Trident Volcano is an eroded

volcanic A volcano is a rupture 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 often found where tectonic plates ...

complex on the

Alaska Peninsula The Alaska Peninsula (also called Aleut Peninsula or Aleutian Peninsula, ale, Alasxix̂; Sugpiaq: ''Aluuwiq'', ''Al'uwiq'') is a peninsula extending about to the southwest from the mainland of Alaska and ending in the Aleutian Islands. The ...

Katmai National Park Katmai National Park and Preserve is an American national park and preserve in southwest Alaska, notable for the Valley of Ten Thousand Smokes and for its brown bears. The park and preserve encompass , which is between the sizes of Connecticut a ...

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 ...

. Up to 23 domes comprise the complex

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 p ...

, with the greatest elevation of . The most recent major activity produced a dome in an amphitheater on the southwest flank of the southwest peak. Volcano

Novarupta Novarupta (meaning "newly erupted" in Latin) is a volcano that was formed in 1912, located on the Alaska Peninsula on a slope of Trident Volcano in Katmai National Park and Preserve, about southwest of Anchorage. Formed during the largest volc ...

formed on its slopes in the largest volcanic eruption of the 20th century. According to the

United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...

, the descriptive name, Trident, was given by Robert Fiske Griggs of the

National Geographic Society The National Geographic Society (NGS), headquartered in Washington, D.C., United States, is one of the largest non-profit scientific and educational organizations in the world. Founded in 1888, its interests include geography, archaeology, ...

, in 1916, because there were three major peaks. The volcano has been known by several variants of the name. The feature was officially named Mount Trident by the United States Board on Geographic Names in 1928. The board assigned the current name in 1968.

Historical volcanic activity

There is no evidence of recent eruptive activity at the summit of Trident, nor have there been any reports of historical activity, except

fumarolic A fumarole (or fumerole) is a vent in the surface of the Earth or other rocky planet from which hot volcanic gases and vapors are emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volcani ...

activity on the east side. The earliest known activity was minor eruptions in 1913, 1949 and 1950. A satellite

cone A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines co ...

formed February 15, 1953 on the southwest flank of Trident following a major explosive eruption that sent ash to an altitude of over . A succession of blocky

lava Lava is molten or partially molten rock ( magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or ...

flows were erupted in 1954, 1957, 1958, 1959-1960 from the new vent. Ash eruptions, some to altitudes over , were associated with several of the lava eruptions. By 1960, the dome had grown nearly high and a sequence of viscous flows, up to thick and covering an area of about south of the volcano, had been extruded. Further explosions were reported in the early to late 1960s. Lava extrusion, accompanied by explosions, was also reported from 1966 to 1968 and 1974 to 1975. In 1983, steam and/or vapor continued to rise from the central vent area of the new cone as well as from numerous fumaroles on the near-vent portion of the blocky lava flows.

Composition

Trident lavas are

andesitic 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 ...

dacitic 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. ...

in composition. The dominant

phenocryst 300px, Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coins, 1 euro coin (diameter 2.3 cm) for scale. A phenocryst is an early forming, relati ...

s are zoned

plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more pro ...

hypersthene Hypersthene is a common rock-forming inosilicate mineral belonging to the group of orthorhombic pyroxenes. Its chemical formula is . It is found in igneous and some metamorphic rocks as well as in stony and iron meteorites. Many references have fo ...

, calcic clinopyroxene,

titanomagnetite Titanomagnetite is a mineral containing oxides of titanium and iron, with the formula Fe2+(Fe3+,Ti)2O4. It is also known as titaniferous magnetite, mogensenite, Ti-magnetite, or titanian magnetite. It is part of the spinel group of minerals. The Cu ...

, and rimmed

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers qui ...

. The five flows which erupted from the new vent during the period from 1953 to 1963 are olivine-bearing, two

pyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...

, high-silica

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 predomina ...

References

External links

Trident Volcano
at the Alaska Volcano Observatory * {{DEFAULTSORT:Trident Volcanoes of Kodiak Island Borough, Alaska Mountains of Kodiak Island Borough, Alaska Stratovolcanoes of the United States Subduction volcanoes Active volcanoes Volcanoes of Alaska Mountains of Alaska Katmai National Park and Preserve Pleistocene stratovolcanoes Holocene stratovolcanoes