Sci: Volcanoes

IN ADDITION TO SILICA CONTENT, THE WATER CONTENT OF MAGMA ALSO DETERMINES WHETHER AN ERUPTION WILL BE QUIET OR EXPLOSIVE

IN ADDITION TO SILICA CONTENT, THE WATER CONTENT OF MAGMA ALSO DETERMINES WHETHER AN ERUPTION WILL BE QUIET OR EXPLOSIVE

what happens when magma and lava cool?

They form solid rock

what's a lava flow?

A lava flow is the spread of lava as it pours out of a vent.

What's a hot spot?

A spot is an area where material from deep within Earth's mantle rises through the crust and melts to form magma. *A volcano forms above a hot spot when magma erupts through the crust and reaches the surface. Hot spots stay in one place for many millions of years while the plate moves over them. Some hot spot volcanoes lie close to plate boundaries. Others lie in the middle of plates. Yellowstone National Park in Wyoming marks a huge hot spot under the North American plate.

what are volcanic necks?

A volcanic neck forms when magma hardens in a volcano's pipe and the surrounding rock later wears away. The landform that looks like a giant tooth stuck in the ground is Shiprock in New Mexico. Shiprock fromed when magma hardened in an ancient volcano's pipe. Later, the softer rock around the pipe wore away, exposing the harder rock inside.

Explosive eruptions

A volcano erupts explosively if its magma is high in silica. High-silica magma is thick and sticky. This type of magma can build up in the volcano's pipe, plugging it like a cork in a bottle. Dissolved gases, including water vapor, can't escape from the thick magma. The trapped gases build up pressure until they explode. The erupting gases and steam push the magma out of the volcano with incredible force. That's what happened during the eruption of Mount St. Helens in Washington State.

Quiet eruptions

A volcano erupts quietly if its magma is hot or low in silica. Hot, low-silica magma 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 km. Mostly quiet eruptions formed the Hawaiian Islands. On the island of Hawaii, lava pours from the crater near the top of Kilauea. Lava also flows out of long cracks on the volcano's sides. In general, the temperature of magma and lava range from about 750 degrees celsius to 1175 degrees celsius - hot enough to melt copper! Quiet eruptions have built up the island of Hawaii over hundreds of thousands of years.

What is a volcano?

A volcano is a mountain that forms in Earth's crust when molten material, or magma, reaches the surface.

What's a 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.

what is an active volcano?

An active, or live, volcano is one that is erupting or has shown signs that it may erupt in the near future.

what is volcanic ash, cinders, and bombs?

An explosive eruption throws lava powerfully into the air where it breaks into fragments that quickly cool and harden into pieces of different sizes. The smallest pieces are volcanic ash. Volcanic ash is made up of fine, rocky particles as small as a speck of dust. Pebble sized particles are called cinders. Larger pieces, called bombs, may range from the size of a golf ball to the size of a car.

what are shield volcanoes?

At some spots on Earth's surface, thin layers of lava pour out of a vent and harden on top of previous layers. Such lava flows slowly build a wide, gently sloping mountain called a shield volcano. Hot spot volcanoes that form on the ocean floor are usually shield volcanoes. For example, in Hawaii, Mauna Loa rises 9,000 meter from the ocean floor!

what are dome mountains?

Bodies of hardened magma can create dome mountains. A dome mountain forms 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. Eventually, the rock above the dome mountain wears away, leaving it exposed. This process formed the Black Hills in South Dakota.

how do scientists know when activity in a volcano is about to change?

Changes in activity in and around a volcano may give warning shortly before a volcano erupts. Geologists use special instruments to detect these changes. For example, tiltmeters can detect slight surface changes in elevation and tilt caused by magma moving underground. Geologists can also monitor gases escaping from the volcano. They monitor the many small earthquakes that occur around a volcano before an eruption. The upward movement of magma triggers these earthquakes. Also, rising temperatures in underground water may signal that magma is nearing the surface.

How is a quiet eruption dangerous?

During a quiet eruption, lava flows from vents, setting fire to, and often burying, everything in its path. A quiet eruption can cover large areas with a thick layer of lava.

how is an explosive eruption dangerous? also what is a pyroclastic flow?

During an explosive eruption, a volcano can belch out a mixture of dangerous materials such as hot rock and ash. This mixture of materials can form a fast-moving cloud that rushes down the sides of the volcano. A pyroclastic flow is the 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 landforms does magma create?

Features formed by magma include volcanic necks, dikes, and sills, as well as dome mountains and batholiths. 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.

How do geologists classify eruptions??

Geologists classify volcanic eruptions as quiet or explosive. Whether an eruption is quiet or explosive depends in part on the magma's silica content and whether the magma is thin and runny or thick and sticky. Temperature also determines how fluid, or runny, magma is.

what are cinder cone volcanoes?

If a volcano's magma has high silica content, it will be thick and sticky. So the volcano can erupt explosively, producing ash, cinders, and bombs. These materials can build up around the vent in a steep, cone shaped hill or small mountain that is called a cinder cone. For example, Paricutin in Mexico erupted in 1943 in a farmer's cornfield. The volcano built up a cinder cone that was about 400 meters high.

what is a caldera?

Large eruptions can empty the main vent and magma chamber beneath a volcano. With nothing to support it, the mountain top may collapse inward. A caldera is the hole left when a volcano collapses. A lake can form, filling the hole. If the volcano erupts again, a steep walled cone may form in the middle.

What happens when a volcano erupts?

Lava begins as magma. Magma usually forms in the somewhat soft layer of hot, solid rock that lies in the upper mantle, just below a layer of harder rock. The magma is less dense than the material that is around it. So it rises into any cracks in the rock above. If this magma reaches the surface, a volcano can form.

What are lava plateaus?

Lava can flow out of several long cracks (fissures) in an area. The thin, runny lava floods the area and travels far before cooling and solidifying. After millions of years, repeated floods of lava can form high, level plateaus. These plateaus are called lava plateaus. The Columbia Plateau is a lava plateau that covers parts of Washington State, Oregon, and Idaho.

What is magma?

Magma is a molten mixture of rock-forming substances, gases, and water from the mantle.

what's a pipe?

Magma moves upward 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.

what is a sill?

Magma that squeezes between horizontal rock layers hardens to form a sill.

what are composite volcanoes?

Sometimes, the silica content of magma can vary. So eruptions of lava flows alternate with explosive eruptions of ash, cinder, and bombs. The result is a composite volcano. Composite volcanoes are tall, cone-shaped mountains in which layers of lava alternate with layers of ash. Mount Fuji in Japan and Mount St. Helens in Washington Stat are composite volcanoes. Composite volcanoes can be more than 4,800 meters tall.

what is the ring of fire?

The ring fire is a major belt of volcanoes. It includes the many volcanoes along the coasts of North and South America and those in Japan and the Philippines.

What is a volcanic belt?

Volcanic belts form along the boundaries of Earth's plates. Here, volcanoes occur in many great, long belts.

What landforms do lava and ash create?

Volcanic eruptions create landforms made of lava, ash, and other materials. These landforms include shield volcanoes, cinder cone volcanoes, composite volcanoes, and lava plateaus. Other landforms include calderas, which are huge holes left by the collapse of volcanoes. Lava has built up much of the islands of Hawaii. In fact, for much of Earth's history, volcanic activity on and beneath Earth's surface has built up Earth's land areas and formed much of the ocean crust.

Where can volcanoes occur?

Volcanoes can occur where two plates diverge. Here, plate movements cause the crust to fracture. The fractures in the crust allow magma to reach the surface. Volcanoes can also occur where two plates converge. As the plates push together, one plate can sink beneath the other plate. Water that is brought down with the sinking plate eventually helps to form magma, which rises to the surface. Also, they can form from hot spots in Earth's mantle.

Diverging boundaries

Volcanoes form along the mid-ocean ridges, where two plates move apart. Mid-ocean ridges form long, underwater mountain ranges that sometimes have a rift valley down their center. Along the rift valley lava pours out of cracks in the ocean floor. This process gradually builds new mountains. Volcanoes also form along diverging plate boundaries on land. For example, large volcanoes are found along the Great Rift Valley in East Africa.

What is lava?

When magma reaches the surface, it is called lava.

when is an eruption over?

When the pressure eases after the gases bubbles out of the magma.

what is a dormant volcano?

a dormant, or sleeping, volcano is a volcano that scientists expect to awaken in the future and become active.

what is silica?

a material found in magma that is formed from the elements oxygen and silicon

What are the stages of volcanic activity?

active, dormant, extinct The activity of a volcano may last from less than a decade to more than 10 million years. But most long-lived volcanoes do not erupt continuously. *Geologists often use the terms active, dormant, or extinct to describe a volcano's stage of activity.

What is an extinct volcano?

an extinct, or dead, volcano is a volcano that is unlikely to ever erupt again. For example, hot-spot volcanoes may become extinct after they drift away from the hot spot.

where are batholiths common?

batholiths are common in the western united states.

why does low-silica magma often erupt quietly?

gas can escape without building too much pressure.

why might gas pressure build up in high-silica magma?

it's thicker, so gas can't escape easily.

What are the parts of a volcano?

magma chamber, pipe, vent, lava flow, crater

what is a dike?

magma that forces itself across rock layers hardens into a dike

what would happen if the gas pressure became higher than the pressure of the surrounding material?

magma would burst to the surface as an explosive eruption.

What are the 2 types of volcanic eruptions?

quiet and explosive

Some eruptions are quiet while others are explosive. This depends on what 2 things?

1. The magma's composition 2. the temperature

what is a batholith?

A batholith is a mass of rock formed when a large body of magma cools inside the crust. Batholiths form the core of many mountain ranges. Over millions of years, the overlying rocks wears away, allowing the batholith to move upward. Flowing water and grinding ice slowly carve the batholith into mountains.

what's a crater?

A crater is a bowl-shaped area that may form at the top of a volcano around the central vent.

Converging boundaries What is an island arc?

Many volcanoes form near converging plate boundaries, where two oceanic plates collide. Through subduction, the older, denser plate sinks into the mantle and creates a deep-ocean trench. Water in the sinking plate eventually leaves the crust and rises into the wedge of the mantle above it. As a result, the melting point of the mantle in the wedge is lowered. So, the mantle partially melts. The magma that forms as a result rises up. This magma can break through the ocean floor, creating volcanoes. The resulting volcanoes sometimes create a string of islands called an island arc. The curve of an island arc echoes the curve of its deep-ocean trench. Major island arcs include Japan, New Zealand, the Aleutians, and the Caribbean islands. Volcanoes also occur where an oceanic plate is subducted beneath a continental plate. Collisions of this type produced the volcanoes of the Andes Mountains in South America. IN the U.S., plate collisions also produced the volcanoes of the Pacific Northwest, including Mount St. Helens and Mount Rainier.

what's a 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 (side vents).

What happens during an eruption?

Perhaps you know that dissolved carbon dioxide gas is trapped in every can of soda. but did you know that dissolved gases are trapped in magma? These dissolved gases are under great pressure. during an eruption, as magma rises toward the surface, the pressure of the surrounding rock on the magma decreases. The dissolved gases begin to expand, forming bubbles. These bubbles are much like the bubbles in the soda can. As pressure falls within the magma, the size of the gas bubbles increases greatly. These expanding gases exert great force. *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. Once magma escapes from the volcano and becomes lava, the remaining gases bubble out.

what is the different types of rock that quiet eruptions produce?

Quiet eruptions can produce different types of lava. The different types of lava harden into different types of rock. Pahoehoe forms from fast moving, hot lava that is thin and runny. The surface of Pahoehoe looks like a solid mass of ropelike coils. Aa forms from lava that is cooler and thicker. The lava that Aa forms from is also slower moving. Aa has a rough surface consisting of jagged lava chunks.