MAPPING AND CHARACTERIZING LATE GLACIAL AND HOLOCENE ALLUVIAL FANS IN UPSTATE NEW YORK

The Butternut Valley in the Appalachian Plateau of upstate New York hosts a considerable number of alluvial fans abutting the valley walls and resting at the mouths of several small tributaries to the Butternut Creek, which is a headwaters drainage to the Susquehanna River. These fans were deposited during a time period ranging from deglaciation to ice free conditions. Ice-contact and post-glacial deposits rest in close contact with each other. We hypothesize that the distribution of post-glacial fans varies between valley types in this area. Basically, valleys that served as outlets for ice streams from the Laurentide ice sheet (through valleys) experienced active ice conditions, whereas non-through valleys experienced stagnant ice conditions. In both cases, exposed upland tributaries delivered sediment into the main valleys which were still occupied by glaciers. Within non-through valleys, alluvial fans experienced deposition against or on stagnant (dead) ice. We propose that fan formation is most common within non-through valleys as opposed to through-valleys, due to greater degree of sediment mobility in through valleys from active ice and increased meltwater.

We present herein new mapping of alluvial fans in a non-through valley setting. Ice contact fans exhibit toes with sharp or distinct angles of repose and an uneven undulating appearance from on-ice deposition. Fans deposited after ice retreat retain a classic fan semblance marked by a nearly linear profile and radial distribution pattern. At many tributaries we find a series of fans which provide a history of deposition during deglaciation. Ice contact fans are typically higher in elevation than younger fans. We are beginning to more formally interpret fan distribution and areal extent using digital topographic data (USGS National Elevation Data), new high resolution LiDAR elevation data for parts of our field area, and field mapping.