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Volcanoes Volcanoes and Plate Tectonics • A _____________ is a weak spot in the crust where molten material, or _______, comes to the surface. • ________ is a molten mixture of rockforming substances, gases, and water from the mantle. • When magma reaches the surface, it is called _________. • Lava released during __________ activity builds up Earth’s surface. Volcanoes and Plate Tectonics • There are about ______ active volcanoes on land. Volcanoes and Plate Tectonics • Volcanoes occur in ________ that extend across continents and oceans • One major volcanic belt is the _________ formed by the many volcanoes that rim the ____________ Ocean. • Volcanic belts form along the _____________ of Earth’s plates. • At plate boundaries, huge pieces of the crust _________ (pull apart) or _________ (push together). Volcanoes and Plate Tectonics • Most volcanoes form along ____________ plate boundaries such as ______________ and along converging plate boundaries where ___________ takes place. • Along the _________, lava pours out of cracks in the ocean floor, gradually building new mountains. • Volcanoes also form along diverging plate boundaries on _________. Volcanoes and Plate Tectonics • Many volcanoes form near ________________ plate boundaries where ________________ plates return to the _____________. • Volcanoes may form where _________ oceanic plates ____________ or where an oceanic plate collides with a ___________________ plate. Volcanoes and Plate Tectonics Volcanoes and Plate Tectonics • Many volcanoes occur near boundaries where two ________________ plates collide. • Through _____________, the older, denser plate _________ beneath a ______________ into the mantle. • Some of the rock above the subducting plate ___________ and forms magma. • Because the magma is less _________ than the surrounding rock, it rises toward the surface. • Eventually, the magma breaks through the ocean floor, creating _________________. Volcanoes and Plate Tectonics • The resulting volcanoes create a string of islands called an ______________. The curve of an island arc ____________ the curve of its deep-ocean trench. • Major island arcs include: – _______________________________________ _______________________________________ _______________________________________ _______________________________________ Volcanoes and Plate Tectonics • Volcanoes also occur where an oceanic plate is subducted beneath a continental plate. • Collisions of this type produced the volcanoes of the ____________ Mountains in South America and the _____________ of the Pacific Northwest in the United States Volcanoes and Plate Tectonics • Some volcanoes result from ______________ in Earth’s mantle. • A hot spot is an ___________ where material from deep within the mantle ______________________, forming magma. • A _____________ forms above a hot spot when magma erupts through the crust and reaches the surface. Volcanoes and Plate Tectonics Volcanoes and Plate Tectonics • A hot spot in the ______________ can gradually form a series of volcanic mountains. • The _______________ Islands formed one by one over millions of years as the _____________ plate drifted over a hot spot. • Hot spots can also form under the _______________. Volcanic Eruptions • Lava begins as _________, which usually forms in the __________________. • The materials of the asthenosphere are under great ____________. • Liquid magma is less _________ than the solid material around it. • As magma rises, it sometimes becomes _____________ beneath layers of rock. • But if an opening in _____________ rock allows the magma to reach the surface, a volcano forms. Volcanic Eruptions Volcanic Eruptions • A volcano is more than a large, ______________________ • All volcanoes have a ___________ of magma beneath the surface and one or more _____________ through which the magma forces its way. • Magma collects in a pocket called a ________________ beneath a volcano. Volcanic Eruptions • The magma moves upward through a __________, a long tube in the ground that connects the magma chamber to the Earth’s surface. • Molten rock and gas leave the volcano through an opening called a ___________. • There is _________ central vent at the top of a volcano. However, many volcanoes also have _________ vents that open on the volcano’s _____________. Volcanic Eruptions • A _____________ is the area covered by lava as it __________ out of a vent. • A _____________ is a bowl-shaped area that may form at the top of a volcano around the central vent. • The _____________ of a volcano is similar to the soda water bubbling out of a warm bottle of soda pop. Volcanic Eruptions • As magma rises toward the surface, the pressure of the surrounding rock on the magma _____________. • When a volcano erupts, the _________ of the expanding gases pushes magma from the ____________________ through the __________ until it _________ or explodes out of the vent. • Once magma escapes from the volcano and becomes _________, the remaining ___________ bubble out. Volcanic Eruptions • Geologist classify volcanic eruptions as _____________________. • The ________________ properties of its magma determine how a volcano erupts. • Eruptions depends on the magma’s _____________ and _____________ content. Volcanic Eruptions • _________________ is the ____________ of a liquid to flow. • The ____________ the viscosity of a liquid, the _____________ it flows. • The viscosity of magma depends on its ______________________________. • The compound ___________ is made up of particles of ___________ and ________________. Volcanic Eruptions • A volcano erupts _________ if its magma is ________ in silica. • Low-silica magma has low __________ and flows ___________. • Lava with low viscosity _________ quietly from the vent and can flow for many __________________. • The _______________ Islands were formed from ___________ eruptions. Volcanic Eruptions • A volcano erupts _____________ if its magma is _________ in _________. • ___________ magma has _________ viscosity, making it _______________. • The high-viscosity magma does not always flow out of the ___________. • Instead, it builds up in the volcano’s _________, plugging it like a ______ in a bottle. • The trapped gases build up pressure until they ____________. Volcanic Eruptions • An ______________ eruption breaks lava into _____________ that quickly cool and harden into pieces of different sizes. • The smallest pieces are _____________ – fine, rocky particles as small as a speck of dust. • Pebble-sized particles are called _____________. Volcanic Eruptions • Larger pieces, called ____________, may range from the size of a baseball to the size of a car. • A ____________________ occurs when an explosive eruption hurls out a mixture of hot gases, ash, cinders, and bombs. • _______________ forms when lava cools very ___________, giving it a smooth, ____________ surface like glass. • _____________ forms when gas bubbles are trapped in fast-cooling lava, leaving spaces in the rock. Volcanic Eruptions • Both types of eruption can cause damage far from the ___________ rim. • During a ____________ eruption, lava flows from __________, setting fire to, and then burying, everything in its path. • During an ___________ eruption, a volcano can __________ out hot clouds of deadly gases as well as ash, ______________, and bombs. Volcanic Eruptions • ______________ can bury entire towns. If it becomes wet, the heavy ash can cause roofs to collapse. • If a jet plant sucks ash into its engine, the engine may stall. • Eruptions can cause _____________ and ________________ of mud, melted snow, and rock. Kinds of Volcanic Eruptions • Within the last ______ years, major volcanic eruptions have greatly affected the land and people around them. Volcanic Eruptions • The activity of a volcano may last from ______ than a decade to more than _____ million years. • Most long-lived volcanoes, however, do not erupt _______________. • Geologists often use the terms ___________, ___________, or _________ to describe a volcano’s stage of activity. Volcanic Eruptions • An active, or ________, volcano is one that is erupting or has shown signs that it may erupt in the near future. • A dormant, or _____________, volcano is like a sleeping bear. • Scientists expect a _______________ volcano to awaken in the future and become ____________. • An ___________, or dead, volcano is unlikely to erupt again. Volcanic Eruptions • The time between volcanic eruptions may span __________ to many ________________ of years. • People living near a ___________ volcano may be unaware of the danger. • But a dormant volcano can become ___________ at any time. Volcanic Eruptions • Geologists have been more ______________ in predicting volcanic eruptions than in predicting earthquakes. • Geologists use _________________ to detect changes in and around a volcano. • Geologists use ________________ and other instruments to detect slight surface changes in _____________ and _______ caused by magma moving underground. Volcanic Landforms • Volcanoes have created some of Earth’s most ________________ landforms. • ____________ activity on and beneath the surface has built up Earth’s land areas. • Volcanic activity also formed the rock of the ______________ floor. Volcanic Landforms • Volcanic eruptions create ____________ made of lava, ash, and other materials. • These landforms include: – _____________________ – _____________________ – _____________________ – _____________________ Volcanic Landforms • Shield Volcanoes – At some places on __________ surface, _________ layers of lava pours out of a vent and harden on top of previous layers. – Such lava flows gradually build a wide, gently ___________________. – Shield volcanoes rising from a hot spot on the ocean floor created the ___________________. Volcanic Landforms • _______________________ – If a volcano’s lava has _________ viscosity, it may produce __________, __________, and ______________. – These materials build up around the vent in a _____________, coneshaped hill or small mountain called a __________________. Volcanic Landforms • _________________ Volcanoes – Sometimes, lava flows _____________ with explosive eruptions of ash, cinder, and bombs. – __________, cone-shaped mountains in which layers of lava alternate with layers of ash. – Examples are Mount Fuji in ___________ and Mount St. Helens in __________________. Volcanic Landforms • Lava ________________ – Instead of forming mountains, some eruptions of lava from high, level areas called _______________. – First, lava flows out of several long _______________ in an area. – The thin, runny lava travels far before cooling and _________________. – Again and again, floods of lava flow on top of earlier __________________. – Example is the _______________ Plateau, which covers parts of the states of Washington, Oregon, and Idaho. Volcanic Landforms • __________________ – ______________________________ ______________________________ – The hole is filled with pieces of the volcano that have fallen ___________, as well as some lava and ash. How a Caldera Forms How a Caldera Forms How a Caldera Forms Volcanic Landforms • ____________ From Lava and Ash – The lava, ash, and cinders that erupt from a volcano are initially ________. – Over time, however, the _________ surface of the lava breaks down to form soil. – When ______________ breaks down, it releases _______________, _______________, and other substances that plants need. – Some volcanic soils are among the _____________ soils in the world. Volcanic Landforms • Landforms From _____________ – Features formed by magma includes; • ______________________ • ______________________ • ______________________ • ______________________ • ______________________ Volcanic Landforms • Volcanic Necks – ______________________________ ______________________________ – Forms when ____________ hardens in a volcano’s ___________. – The ______________ rock around the pipe wears away, exposing the hard rock of the volcanic neck. Volcanic Landforms • Dikes and Sills – Magma that forces itself across rock layers hardens into a ___________. – When magma squeezes ______________ layers of rock, it forms a sill. Volcanic Landforms Volcanic Landforms • Batholiths – ______________ ______________ ______________ ______________. – A mass of rock formed when a _________ body of magma cools inside the crust. Volcanic Landforms • ______________ Mountains – Other, smaller bodies of hardened magma can create ________ mountains. – Forms when uplift pushes a _____________ or smaller body of hardened magma toward the surface. – The hardened magma forces the layers of rock to bend ___________ into a dorm shape. Volcanic Landforms • Geothermal Activity – The word ______________ comes from the Greek ________ meaning “___________” and __________ meaning “_________.” – In geothermal activity, magma a few kilometers beneath Earth’s surface heats _________________ water. Volcanic Landforms • A ______________ of geothermal features occur in volcanic areas. • _______________ and ____________ are types of __________________ activity that are often found in areas of present or past volcanic activity. Volcanic Landforms • Hot Springs – __________________________________ __________________________________ ______________________ – The ______ water rises to the surface and collects in a __________ pool. – Water from hot springs may contain dissolved _________ and other _____________ from deep within Earth. Volcanic Landforms • _______________ – Sometimes, rising hot water and steam become trapped underground in a narrow ______________. – _________________ builds until the mixture suddenly sprays above the surface. – A __________________ of water and steam that erupts from the ground. Volcanic Landforms • Geothermal Energy – ______________________________ ______________________________ – Can also be used as a source of _________________. – Provides some electrical power in _______________ and ___________________.