Chapter 5 Fast Changes on Earth
Lesson 3 Volcanoes
Main Idea
Sudden changes to the Earth’s surface can be caused by volcanoes
Vocabulary
Volcano (262) – a mountain that builds up around an opening in Earth’s crust
Hot spot (264) – a place where magma partially melts through Earth’s crust
Crater (266) – a cup like shape formed around the vent of a volcano
What is a volcano?
Main Idea
Magma making its way to the surface is a volcano
Supporting Details
1. A volcano is a mountain that builds up around an opening in the Earth’s crust.
2. An eruption occurs when the melted rock, gases, and pieces of rock are forced out of a
volcano
3. Trapped gasses build up pressure which can lead to an explopsive eruption
4. Magma rises through the opening (vent) in a volcano.
5. Once the lava reaches the surface, it is called lava
6. Lava can ooze from the volcano slowly or be release in an explosion
7. When lava flows, it cools and hardens – sometimes causing a mountain to form.
Where do volcanoes form?
Main Idea
Volcanoes form along Earth’s moving plates and at hot spots
Supporting Details
1. Where Earth’s plates move together,
a. one plate can be pushed under the other
b. the plate moving down melts and is changed to magma
2. Like heated air or water, magma rises up through the Earth’s crust forming a volcano
3. Rift volcanoes
a. form where the plates move apart
b. form along the edges of the spreading plates
c. Most rift volcanoes form under the ocean
4. Hot spots
a. Volcanoes can form along hot spots where magma melts through the Earths
surface
b. Island of Hawaii is an example of an active volcano over a hot spot
c. Island of Kauai passed over the hot spot long ago and is now dormant, no longer
erupts
What are some kinds of volcanoes?
Main Idea
Some kinds of volcanoes are cinder cones, shields, and composite
Supporting Details
1. A cinder cone
a. has steep sides
b. is formed when gases in thick magma explode
c. causing lava to burst into the air.
d. Consists of rock fragment layers
e. Cuplike shape formed around the vent is the crater
2. Shield volcano
a. Wide, flat sides
b. Formed by layers of lava that flow gently in all directions
3. Composite volcano
a. Made up of layers of rock fragments, lava, and ash
b. Forms during periods of quiet and explosive eruptions
c. Over time, the layers build up forming a cone
d. Is symmetrical – shape on one side of the cone matches the shape on the other
side
How can you be safe around volcanoes?
Main Idea
You can protect yourself during an erupting volcano by being prepared.
Supporting Details
1. Stay away from active volcano sites and flowing lava
2. Have a pair of goggles and breathing mask available for each member of the family in
your safety kit
3. If your town has a warning, follow all directions
4. Leave the area immediately if told to, wear long sleeve shirt and long pants
5. If you are inside during an eruption, close all windows and doors. Ensure all pets are
inside.
6. If you are caught outdoors, find the nearest shelter and stay inside.