1. Lake Geneseo
As the North American ice sheets retreated—but also sometimes readvanced—they left behind a series of recessional moraines, sometimes several hundred feet in height. What has been named the Fowlerville Moraine was one such formation, which extended across a relatively narrow section of the Genesee Valley and created a dam to its waters. Before the river eventually broke through, a 25-mile-long proglacial lake extended up the valley nearly to Dansville and with a depth of perhaps 80 feet. To put this in perspective, for a time Lake Geneseo was longer than all of today’s Finger Lakes except Seneca and Cayuga, and deeper than lakes Honeoye or Conesus. It existed for a period of at most several hundred years and had disappeared by not less than 12,000 years ago.
Some of the factors that created Lake Geneseo played important roles in its subsequent history. The comparatively wide, flat valley—caused in part by glacial rebound of its geologic plates tilting south as the weight of glaciers disappeared—was susceptible to flooding. Prior to construction of the Mount Morris Dam in 1952 few permanent structures were built upon the so-called “Wadsworth Flats” or “Geneseo Flats”; soil there was so fertile because it flooded so often. In 1972, Hurricane Agnes brought so much rain that the ghost lake reappeared—seen here in flood maps created by the Army Corps of Engineers—and was visible from the SUNY-Geneseo campus.
We live in a vanishingly thin slice of geological time, so it’s as difficult to envision the world of Lake Geneseo as it is events 12,000 years in the future. And yet we wobble at the verge of epochal change that is comparable to the Pleistocene’s ending (when ice sheets retreated north) and our own Holocene epoch beginning: namely, the emerging Anthropocene era of rapid global heating. In order to visualize the disruption of a climate we take for granted, this map restores the dormant Lake Geneseo and—using 2015 Livingston County tax rolls—shows more than 1,000 homes in the Genesee Valley newly underwater. The same thing already is occurring in coastal cities and atolls around the world on a much larger scale. Of course, a transformation to our way of life might as easily come through a period of extended drought; climatologists emphasize that they only can speculate about local events in the future because effects are unevenly distributed and the speed of change is unprecedented.
The area surrounding Lake Geneseo is noted for its unusual number of mastodon skeletons. There’s no widely accepted single cause for their extinction; depending upon how their bones are dated it may have involved overhunting by humans, a cooling climate, or indirect effects of cooling upon their preferred foods. For contemporary readers, mastodons are a warning: increasingly, biologists are viewing our times as a sixth mass extinction from which our species is not necessarily exempted. We close with a remark on the sublimity of geological time from an archaelogist working on the Dansville Mastodon dig in 1874: “It appeared that most of the bones lay under and near the stump of a large pine tree, the roots of which no doubt fed upon them and thus stole from us much of the skeleton.”
--Governale, Mike. "Rochester's Great Flood(s)." Rochester Subway 19 May 2014.
--Young, Richard A., and Michael P. Wilson. "Morphogenesis of the Genesee Valley." Northeastern Geology 10.2 (1988): 112-133.