VHP Photo Glossary: Basalt
Basalt
Basalt is a hard, black volcanic rock with less than about 52 weight percent silica (SiOMore about volcanic and plutonic rocks.
Did you know?
- Basalt is the most common rock type in the Earth's crust (the outer 10 to 50 km). In fact, most of the ocean floor is made of basalt.
- Huge outpourings of lava called quot;flood basaltsquot; 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.