REEXMAMINING A POST-GLACIAL DUNE FIELD IN THE ST. LAWRENCE LOWLANDS, NORTHERN NY USING HIGH-RESOLUTION LIDAR HILLSHADE MODELS

Eolian dunes have long been recognized in the St. Lawrence Lowlands, but low relief and vegetation cover hinder description of their morphology and distribution. Detailed mapping with LIDAR data shows their distribution along a >100 km belt from Heuvelton northeast to Trout River State Forest.

The dunes were mapped in ArcGIS using 1-meter resolution LiDAR hillshade models. They typically range tens of meters to several km long, tens of meters wide and <10m high. Dune crests zig-zag in V- or W-shaped patterns with a medial axes that trend ENE-WSW and are asymmetric in profile, with steeper WSW slopes. Many dunes coalesce, producing an imbricate pattern with multiple crests. Dunes with similar morphology occur in southern Quebec where they are interpreted to be parabolic dunes. Their morphology indicates prevailing ENE paleowinds.

Dunes in the St. Lawrence Lowland are generally preserved in low-relief marshland between areas of well-developed ribbed or Rogen moraine and drumlins. Beach ridges deposited in regional proglacial lakes and the Champlain Sea occur on the flanks of these glacial bedforms, especially on their windward margins. Eolian dunes often overlap beach ridges on the lower slopes but are rarely preserved on the highest parts of the Rogen moraines and drumlins.

Parabolic dunes are vegetation-anchored dunes that are common in cold climates or coastal areas of moderate to high sand supply and low to moderate wind strength. The parabolic dunes of the St. Lawrence Lowland probably derived their sand supply from the newly exposed lake and marine bottom sediments, deltaic sand plains, and alluvial floodplains following proglacial lake drainage and regression of the Champlain Sea (~13–10 cal ka) in the region. Their morphological development reflects the influence of anchoring vegetation and a shallow water table. Parabolic dunes reflect environmental conditions that were conducive to the growth of pioneering vegetation on the deglaciated landscape.