Legacies of Glacio-fluvial Interactions in the Finger Lakes, Central New York

The Finger Lakes region of central New York exhibits spectacular examples of the interplay between glacial and fluvial processes. The Finger Lakes themselves were carved by ice sheets and related subglacial hydrologic processes that enlarged, over-deepened, and reversed the drainage direction of pre-existing fluvial valleys. The region's famous gorges flank the glacial troughs and reflect ongoing fluvial adjustment to glacially driven base level variations. Modern tools of topographic analysis permit quantification of the imprint that glacial processes leave on fluvial form and process. Regionally, ice sheet erosion is maximized along the north end of the Seneca/Cayuga trough. Local relief ranges from ~100 m at the north end of Seneca and Cayuga lakes to 250-400 m on the southern ends of these lakes and on the smaller, flanking lakes (Keuka, Canandaigua, Skaneateles, Owasco). Concavity indices for lake-tributary stream profiles are predominantly in the range of -7 to 0, reflecting a convex initial form imposed by glacial processes, while normalized channel steepness (ksn) indices are generally under 40 (reference concavity of 0.45), reflecting the gentle gradients of the glacial uplands. Concavity index and ksn values are maximized (>0, and >75, respectively) along short segments at the downstream ends of the so-called interglacial or post-glacial gorge reaches, again maximized at the southern and peripheral parts of the Seneca/Cayuga trough. Finally, streams that cross former channel courses buried by subglacial debris typically have more numerous and/or more pronounced knickpoints and more concave long profile segments than streams that do not. In short, the legacy of glaciations from the regional to the reach scale appears to be driving patterns of fluvial response in the Finger Lakes.