Chapter 3 Volcanoes

A wide, gently sloping mountain made of hardened layers of low silica lava is a.

Sheild Volcano

II. Volcanic Activity F: Other Types of Volcanic Activity

1. A hot spring forms when groundwater heated by a nearby body of magma rises to the surface and collects in a natural pool. 2. A geyser is a fountain of water and steam that erupts from the ground. 3. In volcanic areas, water heated by magma can provide a clean, reliable energy source called geothermal energy.

II. Volcanic Activity H: Volcano Hazards

1. Although quiet eruptions and explosive eruptions involve different volcanic hazards, both types of eruptions can cause damage far from the crater's rim. 2. During a quiet eruption, lava flows pour from vents, setting fire to and then burying everything in their path. 3. During an explosive eruption, a volcano can belch out hot, burning clouds of volcanic gases as well as cinders and bombs. 4. Volcanic ash can bury entire towns, damage crops, and clog car engines. 5. Eruptions can also cause landslides and avalanches of mud, melted snow, and rock.

II. Volcanic Activity E: Stages of a Volcano

1. An active, or live, volcano is one that is erupting or has shown signs that it may erupt in the near future. 2. A dormant, or sleeping, volcano is like a sleeping bear. Scientists expect a dormant volcano to awaken in the future and become active. 3. An extinct, or dead, volcano is unlikely to erupt again.

II. Volcanic Activity G: Monitoring Volcanoes

1. Geologists use tiltmeters, laser-ranging devices, and other instruments to detect slight surface changes in elevation and tilt caused by magma moving underground. 2. Geologists monitor the local magnetic field, water level in a volcano's crater lake, and any gases escaping from a volcano. 3. They take the temperature of underground water to see if it is getting hotter - a sign that magma may be nearing the surface. 4. Geologists also monitor the many small earthquakes that occur in the area around a volcano before an eruption.

III. Volcanic Landforms B: Soils from Lava and Ash

1. Over time the hard surface of the lava flow breaks down to form soil. 2. Some volcanic soils are among the richest soils in the world. Saying that soil is rich means that it's fertile, or able to support plant growth.

III. Volcanic Landforms A: Landforms From Lava and Ash

1. Rock and other materials formed from lava create a variety of landforms including shield volcanoes, composite volcanoes, cinder cone volcanoes, and lava plateaus. 2. Shield Volcanoes a. At some places of Earth's surface, thin layers of lava pour out of a vent and harden on top of previous layers. b. Such lava flows gradually build a wide, gently sloping mountain called a shield volcano. 3. Cinder Cone Volcanoes a. A volcano can also be a cinder cone, a steep, cone-shaped hill or mountain. b. If a volcano's lava is thick and stiff, it may produce ash, cinders, and bombs. These materials pile up around the vent in a steep, cone shaped pile. 4. Composite Volcanoes a. Sometimes lava flows alternate with explosive eruptions of ash, cinder, and bombs. The result is a composite volcano. b. Composite volcanoes are tall, cone-shaped mountains in which layers of lava alternate with layers of ash. 5. Lava Plateaus a. Instead of forming mountains, some eruptions of lava form high, level areas called lava plateaus. b. First, lava flows out of several long cracks in an area. The thin, runny lava travels far before cooling and solidifying. Again and again, floods of lava flow on top of earlier floods. 6. Calderas a. The huge hole left by the collapse of a volcanic mountain is called a caldera.

I. Volcanoes and Plate Tectonics E: Hot Spot Volcanoes

A hot spot is an area where magma from deep within the mantle melts through the crust like a blow torch. Hot spots often lie in the middle of continental or oceanic plates far from any plate boundaries. The Hawaiian Islands formed one by one over millions of years as the Pacific plate drifted over a hot spot. Hot spots can form under continents. Yellowstone National Park in Wyoming marks a major hot spot under the North American plate.

I. Volcanoes and Plate Tectonics C: Volcanoes at Diverging Plate Boundaries

A mid-ocean ridge is long, underwater rift valley that winds through the oceans.

When magma hardens in a volcano's pipe and is later exposed.

A volcanic neck forms.

1. Volcanoes and Plate Techtonics A: What is a Volcano?

A volcano is a weak spot in the earth's crust where molten material, or magma, comes to the surface. Magma is a molten mixture of rock-forming substances, gases, and water from the mantle When magma reaches the surface it is called lava

Active Volcano.

A volcano that is erupting or had shown signs that it may erupt in the future.

A volcano is

A weak spot in the crust where magma comes through.

Hotspot.

An area where magma melts through the crust in the middle of a plate.

Volcanic Soils.

Are fertile because they contain potassium and phosphorus.

Lava Plateau.

Are layers of thin, runny lava that flow over a wide area before they cool and harden can build up

Pahoehoe and aa

Are produced during quiet eruptions.

II. Volcanic Activity B: Inside a Volcano

Beneath a volcano, magma collects in a pocket called a magma chamber. The magma moves through a pipe, a long tube in the ground that connects the magma chamber to Earth's surface. Molten rock and gas leave the volcano through an opening called a vent. A lava flow is the area covered by lava as it pours out of a vent. A crater is a bowl-shaped area that may form at the top of a volcano around the volcano's central vent.

A volcano's metal content.

Does not affect how thick or thin magma is.

A geyser emits hot water and steam.

Erupts from the ground.

Eruption fountains of sulfur.

Is Volcanoes on Io, a moon of Jupiter, e

Batholith.

Is a mass of rock that formed when a large body of magma cooled inside Earth's crust.

A magma chamber.

Is inside a volcano, magma collects in a pocket.

Olympus Mons.

Is the largest volcano in the solar system, is on the planet Mars.

Liquid magma flows upward through the crust because...

It is less dense than the material around it.

II. Volcanic Activity A: How Magma Reaches Earth's Surface

Lava begins as magma in the mantle. Magma forms in the asthenosphere, which lies beneath the lithosphere. Magma Rises a. Because liquid magma is less dense than the surrounding solid material, magma flows upward into any cracks in the rock above. A Volcano Erupts a. Just like the carbon dioxide trapped in a bottle of soda pop, the dissolved gases trapped in magma are under tremendous pressure. b. During a volcanic eruption, the gases dissolved in magma rush out, carrying the magma with them.

The molten mixture of rock-forming substances, gases, and water deep in the Earth's mantle is called.

Magma

I. Volcanoes and Plate Tectonics D: Volcanoes at Converging Plate Boundaries

Subduction causes slabs of oceanic crust to sink through a deep-ocean trench into the mantle. The crust melts and forms magma, which then rises back toward the surface. When the magma from the melted crust erupts as lava, a volcano is formed. Many volcanoes occur on islands, near boundaries where two oceanic plates collide. The resulting volcanoes create a string of islands called an island arc. Subduction also occurs where the edge of a continental plate collides with an oceanic plate.

A belt of volcanoes around the rim of the Pacific Ocean is.

The Ring of Fire

The more silica the magma contains.

The thicker the magma is.

III. Volcanic Landforms C: Landforms from Magma

1. Sometimes magma forces its way through cracks in the upper crust, but fails to reach the surface. 2. Volcanic Necks, Dikes, and Sills a. A volcanic neck forms when magma hardens in the volcano's pipe. The softer rock around the pipe wears away, exposing the hard rock of the volcanic neck. b. Magma that forces itself across rock layers hardens into a dike. c. When magma squeezes between layers of rock, it forms a sill. 3. Batholiths a. Large rock masses called batholiths form the core of many mountain ranges. b. A batholith is a mass of rock formed when a large body of magma cools inside the crust. 4. Dome Mountains a. A dome mountain forms when rising magma is blocked by horizontal layers of rock. The magma forces the layers of rock to bend upward into a dome shape. Eventually, the rock above the dome mountain wears away, leaving it exposed. Example on pg 167 of "Stone Mountain" GA.

II. Volcanic Activity C: Characteristics of Magma

1. The force of a volcanic eruption depends partly on the amount of gas dissolved in magma. 2. How thick or thin the magma is, its temperature, and its silica content are important factors as well. 3. The hotter the magma, the more fluid it is. 4. Silica, which is a material that is formed from the elements oxygen and silicon, is one of the most abundant materials in the Earth's crust and mantle. 5. The more silica magma contains, the thicker it is. 6. Magma that is high in silica produces light colored lava that is too sticky to flow very far. When this type of lava cools, it forms the rock rhyolite, which has the same composition as granite. 7. Magma that is low in silica flows readily and produces dark colored lava. When this kind of lava cools, rocks such as basalt are formed.

II. Volcanic Activity D: Types of Volcanic Eruptions

1. The silica content of magma helps to determine whether the volcanic eruption is quiet or explosive. 2. Quiet Eruptions a. A volcano erupts quietly if its magma flows easily. b. Thin, runny lava oozes quietly from the vent. c. The islands of Hawaii and Iceland were formed from quiet eruptions. d. Quiet eruptions produce two different types of lava: pahoehoe and aa. e. Pahoehoe is fast-moving, hot lava. The surface of a lava formed from pahoehoe looks like a solid mass of wrinkles, billows, and ropelike coils. f. Lava that is cooler and slower-moving is called aa. When aa hardens, it forms a rough surface consisting of jagged lava chunks. 3. Explosive Eruptions a. If magma is thick and sticky, a volcano erupts explosively. b. The thick magma slowly builds up in the volcano's pipe, plugging it like a cork in a bottle. Dissolved gases cannot escape from the thick magma. The trapped gases build up pressure until they explode. The erupting gases push the magma out of the volcano with incredible force. c. The explosion breaks the lava into fragments that quickly cool and harden into pieces of different sizes. d. The smallest pieces are volcanic ash, fine, rocky particles as small as a grain of sand. e. Cinders are pebble-sized particles. f. Larger pieces, called bombs, may range from the size of a baseball to the size of a car. g. A pyroclastic flow occurs when an explosive eruption hurls out ash, cinders, and bombs as well as gases.

I. Volcanoes and Plate Tectonics B: Location of Volcanoes

1The Ring of Fire is major volcanic belt that rims the Pacific Ocean. Most volcanoes occur along diverging plate boundaries, such as mid-ocean ridges, or in subduction zones around the edges of oceans

When an explosive eruption hurls ash, cinders, bombs, and gases out of a volcano.

A Pyroclastic Flow happens.

When the top of a volcanic mountain collapses.

A caldera forms.