Changes on Earth’s Surface10 Earthquakes and volcanoes can change Earth’s surface?. Weathering, such as abrasion and ice wedging, breaks rock into tiny pieces?. Abrasion happens when t
Trang 11 From tall mountains to flat plains, Earth’s surface has
extremes The physical features of Earth that we observe
today did not always exist Instead, they formed over millions
of years Those long, slow changes still take place, even if we
can’t see them happening
2 But there are other physical changes on Earth that we can
witness These changes happen much more quickly Some are
sudden changes, while others are more gradual Earth is a
restless planet As it changes, so do those who live on it.
Our Changing Earth
Reading Check ✓
1 Recall details
What are two extreme features
on Earth’s surface?
2 Predict What is
one change on Earth that we can see happen?
Synthesize What
do this paragraph and the photograph suggest about some
of Earth’s changes?
Reading Strategy
restless not able to rest
Content
Science
Reading 1
View of Earth from the moon’s surface
Trang 23 Earth’s crust is the layer of rock closest to Earth’s surface
An earthquake is a sudden, violent shaking in Earth’s crust
The crust is divided into a number of blocks of rock, called plates, which cover the planet An earthquake happens when
two of these plates, under great pressure, move past each
other along a fault The violent shaking is caused by seismic waves that travel through the planet These waves can knock down buildings and bridges The place inside Earth where an earthquake starts is the focus The epicenter is the place on Earth’s surface directly above the focus
violent very strong pressure force
Synthesize What
clear idea do the
pictures give you
about earthquakes?
Reading
Strategy
Earthquake
Focus Epicenter
Fault
Seismic Waves
Plates
Tsunami
Plates
306 Unit 5 • Chapter 2
306 Unit 5 • Chapter 2
Trang 3How Do Earthquakes Happen?
4 Most earthquakes result when plates move over, under, or
past each other Plate boundaries are places where two plates
meet Earthquakes happen when the pressure on the rocks at
plate boundaries builds up
5 This happens in different ways Plates can move apart, or
diverge As the rocks pull apart, magma rises from below
Plates can come together, or converge The rocks are pushed
from two different directions This makes them bend and
break Earthquakes can also happen when plates move past
one another without much motion up or down.
Surface Waves and Tsunamis
6 Most waves on a lake or an ocean can occur when wind
energy moves over the surface The energy that causes a
tsunami comes from an earthquake on the sea floor All of the
water above the epicenter is affected A wave forms It does
not seem large at first, but the energy is great When the
water hits the shore, it crashes over the land
magma hot liquid rock
motion movement
Reading Check ✓
1 Recall details
What builds up at plate boundaries?
2 Infer Where are
you most likely to notice a tsunami wave?
Synthesize How
is plate movement related to faults, like the San Andreas Fault pictured above?
Reading Strategy
The San Andreas Fault in California
Trang 47 A volcano forms at an opening, or vent, in the crust
near the edges of plates A volcanic eruption occurs when the plates move apart or when one plate is pushed under
the other Water vapor, particles, gases, and magma pour out onto the surface Volcanoes form new land Gases and
particles from the volcano may affect the weather
particles very small pieces
Lava
Magma
Eruption
Synthesize What
effect does a volcano
have on Earth’s
surface? Connect the
text and pictures on
this page
Reading
Strategy
Vent
Crater
Volcano
308 Unit 5 • Chapter 2
Trang 5Crust
Hot Spot Forming Islands
How Do Volcanoes Form?
8 Volcanoes often form at the boundaries between plates
They occur when the plates pull apart and magma flows up
from below through cracks Volcanoes can also form when
plates come together One plate moves under the other The
rock gets very hot and becomes magma The magma rises,
forming a volcano.
9 The mantle is the layer of earth under the crust Some
areas of mantle are hotter than others Volcanoes can form
at these hot spots As the plates move, the volcanoes form an
island chain The Hawaiian Islands are on a hot spot Synthesizecreates a hot spot? What
Pull together information from the text and diagram
Reading Strategy
Reading Check ✓
1 Recall details
Where can you find volcanoes?
2 Infer How might
gases and particles affect the weather?
Lava from Kilauea Volcano in Hawaii flows into the ocean How does Earth benefit from volcanic eruptions?
Trang 6Changes on Earth’s Surface
10 Earthquakes and volcanoes can change Earth’s surface
These changes happen quickly
11 Earth’s surface can change slowly, too Weathering, such
as abrasion and ice wedging, breaks rock into tiny pieces Abrasion happens when tiny pieces of rock wear down larger pieces of rock Erosion happens when water, glaciers,
or wind carries sediment to new places Sediment is tiny pieces of rock and soil Deposition happens when sediment builds up in a place Deposition builds new landforms such as deltas, moraines, and sand dunes Glaciers, water, and wind can all cause deposition
A glacier is a slowly moving mass
of ice A glacier can cut into rock and carry the pieces away.
Tiny bits of rocks moved by air, water, or a glacier can cause abrasion Ice wedging is the result of ice forming in small spaces in rocks The ice breaks
up the rock.
Wind can cause a sand dune to build up.
Synthesize What
changes to the
earth’s surface are
represented by the
pictures? How are
they different from
each other?
Reading
Strategy
Erosion Weathering
Deposition
Abrasion Glacier
Sand Dune
310 Unit 5 • Chapter 2
Trang 712 Mechanical weathering happens when rocks
are broken into small pieces Abrasion occurs when
pieces of rock are rubbed off by tiny bits of rock
moved by water, wind, or ice Ice and plants also cause
weathering A seed may fall into a crack in a rock When
the seed sprouts and grows, the plant’s roots make the
crack bigger Ice wedging also affects cracks in rock
Water gets into a crack When the water freezes, it
expands, and the crack gets bigger The cracked rock
finally breaks in two
13 In chemical weathering, chemicals in water, such as
oxygen and carbon dioxide, react with chemicals in rock This
breaks down the rock over time
Glaciers
14 Over thousands of years, ice and snow can build up on
mountains They form glaciers As a glacier moves, sand and
rock inside the glacier wear down mountains and change
their shape A mountain’s shape can tell us where glaciers
formed in the past.
Erosion and Deposition
15 Weathering breaks rock into smaller pieces Wind, water,
or ice moves these small pieces, called sediment, to new
places This process is erosion The Grand Canyon was
formed by water erosion Over millions of years, water cut
into the rock and carried pieces away Sand is eroded from
beaches by waves Glaciers carry rocks and soil as they
move Wind carries dust and sand for miles
16 When the wind or water
slows down, the sediment
drops out This is deposition
Deposition forms river
deltas and sand dunes
When a glacier deposits
sediment, it can form a
moraine, a type of hill
Synthesize What kind
of weathering is the Grand Canyon an example of?
Reading Strategy
Reading Check ✓
1 Recall details
What kinds of changes are caused
by wind?
2 Find main idea
What is the main idea of page 310?
Water erosion formed this canyon.
Plant roots push apart rock and cause mechanical weathering.