Present-day tilting of the Great Lakes region based on water level gauges

Abstract

By using monthly mean water levels at 55 sites around the Great Lakes, a regional model of vertical crustal motion was computed for the region. In comparison with previous similar studies over the Great Lakes, 15 additional gauge sites, data from all seasons instead of the 4 summer months, and 8 additional years of data were used. All monthly water levels available between 1860 and 2000, as published by the U.S. National Ocean Survey and the Canadian Hydrographic Service, were used. For each lake basin, the vertical velocities of the gauge sites relative to each other were simultaneously computed, using the least-squares adjustment technique. Our algorithm solves for and removes a monthly bias common to all sites, as well as site-specifi c biases. It also properly weighs the input water levels, resulting in a realistic estimation of the uncertainties in tilting parameters. The relative velocities obtained for each lake were then combined to obtain relative velocities over the entire Great Lakes region. Finally, the gradient of the relative rates for the regional model was found to agree best with the ICE-3G global isostatic model of Tushingham and Peltier, whereas the ICE-4G gradients were too small around the Great Lakes.

Vertical Motion Determined Using Satellite Altimetry and Tide Gauges

“…Figure 5 illustrates the estimates of geocentric vertical motion averaged in each lake compared with a GIA model prediction using the ICE-4G model (Peltier 2002), the ICE-3G GIA model (Tushingham and Peltier 1991), and the water level gauge relative vertical motion solution (Mainville and Craymer 2005). Results show excellent agreement except for the ICE-4G GIA model, which exhibits smaller amplitudes.…”

“…Snay, personal communications, 2004). The triangles present the vertical motions from water level gauge only analysis (Mainville and Craymer 2005). The background of the top panel shows vertical motions predicted by the ICE-3G GIA model (Tushingham and Peltier 1991), while the background of the bottom panel is from the ICE-4G GIA model (Peltier 2002).…”

“…In the Baltic Sea, the comparisons of the vertical motion solution with 10 collocated GPS radial rates and with the BIFROST GIA model show differences of 0.2 ± 0.9 and 1.6 ± 1.8 mm yr -1 , respectively. For the Great Lakes region, the comparisons with the ICE-3G model and with the relative vertical motion estimated using tide gauges only (Mainville and Craymer 2005) show differences of -0.2 ± 0.6 and -0.1 ± 0.5 mm yr -1 , respectively. The Alaskan vertical motion solutions (linear and nonlinear models) have an estimated uncertainty of ~1.2 -1.6 mm yr -1 , which agree qualitatively with GPS velocity and tide gauge-only solutions (Larsen et al 2003).…”

Glacial Isostatic Adjustment of the Laurentian Great Lakes Basin: Using the Empirical Record of Strandline Deformation for Reconstruction of Early Holocene Paleo-Lakes and Discovery of a Hydrologically Closed Phase*

“…The forebulge effect has not been recognized from empirical evidence in the continental region adjoining or south of the Great Lakes basin. However, ice marginal areas in this region could have undergone uplift and subsidence associated with the growth, migration and decay of a glacio-isostatic forebulge (Colman et al, 1994a), and some evidence for subsidence exists, for example, anomalies in modern tilting of the Erie and southern Michigan basins (Mainville and Craymer, 2005).…”

“…This differential rebound proceeded throughout the period of ice retreat and postglacial time at decelerating rates of uplift. It is continuing today, as evidenced by tilting of the Great Lakes basins measured in long-term records of lake level gauges between southern and northern shores of the Great Lakes (CCGLBHHD, 1977;Tushingham, 1992;Mainville and Craymer, 2005). Note: Land elevations and lake surface elevations are relative to present-day sea level.…”