Alexander Island, which is also known as Alexander I Island, Alexander I Land, Alexander Land, Alexander I Archipelago, and Zemlja Alexandra I, is the largest island of Antarctica. It lies in the Bellingshausen Sea west of Palmer Land, Antarctic Peninsula from which it is separated by Marguerite Bay and George VI Sound. The George VI Ice Shelf entirely fills George VI Sound and connects Alexander Island to Palmer Land. The island partly surrounds Wilkins Sound, which lies to its west.^[1] Alexander Island is about 390 kilometres (240 mi) long in a north–south direction, 80 kilometres (50 mi) wide in the north, and 240 kilometres (150 mi) wide in the south.^[2] Alexander Island is the second-largest uninhabited island in the world, after Devon Island.

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Alexander Island

Alexander Island shown within Antarctica
Alexander Island
Geography
Location	Antarctica
Coordinates	71°00′S 70°00′W
Area	49,070 km2 (18,950 sq mi)
Area rank	28th
Length	390 km (242 mi)
Width	80 km (50 mi)
Highest elevation	2,987 m (9800 ft)
Highest point	Mount Stephenson
Administration
Administered under the Antarctic Treaty System
Demographics
Population	0

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Alexander Island was discovered on January 28, 1821, by a Russian expedition under Fabian Gottlieb von Bellingshausen, who named it Alexander I Land for the reigning Tsar Alexander I of Russia.

What, in fact, is an island, was believed to be part of the Antarctic mainland until 1940. Its insular nature was proven in December 1940, by a two-person sledge party composed of Finn Ronne and Carl Eklund of the United States Antarctic Service.^[2][3] In the 1950s, a British base administered as part of the British Antarctic Territory was constructed as Fossil Bluff (Base KG).^[4]

The island was claimed by the United Kingdom in 1908 as part of the British Antarctic Territory. Territorial claims have also been set by both Chile (in 1940) and Argentina (in 1942).^[5] Currently, under the Antarctic Treaty no claim has been officially recognized. The island contains the British Fossil Bluff meteorological centre and refuelling base.^[6]

The surface of Alexander Island is predominantly ice-covered. There exist some exposed nunataks and a few ice-free areas of significant size, including Ablation Point Massif. The nunataks are the peaks of north–south trending mountain ranges and hills. They include the Colbert, Havre, Lassus, Rouen, Sofia University, and Walton Mountains, the Staccato Peaks, the Lully Foothills, the Finlandia Foothills, the Elgar Uplands, and the Douglas Range. These mountains, peaks, hills, and uplands are surrounded by a permanent ice sheet, which consists of glaciers that flow off of Alexander Island. These glaciers flow west into the Bach and Wilkins Ice Shelves and Bellingshausen Sea, and east into the George VI Ice Shelf. The George VI Ice Shelf is fed by both by outlet glaciers from the ice cap on Palmer Land and Alexander Island.^[1][2][7]

Another notable feature of Alexander Island is Hodgson Lake, a former subglacial lake that has emerged from under an ice sheet that had covered it. Hodgson Lake is 2 km (1.2 mi) long by 1.5 km (0.93 mi), and has a 93.4 m (306 ft) deep water column that lies sealed beneath a 3.6 to 4.0 m (11.8 to 13.1 ft) thick perennial lake ice.

The northern side of Hodgson Lake is bounded by the Saturn Glacier, which flows east into George VI Sound, while the southern side of Hodgson Lake is bounded by the northern face of Citadel Bastion. During the Last Glacial Maximum, Hodgson Lake was covered by the ice sheet at least 470 m (1,540 ft) thick.

This ice sheet started thinning about 13,500 years ago. It retreated and left Hodgson Lake covered by perennial ice sometime before 11,000 years ago. This lake has been covered by perennial ice since that time.^[8][9]

Other features on the island include Damocles Point^[10] and Mount Tyrrell.

According to Hole, "The geology of Alexander Island can be attributed mainly to processes associated with the subduction of proto-Pacific oceanic crust along the western margin of the Antarctic Peninsula, from latest Triassic to Late Tertiary times." The LeMay Group accretionary prism complex, along with plutonic and volcanic rocks, are prevalent along the western portion of the island. The LeMay Group consists of variably-deformed and metamorphosed sedimentary and igneous rocks. Although it is dominated by deformed arkosic sedimentary rocks, it includes turbiditic greywackes, black mudstones, and conglomerates. The 4 kilometers (2.5 miles) thick Upper Jurassic to Lower Cretaceous Fossil Bluff Group sedimentary rocks outcrop as a 250 kilometers (160 miles) long by 30 kilometers (19 miles) wide belt along the eastern coast. This Fossil Bluff Group consists of a basal deep-marine assemblage 2,200 meters (7,200 feet) thick, overlain by a mudstone assemblage up to 950 meters (3,120 feet) thick, followed by a shallow-marine assemblage of coarsening upward sandstones. Alkali basalts erupted after the cessation of subduction. These range in age from the tephrites at Mount Pinafore (5.5–7.6 Ma), to the basanites at Rothschild Island (5.5 Ma) and Hornpipe Heights (2.5 Ma), to the alkali and olivine basalts on Beethoven Peninsula (<1-2.5 Ma).^{[13][14][15][16][17][18][19][20]}

The LeMay Range Fault trends N-S, parallel to the George VI Sound, and the Fossil Bluff Formation is downfaulted to the east of this fault against the LeMay Group. Sand dykes are found against this fault zone and in many other parts of the Fossil Bay Formation. Fossils within the Fossil Bluff Formation include ammonites, belemnites, bivalves, and serpulids.^[16]

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