PATERSON — Now for a geology lesson.
The best place to fully grasp the magnitude of North Jersey’s flooding is the footbridge overlooking the Great Falls in Paterson. Here, the storm waters from seven significant rivers race toward a horseshoe gorge with all the speed, power and roar of Niagara Falls. The cliffs are not as towering, but the surge is awesome, in the truest sense of the word.
Saturday, a steady stream of people came to the overlook to take pictures of the Great Falls at their awful best. In those snapshots is a composite geologic history that explains why so much rain brings so much misery to people who live in the valleys of the Watchung Mountains.
While the flooding that perennially swamps the lowlands along North and Central Jersey’s river systems has been exacerbated by development, the big-picture culprit predates local planning boards by a couple hundred million years.
Wherever there is flooding — from Wayne and Lincoln Park to Bound Brook and Manville — ridges of the Watchung Mountains loom not too far off. The most flood-prone section of Wayne is called Mountain View. At the Great Falls, the water blasts through a gap and flows over jagged igneous rock formed in the Jurassic Period. This basalt rock, layered in millions of years of alternate volcanic flows and cooling periods, is some of the Earth’s most durable rock. While sedimentary rock around it eroded, the stubborn basalt stayed put, and the Watchungs were created.
Fast forward to the end of the last Ice Age, about 19,000 years ago. The ice sheet that covered the top of the world, now called the Wisconsin glacier, came as far south as New Jersey. When global warming (circa 17,000 B.C.) began to melt the glacier, the retreating ice sheet left a mess of rock debris. About 13,000 years ago, all this rock closed gaps in the Watchungs and trapped water from higher ground.
This created Glacial Lake Passaic.
When the lake eventually drained, it left the Passaic River as we know it today, with its many twists and turns over an 80-mile meander. How twisting and turning? It crosses Route 80 three times in a 6-mile span.
The most southwest end of Glacial Lake Passaic is today’s 7,768-acre Great Swamp National Wildlife Refuge in Chatham. The prehistoric lake extended as far north as Oakland, in Bergen County, and as far east as Paterson.
That’s why the Passaic River flood plain today covers 935 square miles. In that plain are neighborhoods and business corridors pictured in the news the last few days. But there are also nature preserves, reservoirs and somewhat pristine wetlands. The nearly contiguous Troy Meadows (3,100) acres, Hatfield Swamp (2,500 acres) and Great Piece Meadows (4,275 acres) span East Hanover, Parsippany, Fairfield, Montville and Lincoln Park.
Floods like last week’s don’t send the Passaic raging through these areas. It just returns the river to near its glacial lake state. Routes 80 and 280 are elevated above the floodplain, and for six or seven miles along each, the water is lake-like, except for the partially submerged trees. The Ramapo, Pequannock, Wanaque and Pompton rivers all take runoff from the Watchungs before emptying into the Passaic upstream from Little Falls. Farther west, parts of the Rockaway and Whippany rivers, which also dump into the Passaic, are affected by the Watchungs.
The Raritan River floodplain, too, is in the shadow of the Watchungs. The Blue Brook, Green Brook and Stony Brook tumbled down the rocks into the Raritan, then directly into Bound Brook and Manville.
And there you have it. Maybe it’s arrogance, or hubris, but our species tends to change the landscape around us, and assign blame when we can’t alter the course of nature. But the fact is, Earth does what it wants. That’s why they’re called natural disasters.
MORE FLOOD COVERAGE:
Source: National Weather Service/U.S. Geological Survey.