Stratovolcano
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A stratovolcano is a tall, conical mountain (volcano) composed of many layers of hardened lava, tephra, and volcanic ash. These volcanoes are characterized by a steep profile and periodic, explosive eruptions. The lava flows that form them are highly viscous, and so cool and harden before spreading very far. The source magma of this rock is classified as acidic, or high in silica to intermediate (rhyolite, dacite, andesite, or basalt). This is in contrast to less viscous basic magma that forms shield volcanoes (such as Mauna Loa in Hawaii), which has a wide base and more gently sloping profile. Many stratovolcanos exceed a height of 2500 m.
Stratovolcanoes are a by-product of the subduction of tectonic plates. The source melts of these volcanoes arise as a result of the dewatering of oceanic crust at specific pressure/temperature conditions as the plate subducts to lower depths. The water freed from the subducting slab allows partial melting of the overlying mantle rock, which rises due to its lower density relative to the surrounding mantle rock, and pools at the base of the crust. The melt is initially basic in composition, but as it rises through the crust, it incorporates more acidic adjacent crustal rock, leading to a final intermediate composition. The water remains in the melt and upon eruption conributes to the explosive power of these volcanoes as superheated steam.
Although stratovolcanoes are sometimes called composite volcanoes, volcanologists prefer to use the term stratovolcano to distinguish among volcanoes because all volcanoes of any size have a composite (layered) structure — that is, are built up from sequential outpourings of eruptive materials.
Examples
- Aragats, Armenia
- Ağrı Dağı, Turkey
- Barren Island (Andaman Islands) - The only active volcano in the Indian subcontinent
- Beerenberg, Jan Mayen - The world's northernmost volcano
- Cotopaxi in Ecuador
- Mount Elbrus Caucasus, Russia
- Mount Erebus in Antarctica
- Mount Etna in Italy
- Mount Fuji in Japan
- Mount Hood in northern Oregon, United States
- Mount Rainier in Washington State, United States
- Mount Merapi in Central Java, Indonesia
- Mount Vesuvius in Italy
- Kazbek, Caucasus, Georgia
- Kollóttadyngja in North-East Iceland
- Lanín in the border between Argentina and Chile.
- Mayon Volcano in the Philippines
- El Misti near Peru's southern city of Arequipa
- Mount Pelée in Martinique
- Teide in Tenerife, Canary Islands
- Krakatoa in Indonesia
- Penguin Island, Antarctica
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