THE EPHEMERAL SUSQUEHANNA LAKE SYSTEM: SHORT-LIVED DURING LAURENTIDE RETREAT

Geomorphic and stratigraphic evidence indicate Laurentide retreat left a semi continuous system of moraine dammed, ice-contact and proglacial lakes throughout the upper, eastern Susquehanna system. The sole remaining vestiges are Otsego Lake (current headwaters of the Susquehanna R.) at Cooperstown, and Canadarago Lake at Richfield Springs.

Valley floor water well logs consistently show lake sediments (sand, silt and/or clay) commonly range in thickness between 50 and 75 m in the main trunk valley and virtually all large tributaries. Interstratified with sand and gravel lenses at valley margins beneath deltaic terraces indicate synchronous deposition in an ice-contact lake environment by steams exiting the margins of valley ice-tongues.

Intermittent stability during retreat led to moraine deposition, thus forming a series of dams leading to a fully developed ephemeral lake system.

Similar ice-contact lakes on the eastern margin of Bering Glacier, Alaska serve as modern analogs for similar lacustrine deposition (Fleisher et al, 2003). During a period of five consecutive summers meltwater turbidity averaged 1.4-1.9 g/L from upwelling englacial vents, thus yielding a sediment charged lacustrine environment. Annual rates of sedimentation within 1 km of the ice front were 2.2 to 6.6 m/year as determined from multiple bathymetric surveys. Where complimented by distal-deltaic aggradation the rate was even higher. Assuming a comparable fine-grained sediment source and that similar transport mechanisms apply to the Susquehanna system (Fleisher, 1993), an extrapolation of these rates of aggradation to the Susquehanna Lake System suggests a relatively short life span of 15 to 45 years for individual lakes.

Although formation and existence are incontrovertible the actual timing and sequence of lake drainage remains unknown.

References

Fleisher, P. J., Bailey, P. K., and Cadwell, D. H., 2003, A decade of sedimentation in ice-contact, proglacial lakes, Bering Glacier, Alaska: Journal of Sedimentary Geology; v. 60, I. 4, p. 309-324.

Fleisher, P. J. 1993, Pleistocene sediment sources debris transport mechanisms and depositional environments; a Bering Glacier model applied to northeastern Appalachian Plateau, central New York: Geomorphology, v. 6, p. 331-355