NHNew Hampshire Geography

On 12 April 1934 the observers at the top of Mount Washington clocked a gust at 231 miles an hour. That reading stood as the fastest wind measured anywhere on earth for sixty-two years and remains the record for a staffed weather station. The mountain is 6,288 feet, modest by western standards, but it sits where three major storm tracks converge and its cone funnels air across bare, iced rock. Everything unusual about New Hampshire's geography follows from a small state being tilted hard against that weather.

An arctic summit in the temperate zone

Mount Washington is the highest peak in the northeastern United States. Treeline on its slopes falls at roughly 4,400 feet, thousands of feet lower than at the same latitude in the Rockies, because the summit climate is effectively subarctic. Above that line the Presidential Range carries around eight square miles of alpine tundra, the largest such area east of the Mississippi, holding plant species otherwise found in Labrador.

The mean annual temperature on the summit is about 27 degrees Fahrenheit and the peak sits inside cloud roughly sixty percent of the year. On 3 February 2023 the observatory recorded minus 47 degrees with a wind chill of minus 108, the lowest wind chill ever measured in the United States. Two nineteenth-century engineering projects still climb the mountain: the Auto Road, opened in 1861, and the Cog Railway, opened in 1869 as the first mountain-climbing rack railway anywhere in the world.

Notches, cirques and what the ice left

The Laurentide ice sheet covered New Hampshire completely and rode over the top of Mount Washington. Striations scratched into the summit rocks run northwest to southeast, recording the direction the ice moved.

The state's notches are the clearest legacy. Crawford, Franconia, Pinkham and Dixville are all glacially deepened troughs, valleys the ice widened and steepened as it forced through the mountain wall. Crawford Notch narrows at the Gateway to a gap a few hundred feet across, which is why a single road and a single railway line share it.

Tuckerman Ravine and the Great Gulf are different features altogether: cirques, amphitheatres gouged out by small local glaciers that formed after the main sheet withdrew. Tuckerman's east-facing bowl collects wind-drifted snow all winter and holds it into June, sometimes July.

Granite gave the state its nickname and its rockfalls. The Old Man of the Mountain, five ledges that lined up into a profile 1,200 feet above Franconia Notch, came apart on 3 May 2003 after decades of cabling and epoxy failed to hold the frost-split blocks together.

Eighteen miles of ocean and a river owned outright

New Hampshire's Atlantic frontage runs about 18 miles, from the mouth of the Piscataqua at Portsmouth south to the Massachusetts line at Seabrook. That is the shortest ocean coastline of any coastal state in the country.

Behind it, Great Bay reaches roughly fifteen miles inland, a drowned river valley where seven rivers meet tidewater. The bay fills and empties on a long lag, exposing thousands of acres of mudflat twice a day, which makes it one of the most productive estuaries in New England despite its size. Six miles offshore, the Isles of Shoals are cut in half by the state line, four islands New Hampshire and five Maine.

The western boundary is stranger. New Hampshire owns the whole Connecticut River. The line sits at the low-water mark on the Vermont bank, so the entire river surface, bed and all, is New Hampshire territory. The Supreme Court confirmed this in Vermont v. New Hampshire in 1933, tracing the arrangement to a royal order of 1764. The Maine boundary took even longer: New Hampshire v. Maine, decided in 2001, put the line down the middle of the Piscataqua channel and left the Portsmouth Naval Shipyard, which sits on Seavey's Island and carries a Portsmouth address, inside Maine.

The republic at the top of the state

The 1783 Treaty of Paris fixed the border at the northwesternmost head of the Connecticut River without specifying which headwater stream that meant. Several qualified. Between 1832 and 1835 the settlers living in the disputed ground around Indian Stream, claimed by both New Hampshire and Lower Canada and governed by neither, wrote a constitution, elected an assembly and ran themselves as an independent republic. New Hampshire took control in 1835 and the Webster-Ashburton Treaty settled the international line in 1842.

That territory is now the town of Pittsburg, about 291 square miles and the largest town by area in the state. Fourth Connecticut Lake, a two-acre pond at roughly 2,670 feet, sits directly on the Canadian border there and is the accepted source of the Connecticut River. The boundary swath, a cleared strip through the forest, runs past its edge.

The rest of the state's water sorts into four systems. The Connecticut drains the west, the Merrimack drains the centre from the point at Franklin where the Pemigewasset and Winnipesaukee rivers join, the Androscoggin and Saco carry the northeast into Maine, and the Piscataqua basin drains the seacoast. Lake Winnipesaukee, about 69 square miles with more than 250 islands, fills a basin scoured along a fault zone and closed off by glacial debris. Forest has taken back roughly 84 percent of New Hampshire, second only to Maine, after clearing for sheep and timber left the state close to half open ground in the 1870s.

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