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Lake Agassiz and Lake Missoula were glacier-dammed lakes that periodically overflowed the lowest sill of their basins to cause massive floods. Lake Agassiz is thought to be responsible for the deeply incised Minnesota River valley. The shifting of glaciers and the ice sheet altered the effective relief of the basins over time, so simulating these lakes today takes a lot of work. In the Great Basin, away from glaciers, Lake Bonneville and Lake Lahontan were the largest lakes that formed during a colder, wetter time, as endorheic valleys filled with water and repeatedly overflowed the lowest sill of their basins. Lake Bonneville is thought to have overflowed the outer edge of Great Basin itself at Red Rock Pass near Downey, Idaho; eroding the gap and releasing a huge flood into the Snake River basin. Because a moving ice sheet wasn't a factor in their case, DEM shading can be used to approximate their overflows. This doesn't account for isostatic rebound or tilt in terrain, but gives a visually enlightening approximation, and lets one interactively explore how these outflows may have worked. One can shade a topo map of the Great Basin at 4785 feet -- today's elevation of Red Rock Pass -- to approximate how Lake Bonneville's floods may have worked. Or, shade at these key sill elevations, in feet, to see how Lake Lahontan may have outgrown one valley after another: 3878, 3933, 3976, 4154, 4180, 4301, 4386. Example with Caltopo at 3976 feet: https://caltopo.com/map.html#ll=40.28729,-118.02612&z=8&b=t&... |
https://en.wikipedia.org/wiki/Glen_Roy#The_Parallel_Roads_of...