Igneous Rock Basalt

Associated Smithsonian Expert: Benjamin Andrews, Ph.D.

Geologist Ben Andrews on top of volcano Sant Maria, in Guatemala, looking down on Santiaguito.

Photographed by unknown source, Smithsonian Institution

Dr. Benjamin Andrews is a research geologist at the Smithsonian National Museum of Natural History who specializes in the study of volcanoes around the world. While growing up in Portland, Oregon, he often went hiking and backpacking in the nearby Cascade Range, home to Mount St. Helens and other volcanoes, and the Columbia River Gorge, lined with basalt. Prior to his senior year of high school, Andrews took a six-week geology field course with the Oregon Museum of Science and Industry; an experience that convinced him to make the study of volcanoes his career. After earning his doctorate from the University of Texas in 2009, he worked as a postdoctoral fellow at the University of California at Berkeley before joining the Smithsonian in 2011. In 2012 Andrews and researchers from Italy, Germany, and the United States traveled to Guatemala to study ongoing changes to the active lava dome of Santa Maria, an erupting volcano. At the Smithsonian, he runs experiments that simulate pyroclastic density currents of materials spewing from volcano vents, and he also is doing ongoing research on volcanoes in California and the Kamchatka Peninsula of Russia. Andrews and several of his colleagues participate in the Smithsonian?s Global Volcanism Program, which tracks the activity of volcanoes worldwide.

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This image was obtained from the Smithsonian Institution. The image or its contents may be protected by international copyright laws.
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Contact between igneous diabase (left) and metamorphic hornfels (right), which used to be sedimentary siltstone. Location: Manassas Quarry, Manassas, VA.
Photographed by Donald E. Hurlbert, Smithsonian Institution

About Extrusive Igneous Rocks

When molten rock (magma) reaches Earth's surface, it solidifies or hardens. Scientists call the resulting solid rocks "extrusive" igneous rocks. Extrusion is the process of pushing material out to the surface of the Earth's crust. At some volcanoes, the extrusive rock flows as lava across the ground before it hardens; the ripples in the lava may freeze in place. Hot, rapidly expanding gases within other volcanoes' vents can force the magma out explosively, forming pumice: low-density rock full of vesicles, or frozen bubbles. Extrusive igneous rocks are easy to find near many volcanoes, such as Mount St. Helens in Washington state. Hawai`i Volcanoes National Park, home of two active volcanoes, contains lava flows that cooled only a few decades, or minutes, ago.

Volcanic rock quarry in Washington. Dark gray basalt covered by volcanic ash and soil. Location: White River Quarry, Enumclaw, WA.
Photographed by Donald E. Hurlbert, Smithsonian Institution

How People Build with Rocks from White River Quarry

The 25-million-year-old basalt from the White River Quarry is very hard and durable. This makes it an ideal rock for building walls, roads, dams, and buildings. Because the quarry is located near the coast, its products are also used to stabilize slopes, prevent erosion, build sea-walls, and protect seaports.

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This dam in Washington, USA, is constructed primarily from basalt from a quarry that mines the Ancestral Cascades.
Photographed by Donald E. Hurlbert, Smithsonian Institution

About White River Quarry

The White River Quarry is made up of basalt lava flows that date back to 25 million years ago and is part of what is known as the Ancestral Cascades. This time pre-dates the more well-known volcanoes in the area such as Mt. St. Helens, Mt. Rainier, and Mt. Adams. Above the old basalt lava flows are layers of younger sediments, including those deposited by glaciers and rivers, more recent eruptions, and a 4,800-year-old volcanic mudflow that covers areas all the way from Mt. Rainier to Tacoma, Washington. The old volcanic rock is very hard and dense, which makes it very useful for construction projects.

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