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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
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