Volcanoes Volcanoes and Plate Tectonics A is a

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 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 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 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 __________.