Semisopochnoi Island or Unyak Island (obsolete russian: Семисопочной, modern russian: Семисопочный Semisopochny "having seven hills"; ale, Unyax̂) is part of the

Rat Islands The Rat Islands ( ale, Qax̂um tanangis, russian: Крысьи острова) are a group of American volcanic islands in the Aleutian Islands in southwestern Alaska, between Buldir Island and the Near Islands group to its west, and Amchitk ...

group in the western

Aleutian Islands The Aleutian Islands (; ; ale, Unangam Tanangin,”Land of the Aleuts", possibly from Chukchi ''aliat'', "island"), also called the Aleut Islands or Aleutic Islands and known before 1867 as the Catherine Archipelago, are a chain of 14 large v ...

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U ...

. The island is uninhabited and provides an important nesting area for maritime birds. The island is of volcanic origin, containing several volcanoes including Mount Cerberus. It has a land area of 85.558 square miles (221.59 square km), measuring 11 miles (18 km) in length and 12 miles (20 km) in width. At 179°46' East (+179.7667) (in the

Eastern Hemisphere The Eastern Hemisphere is the half of the planet Earth which is east of the prime meridian (which crosses Greenwich, London, United Kingdom) and west of the antimeridian (which crosses the Pacific Ocean and relatively little land from pole ...

), the easternmost tip of Semisopochnoi is, by longitude, the easternmost land location in the United States and

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

. Semisopochnoi sits only 14 minutes (0.2333 degrees) or west of the

180th meridian The 180th meridian or antimeridian is the meridian 180° both east and west of the prime meridian in a geographical coordinate system. The longitude at this line can be given as either east or west. On Earth, these two meridians form a ...

Wildlife

Semisopochnoi has no native land mammals. Arctic foxes were introduced to the island during the 19th century for fur farming and removed in 1997. Most ground-nesting bird species (

Aleutian cackling goose The Aleutian cackling goose (''Branta hutchinsii leucopareia''), is a small subspecies of the cackling goose averaging in weight. It was one of 122 species of animals, birds, and fish first documented for science by the Lewis and Clark Expediti ...

rock ptarmigan The rock ptarmigan (''Lagopus muta'') is a medium-sized game bird in the grouse family. It is known simply as the ptarmigan in the UK. It is the official bird for the Canadian territory of Nunavut, where it is known as the ''aqiggiq'' (ᐊ� ...

) and most burrow-nesting seabirds (

storm-petrel Storm-petrel may refer to one of two bird families, both in the order Procellariiformes, once treated as the same family. The two families are: *Northern storm petrels (''Hydrobatidae'') are found in the Northern Hemisphere, although some species ...

ancient murrelet The ancient murrelet (') is a bird in the auk family. The English term "murrelet" is a diminutive of "murre", a word of uncertain origins, but which may imitate the call of the common guillemot. Ancient murrelets are called "ancient" because th ...

Cassin's auklet Cassin's auklet (''Ptychoramphus aleuticus'') is a small, chunky seabird that ranges widely in the North Pacific. It is the only species placed in the genus ''Ptychoramphus''. It nests in small burrows and because of its presence on well studied ...

s, tufted puffins) were

extirpated Local extinction, also known as extirpation, refers to a species (or other taxon) of plant or animal that ceases to exist in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinct ...

by foxes; Semisopochnoi Island is currently in the early stages of recovery. The island has remained free of

Norway rats The brown rat (''Rattus norvegicus''), also known as the common rat, street rat, sewer rat, wharf rat, Hanover rat, Norway rat, Norwegian rat and Parisian rat, is a widespread species of common rat. One of the largest muroids, it is a brown o ...

. The large least and crested auklet colony near Sugarloaf Head is one of the largest among the nine auklet colonies in the Aleutian Islands. Crested auklets and least auklets breed in one colony, located on the south facing slopes of Sugarloaf Peak volcano and its associated cinder cones near Sugarloaf Head. Semisopochnoi Island also supports a significant population of

red-faced cormorant The red-faced cormorant (''Urile urile''), red-faced shag or violet shag, is a bird species of the family Phalacrocoracidae. Its range spans from the eastern tip of Hokkaidō in Japan, northern korean peninsula, via the Kuril Islands, the sout ...

s. In total, Semisopochnoi supports well over a million seabirds, most of which are least auklets or crested auklets.

Geology

Semisopochnoi, the largest

subaerial In natural science, subaerial (literally "under the air"), has been used since 1833,Subaerial
in the Merriam ...

volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates ...

of the western Aleutians, is 20 km wide at sea level and contains a caldera 8 km wide that formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of

dacitic Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyol ...

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...

. The high point of the island is 1,221 meter

Anvil Peak Anvil Peak is a cone volcano located in Aleutian Islands, Alaska, United States. Etymology The volcano was originally named in 1951, on a map by the United States Geological Survey. Its name was taken after a plateau located on the northern si ...

, a double-peaked cone that forms much of the island's northern part. The three-peaked, 774-meter high Mount Cerberus is a volcano within the caldera. Each of the peaks contains a summit crater; lava flows on the northern flank of Cerberus appear younger than those on the southern side. Other post-caldera volcanoes include the symmetrical 855 m high Sugarloaf Peak south-southeast of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the northeast part of the caldera. Most documented historical eruptions have originated from Cerberus, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone within the caldera could have been active during historical time. Semisopochnoi's last known volcanic eruptions took place in October 2018 and July 2019. A historic eruption of Semisopochnoi was reported in 1873, and at least four others may have occurred in the previous hundred years, but documentation is scant. These eruptions apparently emanated from the flanks of Mount Cerberus; the most recent flow appears to be less than a century old.Wood, C. A., and Kienle, Juergen, (eds.), 1990, Volcanoes of North America: United States and Canada: New York, Cambridge University Press, 354 p.

Easternmost North America location debate

Semisopochnoi's position in the Aleutian Island Chain gives it the distinction of being the Aleutian island most immediately West of the 180th meridian, giving it longitudinal coordinates in the Eastern Hemisphere. Therefore, some have argued it is technically the easternmost location in North America. This is a counterintuitive argument considering its location near the extreme Western boundary of the United States, and depends on a series of assumptions about the definition of boundaries between hemispheres, boundaries between continents, as well as whether island locations should even be considered part of a continent. The other contenders for the title of easternmost North America location are

Nordost Rundingen Nordostrundingen (corrupted from da, Nordøstrundingen which means Northeastern rounding, in English Northeast Foreland), is a headland located at the northeastern end of Greenland. Administratively it is part of the Northeast Greenland National ...

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland ...

at 12°08' West (-12.1333) and

Cape Spear Cape Spear (french: Cap d'Espoir) is a headland located on the Avalon Peninsula of Newfoundland near St. John's in the Canadian province of Newfoundland and Labrador. At a longitude of 52°37'W, it is the easternmost point in Canada and North Am ...

Newfoundland Newfoundland and Labrador (; french: Terre-Neuve-et-Labrador; frequently abbreviated as NL) is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region ...

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...

at 52°37' West (-52.6167) —which, along with Semisopochnoi, are all island locations.

Cape St. Charles Cape St. Charles is a headland on the coast of Labrador in the Canadian province of Newfoundland and Labrador. At longitude 55°37'15" W, it is the easternmost point of continental North America North America is a continent in the Nor ...

at 55° 37' West (-55.6167) on the

Labrador Peninsula The Labrador Peninsula, or Quebec-Labrador Peninsula, is a large peninsula in eastern Canada. It is bounded by the Hudson Bay to the west, the Hudson Strait to the north, the Labrador Sea to the east, and the Gulf of Saint Lawrence to the so ...

is the easternmost point of mainland North America. Cape Spear is the easternmost location relative to the geographic center of North America if Greenland is excluded because it is not politically part of North America. For this and other reasons, Cape Spear is traditionally considered to be the easternmost location in North America.

References

External links

Semisopochnoi Photos
Photographs from Semisopochnoi Island, July 2008
Google Earth view
{{authority control Rat Islands Volcanoes of Alaska Stratovolcanoes of the United States Uninhabited islands of Alaska Calderas of Alaska Cinder cones of the United States Islands of Alaska Islands of Unorganized Borough, Alaska Volcanoes of Unorganized Borough, Alaska Landforms of Aleutians West Census Area, Alaska VEI-7 volcanoes