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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 structureof the Earth than vertical displacements. Reliable modeling of horizontal motion can therefore helpconstrain further lithospheric elastic properties and allow for more realistic stress calculations, whichcan 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 usingthe spherical harmonic method, whereas horizontal displacements may be significantly biased. Themore recent study by Reusen et al. (2023), focusing on compressible flat-Earth FE models, showedgood agreement in horizontal displacements between FE model with elastic foundations at each densitycontrast and spherical harmonic solutions, with progressively improved agreement for decreasing loadradius. However, vertical displacements for the compressible case were not examined. In this specificcase, compressibility is implemented only partially through the so-called material compressibility, whichaccounts for volume changes but neglects density variations.Modelling present-day GIA in Iceland requires small load radii, low mantle viscosities, and thinelastic lithospheres—parameter ranges that have not yet been fully benchmarked. Here, we extend thestudy of Reusen et al. (2023) by considering glacier loads and Earth structures closer to those of Icelandat the present day glacial retreat. In addition, we also benchmark the vertical displacement. We use aflat-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 reliabledisplacement and stress outputs from Icelandic GIA models, while quantifying uncertainties in mantleviscosity and elastic thickness. Our study highlights the importance of benchmarking small icecaps andthin lithospheres to be used in studies of small glaciated regions.ReferencesReusen et al. (2023). “Simulating horizontal crustal motions of glacial isostatic adjustment usingcompressible cartesian models”. In: Geophysical Journal International 235(1), pp. 542–553.