scholarly journals Lateral variation in slab window viscosity inferred from global navigation satellite system (GNSS)–observed uplift due to recent mass loss at Patagonia ice fields

Geology ◽  
2021 ◽  
Author(s):  
Raymond M. Russo ◽  
Haipeng Luo ◽  
Kelin Wang ◽  
Boudewijn Ambrosius ◽  
Victor Mocanu ◽  
...  
Keyword(s):  
Mass Loss ◽  
Three Dimensional ◽  
Element Model ◽  
Satellite System ◽  
Ice Age ◽  
Ridge Subduction ◽  
The North ◽  
Order Of Magnitude ◽  
Ice Field ◽  
Slab Window

The geographic coincidence of the Chile Ridge slab window and the Patagonia ice fields offers a unique opportunity for assessing the effects of slab window rheology on glacial isostatic adjustment (GIA). Mass loss of these ice fields since the Little Ice Age causes rapid but variable crustal uplift, 12–24 mm/yr around the North Patagonia ice field, increasing to a maximum of 41 mm/yr around the South Patagonia ice field, as determined from newly collected or processed geodetic data. We used these observational constraints in a three-dimensional Maxwell viscoelastic finite element model of GIA response above both the subducting slab and slab window in which the upper-mantle viscosity was parameterized to be uniform with depth. We found that the viscosity of the northern part of the slab window, ~2 × 1018 Pa·s, is lower than that of the southern part by approximately an order of magnitude. We propose that this along-strike viscosity contrast is due to late Cenozoic ridge subduction beneath the northern part of the slab window, which increases asthenospheric temperature and reduces viscosity.

scholarly journals Mass Footprints of the North Pacific Atmospheric Blocking Highs

2015 ◽  
Vol 28 (12) ◽  
pp. 4941-4949 ◽  
Author(s):  
Tae-Won Park ◽  
Yi Deng ◽  
Wenhong Li ◽  
Song Yang ◽  
Ming Cai
Keyword(s):  
Mass Loss ◽  
North Pacific ◽  
Three Dimensional ◽  
Low Frequency ◽  
Lower Troposphere ◽  
Decay Stage ◽  
The North ◽  
Detection And Attribution ◽  
Blocking High ◽  
The North Pacific

Abstract The mass footprints associated with atmospheric blocks over the North Pacific are evaluated by constructing daily tendencies of total mass over the blocking domain from three-dimensional mass fluxes throughout the life cycle of a composite blocking event. The results highlight the major role of mass convergence driven by low-frequency (with periods >1 week) atmospheric disturbances during both the development and decay stage of a block. Specifically, low-frequency eddies are responsible for the accelerated mass buildup 4 days prior to the peak intensity of a block, and they also account for the rapid mass loss afterward. High-frequency, subweekly scale disturbances have statistically significant positive contributions to the mass loss during the decay stage, and also show weak negative contributions to the development of the blocking high prior to the peak of the high. The majority of the mass convergence (divergence) responsible for the intensification (decay) of the blocking high occurs in the middle-to-lower troposphere and is largely attributed to mass flux driven by low-frequency meridional (zonal) winds. Also discussed are the implications of this new mass perspective of atmospheric blocks for understanding dynamics of blocking highs and for model bias detection and attribution.

scholarly journals Rheology of ice at the bed of Engabreen, Norway

2000 ◽  
Vol 46 (155) ◽  
pp. 611-621 ◽  
Author(s):  
Denis Cohen
Keyword(s):  
Three Dimensional ◽  
Field Measurements ◽  
Element Model ◽  
Basal Ice ◽  
Dimensional Finite Element ◽  
Ice Field ◽  
Frictional Forces ◽  
Two Parameters ◽  
Three Dimensional Finite Element ◽  
Sediment Layers

AbstractA three-dimensional finite-element model is used to analyze field data collected as dirty basal ice flowed past an instrumented obstacle at the bed of Engabreen, a temperate glacier in northern Norway The ice is modeled as an incompressible power-law fluid, with viscosity , where ΠD is the second invariant of the stretching tensor, and B and n are two parameters. Using measurements obtained in 1996 and 1997, two values of B are obtained, one using the measured normal stress difference across the obstacle, and the other using the measured bed-parallel force over the instrument. These two values are not equal, probably owing to small frictional forces at the bed unaccounted for in the numerical model. Hence, B ranges between 1.9 × 107 and 3.2 × 107 Pa s1/3 in 1996, and between 2.2 × 107 and 4.1 × 107 Pa s1/3 in 1997. These values are smaller than measured elsewhere for clean glacier or laboratory ice. Field measurements of water content, fabric and texture of the basal ice suggest that unbound water between thin sediment layers and lamellae of clean ice may act as a lubricant and significantly weaken the ice. Near-isotropic fabrics indicate that preferred fabric orientation does not enhance the deformation.

scholarly journals GEOMATIC METHODS APPLIED TO THE CHANGE STUDY OF THE LA PAÚL ROCK GLACIER, SPANISH PYRENEES

2019 ◽  
Vol XLII-2/W13 ◽  
pp. 1771-1775
Author(s):  
A. Martínez-Fernández ◽  
E. Serrano ◽  
J. J. Sanjosé ◽  
M. Gómez-Lende ◽  
A. Pisabarro ◽  
...  
Keyword(s):  
Laser Scanning ◽  
Satellite System ◽  
Ice Age ◽  
Rock Glacier ◽  
Glacier Surface ◽  
The North ◽  
Spanish Pyrenees ◽  
Gnss Receivers ◽  
Rock Glaciers ◽  
Global Navigation Satellite

<p><strong>Abstract.</strong> Rock glaciers are one of the most important features of the mountain permafrost in the Pyrenees. La Paúl is an active rock glacier located in the north face of the Posets massif in the La Paúl glacier cirque (Spanish Pyrenees). This study presents the preliminary results of the La Paúl rock glacier monitoring works carried out through two geomatic technologies since 2013: Global Navigation Satellite System (GNSS) receivers and Terrestrial Laser Scanning (TLS) devices. Displacements measured on the rock glacier surface have demonstrated both the activity of the rock glacier and the utility of this equipment for the rock glaciers dynamic analysis. The glacier has exhibited the fastest displacements on its west side (over 35&amp;thinsp;cm&amp;thinsp;yr<sup>&amp;minus;1</sup>), affected by the Little Ice Age, and frontal area (over 25&amp;thinsp;cm&amp;thinsp;yr<sup>&amp;minus;1</sup>). As an indicator of permafrost in marginal environments and its peculiar morphology, La Paúl rock glacier encourages a more prolonged study and to the application of more geomatic techniques for its detailed analysis.</p>

A Study on Motions and Connector Loads for a New Type of Two-Module Semi-Submersible

2019 ◽  
Author(s):  
Jun Ding ◽  
Chao Tian ◽  
Yuji Miao ◽  
Zhengwei Zhang ◽  
Zhanhua Zhao ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Element Model ◽  
Short Term ◽  
Term Forecast ◽  
Dimensional Finite Element ◽  
Order Of Magnitude ◽  
New Type ◽  
The Subject ◽  
Three Dimensional Finite Element ◽  
Marine Platform

Abstract The hydrodynamic model and three-dimensional finite element model of a new type of two-module marine platform were built for the subject of research. The motions and connector loads were predicted based on the COMPASS THAFTS software and the results were in agreement with the model tests. It shows that the new type platform has a good sea keeping performance. On the other hand, the short-term forecast results indicate that the connector loads, Fz, is larger than other two directions, approaching 200t. The connector loads, Fx and Fy, are usually in the order of magnitude of tens tons. Some useful conclusions obtained in this paper can provide an important reference for the optimal design and construction of the new type platform and its connector system.

scholarly journals Three-dimensional modelling of the dynamics of Johnsons Glacier, Livingston Island, Antarctica

2004 ◽  
Vol 39 ◽  
pp. 1-8 ◽  
Author(s):  
Carlos Martín ◽  
Francisco Navarro ◽  
Jaime Otero ◽  
María L. Cuadrado ◽  
María I. Corcuera
Keyword(s):  
Water Pressure ◽  
Three Dimensional ◽  
Element Model ◽  
Glacier System ◽  
Ice Surface ◽  
Glacier Terminus ◽  
Livingston Island ◽  
Dimensional Finite Element ◽  
Order Of Magnitude ◽  
Three Dimensional Finite Element

AbstractA new three-dimensional finite-element model of the steady-state dynamics of temperate glaciers has been developed and applied to Johnsons Glacier, Livingston Island, Antarctica, with the aim of determining the velocity and stress fields for the present glacier configuration. It solves the full Stokes system of differential equations without recourse to simplifications such as those involved in the shallow-ice approximation. Rather high values of the stiffness parameter B (∼0.19–0.23MPaa1/3) are needed to match the observed ice surface velocities, although these results do not differ much from those found by other authors for temperate glaciers. Best-fit values of the coefficient k in the sliding law (*2.2–2.7 x 103m a–1MPa–2) are also of the same order of magnitude as those found by other authors. The results for velocities are satisfactory, though locally there exist significant discrepancies between computed and observed ice surface velocities, particularly for the vertical ones. This could be due to failures in the sliding law (in particular, the lack of information on water pressure), the use of an artificial down-edge boundary condition and the fact that bed deformation is not considered. For the whole glacier system, the driving stress is largely balanced by the basal drag (80% of the driving stress). Longitudinal stress gradients are only important in the divide areas and near the glacier terminus, while lateral drag is only important at both sides of the terminal zone.

scholarly journals The sensitivity of GNSS measurements in Fennoscandia to distinct three-dimensional upper-mantle structures

2013 ◽  
Vol 5 (2) ◽  
pp. 2389-2418
Author(s):  
H. Steffen ◽  
P. Wu
Keyword(s):  
Upper Mantle ◽  
Gravity Data ◽  
Three Dimensional ◽  
High Sensitivity ◽  
Element Model ◽  
Satellite System ◽  
Underlying Structure ◽  
Gnss Measurements ◽  
Global Navigation Satellite ◽  
Three Dimensional Finite Element

Abstract. We present the sensitivity of Global Navigation Satellite System (GNSS) measurements at selected GNSS stations used both in the EUREF Permanent Network as well as in the BIFROST project to distinct areas in a laterally heterogeneous upper mantle beneath Fennoscandia. We therefore use a three-dimensional finite element model for glacial isostatic adjustment (GIA) calculations. The underlying structure is based on the S20A seismic tomography model, whose shear-wave velocities have been transformed into a viscosity structure of the upper mantle. Lower mantle is not investigated as previous results showed negligible sensitivity of Fennoscandian GIA data to it. We subdivide the upper mantle in four layers with lateral viscosity structure. Areas with similar viscosity within a layer are combined to larger blocks. Further subdivision is made into areas inside and outside the formerly glaciated areas. This leads to about 20 differently shaped areas per layer. We then calculate the sensitivity kernels at 10 selected GNSS stations for all blocks in comparison to a well-fitting one-dimensional GIA model. We find that GNSS stations are most sensitive to mantle viscosity in the near surrounding of the station, i.e. in the nearest about 250 km, and only within the formerly glaciated area. This area can be enlarged up to 800 km when velocities of stations in the uplift center are investigated. There is no indication of sufficiently high sensitivity of all investigated GNSS stations to regions outside the glaciated area. We also note that in the first mantle layer (70–250 km depth) below the lithosphere, there is only small sensitivity to parts along the Norwegian coast. Most prominent features in the Fennoscandian upper mantle may be detected in the second (250–450 km depth) and third layer (450–550 km depth). In future investigations on the lateral viscosity structure using GNSS measurements one should only consider GNSS stations within the area of former glaciation. They can be further grouped to address certain areas. In a combination with other GIA data, e.g. relative sea-level and gravity data, it is then highly recommended to assign more weight on those GNSS results with high sensitivity in order to determine the viscosity of a certain region.

scholarly journals Supplemental Material: Lateral variation in slab window viscosity inferred from global navigation satellite system (GNSS)–observed uplift due to recent mass loss at Patagonia ice fields

2021 ◽  
Author(s):  
Raymond M. Russo ◽  
Victor Mocanu ◽  
et al.
Keyword(s):  
Mass Loss ◽  
Global Navigation Satellite System ◽  
Satellite System ◽  
Modeling Method ◽  
Navigation Satellite ◽  
Lateral Variation ◽  
Uplift Rates ◽  
Global Navigation Satellite ◽  
Gnss Data ◽  
Slab Window

Modeling method, Table S1 (newly obtained uplift rates for the ten continuous GNSS sites shown in Figure1A),Table S2 (slab window viscosity values and RMS data), supplemental figures, and the weekly solutions for GNSS data used in the study.<br>

scholarly journals Accelerated mass loss of Himalayan glaciers since the Little Ice Age

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ethan Lee ◽  
Jonathan L. Carrivick ◽  
Duncan J. Quincey ◽  
Simon J. Cook ◽  
William H. M. James ◽  
...  
Keyword(s):  
Mass Loss ◽  
Little Ice Age ◽  
Ice Age ◽  
Orographic Effects ◽  
Rates Of Change ◽  
Himalayan Glaciers ◽  
Order Of Magnitude ◽  
The Himalaya ◽  
Rapid Mass

AbstractHimalayan glaciers are undergoing rapid mass loss but rates of contemporary change lack long-term (centennial-scale) context. Here, we reconstruct the extent and surfaces of 14,798 Himalayan glaciers during the Little Ice Age (LIA), 400 to 700 years ago. We show that they have lost at least 40 % of their LIA area and between 390 and 586 km3 of ice; 0.92 to 1.38 mm Sea Level Equivalent. The long-term rate of ice mass loss since the LIA has been between − 0.011 and − 0.020 m w.e./year, which is an order of magnitude lower than contemporary rates reported in the literature. Rates of mass loss depend on monsoon influence and orographic effects, with the fastest losses measured in East Nepal and in Bhutan north of the main divide. Locally, rates of loss were enhanced with the presence of surface debris cover (by 2 times vs clean-ice) and/or a proglacial lake (by 2.5 times vs land-terminating). The ten-fold acceleration in ice loss we have observed across the Himalaya far exceeds any centennial-scale rates of change that have been recorded elsewhere in the world.

Non-Iterative Mode Shape Expansion for Beam Structures Based on Coordinate Decomposition

2013 ◽  
Vol 284-287 ◽  
pp. 503-507
Author(s):  
Fu Shun Liu ◽  
Wen Wen Chen ◽  
Chun Fu Peng ◽  
Wei Li
Keyword(s):  
Finite Element ◽  
Mode Shape ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Expansion Method ◽  
Element Model ◽  
Numerical Studies ◽  
Order Of Magnitude ◽  
Convergence Performance ◽  
Weighting Coefficients

The direct mode shape expansion method is an iterative technique, then one can conclude that the convergence performance maybe challenged when applied to three-dimensional structures. In addition, mode shape values at different DOFs (degrees-of-freedom) sometimes are not in a same order of magnitude, which will produce much error for the estimation of small values of unmeasured mode components. Thus, this paper proposed a non-iterative mode shape expansion method based on coordinate decomposition and neglecting modelling errors between the finite element model and the experimental structure. The advantage of coordinate decomposition is that the unmeasured components of mode shape values could be estimated with different weighting coefficients, even in a physical meaningful interval. Numerical studies in this paper are conducted for a 30-DOF (degree-of-freedom) cantilever beam with multiple damaged elements, as the measured modes are synthesized from finite element models. The results show that the approach can estimate unmeasured mode shape values at translational and rotational DOFs in x, y and z directions with different weighting coefficients, respectively; and better mode shape expansion results can be obtained when proper constraints are employed.

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