Add Your Title Here A volcano is a place on the Earth's surface where molten rock, gases and pyroclastic debris erupt through the earth's crust. The most common perception of a volcano… Volcano Classification
Mayon volcano, Philippines Mount Shasta, California Mount Shasta, California Composite Volcanoes or Stratovolcanoes
Andesite magma, tends to form composite cones. -crater at the summit Lava -through breaks in the crater wall -from fissures on the flanks of the cone -8,000 feet above their bases When volcanic activity ceases, erosion begins to destroy the cone.
-cone is stripped away and the hardened magma filling the conduit and fissures (the dikes) become exposed All that is left is the plug or "volcanic neck" and dike complex projecting above the land surface
The Evolution of a Composite volcano A. Magma, rising upward through a conduit, erupts at the Earth's surface to form a volcanic cone. Lava flows spread over the surrounding area. B. As volcanic activity continues, the cone is built to a great height and lava flows form an extensive plateau around its base. C. When volcanic activity ceases, erosion starts to destroy the cone. After thousands of years, the great cone is stripped away to expose the hardened "volcanic plug" in the conduit. D. Continued erosion removes all traces of the cone and the land is worn down to a surface of low relief. All that remains is a projecting plug or "volcanic neck," a small lava-capped mesa, and vestiges of the once lofty volcano and its surrounding lava plateau.
common at subduction zones, forming chains along plate tectonic boundaries where oceanic crust is drawn under continental crust or another oceanic plate
Composite volcanoes usually erupt in an explosive way.This is usually caoused by viscous magma.
Hazards In recorded history, explosive eruptions at subduction zone volcanoes have posed the greatest hazard to civilizations. Subduction-zone stratovolcanoes, like Mount St. HelensandMount Pinatubo, typically erupt with explosive force. Two Decade Volcanoes that erupted in 1991 provide examples of stratovolcano hazards.
Mount Pinatubo (June 15, 1991) located 90 km from Manila -spewed ash 40 kilometres into the air -produced huge pyroclastic flows and mudflows that devastated a large area around the volcano -one of the largest eruptions in the 20th Century Eruption of Mount Pinatubo was global: -cooler-than-usual temperature -the aerosol dispersed -droplets of sulfuric acid -0.5 °C -affect the weather for a few years
Mount Pinatubo, Philippines Composite volcano. June 1991
Unzen Volcano(island of Kyushu about 40 km east of Nagasaki) awakened from its 200-year slumber on 3 June 1991 -pyroclastic flow killed 43 people, including three volcanologists -one of 75 active volcanoes -1792, more than 15.000 people
Pompeii (79AD) On August 24, 79AD Mount Vesuvius literally blew its top, erupting tonnes of molten ash, pumice and sulfuric gas miles into the atmosphere. Pyroclastic flows flowed over the city of Pompeii and surrounding areas.
Pompeii (79AD) Pyroclastic flows of poisonous gas and hot volcanic debris engulfed the cities of Pompeii, Herculaneum and Stabiae suffocating the inhabitants and burying the buildings.
Pompeii (79AD) The cities remained buried and undiscovered for almost 1700 years until excavation began in 1748. These excavations continue today and provide insight into life during the Roman Empire.
Characteristics of hawaiian eruption: effusive emission of fluid lavas mobile nature of these lavas Shield volcanoes vary widely in size with their age. -often measure 5 to 6 km in diameter and surpass 460 to 610 m in height -largest shield volcano (and the largest active volcano) in the world is Mauna Loa in Hawaiʻi, projects 4,169 m above sea level, and is over 97 km wide. contain 80,000 km3 of basalt
The Hawaiian shield volcanoes and the Galápagos islands are unique. -are not located near any plate boundaries; instead, the two chains are fed by the movement of oceanic plates over hotspot -their lavas are characterized by high levels of sodium, potassium, and aluminum
Valentine Cave in Lava Beds National Monument, California. This shows the classic tube shape and the curbs on the wall mark former flow levels. Thurston Lava Tube in Hawaii Volcanoes National Park, Hawaii. East Rift Zone on Kilauea
the solar system Dangers -do not pose much threat to humans -they are hazardous to agriculture and infrastructure -1983 eruption of Kīlauea has destroyed over 200 structures and buried kilometers of highways
Cinder conescoria cones, cinder and spatter cones
Fissure vent large flood basalts and lava channels hard to recognize crack in the ground along rifts and rift zones (Iceland and the Great Rift Valley in Africa) often found in shield volcanoes The Laki fissure system -biggest eruption on earth in historical times -during the Eldgjá eruption A.D. 934, which releas19.6 km³ of lava
Fissure vents of Hawaiian volcanoes-“curtains of fire” A volcanic fissures and lava channels Fissure eruption in Iceland
Lava dome High viscosity : high levels of silica in the magma degassing of fluidmagma Most of the preserved domes have high silica. -heights -several hundred meters -grow slowly and steadily for months, years, or even centuries Image of the rhyoliticlava dome of Chaitén Volcano during its 2008–2009 eruption.
Hazards pyroclastic flows, destruction of property, forest fires… Characteristics hemispherical dome shape cycles of dome growth over long periods sudden onsets of violent explosive activity
the Grímsvötn Volcano beneath the Vatnajökull (Iceland)(November 1996) ice sheet erupted and caused a Jökulhlaup that affected more than 750 km² and destroyed or severely damaged several bridges Iceland’s Grimsvotn Volcano Is Erupting Remnants of bridge twisted by November 5, 1996 flood following Grímsvötn eruption
Stage 1. Early eruptions – pillow lavas and hyaloclastiteStage 2b. Formation of a subglacial moundStage 3b. Formation of a tuya type of distinctive, flat-topped, steep-sided volcano formed when lava erupts through a thick glacier or ice sheet.
VolcanEl Totumo (Colombia) 15 m high and can accommodate 10 to 15 people on its crater Volcan de Lodo El Totumo (MudVolcano), Cartagena
Submarine volcano located near areas of tectonic plate movement, known as ocean ridges exist in shallow water There are three circumstances where tectonic plates can interact with each other and the Earth's molten interior to form submarine volcanoes. tectonic plate slides over a "hot spot" where tectonic plates are spreading apart at the mid-ocean ridges subduction
interaction of water with the molten lava forms a thick glassy crust around the flowing lava
Scientists still have much to learn about the location and activity of underwater volcanoes. The Kolumbo underwater volcano (Aegean Sea) was discovered in 1650 when it burst from the sea and erupted, killing 70 people on the nearby island of Santorini.
formed from extinct volcanoes, rising from a seafloor of 1,000 - 4,000 meters depth.
30,000 seamounts occur across the globe, with only a few
having been studied
Supervolcano magma rises into the crust from a hotspotbut is unable to break through the crust pressure builds in a large and growing magma pool until the crust is unable to contain the pressure form at convergent plate boundaries and continental hotspot locations rate VEI 8 -"super eruptions“ colossal events that throw out at least 1,000 km3Dense Rock Equivalent (DRE) of ejecta
rases virtually all life in a radius of hundreds of kilometers from the site, and entire continental regions further out can be buried meters deep in ash Form circular calderas remain for millions of years after all volcanic activity at the site has died every 50,000 years the Earth experiences a super-volcano
1,000 sq km of land obliterated by pyroclastic ash flows, the surrounding continent is coated in ash and sulphur gases are injected into the atmosphere Taupo in New Zealand,mostrecent super-volcano, around 26,500 years ago the most damaging super-volcano in human history was Toba, on Sumatra, Indonesia, 74,000 years ago -close to the equator -temperatures were dramatically reduced