Chapter 5 Study Guide
Volcanoes
Where do volcanic belts form?
Answer: Volcanic belts form along the boundaries of Earth’s plates.
What is the difference between magma and lava?
Answer: Magma is a molten mixture of rock-forming substances, gases, and water from the mantle. When magma reaches the SURFACE of the Earth, it is called lava.
True or False---
After magma and lava cool, they form solid rock. TRUE!!!!
What is the Ring of Fire?
Answer: It is one major belt of volcanoes that includes the many volcanoes that rim the Pacific Ocean including those along the coasts of North and South America and those in Japan and the Phillipines.
What is a string of islands created by volcanoes formed from converging boundaries?
Answer: an island arc
What is another way that volcanoes can form other than along plate boundaries?
Answer: A volcano forms above a HOT SPOT (an area where material from deep within Earth’s mantle rises through the crust and melts to form magma).
List and explain the parts of a volcano (a system of passageways through which magma moves).
1. Magma chamber-All volcanoes have a pocket of magma beneath the surface. Beneath a volcano, magma collects in a magma chamber. During an eruption, the magma forces its way through one or more cracks in Earth’s crust.
2. Pipe-Magma moves through a pipe, a long tube that extends from Earth’s crust up through the top of the volcano, connecting the magma chamber to Earth’s surface.
3. Vent-Molten rock and gas leave the volcano through an opening called a vent. Some volcanoes have a single central vent at the top. But volcanoes often have vents on the sides also.
4. Lava flow-a lava flow is the spread of lava as it pours out of a vent.
5. Crater-a crater is a bowl-shaped area that may form at the top of a volcano around the central vent.
True or False---
When a volcano erupts, the force of the expanding gases pushes magma from the magma chamber through the pipe until it flows or explodes out of the vent. TRUE!!!!
What is silica?
Answer: Silica is a material found in magma that forms from the elements oxygen and silicon.
Name two types of volcanic eruptions:
1. Quiet eruptions-a volcano erupts quietly if its magma is hot or low in silica. Hot, low silica is thin and runny and flows easily. The gases in the magma bubble out gently. Low-silica lava oozes quietly from the vent and can flow for many kilometers.
Quiet eruptions can produce different types of lava:
Pahoehoe (pah HOH ee hoh ee) forms from fast-moving, hot lava that is thin and runny. The surface of pahoehoe looks like a solid mass of ropelike coils.
Aa (AH ah) forms from lava that is cooler and thicker. The lava that aa forms from is also slower-moving. It has a rough surface consisting of jagged lava chunks.
Example of a quiet eruption: the Hawaiian Islands
2. Explosive eruptions-a volcano erupts explosively if its magma is high in silica. High-silica magma is thick and sticky. It can build 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. Lava is powerfully thrown into the air where it breaks into fragments of different sizes. The smallest pieces are volcanic ash, and the larger pieces, called bombs, may range from the size of a golf ball to the size of a car.
Example of an explosive eruption: Mount St. Helens in Washington State (1980)
What is a pyroclastic flow?
Answer: It is a mixture of hot gases, ash, cinders, and bombs that flow down the sides of a volcano when it erupts explosively. Landslides of mud, melted snow, and rock can also form from an explosive eruption.
What are the stages of volcanic activity?
Answer:
1- Dormant—a sleeping volcano that scientists expect to awaken in the future and become active.
2- Extinct---a dead volcano that is unlikely to ever erupt again.
3- Active---a live volcano is one that is erupting, or has shown signs that it may erupt, in the near future.
What is a caldera?
Answer: A caldera is a huge hole left by the collapse of volcanoes.
What landforms do VOLCANIC ERUPTIONS create?
Answer:
1- Calderas—large holes at the top of volcanoes formed when the roof of a volcano’s magma chamber collapses.
2- Shield Volcanoes---wide, gently sloping mountains made of layers of lava and formed by quiet eruptions.
Example of a shield volcano: Mauna Loa in Hawaii
3- Cinder Cone Volcanoes---steep, cone-shaped hills or small mountains made of volcanic ash, cinders, and bombs piled up around a volcano’s opening.
Example of a cinder cone volcano: Paricutín in Mexico
4. Composite Volcanoes---tall, cone-shaped mountains in which layers of lava alternate with layers of ash and other volcanic materials.
Example of a composite volcano: Mount Fuji in Japan & Mount St. Helens in Washington State
5. Lava Plateaus---thin, runny lava flows out of several long cracks in an area and travels before cooling and solidifying. After millions of years, repeated floods of lava can form high, level plateaus. These are called lava plateaus.
Example of a lava plateau: Columbia Plateau—covers parts of Washington State, Oregon, and Idaho
What landforms does MAGMA create?
*Sometimes magma cools and hardens into rock before reaching the surface. Over time, forces such as flowing water, ice, or wind may strip away the layers above the hardened magma and expose it.
1. Volcanic Necks---form when magma hardens in a volcano’s pipe and the surrounding rock later wears away.
2. Dikes---form when magma forces itself across rock layers and hardens.
3. Sills---form when magma squeezes between horizontal rock layers and harden.
4. Dome Mountains---form when uplift pushes a large body of hardened magma toward the surface. The hardened magma forces the layers of rock to bend upward into a dome shape.
5. Batholiths---masses of rock formed when a large body of magma cools inside the crust.
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