Aleutian Islands

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Lore & Background

The climate of the islands is oceanic, with moderate and fairly uniform temperatures and heavy rainfall. Fogs are almost constant. The mean annual temperature for Unalaska is about 38 °F (3 °C), with about 250 rainy days per year. The growing season lasts approximately 135 days, from early in May until late in September, but agriculture is limited to the raising of few vegetables. With the exception of some stunted willows, the vast majority of the chain is devoid of native trees. On some of the islands, such as Adak and Amaknak, there are a few coniferous trees growing, remnants of the Russian period. Instead of trees, the islands are covered with a luxuriant, dense growth of herbage and shrubs, including crowberry, bluejoint, grasses, sedges, and many flowering plants. Endemic plants include the endangered Aleutian shield fern.

Reader's Guide

The Aleutian Islands are significant as a volcanic arc forming the northernmost part of the Pacific Ring of Fire, with 57 volcanoes. They mark the boundary between the Bering Sea and the Pacific Ocean and contain both the westernmost and easternmost parts of the United States by longitude (Amatignak Island and Semisopochnoi Island, respectively). The westernmost U.S. island, in real terms, however, is Attu Island, west of which runs the International Date Line. The islands were the site of the Aleutian Islands campaign of World War II, including the Japanese landing and occupations of Kiska and Attu in June 1942, one of only two invasions of the United States in North America during WWII. Their remote location and harsh climate have limited human habitation and development. The islands, having biogeographical and ethnocultural affinities to North America, are not ordinarily considered a part of the Oceania region, though some authors have associated them with it due to their status as remote islands in the Pacific.

Did You Know?

• The Aleutian Islands contain both the westernmost and easternmost parts of the United States by longitude: Amatignak Island and Semisopochnoi Island, respectively.
• The Japanese landing and occupations of Kiska and Attu in June 1942 were one of only two invasions of the United States in North America during WWII.
• The volcanic Bogoslof and Fire Islands rose from the sea in 1796 and 1883, respectively.
• The Aleutian Islands were known before 1867 as the Catherine Archipelago.
• The 'Adak National Forest' on Adak Island is a man-made tree group consisting of 33 trees.

The Archipelago's Shape and Reach

The Aleutian Islands stretch roughly 1,200 mi (1,900 km) westward from the Alaska Peninsula mainland toward the Kamchatka Peninsula, forming a sweeping arc of 14 main, larger volcanic islands and 55 smaller ones. Together they cover about 6,821 sq mi (17,666 km2) and serve as a natural dividing line: the Bering Sea lies to the north while the open Pacific Ocean fills the south. The chain is organized into six named groups running east to west—the Fox Islands, Islands of Four Mountains, Andreanof Islands, Rat Islands, Near Islands, and Commander Islands—all sitting between 51° and 55° N latitude and 172° E and 163° W longitude. Unimak Island, with an area of 1,571.41 mi2 (4,069.9 km2), is the largest single island, with Unalaska Island the only other Aleutian Island with an area over 1,000 square miles (2,600 km2). Near Tanaga Island (about 178° W) the chain's axis pivots from a southwest trend to a northwest one, a bend that corresponds to a curve in the line of volcanic fissures that have contributed their products to the building of the islands. The island chain is a western continuation of the Aleutian Range on the mainland, and its general elevation is greatest in the eastern islands and least in the western.

A Volcanic Engine at the Edge of the Ring of Fire

The Aleutian arc is home to 57 volcanoes and sits at the northernmost reach of the Pacific Ring of Fire, where the Pacific Plate subducts under the North American Plate. Geologists date the birth of this island arc to the Early Eocene (55–50 Ma) when that subduction began. The arc is made of separate blocks that have been rotated clockwise. The basement underlying the islands is made of three stratigraphic units: an Eocene layer of volcanic rock, an Oligocene–Miocene layer of marine sedimentary rock, and a Pliocene–Quaternary layer of sedimentary and igneous rock. The islands are not wholly volcanic; many contain crystalline or sedimentary rocks, and also amber and beds of lignite. These volcanic islands reach heights of 6,200 feet (1,900 m). Makushin Volcano (5,691 feet (1,735 m)) on Unalaska Island is not quite visible from within the town of Unalaska, though the steam rising from its cone is visible on a (rare) clear day. The volcanic Bogoslof and Fire Islands, which rose from the sea in 1796 and 1883 respectively, lie about 30 miles (50 km) west of Unalaska Bay. In 1906, a new volcanic cone rose between the islets of Bogoslof and Grewingk, near Unalaska, followed by another in 1907. In 2017, the volcanic cone erupted sending ash and ice particles 30,000 feet (9000 m) into the air.

Longitude, Sovereignty, and the Shadow of War

Because the archipelago crosses longitude 180°, at which point east and west longitude end, it holds a peculiar cartographic distinction: Amatignak Island marks the westernmost part of the United States by longitude, while Semisopochnoi Island marks the easternmost. In practical terms, however, the westernmost U.S. island is Attu Island, west of which runs the International Date Line. Battles and skirmishes took place during the Aleutian Islands campaign of World War II. The Japanese landing and occupations of Kiska and Attu, in June 1942, were one of only two invasions of the United States in North America during WWII; the Philippines, Guam and Wake Atoll, Pacific territories of the United States, were also invaded. Before the 1867 Alaska Purchase, the entire archipelago was known as the Catherine Archipelago. The westernmost group, the Commander Islands (Bering and Medny), belongs to the Russian federal subject of Kamchatka Krai, of the Russian Far East.

A World Wrapped in Fog and Storm

The Aleutians are considered among the most geographically isolated areas of the Northern Pacific, and their climate reflects that remoteness. The climate of the islands is oceanic, with moderate and fairly uniform temperatures and heavy rainfall. Fogs are almost constant. Summer weather is much cooler than Southeast Alaska (around Sitka), but the winter temperature of the islands and of the Alaska Panhandle is nearly the same. According to the Köppen climate classification system, the area southwest of 53.5°N 167.0°W on Unalaska Island has a 'Subpolar Oceanic Climate' (type 'Cfc'), characterized by the coldest month averaging above 0 °C (32 °F), one to three months averaging above 10 °C (50 °F), and no significant precipitation differences between seasons. To the northeast of that point, the climate becomes 'Subarctic With Cool Summers And Year Around Rainfall' (type 'Dfc'), where it is similar albeit colder, with the coldest month averaging below 0 °C (32 °F). During the winter, the islands become the center of a semi-permanent low-pressure area called the Aleutian Low. The coasts are rocky and surf-worn, and the approaches are exceedingly dangerous, the land rising immediately from the coasts to steep, bold mountains. The islands, having biogeographical and ethnocultural affinities to North America, are not ordinarily considered a part of the Oceania region, though Alfred Russel Wallace's 1879 book Australasia, Ian Todd's 1974 book Island Realm: A Pacific Panorama and Dean Kohlhoff's 2002 book Amchitka and the Bomb: Nuclear Testing in Alaska all associate the Aleutian Islands with the Oceania region due to their status as remote islands in the Pacific.