THE SEDIMENTARY RECORD OF MOHAWK RIVER FLOODS PRESERVED IN COLLINS POND, SCOTIA, NY CONFIRMED BY HURRICANE IRENE

Collin’s Pond (42°50’N; 73°57’W; 64 m asl) is a small (0.25 km²), shallow (z_max=8.5 m), eutrophic pond on the floodplain of the Mohawk River near Scotia, New York. The small drainage basin of Collin’s Pond is similar in size to the lake itself, yet Collin’s Pond has accumulated sediment at a high rate (~7 mm yr^-1 for the last 1000 years). The bedrock underlying the Mohawk River drainage basin varies considerably: the northern part of the drainage basin is underlain mainly by gneiss, the central part by calcareous shale and dolostone, and the southern part by carbonates and Paleozoic red beds of the Catskill Mountains. An ~7.5-meter-long sediment core from Collins Pond reveals numerous discrete laminae 0.1-10 cm thick of pink-colored sediment with a mineral magnetic signature similar to that of modern alluvium derived from the Paleozoic red beds of the Catskill region. The red-color intensity of the sediment core was measured continuously with sub-millimeter resolution revealing dozens of probable flood events over the past millennium, many of which correlate with Hurricane landings in the mid Atlantic and New England states. Flood waters of the Mohawk River in response to Hurricane Irene on 29-30 August, 2011 were principally derived from the Catskill region and inundated Collins Pond depositing a layer of pink sediment 0.2-0.5 cm thick throughout the lake basin. Laminae from flood events were sampled and treated to remove organic matter and biogenic silica, and analyzed with a Coulter LS 230 laser diffraction grain size analyzer. Results indicate that flood laminae are composed of fine silt (4-10 µm) that are slightly coarser than background sediment, and in most cases laminae are normally graded suggesting sediment delivery via overflows as opposed to density driven undercurrents.