The Aleutian Arc is a large

volcanic arc A volcanic arc (also known as a magmatic arc) is a belt of volcanoes formed above a subducting oceanic tectonic plate, with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench, with the arc ...

of islands extending from the Southwest tip of the

U.S. state In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its so ...

Alaska Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the north ...

to the

Kamchatka Peninsula The Kamchatka Peninsula (, ) is a peninsula in the Russian Far East, with an area of about . The Pacific Ocean and the Sea of Okhotsk make up the peninsula's eastern and western coastlines, respectively. Immediately offshore along the Pacific ...

of the

Russian Federation Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

. It consists of a number of active and dormant

volcano A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most oft ...

es that have formed as a result of the

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

of the Pacific plate beneath the North American plate along the

Aleutian Trench The Aleutian Trench (or Aleutian Trough) is an oceanic trench along a convergent plate boundary which runs along the southern coastline of Alaska and the Aleutian islands. The trench extends for from a triple junction in the west with the Ula ...

. Although taking its name from the Aleutian Islands, this term is a

geologic Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth s ...

grouping rather than a

geographic Geography (from Ancient Greek ; combining 'Earth' and 'write', literally 'Earth writing') is the study of the lands, features, inhabitants, and phenomena of Earth. Geography is an all-encompassing discipline that seeks an understanding o ...

one. The Aleutian Arc extends through the

Alaska Peninsula The Alaska Peninsula (also called Aleut Peninsula or Aleutian Peninsula, ; Sugpiaq language, Sugpiaq: ''Aluuwiq'', ''Al'uwiq'') is a peninsula extending about to the southwest from the mainland of Alaska and ending in the Aleutian Islands. T ...

following the

Aleutian Range The Aleutian Range is a major mountain range located in southwest Alaska. It extends from Chakachamna Lake (80 miles/130 km southwest of Anchorage) to Unimak Island, which is at the tip of the Alaska Peninsula. It includes all of the mountain ...

through the

Aleutian Islands The Aleutian Islands ( ; ; , "land of the Aleuts"; possibly from the Chukchi language, Chukchi ''aliat'', or "island")—also called the Aleut Islands, Aleutic Islands, or, before Alaska Purchase, 1867, the Catherine Archipelago—are a chain ...

. The arc makes up a sizable portion 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 tectonic belt of volcanoes and earthquakes. It is about long and up to about wide, and surrounds most of the Pa ...

, and is known for generating many strong magnitude earthquakes (magnitude 6–6.7) as well as its volcanism.

Formation and geologic features

Formation

The Aleutian Arc reflects subduction of the Pacific plate beneath the North American plate. It extends from the

in the west to the

Gulf of Alaska The Gulf of Alaska ( Tlingit: ''Yéil T'ooch’'') is an arm of the Pacific Ocean defined by the curve of the southern coast of Alaska, stretching from the Alaska Peninsula and Kodiak Island in the west to the Alexander Archipelago in the ...

in the east. The arc was formed around 55 million years ago during the early Eocene period. Unimak Pass at the southwestern end of the Alaska Peninsula (~165°W) marks the eastward transition from an intra-oceanic in the west to a continental arc in the east. Volcanic activity on the Aleutian Ridge extends from the Southwest corner of Alaska to around 175°E, west of

Attu Island Attu (, ) is an island in the Near Islands (part of the Aleutian Islands chain). It is one of the westernmost points of the U.S. state of Alaska. The island became uninhabited in 2010, making it the largest uninhabited island that is part of th ...

(~173°E). The Aleutian Arc is distinct in that its arc

massif A massif () is a principal mountain mass, such as a compact portion of a mountain range, containing one or more summits (e.g. France's Massif Central). In mountaineering literature, ''massif'' is frequently used to denote the main mass of an ...

is laterally extended and intact, which is unusual for a
intra-oceanic arc
Subduction magma rising

Geologic features

The Aleutian Trench, formed by the subduction of the Pacific plate under the North American plate, sits south of the island arc. A forearc basin reaching depths of 7 km occupies the space between the trench and the island arc and leads up to the Aleutian Ridge, the north side of which being the area where the most volcanic activity occurs. The Aleutian Ridge is largest near tip of the Alaskan Peninsula (160–225 km wide, 25–35 km thick) and decreases in width (80 km wide near the Komandorski Islands) as it extends west towards the Kamchatka Peninsula. Due to th
arcuate geometry
of the trench, the relative velocity vector changes from almos
trench-normal
in the Gulf of Alaska to almos
trench-parallel
in the west. Along the oceanic part of the subduction zone, convergence varies from per year to the north-northwest in the east to per year towards the northwest in the west. The eastern Aleutians see an

orthogonal In mathematics, orthogonality (mathematics), orthogonality is the generalization of the geometric notion of ''perpendicularity''. Although many authors use the two terms ''perpendicular'' and ''orthogonal'' interchangeably, the term ''perpendic ...

direction of

convergence Convergence may refer to: Arts and media Literature *''Convergence'' (book series), edited by Ruth Nanda Anshen *Convergence (comics), "Convergence" (comics), two separate story lines published by DC Comics: **A four-part crossover storyline that ...

relative to the trench, while the more central area sees an oblique direction of convergence relative to the trench. Past Attu Island, the direction of convergence becomes parallel with the trench.

Seismic activity

Tectonic activity

The Pacific plate is continuously converging and moving against the North American plate at a rate of 48 mm/year eastward and 78 mm/year westward. The oblique direction of convergence in the western and central portions of the area is causing westward transportation of the arc. This movement of the Pacific plate relative to the North American plate in the central and west Aleutian Arc also causes portions of the forearc to break off and form rotating crustal blocks between the trench and the island arc. The boundaries of the 5 major blocks that have been identified form areas with cohesive movement that are often disrupted by

strike-slip In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

and normal faults.

Submarine canyon A submarine canyon is a steep-sided valley cut into the seabed of the continental slope, sometimes extending well onto the continental shelf, having nearly vertical walls, and occasionally having canyon wall heights of up to , from canyon flo ...

s are present at the boundaries between the blocks due to the clockwise rotation of each block cutting into the surface of the other crustal blocks.

Earthquakes

Thousands of earthquakes per year are seen in this region due to the constant tectonic activity, making the Aleutian islands the most seismically active area in the United States of America. Faulting within the subduction zone ( Aleutian Megathrust) as well as within the subducting and overriding plates themselves accounts for the majority of earthquakes that occur. Some smaller magnitude earthquakes are also caused by the volcanic activity of the Aleutian Arc. The regionality of the earthquakes makes it possible for inter-plate and intra-plate events to be differentiated. The majority of events have been noted as having a thrusting mechanism, which denotes them as earthquakes occurring from the interface of a plate. Strike-slip and normal faulting does occur in shallow events, where the depth of the event is less than 30 km deep. Events with a normal fault mechanism tend to occur where the Pacific plate bends as it forms the Aleutian Trench, whereas strike-slip mechanisms are concentrated inland along the axis of the islands themselves. The constant activity near the Aleutian Arc has resulted in an area prone to high magnitude earthquakes. One Major earthquake (Mw ≥ 8) occurs every 13 years on average, and strong magnitude earthquakes (Mw 6–7) occur an average of six times per year. The rapid conversion and the gentle subduction angle of the Pacific plate under the North American plate also caused a

back-arc region The back-arc region is the area behind a volcanic arc. In island volcanic arcs, it consists of back-arc basins of oceanic crust with abyssal depths, which may be separated by remnant arcs, similar to island arcs. In continental arcs, the back-a ...

of tectonic deformation that spans 700 km from the Aleutian Arc into the interior of Alaska to form. These conditions have allowed for a multitude of major earthquakes to be measured throughout Alaska's history. Most major earthquakes measured in the region tend to be caused by ruptures in the gentle subduction interface between the subducting and overriding plates.

Volcanic activity

Volcanoes within this arc include: * Mount Adagdak * Mount Akutan * Mount Amak * Mount Amukta * Mount Aniakchak * Augustine Volcano * Black Peak *

Bogoslof Island Bogoslof Island or Agasagook Island () is the summit of a submarine stratovolcano at the south edge of the Bering Sea, northwest of Unalaska Island of the Aleutian Islands chain. It has a land area of and is uninhabited. It is long and wide, ...

* Mount Carlisle * Mount Chiginagak * Cleveland Volcano * Cold Bay Volcano *

Mount Dana Mount Dana is a mountain in the U.S. state of California. Its summit marks the eastern boundary of Yosemite National Park and the western boundary of the Ansel Adams Wilderness. At an elevation of , it is the second highest mountain in Yosemite ...

* Davidof Volcano * Mount Denison * Devils Desk * Mount Douglas *

Mount Dutton Mount Dutton is a stratovolcano in the Aleutian Range of the U.S. state of Alaska, on the Alaska Peninsula. It is also the crash site of a World Airways DC-8. Geography Dutton lies just short of from King Cove, a fishing headquarters for th ...

* Eickelberg Peak * Mount Emmons * Fourpeaked Mountain * Mount Frosty * Gareloi Volcano * Great Sitkin * Mount Gilbert * Mount Griggs *

Hayes Volcano Hayes Volcano is a stratovolcano in southwestern Matanuska-Susitna Borough, Alaska, 135 km northwest of Anchorage, that was not discovered until 1975. It is responsible for a series of six major tephra layers in the Cook Inlet region of Ala ...

* Mount Iliamna * Isanotski Peaks * Mount Kaguyak * Mount Kanaga * Kasatochi Island * Mount Katmai * Mount Kialagvik *

Kiska Kiska (, ) is one of the Rat Islands, a group of the Aleutian Islands of Alaska. It is about long and varies in width from . It is part of Aleutian Islands Wilderness and as such, special permission is required to visit it. The island has ...

* Korovin Volcano * Mount Kukak * Mount Kupreanof * Mount Mageik * Makushin Volcano * Mount Martin *

Novarupta Novarupta is a volcano located on the Alaska Peninsula on a slope of Trident Volcano in Katmai National Park and Preserve, about southwest of Anchorage. Novarupta was formed in 1912, during the largest volcanic eruption of the 20th century, in ...

* Nunivak Island * Mount Okmok * Mount Pavlof * Pavlof Sister * Pogromni Volcano * Mount Recheshnoi * Mount Redoubt * Saint Paul Island * Mount Seguam * Segula Island * Semisopochnoi Island * Mount Shishaldin * Snowy Mountain * Mount Spurr * Mount Steller * Tanaga * Trident Volcano * Ugashik-Peulik * Mount Veniaminof * Mount Vsevidof * Mount Westdahl * Yantarni Volcano

References

External links

Geoprisms.org: Aleutian Arc
{{coord, 52.28, -174.15, dim:1500000_region:US-AK, display=title Geology of the Aleutian Islands Aleutian Range Volcanic arcs Volcanism of Alaska