642 results on '"Crevasse"'
Search Results
2. UWB-Based Human-Following System with Obstacle and Crevasse Avoidance for Polar-Exploration Robots
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Ji-Wook Kwon, Hyoujun Lee, Jongdeuk Lee, Na-Hyun Lee, Jong Chan Kim, Taeyoung Uhm, and Young-Ho Choi
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polar-exploration robot ,human-following ,UWB ,collision avoidance ,crevasse ,Technology ,Engineering (General). Civil engineering (General) ,TA1-2040 ,Biology (General) ,QH301-705.5 ,Physics ,QC1-999 ,Chemistry ,QD1-999 - Abstract
This paper introduces a UWB-based human-following system for polar-exploration robots, integrating obstacle and crevasse avoidance functions to enhance the safety and efficiency of explorers in extreme environments. The proposed system determines the relative position of the explorer using UWB anchors and tags. It also utilizes real-time local obstacle mapping and path-planning algorithms to find safe paths that avoid collisions with obstacles. Simulation and real-world experiments confirm that the proposed system operates effectively in polar environments, reducing the operational burden on explorers and increasing mission success rates.
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- 2024
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3. Numerical investigation of the dynamic response of a simplified floating structure subjected to two underwater explosion bubbles.
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Jiang, Xudong, Wang, Yuxiang, and Sun, Cheng
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UNDERWATER explosions , *BLAST effect , *WARSHIPS - Abstract
The interaction of the two coupling bubble with a floating structure is modelled to investigate the dynamic behavior of the warship under an underwater explosion (UNDEX) by coupled Eulerian-Lagrangian (CEL) method. In this study, the CEL method is first verified by the experimental results for free field underwater explosion. Then, a series of cases for various initial distance and delay intervals between the bubble pair are implemented to analyze the deformation and damage modes of the floating structure. It is observed that for large initial distance between the bubble pair synchronously generated, the floating structure can be damaged with longitudinal bending buckling in the middle domain. When the initial distance between the bubble pair decreases to a critical value, the floating structrure is damaged with a remarkable crevasse besides the longitudinal bending buckling in the middle domain. However, under two bubbles with different phase differences, the floating structure a the deformation of the whipping motion without remarkable local structural damage. This is because there is the conspicuous despression effect between two out-of-phase bubbles, which weakens the bubble pulsation load. These phenomena present a theoretical reference for further studies on the destruction of underwater explosion on the ship structure caused by multiple bubbles generated with various phase differences. [ABSTRACT FROM AUTHOR]
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- 2023
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4. Topographic controls on ice flow and recession for Juneau Icefield (Alaska/British Columbia).
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Davies, Bethan, Bendle, Jacob, Carrivick, Jonathan, McNabb, Robert, McNeil, Christopher, Pelto, Mauri, Campbell, Seth, Holt, Tom, Ely, Jeremy, and Markle, Bradley
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ICE prevention & control ,ALPINE glaciers ,ABLATION (Glaciology) ,LITTLE Ice Age ,ICE caps ,GLACIAL lakes ,GEOMORPHOLOGICAL mapping - Abstract
Globally, mountain glaciers and ice caps are losing dramatic volumes of ice. The resultant sea‐level rise is dominated by contributions from Alaska. Plateau icefields may be especially sensitive to climate change due to the non‐linear controls their topography imparts on their response to climate change. However, Alaskan plateau icefields have been subject to little structural glaciological or regional geomorphological assessment, which makes the controls on their present and former mass balance difficult to ascertain. We inventoried 1050 glaciers and 368 lakes in the Juneau Icefield region for the year 2019. We found that 63 glaciers had disappeared since the 2005 inventory, with a reduction in glacier area of 422 km2 (10.0%). We also present the first structural glaciological and geomorphological map for an entire icefield in Alaska. Glaciological mapping of >20 800 features included crevasses, debris cover, foliation, ogives, medial moraines and, importantly, areas of glacier fragmentation, where glaciers either separated from tributaries via lateral recession (n = 59), or disconnected within areas of former icefalls (n = 281). Geomorphological mapping of >10 200 landforms included glacial moraines, glacial lakes, trimlines, flutes and cirques. These landforms were generated by a temperate icefield during the Little Ice Age (LIA) neoglaciation. These data demonstrate that the present‐day outlet glaciers, which have a similar thermal and ice‐flow regime, have undergone largely continuous recession since the LIA. Importantly, disconnections occurring within glaciers can separate accumulation and ablation zones, increasing rates of glacier mass loss. We show that glacier disconnections are widespread across the icefield and should be critically taken into consideration when icefield vulnerability to climate change is considered. [ABSTRACT FROM AUTHOR]
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- 2022
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5. Linking Enceladus' plume characteristics to the crevasse properties.
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van der Hijden, Nick J., Giordano, Fabrizio, Oliver Scholts, Sebastian O., Sklavenitis, Stavros, Bründl, Tara-Marie, Bourgeois, Yaël R.A., Schrijer, Ferry F.J., and Cazaux, Stéphanie M.
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PLUMES (Fluid dynamics) , *MACH number , *FLUID dynamics , *FLOW velocity , *WATER vapor - Abstract
Supersonic plumes of water vapour and icy particles have been observed by the Cassini spacecraft during several flybys over Enceladus. These plumes originate from the Tiger Stripes located in the South Polar Terrain (SPT), and indicate the presence of a subsurface ocean under the icy crust which is salty and contains complex organic molecules. Other characteristics of the plumes, such as the vent temperature, mass flow rate, velocity and mass fraction of icy particles can be used to determine the conditions in the channel, linking the subsurface ocean to the icy surface. In this paper, we developed a fluid dynamics model that accounts for nucleation, particle growth, wall accretion and sublimation. The channel behaves similarly to a converging–diverging nozzle, which forms supersonic plumes due to a pressure difference between the reservoir where the subsurface ocean is located and the exosphere. The geometry of the channel and its evolution with accretion of gas and sublimation of ice are studied to reproduce the characteristics of the plumes observed by Cassini. We first performed a parameter study on the channel geometry to determine how it influences the plumes' velocity, solid fraction and exit temperature. Our results show that the size of the icy particles is primarily dependent on the length of the channel, indicating that large particles (∼ 75 μ m) must originate from within a kilometer below the surface, while smaller particles (∼ 3 μ m) can originate from only hundreds of meters below the surface. We further show that the velocity of the flow, exit temperature and nucleation depend directly on the exit-to-throat size ratio. We find that the channel geometry evolves within a few tens of hours until an equilibrium is reached, when considering the accretion of gas to the walls, or sublimation of ice from the walls. As the channel closes due to accretion, the flow becomes thinner, which in turn reduces accretion. After around 70 h, the accretion is sufficiently slowed such that the geometry does not evolve anymore. This equilibrium geometry produces higher Mach numbers and a larger particle size and solid fraction compared to the initial geometry. • On Enceladus, a Saturnian moon, supersonic plumes of water ice and vapour have been observed. • These plumes indicate the presence of a liquid subsurface ocean hidden under kilometers of ice. • We studied numerically the plumes as they develop from the ocean to the surface through channels. • We found that the size of the icy grains observed in the plumes can constrain the length of the channels. • The plumes' velocity and temperature constrain the expansion (throat to exit) ratio of the channel. • Water accretion changes the channel's geometry within hours and increases the expansion ratio. [ABSTRACT FROM AUTHOR]
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- 2024
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6. Extraction and Analysis of the Three-Dimensional Features of Crevasses in the Amery Ice Shelf Based on ICESat-2 ATL06 Data
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Guoyuan Li, Jinquan Guo, Liang Pei, Shuaitai Zhang, Xinming Tang, and Jiaqi Yao
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Amery ice shelf (AIS) ,crevasse ,ICESat-2 ,satellite laser altimetry ,three-dimensional (3-D) features ,Ocean engineering ,TC1501-1800 ,Geophysics. Cosmic physics ,QC801-809 - Abstract
Crevasse is an important characteristic of ice shelf internal structure, and also an important index to measure the stability of ice shelf. This study aims to detect crevasses from ICESat-2 data and obtain three-dimensional features of the crevasse. First, the change of along-track surface slope and the depth threshold is combined to obtain the crevasse bottom points and the crevasse edge points. Second, the distance between the crevasse bottom points and the fitted ice shelf surface by crevasse edge points is used as the crevasse bottom points depth. Third, the crevasse direction is judged by the strong and weak laser positions and the width is calculated by the crevasse edge points and crevasse direction. The Amery ice shelf (AIS) is chosen as the test area to validate the method by ATL06 data, combined with the Landsat-8 optical image. The depth of the crevasses in the AIS is about ranges from 2.0 to 60.0 m, and the width is mainly 400 to 1600 m, and the width and length of the L3 rift have dramatically changed, which is an indicator that the AIS is in a new calving cycle. The method in this article can accurately obtain three-dimensional information of the crevasses, find crevasses with abnormal changes in depth and width, and provide effective help for predicting the calving of the ice shelf.
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- 2021
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7. Crevasse accidents in the Swiss Alps Epidemiology and mortality of 405 victims of crevasse accidents from 2010 to 2020.
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Klocker, Eva, Meuli, Lorenz, Rauch, Simon, Kottmann, Alexandre, Mosimann, Ueli, Pasquier, Mathieu, Métrailler, Pierre, Doppman, Pascal, Albrecht, Roland, and Pietsch, Urs
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ACCIDENT victims , *SUMMER , *EPIDEMIOLOGY , *COVID-19 pandemic , *MORTALITY - Abstract
Introduction: The clinical spectrum of injuries in crevasse accidents can range from benign to life-threatening, even including death. To date, little is known about incidence and causes.Methods: We retrospectively analyzed mountain rescue missions that included crevasse accidents and took place in Switzerland from 2010 to 2020. Demographic and epidemiological data were collected. Injury severity was graded according to the National Advisory Committee for Aeronautics (NACA) score. Winter season was defined as December to May, and summer season as June to November.Results: A total of 321 victims of crevasse falls were included in the study. The median age of victims was 41.2 years (interqauartile range [IQR] 31.3 to 51.6), with 82% (n=260) being male and 59% (n=186) foreigners. The typical altitude range at which rescue missions were performed was between 3000 and 3499m (44% of all cases). The median depth of the fall was 15 meters (IQR 8 to 20) during the winter season compared to 8 meters (IQR 5 to 10) during the summer, p<0.001. Overall mortality was 6.5%. The NACA score was ≥4 for 9.4% (n=30) of the victims. 55% (n=177) had a NACA score of 0 or 1. There was a significant positive correlation between the depth of fall and the injury severity (Pearson`s correlation r=0.35, 95%- confidence interval: 0.18 to 0.51), p<0.001.Conclusion: More than half of victims fallen into a crevasse are uninjured or sustain mild injury. Life-threathening injuries were found in about 10% of victims and the crevasse fall was fatal in 6.5% of cases. Injury severity positively correlates with the depth of fall, which is higher during winter season. [ABSTRACT FROM AUTHOR]- Published
- 2022
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8. Borehole‐Based Characterization of Deep Mixed‐Mode Crevasses at a Greenlandic Outlet Glacier
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Bryn Hubbard, Poul Christoffersen, Samuel H. Doyle, Thomas R. Chudley, Charlotte M. Schoonman, Robert Law, and Marion Bougamont
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borehole ,crevasse ,deep crevasse ,glacier ,Greenland Ice Sheet ,optical televiewer ,Geology ,QE1-996.5 ,Geophysics. Cosmic physics ,QC801-809 - Abstract
Abstract Optical televiewer borehole logging within a crevassed region of fast‐moving Store Glacier, Greenland, revealed the presence of 35 high‐angle planes that cut across the background primary stratification. These planes were composed of a bubble‐free layer of refrozen ice, most of which hosted thin laminae of bubble‐rich “last frozen” ice, consistent with the planes being the traces of former open crevasses. Several such last‐frozen laminae were observed in four traces, suggesting multiple episodes of crevasse reactivation. The frequency of crevasse traces generally decreased with depth, with the deepest detectable trace being 265 m below the surface. This is consistent with the extent of the warmer‐than‐modeled englacial ice layer in the area, which extends from the surface to a depth of ∼400 m. Crevasse trace orientation was strongly clustered around a dip of 63° and a strike that was offset by 71° from orthogonal to the local direction of principal extending strain. The traces’ antecedent crevasses were therefore interpreted to have originated upglacier, probably ∼8 km distant involving mixed‐mode (I and III) formation. We conclude that deep crevassing is pervasive across Store Glacier, and therefore also at all dynamically similar outlet glaciers. Once healed, their traces represent planes of weakness subject to reactivation during subsequent advection through the glacier. Given their depth, it is highly likely that such traces—particularly those formed downglacier—survive surface ablation to reach the glacier terminus, where they may represent foci for fracture and iceberg calving.
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- 2021
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9. Mass collapse and resedimentation on a Brigantian–Early Namurian platform margin, Halkyn–Mold area, North Wales, UK.
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Kirkham, Anthony
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SAND bars , *FAULT zones , *CHERT , *LIMESTONE , *SANDSTONE - Abstract
Observations on Late Mississippian strata are summarized including: the Brigantian Cefn Mawr Limestone and Minera formations; and the Namurian Pentre Chert and Cefn‐y‐Fedw Sandstone formations. Many of those observations relate to transitory, commercial quarry exposures, especially in the Cefn Mawr Limestone Formation. During the Late Mississippian, the area was located in proximity to an unstable northeast‐facing platform edge and slope on which earlier workers postulated a megaslide, probably related to the Nant Figillt Fault zone and affecting the Cefn Mawr Limestone and Pentre Chert formations. This study reinforces that general model and highlights new evidence indicative of mass wastage along the platform margin including: synsedimentary faults, slides and slumps. Penecontemporaneous submarine crevassing occurred in the Pentre Chert Formation. Limestone beds previously described as tidal or storm‐related sand bars in the Cefn Mawr Limestone Formation are instead considered as gravity‐driven resedimented deposits. Channelling in relatively deep water facies of the Cefn Mawr Limestone, Pentre Chert, and Cefn‐y‐Fedw Sandstone formations occurred. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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10. Flexural Control of Basal Crevasse Opening Under Ice Shelves.
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Buck, W. Roger and Lai, Ching‐Yao
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ICE shelves , *ELASTIC plates & shells , *NONLINEAR functions , *FREE surfaces , *MAGNITUDE (Mathematics) , *GLACIAL isostasy - Abstract
Classical analyses of basal crevasse opening do not account for the free surface of a floating ice layer. We describe a high‐resolution numerical treatment of the opening of a single crevasse in a finite thickness elastic layer floating on an inviscid substrate. For low extensional stress (less than about half of the expected maximum for a freely floating shelf) the resulting crevasse height and width match previous studies. For larger magnitude applied extensional stresses, the new results predict basal crevasse widths an order of magnitude greater than the classical solution. An analysis using the thin‐layer approximation shows that the greatly increased predicted width of basal crevasse opening results from layer bending. Given that the height and width of basal crevasses are non‐linear functions of the stress experienced by an ice shelf, the new model results may enable better estimation of buttressing stresses for different parts of ice shelves. Plain Language Summary: Basal crevasses are water filled cracks the cut through much of the ice shelves and so contribute to their breakup. A new analysis shows that basal crevasses can break through significantly more of a floating ice layer than previous models that could not consider the bending of the ice layer. This more consistent approach suggests that basal crevasses can be an order of magnitude wider than estimated by the earlier studies. A simple analytic description of flexure of ice layers correctly predicts the maximum width of basal crevasses. Key Points: The first numerical analysis of basal crevasse opening including ice shelf bending is presentedBasal crevasses can be an order of magnitude wider than predicted by classical studiesAn analytic thin elastic plate description matches the numerical results in terms of crevasse width for a freely floating ice layer [ABSTRACT FROM AUTHOR]
- Published
- 2021
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11. Englacial Warming Indicates Deep Crevassing in Bowdoin Glacier, Greenland
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Julien Seguinot, Martin Funk, Andreas Bauder, Thomas Wyder, Cornelius Senn, and Shin Sugiyama
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Bowdoin ,crevasse ,borehole ,refreezing ,temperature ,Greenland ,Science - Abstract
All around the margins of the Greenland Ice Sheet, marine-terminating glaciers have recently thinned and accelerated. The reduced basal friction has yielded increased flow velocity, while the rate of longitudinal stretching has been limited by ice viscosity, which itself critically depends on temperature. However, ice temperature has rarely been measured on such fast-flowing and heavily crevassed glaciers. Here, we present a 3-year record of englacial temperatures obtained 2 (in 2014) to 1 km (in 2017) from the calving front of Bowdoin Glacier (Kangerluarsuup Sermia), a tidewater glacier in northwestern Greenland. Two boreholes separated by 165 (2014) to 197 m (2017) show significant temperature differences averaging 2.07°C on their entire depth. Englacial warming of up to 0.39°C a−1, an order of magnitude above the theoretical rate of heat diffusion and viscous dissipation, indicates a deep and local heat source within the tidewater glacier. We interpret the heat source as latent heat from meltwater refreezing in crevasses reaching to, or near to, the bed of the glacier, whose localization may be controlled by preferential meltwater infiltration in topographic dips between ogives.
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- 2020
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12. Toward the Acoustic Detection of Two‐Phase Flow Patterns and Helmholtz Resonators in Englacial Drainage Systems.
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Podolskiy, Evgeny A.
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HELMHOLTZ resonators , *TWO-phase flow , *DRAINAGE , *ACOUSTIC radiators , *MANUFACTURING processes , *ICE calving - Abstract
Passive acoustic monitoring has revolutionized the characterization of industrial processes and the acoustic wavefield in various environments. However, cryospheric acoustic phenomena remain largely unknown, especially at medium and small scales. Furthermore, the englacial drainage system is poorly documented, even though it is fundamental for understanding water routing through the glacier body. Here I present the first‐of‐its‐kind in situ records of periodic or sustained acoustic signals generated by water drainage through crevasses at the calving front of a glacier, in this case a Greenlandic tidewater glacier. The generative mechanisms of gurgling and bubbling noise are explained as flow‐induced sounds that are excited by intermittent air‐water two‐phase flow and Helmholtz resonance, respectively. This paper demonstrates that there is the tremendous potential to study near‐surface glacier systems using acoustic methods and detect different flow patterns in englacial conduits from their acoustic signatures, both of which can significantly advance our understanding of glaciological processes. Plain Language Summary: The glacier surface is full of various audible sounds. While early polar explorers have documented this noisy glacier environment, these qualitative observations have never been supported by measurements. For example, Nansen (1897), wrote, "I can hear reports from the glacier... whenever it turns cold–it writhes horribly, and crevice after crevice appears in the huge body; there is a noise like the discharge of guns, and the sky and the earth tremble so that I can feel the ground that I am lying on quake" while wintering in Franz Josef Land, and Baldwin (1896) described his crossing of Bowdoin Glacier, which is the subject of this study, as follows: "...shrieking sounds frightful enough, came...to our ears, seeming to vibrate through...our very bodies, spitefully shouting in our ears: Why, presumptuous man, hast thou set disturbing foot upon my chaste bosom?" Here I analyze the first acoustic records that were directly acquired on a glacier, in Greenland, which reveal previously unknown repetitive or continuous sound sources. It appears that different patterns in air‐water interactions give rise to interesting acoustic phenomena, such as bubble resonance and unstable flow in cracks. Future glaciological investigations could consider using microphones to better understand englacial water drainage. Key Points: This is the first report of repeating and continuous acoustic radiators in a near‐surface englacial drainage systemWater‐air phase interactions in the drainage system hold the key to understanding self‐excited flow pulses and bubble burstsThere is tremendous potential in acquiring passive acoustic observations to characterize glaciological processes [ABSTRACT FROM AUTHOR]
- Published
- 2020
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13. Laboratory experiments recreating icy moons' geysers
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Verhoeff, Thom (author) and Verhoeff, Thom (author)
- Abstract
This study is part of an ongoing research project, which aims to increase the physical understanding of the plume formation on Saturn’s icy moon Enceladus. The experimental setup presented in this study is the third iteration of the physical models aiming to recreate the main plume characteristics, where in this study the effects of the channel length, width, type (straight, converging/diverging or diverging), temperature and material are explored and linked to Enceladus’ crevasses. This is done by conduct- ing experiments with 7 different models, where the temperature and pressure are measured along the channels. The models are placed on top of a water-filled reservoir, where the reservoir conditions can be controlled to a limited extent by varying the heating power supplied to the reservoir water. The experimental setup is placed in the test section of the Hypersonic Test Facility Delft (HTFD), which functions as a vacuum chamber. It is shown that the varying geometry of the channel imposes constraints on the maximum expansion angle before flow separation occurs, the sonic point location and the length/width combination in order to achieve a certain vent Mach number and mass flow rate, although this is also decided by the reservoir and ambient conditions. However, besides the physical properties of the model, there is evidence that the flow properties are dominated by the thermal processes occurring inside the setup. Condensation occurs only in the reservoir, releasing latent heat and making the isentropic flow assumption invalid by definition. It is demonstrated that it is likely that the thermal radiation from the test section of the HTFD onto the model is sufficient to thermally choke the flow. It is unlikely that the flows become choked due to the effects of friction alone. Cooling the models by 10-15°C did not result in significant changes in flow properties, and to have noticeable effects on the flow, the models would have to be cooled to much lower, Aerospace Engineering
- Published
- 2023
14. The role of fresh water in driving ice shelf crevassing, rifting and calving.
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Roger Buck, W.
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FRESH water , *RIFTS (Geology) , *ANTARCTIC ice , *MELTWATER , *SALTWATER encroachment , *ICE shelves - Abstract
• Ice shelf rifting can be described with simple force arguments. • Fresh water filling of crevasses can produce rifting with modest buttressing. • A quarter of the area of Antarctic ice shelves is vulnerable to meltwater-driven disintegration. • The heights of isolated basal crevasses are determined numerically. • The heights of closely spaced crevasses are described analytically. Meltwater is widely implicated in the disintegration of ice shelves and the lower density of fresh meltwater relative to salty seawater can reconcile observations and models of ice shelf rifting. Advanced numerical models predict that a seawater-filled basal crevasse will break through a shelf to form a rift only where extensional stresses equal those at the seaward shelf edge. However, rifts open in ice shelf interiors where resistance to flow at the sides and base of the ice shelf, or buttressing, is estimated to significantly reduce extensional stresses compared to those at the shelf edge. The stress in a shelf is often quantified in terms of a buttressing number and rifts are seen to open in areas where the estimated buttressing number is between 0.2 and 0.3. Numerical models assuming fresh meltwater-filled basal crevasses predict rift opening for buttressing numbers up to about 0.2. Published estimates indicate that about a quarter of the area of the Antarctic ice shelves are characterized by buttressing numbers less than 0.2. The present results indicate that those areas are directly vulnerable to rifting in the presence of abundant meltwater and that calving of those areas could drive further rifting. The numerical results suggest that rifting can be understood in terms of a horizontal force balance, justifying derivation of a simple analytic relation between the density of water infilling a rift and the maximum buttressing number allowing rifting. This analytic relation should hold for any spacing of crevasses or any vertical variations in ice rheology. Enforcing a horizontal force balance also allows derivation of an analytic relation between the heights of closely spaced ice shelf crevasses and buttressing numbers. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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15. Crevasse-fill forms – Bridging the gap in glacial geomorphology between East and West based on a case study from eastern Poland
- Author
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Anna Orłowska
- Subjects
Sedimentary depositional environment ,geography ,Crevasse ,geography.geographical_feature_category ,Pleistocene ,Lithology ,Landform ,Facies ,Sedimentary rock ,Glacial period ,Geomorphology ,Geology ,Earth-Surface Processes - Abstract
Genesis of crevasse-fill forms was clearly explained and ascribed to surging ice based on research made particularly in contemporary-glaciated areas of high latitudes. Nonetheless, the understanding and explanation of their formation is still not conclusive for Pleistocene glacigenic forms developing in crevasses what makes differences in their interpretation visible in glacial geomorphology of the East and West. Those forms in the East are still linked to stagnant Pleistocene ice-sheet dynamics and still named crevasse-fill forms what makes a huge misunderstanding in comparison of these modern and ancient equivalents. This paper makes an attempt to investigate this topic through comparison of features of “stagnant” and “surging” crevasse-fill forms, i.e. their morphology, lithology, location against direction of ice advance and – for the first time – sedimentary environment of crevasse-fill deposits. Recognition of deposits with using lithofacies analysis became a crucial method for classification of Pleistocene glacigenic forms, especially in the East. Thus, research on presented tree examples of so-called “crevasse-fill forms” based on facies analysis of sedimentary environments and their other characteristic features allowed to explain the characteristics of landforms developed from stagnant ice and to exclude them from the group of their “surging” equivalents. This misinterpretation results from different schools of thought in glacial geomorphology of the East and West. Based on presented research, no prerequisites were documented to compare these landforms, because the palaeogeographical conditions of their development are completely different.
- Published
- 2022
16. The influence of water level changes on sand bodies at river-dominated delta fronts:The Gubei Sag, Bohai Bay Basin
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Zheng Shi, Yang Zhang, Jun-Wei Wang, Ji Li, Bao-liang Yang, and Jiang Jiguo
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Delta ,Central Zone ,Bohai bay ,Source area ,Energy Engineering and Power Technology ,Geology ,Structural basin ,Geotechnical Engineering and Engineering Geology ,language.human_language ,Water level ,Image stitching ,Geophysics ,Fuel Technology ,Crevasse ,Geochemistry and Petrology ,language ,Economic Geology ,Geomorphology - Abstract
Changes in water level are one of the important factors controlling the constructive characteristics of deltas. The paper studies the influence of water level changes on sand bodies in the third member of the Shahejie Formation (Es3) on the gentle southern slope of the Gubei Sag, Bohai Bay Basin and draw some conclusions that, for complex sand bodies, with the increase in water level the distributary channels bifurcate frequently, from a simple branching shape to a network shape along with the increase in the development of crevasse splays, mouth bars and sheet sands. For single sand bodies, with an increase in water level in the slope zone of the lake basin close to the source area, the superimposition style transitioned from vertical cutting-stacking and lateral isolation to vertical stitching, isolation and lateral stitching. However, in the central zone of the lake basin far from the source area, the superimposition style transitioned from vertical stitching and lateral stitching to vertical isolation and lateral isolation. When water level stays stable, the greater the distance from the source area the greater the disaggregation ratio of a single sand body. At the same distance from the source area, higher water level tends to result in greater disaggregation ratio of a single sand body.
- Published
- 2022
17. Crevasse accidents in the Swiss Alps Epidemiology and mortality of 405 victims of crevasse accidents from 2010 to 2020
- Author
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Lorenz Meuli, Roland Albrecht, Simon Rauch, Alexandre Kottmann, Pierre Métrailler, Mathieu Pasquier, Eva Klocker, Pascal Doppman, Urs Pietsch, and Ueli Mosimann
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Adult ,Male ,Mountain rescue ,medicine.medical_specialty ,business.industry ,Advisory committee ,Incidence (epidemiology) ,Summer season ,Crevasse ,Accidents ,Epidemiology ,Ethnicity ,Humans ,General Earth and Planetary Sciences ,Medicine ,Accidental Falls ,Seasons ,Winter season ,business ,Switzerland ,Retrospective Studies ,General Environmental Science ,Demography - Abstract
The clinical spectrum of injuries in crevasse accidents can range from benign to life-threatening, even including death. To date, little is known about incidence and causes.We retrospectively analyzed mountain rescue missions that included crevasse accidents and took place in Switzerland from 2010 to 2020. Demographic and epidemiological data were collected. Injury severity was graded according to the National Advisory Committee for Aeronautics (NACA) score. Winter season was defined as December to May, and summer season as June to November.A total of 321 victims of crevasse falls were included in the study. The median age of victims was 41.2 years (interqauartile range [IQR] 31.3 to 51.6), with 82% (n=260) being male and 59% (n=186) foreigners. The typical altitude range at which rescue missions were performed was between 3000 and 3499m (44% of all cases). The median depth of the fall was 15 meters (IQR 8 to 20) during the winter season compared to 8 meters (IQR 5 to 10) during the summer, p0.001. Overall mortality was 6.5%. The NACA score was ≥4 for 9.4% (n=30) of the victims. 55% (n=177) had a NACA score of 0 or 1. There was a significant positive correlation between the depth of fall and the injury severity (Pearson`s correlation r=0.35, 95%- confidence interval: 0.18 to 0.51), p0.001.More than half of victims fallen into a crevasse are uninjured or sustain mild injury. Life-threathening injuries were found in about 10% of victims and the crevasse fall was fatal in 6.5% of cases. Injury severity positively correlates with the depth of fall, which is higher during winter season.
- Published
- 2022
18. Current Modeling of Water in a River Meander Considering Civil Engineering Problems in Building the Coastal Walls
- Author
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Mosaddad, S. M., Bidokhti, A. A., Ezam, M., Zhang, Changkuan, and Tang, Hongwu
- Published
- 2009
- Full Text
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19. Experimental simulation and assessment of the geysers of icy moons in the laboratory
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Sklavenitis, Stavros (author) and Sklavenitis, Stavros (author)
- Abstract
The Cassini spacecraft, observing the Saturnian system for over 13 years, discovered aspects of the planetary system that were previously unseen. One such discovery is the eruption of geysers (plumes) from the Tiger Stripes on the surface of the icy moon Enceladus. An unexpected liquid water ocean exists underneath Enceladus’ icy crust (Postberg et al. 2018). A consequence of this finding was the complete revision of the habitability of the Solar System. This liquid ocean is propagated through conduits within the crust, and forms plumes when it reaches the surface. The plume material is believed to accelerate supersonically through nozzle-like channels (Schmidt et al. 2008) before being ejected at high speeds from the plume vents. This thesis aims to improve the physical understanding of the interaction between the ocean, icy crust, and the plumes of Enceladus, by experimentally simulating such a plume in the wind tunnel laboratories of TU Delft, and monitoring and analyzing the dynamic physical processes taking place across the experimental setup. A physical analog, separated into regions simulating the ocean, crevasse, and vent of the plume mechanism, is monitored with pressure and temperature sensors, while plume particles are detected with optical tracing techniques. These observations lead to estimations of the vapor mass flow rate, the outflow Mach number, and the fraction of the plume mass that is condensed. It is found that the ocean conditions can be easily controlled through an adjustable heating power supply. The vapor flow generated by the boiling ocean becomes choked in the crevasse and can attain supersonic velocities. The thermodynamic conditions at the vent of the plume exhibit a greatly varying behavior suggesting that the combined effect of the crevasse geometry and the nucleation of vapor into liquid and icy particles results in considerable diversity in the plume characteristics. Thus, an isentropic description of the plume flow, Aerospace Engineering
- Published
- 2022
20. Steffen K, Abdalati W and Stroeve J (1993) Climate sensitivity studies of the Greenland ice sheet using satellite AVHRR, SMMR SSM/I and in situ data. Meteorology and Atmospheric Physics 51(3–4): 239–258. DOI:10.1007/bf01030497
- Author
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Julienne Stroeve, Jason E. Box, and Waleed Abdalati
- Subjects
Atmospheric physics ,010504 meteorology & atmospheric sciences ,Geography, Planning and Development ,0211 other engineering and technologies ,Climate change ,Greenland ice sheet ,02 engineering and technology ,01 natural sciences ,Crevasse ,Climatology ,Satellite remote sensing ,Earth and Planetary Sciences (miscellaneous) ,General Earth and Planetary Sciences ,Climate sensitivity ,Satellite ,Geology ,021101 geological & geomatics engineering ,0105 earth and related environmental sciences - Abstract
Physical geographer Konrad “Koni” Steffen, lost 8 August 2020 in a crevasse on the Greenland ice sheet, was a pioneer in satellite remote sensing and field observations of the Greenland ice sheet. This Classics Revisited piece honors the memory of Koni Steffen and examines the impact of a work which laid the foundation for numerous studies that made the Greenland ice sheet and the man global icons of climate change.
- Published
- 2021
21. Glacier–plume or glacier–fjord circulation models? A 2-D comparison for Hansbreen–Hansbukta system, Svalbard
- Author
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Francisco Navarro, Waldemar Walczowski, Eva Álvarez de Andrés, and Jaime Otero
- Subjects
geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Front (oceanography) ,Submarine ,Ice calving ,Fjord ,Glacier ,010502 geochemistry & geophysics ,01 natural sciences ,Plume ,Current (stream) ,Crevasse ,Geomorphology ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
Up to 30% of the current tidewater mass loss in Svalbard corresponds to frontal ablation through submarine melting and calving. We developed two-dimensional (2-D) glacier–line–plume and glacier–fjord circulation coupled models, both including subglacial discharge, submarine melting and iceberg calving, to simulate Hansbreen–Hansbukta system, SW Svalbard. We ran both models for 20 weeks, throughout April–August 2010, using different scenarios of subglacial discharge and crevasse water depth. Both models showed large seasonal variations of submarine melting in response to transient fjord temperatures and subglacial discharges. Subglacial discharge intensity and crevasse water depth influenced calving rates. Using the best-fit configuration for both parameters our two coupled models predicted observed front positions reasonably well (±10 m). Although the two models showed different melt-undercutting front shapes, which affected the net-stress fields near the glacier front, no significant effects on the simulated glacier front positions were found. Cumulative calving (91 and 94 m) and submarine melting (108 and 118 m) along the simulated period showed in both models (glacier–plume and glacier–fjord) a 1:1.2 ratio of linear frontal ablation between the two mechanisms. Overall, both models performed well on predicting observed front positions when best-fit subglacial discharges were imposed, the glacier–plume model being 50 times computationally faster.
- Published
- 2021
22. Mass collapse and resedimentation on a Brigantian–Early Namurian platform margin,<scp>Halkyn–Mold</scp>area, North Wales,<scp>UK</scp>
- Author
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Anthony Kirkham
- Subjects
Paleontology ,Crevasse ,Margin (machine learning) ,Collapse (topology) ,Geology - Published
- 2021
23. Extraction and Analysis of the Three-Dimensional Features of Crevasses in the Amery Ice Shelf Based on ICESat-2 ATL06 Data
- Author
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Xinming Tang, Jinquan Guo, Liang Pei, Guoyuan Li, Shuaitai Zhang, and Jiaqi Yao
- Subjects
Optical image ,Atmospheric Science ,010504 meteorology & atmospheric sciences ,Geophysics. Cosmic physics ,Ice calving ,Edge (geometry) ,010502 geochemistry & geophysics ,01 natural sciences ,Ice shelf ,ICESat-2 ,Crevasse ,Extraction (military) ,Computers in Earth Sciences ,TC1501-1800 ,Geomorphology ,0105 earth and related environmental sciences ,satellite laser altimetry ,geography ,geography.geographical_feature_category ,Rift ,QC801-809 ,Amery ice shelf (AIS) ,Ocean engineering ,three-dimensional (3-D) features ,Geology ,crevasse - Abstract
Crevasse is an important characteristic of ice shelf internal structure, and also an important index to measure the stability of ice shelf. This study aims to detect crevasses from ICESat-2 data and obtain three-dimensional features of the crevasse. First, the change of along-track surface slope and the depth threshold is combined to obtain the crevasse bottom points and the crevasse edge points. Second, the distance between the crevasse bottom points and the fitted ice shelf surface by crevasse edge points is used as the crevasse bottom points depth. Third, the crevasse direction is judged by the strong and weak laser positions and the width is calculated by the crevasse edge points and crevasse direction. The Amery ice shelf (AIS) is chosen as the test area to validate the method by ATL06 data, combined with the Landsat-8 optical image. The depth of the crevasses in the AIS is about ranges from 2.0 to 60.0 m, and the width is mainly 400 to 1600 m, and the width and length of the L3 rift have dramatically changed, which is an indicator that the AIS is in a new calving cycle. The method in this article can accurately obtain three-dimensional information of the crevasses, find crevasses with abnormal changes in depth and width, and provide effective help for predicting the calving of the ice shelf.
- Published
- 2021
24. Sharp contrasts in observed and modeled crevasse patterns at Greenland's marine terminating glaciers
- Author
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Ellyn M. Enderlin and Timothy C. Bartholomaus
- Subjects
lcsh:GE1-350 ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Advection ,lcsh:QE1-996.5 ,Elevation ,Ice calving ,Glacier ,010502 geochemistry & geophysics ,01 natural sciences ,lcsh:Geology ,Glacier mass balance ,Crevasse ,Fracture (geology) ,Meltwater ,Geomorphology ,Geology ,lcsh:Environmental sciences ,0105 earth and related environmental sciences ,Earth-Surface Processes ,Water Science and Technology - Abstract
Crevasses are affected by and affect both the stresses and the surface mass balance of glaciers. These effects are brought on through potentially important controls on meltwater routing, glacier viscosity, and iceberg calving, yet there are few direct observations of crevasse sizes and locations to inform our understanding of these interactions. Here we extract depth estimates for the visible portion of crevasses from high-resolution surface elevation observations for 52 644 crevasses from 19 Greenland glaciers. We then compare our observed depths with those calculated using two popular models that assume crevasse depths are functions of local stresses: the Nye and linear elastic fracture mechanics (LEFM) formulations. When informed by the observed crevasse depths, the LEFM formulation produces kilometer-scale variations in crevasse depth, in decent agreement with observations. However, neither formulation accurately captures smaller-scale variations in the observed crevasse depths. Critically, we find that along-flow patterns in crevasse depths are unrelated to along-flow patterns in strain rates (and therefore stresses). Cumulative strain rate is moderately more predictive of crevasse depths at the majority of glaciers. Our reliance on lidar limits the inference we can make regarding fracture depths. However, given the discordant patterns in observed and modeled crevasses, we recommend additional in situ and remote sensing analyses before Nye and LEFM models are considered predictive. Such analyses should span extensional and compressive regions to better understand the influence of advection on crevasse geometry. Ultimately, such additional study will enable more reliable projection of terminus position change and supraglacial meltwater routing that relies on accurate modeling of crevasse occurrence.
- Published
- 2020
25. Not all breaks are equal: Variable hydrologic and geomorphic responses to intentional levee breaches along the lower Cosumnes River, California.
- Author
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Nichols, A. L. and Viers, J. H.
- Subjects
LEVEES ,HYDROGEOLOGICAL modeling ,RIVER sediments ,MARITIME shipping ,FLOODPLAINS - Abstract
The transport of water and sediment from rivers to adjacent floodplains helps generate complex floodplain, wetland, and riparian ecosystems. However, riverside levees restrict lateral connectivity of water and sediment during flood pulses, making the re-introduction of floodplain hydrogeomorphic processes through intentional levee breaching and removal an emerging floodplain restoration practice. Repeated topographic observations from levee breach sites along the lower Cosumnes River (USA) indicated that breach architecture influences floodplain and channel hydrogeomorphic processes. Where narrow breaches (<75 m) open onto graded floodplains, archetypal crevasse splays developed along a single dominant flowpath, with floodplain erosion in near-bank areas and lobate splay deposition in distal floodplain regions. Narrow breaches opening into excavated floodplain channels promoted both transverse advection and turbulent diffusion of sediment into the floodplain channel, facilitating near-bank deposition and potential breach closure. Wide breaches (>250 m) enabled multiple modes of water and sediment transport onto graded floodplains. Advective sediment transport along multiple flow paths generated overlapping crevasse splays, while turbulent diffusion promoted the formation of lateral levees through large wood and sediment accumulation in near-bank areas. Channel incision (>2 m) upstream from a wide levee breach suggests that large flow diversions through such breaches can generate water surface drawdown during flooding, resulting in localized flow acceleration and upstream channel incision. Understanding variable hydrogeomorphic responses to levee breach architecture will help restoration managers design breaches that maximize desired floodplain topographic change while also minimizing potential undesirable consequences such as levee breach closure or channel incision. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
26. Search and recovery of aircraft parts in ice-sheet crevasse fields using airborne and in situ geophysical sensors
- Author
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William Colgan, Anders Vest Christiansen, Dirk van As, Kenneth D. Mankoff, Esben Auken, Joshua Elliott, Karina Hansen, Nanna B. Karlsson, Austin Lines, Olivier Ruault du Plessis, Rune Kraghede, Pascale Dubois-Fernandez, Thue S. Bording, H. Cantalloube, Helene Oriot, Department of Glaciology and Climate, Geological Survey of Denmark and Greenland (GEUS), Thayer School of Engineering at Dartmouth College, Hanover, USA, HydroGeophysics Group, department of Geoscience, Aarhus university, Denmark, DEMR, ONERA, Université Paris Saclay [Palaiseau], ONERA-Université Paris-Saclay, DEMR, ONERA [Salon], and ONERA
- Subjects
Synthetic aperture radar ,Transient electromagnetics ,010504 meteorology & atmospheric sciences ,crevasses ,010502 geochemistry & geophysics ,01 natural sciences ,MCMURDO SHEAR ZONE ,law.invention ,Applied glaciology ,[SPI]Engineering Sciences [physics] ,Crevasse ,law ,Snow bridge ,MASS-BALANCE ,Radar ,0105 earth and related environmental sciences ,Earth-Surface Processes ,[PHYS]Physics [physics] ,geography ,geography.geographical_feature_category ,GREENLAND ,Snow ,Debris ,glaciological instruments and methods ,Ice sheet ,glacier hazards ,Seismology ,Geology - Abstract
International audience; On 30 September 2017, an Air France Airbus A380-800 suffered a failure of its fourth engine while over Greenland. This failure resulted in the loss of the engine fan hub, fan blades and surrounding structure. An initial search recovered 30 pieces of light debris, but the primary part of interest, a ~220 kg titanium fan hub, was not recovered because it had a different fall trajectory than the light debris, impacted into the ice-sheet's snow surface, and was quickly covered by drifting snow. Here we describe the methods used for the detection of the fan hub and details of the field campaigns. The search area included two crevasse fields of at least 50 snow-covered crevasses 1 to ~30 m wide with similar snow bridge thicknesses. After 21 months and six campaigns, using airborne synthetic aperture radar, ground-penetrating radar, transient electromagnetics and an autonomous vehicle to survey the crevasse fields, the fan hub was found within ~1 m of a crevasse at a depth of ~3.3 to 4 m and was excavated with shovels, chain saws, an electric winch, sleds and a gasoline heater, by workers using fall-arrest systems.
- Published
- 2020
27. Depositional settings and palynofacies assemblages of the Upper Triassic fluvio-deltaic Mungaroo Formation, northern Carnarvon Basin, Western Australia
- Author
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Tobias H. D. Payenberg, Joe Scibiorski, Adam Charles, Simon C. Lang, and Daniel Peyrot
- Subjects
Sedimentary depositional environment ,geography ,Crevasse ,geography.geographical_feature_category ,Floodplain ,Geochemistry ,Fluvial ,Geology ,Vegetation ,Paleosol ,Crevasse splay ,Palynofacies - Abstract
Palynofacies analysis was carried out on 92 core samples from the fluvio-deltaic Middle to Upper Triassic Mungaroo Formation, Northern Carnarvon Basin, Western Australia. The analyses demonstrate that each depositional environment (“depofacies”) sampled has a characteristic palynofacies assemblage reflecting the varied origins, transport, sorting, and preservation histories of organic particles in sediments. The sampling covered a wide range of depofacies identified in fluvial channel, floodplain, crevasse splay, distributary channel, and tidal zone paleoenvironments and included laminated to massive mudstones and siltstones, cross-bedded sandstones, immature pedogenically altered paleosols, and coals. Although each depofacies has a characteristic palynofacies association, there is a high degree of variability within and overlap between preparations. Black-opaque particles were the dominant component in active fluvial, crevasse, and distributary channels. In contrast, palynomorphs, brown wood particles, and cuticle were more common in abandoned channels, floodplain lakes, and other lower-energy environments. The composition of palynomorphs also varies greatly between depofacies due to factors including the bioproductivity of the surrounding vegetation source area, water-table levels, preservation potential, and the fluid dynamic properties of organic particles. The depofacies were grouped into five “process regimes” (active channels, abandoned channels, lakes and periodically flooded areas, paleosols and swamps, tidal mudflats) based on their dominant depositional process. Depofacies in the same process regime tended to have similar palynofacies associations. Active channels yielded similar assemblages irrespective of whether they were fluvial, crevasse, or distributary channels because their dominant characteristic is high flow energy, which encourages the bypass of finer-grained particles, enhances the mechanical degradation of plant debris, and may inhibit local vegetation growth. Organic particles found in lower-energy environments (e.g., floodplain lakes) are on average larger, more elongate, and better preserved than particles found in high-energy environments (e.g., active channels). Although this study was restricted to samples from the upper Samaropollenites speciosus and lower Minutosaccus crenulatus biostratigraphic zones in a geographically limited area, its results are not influenced by the specific taxonomic composition of the vegetation but by the physiographic structure of surrounding plant communities; this suggests that palynofacies analysis could be used to distinguish depositional environments in deltaic settings from other stratigraphic intervals.
- Published
- 2020
28. A non-local continuum poro-damage mechanics model for hydrofracturing of surface crevasses in grounded glaciers
- Author
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Jeremy N. Bassis, Stephen Jiménez, and Ravindra Duddu
- Subjects
geography ,geography.geographical_feature_category ,Buoyancy ,010504 meteorology & atmospheric sciences ,Glacier ,Mechanics ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Iceberg ,Stress field ,Stress (mechanics) ,Crevasse ,Rheology ,Damage mechanics ,engineering ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
Hydrofracturing can enhance the depth to which crevasses propagate and, in some cases, allow full depth crevasse penetration and iceberg detachment. However, many existing crevasse models either do not fully account for the stress field driving the hydrofracture process and/or treat glacier ice as elastic, neglecting the non-linear viscous rheology. Here, we present a non-local continuum poro-damage mechanics (CPDM) model for hydrofracturing and implement it within a full Stokes finite element formulation. We use the CPDM model to simulate the propagation of water-filled crevasses in idealized grounded glaciers, and compare crevasse depths predicted by this model with those from linear elastic fracture mechanics (LEFM) and zero stress models. We find that the CPDM model is in good agreement with the LEFM model for isolated crevasses and with the zero stress model for closely-spaced crevasses, until the glacier approaches buoyancy. When the glacier approaches buoyancy, we find that the CPDM model does not allow the propagation of water-filled crevasses due to the much smaller size of the tensile stress region concentrated near the crevasse tip. Our study suggests that the combination of non-linear viscous and damage processes in ice near the tip of a water-filled crevasse can alter calving outcomes.
- Published
- 2020
29. Floodplain forms along the lowland Maros River, Hungary
- Author
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Tímea Kiss, Károly Fiala, Márton Balogh, and István Fehérváry
- Subjects
Cultural Studies ,Hydrology ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Floodplain ,Geography, Planning and Development ,Fluvial ,Point bar ,010502 geochemistry & geophysics ,01 natural sciences ,Natural (archaeology) ,Urban Studies ,Crevasse ,General Earth and Planetary Sciences ,Alluvium ,Levee ,0105 earth and related environmental sciences - Abstract
The floodplain forms of lowland rivers act as fluvial archives, as their morphology, material and spatial characteristics refer to the hydromorphological changes of the river and (dis)connectivity of the alluvial system. The aims of the research are (1) to identify natural levees, crevasses, and point-bars on the Hungarian floodplain section of the Maros River, (2) to measure their morphometric parameters, and (3) to analyse their spatial and temporal variations in connection with various human impacts. Six genetic types of natural levees and pointbar systems developed as the result of various human impacts, thus the development of the forms terminated or became laterally limited.
- Published
- 2020
30. Ice-crevasse sedimentation in the eastern part of the Głubczyce Plateau (S Poland) during the final stage of the Drenthian Glaciation
- Author
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Tomasz Salamon
- Subjects
QE1-996.5 ,010506 paleontology ,Ice-sheet dynamics ,geography ,Plateau ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,glaciomarginal zone ,Geology ,older Saalian ,Environmental Science (miscellaneous) ,Sedimentation ,lithofacies analysis ,01 natural sciences ,Paleontology ,Crevasse ,Stage (stratigraphy) ,Sudeten Foreland ,stagnant ice ,ice sheet dynamics ,General Earth and Planetary Sciences ,Glacial period ,0105 earth and related environmental sciences - Abstract
Glacial sediments in the eastern part of the Głubczyce Plateau, at the Krowiarki site, were studied. Two units were distinguished within the sedimentary succession. The lower unit is composed of mainly sandy sediments with diamicton interbeds, the upper unit of very fine silt and clay sediments that exhibit rhythmic lamination in parts. Based on the textural and structural features of deposits, local deformations and palaeoflow directions, it was found that the sediments had been deposited within an ice crevasse, which was initially open and functioned as an ablation flow artery. The sediments were deposited in the form of a small fan dominated by sheetflows. Glacial tills were also redeposited on its surface. In a later phase, the crevasse was blocked. As a result, it was filled with water, leading to the development of a crevasse lake in which low-energy deposition dominated. The crevasse style of deposition indicates that, in the final stage of glaciation, the marginal part of the ice sheet was in a stagnant phase. This conclusion applies to the part located on the southern side of the watershed of the eastern Głubczyce Plateau. The probable reason for the stagnation of the ice sheet was the distinct loss of ice supply above the local topography barrier due to the decreasing thickness of the ice sheet in the studied area.
- Published
- 2020
31. Meso/Micro-texture analysis of the landslide-dam outburst sediments in the Upper Jinsha River, SE Tibetan Plateau
- Author
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Ruichen Chen, Wendy Zhou, Chao Liu, Jian Chen, and Zhijiu Cui
- Subjects
010506 paleontology ,geography ,Plateau ,geography.geographical_feature_category ,Geochemistry ,Sediment ,Outburst flood ,01 natural sciences ,Crevasse ,General Earth and Planetary Sciences ,Aeolian processes ,Sedimentary rock ,Quartz ,Geology ,Conchoidal fracture ,0105 earth and related environmental sciences ,General Environmental Science - Abstract
Outburst sediments are widely distributed in the Upper Jinsha River in the Southeastern (SE) Tibetan Plateau. In order to understand the sedimentary characteristics of these sediments, gravel fabric, particle size distribution and quartz sand surface textures were used to analyze the mesotextures and microtextures of the Xuelongnang outburst sediments. It was determined that these sediments usually have a short transport distance, and are distributed over a distance of approximately 3.5 km. The gravel fabric and particle size distribution analysis represent the different mesotextures with different transport distances and suggest gradually changing hydrodynamic conditions. The statistical data of quartz surface textures exhibit the transformation process of quartz sands by outburst flood. The variation from abundant sub-angular shapes (> 75%); to common V-shaped percussion cracks, solution crevasse, medium relief, and chatter marks (50% to 75%); to rare meandering ridge, underwater polished surface, large conchoidal fracture (> 100 μm), directional etch pits, and crystalline overgrowths (< 5%), present the features in different combinations to other sedimentary environments. The microtexture characteristics of landslide-dam outburst deposits are also consistent with those of the mesotextures. As the distance from the residual dam increased, the quartz grain microtextures showed gradual or abrupt changes, such as increased frequencies of V-shaped percussion cracks, decreased frequencies of the adhering particles, and growth of the solution crevasses. These findings could potentially be used as a discriminant mark to distinguish outburst sediment from other types of sediments, e.g., subaqueous, eolian, glacial, etc.
- Published
- 2019
32. Microwave imaging of hidden crevasse in glacier terrain using metamaterial loaded eight-slot Vivaldi antenna
- Author
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Vikesh S. Bhadouria, G. Gopikrishnan, Mohammad Jaleel Akhtar, and Zubair Akhter
- Subjects
010302 applied physics ,geography ,geography.geographical_feature_category ,General Physics and Astronomy ,Metamaterial ,020206 networking & telecommunications ,Terrain ,Glacier ,02 engineering and technology ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,law.invention ,Crevasse ,Microwave imaging ,law ,0103 physical sciences ,0202 electrical engineering, electronic engineering, information engineering ,Electrical and Electronic Engineering ,Vivaldi antenna ,Geology ,Remote sensing - Abstract
In this paper, a novel microwave imaging methodology based on the simplified experimental setup for identifying hidden crevasse in a glacier or polar terrain is proposed. For scanning the g...
- Published
- 2019
33. Sedimentary characteristics and internal architecture of a river-dominated delta controlled by autogenic process: implications from a flume tank experiment
- Author
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Qing-Hai Xu, Wenjie Feng, Yanshu Yin, Rui Zhu, Chen Zhe, Changmin Zhang, Yin Taiju, and Jun-Ling Liu
- Subjects
Autogenic succession ,Delta ,010504 meteorology & atmospheric sciences ,Science ,Energy Engineering and Power Technology ,Autogenic process ,010502 geochemistry & geophysics ,Mouth bar ,01 natural sciences ,Sedimentary depositional environment ,Paleontology ,Crevasse ,Geochemistry and Petrology ,River-dominated delta ,Petrology ,0105 earth and related environmental sciences ,QE420-499 ,Geology ,Geotechnical Engineering and Engineering Geology ,Flume tank experiment ,Flume ,Geophysics ,Fuel Technology ,Depositional process ,Economic Geology ,Sedimentary rock ,Stage (hydrology) ,Sedimentary architecture - Abstract
Autogenic processes are widely found in various sedimentary systems and they play an important role in the depositional evolution and corresponding sedimentary architecture. However, autogenic processes are often affected by changing allogenic factors and are difficult to be identified and analyzed from modern and ancient records. Through the flume tank experiment under constant boundary conditions, the depositional process, evolution principles, and the sedimentary architecture of a river-dominated delta was presented, and a corresponding sedimentary architecture model was constructed. The evolution of river-dominated delta controlled only by autogenic process is obviously periodic, and each autogenic cycle can be divided into an initial progradational stage, a middle retrogratational stage, and a late aggradational–progradational stage. In the initial progradational stage, one feeder channel incised into the delta plain, mouth bar(s) was formed in front of the channel mouth, and small-scale crevasse splays were formed on the delta plain. In the middle retrogradational stage, the feeder channel was blocked by the mouth bar(s) which grew out of water at the end of the initial stage, and a set of large-scale distributary splay complexes were formed on the delta plain. These distributary splay complexes were retrogradationally overlapped due to the continuous migration of the bifurcation point of the feeder channel. In the late aggradational–progradational stage, the feeder channel branched into several radial distributary channels, overlapped distributary channels were formed on the delta plain, and terminal lobe complexes were formed at the end of distributary channels. The three sedimentary layers formed in the three stages constituted an autogenic succession. The experimental delta consisted of six autogenic depositional successions. Dynamic allocation of accommodation space and the following adaptive sediments filling were the two main driving factors of the autogenic evolution of deltas.
- Published
- 2019
34. A Generalized Interpolation Material Point Method for Shallow Ice Shelves. 2: Anisotropic Nonlocal Damage Mechanics and Rift Propagation
- Author
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A. Huth, Ben Smith, and Ravindra Duddu
- Subjects
Modeling in Glaciology ,Oceanography ,Biogeosciences ,Volcanic Effects ,Ice shelf ,Global Change from Geodesy ,Volcanic Hazards and Risks ,Damage mechanics ,Oceans ,Sea Level Change ,Disaster Risk Analysis and Assessment ,Global and Planetary Change ,geography.geographical_feature_category ,Climate and Interannual Variability ,Mechanics ,Dynamics ,Climate Impact ,Damage ,Ice Streams ,Earthquake Ground Motions and Engineering Seismology ,Explosive Volcanism ,Earth System Modeling ,Atmospheric Processes ,Ocean Monitoring with Geodetic Techniques ,Ocean/Atmosphere Interactions ,Atmospheric ,Regional Modeling ,Atmospheric Effects ,Physical geography ,Volcanology ,Hydrological Cycles and Budgets ,Decadal Ocean Variability ,Land/Atmosphere Interactions ,Crevasse ,Geodesy and Gravity ,Global Change ,Air/Sea Interactions ,Numerical Modeling ,Solid Earth ,Geological ,Ocean/Earth/atmosphere/hydrosphere/cryosphere interactions ,Water Cycles ,Modeling ,Avalanches ,Volcano Seismology ,Benefit‐cost Analysis ,Ice Shelves ,Fracture (geology) ,Computational Geophysics ,Regional Climate Change ,Natural Hazards ,Necking ,Abrupt/Rapid Climate Change ,Informatics ,Glaciology ,Ice stream ,Surface Waves and Tides ,Atmospheric Composition and Structure ,Volcano Monitoring ,Snow and Ice ,particle method ,Snow ,Seismology ,Climatology ,Radio Oceanography ,Gravity and Isostasy ,Marine Geology and Geophysics ,Physical Modeling ,GB3-5030 ,Oceanography: General ,Creep ,Cryospheric Change ,Cryosphere ,Impacts of Global Change ,Geology ,Oceanography: Physical ,Research Article ,Risk ,Oceanic ,Theoretical Modeling ,material point method ,GC1-1581 ,Radio Science ,Tsunamis and Storm Surges ,Paleoceanography ,Climate Dynamics ,Environmental Chemistry ,Numerical Solutions ,Climate Change and Variability ,geography ,Effusive Volcanism ,Climate Variability ,Ice ,General Circulation ,Policy Sciences ,Climate Impacts ,Mud Volcanism ,Air/Sea Constituent Fluxes ,Mass Balance ,Ocean influence of Earth rotation ,fracture ,Volcano/Climate Interactions ,General Earth and Planetary Sciences ,Hydrology ,Ice sheet ,Sea Level: Variations and Mean - Abstract
Ice shelf fracture is responsible for roughly half of Antarctic ice mass loss in the form of calving and can weaken buttressing of upstream ice flow. Large uncertainties associated with the ice sheet response to climate variations are due to a poor understanding of these fracture processes and how to model them. Here, we address these problems by implementing an anisotropic, nonlocal integral formulation of creep damage within a large‐scale shallow‐shelf ice flow model. This model can be used to study the full evolution of fracture from initiation of crevassing to rifting that eventually causes tabular calving. While previous ice shelf fracture models have largely relied on simple expressions to estimate crevasse depths, our model parameterizes fracture as a progressive damage evolution process in three‐dimensions (3‐D). We also implement an efficient numerical framework based on the material point method, which avoids advection errors. Using an idealized marine ice sheet, we test the creep damage model and a crevasse‐depth based damage model, including a modified version of the latter that accounts for damage evolution due to necking and mass balance. We demonstrate that the creep damage model is best suited for capturing weakening and rifting over shorter (monthly/yearly) timescales, and that anisotropic damage reproduces typically observed fracture patterns better than isotropic damage. Because necking and mass balance can significantly influence damage on longer (decadal) timescales, we discuss the potential for a combined approach between models to best represent mechanical weakening and tabular calving within long‐term simulations., Key Points Our shallow‐shelf creep damage model can represent the full evolution of ice shelf fracture from crevasse initiation to tabular calvingStrongly anisotropic creep damage produces sharp, arcuate rift patterns more consistent with observations than isotropic creep damageThe zero‐stress damage model poorly captures rifting, but a modified form accounts for damage evolution due to mass balance and necking
- Published
- 2021
35. Human induced discharge diversion in a tropical delta and its environmental implications: The Patía River, Colombia
- Author
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Universidad EAFIT. Departamento de Geología, Ciencias del Mar, Restrepo, Juan D., Kettner, Albert, Universidad EAFIT. Departamento de Geología, Ciencias del Mar, Restrepo, Juan D., and Kettner, Albert
- Abstract
The Patía River, the number one in terms of sediment yield ~1500tkm -2yr -1 draining the western South America, has the most extensive and well developed delta on the Pacific coast, measuring 1700km 2. During the Holocene, nature forced the Patía delta to the south; however, a major water diversion, starting in 1972, diverted the Patía flow to the Sanguianga River, the latter, a small stream draining internal lakes from the Pacific lowlands. This human induced discharge diversion shifted the active delta plain back to the north and changed the northern estuarine system into an active delta plain. Overall, major environmental consequences of this discharge diversion in terms of morphological changes along the delta coast and distributary channels, are evidenced by: (1) coastal retreat along the abandoned delta lobe; 63% of the southern shoreline is retreating at maximum rates of 7myr -1, with a corresponding coastal land loss of 106myr -1; (2) transgressive barrier islands with exposed peat soils in the surf zone; (3) abandonment of former active distributaries in the southern delta plain with associated closing of inlets and formation of ebb tidal deltas; (4) breaching events on barrier islands; and (5) distributary channel accretion in the northern delta plain by morphological processes such as sedimentation (also in crevasses), overbank flow, increasing width of levees, interdistributary channel fill, and colonization of pioneer mangrove. The Sanguianga Mangrove National Park (SMNP), the largest mangrove reserve in Colombia, measuring 800km 2, lies in this former estuary, where major hydrologic and sedimentation changes are occurring. Observed environmental changes in the SMNP, include (1) seaward advance of the sub-aqueous delta front at the Sanquianga inlet evidenced by an increase in tidal flat area from 5.4Mm 2 in 1986 to 14Mm 2 in 2001; (2) freshening conditions in the Sanguianga distributary channel, a hydrologic change that has shifted the upper estuarine r
- Published
- 2021
36. Crevasse and rift detection in Antarctica from TerraSAR-X satellite imagery
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Daniel Price, Z.R. Courville, Oliver J. Marsh, and Dana Floricioiu
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Synthetic aperture radar ,Brunt Ice Shelf ,010504 meteorology & atmospheric sciences ,Shear zone ,0211 other engineering and technologies ,02 engineering and technology ,01 natural sciences ,Ice shelf ,law.invention ,Backscatter ,Crevasse ,law ,Radar imaging ,Traverse ,Polarization ,Snow bridge ,Radar ,021101 geological & geomatics engineering ,0105 earth and related environmental sciences ,Remote sensing ,geography ,geography.geographical_feature_category ,Glacier ,Geotechnical Engineering and Engineering Geology ,Snow ,Fracture ,General Earth and Planetary Sciences ,McMurdo Shear Zone ,Geology - Abstract
Surface crevasses covered by snow bridges can be mapped remotely on ice sheets and glaciers using active microwave synthetic aperture radar. They are highlighted against the surrounding snow due to increased scattering from the side-walls and base of snow bridges and usually appear as linear features. The contrast between crevasses and crevasse-free regions depends on the design of the sensor, the image acquisition parameters and the properties of the snow. Here we quantify how crevassed regions are represented at X-band for different polarizations, look directions and incidence angles, and discuss whether additional information about their physical properties can be gained from their radar signature. Snow bridge thicknesses and crevasse widths are measured on the ground in the McMurdo Shear Zone and Brunt Ice Shelf by ground-penetrating radar and excavation. TerraSAR-X is shown to reliably distinguish crevasse location, balancing penetration into the snow and horizontal resolution. We provide recommendations for radar imaging parameters that optimize the identification of individual crevasses and crevassed regions.
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- 2021
37. Evaluating Short-Term Tidal Flat Evolution Through UAV Surveys: A Case Study in the Po Delta (Italy)
- Author
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Riccardo Brunetta, Paolo Ciavola, and Enrico Duo
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Delta ,010504 meteorology & atmospheric sciences ,Science ,PE10_13 ,Wetland ,010502 geochemistry & geophysics ,01 natural sciences ,wetlands ,Crevasse ,salt marshes ,sedimentation rates ,unmanned aerial vehicle ,tidal flats ,Sedimentary budget ,0105 earth and related environmental sciences ,geography ,geography.geographical_feature_category ,Orthophoto ,Ambientale ,Sediment ,geomorphological changes ,Po River delta ,microtidal environment ,Photogrammetry ,Salt marsh ,Microtidal environment ,General Earth and Planetary Sciences ,Environmental science ,Physical geography - Abstract
The use of Unmanned Aerial Vehicles (UAV) on wetlands is becoming a common survey technique that is extremely useful for understanding tidal flats and salt marshes. However, its implementation is not straightforward because of the complexity of the environment and fieldwork conditions. This paper presents the morphological evolution of the Po della Pila tidal flat in the municipality of Porto Tolle (Italy) and discusses the reliability of UAV-derived Digital Surface Models (DSMs) for such environments. Four UAV surveys were performed between October 2018 and February 2020 on an 8 ha young tidal flat that was generated, amongst others, as a consequence of the massive sediment injection into the Po Delta system due to the floods of the 1950s and 1960s. The DSM accuracy was tested by processing (i.e., photogrammetry) diverse sets of pictures taken at different altitudes during the same survey day. The DSMs and the orthophotos show that the tidal flat is characterised by several crevasse splays and that the sediment provision depends strictly on the river. During the study period, the sediment budget was positive (gaining 800 m3/year and an average rate of vertical changes of 1.3 cm/year). Comparisons of DSMs demonstrated that neither lower flight altitudes (i.e., 20–100 m) nor the combination of more photos from different flights during the same surveys necessarily reduce the error in such environments. However, centimetric errors (i.e., RMSEs) are achievable flying at 80–100 m, as the increase of GCP (Ground Control Point) density is the most effective solution for enhancing the resolution. Guidelines are suggested for implementing high-quality UAV surveys in wetlands.
- Published
- 2021
- Full Text
- View/download PDF
38. Borehole-Based Characterization of Deep Mixed-Mode Crevasses at a Greenlandic Outlet Glacier
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Hubbard, Bryn, Christoffersen, Poul, Doyle, Samuel H, Chudley, Thomas R, Schoonman, Charlotte M, Law, Robert, Bougamont, Marion, Christoffersen, Poul [0000-0003-2643-8724], Law, Robert [0000-0003-0067-5537], Bougamont, Marion [0000-0001-7196-4171], and Apollo - University of Cambridge Repository
- Subjects
deep crevasse ,glacier ,Greenland Ice Sheet ,optical televiewer ,borehole ,crevasse - Abstract
Funder: Aberystwyth University Capital Equipment Fund, Optical televiewer borehole logging within a crevassed region of fast‐moving Store Glacier, Greenland, revealed the presence of 35 high‐angle planes that cut across the background primary stratification. These planes were composed of a bubble‐free layer of refrozen ice, most of which hosted thin laminae of bubble‐rich “last frozen” ice, consistent with the planes being the traces of former open crevasses. Several such last‐frozen laminae were observed in four traces, suggesting multiple episodes of crevasse reactivation. The frequency of crevasse traces generally decreased with depth, with the deepest detectable trace being 265 m below the surface. This is consistent with the extent of the warmer‐than‐modeled englacial ice layer in the area, which extends from the surface to a depth of ∼400 m. Crevasse trace orientation was strongly clustered around a dip of 63° and a strike that was offset by 71° from orthogonal to the local direction of principal extending strain. The traces’ antecedent crevasses were therefore interpreted to have originated upglacier, probably ∼8 km distant involving mixed‐mode (I and III) formation. We conclude that deep crevassing is pervasive across Store Glacier, and therefore also at all dynamically similar outlet glaciers. Once healed, their traces represent planes of weakness subject to reactivation during subsequent advection through the glacier. Given their depth, it is highly likely that such traces—particularly those formed downglacier—survive surface ablation to reach the glacier terminus, where they may represent foci for fracture and iceberg calving.
- Published
- 2021
- Full Text
- View/download PDF
39. Imaging the Crevasse of Left Ventricular Assist Device Infection
- Author
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Mandeep R. Mehra and Ann E. Woolley
- Subjects
Heart Failure ,medicine.medical_specialty ,PET-CT ,business.industry ,Heart Ventricles ,medicine.medical_treatment ,equipment and supplies ,medicine.disease ,Article ,Crevasse ,Fluorodeoxyglucose F18 ,Positron Emission Tomography Computed Tomography ,Internal medicine ,Heart failure ,Ventricular assist device ,medicine ,Cardiology ,Humans ,Radiology, Nuclear Medicine and imaging ,Heart-Assist Devices ,Cardiology and Cardiovascular Medicine ,business - Abstract
OBJECTIVES: The purpose of this study was to describe our experience with fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography computed tomography (PET/CT) in diagnosing left ventricular assist device (LVAD) infections and perform a meta-analysis of published studies to determine overall diagnostic accuracy. BACKGROUND: Device-related infections are a common complication of LVADs and are linked to worse outcomes. Diagnosis of LVAD infections remains challenging. FDG PET/CT has demonstrated good diagnostic accuracy in several other infectious conditions. METHODS: This was a single-center, retrospective case series of FDG PET/CT scans in suspected LVAD infection between September 2015 and February 2018. A systematic review of PubMed from database inception through March 2018 was also conducted to identify additional studies. RESULTS: Nineteen FDG PET/CT scans were identified for the retrospective case series. The systematic review identified an additional 3 publications, for a total of 4 studies involving 119 scans assessing diagnostic performance. Axial (n = 36) and centrifugal (n = 83) flow LVADs were represented. Pooled sensitivity was 92% (95% confidence interval [CI]: 82% to 97%) and specificity was 83% (95% CI: 24% to 99%) for FDG PET/CT in diagnosing LVAD infections. Summary receiver-operating characteristic curve analysis demonstrated an AUC of 0.94 (95% CI: 0.91 to 0.95). CONCLUSIONS: FDG PET/CT for suspected LVAD infections demonstrates good diagnostic accuracy, with overall high sensitivity but variable specificity.
- Published
- 2020
40. Crevasse initiation and history within the McMurdo Shear Zone, Antarctica
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L. M. Kaluzienski, Steven A. Arcone, Gordon S. Hamilton, Ellyn M. Enderlin, Peter O. Koons, and Zoe Courville
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Simple shear ,geography ,Crevasse ,Rift ,geography.geographical_feature_category ,Shear (geology) ,Shear zone ,Vorticity ,Strain rate ,Geomorphology ,Geology ,Ice shelf ,Earth-Surface Processes - Abstract
While large-scale observations of intensified fracture and rifting can be observed through remote-sensing observations, understanding crevasse initiation may best be achieved with small-scale observations in which crevasses can be directly observed. Here we investigate the kinematic drivers of crevasse initiation in the McMurdo Shear Zone (MSZ), Antarctica. We delineated 420 crevasses from ~95 km of 400 MHz frequency ground-penetrating radar data and compared these data with kinematic outputs derived from remotely-sensed ice surface velocities to develop a statistical method to estimate crevasse initiation threshold strain rate values. We found the MSZ to be dominated by simple shear and that surface shear strain rates proved best for predicting crevasse features, with regions of higher shear strain rate more likely to have a greater number of crevasses. In the surveyed portion of our study region, values of shear strain rate and vorticity rate derived from the MEaSUREs2 velocity dataset range between 0.005–0.020 and 0.006–0.022 a−1, respectively, with crevasses located at ≥0.011 and ≥0.013 a−1. While threshold values from this study cannot be directly applied to other glacial environments, the method described here should allow for the study of shear margin evolution and assessment of localized damage and weakening processes in other locations where in situ data are available.
- Published
- 2019
41. Automatic mapping and geomorphometry extraction technique for crevasses in geodetic mass-balance calculations at Haig Glacier, Canadian Rockies
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M. Foroutan, Shawn J. Marshall, and Brian Menounos
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geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Elevation ,Geodetic datum ,Glacier ,010502 geochemistry & geophysics ,Geodesy ,01 natural sciences ,Glacier mass balance ,Lidar ,Crevasse ,Geomorphometry ,Digital elevation model ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
Finely resolved geodetic data provide an opportunity to assess the extent and morphology of crevasses and their change over time. Crevasses have the potential to bias geodetic measurements of elevation and mass change unless they are properly accounted for. We developed a framework that automatically maps and extracts crevasse geometry and masks them where they interfere with surface mass-balance assessment. Our study examines airborne light detection and ranging digital elevation models (LiDAR DEMs) from Haig Glacier, which is experiencing a transient response in its crevassed upper regions as the glacier thins, using a self-organizing map algorithm. This method successfully extracts and characterizes ~1000 crevasses, with an overall accuracy of 94%. The resulting map provides insight into stress and flow conditions. The crevasse mask also enables refined geodetic estimates of summer mass balance. From differencing of September and April LiDAR DEMs, the raw LiDAR DEM gives a 9% overestimate in the magnitude of glacier thinning over the summer: −5.48 m compared with a mean elevation change of −5.02 m when crevasses are masked out. Without identification and removal of crevasses, the LiDAR-derived summer mass balance therefore has a negative bias relative to the glaciological surface mass balance.
- Published
- 2019
42. On the Use of Electromagnetics for Earth Imaging of the Polar Regions
- Author
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Graham Hill
- Subjects
Electromagnetics ,010504 meteorology & atmospheric sciences ,Terrain ,Geophysics ,010502 geochemistry & geophysics ,Snow ,01 natural sciences ,Wind speed ,Glaciology ,Crevasse ,Geochemistry and Petrology ,Magnetotellurics ,Polar ,0105 earth and related environmental sciences - Abstract
The polar regions are host to fundamental unresolved challenges in Earth studies. The nature of these regions necessitates the use of geophysics to address these issues, with electromagnetic and, in particular, magnetotelluric studies finding favour and being applied over a number of different scales. The unique geography and climatic conditions of the polar regions means collecting magnetotelluric data at high latitudes, which presents challenges not typically encountered and may result in significant measurement errors. (1) The very high contact resistance between electrodes and the surficial snow and ice cover (commonly MΩ) can interfere with the electric field measurement. This is overcome by using custom-designed amplifiers placed at the active electrodes to buffer their high impedance contacts. (2) The proximity to the geomagnetic poles requires verification of the fundamental assumption in magnetotellurics that the magnetic source field is a vertically propagating, horizontally polarised plane wave. Behaviour of the polar electro-jet must be assessed to identify increased activity (high energy periods) that create strong current systems and may generate non-planar contributions. (3) The generation of ‘blizstatic’, localised random electric fields caused by the spin drift of moving charged snow and ice particles that produce significant noise in the electric fields during periods of strong winds. At wind speeds above ~ 10 m s−1, the effect of the distortion created by the moving snow is broad-band. Station occupation times need to be of sufficient length to ensure data are collected when wind speed is low. (4) Working on glaciated terrain introduces additional safety challenges, e.g., weather, crevasse hazards, etc. Inclusion of a mountaineer in the team, both during the site location planning and onsite operations, allows these hazards to be properly managed. Examples spanning studies covering development and application of novel electromagnetic approaches for the polar regions as well as results from studies addressing a variety of differing geologic questions are presented. Electromagnetic studies focusing on near-surface hydrologic systems, glacial and ice sheet dynamics, as well as large-scale volcanic and tectonic problems are discussed providing an overview of the use of electromagnetic methods to investigate fundamental questions in solid earth studies that have both been completed and are currently ongoing in polar regions.
- Published
- 2019
43. Straddling the crevasse: A review of microservice software architecture foundations and recent advancements
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K. Chandrasekaran and Christina Terese Joseph
- Subjects
Crevasse ,business.industry ,Computer science ,Software architecture ,Software engineering ,business ,Software - Published
- 2019
44. Seismic observations of crevasse growth following rain-induced glacier acceleration, Haupapa/Tasman Glacier, New Zealand
- Author
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Huw J. Horgan, John Townend, Samuel Taylor-Offord, and J. Paul Winberry
- Subjects
Acceleration ,geography ,geography.geographical_feature_category ,Crevasse ,Flow (psychology) ,Glacier ,Strain rate ,Ice sheet ,Induced seismicity ,Rain rate ,Seismology ,Geology ,Earth-Surface Processes - Abstract
Changing rates of water input can affect both the flow of glaciers and ice sheets and their propensity to crevasse. Here we examine geodetic and seismic observations during two substantial (10–18-times background velocity) rain-induced glacier accelerations at Haupapa/Tasman Glacier, New Zealand. Changes in rain rate result in glacier acceleration and associated uplift, which propagate down-glacier. This pattern of acceleration results in a change to the strain rate field, which correlates with an order of magnitude increase in the apparent seismicity rate and an overall down-glacier migration in located seismicity. After each acceleration event the apparent seismicity rate decreases to below the pre-acceleration rate for 3 days. This suggests that seismic events associated with surface crevasse growth occur early during phases of glacier acceleration due to elevated extensional stresses, and then do not occur again until stresses recover.
- Published
- 2019
45. Modeling sediment texture of river-deltaic wetlands in the Lower Barataria Bay and Lower Breton Sound, Louisiana, USA
- Author
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Frank T.-C. Tsai, Kehui Xu, Crawford White, Jiaze Wang, An Li, Samuel J. Bentley, and Qin Chen
- Subjects
Hydrology ,geography ,geography.geographical_feature_category ,River delta ,010504 meteorology & atmospheric sciences ,Sediment ,Wetland ,Environmental Science (miscellaneous) ,Silt ,010502 geochemistry & geophysics ,Geotechnical Engineering and Engineering Geology ,Oceanography ,01 natural sciences ,Sedimentary depositional environment ,Dredging ,Crevasse ,Earth and Planetary Sciences (miscellaneous) ,Overbank ,Geology ,0105 earth and related environmental sciences - Abstract
Wetlands in the Mississippi River Delta Plain (MRDP) have been suffering from a high rate of land loss. Sediment cores have been drilled into the wetlands to understand their growth and degradation and to provide subsurface information for the coastal protection and restoration projects. However, few three-dimensional (3D) stratigraphy models have been developed for the wetlands on a regional scale, due to difficulties in correlating large amount of spatial scattered subsurface data and integrated visualization of stratigraphic features and topobathymetric features. In this study, a 3D model was constructed in the Lower Barataria Bay (LBB) and the Lower Breton Sound (LBS), covering an area of 190 km2 and extending from 0.5 to − 4 m in elevation. Sediment composition (sand%, silt%, and clay%) was spatially interpolated, using a compositional kriging method, extended from ordinary kriging by a log-ratio transformation. Instead of visualizing three composition components independently, sediment composition was translated into sediment texture to be visualized as sediment types. Modeling results intuitively show spatial distribution of stratigraphic features and their spatial relationships with topobathymetric features such as marsh surface, river channel, and dredging channels. Results show a silty depositional package, which consists of crevasse splays and periodic overbank flooding deposits, made up the largest portion of the wetlands. A clayey blanket is observed to cover most part of the LBB and landward side of the LBS. A large area of clayey blanket in the seaward part of the LBS has apparently been eroded away, which is likely caused by coastal reworking processes.
- Published
- 2019
46. Holocene land cover change in south-western Amazonia inferred from paleoflood archives
- Author
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Heinz Veit, Sönke Szidat, Adrien Mestrot, Javier Ruiz-Pérez, Umberto Lombardo, Francis E. Mayle, Leonor Rodrigues, and Marco Madella
- Subjects
Global and Planetary Change ,010504 meteorology & atmospheric sciences ,Fluvial ,Climate change ,020206 networking & telecommunications ,02 engineering and technology ,Land cover ,Oceanography ,01 natural sciences ,Paleosol ,Crevasse ,Paleoclimatology ,0202 electrical engineering, electronic engineering, information engineering ,Physical geography ,Southern Hemisphere ,Geology ,Holocene ,0105 earth and related environmental sciences - Abstract
This study provides new data on the evolution of the landscape in south-western Amazonia during the Holocene and the impact of climate change and fluvial dynamics on the region's ecosystems. South-western Amazonia is covered by an extensive seasonally flooded savannah, known as the Llanos de Moxos. Severe drought during the southern hemisphere winter, followed by months of permanent waterlogging, means that forests only grow on the most elevated parts of the landscape, mostly river and paleoriver levees and crevasse splays. Paleoclimate reconstructions from surrounding areas show that a shift to wetter conditions at around 4 kyr BP caused an increase in forest cover. However, the impact that this change in climate had on the landscape of the Llanos de Moxos is unknown. Published lacustrine archives from the area only cover the last 2 kyr. Here we present new data from the analysis of paleosols located along a 300 km transect across the central Llanos. The analyses of stable carbon isotopes, from 36 paleosols, and biogenic silica, from 29 paleosols, show that the patchwork of forests and savannahs that we see today was established after the 4 kyr BP climate change. During the dry period between 8 and 4 kyr BP, most of the central Llanos de Moxos, nowadays covered with seasonally flooded savannah, were covered by Cerrado-like savannah in the west and by forest in the east. However, results also suggest that, at both regional and local scales, vegetation cover has been influenced by changes in topography resulting from the region's river dynamics.
- Published
- 2019
47. Joint geodetic and seismic analysis of surface crevassing near a seasonal glacier-dammed lake at Gornergletscher, Switzerland
- Author
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Fabian Walter, Debi Kilb, Karen Luttrell, and Louis Garcia
- Subjects
glacier geophysics ,Seismometer ,010506 paleontology ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,crevasses ,Glacier ,glacier flow ,glaciological instruments and methods ,seismology ,01 natural sciences ,Crevasse ,Confluence ,Glacial period ,Shear zone ,Drainage ,Meltwater ,Geomorphology ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
Seasonal lake Gornersee forms at the confluence of Gornergletscher and Grenzgletscher, Switzerland, and experiences outburst floods annually in midsummer. To study the interplay between lake drainage, glacier movement and crevasse activity, high-frequency seismometers and GPS receivers were deployed in networks near Gornersee during the summer ablation seasons of 2004, 2006 and 2007. We use a Rayleigh wave coherence method to locate 3289, 7939 and 4087 icequakes, respectively, primarily along well-defined surface crevasses. We calculate two-dimensional strains from triads of GPS stations and find mean differential strain rates of ~300 × 10−6 d−1 with diurnal variations up to 800 × 10−6 d−1. Crevasse icequake activity and glacial velocity are highest during early season, then decrease as meltwater channels erode and subglacial water pressure decreases. Glacial response to Gornersee drainage varied year-to-year, with icequake activity promoted at some crevasses and inhibited at others, suggesting syn-drainage icequakes may be indicative of local drainage patterns and small-scale features of the stress field. Diurnal pulses in icequake activity exhibit peak activity at different times of day in different locations, coincident with a southeast-to-northwest trending concentrated shear zone near the Gornergletscher–Grenzgletscher confluence, likely due to differences in the timing of peak strain rate in these regions., Annals of Glaciology, 60 (79), ISSN:0260-3055, ISSN:1727-5644
- Published
- 2019
48. Directional properties of glacial relief and sediments as an effect of multi-stage evolution: Case study of the Tczew Hump, northern Poland
- Author
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Piotr Czubla, Piotr Paweł Woźniak, Wojciech Domachowski, and Monika Świrydo
- Subjects
010506 paleontology ,geography ,Provenance ,geography.geographical_feature_category ,Landform ,Ice stream ,010502 geochemistry & geophysics ,01 natural sciences ,Deposition (geology) ,Petrography ,Paleontology ,Crevasse ,Palimpsest (planetary astronomy) ,Glacial period ,Geomorphology ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
This paper focuses on the upland territory south-west of the Gulf of Gdansk characterized by the existence of numerous hills with distinct ordering of their crest-line orientation. Characteristic features of relief in the Tczew Hump were analysed using GIS-based tools. Directional properties and morphometric characteristics are not uniform throughout the study area. Therefore, subsequent detailed analyses were performed after dividing it into three zones: north-western (NW), central and south-eastern (SE). The highest hills are situated in the central part of the Hump. The landforms analysed are mostly elongated, but they show varying elongation ratios (1.0–4.05). In general a NE-SW orientation is observed, however, the azimuthal distribution of their crest-lines shows considerable variation (from N-S to E-W). Two main systems of the crest-line orientation are distinguished: System A (NNE-SSW) and System B (NE-SW/ENE-WSW). The landforms considered are covered with till consisting of two subunits, what reflects two subsequent ice-sheet movement periods in the Late Weichselian but without releasing the area from ice-sheet cover. The subunits can be identified by changes in their petrographic composition – up to ten times more erratics of local provenance in the upper one than in the lower one. Ice flow direction during deposition of both till subunits, based on the till fabric of each of the three analysed sections, coincides with System A of the crest-lines. However, most of the till-covered hills fit System B, which suggests that they retained their previous (older than Late Weichselian) orientation. The complex relief of the Tczew Hump has a palimpsest nature and its arrangement emerged in several stages: (1) formation of the primeval relief before the Late Weichselian (hills built of sediments of heterogeneous ages); (2) partial relief reshaping in subglacial conditions during the two, successive, ice-flow events in the Late Weichselian (till-covered hills, clear bipartition of the till); (3) development of additional landforms during deglaciation − typically not covered with till (or with flow till on the slopes only), showing an orientation determined by the crevasse system developed in the ice.
- Published
- 2019
49. Quantification of historical landscape change on the foreland of a receding polythermal glacier, Hørbyebreen, Svalbard
- Author
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Aleksandra M. Tomczyk, Krzysztof Pleksot, David J.A. Evans, Wojciech Ewertowski, David H. Roberts, and Marek Ewertowski
- Subjects
geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Glacier ,010502 geochemistry & geophysics ,01 natural sciences ,Debris ,Crevasse ,Arctic ,Paraglacial ,Moraine ,Glacial period ,Meltwater ,Geomorphology ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
The assessment of multidecadal scale change in a polythermal glacial landsystem in the high Arctic is facilitated by a quantitative approach that utilises time series of aerial photographs, satellite images, digital elevation models, and field geomorphological mapping. The resulting spatiotemporal analysis illustrates a transition from glacial to proglacial/paraglacial conditions indicating that (1) the areal coverage of ice between the maximum LIA extent and 2013 decreased from 29.35 to 16.07 km2, which is a reduction in the glacierized area in the catchment from 62% to 34%; (2) the ice volume loss in the proglacial area amounted to 214.9 (±3%) million m3, which was attributed mostly to ablation of the glacier snout but to a lesser extent the degradation of ice-cored landforms; (3) the transition from areas formerly covered by glacier ice to ice-cored moraines, glacifluvial deposits, and other landforms was the most intense in the period 1990–2013; (4) two end member scenarios (polythermal glacial landsystem domains) evolve during glacier recession, each one dictated by the volume of debris in englacial and supraglacial positions, and include (a) subglacial surfaces (limited englacial and supraglacial debris) related to temperate basal ice and (b) ice-cored lateral moraines and moraine-mound complexes (significant supraglacial debris accumulations) related to marginal cold-based ice. An additional assemblage of geometric ridge networks (discrete or linear englacial and supraglacial debris concentrations) relates to crevasse and hydrofracture infill branching out from an esker complex and is indicative of either surging or later rapid release of pressurised meltwater from temperate to cold-based parts of the former glacier snout.
- Published
- 2019
50. Sedimentary characteristics and pattern of distributary channels in shallow water deltaic red bed succession: A case from the Late Cretaceous Yaojia formation, southern Songliao Basin, NE China
- Author
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Luxing Dou, Dongsheng Zang, Shuwei Mao, Zecheng Wang, Zhidong Bao, Jiahong Zhao, Jian Song, and Li Zhang
- Subjects
Delta ,010504 meteorology & atmospheric sciences ,Geochemistry ,Fluvial ,Structural basin ,010502 geochemistry & geophysics ,Geotechnical Engineering and Engineering Geology ,01 natural sciences ,Sedimentary structures ,Waves and shallow water ,Fuel Technology ,Crevasse ,Sedimentary rock ,Progradation ,Geology ,0105 earth and related environmental sciences - Abstract
Shallow water delta developed during the Late Cretaceous greenhouse climate depositing in the red bed succession of the Yaojia Formation in the Southern Songliao Basin, NE China. The shallow water delta deposits provide an opportunity to understand the influence of high discharge variability in a semi-arid climate on the fluvial patterns, internal sedimentary details, and reservoir quality of distributary channels. The sedimentary process of the shallow water delta in the Yaojia Formation was controlled by a dual-stage process, including a high-flow stage and a low-flow stage within a semi-arid paleoclimate. During the high-flow stage, crevasse channels formed through avulsion of major distributary channels on the delta plain. Subaqueous terminal distributary channels and mouth bars formed at the delta front during progradation of the delta. During the low-flow stage after flood events, crevasse channels were abandoned and frequently exposed becoming reddish in color. This process can be reason for the classification for two main types of distributary channels: major distributary channels and crevasse channels in the delta plain. Sand bodies in distributary channels are distinguished by sedimentary structures indicate critical and supercritical flow conditions. Based on well logs and 3D seismic data, the sand distribution of was analyzed from the sandstone isopach map of the 2nd sand bed in the first member of the Yaojia Formation. The framework sand belts develop coincides with distribution of the major distributary channels. Based on detailed observational and reservoir test data from cores, the distribution of major distributary channels revealed a belt of high-quality reservoirs in the shallow water delta. This study provides a new perspective on the sedimentary pattern of distributary channels in shallow water deltas with high discharge variability, which has important implications for reservoir exploration in lacustrine basins.
- Published
- 2018
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