Boston Glacier, Largest glacier in North Cascades National Park, Washington, United States

Boston Glacier fills a large cirque below several peaks in North Cascades National Park. It runs about 1 mi (1.6 km) long but nearly 3.5 mi (5.6 km) wide, arcing north from Forbidden Peak, with Boston Peak to the southwest and Buckner Mountain at its eastern margin beneath Ripsaw Ridge. Another arête between Boston Peak, Sharkfin Tower and Forbidden Peak separates it from the adjoining Quien Sabe and Forbidden Glaciers.

Boston Glacier has been retreating overall since the end of the Little Ice Age around 1850. It advanced moderately between 1950 and the mid-1970s, then resumed retreating; between 1972 and 2006 its terminus pulled back 1,470 ft (450 m).

The glacier sits in a large cirque below Ripsaw Ridge, the arête between Boston Peak and Buckner Mountain. A second arête running from Boston Peak past Sharkfin Tower to Forbidden Peak separates it from the adjoining Quien Sabe and Forbidden Glaciers. Its name comes from Boston Peak, which flanks it to the southwest.

The glacier sits in a cirque below Ripsaw Ridge, between Boston Peak to the southwest and Buckner Mountain to the east, about 1 mi (1.6 km) long and nearly 3.5 mi (5.6 km) wide. There are no facilities or marked services; approach is on foot through remote backcountry, so plan for crevasses, rockfall and sudden weather. Its terminus pulled back 1,470 ft (450 m) between 1972 and 2006, so expect bare rock where ice once reached.

Boston Glacier is the largest glacier in North Cascades National Park, yet it is only about 1 mi (1.6 km) long while nearly 3.5 mi (5.6 km) wide. Its arc runs from north of Forbidden Peak, with Boston Peak to the southwest and Buckner Mountain at its eastern margin, below the arête called Ripsaw Ridge.