Glacier and Ice-sheet models in the Geodynamics Group, Research School of Earth Sciences, Australian National University.

Introduction.

The Geodynamics Group is engaged in several different methods of computer assisted ice-mass modeling. Much work has been done with isostatic rebound models - current lithospheric rebound rates have been used to infer the extent of ice caps through paleo time - but on this page physics based forward modeling approaches will be presented. These approaches are currently in the development stage (like everything else on the web) but we think they are interesting enough to present none the less.

This research is being performed by Jonathan Tomkin , a PhD student, and Jean Braun, a Fellow of the Research School of Earth Sciences.

2-D Finite Element Modeling with a twist - Dynamic Lagrangian Remeshing.

A 2-D FEM has been developed for ice sheets by modifying a model (Braun, J. & Sambridge, M., 1994. Dynamical Lagrangian Remeshing (DLR): A new algorithm for solving large strain deformation problems and its application to fault-propagation folding. Earth and Planetary Sciences Letters, 124, 211-220.) designed to examine lithospheric interaction. Like standard time dependent FEMs temperature and stress are solved by iteration. Stress and strain are linked through Glen's flow law and through this displacement is calculated. By incorporating Dynamic remeshing, the node movement caused by this displacement changes the structure of elements over time, but the progress of individual points within the ice mass can be tracked. This allows the creation of zones within the ice that may have different physical properties; anisotropy caused by uniaxial strain for example, or the effects entrained till have on erosion rates.

2-D Shallow Ice Approximation - Cascades on Ice.

Cascades (Braun, J. & Sambridge, M., 1997. Modelling landscape evolution on geological time scales: a new method based on irregular spatial discretization. Basin Research, 9, 27-52. ) is a 2-D erosion model that tracks the path of cascading water to determine the erosion caused by run off. This is performed on an irregular grid. Orographic rainfall, diffusion (rockslides) and tectonic uplift are also in the model, which is run over time to determine the evolution of river systems and landscapes. The time dependence is solved using explicit finite differencing (see Hindmarsh & Payne, 1996, Time-step limits for stable solutions of the ice-sheet equation. Annals of Glaciology, 23, 74-85.) . By including an ice evolution model based on the shallow ice approximation the model can incorporate the erosive effects of glaciers. Snow fall is determined by an altitude and latitude based temperature model.