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| A B C D E F G H I J K L M N O P Q R S T U V W X Y Z |
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basalt
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Credit: U.S. Geological Survey |
Because of basalt's low viscosity, basaltic lava can flow quickly and easily move than 20 km from a vent. The low viscosity typically allows volcanic gases to escape without generating enormous eruption columns. Basaltic lava fountains and fissure eruptions, however, still form explosive fountains hundreds of meters tall. Basalt is erupted at temperatures between 1100° to 1250° C.
Basalt is the most common extrusive igneous rock on the terrestrial planets and is the most common rock type in the Earth's crust (the outer 10 to 50 km). It covers about 70% of Earth's surface, including most of the ocean floor.
Huge outpourings of lava called flood basalts are found on many continents. The Columbia River basalts, erupted 15 to 17 million years ago, cover most of southeastern Washington and regions of adjacent Oregon and Idaho.
Basaltic magma is commonly produced by direct melting of the Earth's mantle, the region of the Earth below the outer crust. On continents, the mantle begins at depths of 30 to 50 km.
Shield volcanoes, such as those that make up the islands of Hawai'i, are composed almost entirely of basalt.
Uses of basalt
Basalt was widely used by the ancient Egyptians for their sculpture, and in the construction of tombs and obelisks. The name is also applied to a pottery of basalic appeaance made by Josiah Wedgewood.
Related category
• GEOLOGY AND PLANETARY SCIENCE
Source: U.S. Geological Survey
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