Johns Hopkins Inlet, Glacier Bay National Park and Preserve

Johns Hopkins Inlet, Glacier Bay National Park and Preserve

by | Dec 1, 2021

Johns Hopkins Inlet is a fjord that starts at the terminus of the Johns Hopkins Glacier and extends for about 10 miles (16 km) to the head of Glacier Bay, about 106 miles (171 km) southeast of Yakutat and 58 miles (93 km) northwest of Gustavus, Alaska. The fjord has depths of over 600 feet (183 m), and the shore is very steep and rocky. The inlet trends northeast from the glacier terminus for 5.8 miles (9.4 km) to Jaw Point and then southeast to the head of Glacier Bay at Russell Island, in Glacier Bay National Park and Preserve. The inlet was named for the glacier, which was named after Johns Hopkins University in Baltimore, Maryland in 1893 by Harry Fielding Reid of the U.S. Geological Survey. Reid was a geophysicist notable for his contributions to seismology, particularly his theory of elastic rebound that related faults to earthquakes. In 1893, Reid had originally called the glacier at the head of Glacier Bay ‘Grand Pacific Glacier’, which at the time was at Russell Island. As the Grand Pacific Glacier retreated, two inlets were formed, one to the north called Tarr Inlet, and the other to the west was named Reid Inlet. The continued retreat of Johns Hopkins Glacier lengthened Reid Inlet, and eventually, the historical relationship to Reid Glacier at Russell Island became obscure and in 1954, the Board of Geographic Names changed the name of the newly exposed fjord to Johns Hopkins Inlet. Today, Johns Hopkins Glacier is about 1 mile (1.6 km) wide, 225-300 feet (68-91 m) high at the terminus, and approximately 200 feet (61 m) deep. It is formed from numerous tributary glaciers, many of which extend 12 miles (19 km) or more into the surrounding peaks. Meltwater from the glacier is discharged from submarine tunnels or conduits located near both the northern and southern edges of the glacier. Water circulation near the glacier is very erratic as freshwater enters at all depths from the terminus face. Swirls and eddies are common and cause drifting ice to move slowly in all directions.

In general, tidewater and terrestrial glaciers have been thinning and slowly receding over the last 100 years. Warmer temperatures coupled with an apparent reduction in cloud cover and precipitation during the summer, have resulted in reduced snow accumulation and retention. Changes in tidewater glaciers are cyclical, with advance rates typically an order of magnitude slower and occurring over much longer periods than retreats. Though these changes are generally in response to shifts in climate, the response of individual glaciers can vary greatly. Similar to terrestrial glaciers, most of the approximately 50 tidewater glaciers in Alaska have retreated, though some are relatively stable or even advancing. For example, Johns Hopkins Glacier is currently the only advancing tidewater glacier on the eastern side of the Fairweather Range, and can discharge enormous quantities of glacial ice into the inlet. The quantity of ice discharged varies from year to year and is greatly affected by seismic activity and local weather. This volume of ice driven by melting at the calving front, as well as through calving itself, creates a highly dynamic fjord environment. Upwelling at the glacier terminus provides nutrients important for plankton, and subsequently fish, seabirds, and marine mammals. Icebergs that calve from the terminus face serve as resting places for seabirds and provide important substrate for harbor seals to haul out. The availability of glacier ice is likely a key environmental variable that influences the abundance and distribution of harbor seals in tidewater glacier fjords in general and at Johns Hopkins Glacier specifically. Because most tidewater glaciers in Alaska are thinning and retreating, there is concern regarding how changes or reductions in glacier ice may impact the organisms that rely on glacier ice as a habitat.

The Pacific harbor seal is a nearshore species whose geographic range extends from the east edge of the Aleutian Islands, down the west coast
of North America, to the tip of Baja California. One of the largest concentra­tions of harbor seals in Southeast Alaska occurs in the iceberg-filled fjords of Muir and Johns Hopkins Inlets. Unlike fully aquatic marine mammals, harbor seals are semi-aquatic, meaning they live in the water, but also haul out on land or ice during critical periods such as reproduction, birthing, nursing young, and molting, and possibly during non-critical periods for resting. Harbor seal abundance in Johns Hopkins Inlet has been precipitously decreasing since 1992, for reasons that are poorly understood, but disease, increased predation, emigration, depletion of prey resources, and disturbance by vessels all have been implicated as causal factors of the abundance decrease. Johns Hopkins Inlet had a historical harbor seal population of greater than 5,000, but current estimates indicate fewer than 1,500 individuals remain. About 1/3 of these animals use terrestrial haulout sites, whereas the other 2/3 haul out on icebergs. Harbor seal abundance in Johns Hopkins Inlet varies on a seasonal and daily basis. Seals are most prevalent during late spring and summer, with the greatest abundance in June during pupping, and August during molting. Although the availability of ice haulout sites is not strongly tidally influenced, these seals exhibit predictable diel haulout behaviors and have been observed vacating the inlet each evening, presumably in search of suitable foraging areas, and returning each morning. Glacier Bay has been changing rapidly as a result of retreating glaciers that covered the entire area as recently as 200 years ago. These ongoing changes have dramatically reduced the number and extent of icebergs available to seals, and in the future may result in the total elimination of this harbor seal habitat. Read more here and here. Explore Johns Hopkins Inlet here:

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