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The islands, formerly known as the Catherine Archipelago, comprise four groups -- the Fox, Andreanof, Rat and Near Islands. They are all located between 52 degrees and 55 degrees North latitude and 172 degrees East and 163 degrees West longitude.
The axis of the archipelago near the mainland of Alaska has a southwest trend, but near the 129th meridian its direction changes to the northwest. This change of direction corresponds to a curve in the line of volcanic fissures which have contributed their products to the building of the islands. Such curved chains are repeated about the Pacific Ocean in the Kuril IslandsThe Kuril Islands ( Russian: ), also known as Kurile Islands stretch northeast from Hokkaido, Japan, to Kamchatka, separating the Sea of Okhotsk from the North Pacific Ocean. They are part of Russia's Sakhalin Oblast. The islands are known in Japanese as, the JapaneseJapan (, Nippon/Nihon literally "the origin of the sun") is a country in East Asia situated on a chain of islands east of the Asian continent on the western edge of the Pacific Ocean. The largest of these islands are, from north to south, Hokkaido , Honsh chain and the PhilippinesThe Republic of the Philippines is an island nation consisting of an archipelago of 7,107 islands, lying in the tropical western Pacific Ocean about 100 kilometers southeast of mainland Asia. Spain (1521-1898) and the United States (1898-1946), colonized. All these island arcs are at the edge of the Pacific PlateThe Pacific Plate is an oceanic tectonic plate beneath the Pacific Ocean. To the north the easterly side is a divergent boundary with the Explorer Plate, the Juan de Fuca Plate and the Gorda Plate forming respectively the Explorer Ridge, the Juan de Fuca and experience lots of seismic activity, but are still habitable; the Aleutians lie between the Pacific and North American tectonic20th century. Plate tectonics (from the Greek word for "one who constructs", τεκτων tekton ) is a theory of geology developed to explain the phenomenon of continental drift. In the theory of plate tectonics the outermost par plates. The general elevation is greatest in the eastern islands and least in the western. The island chain is really a western continuation of the Aleutian RangeThe Aleutian Range is the mountain range of the Alaska Peninsula in southeast Alaska. It is especially notable for its large number of active volcanoes. The mainland part of the range is about 1000 km (600 mi) long; the Aleutian Islands are (geologically) on the mainland.
The great majority of the islands bear evident marks of volcanic origin, and there are numerous volcanic cones on the north side of the chain, some of them active; many of the islands, however, are not wholly volcanic, but contain crystalline or sedimentary rocks, and also amber and beds of lignite. 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 volcano Makushin (5691 ft./1,734.61 m) is visible from Unalaska, and the volcanic islets Bogoslof and Grewingk , which rose from the sea in 1796 and 1883 respectively, lie about 30 miles (48 km) west of the bay.