Glacial Lake Passaic

Lake Passaic was a prehistoric proglacial lake that existed in northern New Jersey in the United States at the end of the last ice age approximately 19,000-14,000 years ago. The lake was formed of waters released by the retreating Wisconsin Glacier, which had pushed large quantities of earth and rock ahead of its advance, blocking the previous natural drainage of the ancestral Passaic River through a gap in the central Watchung Mountains. The lake persisted for several thousand years as melting ice and eroding moraine dams slowly drained the former lake basin. The effect of the lake’s creation permanently altered the course of the Passaic River, forcing it to take a circuitous route through the northern Watchung Mountains before spilling out into the lower piedmont.

Today, the former lake basin is called Passaic Meadows and includes the Great Swamp, Black Meadows, Troy Meadows, Hatfield Swamp, Lee Meadows, Little Piece Meadows, Great Piece Meadows, Glenhurst Meadows, and Bog and Vly Meadows. These remnants of the ancient lake provide prime wetland habitat to a variety of plants and animals while at the same time offering recreational and outdoor opportunities to residents of northern New Jersey.

The discovery of Glacial Lake Passaic is credited to Professor George Hammell Cook, once the State Geologist of New Jersey and Vice President of Rutgers University. Cook’s first official mention of the lake was in the New Jersey Annual Report of the State Geologist for the Year 1880, in which he described flat-topped hills and drift-like deposits in the upper Passaic Valley that appeared to be created or modified by the waters of a lake. Twelve years later, field research conducted under State Geologist John C. Smock began to uncover wave-cut terraces and other shoreline features that more conclusively established the lake’s existence. However, the boundaries of the lake were not completely understood until the following year, 1893, when geologists Rollin D. Salisbury and Henry B. Kümmel completed a study of wave cut terraces, shoreline platforms, and delta deposits within the central and upper Passaic basin. The study was used to create a report, Lake Passaic – An Extinct Glacial Lake, which was included in the New Jersey Annual Report of the State Geologist for the Year 1893.

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