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What Geothermal Heat Causes Rocks to Do

Geothermal energy, the heat stored within the earth, is the result of several processes. These include the friction between tectonic plates and the gradual decay of radioactive particles in the earth's iron core. The extreme temperatures at the center of the earth have a dramatic impact on the movement and formation of rocks.

The Creation of Magma
- The creation of magma depends on the geothermal gradient: the change in the earth's temperature with depth or pressure. Under the right temperature and pressure conditions, rocks melt into a liquid which, combined with crystal and dissolved gases, creates magma. This hot flowing substance, which ranges in temperature from 650 to 1,200 degrees Celcius, can be a powerful force, alters the structure of Earth's crust and forms new types of rock.
Lava Flow and Volcanic Eruption
- Magma is less dense than surrounding rock, therefore it rises through fissures and vents in the earth. Some magma reaches the surface and oozes out gradually, forming lava flow. However, thick magma may become trapped as pressure builds up below the crust, resulting in a violent eruption. When eruptions occur on large, steep volcanoes, rocks and other debris along the slope become unstable, resulting in an avalanche. Movement of the entire base of bedrock down a slope is called a landslide. Avalanches and landslides radically transform the rock structures of an area.
Igneous Rock Formation
- Magma created by geothermal heat can either be extruded (forced out) onto the surface of the earth, as with a volcanic eruption, or can become trapped in small pockets below the earth's crust. In these cases, the magma cools and a gradual crystallization process forms a solid mass, known as igneous rock. The rate of cooling determines the properties of the new rock: slow cooling results in larger crystals.
Metamorphic Rock Formation
- Another source of geothermal heat, the movement of tectonic plates, dramatically affects rock formation. Friction between moving plates causes not only intense heat but tremendous pressure on the rocks at the plate borders. When the atoms in the minerals making up igneous or sedimentary rock are exposed to this heat and pressure, they rearrange, freeing ions (charged atomic particles) and assuming a more stable structure. In this way, geothermal heat alters the basic molecular structure of rocks.

Rocks & Minerals