North Sawyer Glacier originates in the Coast Mountains of British Columbia at an elevation of about 6,600 feet (2,012 m) and flows generally west for 14 miles (23 km) to the Alaska border at 3,600 feet (1,097 m), then another 7 miles (11 km) to a tidewater terminus in Tracy Arm, about 78 miles (126 km) north of Petersburg and 53 miles (85 km) southeast of Juneau, Alaska. The glacier was named in 1889 by Commander Henry B. Mansfield on Carlile P. Patterson and published in 1891 by the US Coast and Geodetic Survey. Tracy Arm is a fjord also named by Mansfield, in 1889, after Secretary of the Navy Benjamin F. Tracy. The fjord extends 30 miles (48 km) from Holkham Bay to the glacier and is part of the Tracy Arm-Fords Terror Wilderness, designated by Congress in 1990. The wilderness encompasses 653,179 acres (264,332 ha) in the Tongass National Forest and comprises Tracy Arm and Endicott Arm—both fjords exceeding 30 miles (48 km) in length. In summer, both carry considerable floating ice ranging from hand-sized pieces to icebergs over 30 feet (9 m) tall.

The Coast Mountains extend north for about 1,000 miles (1,600 km) from the Fraser River in British Columbia through the Boundary Ranges in Southeast Alaska to the Yukon in the north. Southeast Alaska’s geology is defined by a series of tectonostratigraphic terranes that formed in the equatorial Pacific and rafted northward on oceanic plates, eventually accreting to the North American continent. The Boundary Ranges are largely covered by extensive ice fields underlain by volcanic and non-volcanic bedrock. The volcanic rocks are remnants of a Late Cretaceous (about 100 million to 66 million years ago) volcanic arc called the Coast Range Arc. The non-volcanic rocks belong to the Tracy Arm terrane, which accreted to North America between 185 million and 170 million years ago and comprises the Tracy Arm, Endicott Arm, and Port Houghton assemblages. During the Eocene (about 56 million to 34 million years ago), magma intruded the terrane, forming granodiorite plutons and metamorphosing the surrounding sedimentary rocks. The oldest rocks belong to the Tracy Arm assemblage, a metasedimentary succession of biotite schist, gneiss, quartzite, and marble.

Tidewater glaciers are ice streams that terminate in the ocean at either a grounded terminus or a floating ice tongue. The US Geological Survey has identified 59 current and former tidewater glaciers in Alaska, of which only 50 currently terminate at tidewater. The Boundary Ranges of Southeast Alaska retain four tidewater glaciers—North Sawyer, South Sawyer, Dawes, and LeConte—with a combined area of 443,520 acres (179,486 ha); all are thinning and retreating. In 1794, the Vancouver Expedition discovered Holkham Bay and noted ice fronts at its head but did not observe Tracy or Endicott arms. In 1889, Mansfield sailed up Tracy Arm and observed a single Sawyer Glacier ice front. By 1904, that front had divided into North Sawyer and South Sawyer glaciers, representing a retreat of 24 miles (39 km)—roughly 1,320 feet (400 m) per year—since Vancouver’s visit. By 1961, the terminus had retreated nearly to the fjord‘s main channel, and from 1961 to 2022 the glacier receded a further 2 miles (3.3 km). Satellite images from May 2023 show the terminus has withdrawn from Tracy Arm entirely, with only the highest tides reaching the ice at its southernmost point. Read more here and here. Explore more of North Sawyer Glacier and Tracy Arm here: