Volcanoes

The Earth is made up of four layers. From the inside out, there is the inner core, outer core, mantle and crust. The core is about as hot as the surface of the sun. Heat energy from the core is constantly trying to escape. This energy continually pushes outward toward the mantle and crust. The crust usually keeps the mantle contained below, but not always! Earth’s crust is broken up into about 15 different pieces called tectonic plates. The boundaries between these plates are called faults. At these fault lines, magma—molten rock from the mantle mixed with hot gas—can build up. Volcanoes are openings in the ground found at these fault lines. When the pressure beneath Earth’s surface becomes too much, magma releases from deep inside the Earth through a volcano. Once it reaches Earth’s surface, magma is called lava.

Which of the following best describes the relationship between Earth’s crust and tectonic plates?

• Earth’s crust is one large tectonic plate.

• Earth’s crust is found between the outer core and tectonic plates.

• Earth’s crust is made up of separate pieces called tectonic plates.

• Earth’s crust sits above tectonic plates, which are suspended in the mantle.

Volcanoes are made up of several parts. The magma chamber is a pocket of molten rock under the volcano where magma builds up. The vent is the path through which magma travels from the magma chamber to Earth’s surface. The crater is where lava is ejected from the volcano. After eruption, lava, ash and rock often settle on the sides of the volcano, forming layers called strata. These layers build up over time as volcanoes take on a mountain-like shape.

Which of the following best describes the process by which magma reaches Earth’s surface during a volcanic eruption?

• Magma builds up in the strata until it is released through the vent crater to form lava.

• Magma builds up in the vent until it is released through the magma chamber at different strata.

• Magma builds up in the crater then travels through the strata until it is released through the vent.

• Magma builds up in the magma chamber then travels through the vent until it is released through the crater.

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Volcanoes form in different ways and release different types of lava. There are two main types of volcanoes. Shield volcanoes form when thin, runny lava is released. This magma does not contain a lot of gas, so it has less energy. Because of this, it releases relatively gently and lava flows far down the sides of the volcano before cooling. Shield volcanoes are wide and flat, resembling a shield of armor. Composite volcanoes are formed by magma that contains a lot of gas. The thick magma builds up an enormous amount of pressure, causing an explosive eruption. Lava from a composite volcano cools quickly and doesn’t flow very far. As a result, lava piles up and creates mountainous slopes. A composite volcano is most likely what you imagine when you think of a volcano.

Which of the following best describes the relationship between gas and volcanic eruptions?

• The more gas magma contains, the more explosive a volcanic eruption will be.

• The presence of gas in magma decreases the likelihood of a volcanic eruption.

• As gas builds up in magma, volcanic eruptions occur once in the magma chamber and once above ground.

• Gas found in magma determines only the intensity of eruptions involving composite volcanoes and not shield volcanoes.

Volcanoes usually occur at fault lines. Fault lines are where tectonic plates push together, pull apart and slide past each other. The energy created here forms volcanoes and causes eruptions. This isn’t the only way volcanoes form though. Some volcanoes, like those found in Hawaii, occur over hot spots. Hot spots are portions of the mantle at which the temperature is abnormally high. These high temperatures cause magma to rise and break through Earth’s crust. This type of volcano often forms a seamount. A seamount is an undersea mountain that becomes an island if it surpasses sea level. While a seamount is over a hot spot, it remains volcanically active. But over the course of millions of years, as tectonic plates shift and the seamount moves, the volcano eventually becomes extinct.

When is a seamount volcanically active?

• while it is over a hot spot

• when it surpasses sea level

• when it occurs at a fault line

• when tectonic plates move it

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Volcanoes can be categorized as active, dormant or extinct. Although definitions vary from scientist to scientist, a volcano is considered active if it has erupted recently or erupts regularly. A dormant volcano refers to a volcano that has not erupted recently, but will likely erupt again. An extinct volcano is a volcano that will never erupt again because its magma supply has been cut off. One point of disagreement between scientists is their definition of “recently.” For some, it means within the last 10,000 years. For others, much shorter. The line between active, dormant and extinct volcanoes can be blurry. In some rare cases, volcanoes long thought to be extinct have unexpectedly come back to “life.”

Which of the following would most likely be classified as an active volcano?

• a mountain that shows no history of eruption

• a volcano that has erupted twice in the past 350 years

• a volcano that is now an island with a population of 200,000

• a volcano that erupted 12,000 years ago and is still connected to its magma supply

Volcanic eruptions can happen quickly. When an eruption occurs, there isn’t much that can be done to slow its destructive force. Because of this, scientists are continuously working to improve their ability to predict eruptions. Better technology means evacuation warnings can be issued before it’s too late. Earthquakes caused by magma pushing up through the volcano are one indicator of an approaching eruption. Vibrations from these earthquakes can be detected by a device called a seismometer. Another sign a volcano may soon erupt is swelling of the volcano itself. As magma builds up, the magma chamber enlarges and changes the shape of the volcano. These changes can be identified by tilt meters, devices that measure the tilt of a structure. Gas release can also signal an eruption. Although changes in the atmosphere around a volcano tend to be small, scientists have developed devices to detect these minor changes. Predicting eruptions is all about safety. The sooner these indicators can be identified, the more time those who live near volcanoes will have to evacuate.

With which of the following statements would the author of this passage most likely agree?

• Volcanic eruptions are impossible to predict and scientists are wasting their time.

• Volcanic eruptions are no longer an issue as a result of technological advances.

• Scientists have made important progress when it comes to predicting volcanic eruptions.

• Scientists should focus only on earthquake detection when it comes to predicting volcanic eruptions.

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Earth is made up of ________ layers.

• one

• three

• four

• six

True or False: Earth’s crust is one solid piece.

• True

• False

Volcanic eruptions are caused by

• gravity

• pressure

• explosions

• Earth's rotation

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NGSS.MS-ESS3-2

Where do volcanoes usually form?

• within 10 miles of the ocean

• between Earth’s mantle and core

• at fault lines between tectonic plates

• within the boundaries of the United States