Bobrof Volcano
Encyclopedia
Bobrof Volcano is an inactive stratovolcano
in the Aleutian Islands of Alaska
, USA, 1211 miles (1,949 km) from Anchorage. It forms the small Bobrof Island
, 31 miles (50 km) west of Adak
, part of the local sub-archipelago, the Andreanof Islands
, which extend for 275 miles (443 km).
No recorded eruptions have taken place at Bobrof or in its vicinity. It has been considered as Holocene age.
, a smaller chain that is considered part of the Aleutian Islands. It is roughly 31 miles (50 km) west of Adak
and 9 miles (14 km) west of Kanaga Island
. The volcanic crater, or cone, has been heavily dissected. Bobrof Island is small, only 3 kilometers by 4 kilometers in area. Underwater deposits adjacent to the island's northeast flank suggest an immense debris-avalanche has taken place.
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
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
, 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
. 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
and dacite
. No complete publications exist for Bobrof's definite geology, just those with facts and some information.
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...
in the Aleutian Islands of Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
, USA, 1211 miles (1,949 km) from Anchorage. It forms the small Bobrof Island
Bobrof Island
Bobrof Island is one of the Andreanof Islands subgroup of the Aleutian Islands in southwestern Alaska, USA. Bobrof Island is a small, uninhabited island about north and west of Kanaga Island, and northeast of Cape Sudak on Tanaga Island...
, 31 miles (50 km) west of Adak
Adak Island
Adak Island is an island near the western extent of the Andreanof Islands group of the Aleutian Islands in Alaska. Alaska's southernmost town, Adak, is located on the island...
, part of the local sub-archipelago, the Andreanof Islands
Andreanof Islands
The Andreanof Islands are a group of islands in the Aleutian Islands in southwest Alaska. They are located between Amchitka Pass and the Rat Islands group to the west, and Amukta Pass and the Islands of Four Mountains group to the east, at about 52° North and 172°57' to 179°09' West. The islands...
, which extend for 275 miles (443 km).
No recorded eruptions have taken place at Bobrof or in its vicinity. It has been considered as Holocene age.
Geography and geology
Bobrof is part of the Andreanof IslandsAndreanof Islands
The Andreanof Islands are a group of islands in the Aleutian Islands in southwest Alaska. They are located between Amchitka Pass and the Rat Islands group to the west, and Amukta Pass and the Islands of Four Mountains group to the east, at about 52° North and 172°57' to 179°09' West. The islands...
, a smaller chain that is considered part of the Aleutian Islands. It is roughly 31 miles (50 km) west of Adak
Adak Island
Adak Island is an island near the western extent of the Andreanof Islands group of the Aleutian Islands in Alaska. Alaska's southernmost town, Adak, is located on the island...
and 9 miles (14 km) west of Kanaga Island
Kanaga Island
Kanaga Island is a part of the Andreanof Islands group of the Aleutian Islands in Alaska. The island measures roughly 30 miles long and between 4 and 8 miles wide with an area of 142 sq mi , making it the 42nd largest island in the United States...
. The volcanic crater, or cone, has been heavily dissected. Bobrof Island is small, only 3 kilometers by 4 kilometers in area. Underwater deposits adjacent to the island's northeast flank suggest an immense debris-avalanche has taken place.
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
Seamount
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
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
Pacific Ring of Fire
The Pacific Ring of Fire is an area where large numbers of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. In a horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements...
, 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
Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...
. 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
Shield volcano
A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes...
. In collected samples, there are traces of basaltic andesite
Basaltic andesite
Basaltic andesite is a black volcanic rock containing about 55% silica. Minerals in basaltic andesite include olivine, augite and plagioclase. Basaltic andesite can be found in volcanoes around the world, including in Central America and the Andes of South America. Basaltic andesite is common in...
and dacite
Dacite
Dacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram...
. No complete publications exist for Bobrof's definite geology, just those with facts and some information.