THE FINAL STAGES OF DEGLACIATION IN NORTHEASTERN NEW YORK

High-resolution mapping and spatial analysis of glacial, lacustrine, and marine deposits using LiDAR elevation models provide new details and insights on ice recession and the evolution of lake and marine water bodies during the final stages of deglaciation in New York. The principal area of study straddles the St. Lawrence–Champlain drainage divide in Clinton County, northeastern New York and extends northward to the Covey Hill area in southern Québec.

Spatial analysis of beach ridge elevations provides a high-resolution record of falling water level in proglacial lakes and the Champlain Sea during deglaciation. Shoreline regression, controlled by gradual outlet incision and the net effects of differential isostatic rebound and sea-level changes produced off-lapping beach deposits that adjusted continuously during deglaciation. The general progression of gradually falling water levels recorded by beach ridge deposits was interrupted by breakout floods when water catastrophically discharged from source reservoirs in the Ontario and St. Lawrence lowlands to receiving water bodies in the Champlain–Hudson Lowland and the Gulf of St. Lawrence. Water levels in the source lakes fell rapidly during breakouts but returned to gradual decline after water levels in the source and receiving reservoirs equilibrated.

We present a refined deglacial history that delineates and chronicles the late glacial moraines and ice-marginal drainage systems during the latest stages of deglaciation in New York. The chronology begins with a period of westward ice-marginal drainage that led to the formation of the Churubusco-Chateaugay channels in northeastern Franklin County. This was followed by a regional ice readvance into proglacial Lake Iroquois and the Champlain Lowland, a two-stage breakout of Lake Iroquois that created the Flat Rock sandstone pavements in the Champlain Lowland, and a post-Iroquois breakout ice readvance in the Champlain Valley. Deglacial activity culminated with the breakout of proglacial lakes to the Champlain Sea.

We propose new nomenclature for successive lake stages in the Ontario, St. Lawrence, Champlain, and Hudson lowlands that is compatible with these data. The proposed names provide an alternative to the overlapping and sometimes confusing nomenclature currently in use.