Adagdak

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From Baten (2002): "Mt. Adagdak is located on the northeastern portion of Adak Island, central Aleutian Islands, Alaska. Mt. Adagdak is built from three primary stages of volcanism: 1) the shield stage composed primarily of thick basaltVolcanic rock (or lava) that characteristically is dark in color, contains 45% to 54% silica, and generally is rich in iron and magnesium.ic lavaLava is the word for magma (molten rock) when it erupts onto the Earth's surface. Geologists also use the word to describe the solidified deposits of lava flows and fragments hurled into the air by explosive eruptions (for example, lava bombs or blocks). Lava is from the Italian word for stream, which is derived from the verb lavare--to wash. flows, 2) two composite cones, the older cone yields an 40Ar/39Ar date of 2.20 +/- 0.37 Ma (2 sigma error) and the younger cone has a date of 1.2 +/- 0.15 Ma and 3) three domeA steep-sided mass of viscous (doughy) lava extruded from a volcanic vent (often circular in plane view) and spiny, rounded, or flat on top. Its surface is often rough and blocky as a result of fragmentation of the cooler, outer crust during growth of the dome.s, one of which has a date of 0.21 +/- 0.05 Ma."

From Wood and Kienle (1990): "Adak is a large Tertiary island in the central Aleutians with a small (~40 cubic km) volcanic center at its northern extremity. Kanaga lies to the west and Great Sitkin to the east. Because of its easy access, Adak is certainly the most frequently visited and sampled island in the Aleutians. Andrew Bay (~350 m, oldest), Mount Moffet (1,200 m), and Mount Adagdak (650 m) volcanoA vent in the surface of the Earth through which magma and associated gases and ash erupt; also, the form or structure (usually conical) that is produced by the ejected material.es have produced essentially all the Recent volcanic material. Only the erosional vestiges of Andrew Bay volcano remain (now filled by Andrew Bay and Lake); it was apparently obliterated by calderaA large crater formed by collapse or subsidence of the ground surface following a great eruption. During a typical caldera-forming eruption, the magma chamber is partially emptied and large amounts of ash and pyroclastic debris are extruded. formation, encroachment of the sea, and glaciation. Heavily glaciated, Mount Moffet consists of principally of thick andesite flows, flank domes, and a substantial parasitic cone of many thin basalt flows. The scoriaA cinder-like volcanic rock, usually dark brown, red-brown, or black in color.ceous, blockA volcanic block is a solid rock fragment greater than 64 mm in diameter that was ejected from a volcano during an explosive eruption. Blocks commonly consist of solidified pieces of old lava flows that were part of a volcano's cone.y dome on the outward south flank of Mount Moffet may be one of the youngest volcanic features of this center. Mount Adagdak is a model composite cone with a distinct lower shield of one or two basalt flows and interbedded scoria. At ~350 m the small stratovolcano(also called a stratocone or composite cone). A steep-sided volcano, usually conical in shape, built of lava flows and fragmental deposits from explosive eruptions. begins, consisting mainly of volcaniclasticA volcanic rock or unconsolidated deposit composed of pre-existing fragments, particles or clasts of volcanic origin. debris and an occasionally thin, fragmentary andesiticA fine-grained volcanic rock made up of feldspars and ferromagnesian minerals; typically has a silica content of 54 to about 62 percent. flow. The summit craterA steep-sided, usually circular depression formed by either explosion or collapse at a volcanic vent., with a well-defined south rim, is occupied by a hornblende andesite plugSolidified lava that fills the conduit of a volcano. It is usually more resistant to erosion than the material making up the surrounding cone, and may remain standing as a solitary pinnacle when the rest of the original structure has eroded away.; in places it has vertical, smooth walls peppered with indigenous xenolithsA foreign inclusion in an igneous rock.. At one time this plug may have been partly a Pelean spine, large blocks of which are scattered across the shield. A northwesterly directed explosion and ashFine fragments (less than 2 millimeters across) of lava or rock formed in an explosive volcanic eruption. flow may have strongly breached the summit crater prior to the ventAn opening in the Earth's surface through which magma erupts or volcanic gases are emitted.-filling event. A late stage basaltic dome lies on the southeast flank.

"Although Moffet and Adagdak are certainly volcanoes, when compared to large Aleutian volcanoes, both vents represent small, almost futile outpourings. This is perhaps reflected in the heterogeneous nature and composition of the erupted materials. Mafic, olivine-rich xenolithicOf or pertaining to stone. material is common in a thick andesite flow on the north shore of Mount Moffet, and also in an apparently phreatic vent on the west shield of Mount Adagdak; gabbroic and dioritic xenoliths are found along the bouldery beach north of Mount Adagdak."