The Changing Earth

Chapter 3: Mountains

and Volcanoes

Section 3.1

Movement of Rock Builds Mountains

Most mountains form along plate boundaries.

• Formation of most mountain ranges• Begins as a collision between tectonic

plates.• Land is pushed upward.• May continue growing indefinitely or

stop.

Continued – See page 78

Continued – See page 78

Continued

• Some processes wear mountains down.• Running water and wind constantly

break rocks into pieces called sediment and carry them away.

• The sediment may settle in valleys or be carried to the ocean.

• Tall jagged mountains eventually become low, rounded hills, then flat land.

Continued – See page 79

Mountains can form as rock folds.

• Rock bends under certain conditions.• High temperatures and pressure can

slowly fold and crumple rock like soft modeling clay.

• Folded mountains form as an ocean plate sinks under a continental plate, or as two continental plates collide. (Himalayas)

Continued – See page

81

Mountains can form as rocks move along faults.

• Fault-block mountains form where continental crust is being pulled apart.• The crust is stretched, it breaks into blocks

along fault lines.• The tilting and dropping of the blocks in

various ways creates mountains and valleys

Continued – See page 83

Section 3.2

Volcanoes Form as Molten Rock Erupts

Volcanoes erupt many types of material.

• Volcano: an opening in Earth’s crust through which molten rock, rock fragments, and hot gases erupt.

• Magma that is high in silicon resists flowing and can prevent gases from escaping until the pressure builds and the gases blast out.

• Rock fragments can be as big as a house or as small as a dust particle. Fragments form as lava cool.

Continued – See page 88

Continued

• The main gases from a volcano are water vapor and carbon dioxide.

• Pyroclastic flows: fast moving mixtures of gases and ash that can sweep up and over hills, then race down a neighboring valley, causing deadly damage within minutes.

Continued – See page 87

Most volcanoes form along plate boundaries.

• Volcanoes, like earthquakes, are explained by plate tectonics.

• Volcanoes are commonly found at:• subduction zones where an oceanic

plate is sinking beneath another plate.• spreading centers where plates are

pulling apart.• hot spots where a plate is moving

over an unusually hot area in the mantle.

Continued - See page 89

Volcanoes can have many shapes and sizes.

• The size of a volcano depends on the magma type feeding it. Eruptions form three basic kinds of volcanoes.• Shield volcano: built from many eruptions

of lava that is low in silica and flows easily. It is a broad, flat cone.

• Cinder Cone: built of pieces of magma that harden in the air and fall to form a small, steep-sided volcano.

• Composite volcano: built of high silica magma, The tall cone consists of layers of lava and layers of rock fragments.

Continued - See page 90

Continued – See page 91

Scientists monitor volcanoes.

• Scientists monitor volcanoes to look for warning signs that an eruption may be coming. Warning signs include:• Earthquakes• Changes in the tilt of the ground• Rising temperatures of openings• Changes in volcanic gases being

tested.

Both shield and composite volcanoes can form features called calderas, a huge crater formed by the collapse of the volcano when magma rapidly erupts from underneath it.

Section 3.3

Volcanoes Affect Earth’s Land, Air, and Water

Volcanic eruptions affect the land.

• Volcanic eruptions can be extremely destructive.

• Damage depends on how much and which types of material the volcano ejects.•Lava flows knock down and burn

trees, fields, roads, and buildings.•Volcanic ash can suffocate plants,

people, and animals. It can collapse buildings and damage machinery.

Continued – See page 97

Continued

• Mudflows have buried towns as a mixture of ash, rocks, soil, and water race down a mountain valley.

• Landslides occur when part of a volcano collapses. They can change the landscape and cause tsunamis.

• Steam explosions occur when magma comes near or in contact with water, resulting in an explosion. These are not very common.

Continued

Materials From Volcanic Eruptions Affect Earth

Land Air Water

Lava Poisonous Gases Hot Springs

Volcanic Ash Adds to Acid Rain

Geysers

Landslides Haze Fumaroles

Mudflows Lower Temperature

Deep –Sea Vents

Continued

• Some of the long-term effects of eruptions can be beneficial.• Over many years, volcanic rock

breaks down to form a rich soil.• Highly productive farmland surrounds

some volcanoes.• Volcanoes can also create beautiful

landscapes.

Volcanic gases and ash affect the air.

• Volcanoes release gases before, during, and after eruptions. Sometimes these gases are dangerous.• Carbon dioxide in large amounts can be

deadly.• Sulfur dioxide and other gases mix with

moisture to form acids that add to acid rain.• Large amounts of gases and ash can travel

around the world and affect weather for months or even years.

Volcanic activity affects water.

• Hot springs: pools that form when water moves underground near magma or hot rock. The water gets heated and rises to the surface.

• Geysers: similar to hot spring but water shoots into the air.

• Fumaroles: release steam and other gases rather than liquid water.

• Deep-sea vents: hot springs that form at spreading centers in the ocean. They support life forms that do not exist anywhere else on earth.

Continued - See page 101

Geyser

Fumarole

Hot Spring

Deep-Sea Vent