Igneous Rock Tuff

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.

Meet our associated expert

This image was obtained from the Smithsonian Institution. The image or its contents may be protected by international copyright laws.

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Detailed geologic time scale.
From the Geologic Society of America, used with permission

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.

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

About Pyroclastic Density Currents

During an explosive eruption, a volcano ejects very hot ash, rock, pumice, and gas. This mixture can be directed up to the sky as an eruption column, or it can fall back to earth. When it falls to the ground, or when it is directed laterally (sideways), it produces a pyroclastic density current (PDC), commonly called a pyroclastic flow. These flows can move faster than 100 km/h (60 mph). Because they are loaded with rocks and pumice they can destroy almost anything in their path including trees and buildings. These are one of the most hazardous volcanic processes and have claimed many human lives. Sometimes PDCs deposit ash, pumice, and rock that are hot enough to melt back together. If such deposits are thick enough, the pumice are squeezed flat.

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