Download Lesson 4: What causes rapid changes to landforms?

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landslide the rapid downhill movement of a large amount of rock and
soil
volcano place on Earth’s crust where magma reaches the surface
fault a break or crack where Earth’s crust can move
Rapid Changes
Earth’s surface can change slowly, but it
can also change quickly. They can happen
in a few days or even a few seconds.
Landslides, earthquakes, and volcanoes can
cause rapid changes.
again. An active volcano has frequent
eruptions, and scientists think it will erupt
again. When a volcano erupts, the land
around it can change rapidly. A bowlshaped crater may form around the main
vent in the center.
Gravity and Landslides
Earthquakes
In a landslide, a large amount of rock
and soil moves rapidly downhill. Heavy
rains can loosen rock on a steep slope or
hill. Then gravity or floods can pull the
rock and soil down to the bottom of the
slope. Landslides can destroy buildings,
trees, and roads.
Volcanoes
Deep under Earth’s surface, rock gets
very hot and melts, forming magma. Gases
in the magma make it rise toward the
surface. A volcano is a place on Earth’s
crust where magma reaches the surface. A
volcano is cone-shaped. Magma that flows
from a volcano is called lava. Sometimes
a volcano explodes in a violent eruption.
Hot rocks, ash, and gases burst from the
volcano’s openings, or vents. Sometimes the
lava flows out slowly.
Dormant and Active Volcanoes
A volcano is called dormant if it has not
erupted in a long time. A volcano is called
extinct if scientists think it will not erupt
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Chapter 7, Lesson 4 Summary
Earth’s crust is on top of another layer
called the upper mantle. The crust is
divided into large pieces called plates.
The plates are always moving. Most
earthquakes and volcanoes happen where
the plates meet.
A fault is a break or crack where Earth’s
crust can move. Sometimes, rocks get stuck
along a fault, but the plates keep moving
slowly. This puts pressure on the rocks until
they break. Then the plates move suddenly.
The sudden movement is an earthquake.
An earthquake causes vibrations that move
as waves. The waves move back and forth
and up and down. They can cause Earth’s
crust to crack.
In California, many people live along a
huge fault system called the San Andreas
Fault. It is more than 1300 kilometers (800
miles) long. Most earthquakes are small,
but some are strong. Strong earthquakes
can damage buildings, roads, and bridges.
Earthquakes can also cause landslides.
Landslides in the ocean can cause big
waves and flooding.
Intervention Study Guide
© Pearson Education, Inc. 4
earthquake a sudden movement that causes Earth’s crust to shake