Volcano
A vent in the crust of Earth allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. Most volcanoes form where tectonic plates diverge or converge. The Mid-Atlantic Ridge features volcanoes caused by divergent tectonic plates moving apart. Hot mantle rock creeps upwards beneath the thinned oceanic crust at these ridges. This process creates new seafloor through adiabatic expansion and partial melting of rising rock. Black smokers serve as evidence of this submarine volcanic activity. In contrast, subduction zones occur where an oceanic plate dives beneath a continental plate. Water released from the subducting plate lowers the melting temperature of the overlying mantle wedge. This flux melting creates magma that tends to be extremely viscous due to high silica content. When this magma reaches the surface, it forms chains of volcanoes called volcanic arcs. The Pacific Ring of Fire contains many such examples like the Cascade Volcanoes. Volcanism also arises from stretching and thinning of crustal plates away from boundaries. The East African Rift and the Rio Grande rift demonstrate this intraplate activity. Mantle plumes rise from the core-mantle boundary to create hotspot volcanism. The Hawaiian Islands formed as the North American plate moved over the Yellowstone hotspot.
Volcanic fissure vents are flat linear fractures through which basaltic lava emerges. These vents often relate or constitute shield volcanoes with broad shield-like profiles. Shield volcanoes form by the eruption of low-viscosity basaltic or andesitic lava that can flow great distances. The Hawaiian volcanic chain is a series of these shield cones. Lava domes have steep convex sides built by slow eruptions of highly viscous rhyolite. Lassen Peak in California stands as an example of a volcano formed from felsic lava. Cinder cones result from eruptions of mostly small pieces of scoria and pyroclastics. Parícutin in Mexico and Sunset Crater in Arizona serve as classic examples of cinder cones. Stratovolcanoes are tall conical mountains composed of lava flows and tephra in alternate layers. Mount Fuji in Japan and Mayon Volcano in the Philippines exemplify this composite structure. Plinian eruptions produce sustained huge eruption columns whose collapse creates catastrophic pyroclastic flows. The 1902 eruption of Mount Pelée destroyed the city of Saint-Pierre in Martinique. A supervolcano produces over one cubic kilometer of volcanic deposits in a single explosive event. Lake Taupō in New Zealand sits within the caldera of a known supervolcano.
Most of Earth's plate boundaries lie underwater, meaning most volcanoes exist beneath the ocean surface. Submarine volcanoes are common features of the ocean floor with pillow lava forming thick sequences of discontinuous masses. In shallow water, active volcanoes disclose their presence by blasting steam and rocky debris high above the ocean's surface. Hydrothermal vents support peculiar ecosystems based on chemotrophs feeding on dissolved minerals. The Smithsonian Institution's Global Volcanism Program database lists 9,901 confirmed eruptions from 859 volcanoes during the Holocene Epoch. Decade Volcanoes include 16 specific sites identified for study due to history of large destructive eruptions. Avachinsky-Koryaksky towers over Petropavlovsk-Kamchatsky on Kamchatka Peninsula in Russia. Mount Etna in Sicily has erupted continuously for thousands of years earning its nickname Lighthouse of the Mediterranean. Mount Rainier in Washington State and Vesuvius in Naples Italy remain critical monitoring targets. Iceland hosts numerous shield volcanoes including Skjaldbreiður whose name means broad shield. The Tuya Mountains Provincial Park protects unusual landscape formations called tuyas found near Tuya Lake in British Columbia.
The 1815 eruption of Mount Tambora created global climate anomalies known as the Year Without a Summer. Sulfur dioxide from the Huaynaputina eruption may have caused the Russian famine of 1601, 1603. Ash thrown into the air presents hazards to aircraft where particles melt by high operating temperatures. The melted particles adhere to turbine blades altering their shape and disrupting operation. A volcanic winter thought to have taken place around 70,000 years ago followed the supereruption of Lake Toba. This event may have created a population bottleneck affecting genetic inheritance of all humans today. Despite these dangers, tuff formed from volcanic ash is used for construction since ancient times. Romans often used tuff abundant in Italy for building structures. Volcanic ash and weathered basalt produce some of the most fertile soil rich in iron magnesium potassium calcium and phosphorus. Geothermal power taps high rates of heat flow from Earth's interior. Tourism associated with volcanoes constitutes a worldwide industry. The Mount Pinatubo evacuation of 1991 saved approximately 20,000 lives through timely warnings. Modern monitoring allows advance warnings minimally of hours or usually days prior to eruptions.
Jupiter's moon Io is the most volcanically active object in the Solar System due to tidal interaction with Jupiter. Its lavas are the hottest known anywhere exceeding 1,800 Kelvin or 1,500 degrees Celsius. In February 2001 the largest recorded volcanic eruptions in the Solar System occurred on Io. Mars features four vast shield volcanoes far bigger than any on Earth including Olympus Mons. Olympus Mons stands as the tallest known mountain in the Solar System. Europa appears to have an active volcanic system entirely in the form of water freezing into ice. This process is known as cryovolcanism and is common on moons of outer planets. Voyager 2 observed cryovolcanoes on Triton a moon of Neptune in 1989. Cassini, Huygens photographed fountains of frozen particles erupting from Enceladus a moon of Saturn in 2005. Titan hosts evidence of a methane-spewing cryovolcano believed to be a significant source of atmospheric methane. A 2010 study suggested intense volcanic activity similar to Io exists on exoplanet COROT-7b detected by transit in 2009.
Footprints of hominina found in East African volcanic ash dated at 3.66 million years old provide early evidence of human encounter with volcanoes. Ancient accounts often ascribed volcanic eruptions to supernatural causes such as actions of gods or demigods. The neolithic goddess at Çatalhöyük represents one of the earliest known examples of this belief. Anaxagoras proposed eruptions were caused by a great wind in the fifth century BC. Seneca the Younger suggested combustion as the cause by 65 CE. Jesuit Athanasius Kircher published his view of an Earth in Mundus Subterraneus with a central fire connected to numerous others. James Hutton synthesized works of Descartes and others into geology by 1785 regarding igneous intrusions of magma. Alfred Lacroix built upon knowledge with studies on the 1902 eruption of Mount Pelée. Arthur Holmes work brought together concepts of radioactive generation of heat and partial decompression melting of magma by 1928. This eventually led to acceptance of plate tectonics theory explaining global distribution patterns.
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Common questions
What is a volcano and how does it form?
A volcano is a rupture in a planet's crust where material escapes from a magma chamber below the surface. Most volcanoes form where tectonic plates diverge or converge, allowing hot lava, volcanic ash, and gases to escape through vents.
When did the 1902 eruption of Mount Pelée occur and what was its impact?
The 1902 eruption of Mount Pelée destroyed the city of Saint-Pierre in Martinique during the year 1902. This Plinian eruption produced sustained huge eruption columns whose collapse created catastrophic pyroclastic flows that killed thousands of people.
Where are submarine volcanoes located and what evidence exists for their activity?
Most of Earth's plate boundaries lie underwater, meaning most volcanoes exist beneath the ocean surface as common features of the ocean floor. Black smokers serve as evidence of this submarine volcanic activity while pillow lava forms thick sequences of discontinuous masses on the seafloor.
Why do some volcanoes produce highly viscous lava compared to others?
Volcanoes at subduction zones tend to be extremely viscous due to high silica content in the magma formed by flux melting. In contrast, shield volcanoes form by the eruption of low-viscosity basaltic or andesitic lava that can flow great distances.
How many confirmed eruptions does the Smithsonian Institution's Global Volcanism Program database list from the Holocene Epoch?
The Smithsonian Institution's Global Volcanism Program database lists 9,901 confirmed eruptions from 859 volcanoes during the Holocene Epoch. Decade Volcanoes include 16 specific sites identified for study due to history of large destructive eruptions such as Mount Etna in Sicily.