page_title: Volcano
section_title: Active
hierarchical_section_title: Volcano / Volcanic activity / Popular classification of volcanoes / Active
caption_attribution_description: English: Pictures taken by Peter Hartree between 14.30 and 15.00 on September 4th 2014. I'm sorry for the less than ideal quality of these - this wasn't a professional photo shoot. All photos are unedited. I have a bunch more (fairly similar) shots - if you'd like to see them, write to peter@reykjavikcoworking.is. Many thanks to pilot Siggi G for the ride.
context_page_description: 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.
  Earth's volcanoes occur because its crust is broken into 17 major, rigid tectonic plates that float on a hotter, softer layer in its mantle. Therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging, and most are found underwater. For example, a mid-oceanic ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates whereas the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates. Volcanoes can also form where there is stretching and thinning of the crust's plates, e.g., in the East African Rift and the Wells Gray-Clearwater volcanic field and Rio Grande Rift in North America. This type of volcanism falls under the umbrella of "plate hypothesis" volcanism. Volcanism away from plate boundaries has also been explained as mantle plumes. These so-called "hotspots", for example Hawaii, are postulated to arise from upwelling diapirs with magma from the core–mantle boundary, 3,000 km deep in the Earth.
context_section_description: There is no consensus among volcanologists on how to define an "active" volcano. The lifespan of a volcano can vary from months to several million years, making such a distinction sometimes meaningless when compared to the lifespans of humans or even civilizations. For example, many of Earth's volcanoes have erupted dozens of times in the past few thousand years but are not currently showing signs of eruption. Given the long lifespan of such volcanoes, they are very active. By human lifespans, however, they are not.
  Scientists usually consider a volcano to be erupting or likely to erupt if it is currently erupting, or showing signs of unrest such as unusual earthquake activity or significant new gas emissions. Most scientists consider a volcano active if it has erupted in the last 10,000 years (Holocene times)—the Smithsonian Global Volcanism Program uses this definition of active. Most volcanoes are situated on the Pacific Ring of Fire. An estimated 500 million people live near active volcanoes.
  Historical time (or recorded history) is another timeframe for active. The Catalogue of the Active Volcanoes of the World, published by the International Association of Volcanology, uses this definition, by which there are more than 500 active volcanoes. However, the span of recorded history differs from region to region. In China and the Mediterranean, it reaches back nearly 3,000 years, but in the Pacific Northwest of the United States and Canada, it reaches back less than 300 years, and in Hawaii and New Zealand, only around 200 years.
  As of 2013, the following are considered Earth's most active volcanoes:
  Kīlauea, the famous Hawaiian volcano, was in nearly continuous, effusive eruption (in which lava steadily flows onto the ground) between 1983 through 2018, and had the longest-observed lava lake.
  Mount Etna and nearby Stromboli, two Mediterranean volcanoes in "almost continuous eruption" since antiquity.
  Piton de la Fournaise, in Réunion, erupts frequently enough to be a tourist attraction.
  As of 2010, the longest ongoing (but not necessarily continuous) volcanic eruptive phases are:
  Mount Yasur, 111 years
  Mount Etna, 109 years
  Stromboli, 108 years
  Santa María, 101 years
  Sangay, 94 years
  Other very active volcanoes include:
  Mount Nyiragongo and its neighbor, Nyamuragira, are Africa's most active volcanoes.
  Erta Ale, in the Afar Triangle, has maintained a lava lake since at least 1906.
  Mount Erebus, in Antarctica, has maintained a lava lake since at least 1972.
  Mount Merapi
  Whakaari / White Island, has been in a continuous state of releasing volcanic gas since before European observation in 1769.
  Ol Doinyo Lengai
  Ambrym
  Arenal Volcano
  Pacaya
  Klyuchevskaya Sopka
  Sheveluch
caption: Lava flows at Holuhraun, Iceland, September 2014
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