Computer models of the advance and retreat of the past great ice sheets can be built that incorporate the Earth's response to the changing load. Postglacial rebound models integrate disparate observations related to the last glaciation including geological observations of ice sheet extent,thickness, and retreat history as well as uplift and tilting of former ocean and lake shorelines. Modern geodetic observations of crustal motion andsurface gravity change give new constraints which are just now beginning to be included.
Because these models include a somewhat realistic Earth response, they can be used to give numerical predictions of the crustal response in regions where observations are lacking. For example, postglacial rebound models have largely been constrained by relative sea level observations (from Carbon14 dating of features related to former sea level, such as raised beaches), which are only found at former ocean shorelines.However, a model built on relative sea level observations can be used to predict the crustal response in other regions. The predictions can then becompared to other kinds of observations, such as GPS or absolute gravity.
These models can also give numerical estimates of quantities for which there are few, if any, direct observations, such as the crustal stress andstrain changes due to glacial loading and unloading. Estimates of these stress and strain changes can help significantly with studies of earthquake processes.
Although our efforts concentrate on reconstructing the North American ice sheets, ice sheet models are necessarily global in scope. This is because relative sea level observations remain key to these reconstructions. They are sensitive to the total amount of water in the oceans, which in turn depends on the net mass increase or decrease of all the ice sheets.