Johns Hopkins Glacier flows generally east-northeast for 13 miles (21 km) to the head of Johns Hopkins Inlet in Glacier Bay National Park and Preserve, about 104 miles (167 km) southeast of Yakutat and 58 miles (93 km) northwest of Gustavus, Alaska. The glacier begins at an elevation of about 8,000 feet (2,438 m) on the eastern flank of Mount Lituya in the Fairweather Range of the Saint Elias Mountains. In 1893, the terminus of what was originally named Grand Pacific Glacier by Harry F. Reid was 14 miles (23 km) farther west, situated between Reid Glacier and Russell Island in Reid Inlet. The glacier retreated, separating into two ice fronts and exposing new fjords. The northern ice front retained the name Grand Pacific Glacier, while the new fjord was named Tarr Inlet by Lawrence Martin, after Ralph S. Tarr, a professor of physical geography at Cornell University. The other fjord retained the name Reid Inlet, and its ice front was named Johns Hopkins Glacier by William S. Cooper in 1931, after Johns Hopkins University in Baltimore, Maryland. With the glacier’s further retreat, Reid Inlet lengthened, and its historical connection to Reid Glacier became obscure. In 1954, the U.S. Board of Geographic Names renamed Reid Inlet to Johns Hopkins Inlet. In 1893, the retreating glacier terminus at the head of present-day Glacier Bay exposed bedrock consisting mainly of granodiorite, an igneous rock. This rock had intruded into the Alexander terrane as magma during the Late Cretaceous. By the early 20th century, the glacier had retreated farther, revealing sedimentary rocks of the Chugach terrane in Johns Hopkins Inlet. These rocks are primarily sandstone and mudstone turbidites, along with graywacke, which were intruded by magma during the Oligocene and Eocene, forming plutons of granodiorite and quartz diorite. The Alexander terrane to the east is separated from the Chugach terrane by the Border Ranges Fault, roughly aligned with the axis of Tarr Inlet. The Chugach terrane is separated from the Yakutat terrane to the west by the Fairweather Fault, aligned with Desolation Valley. These faults have created a shear zone, resulting in significant seismic activity and geological deformation.

There is regional archeological evidence of human settlement in Icy Strait and near the mouth of Glacier Bay, but it cannot be conclusively determined who these prehistoric people were. Tlingit oral tradition tells of a village in Glacier Bay that they were forced to abandon due to an encroaching ice front. Historical settlements are known to have existed in Dundas Bay, Bartlett Cove, and Excursion Inlet. In 1794, Lieutenant Joseph Whidbey, master of HMS Discovery during the Vancouver Expedition from 1791 to 1795, reported that his survey of the north shore of Icy Strait was blocked by a wall of ice 2 miles (3.2 km) wide. Vancouver claimed the land for Britain, conflicting with an earlier Russian claim from Yakutat. The issue was resolved in 1825 by the Treaty of Saint Petersburg, which favored the Russians. In 1867, the Alaska Purchase transferred the territory from Russia to the United States. By then, the glacier terminus in Icy Strait had retreated about 15 miles (24 km), revealing the entrance to Glacier Bay and present-day Bartlett Cove. In 1879, naturalist John Muir recorded the ice front about 32 miles (51 km) from Icy Strait. In 1899, Edward H. Harriman financed an expedition to Alaska that visited Glacier Bay and discovered an uncharted fjord with many unnamed glaciers. These glaciers were subsequently well documented. A dispute with Britain about the boundary location between Canada and the District of Alaska was resolved by arbitration in 1903. By 1916, the Grand Pacific Glacier, which once filled Glacier Bay, had retreated about 60 miles (97 km) from Icy Strait—one of the fastest known glacial retreats. Today, the glacier terminus is within 1 mile (1.6 km) of the Canadian border. In 1925, after intense lobbying by Muir, Cooper, Harriman, and others, President Calvin Coolidge declared Glacier Bay a national monument. In 1939, another proclamation added more land to the monument. The Alaska National Interest Lands Conservation Act of 1980 redesignated it as a national park, covering about 3.3 million acres (1.3 million ha) and added a preserve of 57,000 acres (23,067 ha).

Most glaciers in the Saint Elias Mountains are retreating, but Johns Hopkins Glacier is one of the few advancing tidewater glaciers. The glacier is about 1 mile (1.6 km) wide, 250 feet (76 m) high at the terminus, and 200 feet (61 m) deep at the waterline. It is formed from numerous tributary glaciers, many of which extend 12 miles (19 km) or more into the surrounding peaks. About 50 medial moraines develop from the joining of these tributary glaciers. The debris in these moraines appears as prominent dark bands in the ice face and extends up the glacier. This debris is transported within and on the ice and released either by melting of the ice face or calving of icebergs into Johns Hopkins Inlet. Meltwater from the glacier discharges from submarine tunnels or conduits near both the eastern and western edges of the glacier. Sometimes, this water emerges at the inlet surface as turbulent roils or fountains. In the 1970s, Johns Hopkins Glacier flowed at about 3,000 feet (900 m) per year or approximately 8 feet (2.4 m) per day. The glacier front has advanced about 2 miles (3.2 km) since 1932. It has merged with and separated from the Gilman Glacier at its eastern edge several times. The glaciers were most recently attached in 2000 but have been slightly separated since 2016. The rate of glacial advance and retreat is linked to the concentration of icebergs calving from the glacier terminus. Hundreds of harbor seals haul out on these icebergs. In June, females and pups primarily use the icebergs, while in August, molting seals do. The number of seals hauled out correlates with the percentage of ice cover, and the availability of suitable icebergs may limit seal abundance in the area. Consequently, the number of predators, such as killer whales, Steller sea lions, and sleeper sharks, is indirectly affected by the iceberg availability. Read more here and here. Explore more of Johns Hopkins Glacier and Glacier Bay National Park and Preserve here: