WASHBOARD MORAINE IN THE SARANAC VALLEY, NORTHEASTERN ADIRONDACK MOUNTAINS, NEW YORK–EVIDENCE FOR SURGE BEHAVIOR DURING REGIONAL LATE WISCONSINAN DEGLACIATION?

The non-genetic term washboard (or corrugated) moraine describes the morphology of closely spaced, low-relief ridges composed of till or stratified deposits that are transverse to glacial paleoflow. Two areas of washboard moraine are recognized on LiDAR hillshade models of the middle Saranac River watershed in the Adirondack Mountains of northeastern New York. Washboard moraine ridges are generally a few hundred meters to a kilometer or two long, tens of meters wide, and >5 m high. Spacing between ridge crests varies from tens of meters to about 200 m.

Washboard moraine deposits in the Franklin Falls area overlie fluted till surfaces and are associated with reticulate ice-disintegration ridges. Larger and more continuous ridges occur at the distal end of the moraine field and may represent push or ice-thrust moraines. The Franklin Falls moraine may have formed contemporaneously with pitted outwash deposits at Loon Lake, approximately 16 km to the northwest. Washboard moraine in the Cadyville area is part of a larger moraine complex that includes possible ice-thrust moraines, deep meltwater channels, and glacial-fluvial inwash and deltaic deposits. The southern boundary of this moraine field corresponds closely to the upper limit of proglacial lake inundation in the lower Saranac River valley. The moraine belt on the north flank of the valley is extensively modified by glacial-fluvial processes or lies buried beneath proglacial deltaic deposits.

Washboard moraine has been attributed to ice-marginal push or thrusting, subglacial boundary instability, or intrusion of soft subglacial sediment into basal crevasses. The morphology of moraine fields in the Saranac Valley conform to the crevasse-squeeze model, which is associated with extensional flow in the terminal zone of surging glaciers. The occurrence of possible ice-marginal push or thrust moraines, and ridge truncation and overlap in some moraine fields may be evidence for multiple surge events.