scholarly journals Mechanisms leading to the 2016 giant twin glacier collapses, Aru range, Tibet

2018 ◽  
Author(s):  
Adrien Gilbert ◽  
Silvan Leinss ◽  
Jeffrey Kargel ◽  
Andreas Kääb ◽  
Tandong Yao ◽  
...  
Keyword(s):  
Drainage System ◽  
Stress Transfer ◽  
Friction Angle ◽  
Shear Stresses ◽  
Fine Grained ◽  
Field Investigations ◽  
Lateral Shearing ◽  
Bed Roughness ◽  
Polythermal Glacier ◽  
Basal Shear

Abstract. In northwestern Tibet (34.0° N, 82.2° E) near lake Aru Co, the entire ablation area of two glaciers (Aru-1 and Aru-2) suddenly collapsed on 17 July 2016 and 21 September 2016, respectively, and transformed into 68 and 83 106 m3 mass flows that ran out up to 7 km, killing nine people. The only similar event currently documented is the 2002 Kolka Glacier mass flow (Caucasus Mountains). Using climatic reanalysis, remote sensing and 3D thermo-mechanical modeling, we reconstructed in detail the glaciers' thermal regimes, thicknesses, velocities, basal shear stresses and ice damage prior to the collapse. We show that frictional change leading to the collapses occurred in the temperate areas of polythermal glacier structures and are not linked to thaw of cold based ice. The two glaciers experienced a similar stress transfer from predominant basal drag towards predominant lateral shearing in the later detachment areas and during the 5–6 years before the collapses, though with a high friction patch on Aru-2 tongue which is inexistent on Aru-1. The latter led to distinctly disparate behaviour making the development of the instability more visible for the Aru-1 glacier compared to Aru-2 through enhanced crevassing over a longer period and terminus advance. Field investigations reveal that those two glaciers are flowing on a soft, highly erodible, and fine-grained sedimentary lithology. We propose that specific bedrock lithology played a key role in the two Tibet, and also in the Caucasus gigantic glacier collapses documented to date by producing low bed roughness and large amount of till rich in clay/silt with low friction angle. The twin Aru collapses would have been driven by a failing substrate linked to increasing water pore pressure in the subglacial drainage system in response to recent increases of surface melting and rain.

scholarly journals Mechanisms leading to the 2016 giant twin glacier collapses, Aru Range, Tibet

2018 ◽  
Vol 12 (9) ◽  
pp. 2883-2900 ◽  
Author(s):  
Adrien Gilbert ◽  
Silvan Leinss ◽  
Jeffrey Kargel ◽  
Andreas Kääb ◽  
Simon Gascoin ◽  
...  
Keyword(s):  
Pore Water Pressure ◽  
Water Pressure ◽  
Three Dimensional ◽  
Drainage System ◽  
Stress Transfer ◽  
Friction Angle ◽  
Shear Stresses ◽  
Horizontal Distance ◽  
Mountain Glacier ◽  
Caucasus Mountains

Abstract. In north-western Tibet (34.0∘ N, 82.2∘ E) near lake Aru Co, the entire ablation areas of two glaciers (Aru-1 and Aru-2) suddenly collapsed on 17 July and 21 September 2016. The masses transformed into ice avalanches with volumes of 68 and 83×106 m3 and ran out up to 7 km in horizontal distance, killing nine people. The only similar event currently documented is the 130×106 m3 Kolka Glacier rock and ice avalanche of 2002 (Caucasus Mountains). Using climatic reanalysis, remote sensing, and three-dimensional thermo-mechanical modelling, we reconstructed the Aru glaciers' thermal regimes, thicknesses, velocities, basal shear stresses, and ice damage prior to the collapse in detail. Thereby, we highlight the potential of using emergence velocities to constrain basal friction in mountain glacier models. We show that the frictional change leading to the Aru collapses occurred in the temperate areas of the polythermal glaciers and is not related to a rapid thawing of cold-based ice. The two glaciers experienced a similar stress transfer from predominant basal drag towards predominant lateral shearing in the detachment areas and during the 5–6 years before the collapses. A high-friction patch is found under the Aru-2 glacier tongue, but not under the Aru-1 glacier. This difference led to disparate behaviour of both glaciers, making the development of the instability more visible for the Aru-1 glacier through enhanced crevassing and terminus advance over a longer period. In comparison, these signs were observable only over a few days to weeks (crevasses) or were absent (advance) for the Aru-2 glacier. Field investigations reveal that those two glaciers were underlain by soft, highly erodible, and fine-grained sedimentary lithologies. We propose that the specific bedrock lithology played a key role in the two Tibet and the Caucasus Mountains giant glacier collapses documented to date by producing low bed roughness and large amounts of till, rich in clay and silt with a low friction angle. The twin 2016 Aru collapses would thus have been driven by a failing basal substrate linked to increasing pore water pressure in the subglacial drainage system in response to increases in surface melting and rain during the 5–6 years preceding the collapse dates.

Photoelastic Determination of Interfacial Shear Stresses in Model Composites

2007 ◽  
Vol 334-335 ◽  
pp. 289-292 ◽  
Author(s):  
F.M. Zhao ◽  
Z. Liu ◽  
F.R. Jones
Keyword(s):  
Glass Fibre ◽  
Mechanical Response ◽  
Interfacial Shear Stress ◽  
Stress Transfer ◽  
Interfacial Shear ◽  
Shear Stresses ◽  
Contour Maps ◽  
Phase Stepping ◽  
Fibre Matrix

Phase-stepping photoelasticity has been used to study the fragmentation of an E-glass fibre in epoxy resin and examine quantitatively the effect of a transverse matrix crack on the stress transfer at an interphase. Unsized glass fibre was coated by plasma polymerisation with a crosslinked conformal film of 90% acrylic acid and 10% 1,7-octadiene. The micro-mechanical response at the fibre-matrix interphase and in the adjacent matrix has been described in detail using contour maps of fringe order. From these, the interfacial shear stress profiles at fibre-break have been calculated.

scholarly journals Abrupt glacier motion and reorganization of basal shear stress following the establishment of a connected drainage system

2001 ◽  
Vol 47 (158) ◽  
pp. 472-480 ◽  
Author(s):  
Jeffrey L. Kavanaugh ◽  
Garry K. C. Clarke
Keyword(s):  
Pressure Sensors ◽  
Drainage System ◽  
Yukon Territory ◽  
Stable Configuration ◽  
Drainage Patterns ◽  
Pressure Pulses ◽  
Gradual Failure ◽  
Basal Shear ◽  
Pressure Changes ◽  
Glacier Motion

AbstractThree episodes of strong basal motion occurred at Trapridge Glacier, Yukon Territory, Canada, on 11 June 1995 following the establishment of a connected subglacial drainage system. Responses to these “spring events” are noted in the records for 42 instruments and were recorded throughout the ∼60 000 m2 study area. Strong basal motion during the events is indicated by ploughmeter, load-bolt and vertical-strain records, and abrupt pressure changes in several transducer records denote damage caused by extreme pressure pulses. These pressure pulses, generated by the abrupt basal motion, also resulted in the failure of seven pressure sensors. Records for pressure, turbidity and conductivity sensors indicate that basal drainage patterns did not change significantly during the events. Geophone records suggest that the episodes of basal motion were precipitated by the gradual failure of a “sticky spot” following hydraulic connection of part of the study area. This failure resulted in the transfer of basal stress to the unconnected region of the bed during the course of the events. No evidence for strong basal motion is seen in the instrument records for several weeks following the events, suggesting that the mechanical adjustments resulted in a stable configuration of basal stresses. This event illustrates how unstable situations can be quickly accommodated by mechanical adjustments at the glacier bed.

scholarly journals Numerical and Experimental Investigations of the Interactions between Hydraulic and Natural Fractures in Shale Formations

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2541 ◽  
Author(s):  
Xin Chang ◽  
Yintong Guo ◽  
Jun Zhou ◽  
Xuehang Song ◽  
Chunhe Yang
Keyword(s):  
Hydraulic Fracture ◽  
Interaction Mechanism ◽  
Stress Transfer ◽  
Displacement Discontinuity ◽  
Tensile Fracture ◽  
Experimental Investigations ◽  
Shear Stresses ◽  
Natural Fractures ◽  
Stick Slip ◽  
Joint Element

Natural fractures (NFs) have been recognized as the dominant factors that increase hydraulic fracture complexity and reservoir productivity. However, the interactions between hydraulic and natural fractures are far from being fully understood. In this study, a two-dimensional numerical model based on the displacement discontinuity method (DDM) has been developed and used to investigate the interaction between hydraulic and pre-existing natural fractures. The inelastic deformation, e.g., stick, slip and separation, of the geologic discontinuities is captured by a special friction joint element called Mohr-Coulomb joint element. The dynamic stress transfer mechanisms between the two fracture systems and the possible location of secondary tensile fracture that reinitiates along the opposite sides of the NF are discussed. Furthermore, the model results are validated by a series of large tri-axial hydraulic fracture (HF) tests. Both experimental and numerical results showed that the displacements and stresses along the NFs are all in highly dynamic changes. When the HF is approaching the NF, the HF tip can exert remote compressional and shear stresses on the NF interface, which results in the debonding of the NF. The location and value of the evoked stress is a function of the far-field horizontal differential stress, inclination angle of the NF, and the net pressure used in fracturing. For a small approaching angle, the stress peak is located farther away from the intersection point, so an offset fracture is more likely to be generated. The cemented strength of the NF also has an important influence on the interaction mechanism. Weakly bonded NF surfaces increase the occurrence of a shear slippage, but for a moderate strength NF, the hybrid failure model with both tensile and shear failures, and conversion may appear.

scholarly journals Glaciodynamic context of subglacial bedform generation and preservation

1999 ◽  
Vol 28 ◽  
pp. 23-32 ◽  
Author(s):  
Chris D. Clark
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Shear Stresses ◽  
Morphometric Characteristics ◽  
Glacial Cycle ◽  
Sheet Flow ◽  
Ice Flow ◽  
Ice Stream ◽  
Highly Sensitive ◽  
Basal Shear

AbstractSubglacially-produced drift lineations provide spatially extensive evidence of ice flow that can be used to aid reconstructions of the evolution of former ice sheets. Such reconstructions, however, are highly sensitive to assumptions made about the glaciodynamic context of lineament generation; when during the glacial cycle and where within the ice sheet were they produced. A range of glaciodynamic contexts are explored which include: sheet-flow submarginally restricted; sheet-flow pervasive; sheet- flow patch; ice stream; and surge or re-advance. Examples of each are provided. The crux of deciphering the appropriate context is whether lineations were laid down time-trans-gressively or isochronously. It is proposed that spatial and morphometric characteristics of lineations, and their association with other landforms, can be used as objective criteria to help distinguish between these cases.A logically complete ice-sheet reconstruction must also account for the observed patches of older lineations and other relict surfaces and deposits that have survived erasure by subsequent ice flow. A range of potential preservation mechanisms are explored, including: cold- based ice; low basal-shear stresses; shallowing of the deforming layer; and basal uncoupling.

Coefficients of active earth pressure with seepage effect

2012 ◽  
Vol 49 (6) ◽  
pp. 651-658 ◽  
Author(s):  
Pérsio L.A. Barros ◽  
Petrucio J. Santos
Keyword(s):  
Pore Water Pressure ◽  
Water Pressure ◽  
Retaining Wall ◽  
Drainage System ◽  
Numerical Procedure ◽  
Ground Surface ◽  
Earth Pressure ◽  
Friction Angle ◽  
Active Earth Pressure ◽  
Plane Failure

A calculation method for the active earth pressure on the possibly inclined face of a retaining wall provided with a drainage system along the soil–structure interface is presented. The soil is cohesionless and fully saturated to the ground surface. This situation may arise during heavy rainstorms. To solve the problem, the water seepage through the soil is first analyzed using a numerical procedure based on the boundary element method. Then, the obtained pore-water pressure is used in a Coulomb-type formulation, which supposes a plane failure surface inside the backfill when the wall movement is enough to put the soil mass in the active state. The formulation provides coefficients of active pressure with seepage effect which can be used to evaluate the active earth thrust on walls of any height. A series of charts with values of the coefficients of active earth pressure with seepage calculated for selected values of the soil internal friction angle, the wall–soil friction angle, and the wall face inclination is presented.

Measuring the onset of mine tailings erosion

2007 ◽  
Vol 44 (4) ◽  
pp. 473-489 ◽  
Author(s):  
M Haneef-Mian ◽  
Ernest K Yanful ◽  
Robert Martinuzzi
Keyword(s):  
Shear Stress ◽  
Power Law ◽  
Mine Tailings ◽  
Laser Doppler Anemometry ◽  
Critical Shear Stress ◽  
Laser Doppler ◽  
Shear Stresses ◽  
Cohesive Sediments ◽  
Fine Grained ◽  
Power Law Equation

The present study gives details of a methodology for estimating the critical shear stress for erosion of mine tailings and other naturally occurring cohesive sediments. Erosion of a cohesive sediments bed occurs when the critical shear stress is exceeded to break the interparticle bond. Experiments were conducted in a 30 cm diameter laboratory column and calibrated using laser Doppler anemometry. The results showed that the erosion pattern of mine tailings particles was similar to those of fine-grained cohesive sediments. A power-law relation of the form E = α[(τ – τcr)/τcr]n is suggested for mine tailings, where E is the erosion rate, α is a coefficient, τ is the shear stress, τcr is the critical shear stress, and n is an exponent. The computed values of α, n, and τcr in the power-law equation were found to be comparable to values derived from experiments in a rotating circular flume. The derived expression for rate of erosion may be incorporated in resuspension and transport models for fine mine tailings of a similar nature.Key words: mine tailings, laser Doppler velocimetry, wall shear stresses, critical shear stress for erosion, erosion – shear stress relationship.

scholarly journals Theoretical Interpretation of the Exceptional Sediment Transport of Fine-grained Dispersal Systems Associated with Bedform Categories

2018 ◽  
Author(s):  
Tian Zhao ◽  
Qian Yu ◽  
Yunwei Wang ◽  
Shu Gao
Keyword(s):  
Sediment Transport ◽  
Regime Shift ◽  
Sedimentary Environment ◽  
Sediment Flux ◽  
Theoretical Interpretation ◽  
Fine Grained ◽  
Transport Regime ◽  
Source To Sink ◽  
Bed Roughness ◽  
Set Up

Abstract. Being a widespread source-to-sink sedimentary environment, the fine-grained dispersal system (FGDS) features remarkably high sediment flux, interacting closely with local morphology and ecosystem. Such exceptional transport is believed to be associated with changes in bedform geometry, which further demands theoretical interpretation. Using van Rijn (2007a) bed roughness predictor, we set up a simple numerical model to calculate sediment transport, classify sediment transport behaviors into dune and (mega-)ripple dominant regimes, and discuss the causes of the sediment transport regime shift linked with bedform categories. Both regimes show internally consistent transport behaviors, and the latter, associated with FGDSs, exhibits considerably higher sediment transport rate than the previous. Between lies the coexistence zone, the sediment transport regime shift accompanied by degeneration of dune roughness, which can considerably reinforce sediment transport and is further highlighted under greater water depth. This study can be applied to modeling of sediment transport and morphodynamics.

Field Investigations on Sediment Occurrence and Behaviour in Brussels Combined Sewers

1992 ◽  
Vol 25 (8) ◽  
pp. 71-82 ◽  
Author(s):  
M. Verbanck
Keyword(s):  
Drainage System ◽  
Solid Material ◽  
Field Studies ◽  
Main Trunk ◽  
Limited Mobility ◽  
Sediment Bed ◽  
Research Activities ◽  
Field Investigations ◽  
Dry Spells ◽  
Receiving Waters

Although sewer sediments are now widely recognized as a major source of misfunction of urban drainage systems (for both hydraulic and environmental considerations), it is still too infrequent that priority of research activities in this area is given to field studies. The measuring campaigns conducted since 1986 in the drainage system of Brussels-North have been focused on sedimentation processes in the major sewer lines. There is an obvious distinction to be made between solids constituting the sediment bed of a man-entry sewer, which are relevant for its hydraulic capacity, and the ones contributing to the pollutional impact of CSOs upon receiving waters. The material which is removed several times a year from the main trunk sewer of Brussels is coarse, granular and has a low environmental impact, notably because of its limited mobility. This appears to be due to a very efficient granulometric grading, as a result firstly of the retention of the coarsest solids in highly selective gully-pot inlets, and secondly of an elutriation process removing from the sediment bed all fine organic-rich particles during daily peak flows. There is evidence to show that the build-up of the sediment bed in these large-sized sewers is driven by a bed-load process (active even during dry spells), while the solid material responsible for the detrimental effects of CSOs (which is much finer) is primarily transported through wash-load and suspended-load.

scholarly journals Flow of Rutford Ice Stream and Comparison with Carlson Inlet, Antarctica

1989 ◽  
Vol 12 ◽  
pp. 51-56 ◽  
Author(s):  
R.M. Frolich ◽  
D.G. Vaughan ◽  
C.S.M. Doake
Keyword(s):  
Surface Expression ◽  
Ice Thickness ◽  
Shear Stresses ◽  
Lateral Shear ◽  
Ice Stream ◽  
Grounding Line ◽  
Subglacial Topography ◽  
Characteristic Features ◽  
Basal Shear ◽  
Thickness Measurements

Results from movement surveys on Rutford Ice Stream are presented with complementary surface-elevation and ice-thickness measurements. Surface velocities of 300 m a−1 occur at least 130 km up-stream of the grounding line and contrast strongly with the neighbouring Carlson Inlet, where a velocity of 7 m a−1 has been measured. This contrast in velocity is not topographically controlled but appears to be due instead to differences in basal conditions, with Carlson Inlet probably being frozen to its bed. Concentration of lateral shear close to the margins and surface expression of subglacial topography both support a view of significant basal shear stresses in the central part of Rutford Ice Stream. The pattern of principal strain-rate trajectories shows a small number of characteristic features which can be compared with results from future modelling of the glacier's flow.

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