1. Chapter 8 Preview Section 1 Why Volcanoes Form
Section 2 Types of Volcanoes
Section 3 Effects of Volcanic Eruptions
Concept Map

2. Chapter 8
Section 1 Why Volcanoes Form
Bellringer
List observations of volcanoes you have seen in person or on television.
Write your observations in your Science Journal.

3. Chapter 8 What You Will Learn
Section 1 Why Volcanoes Form
What You Will Learn
Most volcanoes are located at or near tectonic plate boundaries.
Volcanoes form at divergent boundaries, convergent boundaries, and hot spots.
The temperature, pressure, and fluid content of rock play roles in the formation of magma.

4. Chapter 8 Where Volcanoes Form
Section 1 Why Volcanoes Form
Where Volcanoes Form
A volcano is a vent or fissure in Earth’s surface through which melted rock and gases pass.
An estimated 1,500 volcanoes have been active above sea level during the past 10,000 years.
Many more volcanoes have been active beneath the ocean.

5. Where Volcanoes Form, continued
Chapter 8
Section 1 Why Volcanoes Form
Where Volcanoes Form, continued
The map in the next slide shows the locations of some of the world’s most active volcanoes.
The map also shows the boundaries between tectonic plates.
A large number of volcanoes lie directly on tectonic plate boundaries.

6. Where Volcanoes Form, continued
Chapter 8
Section 1 Why Volcanoes Form
Where Volcanoes Form, continued

7. Where Volcanoes Form, continued
Chapter 8
Section 1 Why Volcanoes Form
Where Volcanoes Form, continued
The plate boundaries that surround the Pacific Ocean have so many volcanoes that the area is called the Ring of Fire.
At tectonic plate boundaries, several processes cause rock to melt at lower-crustal or upper-mantle depths.

8. Where Volcanoes Form, continued
Chapter 8
Section 1 Why Volcanoes Form
Where Volcanoes Form, continued
Molten rock is called magma.
Because magma is less dense than the solid rock surrounding it, magma travels up toward the surface.
When magma reaches the surface, it erupts to form a volcano.

9. Where Volcanoes Form, continued
Chapter 8
Section 1 Why Volcanoes Form
Where Volcanoes Form, continued
Volcanoes can form at divergent boundaries, convergent boundaries, or hot spots.
Divergent Boundaries
As tectonic plates pull away from each other at a divergent boundary, a set of deep vertical fractures called fissures form.

10. Where Volcanoes Form, continued
Chapter 8
Section 1 Why Volcanoes Form
Where Volcanoes Form, continued
Molten rock flows through these fissures onto the ocean floor.
The molten rock also forms submarine volcanoes.
Underwater mountain chains known as mid-ocean ridges are common at divergent boundaries.

11. Where Volcanoes Form, continued
Chapter 8
Section 1 Why Volcanoes Form
Where Volcanoes Form, continued
Most volcanic activity on Earth happens at mid-ocean ridges.
Most divergent boundaries are underwater.
However, Iceland is an island that is being pulled apart by a mid-ocean ridge.

12. Where Volcanoes Form, continued
Chapter 8
Section 1 Why Volcanoes Form
Where Volcanoes Form, continued

13. Where Volcanoes Form, continued
Chapter 8
Section 1 Why Volcanoes Form
Where Volcanoes Form, continued
Convergent Boundaries
At a convergent boundary, two plates collide.
The denser plate slides under the other plate.
As the denser plate bends, a deep depression known as a trench forms.

14. Where Volcanoes Form, continued
Chapter 8
Section 1 Why Volcanoes Form
Where Volcanoes Form, continued
At a trench, one plate moves downward into the mantle.
The process in which one plate moves beneath another is called subduction

15. Where Volcanoes Form, continued
Chapter 8
Section 1 Why Volcanoes Form
Where Volcanoes Form, continued
As the plate moves farther downward into Earth’s mantle, the rock is subjected to greater heat and pressure.
As a result, the plate releases fluids, which causes surrounding rock to melt.
Magma then moves upward through cracks in the Earth to form a volcano.

16. Where Volcanoes Form, continued
Chapter 8
Section 1 Why Volcanoes Form
Where Volcanoes Form, continued
Hot Spots
Hot spots are volcanically active places that are not located at tectonic plate boundaries.
Hot spots lie directly above columns of hot rock that rise through Earth’s mantle.
These columns are called mantle plumes.

17. Where Volcanoes Form, continued
Chapter 8
Section 1 Why Volcanoes Form
Where Volcanoes Form, continued
Mantle plumes are stationary.
As a tectonic plate moves over a mantle plume, rising magma causes a chain of volcanic islands to form.
The Hawaiian Islands formed as the Pacific Plate passed over a mantle plume.

18. Hot Spots and Mantle Plumes
Chapter 8
Volcanoes
Hot Spots and Mantle Plumes

19. Chapter 8 How Magma Forms
Section 1 Why Volcanoes Form
How Magma Forms
Magma forms in the deeper parts of Earth’s crust and in the uppermost parts of the mantle.
In these locations, temperature and pressure are very high.
Changes in temperature and pressure cause magma to form.

20. Chapter 8
Section 1 Why Volcanoes Form
Rock melts when its temperature increases or when the pressure on the rock decreases.
Water can lower the melting temperature of rock and cause the rock to melt.

21. How Magma Forms, continued
Chapter 8
Section 1 Why Volcanoes Form
How Magma Forms, continued
Increasing Temperature
As a tectonic plate moves downward into the mantle, the plate is exposed to greater temperatures at depth.
This increase in temperature may cause minerals in the rock to melt.

22. How Magma Forms, continued
Chapter 8
Section 1 Why Volcanoes Form
How Magma Forms, continued
Not all minerals in the rock melt at the same time.
Different minerals have different melting temperatures.
Minerals that have low melting temperatures melt before minerals that have high melting temperatures.

23. How Magma Forms, continued
Chapter 8
Section 1 Why Volcanoes Form
How Magma Forms, continued
Decreasing Pressure
Magma can form when pressure on rock decreases.
In Earth’s mantle, the pressure on rock is so great that the rock cannot expand.
Expansion is important in the formation of magma, because magma takes up more space than solid rock does.

24. How Magma Forms, continued
Chapter 8
Section 1 Why Volcanoes Form
How Magma Forms, continued
At divergent boundaries and hot spots, hot mantle rock rises.
At a shallower depth, the pressure on the rock decreases.
The decrease in pressure allows the hot rock to expand and melt.

25. How Magma Forms, continued
Chapter 8
Section 1 Why Volcanoes Form
How Magma Forms, continued
Adding Fluids
Oceanic lithosphere is composed of sediments and volcanic rocks that contain water and other fluids.
When oceanic lithosphere moves downward into the mantle, the fluids contact surrounding rock.
When fluids enter the hot mantle rock, the melting temperature of the rock decreases.

26. Chapter 8
Section 2 Types of Volcanoes
Bellringer
Look through the section. Then, write definitions for each of the following words:
composite volcano
shield volcano
cinder cone volcano
Write your answers in your Science Journal. Review and, if necessary, revise your definitions after reading this section.

27. Chapter 8 What You Will Learn
Section 2 Types of Volcanoes
What You Will Learn
Nonexplosive eruptions of basaltic magma occur at divergent boundaries.
Shield volcanoes that form from enormous volumes of basaltic magma occur at hot spots.
Explosive eruptions of silica-rich magma occur at convergent boundaries.

28. Chapter 8 Types of Volcanoes
Section 2 Types of Volcanoes
Types of Volcanoes
The process of magma formation is different at each type of plate boundary.
Therefore, the composition of magma differs in each tectonic setting.
Tectonic settings determine the types of volcanoes that form and the types of eruptions that take place.

29. Volcanoes at Divergent Boundaries
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Divergent Boundaries
At a divergent boundary, the lithosphere becomes thinner as two plates pull away from each other.
A set of deep cracks form in an area called a rift zone.
Hot mantle rock rises to fill these cracks.

30. Volcanoes at Divergent Boundaries, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Divergent Boundaries, continued
As the rock rises, a decrease in pressure causes hot mantle rock to melt and form magma.
The magma that reaches Earth’s surface is called lava.
Lava that flows at divergent boundaries forms from melted mantle rock.

31. Volcanoes at Divergent Boundaries, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Divergent Boundaries, continued
This lava is rich in the elements iron and magnesium. It is relatively poor in silica.
Because of its composition, lava from mantle rock cools to form dark-colored rock.
The term mafic describes magma, lava, and rocks that are rich in iron and magnesium.

32. Volcanoes at Divergent Boundaries, continued
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Section 2 Types of Volcanoes
Volcanoes at Divergent Boundaries, continued
Because it is low in silica, mafic lava is runny and not sticky.
This type of lava generally produces nonexplosive eruptions.

33. Volcanoes at Divergent Boundaries, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Divergent Boundaries, continued
Mid-ocean ridges are underwater mountain chains that form where two tectonic plates are moving apart.
As the plates move apart, magma from the mantle rises to fill cracks that form in the crust.
Some of the magma erupts as basaltic lava on the ocean floor.

34. Volcanoes at Divergent Boundaries, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Divergent Boundaries, continued
The magma and lava cool to become part of the oceanic lithosphere.
As the plates continue to move, older oceanic lithosphere moves away from the mid-ocean ridge.
New cracks form, and new lithosphere forms in the rift zone.

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Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Divergent Boundaries, continued
The process in which new sea floor forms as older sea floor is pulled apart is called sea-floor spreading.

36. Volcanoes at Divergent Boundaries, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Divergent Boundaries, continued
The mid-ocean ridge called the Mid-Atlantic Ridge is unusually active.
This activity has built part of the ridge into a large island known as Iceland.
Long linear cracks called fissures have formed where the Atlantic and Eurasian plates are moving apart.

37. Volcanoes at Divergent Boundaries, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Divergent Boundaries, continued
Basaltic magma rises to Earth’s surface through these fissures and erupts nonexplosively.
Icelandic volcanoes, such as Krafla, are often associated with large, connected fissure systems.
Lava erupts frequently through these fissures. As a result, Iceland is continually getting bigger.

38. Chapter 8 Volcanoes at Hot Spots
Section 2 Types of Volcanoes
Volcanoes at Hot Spots
A hot spot forms in a tectonic plate over a mantle plume.
Mantle plumes are columns of hot, solid rock that rise through the mantle by convection.
Plumes are thought to originate at the boundary between the mantle and the outer core.

39. Volcanoes at Hot Spots, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Hot Spots, continued
When the top of a mantle plume reaches the base of the lithosphere, the mantle rock spreads out and “pools” under the lithosphere.
Because pressure on the rock is low at this shallow depth, the rock melts.
Large volumes of magma are released onto the ocean floor.

40. Volcanoes at Hot Spots, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Hot Spots, continued
Continuous eruptions may produce a volcanic cone.
As the plate continues to move over the mantle plume, a chain of volcanoes may form.

41. Volcanoes at Hot Spots, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Hot Spots, continued
Because lava at hot spots comes from the mantle, it is mafic and fluid.
Most eruptions at hot spots are nonexplosive.
The type of rock that forms from this lava depends on the temperature, gas content, flow rate, and slope of the lava flow.

42. Volcanoes at Hot Spots, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Hot Spots, continued

43. Volcanoes at Hot Spots, continued
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Section 2 Types of Volcanoes
Volcanoes at Hot Spots, continued
Shield Volcanoes
Shield volcanoes usually form at hot spots.
Shield volcanoes form from layers of lava left by many nonexplosive eruptions.
The lava is very runny, so it spreads out over a wide area.

44. Volcanoes at Hot Spots, continued
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Section 2 Types of Volcanoes
Volcanoes at Hot Spots, continued
Over time, the layers of lava create a volcanic mountain that has gently sloping sides.
The sides of shield volcanoes are not very steep, but the volcanoes can be very large.
The Hawaiian shield volcano, Mauna Kea, is the tallest mountain on Earth.

45. Volcanoes at Hot Spots, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Hot Spots, continued
Parts of a Volcano
Most volcanoes share a specific set of features.
The magma that feeds the eruptions pools deep underground in a structure called a magma chamber.
At Earth’s surface, lava is released through openings called vents.

46. Chapter 8
Volcanoes
Magma and Vents

47. Volcanoes at Hot Spots, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Hot Spots, continued
Before erupting as lava, magma rises from the magma chamber to Earth’s surface through cracks in the crust.
This movement of magma causes small earthquakes that can be used to predict an eruption.

48. Volcanoes at Hot Spots, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Hot Spots, continued
Lava may erupt from a central summit crater of a shield volcano.
Lava may also erupt from fissures along the sides of the shield volcano.
After erupting from a vent, the fluid lavas move downslope in lava flows.

49. Volcanoes at Hot Spots, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Hot Spots, continued
A lava flow is a long river of molten rock.
Often the flow will cool and solidify on top while lava in the interior continues to flow.
Flowing lava in the interior travels through long, pipelike structures known as lava tubes.

50. Volcanoes at Convergent Boundaries
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Convergent Boundaries
At a convergent boundary, a plate that contains oceanic lithosphere may descend into the mantle beneath another plate.
The descending lithosphere contains water.
As the lithosphere descends into the mantle, temperature and pressure increase.

51. Volcanoes at Convergent Boundaries, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Convergent Boundaries, continued
The subducting lithosphere releases water into the surrounding mantle and overlying crust.
The water lowers the temperature of the rock, and the rock melts.
The magma that forms rises through the crust and erupts. These eruptions form a chain of volcanoes parallel to the plate boundary.

52. Volcano Formation at Convergent Boundaries
Chapter 8
Volcanoes
Volcano Formation at Convergent Boundaries

53. Volcanoes at Convergent Boundaries, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Convergent Boundaries, continued
Magmas at convergent boundaries are composed of melted mantle rock and melted crustal rock.
Therefore, fluid mafic lava and lava rich in silica and feldspar form at these boundaries.
Lavas rich in silica and feldspar cool to form light-colored rocks.

54. Volcanoes at Convergent Boundaries, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Convergent Boundaries, continued
The term felsic is used to describe magma, lava, and rocks that are rich in silica and feldspars.
Silica-rich magma tends to trap water and gas bubbles.
This causes enormous gas pressure to develop within the magma.

55. Volcanoes at Convergent Boundaries, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Convergent Boundaries, continued
As the gas-filled magma rises to Earth’s surface, pressure is rapidly released.
This change in pressure causes a powerful explosive eruption.
Pyroclastic materials are released during the eruption.

56. Volcanoes at Convergent Boundaries, continued
Chapter 8
Section 2 Types of Volcanoes
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Pyroclastic material forms when magma explodes from a volcano and solidifies in the air.
Pyroclastic material also forms when powerful eruptions shatter existing rock.
Four types of pyroclastic material include volcanic bombs, lapilli, volcanic ash, and volcanic blocks.

57. Volcanoes at Convergent Boundaries, continued
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Section 2 Types of Volcanoes
Volcanoes at Convergent Boundaries, continued

58. Volcanoes at Convergent Boundaries, continued
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Pyroclastic flows are produced when a volcano ejects enormous amounts of hot ash, dust, and toxic gases.
This glowing cloud of pyroclastic material can race down the slope of a volcano at speeds of more than 200 km/h.
This speed is faster than the speed of most hurricane-force winds.

59. Volcanoes at Convergent Boundaries, continued
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Section 2 Types of Volcanoes
Volcanoes at Convergent Boundaries, continued
The temperature at the center of a pyroclastic flow can exceed 700°C.
At this high temperature, a pyroclastic flow burns everything in its path.
Extreme winds and temperatures make pyroclastic flows the most dangerous of all volcanic phenomena.

60. Volcanoes at Convergent Boundaries, continued
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Section 2 Types of Volcanoes
Volcanoes at Convergent Boundaries, continued
Cinder Cone Volcanoes
Cinder cone volcanoes are the smallest type of volcano.
They generally reach heights of no more than 300 m.
Cinder cone volcanoes are made of pyroclastic material.

61. Volcanoes at Convergent Boundaries, continued
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Section 2 Types of Volcanoes
Volcanoes at Convergent Boundaries, continued
Cinder cone volcanoes most often form from moderately explosive eruptions.
They have steep sides and a wide summit crater.
Unlike other types of volcanoes, cinder cone volcanoes usually erupt only once in their lifetime.

62. Volcanoes at Convergent Boundaries, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Convergent Boundaries, continued
Composite Volcanoes
Composite volcanoes are also called stratovolcanoes.
They form from both explosive eruptions of pyroclastic material and quieter flows of lava.
This combination of eruptions forms alternating layers of pyroclastic material and lava.

63. Volcanoes at Convergent Boundaries, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Convergent Boundaries, continued
Composite volcanoes have a broad base and sides that get steeper toward the crater.
These volcanoes may generate many eruptions. However, eruptions may occur at intervals of hundreds of years or more.
Mount Fuji in Japan is a famous composite volcano.

64. Volcanoes at Convergent Boundaries, continued
Chapter 8
Section 2 Types of Volcanoes
Volcanoes at Convergent Boundaries, continued

65. Section 3 Effects of Volcanic Eruptions
Chapter 8
Bellringer
Create a labeled drawing based on what you think happens when a volcano erupts. Then, write a hypothesis about how the volcanic eruption may affect the surrounding areas.
Write your answers in your Science Journal.

66. Chapter 8 What You Will Learn
Section 3 Effects of Volcanic Eruptions
Chapter 8
What You Will Learn
Volcanic eruptions can cause the loss of human life and the devastation of wildlife habitats.
Volcanic eruptions can cause the average global temperature of Earth to decrease.
Volcanic eruptions provide benefits to humans and to the environment.

67. Negative Effects of Volcanic Eruptions
Section 3 Effects of Volcanic Eruptions
Chapter 8
Negative Effects of Volcanic Eruptions
Volcanic explosions can have local and global effects.
In April 1815, Tambora volcano in Indonesia erupted explosively.
The pyroclastic flows and falling debris killed about 10,000 people in the area.

68. Negative Effects of Volcanic Eruptions, continued
Section 3 Effects of Volcanic Eruptions
Chapter 8
Negative Effects of Volcanic Eruptions, continued
High in the atmosphere, ash and gas spread around Earth.
The average global temperature decreased by as much as 3°C for one to two years.
The lower temperature caused crop failures and starvation, particularly in New England and Europe.

69. Negative Effects of Volcanic Eruptions, continued
Section 3 Effects of Volcanic Eruptions
Chapter 8
Negative Effects of Volcanic Eruptions, continued
The effects of lower temperatures led to the deaths of about 82,000 people.
Therefore, an estimated total of 92,000 people around the world lost their lives as a result of the Tambora eruption.

70. Effects of Volcanoes on Earth
Chapter 8
Volcanoes
Effects of Volcanoes on Earth

71. Negative Effects of Volcanic Eruptions, continued
Section 3 Effects of Volcanic Eruptions
Chapter 8
Negative Effects of Volcanic Eruptions, continued
Local Effects of Volcanic Eruptions
Volcanic eruptions can cause loss of human life and loss of wildlife habitat.
The blast from an explosive eruption can knock down trees, destroy buildings, and kill humans and animals.

72. Negative Effects of Volcanic Eruptions, continued
Section 3 Effects of Volcanic Eruptions
Chapter 8
Negative Effects of Volcanic Eruptions, continued
Pyroclastic flows can burn everything in their path.
Hot volcanic materials can melt the snowcap on a mountain, causing devastating floods.
Volcanic ash can mix with water to form fast-moving mudflows called lahars.

73. Negative Effects of Volcanic Eruptions, continued
Section 3 Effects of Volcanic Eruptions
Chapter 8
Negative Effects of Volcanic Eruptions, continued
The weight of falling ash can collapse structures, bury crops, and damage engines.
Volcanic ash can also cause respiratory problems in humans.

74. Negative Effects of Volcanic Eruptions, continued
Section 3 Effects of Volcanic Eruptions
Chapter 8
Negative Effects of Volcanic Eruptions, continued
Global Effects of Volcanic Eruptions
Large volcanic eruptions can affect Earth’s climate for several years.
During large eruptions, ash and sulfur-rich gases can be pushed into the stratosphere.
As the ash and gases spread around the planet, they absorb and scatter sunlight.

75. Negative Effects of Volcanic Eruptions, continued
Section 3 Effects of Volcanic Eruptions
Chapter 8
Negative Effects of Volcanic Eruptions, continued
Enough sunlight may be absorbed or scattered to lower the average global temperature of Earth.
In 1991, after the eruption of Mount Pinatubo in the Philippines, the amount of sunlight to reach Earth’s surface decreased by 2-4%.
This decrease caused the average global temperature of Earth to decrease by several tenths of a degree for several years.

76. Benefits of Volcanic Eruptions
Section 3 Effects of Volcanic Eruptions
Chapter 8
Benefits of Volcanic Eruptions
Volcanic Soils
Volcanic soils are some of the most fertile soils on Earth.
Volcanic rocks are made of minerals that contain elements important to plant growth.
When volcanic rocks break down, they form soils that contain many nutrients that plants can use.

77. Benefits of Volcanic Eruptions, continued
Section 3 Effects of Volcanic Eruptions
Chapter 8
Benefits of Volcanic Eruptions, continued
Geothermal Energy
Magma heats the rocks that surround it.
These rocks often hold water that also becomes heated.
This heated water, called geothermal water, may reach temperatures of hundreds of degrees Celcius.

78. Benefits of Volcanic Eruptions, continued
Section 3 Effects of Volcanic Eruptions
Chapter 8
Benefits of Volcanic Eruptions, continued
Geothermal water contains large amounts of heat energy.
This energy can be tapped by drilling wells to reach the hot water.
Water can also be pumped through heated rocks to obtain energy.

79. Benefits of Volcanic Eruptions, continued
Section 3 Effects of Volcanic Eruptions
Chapter 8
Benefits of Volcanic Eruptions, continued
Geothermal water can be used to drive turbines that generate electricity.
It can also be used to heat homes, grow crops, or keep roads free of ice.
In Reykjavik, Iceland, 85% of all homes are heated with geothermal water.

80. Benefits of Volcanic Eruptions, continued
Section 3 Effects of Volcanic Eruptions
Chapter 8
Benefits of Volcanic Eruptions, continued
Volcanic rocks are often used in construction.
As early as 300 BCE, Romans made concrete from volcanic ash and lime.
This material was used to build the Colosseum in Rome in 80 CE. The strength of this material has allowed the Colosseum to stand for nearly two thousand years.

81. Benefits of Volcanic Eruptions, continued
Section 3 Effects of Volcanic Eruptions
Chapter 8
Benefits of Volcanic Eruptions, continued
As recently as the 20th century, volcanic ash was used to make concrete for dams in the United States.
Today, basalt and pumice are often used in the construction of roads and bridges, and the production of concrete.

82. Benefits of Volcanic Eruptions, continued
Section 3 Effects of Volcanic Eruptions
Chapter 8
Benefits of Volcanic Eruptions, continued
Volcanic rocks have many other uses.
Volcanic ash absorbs moisture, so it is used in cat litter.
Because pumice is abrasive, it is used in facial scrubs, soaps, cleaners, and polishes.

83. Benefits of Volcanic Eruptions, continued
Section 3 Effects of Volcanic Eruptions
Chapter 8
Benefits of Volcanic Eruptions, continued
Pumice is added to soil to allow air and water to circulate more easily through the soil.
Because metals in pumice are not water soluble, pumice is used alone or with silica sand to filter drinking water.

84. Chapter 8
Volcanoes
Concept Map
Use the terms below to complete the concept map on the next slide.
eruptions
shield volcanoes
cinder cone volcanoes
composite volcanoes
lava

85. Chapter 8
Volcanoes
Concept Map

86. Chapter 8
Volcanoes
Concept Map