ◽  
Glacier Surface ◽  
Ice Surface ◽  
Grey Scale ◽  
Scale Range ◽  
Colour Composite ◽  
Channel Image ◽  
False Colour

According to the analysis of grey scale range on MSS-4, -5, -6 and -7 channel image films for five snow-ice categories on glacier surface, the grey scale among snow, bare ice, ice pinnacle, moraine-covered ice surface and gully bed has been spread nonlinearly by using duplicative processing on high-contrast film. As a result of the rescaling of grey levels, the colour differences of morphological features of Rongbu Glacier in the Qpmolangma region have been increased on false colour composite photography. It is also shown that using MSS-6 to composite false colour images compared to MSS-5 will supply more information for the interpretation of the glacier area.

Temperate Alpine glacier surface dynamics linked to collapsing subglacial conduits

2021 ◽  
Author(s):  
Pascal Egli ◽  
Stuart Lane ◽  
James Irving ◽  
Bruno Belotti
Keyword(s):  
Three Dimensional ◽  
Swiss Alps ◽  
Glacier Retreat ◽  
Collapse Mechanism ◽  
Glacier Mass Balance ◽  
Glacier Surface ◽  
Alpine Glacier ◽  
Surface Loss ◽  
Ice Surface ◽  
Surface Melt

<p>If tongues of temperate Alpine glaciers are subjected to high temperatures their topography may change rapidly due to the effects of differential melt related to aspect and debris cover. Independent of local surface melt, the position of subglacial conduits may have an important influence on ice creep and so on changes in topography at the ice surface. This reflects analyses that suggest that subglacial conduits at glacier margins may not be permanently pressurised; and that creep closure rates are insufficient to close subglacial conduits completely. Rapid climate warming may exacerbate this process, due both to surface-melt driven glacier thinning and over-enlargement of conduits due to high upstream melt rates. Over-enlarged conduits that are not permanently pressurised would lead to the development of structural weaknesses and eventual collapse of the ice surface into the conduits. We hypothesise that this collapse mechanism could represent an important and alternative driver of rapid glacier retreat.</p><p>In this paper we combine: (1) an extensive survey of glacier margin collapse in the Swiss Alps with (2) intensive monitoring of the dynamics of such collapse at the Otemma Glacier in the south-western Swiss Alps. Daily UAV surveys were undertaken at a high spatial resolution and with precise and accurate ground control. These datasets were used to generate surface change information using SfM-MVS photogrammetry. Surfaces of difference showed surface loss that could not be related to ablation alone. Combining them with three-dimensional ground-penetrating radar (GPR) surveys in the same zone showed that the surface loss was coincident spatially with the positions of sub-glacial conduits, for ice thicknesses between 20 m and 50 m. We show that this form of subglacial conduit collapse is also happening for several other glaciers in the Swiss Alps, and that this mechanism of snout collapse and glacier retreat has become more common than has hitherto been the case. It also leads to temporal patterns of glacier margin retreat that differ from those that might be expected due to glacier mass balance and ice mass flux effects alone.</p>

scholarly journals Seasonal Variations of the Depletion Factor during Recession Periods in the Senegal, Gambia and Niger Watersheds

Water ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2520
Author(s):  
Jean-Claude Bader ◽  
Honoré Dacosta ◽  
Jean-Christophe Pouget
Keyword(s):  
Seasonal Variations ◽  
Conceptual Models ◽  
Hydraulic Structure ◽  
Intermediate Period ◽  
Precise Knowledge ◽  
Seasonal Flow ◽  
Specific Discharge ◽  
The One ◽  
The Relationship ◽  
Decimal Logarithm

The daily depletion factor K describes the discharge decrease of rivers only fed by groundwater in the absence of rainfall. In the Senegal, Gambia and Niger river basins in West Africa, the flow recession can exceed 6 months and the precise knowledge of K thus allows discharge forecasts to be made over several months, and is hence potentially interesting for hydraulic structure managers. Seasonal flow recession observed at 54 gauging stations in these basins from 1950 to 2016 is represented by empirical and usual conceptual models that express K. Compared to conventional conceptual models, an empirical model representing K as a polynomial of the decimal logarithm of discharge Q gives better representations of K and better discharge forecasting at horizons from 1 to 120 days for most stations. The relationship between specific discharge Qs and K, not monotonous, is highly homogeneous in some sub-basins but differs significantly between the Senegal and Gambia basins on the one hand and the Niger basin on the other. The relationship K(Q) evolves slightly between three successive periods, with values of K generally lower (meaning faster discharge decrease) in the intermediate period centered on the years 1970–1980. These climate-related interannual variations are much smaller than the seasonal variations of K.

Shelf Space Allocation and Profit Maximization in Mass Retailing

1973 ◽  
Vol 37 (3) ◽  
pp. 54-60 ◽  
Author(s):  
Ronald C. Curhan
Keyword(s):  
Conceptual Models ◽  
Empirical Studies ◽  
Profit Maximization ◽  
Shelf Space ◽  
For Profit ◽  
Space Allocation ◽  
Practical Management ◽  
Shelf Space Allocation ◽  
Relationship Of ◽  
The Relationship

Conceptual models and empirical studies of the relationship of shelf space allocation to unit sales are reviewed in this article. This knowledge is organized to support specific recommendations for the practical management of shelf space for profit maximization.

scholarly journals Modelling of a marine glacier and ice-sheet-ice-shelf transition zone based on asymptotic analysis

1996 ◽  
Vol 23 ◽  
pp. 59-67 ◽  
Author(s):  
Vladimir A. Chugunov ◽  
Alexander V. Wilchinsky
Keyword(s):  
Boundary Conditions ◽  
Transition Zone ◽  
Spatial Scales ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Stream Length ◽  
Glacier Surface ◽  
Ice Surface ◽  
Grounding Line ◽  
The Difference

All parts of a two-dimensional, isothermal, stationary marine glacier (grounded ice sheet, ice shelf and transition zone) with constant viscosity are analysed by perturbation methods. In so doing, all zones of different flow patterns can be considered separately. Correlations between spatial scales for all parts can be expressed in terms of the typical ice-surface slope distant from the ocean, which reflects exterior conditions of the glacier’s existence. In considering the ice-sheet–ice-shelf transition zone, a small parameter characterizing the difference between ice and water densities is used. Such an analysis allows us to find boundary conditions at the grounding line for the grounded ice mass. Glacier-surface profiles are determined by numerical methods. The grounding-line position found by using the boundary conditions derived in this paper differs from that obtained by using Thomas and Bentley’s (1978) boundary conditions by about 10% of the grounded ice-stream length.

Minimum Input Variances for Modelling Rainfall-runoff Using ANN

2014 ◽  
Vol 69 (3) ◽  
Author(s):  
Zulkarnain Hassan ◽  
Supiah Shamsudin ◽  
Sobri Harun
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Conceptual Models ◽  
Data Series ◽  
Rainfall Runoff ◽  
Antecedent Rainfall ◽  
Runoff Series ◽  
Artificial Neural Network Ann ◽  
The Relationship

This paper presents the study of possible input variances for modeling the long-term runoff series using artificial neural network (ANN). ANN has the ability to derive the relationship between the inputs and outputs of a process without the physics being provided to it, and it is believed to be more flexible to be used compared to the conceptual models [1]. Data series from the Kurau River sub-catchment was applied to build the ANN networks and the model was calibrated using the input of rainfall, antecedent rainfall, temperature, antecedent temperature and antecedent runoff. In addition, the results were compared with the conceptual model, named IHACRES. The study reveal that ANN and IHACRES can simulate well for mean runoff but ANN gives a remarkable performance compared to IHACRES, if the model customizes with a good configuration.  

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