T39 Sigma Gamma Epsilon Undergraduate Research (Posters)

Sunday, 9 October 2011
9:00 AM - 6:00 PM
Hall C

MODELING THE GLACIAL HISTORY OF THE ASHOKAN WATERSHED IN THE CATSKILL MOUNTAINS OF NEW YORK USING GIS

Paper number: T39-13
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

New York City drinking water is partially supplied through the Ashokan Reservoir located in the Upper Esopus drainage basin of the Catskill Mountains. Fine sediment sources such as varved lacustrine clays and clay-rich tills are contributing to the suspended sediment load of the watershed and degrading water quality. Students of the 2011 SUNY New Paltz REU program in collaboration with the New York City Department of Environmental Protection modeled glacial lakes and ice margins as a means of finding the extent of the fine sediment sources. Two hypotheses were posed as to the nature and extent of glacial lakes. The first hypothesis envisions large regional lakes with at least two stages comparable to Rich’s (1935) interpretation. A second hypothesis predicts the formation of small local valley lakes during deglaciation with dead ice filling portions of narrow valleys in the high relief terrain.

A raster GIS digital elevation model of possible lakes modified to correct for post-glacial isostatic rebound was created using potential thresholds at Wagon Wheel Gap, Peekamoose Gorge, Deep Notch, and the Hudson-Delaware drainage divide pass. Variations of modeled glacial lacustrine extents were field checked to accept or reject model hypotheses. Thick packages of varved lacustrine sediments of fine silt and clay were found throughout these valleys. Well logs indicate a widespread occurrence of fine grained lacustrine sediments. This supports the former existence of a large regional lake in the area.

A red diamicton facies consisting of compact clay-rich matrix and small pebbles overlies the lacustrines. Where observed, the contact shows extensive deformation that includes folded lacustrines with thrust faults. This facies was previously considered a slump or debris flow deposit but is here interpreted as the basal facies of the overlying red till on valley floors. The red till records an ice advance across valley floors covered with lacustrines. Varved sediments of coarser silt and sand found only in some valleys supports the hypothesis that local lakes also existed at some time. These lakes were distinct from regional lakes in the Esopus drainage basin.