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GIA accounts for 4-5 cm of total head decline

The Study identified two different types of GIA effects to consider with regards to the Lake Michigan-Huron to Lake Erie head difference relationship: • The apparent effect on water levels resulting from the change in the land-to-water relationship around each lake due to the “tilting” of the earth’s crust; and • The physical effect of GIA due to the impact of movement of the earth’s crust on the absolute water levels of the two lakes (i.e., their actual surface elevation at any given time relative to mean sea level). The Study found that the apparent effect of GIA accounts for about 4 to 5 cm (1.6 to 2 in) of the approximately 23 cm (9 in) decline in the head difference between Lake Michigan-Huron and Lake Erie between 1963 and 2006. The Study identified important challenges with respect to data availability and reliability. For example, due to limitations in current knowledge regarding absolute movement between key locations on each lake, it is not yet possible to accurately determine changes in the actual water levels on each lake over time and in turn, the physical effect of GIA on the head difference between Lake Michigan-Huron and Lake Erie over time. Efforts using satellite-based GPS techniques are underway that will enable researchers, over several years, to accurately establish the absolute rates of vertical movement at points throughout the Great Lakes region and therefore more precisely determine the rates of relative movement between points on each of the Great Lakes. GIA effects will also need to be better understood to support future management decisions on Lake Superior regulation. For example, public concerns about declining or rising water levels on shorelines, and declines in water levels in the upper Great Lakes as a result of climate change will be exacerbated by the effects of GIA.
Related Projects
GIA Workshop
Review of Apparent Vertical Movement Rates
Great Lakes Volume Changes from GIA
Pre-1960 Parry Sound Water Levels
Huron and Erie Water Level Gauge Analysis
GIA Impacts on Huron - Erie Head Difference