Developing an open-source 3D glacial isostatic adjustment modeling code using ASPECT

Models of Glacial Isostatic Adjustment (GIA) processes are useful because they help us understand landscape evolution in past and current glaciated regions. Such models are sensitive to ice and ocean loading as well as to Earth material properties, such as viscosity. Many current GIA models assume radially-symmetric (layered) viscosity structures, but viscosity may vary laterally and these variations can have large effects on GIA modeling outputs. Here we present the potential of using ASPECT, an open-source finite element mantle-convection code that can handle lateral viscosity variations, for GIA modeling applications. ASPECT has the advantage of adaptive mesh refinement, making it computationally efficient, especially for problems such as GIA with large variations in strain rates. Furthermore, ASPECT is open-source, as will be the GIA extension, making it a valuable future tool for the GIA community.

 

Our GIA extension is benchmarked using a similar case as in Martinec et al. (GJI, 2018), such that the performance of our GIA code can be compared to other GIA codes. In this case, a spherically symmetric, five-layer, incompressible, self-gravitating viscoelastic Earth model is used (Spada et al, GJI 2011). The surface load consists of a spherical ice cap centered at the North pole, and is applied as a Heaviside loading. The ice load remains constant with time, and thus we have not yet implemented the full sea level equation (SLE). Beyond this benchmark, we have incorporated lateral viscosity variations underneath the ice cap, to demonstrate the ability of efficiently implementing laterally-varying material properties in ASPECT.

 

We show the possibilities, capabilities, and potential of ASPECT for GIA modeling. In the near future we will further develop the code with the sea level equation and an ocean basin, and will explore ASPECT’s current capability of using time-varying distributed surface loads. These functions will allow for modeling of GIA for realistic ice load scenarios imposed above potentially complex earth structures.