Amak Volcano
Encyclopedia
Amak Volcano is a basaltic andesite
stratovolcano
in the Aleutian Islands of Alaska
, USA, 618 miles (994.6 km) from Anchorage. It is located on the eponymous island
, 31 miles (50 km) from Frosty Volcano
, near the edge of the Alaskan Peninsula's western flank. Only boats are allowed to access the island, and only with a certain permit.
Blocky (dotted with flat blocks of minerals and crystals) lava flows stream from its summit to its flanks. Three historical eruptions have taken place – two within the 18th century, the first from 1700–1710, and the latter in 1796. The earliest prehistoric eruption was believed to have taken place between 3050 and 2050 BCE.
, the city nearest Amak, is easily accessible by plane. Amak is accessible only by boat; airplanes are disallowed. Private boat rides to the island are available in Cold Bay, but for access to the islands, a permit is required from the United States Fish and Wildlife Service
.
, north of the main archipelago
of the Aleutians. It is one of two islands (along with Bogoslof Island
) that are significantly north (31 miles (50 km)) of the main range.
The United States has the most 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. The state accounts for ~80% of the United States' volcanoes, excluding the seamount
s in the area, ~8% of world volcanoes, and most of these are located among the Aleutian Islands. The Aleutian Islands arc serves as the northern boundary of the Pacific Ring of Fire
, where tectonic activity generates earthquakes and volcanic eruptions in masses.
The volcano is basaltic-andesitic
in composition. It is a modest stratovolcano, rising no more than 1683 feet (513 m) above sea level. The volcanic crater is distinct, and has erupted in historical times, only "blocky" lava flows. Charles Wood and Jürgen Kienle, volcanologist
s, propose that earlier activity, 4,000–5,000 years ago, consisted primarily of lavas of ethereal (fine) platy and thick andesite. Amak Volcano is unique in that its andesitic lavas, while composed the same as the other Aleutians, contain an abundance of potash
. They also could contain more sodium carbonate
and rare earth element
deposits than the Aleutian norm. Between Bogoslof, the other Aleutian island north of the main arc, and Amak, Amak's lavas are more alkalic
and silicic
.
Glaciation took place around the volcano roughly 6700 years BP, carving out U-shaped valleys. At the southwest flank of the island, a crater, likely a maar
, can be found amid an alluvial plain
.
. Each eruption has been characterized by lava flows, and the two most recent eruptions have included a crater eruption.
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...
stratovolcano
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, 618 miles (994.6 km) from Anchorage. It is located on the eponymous island
Amak Island
Amak Island is an uninhabited island in Aleutians East Borough, Alaska, USA. The island lies north of the western tip of the Alaska Peninsula, and northwest of the mainland city of Cold Bay. The island's land area is and its maximum elevation is...
, 31 miles (50 km) from Frosty Volcano
Frosty Volcano
Frosty or Mt. Frosty is a stratovolcano and the westernmost Holocene volcano of the Alaska Peninsula in Alaska, USA. Frosty is the youngest of the two large volcanic structures of the Cold Bay volcanic complex. It has a summit elevation of . Frosty's last known eruption is unknown...
, near the edge of the Alaskan Peninsula's western flank. Only boats are allowed to access the island, and only with a certain permit.
Blocky (dotted with flat blocks of minerals and crystals) lava flows stream from its summit to its flanks. Three historical eruptions have taken place – two within the 18th century, the first from 1700–1710, and the latter in 1796. The earliest prehistoric eruption was believed to have taken place between 3050 and 2050 BCE.
Accessibility
Cold BayCold Bay, Alaska
Cold Bay is a city in Aleutians East Borough, Alaska, United States.Cold Bay is one of the main commercial centers of the Alaska Peninsula, and is home to Cold Bay Airport.-History:...
, the city nearest Amak, is easily accessible by plane. Amak is accessible only by boat; airplanes are disallowed. Private boat rides to the island are available in Cold Bay, but for access to the islands, a permit is required from the United States Fish and Wildlife Service
United States Fish and Wildlife Service
The United States Fish and Wildlife Service is a federal government agency within the United States Department of the Interior dedicated to the management of fish, wildlife, and natural habitats...
.
Geography and geology
Amak Island lies in the Bering SeaBering Sea
The Bering Sea is a marginal sea of the Pacific Ocean. It comprises a deep water basin, which then rises through a narrow slope into the shallower water above the continental shelves....
, north of the main archipelago
Archipelago
An archipelago , sometimes called an island group, is a chain or cluster of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi- and πέλαγος – pélagos through the Italian arcipelago...
of the Aleutians. It is one of two islands (along with Bogoslof Island
Bogoslof Island
Bogoslof Island or Agasagook Island is the summit of a largely submarine stratovolcano located in the Bering Sea in the U.S. state of Alaska, behind the main Aleutian volcanic arc. It has a land area of and is unpopulated. The peak elevation of the island is...
) that are significantly north (31 miles (50 km)) of the main range.
The United States has the most 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. The state accounts for ~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, ~8% of world volcanoes, and most of these are located among the Aleutian Islands. The Aleutian Islands arc serves as 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 in masses.
The volcano is basaltic-andesitic
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,...
in composition. It is a modest stratovolcano, rising no more than 1683 feet (513 m) above sea level. The volcanic crater is distinct, and has erupted in historical times, only "blocky" lava flows. Charles Wood and Jürgen Kienle, volcanologist
Volcanologist
A volcanologist is a person who studies the formation of volcanoes, and their current and historic eruptions. Volcanologists frequently visit volcanoes, especially active ones, to observe volcanic eruptions, collect eruptive products including tephra , rock and lava samples...
s, propose that earlier activity, 4,000–5,000 years ago, consisted primarily of lavas of ethereal (fine) platy and thick andesite. Amak Volcano is unique in that its andesitic lavas, while composed the same as the other Aleutians, contain an abundance of potash
Potash
Potash is the common name for various mined and manufactured salts that contain potassium in water-soluble form. In some rare cases, potash can be formed with traces of organic materials such as plant remains, and this was the major historical source for it before the industrial era...
. They also could contain more sodium carbonate
Sodium carbonate
Sodium carbonate , Na2CO3 is a sodium salt of carbonic acid. It most commonly occurs as a crystalline heptahydrate, which readily effloresces to form a white powder, the monohydrate. Sodium carbonate is domestically well-known for its everyday use as a water softener. It can be extracted from the...
and rare earth element
Rare earth element
As defined by IUPAC, rare earth elements or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium...
deposits than the Aleutian norm. Between Bogoslof, the other Aleutian island north of the main arc, and Amak, Amak's lavas are more alkalic
Igneous rock
Igneous rock is one of the three main rock types, the others being sedimentary and metamorphic rock. Igneous rock is formed through the cooling and solidification of magma or lava...
and silicic
Silicic
Silicic is a term used to describe magma or igneous rock rich in silica. The amount of silica that constitutes a silicic rock is usually put at at least 65 percent. Granite and rhyolite are typical silicic rocks....
.
Glaciation took place around the volcano roughly 6700 years BP, carving out U-shaped valleys. At the southwest flank of the island, a crater, likely a maar
Maar
A maar is a broad, low-relief volcanic crater that is caused by a phreatomagmatic eruption, an explosion caused by groundwater coming into contact with hot lava or magma. A maar characteristically fills with water to form a relatively shallow crater lake. The name comes from the local Moselle...
, can be found amid an alluvial plain
Alluvial plain
An alluvial plain is a relatively flat landform created by the deposition of sediment over a long period of time by one or more rivers coming from highland regions, from which alluvial soil forms...
.
Eruptive history
The Amak Volcano has erupted three times in historical times, in 2550 BC ± 500 years, 1700–10, and 1796; the first of these events was identified with tephrochronologyTephrochronology
250px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at the height of the [[volcanologists]] hands is [[rhyolitic]] [[tephra]] from [[Hekla]]....
. Each eruption has been characterized by lava flows, and the two most recent eruptions have included a crater eruption.