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Types of volcanic eruptions
The types of volcanic eruption are often named after famous volcanoes where characteristic behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during an interval of activity—others may display an entire sequence of types. i smell
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Subglacial eruptions are named because of activity under ice, or under a glacier. They can cause dangerous floods, lahars, and create hyaloclastite and pillow lava. Only five of these types of eruptions have occurred in the present day.
Strombolian eruptions are named because of activity of Stromboli in Sicily. They are characterised by huge clots of molten lava bursting from the summit crater to form luminous arcs through the sky. Collecting on the flanks of the cone, lava clots combine to stream down the slopes in fiery rivulets. The explosions are driven by bursts of gas slugs that rise faster than surrounding magma.
Vulcanian eruptions are named after Vulcano, following Giuseppe Mercalli's observations of its 1888-1890 eruptions. Another example was the eruption of Parícutin in 1947. They are characterised by a dense cloud of ash-laden gas exploding from the crater and rising high above the peak. Steaming ash forms a whitish cloud near the upper level of the cone.
In a Peléan eruption or nuée ardente (glowing cloud) eruption, such as occurred on the Mayon Volcano in the Philippines in 1968, a large amount of gas, dust, ash, and lava fragments are blown out of a central crater, fall back, and form avalanches that move downslope at speeds as great as 100 miles per hour. Such eruptive activity can cause great destruction and loss of life if it occurs in populated areas, as demonstrated by the devastation of Saint-Pierre during the 1902 eruption of Mont Pelée on Martinique, Lesser Antilles..
Hawaiian eruptions may occur along fissures or fractures that serve as vents, such as during the eruption of Mauna Loa Volcano in Hawaii in 1950. Also, they can occur at a central vent, such as during the 1959 eruption in Kilauea Iki Crater of Kilauea Volcano, Hawaii. In fissure-type eruptions, lava spurts from a fissure on the volcano's rift zone and feeds lava stream s that flow downslope. In central-vent eruptions, a fountain of lava spurts to a height of several hundred feet or more. Such lava may collect in old pit craters to form lava lakes, or form cones, or feed radiating flows.
Phreatic eruptions (or steam-blast eruptions) are driven by explosive expanding steam resulting from cold ground or surface water coming into contact with hot rock or magma. The distinguishing feature of phreatic explosions is that they only blast out fragments of preexisting solid rock from the volcanic conduit; no new magma is erupted. Phreatic activity is generally weak, but has been known to be strong, such as the 1965 eruption of Taal Volcano, Philippines, and the 1975-1976 activity at La Soufrière, Guadeloupe (Lesser Antilles).
Plinian eruptions are usually the most powerful, and involve the explosive ejection of relatively viscous lava. Large plinian eruptions— such as during 18 May 1980 at Mount St. Helens or, more recently, during 15 June 1991 at Pinatubo in the Philippines— can send ash and volcanic gas tens of miles into the air. The resulting ash fallout can affect large areas hundreds of miles downwind. Fast-moving pyroclastic flows (“nuées ardentes”) are also commonly associated with plinian eruptions.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Types_of_volcanic_eruptions". A list of authors is available in Wikipedia.|