thumb|right|300px|Approximation of the extent of 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.

Discovery

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.

Geology

During the late Triassic and early Jurassic periods, when the North American plate separated from the African plate, an aborted rift system was created. The resulting rift valley, known as the Newark Basin, was filled with alternating layers of red bed sediment and flood basalts. Over millions of years, the rift valley was faulted, tilted, and eroded, until the edges of the hard flood basalt layers formed ridges. Prior to 20,000 years before the present, an ancestral Passaic River flowed through a gap in these ridges. This changed when the Wisconsin Glacier, a massive continental ice sheet which formed during the last ice age, advanced on the region and permanently plugged the gap. As the glacier eventually melted back, water pooled behind the ridges (known today as the Watchung Mountains), forming Glacial Lake Passaic.

Lake stages

Glacial Lake Passaic was a dynamic water body during its five millennia of existence. At present, the lake is believed to have existed in four major stages, the final stage being split between three smaller sub-stages. Each stage saw a new shoreline elevation of the lake as ice or earthen moraine dams were built or gave way, often over brief spans of time. Within this watershed, Black Brook, Great Brook, Loantaka Brook, Primrose Brook, and the Upper Passaic River combine their waters in the Great Swamp to form the Passaic River, which exits the swamp via the Millington Gorge.

Following the largest American conservation effort by residents in response to a proposal to build a huge fourth regional airport that would have destroyed the ecosystem, a major portion of this watershed was acquired through assembling purchases made during a year-long effort that began in 1959. Those properties, entailing or just under twelve square miles, were preserved through a donation to the federal government on November 3, 1960, setting them aside as a park for perpetual protection. The area given to the government has since become the Great Swamp National Wildlife Refuge and now is watched over by citizens from the ten communities that ring the swamp, who have formed thirteen separate oversight organizations. Additions to the area have continued to the present day.

Flooding

Chronic flooding in the central Passaic basin, particularly around the confluence of the Passaic and Pompton rivers, has been severe enough to lead to government buyouts of private land. This section of the basin, upstream of the chokepoint created by the Little Falls and the Great Falls, occasionally fills with so much water that some of the Totowa Stage of Glacial Lake Passaic briefly reappears until enough time has gone by for the water to drain out. The Passaic River Flood Tunnel, a floodwater diversion system, has been proposed to create a new escape route for water trapped behind the Watchung Mountains.

See also

  • List of prehistoric lakes

References

  • Depiction of Lake Passaic as it Existed 11,000 to 13,000 years ago.