REASSESSING THE SURFICIAL GEOLOGY AND DEGLACIAL CHRONOLOGY OF THE LOWER SARANAC VALLEY, NORTHEASTERN NEW YORK USING HIGH-RESOLUTION LIDAR ELEVATION AND HILLSHADE MODELS

The present understanding of the lower Saranac Valley deglacial history in northeastern New York is derived from interpretations based upon pre-1980 surficial geologic mapping at scales of 1:62,500 or smaller. Newly acquired high-resolution LiDAR elevation and hillshade models facilitate reevaluation of previously mapped portions of the lower Saranac Valley and refinement of the regional deglacial chronology.

The Saranac Valley in the study area cuts through a generally sparsely populated and forested upland region. The reliability of conventional maps tends to be biased toward accessible areas where the deposits and landforms are visually traceable. LiDAR spatial databases enable better delineation of previously mapped surficial deposits and identification of previously unrecognized deposits and landforms, especially in remote areas where landform scale, relief and access make field identification difficult. LiDAR hillshade models are particularly useful in identifying subtle landforms such as streamlined subglacial bedforms and ice-marginal landforms such as channeled and hummocky ice-contact deposits and moraines. Moraines in the Saranac Valley occur as narrow, single-crested, low-relief ridges and as clusters of closely spaced, irregular moraine ridges that resemble grounding-line push moraines or washboard moraines. The extents of former proglacial lakes in the region are associated with deltaic sand plains, curvilinear beach ridges, eolian dunes, stream terraces and outlet channels.

Our reexamination of glacial deposits and landforms provides new information about deglacial events in the lower Saranac Valley. These events occurred at a time when outflow from local proglacial lakes confined to the Saranac Valley transitioned from southward flow to the AuSable Valley to eastward flow through a falling series outflow channels to regional proglacial lakes and marine water levels in the Champlain Valley.