EarthWord: Batholith

Release Date:

Despite sounding like something out of Harry Potter, a batholith is a type of igneous rock that forms when magma rises into the earth’s crust, but does not erupt onto the surface. The magma cools beneath the earth’s surface, forming a rock structure that extends at least one hundred square kilometers across (40 square miles), and extends to an unknown depth.

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Image: Moon over Half Dome
Moonrise over Yosemite’s Half Dome, a prominent feature of the Sierra Nevada batholith. Image credit: Alex Demas, USGS.

Definition:

  • Despite sounding like something out of Harry Potter, a batholith is a type of igneous rock that forms when magma rises into the earth’s crust, but does not erupt onto the surface. The magma cools beneath the earth’s surface, forming a rock structure that extends at least one hundred square kilometers across (40 square miles), and extends to an unknown depth.

Etymology:

  • Bath– comes from the Greek for “deep,” and -lith, also from Greek, means “rock.” For instance, another name for the Stone Age is the Paleolithic age.

Use/Significance in the Earth Science Community:

  • Batholiths and other geologic formations are important to geologists and geophysicists, as various rock types have different meanings for natural hazards, mineral resources, and ecology.

USGS Use:

  • Knowing the origin and type of rock formations is helpful to a variety of USGS scientific projects. Batholiths are often subject to significant internal stress, which affects natural hazards like landslides and earthquakes. In addition, since batholiths are nearly always made of rocks that contain feldspar and quartz, knowing the location of batholiths helps with our mineral studies.

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