Alexander Island, which is also known asAlexander I Island,Alexander I Land,Alexander Land,Alexander I Archipelago, andZemlja Alexandra I, is the largest island ofAntarctica. It lies in theBellingshausen Sea west ofPalmer Land,Antarctic Peninsula from which it is separated byMarguerite Bay andGeorge VI Sound. TheGeorge VI Ice Shelf entirely fills George VI Sound and connects Alexander Island to Palmer Land. The island partly surroundsWilkins 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, afterDevon Island.
Satellite photo of Alexander Island (NASA imagery)Alexander Island Mountain Ranges
The surface of Alexander Island is predominantly ice-covered. There exist some exposednunataks 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 theColbert,Havre,Lassus,Rouen,Sofia University, andWalton Mountains, theStaccato Peaks, theLully Foothills, theFinlandia Foothills, theElgar Uplands, and theDouglas 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 theBach andWilkins Ice Shelves and Bellingshausen Sea, and east into the George VI Ice Shelf. The George VI Ice Shelf is fed by both byoutlet glaciers from the ice cap on Palmer Land and Alexander Island.[1][2][7]
Another notable feature of Alexander Island isHodgson Lake, a formersubglacial 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) deepwater 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 theSaturn Glacier, which flows east into George VI Sound, while the southern side of Hodgson Lake is bounded by the northern face ofCitadel Bastion. During theLast 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]
Antarctic Peninsula'stectonic movementFossil Bluff base on Alexander Island
According to Hole, "The geology of Alexander Island can be attributed mainly to processes associated with thesubduction of proto-Pacificoceanic crust along the western margin of the Antarctic Peninsula, from latestTriassic toLate Tertiary times." The LeMay Groupaccretionary prism complex, along withplutonic andvolcanic rocks, are prevalent along the western portion of the island. The LeMay Group consists of variably-deformed andmetamorphosed sedimentary and igneous rocks. Although it is dominated by deformedarkosic sedimentary rocks, it includesturbiditicgreywackes, black mudstones, andconglomerates. The 4 kilometers (2.5 miles) thickUpper Jurassic toLower Cretaceous Fossil Bluff Group sedimentary rocksoutcrop 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 amudstone assemblage up to 950 meters (3,120 feet) thick, followed by a shallow-marine assemblage of coarsening upwardsandstones.Alkali basalts erupted after the cessation of subduction. These range in age from thetephrites at Mount Pinafore (5.5–7.6 Ma), to thebasanites atRothschild Island (5.5 Ma) and Hornpipe Heights (2.5 Ma), to the alkali andolivine basalts onBeethoven Peninsula (<1-2.5 Ma).[13][14][15][16][17][18][19][20]
The LeMay RangeFault trends N-S, parallel to theGeorge 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 includeammonites,belemnites,bivalves, andserpulids.[16]
^Smith, James A.; Bentley, Michael J.; Hodgson, Dominic A.; Cook, Alison J. (2007). "George VI Ice Shelf: Past history, present behaviour and potential mechanisms for future collapse".Antarctic Science.19 (1):131–142.Bibcode:2007AntSc..19..131S.doi:10.1017/S0954102007000193.S2CID128840101.
^Hodgson, Dominic A.; Roberts, Stephen J.; Bentley, Michael J.; Smith, James A.; Johnson, Joanne S.; Verleyen, Elie; Vyverman, Wim; Hodson, Andy J.; Leng, Melanie J.; Cziferszky, Andreas; Fox, Adrian J.; Sanderson, David C.W. (2009). "Exploring former subglacial Hodgson Lake, Antarctica Paper I: Site description, geomorphology and limnology".Quaternary Science Reviews.28 (23–24):2295–2309.Bibcode:2009QSRv...28.2295H.doi:10.1016/j.quascirev.2009.04.011.
^Hodgson, Dominic A.; Roberts, Stephen J.; Bentley, Michael J.; Carmichael, Emma L.; Smith, James A.; Verleyen, Elie; Vyverman, Wim; Geissler, Paul; Leng, Melanie J.; Sanderson, David C.W. (2009). "Exploring former subglacial Hodgson Lake, Antarctica. Paper II: Palaeolimnology".Quaternary Science Reviews.28 (23–24):2310–2325.Bibcode:2009QSRv...28.2310H.doi:10.1016/j.quascirev.2009.04.014.
^Hole, M.J.; Smellie, J.L.; Marriner, G.F. (1991). Thomson, M.R.A.; Crame, J.A.; Thomson, J.W. (eds.).Geochemistry and tectonic setting of Cenozoic alkalne basalts from Alexander Island, Antarctic Peninsula, in Geological Evolution of Antarctica. Cambridge: Cambridge University Press. pp. 521–522.ISBN9780521372664.
^Butterworth, P.J.; Macdonald, D.I.M. (1991). Thomson, M.R.A.; Crame, J.A.; Thomson, J.W. (eds.).Basin shallowing from the Mesozoic Fossil Bluff Group of Alexander Island and its regional tectonic significance, in Geological Evolution of Antarctica. Cambridge: Cambridge University Press. pp. 449–453.ISBN9780521372664.
^Tranter, T.H. (1991). Thomson, M.R.A.; Crame, J.A.; Thomson, J.W. (eds.).Accretion and subduction processes along the Pacific margin of Gondwana, central Alexander Island, in Geological Evolution of Antarctica. Cambridge: Cambridge University Press. pp. 437–441.ISBN9780521372664.
^abNell, P.A.R.; Storey, B.B. (1991). Thomson, M.R.A.; Crame, J.A.; Thomson, J.W. (eds.).Strike-slip tectonics within the Antarctic Peninsula fore-arc, in Geological Evolution of Antarctica. Cambridge: Cambridge University Press. pp. 443–448.ISBN9780521372664.
^Macdonald, D.I.M. and P.J. Butterworth (1990) "The stratigraphy, setting and hydrocarbon potential of the Mesozoic sedimentary basins of the Antarctic Peninsula." in B. John, ed., pp. 101–125.Antarctica as an exploration frontier; hydrocarbon potential, geology, and hazards. AAPG Studies in Geology. vol. 31 American Association of Petroleum Geologists, Tulsa, Oklahoma.doi:10.1306/St31524C8
^Vaughan, Alan P. M.; Storey, Bryan C. (2000). "The eastern Palmer Land shear zone: A new terrane accretion model for the Mesozoic development of the Antarctic Peninsula".Journal of the Geological Society.157 (6):1243–1256.Bibcode:2000JGSoc.157.1243V.doi:10.1144/jgs.157.6.1243.S2CID128496050.
^McCarron, J. J.; Smellie, J. L. (1998). "Tectonic implications of fore-arc magmatism and generation of high-magnesian andesites: Alexander Island, Antarctica".Journal of the Geological Society.155 (2):269–280.Bibcode:1998JGSoc.155..269M.doi:10.1144/gsjgs.155.2.0269.S2CID129620018.
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