We welcome contributions on GIA's effects across various scales, including geodetic measurements, complex GIA modelling, GIA-induced sea-level changes, the Earth's response to current ice-mass changes, and overview on emerging GIA data collections. We also invite abstracts on GIA's impact on nuclear waste sites, volcanism, groundwater, permafrost, and carbon resources. We especially appreciate new model developments in local, high spatial and temporal resolution for GIA assessments, results of fully coupled ice dynamics-GIA models, studies of broader environmental relevance, and improved GIA corrections for other geoscientific fields.
Orals: Mon, 4 May, 10:45–12:30 | Room -2.31
Owing to vertical land movement (VLM), Norway has long had falling or stable relative sea levels and is yet to feel the impacts of sea-level rise. The danger is that this can foster a false sense of security, where the long-term risks are not understood or ignored.
Results from a recent national assessment show that sea-level rise is starting to push up water levels in some parts of the coast, most notably in Western and Southern Norway. Owing to global warming, Norway is transitioning from a country with on average falling or stable relative sea level, to one with rising relative sea levels. Measured coastal average geocentric (the ocean surface) sea-level rise is 2.3 ± 0.3 mm/yr for the period 1960-2022, i.e., an increase of 14 ± 2 cm over that time.
IPCC AR6 sea-level projections are tailored to the Norwegian coast using the semi-empirical model NKG2016LU to estimate VLM and associated geoid changes. Although the broad pattern of regional VLM is caused by glacial isostatic adjustment, there is evidence of other processes driving changes, especially on local scales. Projections show Norway’s coastal average relative sea-level change for 2100, compared to the period 1995-2014, will range from 0.13 m (likely -0.12 to 0.41 m) for the very low emissions scenario (SSP1-1.9) to 0.46 m (likely 0.21 to 0.79 m) for the very high emissions scenario (SSP5-8.5). A rise between 40% and 70% lower than the projected global average. For scenarios with higher greenhouse gas emissions than SSP1-2.6, a majority of the coast will likely experience relative sea-level rise for 2100.
Sea-level rise will increase flood risk in Norway by pushing up the height of sea level extremes (the combination of tides, storm surges, and waves) which will reach higher and further inland. Sea-level rise will also drive sharp increases in flooding frequency. There are large differences in the timing and extent of flooding frequency changes that partly depend on projected sea level and the regional VLM signal. Western and Southern Norway will experience increases in flooding frequency first.
In summary, careful treatment of VLM and its uncertainties is important for assessing observed sea level and tailoring national sea-level projections for their eventual use in adaptation planning. VLM also has important implications for how sea level information is communicated to decision makers and stakeholders.
How to cite: Simpson, M. J. R., Bonaduce, A., Borck, H. S., Breili, K., Breivik, Ø., Ravndal, O. R., and Richter, K.: Sea-Level Rise and Extremes in Norway: Observations and Projections Based on IPCC AR6, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5229, https://doi.org/10.5194/egusphere-egu26-5229, 2026.
A glacial forebulge is a load-driven bending-related upheaval of the lithosphere outside a glaciated area. As a typical feature of the glacial isostatic adjustment process the forebulge forms contemporaneously to the depression of the lithosphere below the ice sheet. Forebulge development and collapse related to the last glaciation has led to significant topographic changes in the order of several tens of meters in North America and Europe. Furthermore, forebulge behaviour has a significant effect on the evolution of lithospheric stresses, which can induce intraplate earthquakes, even in areas that were not covered by an ice sheet. Therefore, quantifying the present-day position, amplitude and subsidence of the forebulge is crucial for the estimation of future sea-level changes, the evolution of fluvial networks and understanding the distribution of deglaciation seismicity. Though the forebulge of the last glaciation attracted attention over more than one century, quantitative descriptions on the geometry and position of the forebulge are still rare. Key controlling factors for the position, amplitude and dynamic behaviour of the forebulge are the flexural rigidity of the lithosphere, asthenospheric flow processes, as well as ice-sheet geometry and history. Numerical simulations indicate that a higher flexural rigidity of the lithosphere leads to a lower amplitude of the forebulge and a greater distance to the load. Forebulge formation is also supported by the flow of asthenospheric material, which can occur as channel-flow or deep flow. In case of channel-flow, the forebulge shows an outward migration during collapse, whereas deep-flow leads to an inward migration. A non-linear mantle rheology is seen as a reason for stationary forebulge collapse. The height of the glacial forebulge of the last glaciation was in a range of several tens of meters, with a greater height in North America than in Europe due to the larger Laurentide ice sheet.
How to cite: Brandes, C., Steffen, H., Steffen, R., Li, T., and Wu, P.: Quantifying the forebulge of the last glaciation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2315, https://doi.org/10.5194/egusphere-egu26-2315, 2026.
Glacial isostatic adjustment (GIA) induces lithospheric bending that can strongly influence depositional systems located within ice-sheet forebulges. While previous studies have documented the role of GIA in river-network reorganization during the last glacial cycle, its impact on sedimentary systems earlier in the Quaternary remains poorly constrained.
Here, we investigate the pre-glacial Daumantai Formation, exposed in several outcrops beneath the oldest tills in the Baltija Highlands of eastern Lithuania. This fluvial succession was dated using combined 10Be–26Al exposure–burial dating to ~0.95 ± 0.1 Ma, while the same approach indicates that the overlying tills were deposited only ~30–50 kyr later. Importantly, the succession records a distinct change in palaeocurrent directions, initially toward the southeast and subsequently toward the northwest, occurring prior to the first documented advance of the Fennoscandian Ice Sheet (FIS) into the region. This shift is interpreted as a reorganization of the river network rather than merely a modification of river planform geometry, as the palaeocurrent reorientation is consistently documented at several sites across distances exceeding 10 km.
GIA was simulated using the ICEAGE normal-mode modelling framework to assess the potential role of lithospheric bending and associated slope changes in river-network reorganization. Four ice-sheet configurations were tested: (1) a late Gauss and (2) an early Matuyama extent after Batchelor et al. (2019, https://doi.org/10.1038/s41467-019-11601-2), (3) an additional, larger ice sheet extending ~150 km northwest of the study area, and (4) a MIS 20–24 ice-sheet extent from Batchelor et al., which directly overlies the analysed succession. A 380 kyr modelling scenario included five glacial cycles comprising ice growth, deglaciation, and ice-free periods, with 40 kyr and 100 kyr periodicities and increasing amplitudes. The modelling results indicate that the study area was affected by forebulge development associated with all tested ice-sheet extents. The two smaller ice sheets induced southeastward surface tilting, whereas the larger configuration produced northwestward tilting, with maximum slope changes reaching ~0.002°.
The resulting time-dependent uplift and subsidence fields were subsequently used as inputs for landscape evolution modelling to investigate the impact of episodic glacial loading and unloading on surface processes. Erosion and sedimentation were simulated using a stream-power–law, finite-difference approach under imposed time-varying three-dimensional deformation. Preliminary results suggest that repeated north–south tilting associated with glacial cycles exerts a strong control on fluvial dynamics and can locally lead to drainage reversals.
The postdoctoral project CosmoLith was caried out under the “New Generation Lithuania” plan (Nr. 10-036-T-0008) financed under the European Union economic recovery and resilience facility instrument NextGenerationEU. The research was supported by the Slovak Research and Development Agency under the contract No. APVV-21-0281.
How to cite: Šujan, M., Bitinas, A., Steffen, H., Balázs, A., Gedminienė, L., Kováčová, M., Chyba, A., Damušytė, A., Pan, R., Aherwar, K., and Rózsová, B.: Testing glacial isostatic adjustment as a cause of Early Pleistocene river network reorganization in the area of Lithuania (NE Europe), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10025, https://doi.org/10.5194/egusphere-egu26-10025, 2026.
The deglacial forebulge along the Atlantic coasts of North America and Europe has been a key area for glacial isostatic adjustment (GIA) studies. Relative sea level (RSL) changes in this region are highly sensitive to the 3D Earth structure, and the area hosts abundant RSL data that can help constrain the 3D Earth structure. However, many previous studies either relied primarily on 1D Earth models or adopted 3D structures without systematically exploring the magnitude of lateral heterogeneity or the uncertainty associated with deglacial ice histories.
Here, we use the latest standardized deglacial RSL databases from the Atlantic coasts of North America and Europe for comparison with 3D GIA models coupled with two widely used ice models, ICE-6G_C and ANU-ICE. Our 3D Earth model consists of a 1D background viscosity model (ηo) and lateral viscosity variations; the latter are derived from shear velocity anomalies in a seismic tomography model and scaled by a factor (β) denoting the magnitude of lateral heterogeneity. We explore a range of ηo and β to assess the sensitivity of RSL predictions to both the background viscosity and the magnitude of lateral heterogeneity. The RSL databases include sea-level index points and limiting data, which we further classify by depositional setting (base of basal, basal, intercalated). We compare the RSL data to the GIA model predictions using a weighted misfit approach that reflects data type and interpretive uncertainty.
We find that 3D Earth structure has significant influence on RSL predictions, and the optimal 3D models substantially improve the fit to RSL data compared with 1D GIA models (e.g., ICE-6G_C VM5a). The Atlantic coast RSL datasets from North America and Europe favor different combinations of ηo and β, although the former provides stronger constraints owing to its higher spatial coverage and lower data uncertainty. Notably, despite differences in ice history, ICE-6G_C and ANU-ICE prefer similar 3D Earth structures. Ongoing work will quantify the uncertainty of the 3D model resolved by the available RSL data.
How to cite: Li, T. and Walker, J.: 3D Glacial Isostatic Adjustment along the deglacial forebulge of the Atlantic coasts of North America and Europe, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15680, https://doi.org/10.5194/egusphere-egu26-15680, 2026.
During the last deglaciation, the retreating Laurentide Ice Sheet made way for massive proglacial lakes to form and then drain. In a similar fashion, dramatic changes in climate over the deglaciation were reflected in changing groundwater storage through time. We evaluate the impacts of these long-term changes in water storage on Glacial Isostatic Adjustment (GIA) in North America. To do so, we couple the Water Table Model (WTM) – which simulates depth to water table – with a gravitationally self-consistent GIA model to find both changing lake and groundwater storage volumes, and the impacts that these have on changing GIA.
Our WTM results show an evolving water table that includes proglacial and pluvial lakes consistent with the geological record. Lake and groundwater loading deflect topography by tens of metres at some locations. Because depth to water table is topography-dependent, we repeat our WTM simulation using updated topographic inputs and find that water table depth is modified by several metres at some locations. The results are highly heterogeneous, reflecting that GIA and hydroclimate together drive long-term water-table change.
How to cite: Callaghan, K. L., Wickert, A. D., and Austermann, J.: Glacial isostatic adjustment under a changing groundwater load since the Last Glacial Maximum, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15241, https://doi.org/10.5194/egusphere-egu26-15241, 2026.
The hypothesis of the ISVOLC project is that retreat of Icelandic glaciers since the end of the 19th Century has the potential to impact both volcanic and seismic activity. As volcanic activity increased significantly during (and in the <2kyr after) the late Pleistocene deglaciation, it is expected that present day deglaciation will once again effect volcanic activity in Iceland. The unloading of glaciers and subsequent rebound response of the Earth can significantly alter the state of stress in the crust and mantle. Within the ISVOLC project (https://isvolc.is) we have developed a new generation of Finite Element Glacial Isostatic Adjustment (GIA) models, using the COMSOL Multiphysics software package, which employ spaciotemporal estimates of glacier mass balance. Utilizing this new detailed ice history, we simulate GIA numerically and, once best fit earth parameters are found by utilizing InSAR and GNSS measurements, produce revised estimates for stress changes in the crust and mantle. From these we can calculate mantle decompression melting increases and shallow crustal stressing which may already be affecting volcanism and seismicity. We find that rates of total magma production beneath Iceland are enhanced by up to a factor of ~3 due to the glacier retreat induced decompression melting. However, it is highly uncertain when this additional magma will reach the surface and in what volumes. Stress changes around magma bodies at shallow level in the crust can bring such magma bodies closer to or further away from failure, depending on their geometry. Our new models predict stressing rates in the shallow crust that are comparable to those from tectonic extension for volcanic systems, seismic zones, and fissure swarms that are near or underneath Vatnajökull (Bardarbunga, Grímsvötn, northeastern Volcanic Zone, south Northern Volcanic Zone), with a unique pattern for each system. Glacially induced stressing in these areas may significantly shorten the timeline to seismic, diking, or eruptive events and alter the preferred orientations of dike propagation. Stressing rates from glacial mass loss are an order of magnitude smaller for systems beneath smaller glaciers and those not beneath ice (e.g. Askja, Katla, South Iceland Seismic Zone, Tjornes Fracture Zone), but still significant enough to consider when assessing hazard. Efforts in further improving the GIA modeling include effects of more realistic non-linear mantle rheology leading overall to somewhat higher viscosity estimates and more subdued GIA response in the far-field, as well as increases in the rate of magma production predicted by our models. Near-future work will involve the projection of glacial unloading and the subsequent earth response to evaluate effects on long-term hazards.
How to cite: Givens, T., Bellagamba, G., Parks, M., Schmidt, P., Sigmundsson, F., Geirssson, H., O´Hara, C., Sturkell, E., Ófeigsson, B., Drouin, V., Frídriksdóttir, H., Greiner, S., Vallson, G., Halldórsson, H., Magnússon, E., Pálsson, F., and Hreinsdóttir, S.: ISVOLC: Deglaciation and GIA Affecting Crustal and Mantle Stresses in Iceland. Much More Magma?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1014, https://doi.org/10.5194/egusphere-egu26-1014, 2026.
Systematic subsidence of ~1 mm/yr is observed across the Pacific at GNSS sites on islands that lack significant local tectonic and volcanic processes (Altamimi et al., 2023; Ballu et al., 2019; Hammond et al., 2021). However, the horizontal motion of these sites is well described by Pacific plate motion. This suggests that the observed subsidence represents a deeply rooted geophysical signal, rather than just localized deformation.
Both ongoing and past ice mass redistribution are known to produce global deformation. Previous models of recent global ice mass redistribution (Coulson et al., 2021; Riva et al., 2017) predict tenths of a mm/yr of subsidence in far field locations such as the Pacific. In addition, post-LGM GIA models like ICE-6G also predict subsidence in the Pacific on the order of tenths of a mm/yr.
Here we evaluate three new models of the global deformation associated with present day ice mass redistribution. These models use the methods of the elastic loading model originally published by Coulson et al. (2021), utilizing new mass change estimates with increased spatial and temporal coverage as input. The three updated models all use Velicogna et al.’s (2020) mass change estimates for the Antarctic and Greenland ice sheets, paired with global glacier mass change estimates from either Ciraci et al. (2020), the Copernicus group (Dussaillant et al., 2024), or Hugonnet et al. (2021). These models are evaluated at selected GPS sites near field to glaciers in regions such as SE Alaska, Greenland, etc., as well as 27 Pacific GPS sites located far field from ice mass change. We also use these far field sites to evaluate 39 different long-term GIA models that predict the present-day viscoelastic response of the earth to past loading.
We find that all three models of elastic deformation due to recent global ice mass change produce very similar results in the far field. The most significant differences in the models are seen in the near field in SE Alaska and Svalbard. Additionally, there is a set of 15 long-term GIA models that improve the fit of both the horizontal and vertical observations in the Pacific when used in combination with an ongoing cryospheric loading model to correct the GPS data. Overall, we find that the sum of the deformation due to ongoing ice mass changes and long-term GIA explains about half of the subsidence signal that we observe in the far field.
Studies of the contribution of different components of barystatic sea level (BSL) suggest that though cryospheric melting is the largest contributor, non-cryospheric terrestrial water storage (TWS) could be responsible for ~17 – 25% of BSL over the past couple of decades (Nie et al., 2025; McGirr et al., 2024). Since changes in TWS may represent a non-trivial global loading signal, we choose to also consider if deformation associated with TWS may explain part of the residual ~0.5 mm/yr subsidence signal that we see in the far field after our cryospheric loading corrections.
How to cite: Vance, K., Freymueller, J., and Coulson, S.: Evaluating global models of deformation from ongoing ice mass changes and long-term GIA, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13801, https://doi.org/10.5194/egusphere-egu26-13801, 2026.
The Greenland Ice Sheet (GrIS) is currently undergoing substantial mass loss, with major consequences for both the Earth system and human societies, including a significant contribution to the ongoing acceleration of global mean sea level rise. Accurately estimating the GrIS mass balance therefore represents a major focus of current research. However, it remains challenging and, to date, still imprecise.
One of the main reasons is Glacial Isostatic Adjustment (GIA) - the viscoelastic response of the solid Earth to the growth and decay of ice sheets at its surface. Because geodetic observations are among the most used tools to quantify ice mass changes, robust estimates of GIA corrections are essential for the accurate interpretation of these measurements.
This study focuses on deformations induced by ice mass loss since the Little Ice Age (LIA) and their impact on present-day vertical land motion inferred from GNSS observations. Using a reconstructed history of the GrIS and its peripheral glaciers, we model LIA-driven viscoelastic deformations assuming different Earth models, exploring a range of values for two rheological parameters: the lithosphere thickness and the upper mantle viscosity. These simulations, combined with corrections for GIA associated with the last glacial maximum and the elastic response to contemporary ice melting, are compared against GNSS observations. Our results explain the uplift rates at most of the GNSS stations and are consistent with existing literature, with LIA-induced vertical land motion best accounted for by a 160 km thick lithosphere and an upper mantle viscosity of 2.73 × 10¹⁹ Pa·s.
As we explore the rheological structure beneath Greenland, we pay particular attention to the southeastern region, where uplift rates are unusually high. Southeastern Greenland exhibits significant lateral variations in mantle viscosity and lithospheric thickness, likely related to the track of soft material left by the Iceland hotspot. Our simulations support the presence of a low viscosity/thin lithosphere zone in this region, and we further investigate its effects by adding to our modeling an asthenospheric layer within the upper mantle.
Overall, this study demonstrates that deformations induced by the LIA constitute a non-negligible contribution to present-day geodetic signals. Accounting for this component is therefore essential to reduce uncertainties in ice mass balance estimates and to better understand Greenland’s contribution to global sea level rise.
How to cite: Gourrion, E., Métivier, L., and Greff-Lefftz, M.: The influence of LIA-induced viscoelastic deformations on geodetic observations in Greenland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12406, https://doi.org/10.5194/egusphere-egu26-12406, 2026.
Vertical land motion in the Great Lakes Basin (GLB) arises from the combined effects of ongoing Glacial Isostatic Adjustment (GIA) and shorter-term environmental and hydrological loadings. Because the present-day GIA hinge line crosses the region, even small errors in separating long-term uplift from elastic responses can strongly bias geophysical interpretations. Over the past two decades, the GLB has experienced pronounced lake-level fluctuations. An analysis of GRACE/FO data indicates minimal Total Water Storage (TWS) changes across the GLB during 2002-2012, a period during which lake levels were relatively stable and vertical motions should therefore reflect GIA alone. In contrast, from 2012 to 2019 lake levels rose to record highs, and since 2020 they have been falling at a comparable rate. The area is densely instrumented with continuous GNSS stations, providing an exceptional opportunity to investigate how long-term GIA and short-term hydrological forcing interact. Our goal is to develop a robust, precise and accurate estimate of the GIA signal so that we can accurately remove GIA from observations and constrain surface/groundwater storage changes.
We compared the predictions of many GIA models with the pre-2012 observations, which should reflect the GIA signal alone, but none of the existing models adequately reproduce the observed data. Despite differences in viscosity structure or ice history, every model produces the same systematic bias: the hinge line (zero uplift) is positioned too far south. However, the shape of the modelled profiles matches the GNSS curvature extremely well. Therefore, we developed a spatial optimization framework to minimize geometric misalignments between GIA model predictions and GNSS vertical velocities across the Great Lakes (2002–2012.5). Seventy-two GIA realizations based on diverse ice histories (ICE-6G_C, ICE-6G_D, ICE-7G_NA, ANU-ICE, NAICE, etc.) and Earth rheologies were subjected to systematic horizontal translations (via a grid search with limits ranging from ±2° to ±8°), with and without allowing for small planar rotations, yielding 576 model-configuration combinations evaluated using RMS misfit, concordance correlation, and 5-fold cross-validation. The best-fitting models achieve the lowest misfits (approximately 0.40 mm/yr), and highest concordance (ccc > 0.90). The models that fit well give very consistent hinge line predictions across the core of our region but are more variable toward the edges of the model domain.
We introduced a hierarchical set of model ensembles constructed by ranking all 576 optimized configurations by post-alignment RMS and grouping them into four tiers: ELITE (RMS ≤ 0.49 mm/yr), GOOD (≤ 0.59 mm/yr), MEDIUM (≤0.79 mm/yr), and ALL (>0.80 mm/yr). These hybrid fields reveal a systematic progression, with the ELITE and GOOD ensembles capturing the GNSS-derived deformation shape with narrow uncertainty bands, while the MEDIUM and ALL ensembles exhibit progressively larger uncertainties that grow with ensemble size. The mean models of the ELITE and GOOD ensembles are nearly identical and provide the most stable uplift geometry and the smallest GPS-calibrated uncertainties, with representative values below 0.18 mm/yr (ELITE) and 0.26 mm/yr (GOOD) for Michigan, demonstrating that tightly constrained multi-model ensembles can outperform any individual GIA realization.
How to cite: Guerra Neto, H. L. and Freymueller, J.: An Empirical Estimate of GIA-Induced Vertical Motion in the Great Lakes Basin Derived from an Ensemble of GIA Models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1437, https://doi.org/10.5194/egusphere-egu26-1437, 2026.
The future stability of the Antarctic Ice Sheet is determined by the marine ice sheet instability (MISI), an amplifying feedback, leading to potentially irreversible retreat. Glacial isostatic adjustment (GIA) potentially provides a stabilizing feedback, yet its influence on the timing and nature of ice-sheet tipping dynamics remains poorly constrained. Using an ensemble of idealized simulations in a synthetic Antarctic-type ice-sheet–shelf system, we systematically investigate how interactions between ice dynamics and the visco-elastic solid Earth affect MISI tipping dynamics under increasing basal ice-shelf melt. We find that the critical thresholds for bifurcation tipping strongly depend on the timescale and spatial extent of Earth deformation, increasing substantially (order of magnitude) relative to a fixed-bed (rigid) case.
For half of the ensemble members, rate-induced tipping occurs when melt rates increase sufficiently rapidly, triggering MISI before the threshold for bifurcation tipping is reached and reducing the effective tipping threshold by up to 80%. Bed uplift cannot halt MISI once initiated, due to rapid grounding-line retreat. We further identify grounding-line overshoots and self-sustained oscillations driven solely by internal ice - Earth interactions.
We find similar dynamics in more realistic simulations of the Antarctic Ice Sheet with a coupled ice sheet - solid Earth and sea-level model considering a three-dimensional Earth structure. Our results highlight that both the magnitude and rate of future climate forcing critically influence Antarctic ice-sheet stability.
How to cite: Albrecht, T., Feldmann, J., Klose, A. K., Wullenweber, N. K., Mojtabavi, S., Klemann, V., and Winkelmann, R.: Rate-induced tipping of ice sheets interacting with the visco-elastic solid Earth, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9816, https://doi.org/10.5194/egusphere-egu26-9816, 2026.
Posters on site: Mon, 4 May, 14:00–15:45 | Hall X2
Horizontal deformation data are not commonly used as constraints in Glacial Isostatic Adjustment
(GIA) studies. In GIA modelling, horizontal displacements are more sensitive to the elastic structure
of the Earth than vertical displacements. Reliable modeling of horizontal motion can therefore help
constrain further lithospheric elastic properties and allow for more realistic stress calculations, which
can be used in studies of e.g. fault stability and magma migration modulated by GIA induced stresses.
Previous GIA benchmarking studies have shown that, for incompressible models, vertical displace-
ments produced by flat-Earth Finite Element (FE) models compare well with solutions obtained using
the spherical harmonic method, whereas horizontal displacements may be significantly biased. The
more recent study by Reusen et al. (2023), focusing on compressible flat-Earth FE models, showed
good agreement in horizontal displacements between FE model with elastic foundations at each density
contrast and spherical harmonic solutions, with progressively improved agreement for decreasing load
radius. However, vertical displacements for the compressible case were not examined. In this specific
case, compressibility is implemented only partially through the so-called material compressibility, which
accounts for volume changes but neglects density variations.
Modelling present-day GIA in Iceland requires small load radii, low mantle viscosities, and thin
elastic lithospheres—parameter ranges that have not yet been fully benchmarked. Here, we extend the
study of Reusen et al. (2023) by considering glacier loads and Earth structures closer to those of Iceland
at the present day glacial retreat. In addition, we also benchmark the vertical displacement. We use a
flat-Earth, material compressible model with an elastic layer overlying a Maxwellian viscoelastic mantle,
applying spring foundations to every density contrast. Our goal is to identify strategies to obtain reliable
displacement and stress outputs from Icelandic GIA models, while quantifying uncertainties in mantle
viscosity and elastic thickness. Our study highlights the importance of benchmarking small icecaps and
thin lithospheres to be used in studies of small glaciated regions.
References
Reusen et al. (2023). “Simulating horizontal crustal motions of glacial isostatic adjustment using
compressible cartesian models”. In: Geophysical Journal International 235(1), pp. 542–553.
How to cite: Bellagamba, G., Schmidt, P., Geirsson, H., Givens, T., and Steffen, H.: Benchmarking Horizontal and Vertical Deformation in Material Compressible Finite Element Models of Glacial Isostatic Adjustment of Iceland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21552, https://doi.org/10.5194/egusphere-egu26-21552, 2026.
Stress changes , such as those imposed by to earthquakes or ice mass loss, lead to viscous relaxation in the Earth’s interior. Stress relaxation is often modelled using steady-state rheological behaviours, based on linear diffusion creep or power-law stress dependence creep. However, rock mechanical experiments and microphysical models show that steady-state flow is always preceded by a transient phase, during which resistance to shear stress can be orders of magnitude lower than at eventual steady state, which leads to higher strain rates than predicted by steady-state flow laws.
We are interested in the effects of transient upper-mantle deformation on surface deformation of the Earth. Deformation at the grain scale can be accommodated by different types of defects in the crystal lattice. We focus on the role of dislocations and their elastic interactions in olivine grains. We use a flow law for dislocation creep that includes the effect of dislocation interactions on strain rates and evolution of dislocation density with strain and time. This flow law is based on new experimental and theoretical work on olivine. It has two main elements: 1) dislocation interactions reduce the amount of available stress driving motion of dislocations and thus of the rate of dislocation creep; 2) evolution of dislocation density is affected by viscous creep. This model leads to transient high strain rates in environments where stress is changing and steady-state (approximately power-law) behaviour sufficiently long after a stress change.
We use the finite element platform (GTECTON) to model the viscoelastic response to surface loads, such as hydrological loading or the loads of melting glaciers. The transient deformation involved may result in fast and slow deformation at different time scales, so numerical stability can become an issue. The sharp non-linearity of the flow laws plays an important role in this instability. The size of time steps in the models is a crucial factor in stability, and leads to a trade-off between accuracy and efficiency. In this study we explore implicit time marching strategies to improve the numerical stability and accuracy of the solutions. This allows us to run efficient models of solid earth deformation for problems in which loads are rapidly changing, where we aim at building a better understanding of the time dependent strength of the upper mantle.
How to cite: Broerse, T., Van Calcar, C., Breithaupt, T., Govers, R., Ioannidi, I., Wallis, D., and Riva, R.: Fast viscous flow in the upper mantle: numerical stability in finite element models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5629, https://doi.org/10.5194/egusphere-egu26-5629, 2026.
Glacial isostatic adjustment (GIA) is identified as a crucial feedback mechanism between ice-sheet dynamics and viscoelastic deformation of the solid Earth. In addition, the interpretation of geodetically inferred ice-mass change requires the consideration of a realistic GIA correction. Specifically in Antarctica, regions of low mantle viscosity can significantly impact ice sheet dynamics due to different feedback strengths.
In this study we discuss the effect of lateral viscosity contrasts on the response of the solid Earth to ice-mass changes in view of bedrock displacement and geoid change. Considering different geometries of low-viscosity bodies, we infer their impact on geodetic observables. As the main question we will investigate to which extent geodetically inferred viscosity values are biased due to the fact that, in general, they are based on assuming a viscosity structure that only varies with depth. Furthermore, such structural features might also impact the interaction between the solid-Earth and the Antarctic ice-sheet dynamics.
This work contributes to the German Climate Modeling Initiative PALMOD.
How to cite: Klemann, V., Schachtschneider, R., Wullenweber, N., Albrecht, T., and Scheinert, M.: Impact of lateral and radial viscosity variations on vertical land motion in view of Antarctic GIA, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9924, https://doi.org/10.5194/egusphere-egu26-9924, 2026.
Tidal forcing induces significant deformation of the Earth, investigated as early as the 19th century by Kelvin and later formalized by Love through the Love number formalism. The viscoelastic response of Earth’s mantle is traditionally modelled using the Maxwell rheology, and more rarely using the Burgers rheology. This work presents a comparative analysis of four viscoelastic rheological models: the Maxwell, Burgers, Andrade, and Sundberg–Cooper models. Although rarely used for the Earth, the Andrade and Sundberg–Cooper models have proven to be relevant for other planetary bodies. Theoretical responses have been developed for these models over a broad frequency range, from the seismic band to very long periods. Model predictions are compared with observations from the IGETS (International Geodynamics and Earth Tide Service) worldwide network of superconducting gravimeters, low-degree time-varying space gravity measurements, and length-of-day variations to better constrain Earth’s mantle rheology and viscosity.
How to cite: Saad, T., Boy, J.-P., and Rosat, S.: Constraining Mantle Rheology with Long-Period Tides:Modeling Earth Tidal Response with Maxwell, Burgers, Andrade, and Sundberg-Cooper models and comparison with superconducting gravimeters, low-degree time-variable gravity & length-of-day observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7241, https://doi.org/10.5194/egusphere-egu26-7241, 2026.
Accurate mantle viscosity structures are essential when modelling glacial isostatic adjustment (GIA). In principle there are two strategies to constrain the viscosity structure. The first one is to invert it from the GIA process itself, which results generally in a radial stratification into upper and lower mantle viscosities and an effective elastic thickness of the lithosphere. These values are usually obtained for the cratonic regions of Laurentide and Fennoscandia, or are further adjusted to represent regions of a different tectonic setting. The second one is to obtain such structures from seismological tomography models, where variations in velocity are transferred to temperature and then to viscosity variations. Whereas the conversion from velocity to temperature is constrained from geodynamics, the conversion of temperature to viscosity involves uncertainty parameters in the Arrhenius law, e.g., the activation enthalpy.
In this study we quantify the dependency of GIA signals on the choice of the activation enthalpy factor. We compute an ensemble of viscosity structures using different conversion factors and show to which extent the choice influences the resulting obtained deformation and relative sea-level changes. That way we link uncertainties in viscosity structure generation to uncertainties in the observables and identify regions that are most affected.
This work contributes to the German Climate Modeling Initiative PALMOD.
How to cite: Schachtschneider, R., Klemann, V., Steinberger, B., and Thomas, M.: Effects of uncertainty in mantle viscosity structure inferred from seismic tomography on glacial isostatic adjustment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9831, https://doi.org/10.5194/egusphere-egu26-9831, 2026.
We present a new relative sea level (RSL) database for Norway and for modelling studies. The total database contains 1011 data points, of which 558 (55%) are index points and 453 (45%) limiting dates. The new RSL database differs from earlier efforts in two key ways. Firstly by having fewer limiting dates as we have removed redundant data. Secondly, it contains new RSL data collected over 2018-2024 which are largely index point data.
The new RSL database is compared to 9,900 ice-Earth combinations from a 1-D glacial isostatic adjustment (GIA) model. From these combinations, the ice models tested come from a high-variance subset of 10 Eurasian Ice Sheet chronologies. These (GLAC3) chronologies are from a last glacial cycle history matching of the physics-based Glacial Systems Model against a diverse set of constraints. The 10 Eurasian ice chronologies are combined with 3 different reconstructions of global ice changes (i.e., a total of 30 ice models).
We show how data-model fits vary for the ice chronologies and Earth model parameters explored. Results indicate relatively weak upper mantle viscosities for Norway. While some ice-Earth model combinations can reproduce the general RSL trends and show features of the Younger Dryas and Tapes transgressions, no model parameter sets provide quality fits to all the data or can follow all the observed RSL fluctuations. This suggests inaccuracies in the model and/or the need to explore a larger parameter space.
RSL uncertainties are calculated using a nominal Bayesian approach and capture ~80% of the Norwegian RSL data. By splitting the data into 3 subregions, we show how data-model fits vary geographically and which ice-Earth model combinations are preferred where. This reveals that data-model fits are poorest in South Norway, where only 40% of the RSL are captured (and only 22% of the index point data). We hypothesise that the poor fits in this region are due to inaccuracy in the regional and/or background (global) ice models considered.
How to cite: Simpson, M. J. R., Parang, S., Lakeman, T., Milne, G. A., Love, R., and Tarasov, L.: A new relative sea level database for Norway tested against glacial isostatic adjustment models with an ensemble of physics-based history-matched Eurasian Ice Sheet chronologies. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19132, https://doi.org/10.5194/egusphere-egu26-19132, 2026.
The glacial isostatic adjustment (GIA) and sea level modeling communities have historically lagged other fields in adhering to the FAIR principles of making model outputs findable, accessible, interoperable, and reusable – a delay that has slowed scientific discovery. While sharing model outputs has improved recently, usability of available outputs continues to be hindered by lack of standardization. Meanwhile, legacy model outputs can be lost as the technology storing them grows obsolete and their creators retire or leave academia.
The GIAmachine initiative addresses this problem. GIAmachine aims to make accessible as many published GIA and sea level model outputs as are retrievable by
- cataloguing and standardizing published GIA and sea level model outputs;
- contacting authors of published-but-inaccessible models to encourage them to upload their outputs to DOI-minting repositories;
- partnering with the GHub science gateway to make a long-term home for these newly available outputs;
- building Jupyter notebooks on GHub that make these models interoperable and easy to use; and
- encouraging the GIA and sea level modeling communities to follow the FAIR principles.
Our poster will introduce the GIAmachine online portal and outline outstanding challenges. We appreciate community input for designing a living resource that meets the specific needs of current and future scientists.
How to cite: Steffen, H., Creel, R. C., Kodama, S. T., Tulenko, J. P., Steffen, R., Riva, R. E. M., Quinn, J., and Briner, J. P.: GIAmachine: a community-driven rescue and recovery initiative for legacy sea level and glacial isostatic adjustment modeling data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16724, https://doi.org/10.5194/egusphere-egu26-16724, 2026.
How to cite: van Calcar, C., Broerse, T., Ioannidi, I., Breithaupt, T., Wallis, D., Willen, M., Riva, R., van der Wal, W., and Govers, R.: Time-dependent rheological behaviour of the solid Earth greatly influence Antarctica's future sea-level contribution., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1883, https://doi.org/10.5194/egusphere-egu26-1883, 2026.
The Glacial Isostatic Adjustment (GIA) is the deformation of the Earth in response to changes in the cryosphere. It can produce significant uplift rates up to 1.5 cm/yr in North America. Therefore, it is crucial to remove these signals from space-based gravimetry and altimetry missions to improve our understanding of sea-level changes or to better assess other geophysical processes like ice-mass loss in Antarctica. Specifically, GIA in Antarctica remains poorly constrained due to the lack of in situ observations and the absence of paleo-shorelines dating. To compensate this observational gap, combinations of geodetic and gravimetry observations have been proposed. Wahr et al. (1995, doi:10.1029/94GL02840) introduced the ratio between rates of surface gravity changes and vertical displacements with a value of –0.15 microGal/mm and Sato et al. (2012, doi:10.1029/2011JB008485) theoretically showed that this ratio varies spatially and temporally. In this study, we investigate this ratio more thoroughly. We use the Love number formalism to compute gravity rates and vertical velocities induced by several ice-loading histories for a radially layered spherical Earth using the ALMA and TABOO software packages. We specifically assess the effect of different viscosity profiles and rheological laws such as Maxwell, Andrade, and Burger as a function of spatial wavelength and timing of the glacial history.
How to cite: Cambours, C., Mémin, A., and Tregoning, P.: About gravity rates to vertical velocities ratio induced by ice-sheet changes in Antarctica , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5471, https://doi.org/10.5194/egusphere-egu26-5471, 2026.
The primary indicators of relative sea-level change along the coasts of Antarctica are the uplifted paleoshorelines, which are documented with geomorphological and geochronological studies, particularly from the Antarctic Peninsula. Some of the most prominent examples are found along the shores of Marguerite Bay, situated in the central part of the Antarctic Peninsula. Here, we present that the shorelines of Calmette Bay, located within the research area, have experienced approximately 40 m of uplift over the past 7500 years. This study aims to quantify the amount of ice mass loss required to produce such a rapid uplift and to assess the magnitude of climate change necessary to drive this degree of ice mass reduction. In addition, our goal is to constrain the mantle rheology and viscosity conditions required to produce the observed crustal response in the region. Our approach integrates various Antarctic ice-deglaciation scenarios with crustal viscosity models. We employ the numerical code SELEN4 to compute the sea-level equation and generate theoretical uplift/subsidence curves. We compare our results with geological data to assess alternative ice deglaciation histories and to constrain the mantle-rheology parameters that most effectively reproduce the observed uplift pattern.
How to cite: Güven, A. and Yıldırım, C.: Glacio-isostatic Adjustment (GIA) in Marguerite Bay, Antarctic Peninsula: inferences from uplifted Holocene paleoshorelines, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-839, https://doi.org/10.5194/egusphere-egu26-839, 2026.
Global Navigation Satellite System (GNSS) data provide critical insights into solid Earth deformation. GNSS observations at bedrock in glaciated areas like Antarctica serve as essential constraints to model the glacial isostatic adjustment (GIA). Likewise, they may serve to aid the empirical estimation of GIA and of ice-mass balance. Since the last International Polar Year 2007/08, GNSS coverage has significantly been expanded in West Antarctica, the Antarctic Peninsula, and parts of Victoria Land. In East Antarctica, however, logistical challenges and sparse bedrock outcrops have limited the establishment and (re-)observation of new GNSS stations.
In order to address this gap, a GNSS network of mostly episodic site was deployed across western and central Dronning Maud Land, East Antarctica. Measurements were initiated in the mid-1990s while the most recent observation campaign was conducted during the 2022/2023 Antarctic season. Additionally, two new permanent GNSS sites were installed in western Dronning Maud Land in the beginning of 2020.
This study presents results from a consistent analysis of both episodic and continuous GNSS datasets over a time span of more than 20 years. We demonstrate how this extended temporal coverage enhances the accuracy of secular trends derived from GNSS time series. To isolate the GIA displacement signal, we account for elastic displacement caused by present-day ice mass changes using satellite altimetry and surface mass balance models. The resulting trends are compared to GIA estimates inferred from a number of models. Thus, we come up with new insights into the deformation pattern in a region that lack respective information so far. Our findings emphasize the importance of long-term GNSS measurements in refining GIA models for East Antarctica.
How to cite: Scheinert, M., Buchta, E., Kappelsberger, M., Eberlein, L., and Willen, M.: Investigation of glacial isostatic adjustment in Dronning Maud Land, East Antarctica, using long-term GNSS observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22615, https://doi.org/10.5194/egusphere-egu26-22615, 2026.
Reducing uncertainties in the projections of the future contribution of the Antarctic Ice Sheet (AIS) to global sea-level rise is crucial for coastal communities and policymakers worldwide. Self-amplifying feedback mechanisms can lead to accelerated and irreversible ice loss once certain temperature regimes are crossed. Such tipping behaviour will ultimately lead to a new equilibrium state, even if boundary conditions remain constant. In contrast, negative feedback loops, such as the sea-level feedback due to glacial isostatic adjustment (GIA), potentially slow down the rate of ice loss by reducing the local water depth at the grounding line. The rebound rate of the bedrock following a reduction in ice mass depends heavily on the Earth structure beneath Antarctica, with mantle viscosities and corresponding response timescales that can vary laterally by two to three orders of magnitude. Yet, it is unclear whether GIA feedbacks can shift ice sheet tipping points or even prevent tipping as a result of path dependency, as bifurcation-tipping theory considers stationary states only, where the ice sheet load and solid Earth deformation are in isostatic equilibrium.
By employing different Earth structures in (quasi-)equilibrium simulations and varying temperature forcing rates, using a 3D coupled ice sheet–GIA model (PISM-VILMA), we explore their influence on the AIS's stability and tipping thresholds, focusing on the West Antarctic Ice Sheet and the Wilkes Subglacial Basin. Our simulations demonstrate that the Earth structure significantly affects both the temperature threshold at which self-sustained retreat of the AIS is initiated and the long-term committed contribution to global sea-level rise; this as a result of path dependency.
Moreover, our results highlight the competing timescales of ice sheet and solid Earth dynamics. We find that the rate of temperature increase represents a crucial parameter. Rate-induced tipping can lead to abrupt changes at lower thresholds than in the quasi-equilibrium case, in particular for stronger Earth structures, leading to higher sea-level contribution for the same warming levels.
How to cite: Wullenweber, N., Albrecht, T., Mojtabavi, S., Klemann, V., and Winkelmann, R.: The impact of Earth structure on Antarctic ice sheet tipping thresholds, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10748, https://doi.org/10.5194/egusphere-egu26-10748, 2026.
