STEADY THEN STAGNANT – ASPECTS OF LGM DEGLACIATION IN FLUSHING MEADOWS, QUEENS, NEW YORK
Below Flushing Meadows the ancient Hudson River cut a deep, narrow valley through Cretaceous Raritan Clay down to the bedrock. The valley filled with till, outwash and varves from an earlier Wisconsinan age glaciation – likely the Ronkonkoma advance that is occasionally found in the subsurface (Moss 2011), but has an unknown terminus in NYC. These soils were glacially loaded and scoured out to roughly elevation -190’ by the later LGM Harbor Hill event. This scour pattern extends at least to the south end of the National Tennis Center, indicating that the Ronkonkoma advance reached at least this far south in Flushing Meadows.
During LGM retreat a thick layer of glacial lake varved silt and clay filled in much of the valley north of the Harbor Hill terminal moraine. Northward retreat paused (at the southern edge of the ’64 World’s Fair grounds) depositing till along the valley sides directly above the Raritan Clay. This recessional moraine (mapped in Merrill & Others, 1902) aligns best with the EZ ice margin. Deep boring data is too sparse to interpret details of deglaciation between the terminus and this margin, but data improves over the feature’s northern half (beneath the Tennis Center) where varved soils lie above the till. There is no sign of the typical glacial loading &/or outwash and till that would be associated with a readvance as the ice resumed its retreat.
Heading northward, layers of outwash sand from late glacial readvances finally start to appear within the varved deposits, ultimately becoming the dominant soil type at the northern end of the valley where they align best with the M1 ice margin. Outwash from an early advance, at roughly El -150’, reaches the northern edge of the Tennis Center. Later advances at El -120’ and -85’ do not extend south of the Citifield site. In Flushing Meadows retreat from the EZ line was fairly steady until the ice stalled at the M1 margin, where the more active front fluctuated before its final retreat north of Queens.