Proposed sequence of events associated with the formation of the parabolic dunes at the Grandifolia Sand Hills

bp is years before present

20,000 bp Glacier front begins retreat north away from the Harbor Hill Moraine. 

19,000 bp The Long Island Sound Basin is dammed forming glacial Lake Connecticut with a level of -10 meters relative to present day sea level (Lewis and Stone, 1991).

18,000 to 15,500 bp Glacial Lake Connecticut is lowered to -20 meters relative to present day sea level by progressive erosion at the Race near Orient Point before draining at 15,500 bp. 

15,500 to 10,000 bp Long Island Sound Basin is a partially sandy fluvial system that experiences minor incursions of the sea with a level of -40 meters relative to present day sea level. Gales and Bokuniewicz, 1991, suggest that sea level in the Sound begins to rise from the -40 meter level at about 10,000 bp. Dunes climb and cease to migrate as they become "welded" to the north side of the Harbor Hill Moraine. Fagus Grandifolia forest, possibly as a dwarf form at the edge of its range, is established as a pioneer tree on the dunes displacing tundra vegetation.  Pitch pine-oak forest is established on the outwash plain to the south of the Harbor Hill Moraine.

10,000 to 5,000 bp Around this time period, larger growth forms of Fagus grandifolia colonized the protected soil-enriched low lying areas, whereas the dwarf form still dominated the exposed ridge tops and bluff faces. Possible genetic drift occurs favoring taller trees. Fire maintains pines as climate warms.

5,000 bp High erosional scarp forms and bluff retreats at approximately one foot per year. Fagus grandifolia is subjected to progressive undercutting at its boundary with Long Island Sound.

Present Increased environmental stress resulting from erosion associated with sea level rise results in a proliferation of the dwarf form of Fagus grandifolia. Fagus grandifolia adapts to salt spray stress and soil loss by dwarfing, especially where bluffs are undercut by Sound. Possible genetic drift occurs. Relict parent forest remains on dune areas.