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 High islands, volcanic islands in the Aleutian Islands in southwestern Alaska, between Buldir Island and the Near Islands group to its west, ...
group in the western
Aleutian Islands
The Aleutian Islands (; ; ale, Unangam Tanangin,”Land of the Aleuts", possibly from Chukchi language, Chukchi ''aliat'', "island"), also called the Aleut Islands or Aleutic Islands and known before 1867 as the Catherine Archipelago, are a cha ...
of
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.S., ...
. 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 to pol ...
), 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 the Car ...
. Semisopochnoi sits only 14 minutes (0.2333 degrees) or west of the
180th meridian
The 180th meridian or antimeridian is the meridian (geography), meridian 180° both east and west of the prime meridian in a Geographic coordinate system, geographical coordinate system. The longitude at this line can be given as either east ...
.
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 Expedi ...
,
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'' (ᐊᕿ ...
) and most burrow-nesting seabirds (
storm-petrels,
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 ...
s,
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
The tufted puffin (''Fratercula cirrhata''), also known as crested puffin, is a relatively abundant medium-sized pelagic seabird in the auk family (Alcidae) found throughout the North Pacific Ocean.
It is one of three species of puffin that make ...
) 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 cormorants.
In total, Semisopochnoi supports well over a million seabirds, most of which are least auklets or crested auklets.
Geology
![Semisopochnoi EO labelled](https://upload.wikimedia.org/wikipedia/commons/9/9a/Semisopochnoi_EO_labelled.jpg)
Semisopochnoi, the largest
subaerial 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 are ...
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 vol ...
. The high point of the island is 1,221 meter
Anvil Peak, 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
![semisopochnoiNauticalChart](https://upload.wikimedia.org/wikipedia/commons/8/8e/SemisopochnoiNauticalChart.png)
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,
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 is t ...
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 ...
,
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 tot ...
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
Longitude (, ) is a geographic coordinate that specifies the east– west position of a point on the surface of the ...
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 sout ...
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 PhotosPhotographs 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