Global change studies in the Geodynamics Program focus on "postglacial rebound". The surface load caused by the continental-scale glaciers of the last ice age depressed the surface of the Earth. With the decay and retreat of the great ice sheets, which were at their peak about 20,000 years ago, the depressed areas began to rise toward their former position. Postglacial rebound doesn't happen instantly because at great depths the Earth acts like a thick, viscous fluid with a delayed response.

Figure 1. Present day crustal motion predicted by a computer model of postglacial rebound called ICE-3G. Blue areas are sinking. Peak uplift near James Bay is around 12-13 mm/year. Arrows show horizontal motions due to postglacial rebound. ICE-3G reference: Tushingham, A.M., and W. R. Peltier, ICE-3G: A new global model of late Pleistocene deglaciation based upon geophysical predictions of postglacial sea level, J. Geophys. Res., 96, 4497-4523, 1991. larger image [GIF, 309.9 kb, 698 X 699, notice]

Postglacial rebound is still occurring today. The figure shows the vertical and horizontal present day crustal motion produced by a computermodel of glacial rebound called ICE-3G which was developed by M. Tushingham and W. R. Peltier at the University of Toronto. Regions nearsoutheastern Hudson Bay, including most of James Bay, are predicted to be rising at rates in excess of 1 cm/yr.

The ongoing uplift and tilting caused by postglacial rebound affects lake levels and, consequently, shoreline erosion. River flow is also affectedthrough changes in stream bed gradients and the elevation of lake outlets. To better determine postglacial tilting in Manitoba, the GeodynamicsProgram is monitoring crustal motion in this region using modern geodetic techniques. (See Mid-continent Tilt Project).

Our global change studies are also concerned with changing sea level. This arises quite naturally from postglacial rebound, as it is primarily thechanging mass balance of glaciers and ice sheets that affect global sea level. In particular, the mass balance of the Antarctic ice sheet, both presentand past, remains a key unknown in developing sea level budgets. (See Antarctic Ice Sheet Balance).

Observations related to postglacial rebound can be evaluated in a consistent manner through development of computer models. Postglacialrebound models include the response of the Earth to the surface load caused by the weight of the changing ice sheets. (See Ice Sheet Modelling)