| Northfield Mountain | |
|---|---|
Map showing ridgeline and pumped-storage hydroelectric reservoir |
|
| Elevation | 1,206 ft (368 m) |
| Location | |
| Location | Erving and Northfield, Massachusetts |
| Range | Millers River highlands |
| Geology | |
| Type | Metamorphic rock |
| Age of rock | 400 million years |
| Climbing | |
| Easiest route | Metacomet-Monadnock Trail |
Northfield Mountain, 1,206 feet (368 m), is a mountain ridge located in Erving and Northfield, Massachusetts. 2.5 miles (4.0 km) long by 1.8 miles (2.9 km) long, the mountain is composed of several distinct peaks and ledges, most notabily Rattlesnake Mountain (also known as Farley Ledge) 1,067 feet (325 m), Rose Ledges 330 metres (1,080 ft), and Hermit Mountain (the high point). A pumped-storage hydroelectric plant and reservoir occupies the top of the mountain west of the summit.
The 110 mi (180 km) Metacomet-Monadnock Trail crosses the summit ridge of Northfield Mountain; a series of shorter hiking trails, cross country ski trails, and rock climbing routes are also located on the mountain and its ledges. Northfield Mountain is located at the confluence of the Connecticut River and Millers River. A waterfall, Briggs Brook Falls, plunges from its southeast side.
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Engineering studies began in October 1964, with early site preparation starting three years later. In 1972 its 1,080-megawatt hydroelectric plant became operational as the largest such facility in the world.
The plant was built entirely underground, and located about 5.5 miles (8.9 km) up the Connecticut River from Turners Falls Dam. A stretch of the Connecticut River, extending some 20 miles (32 km) north from this dam to the Vernon Dam, Vermont, serves as the station's lower reservoir. During periods of lower electrical power demand, the plant pumps water from this lower reservoir through the Northfield Mountain Tailrace Tunnel to a man-made upper reservoir. At times of high demand, water is released to flow downhill from this upper reservoir through a turbine generator, where it then collects in the lower reservoir to be stored until again pumped to the upper reservoir.
Northfield Mountain's upper reservoir covers 300 acres (1.2 km2) at 800 feet (240 m) above the river, with total storage of 5.6 billion US gallons (21,000,000 m3) of water. Its underground powerhouse lies at 700 feet (210 m) below the surface and is accessible through a 2,500-foot (760 m)-long tunnel; it includes four large reversible turbines, each of which can pump about 20,000 US gallons (76,000 L) of water per second and generate 270,000 kilowatts of electricity.
The "lower reservoir" noted above is a pool along the Connecticut River above Turner's Falls Dam. Since the dam at Turner's Falls was raised in the early 1970s for Northfield Mountain, the banks of the Connecticut River have been re-adjusting to the new water level.
FirstLight Power Resources also manages recreational resources on the mountain as part of their agreement with the state of Massachusetts. A cross-country ski area is located on the mountain; it includes groomed trails, warming huts, and ski instruction. The 110-mile (180 km) Metacomet-Monadnock Trail traverses the mountain, as do a number of shorter trails. FirstLight also offers camping at nearby Barton Cove, environmental programs, and boat tours of the Connecticut River.
Rose Ledge and Farley Ledges are popular among rock climbers. Farley Ledge has been subject to recent conservation and climbing access initiatives. Hermit Mountain is the site of "Hermit's Castle," a state historic site where John Smith, a local recluse, made his home from 1857 to 1900.
Northfield Mountains' geologic story can begin in the late pre-Cambrian Period. The ancient pre-Cambrian rocks are more than 600 million years old and are found only in the Western Berkshires of Massachusetts and in the Green Mountains of Vermont.