- Some people have theorized that if a huge asteroid hits the Earth, the results would be
catastrophic. How might an asteroid impact and a supervolcano eruption be similar?
8.4 Volcanic 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.
Introduction
As you know, magma is molten rock found beneath the Earth’s surface. Sometimes, it
appears at the surface of the Earth as lava after moving through a volcano. At other times,
magma does not come to the surface, but stays underground. In both cases, the magma
eventually solidifies and the resulting rocks and formations are igneous. The rocks that
solidify beneath the ground are calledintrusiverocks, while those that solidify above the
surface are calledextrusiverocks. Extrusive rocks are sometimes small rocks that you can
hold in your hand. At other times, entire landforms are created when lava flows onto the
surface. Intrusive rocks do not always remain hidden below the surface. They can appear
on the surface when rocks that once covered them are eroded away, exposing the intrusive
igneous rock. Hot springs and geysers are some more examples of surface features related to
igneous rock.
Landforms from Lava
The most obvious landforms created by lava are volcanoes. Volcanoes, of course, are the
places where lava comes to the surface. As already discussed, volcanoes come in many forms,
most commonly as cinder cones, stratovolcanoes, and shield volcanoes. However, lava can
create other notable landforms, as described below.
Lava Domes
When lava is fairly viscous, it is thick and flows slowly. Although it might not be so viscous
that it causes an explosive eruption, it can create a large sort of round “blob” or alava
dome.Because it is so thick, it does not flow far from the vent from which it came. In fact,
lava flows often make mounds right in the middle of craters at the top of volcanoes (Figure
8.27andFigure8.28).