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 rock- forming 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

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

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

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 _____________, cone- shaped 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

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

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 ___________________.