Bryn Mawr Glacier, College Fjord

Bryn Mawr Glacier, College Fjord

by | Sep 24, 2021

Bryn Mawr Glacier flows southeast for about 4.5 miles (7 km) to Harvard Arm of College Fjord in northwestern Prince William Sound, about 52 miles (84 km) west of Valdez and 44 miles (71 km) northeast of Whittier, Alaska. The terminus of Bryn Mawr Glacier is 1.8 miles (2.9 km) south-southwest of Smith Glacier and 1.8 miles (2.9 km) north-northeast of Vassar Glacier. Bryn Mawr Glacier has two main tributary branches, each starting at elevations near 8,000 feet (2,438 m) on the east side of a ridge separating College Fjord from Barry Glacier. College Fjord was first mapped in 1794 by Joseph Whidbey on Captain George Vancouver‘s voyage of discovery, and again in 1887 by Samuel Applegate of the U.S. Coast and Geodetic Survey on the schooner Nellie Juan. College Fjord extends northeast for 16 miles (26 km) from the head of Port Wells to College Point where it divides into Harvard Arm to the west and Yale Arm to the east. Harvard Arm continues for about 4 miles (6.5 km) northeast of College Point. College Fjord contains five glaciers that terminate in seawater, five large valley glaciers that no longer extend to sea level, and dozens of smaller glaciers mostly named after renowned east coast colleges, with women’s colleges on the northwest side and men’s colleges on the southeast side. Bryn Mawr Glacier was named by members of the Harriman Alaska Expedition in 1899 after Bryn Mawr College, a women’s liberal arts college founded as a Quaker institution in 1885 in Bryn Mawr, Pennsylvania. Bryn Mawr is a Welsh phrase meaning ‘large hill’.

The two tributary branches of Bryn Mawr Glacier start in mountain cirques and flow east for about 2.5 miles (4 km) through deep mountain valleys with a fairly gentle slope. Just before merging they each plunge over a steep slope creating icefalls about 0.8 miles (1.3 km) long. Below the icefall, about 1.3 miles (2.1 km) from tidewater, the branches merge creating a distinctive medial moraine, and then flow along a gentle gradient for about 0.5 miles (0.8 km) before tumbling over another icefall to tidewater. The cliffs underlying the ice and represented by the icefalls were probably created by the trunk glacier of Harvard Arm at two earlier stages in its history. The elevation of the upper slope break of these icefalls likely approximates the surface elevation of the historical glacier that once filled Harvard Arm and College Fjord. Photographs were obtained of the glacier terminus by the Harriman Expedition in 1899 and on subsequent visits by the U.S. Geological Survey in 1905 and 1909. A comparison of these photographs indicates that Bryn Mawr Glacier had retreated about 500 feet (152 m) between 1899 and 1905, but had advanced again by the same distance between 1905 and 1909. In 1914, a survey of the glaciers by the National Geographic Society indicated the Harvard Glacier had retreated slightly since 1909, but many of the smaller glaciers in College Fjord showed no observable change. Bryn Mawr Glacier may have retreated slightly since the barren zone at its northern border was wider.

The terminus fluctuations of six tidewater and near-tidewater glaciers in College Fjord have been monitored since 1931 by ground surveys, aerial photogrammetry, and most recently by satellite imagery. In 1926, an expedition of several months’ duration was required to get to the glaciers and do the mapping. Glacier termini were surveyed using a theodolite from ground control points established by triangulation. By the 1940s, aerial photography of Alaskan glaciers began to be used to monitor terminus fluctuations. The photogrammetric measurements can be related to the older surveys if the ground control points can be identified on the photographs. Within the last 50 years, it has become possible to measure glaciers from space. The satellite images can be related to aerial photographs by matching topographic features, and to the older terrestrial surveys by identifying topographic features near the survey points. These measurements over time indicate that the smaller glaciers in College Fjord, for example, Wellesley, Vassar, Bryn Mawr, and Smith Glaciers reached their maximum positions at the end of the 19th century. Since that time, they have undergone modest retreat punctuated by small advances. Around 1910, all four glaciers experienced a small advance. In the mid-1930s, Bryn Mawr and Wellesley Glaciers experienced another small advance, and these same two glaciers, along with Smith Glacier experienced a third advance in the late 1960s. The most recent observations suggest that Bryn Mawr Glacier has advanced since 1976, while the others have shown little change. In general, the terminus positions of tidewater glaciers are thought to be the result of a complex interaction of fjord depth, ice thickness, and calving rate with climate and mass balance playing a secondary role. A distinct cycle of dynamically controlled advance and retreat of tidewater glaciers consists of three phases. The first phase is a period of slow advance with the glacier maintaining a submarine moraine shoal in front of the terminus. This shoal, which is moved in front of the glacier greatly reduces iceberg calving, thereby maintaining the glacier in a positive mass balance. The second phase is a period of relative stability during which the terminus is nearly stationary, terminating in shallow water while grounded on a submarine moraine. The third phase is a period of rapid retreat during which the terminus retreats off its submarine moraine shoal into deep water. This produces calving at a high rate which overwhelms the ability of the glacier to supply ice to the terminus, and the retreat continues until the glacier stabilizes on another submarine shoal or retreats from tidewater. Read more here and here. Explore more of Bryn Mawr Glacier here:

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