Glacial Lake Passaic
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Glacial 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 13,000 years ago, which was formed of waters released by the melting of the retreating Wisconsin Glacier that had pushed large quantities of earth and rock ahead of its advance, blocking previous natural drainage.
The lake was formed on the western side of the Watchung Mountains by a blockage of the Passaic River at Moggy Hollow from a moraine left by the retreat of the glacier. The river had previously passed through the Watchungs on a northerly course near present-day Summit and Chatham and turning eastward at what is called the Short Hills Gap that separates the present day communities of Short Hills and Summit. After the raising of the lake's level, the river found a new temporary course to the sea near present-day Bernardsville from Moggy Hollow along the Long Hills using a gorge at Millington.
Eventually the river formed its present course, a circuitous detour around the north end of the Watchung range through present-day Paterson. As the glacier retreated, the lake found a new outflow to the ocean via Great Notch near Totowa and Upper Montclair, which eventually drained most of the once mighty lake, leaving smaller lakes that eventually dried up or formed marshes and swamps.
As the glacier retreated farther to the north, the outflow of the lake drained toward the north and formed the gorge of the Great Falls of the Passaic River in Paterson.
The remnants of the Glacial Lake Passaic lake bed are found in several swamps in northern New Jersey, most notably, the Great Swamp that is south of Morristown through Chatham Township, laying in extreme southern Morris County and northeastern Somerset County. It is the source of the Passaic River, which results from the flow into the Great Swamp of Black Brook, Great Brook, Loantaka Brook, Primrose Brook, and the Upper Passaic River that exit as the Passaic River flowing northerly via Millington Gorge. The Great Swamp entails a watershed of fifty-five square miles. [1]
Following the largest American conservation effort by residents, a major portion of this watershed was acquired through assembling purchases made during a year-long effort that began in 1959. Those properties, entailing 7,600 acres or just under twelve square miles, have been preserved by being donated to the federal government on November 3, 1960 as a park for perpetual protection. The area donated has 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.
Higher elevations in these areas, such as Long Hill Township, the Long Hill ridge that runs from Basking Ridge through Chatham Township, Chatham, and parts of Madison, formed islands within the massive glacial lake. Morristown is on a plateau between ranges and was the most westerly point of the massive lake that was retained by the range to its west.
