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

• geyser
• hot spring
• lava dome
• lava plateau

Introduction

Volcanoes are associated with many types of landforms. The landforms vary with the composition of the magma that created them. Hot springs and geysers are also examples of surface features related to volcanic activity.

Landforms from Lava

Volcanoes and Vents

The most obvious landforms created by lava are volcanoes, most commonly as cinder cones, composite volcanoes, and shield volcanoes. Eruptions also take place through fissures (Figure below). The eruptions that created the entire ocean floor are essentially fissure eruptions.

Lava Domes

When lava is viscous, it is flows slowly. If there is not enough magma or enough pressure to create an explosive eruption, the magma may form a lava dome. Because it is so thick, the lava does not flow far from the vent. (Figure below).

Lava flows often make mounds right in the middle of craters at the top of volcanoes, as seen in the Figure below.

Lava Plateaus

A lava plateau forms when large amounts of fluid lava flows over an extensive area (Figure below). When the lava solidifies, it creates a large, flat surface of igneous rock.

Land

Lava creates new land as it solidifies on the coast or emerges from beneath the water (Figure below).

Over time the eruptions can create whole islands. The Hawaiian Islands are formed from shield volcano eruptions that have grown over the last 5 million years (Figure below).

Landforms from Magma

Magma intrusions can create landforms. Shiprock in New Mexico is the neck of an old volcano that has eroded away (Figure below).

Hot Springs and Geysers

Water sometimes comes into contact with hot rock. The water may emerge at the surface as either a hot spring or a geyser.

Hot Springs

Water heated below ground that rises through a crack to the surface creates a hot spring (Figure below). The water in hot springs may reach temperatures in the hundreds of degrees Celsius beneath the surface, although most hot springs are much cooler.

Geysers

Geysers are also created by water that is heated beneath the Earth’s surface, but geysers do not bubble to the surface — they erupt. When water is both superheated by magma and flows through a narrow passageway underground, the environment is ideal for a geyser. The passageway traps the heated water underground, so that heat and pressure can build. Eventually, the pressure grows so great that the superheated water bursts out onto the surface to create a geyser (Figure below).

Conditions are right for the formation of geysers in only a few places on Earth. Of the roughly 1,000 geysers worldwide and about half are found in the United States.

Lesson Summary

• Viscous lava can produce lava domes along a fissure or within a volcano.
• Lava plateaus form from large lava flows that spread out over large areas.
• Many islands are built by or are volcanoes.
• Igneous intrusions associated with volcanoes may create volcanic landforms.
• When magma heats groundwater, it can reach the surface as hot springs or geysers.

Review Questions

1. What are four different landforms created by lava?
2. What is the major difference between hot springs and geysers?
3. The geyser called Old Faithful has been erupting for perhaps hundreds of years. One day, it could stop. Why might geysers completely stop erupting?
4. After earthquakes, hot springs sometimes stop bubbling, and new hot springs form. Why might this be?

Points to Consider

• What might the Earth look like if there were no tectonic plates? Are there any planets or satellites (moons) that may not have tectonic plates? How is their surface different from that of the Earth?
• The largest volcano in the solar system is Olympus Mons on Mars. How could this volcano have formed?
• What kind of land formations are the result of volcanic activity? Are all of these created by extrusive igneous rocks?
• How are hydrothermal vents at mid-ocean ridges like the geysers of Yellowstone?