Elmer/Ice News

Backstress induced failure at Thwaites Eastern Ice Shelf

The Thwaites Eastern Ice Shelf (TEIS), the only remaining pinned floating extension of Thwaites Glacier, has Modelled and observed fracture on TEIS (from the article)undergone a phase of significant fragmentation during the last decade.  Observations as well as simulations support the theory that the glacier's acceleration increased the damage in the floating part of the ice by backstress imposed from its pinning points. HiDEM (Helsinki Discrete Element Model) simulations primed with basal friction coefficients obtained by means of Elmer/Ice simulations using data assimilation indicate a significant zone of shear, upstream of the main pinning point, seeding damage on the shelf. Subsequently, basal melting and positive feedback between damage and strain rates weakened TEIS, allowing damage to accumulate. Despite a diminishing backstress caused by a shrinking pinning point, accumulation of damage has ensured that the ice in TEIS in the shear zone remained the weakest link in the system. Besides hydro-fracturing and detachment from pinning points, this study suggest a third mechanism for ice-shelf instability: backstress triggered failure. 

Read more: Benn, D. I., A. Luckman, J.A. Åström, A. Crawford, S.L. Cornford, S.L.. Bevan, T. Zwinger, R. Gladstone, K. Alley, E. Pettit, and J. Bassis, 2022, Rapid fragmentation of Thwaites Eastern Ice Shelf.  The Cryosphere, 16, 2545–2564, doi:10.5194/tc-16-2545-2022 

 

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Dynamics of tidewater glaciers in reaction to calving events

Significant change in the dynamics of tidewater glaciers after a calving event are mainly tied to a sudden loss of resistive stresses. This article investigates how such a stress perturbation affects the whole glacier upstream. Simulations (using Elmer/Ice) and perturbation theory revealed that calving events and subsequent terminus readvance produce quasi-periodic, sawtooth oscillations in stress that originate at the terminus and propagate upstream with speeds significantly exceeding ice velocities. In laterally resisted glaciers, these signals decay within an upstream distance equivalent to a few ice thicknesses. Terminus fluctuations caused by individual calving events tend to be much higher frequency than climate variations. Thus, individual calving events have little direct impact on the viscous delivery of ice to the terminus. This suggests that the primary mechanism by which calving events can trigger instability is by causing fluctuations in stress that weaken the ice and lead to additional calving and sustained terminus retreat. Our results further demonstrate a stronger response to calving events in simulations that include the full stress tensor, highlighting the importance of accounting for higher order stresses when developing calving parameterizations for tidewater glaciers.

Read more: Amundson, J., M. Truffer, and T. Zwinger, 2022. Tidewater glacier response to individual calving events. Journal of Glaciology, 1-10, doi:10.1017/jog.2022.26 

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Evolution of Da Anglong Glacier, Western Tibetan Plateau

The response of glaciers in Tibet Plateau and the wider area of High Mountain Asia to on-going and future climatefig15-2.jpg change is a topic of concern. Little work has been done on small Tibetan Plateau glacier responses to climate warming with mechanistic models, but no simulations on a large Tibet glacier to our knowledge. We apply three-dimensional full-Stokes model to simulate the evolution of Da Anglong Glacier, a large glacier (6.66 km2) in the western Tibet Plateau from the year 2016 to 2098, using projected temperatures and precipitations from the 25-km-resolution RegCM4 nested within 3 Earth System Models simulating the RCP2.6 and RCP8.5 scenarios. The surface mass balance is estimated by degree-day method using a quadratic elevation-dependent precipitation gradient. A geothermal flux of 60 mW m-2 produces a better fit to measured surface velocity than lower heat fluxes, and represents a new datum in this region of sparse heat flux observations. The ensemble mean simulated glacier volume loss during 2016-2098 amounts to 38% of the glacier volume in the year 2016 under RCP2.6 and 83% under RCP8.5. Simulation from 2016 to 2098 without ice dynamics leads to an underestimation of ice loss of 22-27% under RCP2.6 and 16-24% under RCP8.5, showing that ice dynamics play an important amplifying factor in ice loss for this glacier, unlike for small Tibetan glaciers where SMB dominates glacier change.

Read more:  Zhao W., L. Zhao, L. Tian, M. Wolovick and J.C. Moore, 2022. Simulating the Evolution of Da Anglong Glacier, Western Tibetan Plateau over the 21st Century. Water, 14(2), 271, doi:10.3390/w14020271 

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