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Igneous Landforms and
Geothermal Activity
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Printed: March 10, 2013
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C ONCEPT
Concept 1. Igneous Landforms and Geothermal Activity
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Igneous Landforms and
Geothermal Activity
Lesson Objectives
• List and describe landforms created by lava.
• Explain how magma creates different landforms.
• Describe the processes that create hot springs and geysers.
Vocabulary
•
•
•
•
•
lava dome
lava plateau
intrusion
hot spring
geyser
Landforms from Lava
Extrusive igneous rocks cool at the surface. Volcanoes are one type of feature that forms from extrusive rocks.
Several other interesting landforms are also extrusive features. Intrusive igneous rocks cool below the surface.
These rocks do not always remain hidden. Rocks that formed in the crust are exposed when the rock and sediment
that covers them is eroded away.
Lava Domes
When lava is thick, it flows slowly. If thick lava makes it to the surface, it cannot flow far from the vent. It often
stays right in the middle of a crater at the top of a volcano. Here the lava creates a large, round lava dome (Figure
1.1).
Lava Plateaus
A lava plateau is made of a large amount of fluid lava. The lava flows over a large area and cools. This creates a
large, flat surface of igneous rock. Lava plateaus may be huge. The Columbia Plateau covers over 161,000 square
kilometers (63,000 square miles). It makes up parts of the states of Washington, Oregon, and Idaho.
Thin, fluid lava created the rock that makes up the entire ocean floor. This is from multiple eruptions from vents at
the mid-ocean ridge. While not exactly a lava plateau, it’s interesting to think about so much lava!
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FIGURE 1.1
The Mono Craters in California are lava
domes.
New Land
New land is created in volcanic eruptions. The Hawaiian Islands are shield volcanoes. These volcanoes formed from
fluid lava (Figure 1.2). The island grows as lava is added on the coast. New land may also emerge from lava that
erupts from beneath the water. This is one way that new land is created.
FIGURE 1.2
Lava erupts into the Pacific Ocean in
Hawaii, creating new land.
Landforms from Magma
Magma that cools underground forms intrusions (Figure 1.3). Intrusions become land formations if they are
exposed at the surface by erosion.
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Concept 1. Igneous Landforms and Geothermal Activity
FIGURE 1.3
The granite intrusions that form the Sierra
Nevada in California are well exposed.
Hot Springs and Geysers
Water works its way through porous rocks or soil. Sometimes this water is heated by nearby magma. If the water
makes its way to the surface, it forms a hot spring or a geyser.
Hot Springs
When hot water gently rises to the surface, it creates a hot spring. A hot spring forms where a crack in the Earth
allows water to reach the surface after being heated underground. Many hot springs are used by people as natural
hot tubs. Some people believe that hot springs can cure illnesses. Hot springs are found all over the world, even in
Antarctica!
Geysers
Geysers are also created by water that is heated beneath the Earth’s surface. The water may become superheated by
magma. It becomes trapped in a narrow passageway. The heat and pressure build as more water is added. When the
pressure is too much, the superheated water bursts out onto the surface. This is a geyser.
There are only a few areas in the world where the conditions are right for the formation of geysers. Only about 1,000
geysers exist worldwide. About half of them are in the United States. The most famous geyser is Old Faithful at
Yellowstone National Park (Figure 1.4). It is rare for a geyser to erupt so regularly, which is why Old Faithful is
famous.
Lesson Summary
• Very thick lava that doesn’t travel very far can produce lava domes at or near the Earth’s surface or even within
a volcano.
• Lava plateaus and the entire ocean floor form from large lava flows that spread out over large areas.
• Many islands are formed from volcanoes.
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FIGURE 1.4
Old Faithful geyser in Yellowstone National Park erupts every 60 to 70
minutes, with a plume of hot water shooting up nearly 60 meters in the
air.
• Magma can also cool and crystallize below the Earth’s surface forming igneous intrusions.
• When magma heats groundwater, it can form hot springs and geysers.
Lesson Review Questions
Recall
1. What types of landforms form from intrusive igneous activity?
2. What types of landforms are created by lava?
Apply Concepts
3. How does new land form? Are the oceans being taken over by land? Why or why not?
Think Critically
4. Millions of people flock to Yellowstone National Park each year. Why are they drawn to the place? Would it be
visited as much if the park were full of hot springs that were not geysers?
5. Do you think that Old Faithful will some day stop erupting? Why would it do that?
Points to Consider
• What might the Earth look like if there were no tectonic plates? Can you think of any planets or satellites
(moons) that may not have tectonic plates? How is their surface different from that of the Earth?
• What kind of land formations have you seen that may have been created by volcanic activity? Did these rocks
cool above or below the Earth’s surface?
• Water is not the only material that can be ejected from geysers and hot springs. What other materials might be
ejected from geysers and hot springs?
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Concept 1. Igneous Landforms and Geothermal Activity
Opening image by Boaworm. http://en.wikipedia.org/wiki/File:Fimmvorduhals_second_fissure_2010_04_02.JPG.
CC-BY 3.0.
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