Volcanoes and Pompeii – Flashcards

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Any opening in Earth's crust where hot molten rock, ashes, gases, and rock fragments erupt. By transporting material that was once inside Earth to the surface, volcanoes are the primary way that Earth builds land.
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volcano
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Whenever molten rock, debris, and gases from Earth's interior reach the surface.
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When does eruption occur?
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When magma first breaks through the surface of Earth and erupts as lava. Solidifying quickly this lava has the potential to become mountains of igneous rock.
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When does the formation of a volcano begin?
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A liquid's resistance to flow.
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viscosity
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An avalanche of gas, ash, and rock flowing down the side of a volcano, leaving destruction in its path.
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pyroclastic flow
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A large underground pool of liquid rock found beneath the surface of the Earth.
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magma chambers
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A large body of igneous rock that forms from cooled magma deep in the Earth's crust. Example: Sierra Nevada mountain range
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batholiths
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Islands that were made from volcanoes erupting from the ocean floor.
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volcanic islands
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A string of volcanic islands in the ocean. Island arcs are volcanic islands that form parallel to ocean trenches in subduction zones. The Pacific Ring of Fire is home to many of these groups of islands.
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island arc
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Most consist of two parallel, rows of arch shaped islands. The inner row of such a double arc is composed of a string of explosive volcanoes, while the outer row is made up of nonvolcanic islands. In the case of single arcs, many of the constituent islands are volcanically active.
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island arc
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Mariana Islands Japan the Aleutians the Lesser Antillies
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examples of island arc
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Is the only active volcano in mainland Europe, and has produced some of the continent's largest volcanic eruptions. It is located on Italy's west coast. Vesuvius is most famous for the 79 AD eruption which destroyed the Roman cities of Pompeii and Herculaneum. Though the volcano's last eruption was in 1944, it still represents a great danger to the cities that surround it, especially the busy metropolis of Naples
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Mount Vesuvius
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Vesuvius is part of the Campanian volcanic arc, a line of volcanoes that formed over a subduction zone created by the convergence of the African and Eurasian plates.
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Mount Vesuvius: Plate Tectonic Setting
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Eight major eruptions in the last 17,000 years
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How many eruptions has Mount Vesuvius experienced in the last 17,000 years?
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For the casts the hot ash formed around victims of the eruptions. The people of Pompeii suffocated on ash in the air, which then covered them and preserved amazing details of their clothing and faces.
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Pompeii is famous for what?
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Some of the most spectacular features on Earth. They are large volcanic craters that form by two different methods: 1) an explosive volcanic eruption; or, 2) collapse of surface rock into an empty magma chamber. The image at right is a satellite view of one of the most famous calderas - Crater Lake in Oregon. Crater Lake was formed about 7700 years ago when an enormous volcanic eruption of Mount Mazama emptied a large magma chamber below the mountain. The fractured rock above the magma chamber collapsed to produce a massive crater over six miles across. Centuries of rain and snow filled the caldera creating Crater Lake. With a depth of 1932 feet (589 meters), Crater Lake is the deepest lake in the United States and the seventh deepest lake in the world.
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What is a Caldera?
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Form when a large magma chamber is emptied by a volcanic eruption or by subsurface magma movement. The unsupported rock that forms the roof of the magma chamber then collapses to form a large crater. Crater Lake and many other calderas are thought to have formed by this process.
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Collapse Calderas
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Formed when very large magma chambers filled with silica-rich melt and abundant gas move upwards from depth. Silica-rich magmas have a very high viscosity that enables them to hold gas bubbles under very high pressures. As they rise to the surface the reduction of pressure causes the gases to expand. When break-through occurs the result can be an enormous explosion which blasts away large volumes of rock to form the caldera. Some of these blasts eject many cubic kilometers of magma and rock.
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Explosive Calderas
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Many of Kilauea's pre-1924 explosive eruptions that produced significant ash deposits probably happened when the volcano's summit crater was so deep that its floor was below the water table, letting ground water seep in to form a lake. Whenever magma erupted into the lake water, violent explosions of steam and volcanic gases resulted, fragmenting the magma into tiny ash particles and driving fast-moving, extremely hot ash-laden steam clouds (pyroclastic surges) out of the crater. Image and caption by USGS.
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What Causes Explosive Eruptions at Kilauea?
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Landsat Geocover image of the caldera formed by the Toba Supervolcano. It is now the world's largest volcanic lake. The image above was produced using Landsat GeoCover data from NASA.
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World's Largest Explosive Eruption
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An eruption that rates a magnitude of 8 on the Volcanic Explosivity Index. The VEI is a scale that rates eruptions on their ejecta volume, plume height and duration. The scale ranges from 0 through 8. Only a few dozen eruptions in all of Earth's history are known to have a VEI of 8. Two of those eruptions, the Lava Creek eruption (640,000 years ago) and the Huckleberry Ridge eruption (2.2 million years ago), occurred at Yellowstone. These eruptions were given the VEI rating because their ejecta volume exceeded 1000 cubic kilometers!
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What is a Supervolcano?
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Consists of powder-size to sand-size particles of igneous rock material that have been blown into the air by an erupting volcano (see image at right). The term is used for the material while it is in the air, after it falls to the ground and sometimes after it has been lithified into rock. The terms "volcanic dust" and "volcanic ash" are both used for the same material, however "volcanic dust" is more appropriately used for powder-size material.
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What is Volcanic Ash?
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They are fast-moving fluidized bodies of hot gas, ash and rock. The flows normally hug the ground and travel downhill under gravity, their speed depending upon the gradient of the slope and the size of the flow. Flows usually consist of two parts: the basal flow hugs the ground and contains larger, coarse boulders and rock fragments, while an ash cloud rises above it because of the turbulence between the flow and the overlying air.
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Pyroclastic flows
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Low Silica magmas which cool to form black rocks.
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basaltic magma
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Like earthquakes, volcanoes are often located close to plate boundaries. Countries near or on plate boundaries, like Japan, Indonesia, and New Zealand, are prone to earthquakes, and are also host to a large number of volcanoes.
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Where do volcanoes form?
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- Italy - Active - Composite/Strato volcano - Large mountain & coldera - Capable of large, explosive eruptions - On plate boundary - Most recent eruptions 1944 during WWII
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Mt. Vesuvius
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1. Extinct: no record or proof of eruption. We know it's a volcano because of the shape of the volcano, type or rock found there, region on Earth. 2. Dormant volcano: We have record of eruption, but not recently. Scientists debate wether it is dormant. Hotly debated. Ex: Mt. Hood in Oregon 3. Active: having proof ; record that it is periodically erupting (recently). Ex: Mt. St. Helens in Washington
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3 Stages of a Volcano Lifecycle
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Cinder cones Composite volcanoes Shield volcanoes
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3 kids of volcanoes
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No record or proof of eruption. We know it's a volcano because of the shape of the volcano, type or rock found there, region on Earth.
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Volcano Lifecycle: Extinct
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We have record of eruption, but not recently. Scientists debate wether it is dominate. Hotly debated.
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Volcano Lifecycle: Dormant volcano
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Having proof & record that it is periodically erupting (recently). Ex: Mount St. Helens in Washington
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Volcano Lifecycle: Active
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Igneous rock is formed when lava or magma cools. (derived from the Latin word *ignis* meaning *fire*)
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Igneous rock
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- Affected by its temperature and chemical composition - Silica levels affect viscosity - Igneous rock formations - Pahoehoe and Aa lava - two types based on Hawaiian words - Subduction zones most common for large volcano with viscous lava - When lava or magma cools you get igneous rock
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Viscosity of Lava (on surface) or Magma (underneath surface)
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These eruptions are those rare events when more than 1000 cubic kilometers (240 cubic miles) of pyroclastic material are blown out of a volcano during one eruption. These devastating events rarely occur and a supervolcano eruption has not occurred in recorded history.
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Super Volcanoes
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A fine-grained, extrusive igneous rock composed mainly of plagioclase with other minerals such as hornblende, pyroxene and biotite.
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What is Andesite?
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Explosions of magma from a pool in the volcano's conduit.
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Strombolian eruptions
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Huge explosions that create columns of gas, ash and rock which can rise dozens of kilometers into the atmosphere. Ex: Mount St. Helens in 1980 and Pinatubo in 1990
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Plinian eruptions
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Mount Vesuvius is located above a subduction zone formed where the African plate descends beneath Italy. Magma produced from the melting African plate creates the large, violently explosive volcanoes of the Italian Peninsula.
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Simplified plate tectonics cross section (A to B) Plate tectonics of Mount Vesuvius
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Map showing the location of Mount Vesuvius on the west coast of Italy. Nearby Volcanoes: Etna Stromboli
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Map: Where is Vesuvius?
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