Chapter 8

VOLCANOES

Section 1 - Volcanic Eruptions

There are two types of volcanic eruptions, Nonexplosive and Explosive

1) NONEXPLOSIVE ERUPTIONS When most people think about volcanic

eruptions they think of rivers of red-hot lava (lava flows)

Lava flows come from nonexplosive eruptions These calm outpourings of lava can release a HUGE

amount of molten rock Some of the LARGEST mountains in the world

grew from repeated lava flows over hundreds of thousands of years

There are two types of volcanic eruptions, Nonexplosive and Explosive

1) NONEXPLOSIVE ERUPTIONS When most people think about volcanic

eruptions they think of rivers of red-hot lava (lava flows)

Lava flows come from nonexplosive eruptions These calm outpourings of lava can release a HUGE

amount of molten rock Some of the LARGEST mountains in the world

grew from repeated lava flows over hundreds of thousands of years

2) EXPLOSIVE ERUPTIONS During this type of eruption clouds of hot debris and

gases SHOOT out of the volcano This often happens at SUPERSONIC speeds

These eruptions do not produce lava flows Instead molten rock is blown into millions of pieces that

harden in the air The dust size particles can circle the Earth for years in the

upper atmosphere This type of eruption can also blast millions of tons of

solid rock from the volcano itself In a matter of minutes, an explosive eruption can

demolish rock formations that took thousands of years to build

In this case a volcano will actually shrink instead of grow

2) EXPLOSIVE ERUPTIONS During this type of eruption clouds of hot debris and

gases SHOOT out of the volcano This often happens at SUPERSONIC speeds

These eruptions do not produce lava flows Instead molten rock is blown into millions of pieces that

harden in the air The dust size particles can circle the Earth for years in the

upper atmosphere This type of eruption can also blast millions of tons of

solid rock from the volcano itself In a matter of minutes, an explosive eruption can

demolish rock formations that took thousands of years to build

In this case a volcano will actually shrink instead of grow

Cross Section of a Volcano

All volcanoes share the same basic features Magma - hot liquid material (rock) that creates

volcanoes Magma collects underground in Magma Chambers Some chambers can be up to 160km below the surface

Vents - holes in the Earth through which magma rises Lava - magma that erupts and flows onto the Earth’s

surface Pyroclastic Material - is magma that erupts as

fragments of molten material that solidify in the air Volcano - a vent or group of vents combined with the

build up of lava and/or pyroclastic material

All volcanoes share the same basic features Magma - hot liquid material (rock) that creates

volcanoes Magma collects underground in Magma Chambers Some chambers can be up to 160km below the surface

Vents - holes in the Earth through which magma rises Lava - magma that erupts and flows onto the Earth’s

surface Pyroclastic Material - is magma that erupts as

fragments of molten material that solidify in the air Volcano - a vent or group of vents combined with the

build up of lava and/or pyroclastic material

Magma

By comparing the composition of magma from different types of eruptions, scientists have determined that the composition of the magma dictates whether an eruption will be nonexplosive, explosive, or somewhere in between

Water A volcano is more likely to erupt explosively if the

magma has a high water content The more water there is in magma, the greater the

pressure (like a can of soda) and the greater chance that there will be a violent eruption

Gases (steam) need more room than liquids (pressure)

By comparing the composition of magma from different types of eruptions, scientists have determined that the composition of the magma dictates whether an eruption will be nonexplosive, explosive, or somewhere in between

Water A volcano is more likely to erupt explosively if the

magma has a high water content The more water there is in magma, the greater the

pressure (like a can of soda) and the greater chance that there will be a violent eruption

Gases (steam) need more room than liquids (pressure)

Silica - Explosive eruptions are also caused by magma that contains a large percentage of silica

Silica rich magma is very thick and has a tendency to harden inside the volcano This causes magma and gases to get trapped

inside the volcano until so much pressure builds up that the volcano goes BOOM !!!!!!

Low silica magma is runny which allows gases to escape easily, keeping pressure low

Silica - Explosive eruptions are also caused by magma that contains a large percentage of silica

Silica rich magma is very thick and has a tendency to harden inside the volcano This causes magma and gases to get trapped

inside the volcano until so much pressure builds up that the volcano goes BOOM !!!!!!

Low silica magma is runny which allows gases to escape easily, keeping pressure low

What Erupts from a Volcano?

Nonexplosive eruptions produce mostly lava, while explosive eruptions produce mostly pyroclastic material

Over many years, a volcano may alternate between eruptions that produce lava or pyroclastic material Eruptions of lava and pyroclastic material

may also occur as separate stages of a single eruption event

Nonexplosive eruptions produce mostly lava, while explosive eruptions produce mostly pyroclastic material

Over many years, a volcano may alternate between eruptions that produce lava or pyroclastic material Eruptions of lava and pyroclastic material

may also occur as separate stages of a single eruption event

Lava Lava is magma that flows onto the Earth’s

surface Like magma lava ranges in consistency from

thick to thin Blocky Lava is cool, stiff lava that cannot

travel far from the erupting vent Blocky lava forms jumbled heaps of sharp edged

chunks Pahoehoe is lava that flows slowly, like wax

dripping from a candle forming a glassy surface with round wrinkles that look like “ropes”

Aa is slightly stiffer lava that pours out quickly and forms a brittle crust that can break and harden into jagged pieces

Pillow Lava forms when lava erupts underwater It forms rounded lumps that are the size and shape

of pillows

Lava Lava is magma that flows onto the Earth’s

surface Like magma lava ranges in consistency from

thick to thin Blocky Lava is cool, stiff lava that cannot

travel far from the erupting vent Blocky lava forms jumbled heaps of sharp edged

chunks Pahoehoe is lava that flows slowly, like wax

dripping from a candle forming a glassy surface with round wrinkles that look like “ropes”

Aa is slightly stiffer lava that pours out quickly and forms a brittle crust that can break and harden into jagged pieces

Pillow Lava forms when lava erupts underwater It forms rounded lumps that are the size and shape

of pillows

Pyroclastic Material Pyroclastic material refers to the rock fragments

created by explosive volcanic eruption and is produced when magma EXPLODES from a volcano and solidifies in the air. It can come in a variety of sizes that include:

Volcanic Blocks - are the largest pieces upwards to the size of a house

Volcanic blocks are large pieces of rock (not magma) from the mountain

Volcanic Bombs - are large blobs of magma that harden in a flattened, elongated shape, like a bomb

Volcanic bombs are greater than 64mm in diameter Lapilli - which means “little stones” in Italian, are pebble

like bits of pyroclastic material between 2 and 64mm in diameter

Volcanic Ash - consist of particles that are less than 2mm in diameter

Pyroclastic Material Pyroclastic material refers to the rock fragments

created by explosive volcanic eruption and is produced when magma EXPLODES from a volcano and solidifies in the air. It can come in a variety of sizes that include:

Volcanic Blocks - are the largest pieces upwards to the size of a house

Volcanic blocks are large pieces of rock (not magma) from the mountain

Volcanic Bombs - are large blobs of magma that harden in a flattened, elongated shape, like a bomb

Volcanic bombs are greater than 64mm in diameter Lapilli - which means “little stones” in Italian, are pebble

like bits of pyroclastic material between 2 and 64mm in diameter

Volcanic Ash - consist of particles that are less than 2mm in diameter

Chapter 8 Quiz 1 1) __________ is the hot liquid material found

deep in the ground, and is the driving force that creates volcanoes

2) __________ are holes in the Earth’s crust in which the above material (#1) flows

3) __________ includes hot liquid material (#1) and rock fragments that are BLASTED into the air

4) __________ are large pieces of rock (from the mountain) that are blasted into the air, and can be upwards of the size of a house

5)___________ is lava that hardens into jagged pieces

Bonus) _________ forms when a magma chamber collapses causing the “roof” above it to collapse

1) __________ is the hot liquid material found deep in the ground, and is the driving force that creates volcanoes

2) __________ are holes in the Earth’s crust in which the above material (#1) flows

3) __________ includes hot liquid material (#1) and rock fragments that are BLASTED into the air

4) __________ are large pieces of rock (from the mountain) that are blasted into the air, and can be upwards of the size of a house

5)___________ is lava that hardens into jagged pieces

Bonus) _________ forms when a magma chamber collapses causing the “roof” above it to collapse

Section 2 - Volcanoes Effects on Earth

The effects of volcanic eruptions can be seen both on land (mountains, plateaus, etc.) and in the air (ash and escaping gases) Ash and escaping gases can affect global

climate patterns

The effects of volcanic eruptions can be seen both on land (mountains, plateaus, etc.) and in the air (ash and escaping gases) Ash and escaping gases can affect global

climate patterns

An Explosive Impact

Because ash and gases can be ejected high into the air it can have widespread effects on Earth, including blocking out the sun for days and over thousands of miles. Ash can also blow down trees and knock down

buildings Flows - are clouds of hot ash that can flow

rapidly downhill like an avalanche, searing everything in its path Large amounts of ash can sometimes mix with water,

turning the flow into the consistency of wet cement These flows can pick up boulders, trees, and buildings

causing MASSIVE destruction

Because ash and gases can be ejected high into the air it can have widespread effects on Earth, including blocking out the sun for days and over thousands of miles. Ash can also blow down trees and knock down

buildings Flows - are clouds of hot ash that can flow

rapidly downhill like an avalanche, searing everything in its path Large amounts of ash can sometimes mix with water,

turning the flow into the consistency of wet cement These flows can pick up boulders, trees, and buildings

causing MASSIVE destruction

Fallout - happens when volcanic ash falls back to the ground Buildings have been known to collapse under the

weight of accumulating ash Ash can also dam up river valleys, resulting in

MASSIVE floods Too much ash can smoother crops causing food

shortages and loss of livestock

Climatic Fluctuation - are changes in global temperatures and moisture levels due to the release of ash and sulfur rich gases that reach our upper atmosphere Temperature shifts can disrupt climates all over the

world causing milder wetter summers and longer harsher winters resulting in starvation and disease

Fallout - happens when volcanic ash falls back to the ground Buildings have been known to collapse under the

weight of accumulating ash Ash can also dam up river valleys, resulting in

MASSIVE floods Too much ash can smoother crops causing food

shortages and loss of livestock

Climatic Fluctuation - are changes in global temperatures and moisture levels due to the release of ash and sulfur rich gases that reach our upper atmosphere Temperature shifts can disrupt climates all over the

world causing milder wetter summers and longer harsher winters resulting in starvation and disease

Different Types of Volcanoes

There are three basic types of volcanoes: 1) Shield Volcanoes - are volcanoes built out of layers of

lava from repeated nonexplosive eruptions Because lava is runny it spreads out over a wide area, which

over time builds up to form volcanoes with wide bases and gently sloping sides

Though their sides are not steep, shield volcanoes can be enormous and include the largest mountain on Earth, Mauna Kea in Hawaii

2) Cinder Cone Volcanoes - are small volcanic cones made entirely of pyroclastic material from moderately explosive eruptions

These volcanoes have narrow bases and steeper slopes Cinder cone volcanoes usually erupt for a short period of time

and occur in clusters These volcanoes erode quickly because the pyroclastic

material of the volcano is not cemented together by lava 3) Composite Volcanoes - form from explosive eruptions of

pyroclastic material, followed by quieter outpourings of lava These are the most common types of volcanoes and are also known as

stratovolcanoes These have broad bases and sides that get steeper toward the summit

There are three basic types of volcanoes: 1) Shield Volcanoes - are volcanoes built out of layers of

lava from repeated nonexplosive eruptions Because lava is runny it spreads out over a wide area, which

over time builds up to form volcanoes with wide bases and gently sloping sides

Though their sides are not steep, shield volcanoes can be enormous and include the largest mountain on Earth, Mauna Kea in Hawaii

2) Cinder Cone Volcanoes - are small volcanic cones made entirely of pyroclastic material from moderately explosive eruptions

These volcanoes have narrow bases and steeper slopes Cinder cone volcanoes usually erupt for a short period of time

and occur in clusters These volcanoes erode quickly because the pyroclastic

material of the volcano is not cemented together by lava 3) Composite Volcanoes - form from explosive eruptions of

pyroclastic material, followed by quieter outpourings of lava These are the most common types of volcanoes and are also known as

stratovolcanoes These have broad bases and sides that get steeper toward the summit

Craters and Calderas

Crater - is a funnel shaped pit found at the top of the central vent in most volcanoes A craters funnels shape results from

explosions of material out of the vent, as well as the collapse of material from the craters rim back into the vent

Caldera - forms when a magma chamber that supplies material to a volcano empties and its roof collapses This causes the ground to sink, leaving a large

circular depression

Crater - is a funnel shaped pit found at the top of the central vent in most volcanoes A craters funnels shape results from

explosions of material out of the vent, as well as the collapse of material from the craters rim back into the vent

Caldera - forms when a magma chamber that supplies material to a volcano empties and its roof collapses This causes the ground to sink, leaving a large

circular depression

Lava Plateaus

Most of the lava on Earth’s continents do NOT come from volcanoes, but ooze from a series of long cracks called fissures Runny lava oozing from fissures can spread

out over thousand of square kilometers forming Lava Plateau i.e. The Columbia River Plateau formed about 15

million years ago

Most of the lava on Earth’s continents do NOT come from volcanoes, but ooze from a series of long cracks called fissures Runny lava oozing from fissures can spread

out over thousand of square kilometers forming Lava Plateau i.e. The Columbia River Plateau formed about 15

million years ago

Chapter 8 Quiz 2

1) _________ are clouds of hot ash that can flow rapidly downhill like an avalanche

2) _________ are built out of layers of lava from repeated nonexplosive eruptions

3)__________ are also referred to as Statovolcanoes

4) __________ forms when a magma chamber empties and its roof collapses

Bonus) _________ are places within tectonic plates where columns of rising magma are

1) _________ are clouds of hot ash that can flow rapidly downhill like an avalanche

2) _________ are built out of layers of lava from repeated nonexplosive eruptions

3)__________ are also referred to as Statovolcanoes

4) __________ forms when a magma chamber empties and its roof collapses

Bonus) _________ are places within tectonic plates where columns of rising magma are

Section 3 - What Causes Volcanoes

The Formation of Magma The key to understanding why volcanoes erupt is understanding

how magma forms All volcanoes begin when magma collects in pockets in the deep

regions of the Earth’s crust and uppermost layers of the mantle The zone of magma formation is between 25 - 160 km below the

surface Although the rocks of the mantle are hot and pliable, it is still

not a liquid. Why? The weight of the rock above the mantle exerts so much PRESSURE

that the atoms are forced close together This increases the melting point (temperature point) at which the

rock will melt Mantle rock will not melt (turn into magma) until the

temperature increases or the pressure on it releases Because the temperature of the mantle is fairly constant, pressure

release is the main reason why rock melts

The Formation of Magma The key to understanding why volcanoes erupt is understanding

how magma forms All volcanoes begin when magma collects in pockets in the deep

regions of the Earth’s crust and uppermost layers of the mantle The zone of magma formation is between 25 - 160 km below the

surface Although the rocks of the mantle are hot and pliable, it is still

not a liquid. Why? The weight of the rock above the mantle exerts so much PRESSURE

that the atoms are forced close together This increases the melting point (temperature point) at which the

rock will melt Mantle rock will not melt (turn into magma) until the

temperature increases or the pressure on it releases Because the temperature of the mantle is fairly constant, pressure

release is the main reason why rock melts

Where Volcanoes Form

Most volcanoes are found on tectonic plate boundaries These boundaries are where plates either

collide or separate from each other The plate boundaries around the Pacific Ocean is

called the RING OF FIRE !!!!!!

At these types of boundaries it is easier for magma to travel upward through the crust

Most volcanoes are found on tectonic plate boundaries These boundaries are where plates either

collide or separate from each other The plate boundaries around the Pacific Ocean is

called the RING OF FIRE !!!!!!

At these types of boundaries it is easier for magma to travel upward through the crust

When Tectonic Plates Separate

As two tectonic plates separate a deep crack, called a rift, forms

Mantle material is then able to rise up, decreasing the pressure on it, and causing it to melt and turn into magma

Magma continuously rises up through the rift creating new crust

Most divergent boundaries are found under the oceans where they produce long underwater mountain chains called mid-ocean ridges

As two tectonic plates separate a deep crack, called a rift, forms

Mantle material is then able to rise up, decreasing the pressure on it, and causing it to melt and turn into magma

Magma continuously rises up through the rift creating new crust

Most divergent boundaries are found under the oceans where they produce long underwater mountain chains called mid-ocean ridges

When Tectonic Plates Collide

The place where two tectonic plates collide is called a convergent boundary

The movement of one plate under another is called a subduction zone

Convergent boundaries are commonly located where oceanic plates collide with continental plates

As the oceanic plate slides under the continental plate it sinks deeper into the mantle causing it to melt

As the magma rises to the surface it cause the silica rich continental crust to also melt becoming part of the gooey lava that can cause an explosive eruption

The place where two tectonic plates collide is called a convergent boundary

The movement of one plate under another is called a subduction zone

Convergent boundaries are commonly located where oceanic plates collide with continental plates

As the oceanic plate slides under the continental plate it sinks deeper into the mantle causing it to melt

As the magma rises to the surface it cause the silica rich continental crust to also melt becoming part of the gooey lava that can cause an explosive eruption

Hot Spots

Not all magma develops along tectonic plate boundaries i.e. The Hawaiian Islands are formed over

hot spots Hot Spots - are places within tectonic

plates that are directly above columns of rising magma called mantle plumes

Not all magma develops along tectonic plate boundaries i.e. The Hawaiian Islands are formed over

hot spots Hot Spots - are places within tectonic

plates that are directly above columns of rising magma called mantle plumes