Figure 8.31: Even some animals enjoy relaxing in nature’s hot tubs. ( 7 )derground, the environment becomes ideal for a geyser. The narrow passageway traps the
heated water underground, where heat and pressure continue to build. Sooner or later, the
pressure grows so great that the superheated water bursts out onto the surface. This explo-
sion is called ageyser. There are only a few areas in the world where the conditions are
right for the formation of geysers. About 1,000 geysers exist worldwide and about half of
those are found in the United States of America. Perhaps the most famous geyser is Old
Faithful, which erupts every 60 to 70 minutes in a plume of hot water nearly 60 meters in
the air. It is rare for a geyser to erupt regularly, which contributes to Old Faithful’s fame
(Figure8.32).
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 form from large lava flows that spread out over large areas.
- Many islands are formed from volcanoes.
- Magma can also cool and crystallize below the Earth’s surface forming igneous intru-
sions. - When magma heats groundwater, it can form hot springs and geysers.
Review Questions
- What is the difference between intrusive and extrusive rocks?