Volcanoes

Composite Volcanoes | Shield Volcanoes | Cinder Volcanoes | Spatter Volcanoes | Complex Volcanoes | Lava Domes

A volcano is where molten rock erupts through the surface of the planet.

When the gases from the volcano escape from the opening of the surface of the Volcano, the molten rock and the ash become solid as they cool, this is how Volcanos happen.

What is the Difference Between Magma and Lava?

When there is magma, it means that there is a liquid rock that is found inside of a volcano.  Lava is the magma when it flows out of the Volcano.

When lava just flows, it is usually red, but when it flows for a while, it will turn white.

What Are the Types of Volcanos?

• Composite Volcanoes-Composite volcanoes are volcanoes that are made from all kinds of layers of volcanic rocks.  They are steep and have tall sides.  Mount St. Helens is a composite volcano.
• Shield Volcano-A volcano that is shaped like a bowl is a shield volcano.  This type of Volcano has long slopes that are made when the lava flows.  This type of lava is basaltic lava, and so these types of volcanoes are called flood basalts.  The Columbia Platea has many shield volcanoes.
• Cinder Cones-These types of volcanoes are round or oval cones that are made up of small pieces of lava from magma and gas that have erupted and been pushed into the air.  This lava cools as it falls around the opening, and this is a cinder cone.
• Splatter Volcanoes – A spatter volcanoes are different from other volcanoes in the way lava is released. They release lava in clots called spatter.
• Complex volcanoes – These are volcanoes that have a lot more features thank a single type of Volcano.
• Lava Volcanoes-Lava volcanoes happen when a volcano erupts quickly, and it has a very thick flow.  This type of Volcano makes a steep mound, and the lava piles up close to the opening.  When these volcanoes erupt, they cause gas and steam to go into the air.

Composite Volcanoes

There are a few different types of volcanoes, but the most dangerous ones are called composite volcanoes.

Many volcanoes that you have probably heard of are composite volcanoes. Some have erupted in recent years, while others have remained still for a very long time.

What are composite volcanoes?

To understand composite volcanoes, there are a few facts you should know.

• Composite volcanoes are also known as stratovolcanoes.
• Composite volcanoes are the largest volcanoes, and they have the most violent eruptions.
• They get their name from the fact that they form in layers. Each layer is made of a different type of material.
• The layers of a composite volcano maybe rock, ash or lava.
• Most composite volcanoes are in the form of steep mountains, which often reach peaks of more than 2500m.
• Composite volcanoes take hundreds of thousands of years to form.

Composite volcanoes have many conduits, which are like tubes or pipes that allow material from deep inside the Volcano to reach its surface and pour out. When the Volcano fills with magma, it erupts. Magma starts as the molten (hot) rock that forms deep below the surface of the Earth and then builds up inside the Volcano.

What causes a composite volcano to erupt?

The deeper you go beneath the surface of the Earth, the hotter it gets. Far below the surface of the planet, just above its core, is the area known as the mantle.

The rock here can reach temperatures of 1000 degrees C. At that temperature. The rock becomes liquid. When it builds up, it squeezes out of the mantle to cooler areas and becomes magma. As the magma builds up, it travels through the entire system of tubes (the Volcano’s conduit).

When it builds up so much that it reaches the surface, the Volcano erupts. When this happens, water and gases mix with the material the Volcano is made of and causes something called a pyroclastic flow. This is the quickly-moving liquid mixture of lava, ash, and hot rock that spews out of the Volcano.

When a composite volcano erupts, the eruption can be very violent. First, the Volcano spits ash, cinder, and hot rocks. Then it spews lava or molten rock. Then it releases more ash. The magma in a composite volcano can splatter like the foam on a milkshake because it is so hot that it heats rocks and water, causing the water to steam.

After the eruption

Once the lava cools down, it becomes hard and forms plugs. If the plugs build up too much pressure, another eruption can occur. If not, the Volcano stays dormant (still). It may not erupt again for tens of thousands of years. At this stage, the Volcano can also become extinct, meaning that scientists do not expect it ever to erupt again.

When a large composite volcano has erupted, it may remain as a depression in the Earth called a caldera. A caldera is a deep hole in the Earth where the Volcano once existed. Overtime (in the case of a composite volcano, a very long time), a new volcano can form in this space.

Shield Volcanoes

If you saw a shield volcano, you might not even know it was a volcano. You can even visit one. The island of Hawaii has the biggest shield volcano in the world, Mauna Loa, or “Long Mountain.”

Here are some basic facts about shield volcanoes:

• Shield volcanoes get their name from their shape, which looks like a warrior’s shield.
• Shield volcanoes are very wide.
• They are not very steep. They rise slightly toward their centers and then become flat again at the summit (very top).
• Many islands are shield volcanoes.
• Shield volcanoes erupt often, but their eruptions are not usually violent.
• Shield volcanoes are mostly made of lava from previous eruptions.
• Compared to the lava from other types of volcanoes, the lava that erupts from a shield volcano is not very thick.
• Over time, they can become huge mountains.
• A shield volcano’s eruption is called a “Hawaiian eruption” because many of the Hawaiian Islands are shield volcanoes.
• An area in the Pacific Ocean that includes Hawaii is known as the “Ring of Fire” because it contains many shield volcanoes.

How do shield volcanoes erupt?

When a shield volcano erupts, a lot of hot lava flows out of it. Because it is not very thick, the lava travels a greater distance than the lava from the eruption of other kinds of volcanoes.

The lava spreads out in large areas, which is why these volcanoes are low and very wide. Large shield volcanoes can be 5 to 6 km wide and about 460 to 610 km high. Some are much larger.

Mauna Lao is the world’s largest shield volcano. It rises to 4,169 m above sea level and is 97 km wide! The Volcano is so heavy that it has fallen into the Earth’s crust.

Where do shield volcanoes form?

Volcanoes form in areas called hot spots. These are places where a large volume of rock in the Earth’s mantle, an area beneath its surface, melts. When hot spots are in the ocean, shield volcanoes are formed. They rise out of the sea as islands.

How are shield volcanoes unique?

A few things that make shield volcanoes different from other kinds of volcanoes are

• Rift zones
• Fissures
• Lava tubes

Rift zones are places along with volcanoes that contain lines called fissures. These volcanoes may erupt along the fissures instead of in the center like other volcanoes.

Fissure eruptions create a “wall of fire.” The wall of fire eventually dies down until the Volcano is erupting only in a few spots.

Lava tubes are tubes within shield volcanoes that contain lava. The existence of lava tubes in shield volcanoes is one reason that they produce so much lava when they erupt.

There are three kinds of lava produced by shield volcanoes:

• Pahoehoe (pa-hoy-hoy) lava is the thinnest type of lava.
• A’a (ah-ah) lava is a little thicker than pahoehoe lava.
• Pillow lava forms under the sea.

Since shield volcanoes usually form in a body of water, they can also have a kind of eruption called a hydrovolcanic eruption. “Hydro” means water, so hydrovolcanic eruptions occur when water and lava mix.

This type of eruption can happen underwater, creating clouds of ash and steam. The water cools the lava and causes it to form in mounds that resemble pillows. That’s why lava that forms under the sea is called pillow lava.

Shield volcanoes can erupt continuously for long periods, but as mentioned, their eruptions are not usually violent or dangerous. One of the shield volcanoes in Hawaii has been erupting for nearly 30 years.

Cinder Volcanoes

Cinder cone volcanoes are small compared to composite volcanoes that form huge mountains and shield volcanoes, which are low and wide.

Cinder volcanoes are the simplest type of Volcano. They have steep sides and a bowl-shaped crater at the top.

These volcanoes can form very quickly, sometimes in a matter of days.

Some basic things to know about cinder cone volcanoes are:

• Cinder cone volcanoes are small and have a simple structure.
• Cinder cone volcanoes are shaped like cones.
• Cinder cones are also known as scoria cones.
• The pieces of ash and cinder that form cinder cone volcanoes are known as basaltic fragments.
• Cinder cone volcanoes are formed by Strombolian eruptions.
• The lava from a cinder cone volcano is very thick.

How do cinder cone volcanoes form?

When hot lava forms under the Earth near an opening in its surface, the lava can build up to the point that gases carry it through the opening – called a vent – and into the atmosphere.

The lava then falls back to the ground and forms a cinder cone volcano. The pressure from gas beneath the surface of the Earth propels lava through the vent like a bomb. The lava that forms cinder cone volcanoes cools very quickly.

By the time it falls back to Earth, it has become pieces of ash and cinder. The ash and cinder build up around the vent and forms a cone. Cinder cone volcanoes are more the size of hills than mountains. They are usually symmetrical, often forming a perfect bowl or cone shapes.

The Strombolian eruptions that cause cinder cone volcanoes are low-level eruptions. This type of eruption is named for the volcano island of Stromboli in Italy. The eruptions don’t last very long are not very high. At most, hey will go a few hundred meters into the air. The thick lava from a Strombolian eruption does not travel very far, which is why cinder cone volcanoes are not very big.

Because the sides of cinder cone volcanoes are not very strong, eruptions can push through the sides of the Volcano as well as shoot straight up through the top. When a cinder cone erupts through one of its sides, the side may collapse. The result is a “partial cone” or a horse-shaped volcano instead of the usual rounded dome shape.

Cinder cone volcanoes may form in groups, or they can occur alone. They can also occur on the sides of shield volcanoes and other kinds of volcanoes.

Spatter Volcanoes

A spatter volcano is a special type of Volcano.

The main difference between spatter volcanoes and other volcanoes is the way lava is released from the Volcano and the type of lava that is released.

While other volcanoes usually release tall fountains of lava, spatter volcanoes release lava in clots called spatter. The release of spatter is called a spatter fountain.

Spatter fountains do not shoot up as high as the fountains created in the kind of eruption that you probably imagine when you think of a volcano. A spatter fountain is usually only a few meters high. The eruption of a spatter volcano may look more like a fire than a volcano eruption.

Here are some facts about spatter volcanoes:

• Spatter volcanoes are named for the way lava flows out of them.
• Lava flows out of a spatter volcanoes and forms glob called spatters that flatten and congeal on the ground.
• Spatter volcanoes eject lava either from a single vent or from a fissure on the surface of the Earth.
• Spatter builds cones or walls of lava that hardens around the vent or fissure.
• They often have an irregular shape.
• Spatter volcanoes occur in areas where there is a lot of liquid magma (underground lava), such as the Hawaiian Islands.

What do spatter volcanoes look like?

Spatter volcanoes can be cones or ramparts (walls). If a spatter volcano forms around a single vent, it will form in a circular shape around the vent. This is a spatter cone. If the spatter is ejected from a fissure (a long crack in the ground), it will look more like a wall that forms on either side of the fissure. This is a spatter rampart. Sometimes after a spatter eruption, lava will drain back into the fissure.

How does a spatter volcano form?

Like all volcanoes, spatter volcanoes are formed when molten (melted) rock called magma breaks through the surface of the Earth and forms a lava fountain. Molten rock below a volcano’s surface is called magma. Once it breaks through the surface, it is called lava.

Spatter volcanoes usually have a lot of liquid magma beneath their surfaces. When explosive gases mix with the magma, the gas and lava are released together from the Volcano, forming spatter.

Spatter is very sticky and fluid. For spatter to form, just the right amount of gas is needed to create it. There has to be enough gas to prevent a lava flow but not enough to break the lava apart into very small pieces.

Another way to put this is that if there is a lot of gas, lava will flow far from the spot of the eruption and create a much bigger volcano. If there is not enough gas, the smaller lava particles become smaller ash and cinder cone volcanoes instead.

How does spatter form?

Spatter forms when gases expand and break the lava apart into clots. The clots may be anywhere from 1 cm to 50 cm across. When the clots fall back to the surface of the Earth, they spread out and harden into spatter walls (ramparts) or spatter cones, which are rounder in shape.

Spatter is formed mainly from liquid rock (lava). The rock cools and hardens quickly before it can flow very far or become smooth, which is why most spatter volcanoes have irregular shapes. The walls around the vents of spatter cone volcanoes are very steep because spatter is sticky and can build high walls.

Complex Volcanoes

Complex volcanoes are volcanoes that have features of more than one single type of Volcano.

The main types of volcanoes are:

• Composite volcanoes – large mountains composed of layers of volcanic material; these have the most violent eruptions.
• Shield volcanoes – low, flat volcanoes created mostly by lava flow; they have less violent eruptions than composite volcanoes.
• Cinder cone volcanoes– simple volcanoes that form when lava blasts through a vent in the Earth
• Spatter volcanoes – similar to cinder cone volcanoes but created when gases mix with lava to form “spatter.”

If a volcano has more than one lava vent or more than one dome, it is usually considered a complex volcano. Complex volcanoes are also called compound volcanoes. “Compound” means that two or more things are joined together to form a single unit.

How do complex volcanoes form?

A complex volcano can be created when a large composite volcano overlaps a simple volcano, such as a cinder cone or spatter Volcano. It can also be created over time when many eruptions of a composite volcano cause more vents to open in the Earth.

This creates a complex system that can have more than one type of eruption. Multiple eruptions can lead to the creation of more than one lava dome or summit in the same area as well as different kinds of small, simple volcanoes.

Another feature of volcanoes that is important in understanding how complex volcanoes develop is a caldera. Very old volcanoes form one or more calderas, which are large basins in the ground. Calderas are left behind when volcanoes or parts of volcanoes collapse.

Some calderas fill with water and become lakes. For example, Crater Lake in the United States formed after the eruption of a volcano called Mount Mazama in 4600 B.C. The mountain was almost entirely destroyed in the eruption, and the part that remained collapsed into the Earth and formed a basin. The basin eventually filled with water and became a lake that is 9.7 km wide and 1219 m deep.

Even after a caldera develops, volcanoes can continue to erupt, though sometimes they become extinct at this point. If a caldera does not become a lake, groups of small cinder cones, spatter cones, and craters can develop around its rim, creating a complex volcano. A famous example of this is Yellowstone in the United States, which is actually a group of three calderas.

Lava Domes

What causes lava domes to form?

Lava domes can be formed from the inside out or from the accumulation of layers of lava. When they form from the inside out, each new eruption causes a new layer inside the dome that pushes the older layers out. When they form from the accumulation of layers of lava, each eruption causes a new layer of lava to pile on top of the existing dome.

Types of Lava Domes – there are four different types:

• Torta domes are shaped like cakes.
• Peléean domes have tall spines on top
• Coulées are part of the lava dome and part lava flow.
• Upheaved plugs are caused by strong eruptions.

What are the characteristics of different lava domes?

Torta domes are named because they resemble a cake. The word “torta” means cake in Spanish. Tortas are caused mainly by eruptions on flat ground. Many of these kinds of domes can be found in South America. When a torta dome forms, the lava from the eruption is pushed outward but does not go very far.

The result is a circular dome with a flat top. Tortas form in layers. Every time lava erupts through the vent at the center of the dome, a new layer is formed inside, and the older layers are pushed further outwards.

The first lava dome to be called a Peléean dome formed on Mount Pelee on the Caribbean island of Martinique. Peléean lava domes are the steepest type of lava dome. They are circular like tortas, but instead of having a flat top, they have tall spines at the top. Peléean domes are usually caused by the eruptions of composite volcanoes.

Coulées are part of the lava dome and part lava flow. Coulées usually form on very steep slopes. Some of the lava flows away from the dome and hardens into ridges a distance away from the dome itself.

An upheaved plug is caused by a stronger eruption of lava than the eruptions that cause other types of lava domes. They are the least common type of lava dome. The force of the eruption causes an “upheaval” in the ground, and lava is pushed straight up with great force. Upheaved plugs are very high and often carry rock and sediment from the surface of the Earth along with the lava.

Cryptodomes

There is another type of structure that is not exactly a lava dome but is related to one. It is called a cryptodome.

Cryptodomes begin to form beneath the surface of the Earth.

“Crypto” means mysterious or hidden, so the name cryptodome refers to the fact that these domes cannot be seen when they first begin to form. They are formed by magma, which is molten rock, gas, and other particles beneath a volcano’s surface.

Magma is basically the same thing as lava, but it has not yet broken through the Earth’s surface.

Cryptodomes can get large enough to form a bulge on the surface of the Earth by expanding and pushing on the surrounding rock.

An example of a cryptodome is a bulge that began to form on Mount St. Helens, a volcano in the United States.

The bulge became larger and more and more unstable, and vulcanologists (people who study volcanoes) realized that the Volcano was going to erupt. Sure enough, the eruption occurred in 1980.

What Happens When a Volcano Erupts?

When there is the pressure that builds up in the Volcano, it will cause an eruption.  When the pressure becomes so strong, the gases, rock, and lava will shoot up and will flow out of the opening of the Volcano.

When a volcano erupts, hot lava goes down the slope of the Volcano along with ash and gases that go into the air.

What Do Volcanoes Cause?

When a volcano erupts, it can cause all kinds of disasters.

• Mudslides
• Avalanches
• Hot ash to fall
• Floods
• Earthquakes
• Mudflows
• Rockslides
• Flooding
• Tsunamis
• The fall of forests

What Causes a Volcano to Form?

There are volcanos that form when magma that is in the mantle of the Earth starts to come to the surface of the Earth through cracks.

As the lava continues to flow and then harden because it becomes cooler, it will get bigger and bigger.

The Volcano will continue to erupt, and eventually, it can be a very large volcano.

What Causes a Volcano to Erupt?

Since the crust of the Earth is made up of plates that fit together, these plates move around.  When the plates move, it causes there to be friction.

When friction happens in an area where volcanoes are formed, it can cause the magma to come through the cracks between the plates.  When magma and gas build-up, it causes an eruption.

What Are the Different Stages of a Volcano?

• Active
• Dormant
• Extinct

An active volcano is one that has erupted recently and may erupt again soon.

A volcano that is dormant is a volcano that can erupt but has not for a very long time.

An extinct volcano is a volcano that will never erupt again but has erupted thousands of years ago.

 

Pyroclastic Flow

When a volcano erupts, much rock, gases, and lava flow out of the Volcano and out of the sides of the Volcano.  These things that come out of the Volcano are usually either solid or partly solid.

When a pyroclastic flow happens, it looks like a rockslide or an avalanche, except it is hot lava that is pouring down the Volcano.  This happens so fast that the flow is as fast as a hurricane.

A pyroclastic flow volcano is the deadliest of all volcanic eruptions.

Lahar

A lahar is made up of debris, pyroclastic material, rock, and water.

This material will flow down a volcano close to rivers or valleys.  When this happens, the material is a liquid when it moves, but when it stops, it is like cement, and it becomes very hard and solid.

This causes a lot of damage to different areas that are hit with lahars.

Pumice

When there are eruptions, pumice is formed.  Pumice is a volcanic rock that is light and porous.

This type of rock looks like a sponge because it has gas bubbles that form in it when it becomes solid.  Any type of magma will create pumice.  Some types of magma include:

• Andesite
• Dacite
• Rhyolite
• Basalt

Famous Volcanoes

There are many volcanoes that are famous because of their large eruptions.

• Mauna Loa is 13,677 feet high above sea level.  This is the largest Volcano that is active.  It is located in Hawaii.
• The Ring of Fire is an area of volcanoes that are found around the Pacific Ocean.  There are 452 volcanoes here, and more than 50% of them are considered to be active volcanoes.
• Krakatoa is a volcano in Indonesia that was dormant until 1883.  In 1883 it erupted and killed more than 40,000 people and destroyed a chain of islands.
• Mount Pelee was a dormant volcano until 1902.  It is located in Martinique.  When it erupted, more than 30,000 people were killed in just minutes.
• Mount Fujiyama is found in Japan.  It is 3,776 meters high.  It has not erupted for more than 300 years and is right now considered to be a dormant volcano.

What Should You Do If You Live Close to an Active Volcano?

• Have a disaster plan.
• Watch out for flooding, earthquakes, falling ash, tsunamis, and mudslides.
• Always have a first aid kit available.
• Keep food, drinks, and openers close to where you can find them.
• Always keep a radio that works on batteries.
• Always keep a flashlight that works on batteries.
• Evacuate if necessary.
• Avoid areas that go in river valleys or are downstream of the Volcano.
• If you get caught inside, make sure that you close all the doors and windows.
• Bring the animals inside.
• Put away all the things in your yard.
• If you are outside, find somewhere to get inside.
• If there is falling rock, cover your head.
• If you are by a stream, watch out for mudslides.
• Wear long sleeves and pants to protect you from ash that is falling.
• Wear goggles to protect your eyes.
• Wear a mask to keep from breathing the ash and smoke.
• Clear all ash from the roofs because it can cause your roof to cave in.

Volcano Facts for Kids:

• Volcanoes can cause damage for miles and miles.
• Volcanic ash can cause airplane engines to not work.
• Ash is small pieces of lava and rock that are shot out when a volcano happens.
• Crops can be destroyed by volcanoes.
• When there is a lot of ash that covers a large area, it is called ash carpet.
• Most volcanoes happen where two plates meet.
• Over 50 volcanoes have erupted in the last 200 years.
• Hot stuff below the surface is magma, but when it is above the surface, it is called lava.
• The word Volcano comes from the god of fire in Roman mythology, Vulcan.
• When there are narrow cracks in the crust of the Earth, this is called fissures.
• Geysers happen because volcanic heat warms water that is trapped in the ground, and the geysers shoot the water out in the air.  The water is boiling hot.

What Did You Learn?

• What is a volcano?  A volcano is a landform, usually a tall or steep mountain that has a molten rock that erupts and slides down the landform.
• What is magma?  Magma is the lava that is below the surface.
• What is lava?  Lava is magma that is above the surface.
• Are volcanoes dangerous?  Volcanoes can be very dangerous and can destroy cities in seconds.
• What are the three stages of volcanoes?  The three stages of volcanoes are active, dormant, and extinct.

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