Nantucket - Geology and Geography

Geology and Geography

Nantucket was formed by the uttermost reach of the Laurentide Ice Sheet during the recent Wisconsin Glaciation, shaped by the subsequent rise in sea level. The island's low ridge across the northern section was deposited as glacial moraine during a period of glacial standstill, a period during which till continued to arrive, but melted at a stationary front. The southern part of the island is an outwash plain, sloping away from the arc of moraine and shaped at its margins by the sorting actions and transport of longshore drift. Nantucket became an island when rising sea levels reflooded Buzzards Bay about 5,000–6,000 years ago.

According to the U.S. Census Bureau, Nantucket County has a total area of 303.5 square miles (786 km2), the smallest county in Massachusetts, 84.25% of which is water. The area of Nantucket Island proper is 47.8 square miles (124 km2). The triangular region of ocean between Nantucket, Martha's Vineyard, and Cape Cod, is Nantucket Sound. The highest point on the island is Folger Hill which stands 109 feet (33 m) above sea level. Altar Rock is a close second at a height of 108 feet (33 m) above sea level.

The entire island, as well as the adjoining islands of Tuckernuck and Muskeget, comprise both the Town of Nantucket and the County of Nantucket. The main settlement, also called Nantucket, is located at the western end of Nantucket Harbor, where it opens into Nantucket Sound. Key localities on the island include Madaket, Surfside, Polpis, Wauwinet, Massachusetts, Miacomet and Siasconset (often abbreviated as 'Sconset).