PARABOLIC DUNES IN THE ST. LAWRENCE LOWLANDS, NORTHERN NEW YORK: EVIDENCE FOR POST-GLACIAL ANTI-CYCLONAL WINDS

Eolian dunes in the St. Lawrence Lowlands of Northern New York are easily overlooked because of their low relief and heavy vegetation but LiDAR data reveal their abundance and geomorphologic detail. Recent interpretation of LiDAR elevation and hillshade models indicate parabolic dunes are distributed along a belt from Heuvelton, New York, to the Canadian border. Dune preservation varies but shapes include singular dunes, partially preserved limbs, overlapping composite dunes, and complex dunes with zig-zag noses and limbs. Dunes range from several 100 meters to several km in length, 10’s of meters wide and up to 8 m high. The largest dunes have asymmetric profiles with steeper slopes to the SW. Where discernible, medial axes trend WSW. Areas of distinct cross-hatched map texture suggest more widespread presence of smaller, lower relief dunes along the belt. Dunes likely correlate with similarly described ones in Ontario and Quebec.

New ground-penetrating radar data at three locations along the dune belt support their origin under conditions of predominantly northeasterly winds. Subsurface data reveal dune foresets with apparent dips up to 25˚ dominantly to the SW on the noses of parabolic landforms. Great variability is observed in the apparent dip directions and most likely relates to their complex internal nature. Dunes rest on glacial landforms (e.g., Rogen moraine, drumlins, flutes) as well as beach terraces formed during regression of proglacial lakes and the Champlain Sea. Dunes often overlap beach ridges on lower slopes but are only rarely preserved on topographic highs. They are partially buried by wetlands and other post-glacial sedimentary environments.

Parabolic dunes are common in cold climates of moderate to high sand supply and low to moderate wind strength. St. Lawrence Lowland dunes probably derived their sand supply from newly exposed lake and marine sediments, deltaic sand plains, and alluvial floodplains following proglacial lake drainage and regression of the Champlain Sea. Dunes may have formed during the waning stages of a retreating Laurentide ice sheet when anticyclonic wind patterns still extended over northern New York. Vegetation and subsequent anchoring of the dunes reflect a transition to dominantly westerly winds under warmer and more humid conditions.