Bobrof Island ( ale, Walĝa) is one of the

Andreanof Islands The Andreanof Islands ( ale, Niiĝuĝim tanangis, russian: Андреяновские острова) are a group of islands in the Aleutian Islands in southwestern Alaska. They are located at about 52° North and 172°57' to 179°09' West. Geogr ...

subgroup of the

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 ...

in southwestern

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., ...

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

. Bobrof Island is a small, uninhabited island about north and west of

Kanaga Island Kanaga Island ( ale, Kanaga; russian: Остров Канага) is a part of the Andreanof Islands group of the Aleutian Islands in Alaska. The island measures long and between wide with an area of , making it the 42nd largest island in the U ...

, and northeast of Cape Sudak on

Tanaga Island Tanaga Island ( ale, Tanax̂ax; russian: остров Танага) is an island in the western Andreanof Islands, in the southwest part of the Aleutian Islands, Alaska. The island has a land area of , making it the 33rd largest oceanic island i ...

. Bobrof Island is long and wide with an area of , and consists primarily of the high Bobrof Volcano. The volcanic crater, or cone, has been heavily dissected. Underwater deposits adjacent to the island's northeast flank suggest an immense debris-avalanche has taken place.

Bobrof Volcano

Bobrof Volcano is an

inactive Inactive is a TRPV channel in invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping ...

stratovolcano A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and per ...

which forms the small Bobrof Island. No recorded eruptions have taken place at Bobrof or in its vicinity. It has been considered as

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

age.

Geography and geology

Because of the inclusion of Alaska, the United States has the largest number of active volcanoes in the world, many of them geologically young. In Alaska, at least 50 volcanoes, including those in the Aleutian archipelago, have erupted in historical time. Alaska accounts for about 80% of the United States' volcanoes, excluding the

seamount A seamount is a large geologic landform that rises from the ocean floor that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abru ...

s in the area, about 8% of the world's volcanoes, and most of these are located among the Aleutian Islands. The Aleutian Islands arc forms the northern boundary of the

Pacific Ring of Fire The Ring of Fire (also known as the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire or the Circum-Pacific belt) is a region around much of the rim of the Pacific Ocean where many Types of volcanic eruptions, volcanic eruptions and ...

, where tectonic activity generates earthquakes and volcanic eruptions regularly. The volcano is thought to be of Holocene age. Though no historical eruptions have taken place at Bobrof, it has erupted at least once. This data can be confirmed through pyroclastic flow deposits containing

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomi ...

. Once these flows were studied, at a building intended for earthquake monitoring, they confirmed that Bobrof was prone to explosive activity. There are lava deposits on the mountain which also suggest activity similar to shield eruptions. In collected samples, there are traces of

basaltic andesite Basaltic andesite is a volcanic rock that is intermediate in composition between basalt and andesite. It is composed predominantly of augite and plagioclase. Basaltic andesite can be found in volcanoes around the world, including in Central Ameri ...

and

dacite 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 rhyolite. ...

. No complete publications exist for Bobrof's definite geology, just those with facts and some information.

References

External links

Bobrof Island Photos
Photographs from Bobrof Island, July 2008 {{Authority control Andreanof Islands Volcanoes of the Aleutian Islands Landforms of Aleutians West Census Area, Alaska Inactive volcanoes Volcanoes of Alaska Uninhabited islands of Alaska Islands of Aleutians West Census Area, Alaska Volcanoes of Unorganized Borough, Alaska Mountains of Unorganized Borough, Alaska Stratovolcanoes of the United States Islands of Alaska

Bobrof Volcano

Geography and geology

References

Further reading

External links