Dormant volcanoes are those that are not currently active (as defined above), but could become restless or erupt again. Confusion however, can arise because many volcanoes which scientists consider to be active are referred to as dormant by laypersons or in the media.

Extinct volcanoes are those that scientists consider unlikely to erupt again. Whether a volcano is truly extinct is often difficult to determine. Since "supervolcano" calderas can have eruptive lifespans sometimes measured in millions of years, a caldera that has not produced an eruption in tens of thousands of years is likely to be considered dormant instead of extinct.

For example, the Yellowstone Caldera in Yellowstone National Park is at least two million years old and hasn't erupted violently for approximately 640,000 years, although there has been some minor activity relatively recently, with hydrothermal eruptions less than 10,000 years ago and lava flows about 70,000 years ago. For this reason, scientists do not consider the Yellowstone Caldera extinct. In fact, because the caldera has frequent earthquakes, a very active geothermal system (i.e., the entirety of the geothermal activity found in Yellowstone National Park), and rapid rates of ground uplift, many scientists consider it to be an active volcano.

Notable volcanoes

On Earth

The Decade Volcanoes are 17 volcanoes identified by the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) as being worthy of particular study in light of their history of large, destructive eruptions and proximity to populated areas. They are named Decade Volcanoes because the project was initiated as part of the United Nations-sponsored International Decade for Natural Disaster Reduction. The 17 current Decade Volcanoes are

  • Avachinsky-Koryaksky (grouped together), Kamchatka, Russia
  • Nevado de Colima, Jalisco and Colima, Mexico
  • Mount Etna, Sicily, Italy
  • Galeras, Nariño, Colombia
  • Mauna Loa, Hawaii, USA
  • Mount Merapi, Central Java, Indonesia
  • Mount Nyiragongo, Democratic Republic of the Congo
  • Mount Rainier, Washington, USA
  • Sakurajima, Kagoshima Prefecture, Japan
  • Santa Maria/Santiaguito, Guatemala
  • Santorini, Cyclades, Greece
  • Taal Volcano, Luzon, Philippines
  • Teide, Canary Islands, Spain
  • Ulawun, New Britain, Papua New Guinea
  • Mount Unzen, Nagasaki Prefecture, Japan
  • Vesuvius, Naples, Italy

Elsewhere in the Solar System

Olympus Mons (Latin, "Mount Olympus") is the tallest known mountain in our solar system, located on the planet Mars.

The Earth's Moon has no large volcanoes and no current volcanic activity, although recent evidence suggests it may still possess a partially molten core.1 However, the Moon does have many volcanic features such as maria (the darker patches seen on the moon), rilles and domes.

The planet Venus has a surface that is 90 percent basalt, indicating that volcanism played a major role in shaping its surface. The planet may have had a major global resurfacing event about 500 million years ago2 from what scientists can tell from the density of impact craters on the surface. Lava flows are widespread and forms of volcanism not present on Earth occur as well. Changes in the planet's atmosphere and observations of lightning, have been attributed to ongoing volcanic eruptions, although there is no confirmation of whether or not Venus is still volcanically active.

There are several extinct volcanoes on Mars, four of which are vast shield volcanoes far bigger than any on Earth. They include Arsia Mons, Ascraeus Mons, Hecates Tholus, Olympus Mons, and Pavonis Mons. These volcanoes have been extinct for many millions of years, but the European Mars Express spacecraft has found evidence that volcanic activity may have occurred on Mars in the recent past as well.3

The Tvashtar volcano erupts a plume 330 km (205 mi) above the surface of Jupiter's moon Io.

Jupiter's moon Io is the most volcanically active object in the solar system because of tidal interaction with Jupiter. It is covered with volcanoes that erupt sulfur, sulfur dioxide and silicate rock, and as a result, Io is constantly being resurfaced. Its lavas are the hottest known anywhere in the solar system, with temperatures exceeding 1,800 K (1,500 °C). In February 2001, the largest recorded volcanic eruptions in the solar system occurred on Io.4 Europa, the smallest of Jupiter's Galilean moons, also appears to have an active volcanic system, except that its volcanic activity is entirely in the form of water, which freezes into ice on the frigid surface. This process is known as cryovolcanism, and is apparently most common on the moons of the outer planets of the solar system.

In 1989 the Voyager 2 spacecraft observed cryovolcanos (ice volcanoes) on Triton, a moon of Neptune, and in 2005 the Cassini-Huygens probe photographed fountains of frozen particles erupting from Enceladus, a moon of Saturn.5 The ejecta may be composed of water, liquid nitrogen, dust, or methane compounds. Cassini-Huygens also found evidence of a methane-spewing cryovolcano on the Saturnian moon Titan, which is believed to be a significant source of the methane found in its atmosphere.6 It is theorized that cryovolcanism may also be present on the Kuiper Belt Object Quaoar.

Effects of volcanoes

Volcanic "injection"Solar radiation reduction from volcanic eruptionsSulfur dioxide emissions by volcanoes.Average concentration of sulfur dioxide over the Sierra Negra Volcano (Galapagos Islands) from October 23-November 1, 2005

There are many different kinds of volcanic activity and eruptions: phreatic eruptions (steam-generated eruptions), explosive eruption of high-silica lava (e.g., rhyolite), effusive eruption of low-silica lava (e.g., basalt), pyroclastic flows, lahars (debris flow) and carbon dioxide emission. All of these activities can pose a hazard to humans. Earthquakes, hot springs, fumaroles, mud pots and geysers often accompany volcanic activity.

The concentrations of different volcanic gases can vary considerably from one volcano to the next. Water vapor is typically the most abundant volcanic gas, followed by carbon dioxide and sulphur dioxide. Other principal volcanic gases include hydrogen sulphide, hydrogen chloride, and hydrogen fluoride. A large number of minor and trace gases are also found in volcanic emissions, for example hydrogen, carbon monoxide, halocarbons, organic compounds, and volatile metal chlorides.

Large, explosive volcanic eruptions inject water vapor (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), hydrogen chloride (HCl), hydrogen fluoride (HF) and ash (pulverized rock and pumice) into the stratosphere to heights of 10-20 miles above the Earth's surface. The most significant impacts from these injections come from the conversion of sulphur dioxide to sulphuric acid (H2SO4), which condenses rapidly in the stratosphere to form fine sulfate aerosols. The aerosols increase the Earth's albedo-its reflection of radiation from the Sun back into space - and thus cool the Earth's lower atmosphere or troposphere; however, they also absorb heat radiated up from the Earth, thereby warming the stratosphere.

Several eruptions during the past century have caused a decline in the average temperature at the Earth's surface of up to half a degree (Fahrenheit scale) for periods of one to three years. The sulphate aerosols also promote complex chemical reactions on their surfaces that alter chlorine and nitrogen chemical species in the stratosphere. This effect, together with increased stratospheric chlorine levels from chlorofluorocarbon pollution, generates chlorine monoxide (ClO), which destroys ozone (O3). As the aerosols grow and coagulate, they settle down into the upper troposphere where they serve as nuclei for cirrus clouds and further modify the Earth's radiation balance. Most of the hydrogen chloride (HCl) and hydrogen fluoride (HF) are dissolved in water droplets in the eruption cloud and quickly fall to the ground as acid rain. The injected ash also falls rapidly from the stratosphere; most of it is removed within several days to a few weeks. Finally, explosive volcanic eruptions release the greenhouse gas carbon dioxide and thus provide a deep source of carbon for biogeochemical cycles.

Gas emissions from volcanoes are a natural contributor to acid rain. Volcanic activity releases about 130 to 230 teragrams (145 million to 255 million short tons) of carbon dioxide each year.7 Volcanic eruptions may inject aerosols into the Earth's atmosphere. Large injections may cause visual effects such as unusually colorful sunsets and affect global climate mainly by cooling it. Volcanic eruptions also provide the benefit of adding nutrients to soil through the weathering process of volcanic rocks. These fertile soils assist the growth of plants and various crops. Volcanic eruptions can also create new islands, as the magma cools and solidifies upon contact with the water.

In culture

Past beliefs

Kircher's model of the Earth's internal fires, from Mundus Subterraneus

Many ancient accounts ascribe volcanic eruptions to supernatural causes, such as the actions of gods or demigods. One early idea counter to this was Jesuit Athanasius Kircher (1602-1680), who witnessed eruptions of Aetna and Stromboli, then visited the crater of Vesuvius and published his view of an Earth with a central fire connected to numerous others caused by the burning of sulfur, bitumen and coal.

Various explanations were proposed for volcano behavior before the modern understanding of the Earth's mantle structure as a semisolid material was developed. For decades after awareness that compression and radioactive materials may be heat sources, their contributions were specifically discounted. Volcanic action was often attributed to chemical reactions and a thin layer of molten rock near the surface.


The volcano appears as a charge in heraldry.


Volcán Irazú, Costa Rica


  1. ↑ M. A. Wieczorek, B. L. Jolliff, A. Khan, M. E. Pritchard, B. P. Weiss, J. G. Williams, L. L. Hood, K. Righter, C. R. Neal, C. K. Shearer, I. S. McCallum, S. Tompkins, B. R. Hawke, C. Peterson, J, J. Gillis, and B. Bussey, "The Constitution and Structure of the Lunar Interior." Reviews in Mineralogy and Geochemistry 60(1) (2006): 221-364.
  2. ↑ D. L. Bindschadler, Magellan: A new view of Venus' geology and geophysics. Reviews of Geophysics, July 1995. Retrieved May 18, 2018.
  3. ↑ Glacial, volcanic and fluvial activity on Mars: latest images European Space Agency, February 25, 2005. Retrieved May 18, 2018.
  4. ↑ Exceptionally Bright Eruption on lo Rivals Largest in Solar System. W. M. Keck Observatory, November 13, 2002. Retrieved May 18, 2018.
  5. ↑ Cassini Finds an Atmosphere on Saturn's Moon Enceladus. Jet Propulsion Laboratory. Retrieved May 18, 2018.
  6. ↑ David L Chandler, Hydrocarbon volcano discovered on Titan New Scientist, June 8, 2005. Retrieved May 8, 2018.
  7. ↑ Volcanic gases can be harmful to health, vegetation and infrastructure U.S. Geological Survey. Retrieved May 18, 2018.


  • Cas, R. A. F., and J. V. Wright. Volcanic Successions. Norwell, MA: Unwin Hyman Inc., 1987. ISBN 0045520224
  • Macdonald, Gordon A., and Agatin T. Abbott. Volcanoes in the Sea. Honolulu, HI: University of Hawaii Press, 1970. ISBN 0824808320
  • Marti, Joan, and Gerald Ernst. Volcanoes and the Environment. Cambridge, UK: Cambridge University Press, 2005. ISBN 0521592542
  • Ollier, Cliff. Volcanoes. Oxford, UK: Basil Blackwell, 1988. ISBN 0631159770
  • Sigurðsson, Haraldur (ed.) Encyclopedia of Volcanoes. Burlington, MA: Academic Press, 1999. ISBN 012643140X This is a reference aimed at geologists, but many articles are accessible to non-professionals.

External links

All links retrieved May 18, 2018.

  • Smithsonian Institution - Global Volcanism Program.
  • How Volcanoes Work by Tom Harris.
  • How Volcanoes Work - Educational resource on the science and processes behind volcanoes, intended for university students of geology, volcanology and teachers of earth science.
  • Volcanic Materials Identification.
  • Natural Disasters - Volcano Great research site for kids.
  • Mount St. Helens Post-Eruption Chemistry Database This collection contains photographs of Mount St. Helens, post-eruption, taken over the span of three years to provide a look at both the human and the scientific sides of studying the eruption of a volcano.
  • Mount St. Helens Succession Collection This collection consists of 235 photographs in a study of plant habitats following the May 18, 1980 eruption of Mount St. Helens.