The Impact of a 3‐D Earth Structure on Glacial Isostatic Adjustment in Southeast Alaska Following the Little Ice Age

Abstract

In Southeast Alaska, glacial isostatic adjustment (GIA) is the dominant process causing present-day vertical crustal motions. Since the early 2000s, GPS observations have highlighted two major uplift areas centered at the Yakutat (YK) and Glacier Bay (GB) ice fields, exceeding 30 mm/yr , as shown in Figure 1. Past studies, beginning with Larsen et al. (2005), have shown that these uplift rates are the result of the Earth's viscoelastic response to the decline of glaciers after the Little Ice Age (LIA), and elastic rebound to present-day ice melt (PDIM). Raised shorelines indicate that uplift started at the end of

Solid Earth Uplift Due To Contemporary Ice Melt Above Low‐Viscosity Regions of the Upper Mantle

“…A 1D approach may be valid in regions with a broad LV region, as Marsman et al. (2021) found for Alaska, where lateral viscosity variations (1.6 ⋅ 10 19 to 5.0 ⋅ 10 19 Pa s in the shallow upper mantle) across a broad region (1,425 by 2,325 km) did not improve the fit to observations compared to a 1D model. However, southeast Greenland is likely characterized by a confined LV region (Figure 1a) that is small enough to significantly reduce uplift rates compared to a 1D case (LV layer).…”

“…Furthermore, even if the LV region is very wide (e.g., as wide as the drainage basin), deformation in neighboring drainage basins (without an LV layer) may also be affected (Figures 3d and 4d) because the influence of a nearby LV region cannot be captured in the 1D approach. A 1D approach may be valid in regions with a broad LV region, as Marsman et al (2021) found for Alaska, where lateral viscosity variations (1.6 ⋅ 10 19 to 5.0 ⋅ 10 19 Pa s in the shallow upper mantle) across a broad region (1,425 by 2,325 km) did not improve the fit to observations compared to a 1D model. However, southeast Greenland is likely characterized by a confined LV region (Figure 1a) that is small enough to significantly reduce uplift rates compared to a 1D case (LV layer).…”

Identifying Geographical Patterns of Transient Deformation in the Geological Sea Level Record

“…However, both post-seismic deformation studies and rock physics experiments indicate that a Maxwell model misses a transient phase of deformation that is observed after earthquakes as well as in the laboratory (e.g., Faul & Jackson, 2015;Freed et al, 2012;Hanson & Spetzler, 1994;Pollitz, 2005). And while the follow-on generation of Earth models often incorporate increasing complexity, 3D and nonlinear type Earth models can be computationally expensive, and do not always yield improved fits to data relative to simpler 1D Earth models (Marsman et al, 2021). Furthermore, these models have many free and often poorly constrained parameters (e.g., Karato & Wu, 1993) based on extrapolation of empirical relations for steady-state viscous creep, and thereby neglect transient creep.…”

Modeling Viscoelastic Solid Earth Deformation Due To Ice Age and Contemporary Glacial Mass Changes in ASPECT

“…The rapid viscous response is mixed with the elastic and long‐term viscous deformation components of GIA, making it difficult to distinguish between solid Earth deformation due to past and contemporary ice load changes (Whitehouse, 2018). The effect of lateral viscosity variations on solid Earth deformation (Kaufmann et al., 1997; Sabadini & Portney, 1986) and whether a 3D Earth can be represented by 1D models for glacial cycle timescales (Blank et al., 2021; Marsman et al., 2021; Milne et al., 2018; van der Wal et al., 2013, 2015) and contemporary ice melt timescales (Powell et al., 2020) has been a long‐standing question. Furthermore, recent efforts showed the need for 3D modeling to predict solid Earth deformation rates due to contemporary ice load changes near confined low‐viscosity regions (Weerdesteijn et al., 2022).…”