Volcanoes - gcsdstaff.org · This is a map showing the active volcanoes around the world. Each red dot represents an ac-tive volcano! Gallery 2.2 Active Volcanoes Around the World

Volcanoes

Beaker Productions

! Are these questions you have asked in the past when you saw a volcano on the television or read about them in a book? Perhaps your teacher has discussed volcanos before, or maybe you even saw something on the news. Few natural events cause such wonder and fright all at the same time.

CHAPTER 1

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What is a Volcano, and How Is it Formed?Interactive 1.1 Taking Notes!

Click on the icon above to take notes as you go through this book. There will be a quiz at the end of the book.

SECTION 1

! A volcano is a mountain that opens downward to a pool of molten rock below the surface of the earth. When pressure builds up, eruptions occur. Gases and rock shoot up through the opening and spill over or fill the air with lava fragments. Eruptions can cause lateral blasts, lava flows, hot ash flows, mudslides, ava-

lanches, falling ash and floods. Volcano eruptions have been known to knock down entire forests. An erupting volcano can trig-ger tsunamis, flash floods, earthquakes, mudflows and rockfalls.

What is a Volcano?

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Reverse-pinch the picture to see the diagram in full scale.

Gallery 1.1 Parts of a Volcano

SECTION 2

! Volcanoes are formed when magma from within the Earth's upper mantle works its way to the surface. At the surface, it erupts to form lava flows and ash deposits. Over time as the volcano continues to erupt, it will get bigger and bigger.

How Are Volcanoes Formed?

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Click the play button to view a video showing how volcanoes formed.

Movie 1.1 How Volcanoes Formed

SECTION 3

Beneath the Earth flows molten rock known as magma.

! When a volcano erupts, the resulting explosion shoots this magma out into the atmosphere. At this point the magma becomes known as lava. There is no major differ-ence between magma and lava – the terms merely distin-guish whether the molten rock is beneath or above the sur-face.

! Caused by gas pressure under the surface of the Earth, a giant volcanic eruption can be incredibly powerful with lava shooting up to 2,000 feet into the air.

! Lava can reach temperatures of 700-1,200°C (1,300-2,200°F) and varies in colour from bright orange to brownish red, hottest to coldest, respectively. This viscous liquid can range from the consistency of syrup to extremely stiff, with little or no flow apparent. This is regulated by the amount of silica in the lava, with higher levels of the mineral resulting in a higher viscosity. When lava eventually cools and solidi-fies it forms igneous rock.

! Inside lava are volcanic gases in the form of bubbles, which develop underground inside the magma. When the lava erupts from inside the volcano, it is full of a slush of crystalline minerals (such as olivine). Upon exposure to air

the liquid freezes and forms volcanic glass. Different types of lava have different chemical compositions, but most have a high percentage of silicon and oxygen in addition to smaller amounts of elements such as magnesium, calcium and iron.

What is the Difference Between Magma and Lava?

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Lava above the earth’s surface.

Gallery 1.2 Lava and magma

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Interactive 1.2 Chapter 1 Quiz

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Scientists have categorized volcanoes into three main categories:

ActiveDormantExtinct

CHAPTER 2

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Volcanic Stages

This photo was taken by NASA and shows Cleveland Volcano from the sky. This volcano is located in the Aleutian Islands.

Gallery 2.1 Cleveland Volcano

SECTION 1

Active

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This is a map showing the active volcanoes around the world. Each red dot represents an ac-tive volcano!

Gallery 2.2 Active Volcanoes Around the World

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! An active volcano is one that has had a recent eruption, and does have the chance of erupting again. There are more than 500 active volca-noes throughout the world! An eruption can send volcanic ash and de-bris up to 17 miles about the earth’s surface! When an active volcano is not erupting, it will still be emitting toxic gases, ash, and even lava. When this activity increases, the chances of it erupting are even greater.

Interactive 2.1 US Volcanoes

Click on the photo above to take you to the map of US volcanoes. Click on each one to view each volcano and the status.

SECTION 2

Dormant

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A dormant volcano is one that has not erupted in a long time, but it is still possible that it could.

Interactive 2.2 Mt. St. Helens

Click on the icon above to view photos from inside the crater of Mt. St. Helens in Washington!

SECTION 3

Extinct

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Interactive 2.4 Croscat Volcano in Spain

Click the icon above to view a 360˚ view of Croscat Volcano.

Simply put, extinct volcanoes haven’t erupted for tens of thousands of years, and aren’t ex-pected to erupt again. This is due to the possibil-ity that the volcano no longer has a lava supply.

Interactive 2.3 Click to zoom in on the photo above.

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Click on the icon above to take a quiz about chapter 2.

There are three main types of volcanoes: Cinder cones, composite volcanoes, and shield volcanoes.

CHAPTER 3

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Types of Volcanoes

Interactive 3.1 Types of Volcanoes

Click on the icon above to view and read about the different types of volcanoes.

SECTION 1

! Cinder cone volcanoes are the most common kind of volcanoes. They are steep sided cones of basaltic fragments and are smaller and simpler than composite volcanoes. Streaming gases carry liquid lava blobs into the atmosphere that fall back to earth around a single vent to form the cone. The volcano forms when ash, cinders and bombs pile up around the vent to form a circular or oval cone.

! Cinders are melted volcanic rock that cooled and formed pebble-sized pieces when it was thrown out into the air. They are ejected from a sin-gle vent and accumulate around the vent when they fall back to earth.

! Bombs are melted volcanic rock that cooled and formed large pieces of rock when it was thrown out into the air before landing on the ground.

! Cinder cones grow rapidly and soon reach their maximum size. They can occur alone or in small to large groups or fields. Most have a bowl-shaped crater at the summit. The longer the erup-tion, the higher the cone. They rarely exceed 250

meters in height and 500 meters in diameter, al-though some may rise to as high as 650 meters or more. If gas pressure drops, the final stage cinder cone construction may be a lava flow that breaks through the base of the cone. The shape of a cin-der cone can be modified during its life. When the position of the vent alters, aligned twin cones de-velop. Nested, buried or breached cones are formed when the power of the eruption varies.

Cinder Cones

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Interactive 3.2 Cinder Cone - Lassen Volcanic National Park, California

Click to see the cinder cone exam-ple in Google Maps. Feel free to zoom, click, or zoom out to get a better view.

Capulin designated a U.S. National Monu-ment on August 9, 1916. It is an example of an extinct cinder cone volcano.

Gallery 3.1 Capulin Volcano in New Mex-ico

SECTION 2

! Sometimes called Stratovolcanoes, Compos-ite volcanoes form when runny lava escapes through a fissure and flows a long way. Compos-ite volcanoes are tall cone-shaped mountains that are typically steeply-sided, symmetrical cones of large dimensions. The essential feature of a com-posite volcano is a conduit system through which magma from a reservoir deep in the earth's crust rises to the surface. The volcano is built up by the accumulation of material erupted through the conduit and increases in size as lava, cinders, ash etc. are added to its slopes.

! Composite volcanoes erupt in different ways at different times. These volcanoes are built in layers by multiple eruptions, sometimes recur-ring over hundreds of thousands of years, some-times over a few hundred. Andesite magma (the most common but not the only magma type), tends to form composite cones. During some eruptions, cinders, bombs and blocks form a mountain or add height to one that earlier vol-canic eruptions had built. During other erup-tions, lava flows cement these rocks together. Most composite volcanoes have a crater at the

summit which contains a central vent or a clus-tered group of vents. Lava either flows through and breaks in the crater wall or from fissures on the flanks of the cone. Lava, solidified within the fissures, forms dikes that act as ribs which help to strengthen the cone. They may rise as much as 8,000 feet above their bases. Depending on the type of volcanic material it is composed of, some can grow to such heights that their slopes be-come unstable and are susceptible to collapse from the pull of gravity.

! When volcanic activity ceases, erosion be-gins to destroy the cone. After thousands of years, the cone is stripped away and the hard-ened magma filling the conduit (the volcanic plug) and fissures (the dikes) become exposed, and it too is slowly reduced by erosion. Finally, all that is left is the plug or "volcanic neck" and dike complex projecting above the land surface.

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Composite Volcanoes

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Interactive 3.3 Mount St. Hel-ens Before and After

Click on the icon above to view what Mount St. Helens looked like before and after the 1980 eruption!

SECTION 3

! Shield volcanoes are large volcanoes that are built almost en-tirely of fluid lava flows. It has broad sloping sides and is usually surrounded by gently sloping hills in a circular or fan shaped pat-tern, that looks like a warrior's shield.

! The volcano is produced by the action of the gas (steam or water vapor) with heat from the earth's core. This action melts rock turning it into magma. The pressure from the heat of the gas pushes the magma upwards till it explodes. Molten magma shoots upward from deep below the ocean floor and breaks through the drifting plates to form shield volcanoes. Lava flows gently and continuously out of the central volcanic vent or group of vents. This lava is very runny, and can't be piled up into steep mounds. It gradually accumulates and cools around the volcano. The erup-tions are characterized by low explosivity lava-fountaining that forms cinder cones and spatter cones at the vent. The volcanoes are built up slowly by the accretion of thousands of highly fluid lava flows called basalt lava. The lava spread widely over great distances, then cools as thin gently dipping sheets. Lavas also erupt from vents along fractures (rift zones) that form on the flanks of the cone. Some of the largest volcanoes in the world are Shield volcanoes.

! Shield volcanoes may be produced by hot spots which lay far away from the edges of tectonic plates. Shields also occur

along the mid-oceanic ridge, where sea floor spreading is in pro-gress and along subduction related volcanic arcs.

! In northern California and Oregon, many shield volcanoes have diameters of three or four miles and heights of 1,500 to 2,000 feet. A good example of a shield volcano is the Island of Hawaii. The Big Island is formed of five coalesced volcanoes of succes-sively younger ages. The Hawaiian Islands are composed of linear chains of volcanoes including Kilauea and Mauna Loa on the is-land of Hawaii.

Shield Volcanoes

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Interactive 3.4 Drawing the Types of Volca-noes

Click on the icon above to open the drawing pad. Draw and label the three types of vol-canoes. Email your picture to your teacher.

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Click on the icon above to take a quiz on chapter 3.

Active volcano

A volcano that has erupted since the last ice age.

Related Glossary Terms

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Ash

Volcanic ash consists of fragments of pulverized rock, minerals and volcanic glass, created during volcanic eruptions


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Cinder cone

A cinder cone or is a steep conical hill of tephra that accumulates around and downwind from a volcanic vent.


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Composite volcano

A composite volcano is a conical volcano built up by many layers (strata) of hardened lava, tephra, pumice, and volcanic ash.


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Dormant volcano

A volcano that has not erupted for a considerable length of time, but is still capable of erupt-ing.


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Extinct volcano

Extinct volcanoes are those that scientists consider unlikely to erupt again, because the vol-cano no longer has a lava supply.


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Lava

Lava is magma that reaches the earth’s surface. It is hot, liquid rock.


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Magma

Magma is the melted rock inside of the earth.


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Shield volcano

A shield volcano is a type of volcano usually built almost entirely of fluid lava flows.


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Volcanoes - gcsdstaff.org · This is a map showing the active volcanoes around the world. Each red dot represents an ac-tive volcano! Gallery 2.2 Active Volcanoes Around the World

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