1. Earthquakes and Volcanoes Constructive Forces
Chapter 4 Lesson 2
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2. What is an earthquake? A sudden movement of Earth’s crust
The rock on both sides of a fault is pushed and pulled by forces in the crust
When layers of rock that are stuck together suddenly slip, an earthquake occurs
Slipping along a fault begins beneath Earth’s surface
The place where the slipping begins is called the earthquake’s focus
Waves of energy ripple outward from the focus. When they reach Earth’s surface, the waves spread out from a point directly above the focus: that point Is known as the epicenter
The amount of damage an earthquake causes partly depends on the amount of energy released at the earthquake’s focus
When more energy is released, more damage is likely to occur

3. What is an earthquake?
Earthquakes happen along the boundaries of tectonic plates because the pressure from the movement of the plates pushes on nearby faults
Alaska, Oregon, Washington, and California are near tectonic plates and most of the US Earthquakes occur here

4. How destructive is an earthquake?
Earthquakes release more energy than others.
There are two measure of earthquakes:The Richter Scale and the Mercalli Scale
The Richter scale measures magnitude at the epicenter
The Mercalli Scale measures what people felt and what happened to objects at a specific location when an earthquake occurs.
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5. What are volcanoes?
An opening in Earth’s crust.
They can form on land and on the ocean floor
Most volcanoes are found where tectonic plates meet and more likely to erupt at these places
Eruption is an outpouring of melted rock, ash, gases, or a combination of these
Scientists conclude that volcanoes tend to erupt where one plate is pushed under another plate
Plates melt under great heat and pressure as they are pushed down into the mantle
All volcanoes have at least one vent or opening.
Once magma reaches Earth’s surface it is called lava.

6. What are volcanoes?
An active volcano is currently erupting or has recently erupted.
A dormant volcano is one that has not erupted for some time
An extinct volcano has stopped erupting or is “dead”
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7. How do volcanoes BUILD land?
Sometimes magma cools and hardens before it reaches the surface
Lava forms solid rock as it hardens. Over thousands of years, new lava can increase the height of a volcano and form a volcanic mountain= new land
Shield Volcanoes, Cinder-Cone Volcanoes, and Composite Volcanoes are all examples of new land
See page 187 for pictures

8. How do volcanoes build islands?
The Hawaiian Islands are an island chain, or a line of volcanic mountains.
As the islands move, they pass over a stationary pool of magma called a hot spot.
Over millions of years, lava erupting from the hot spot formed a mountain