Dacite
Volcano Terms and Definition


NOVA - In the Path of a Killer Volcano
The scientists who remain behind- and see some astonishing footage of the world's largest volcanic eruption in 80 years. Local tribes people were the first to see the signs. "There was a flash of light from the sky"

Close view of dacite lava from the May 1915 eruption of Lassen Peak, California
Dacite


Dacite lava is most often light gray, but can be dark gray to black. Dacite lava consists of about 63 to 68 percent silica (SiO 2 ). Common minerals include plagioclase feldspar, pyroxene, and amphibole. Dacite generally erupts at temperatures between 800 and 1000°C. It is one of the most common rock types associated with enormous Plinian-style eruptions. When relatively gas-poor dacite erupts onto a volcano's surface, it typically forms thick rounded lava flow in the shape of a dome.

  • Even though it contains less silica than rhyolite, dacite can be even more viscous (resistant to flow) and just as dangerous as rhyolites. These characteristics are a result of the high crystal content of many dacites, within a relatively high-silica melt matrix. Dacite was erupted from Mount St. Helens 1980-86, Mount Pinatubo in 1991, and Mount Unzen 1991-1996.
  • The word dacite comes from Dacia, a Roman province found between the Danube River and Carpathian Mountains, where the rock was first described.

National Geographic - Volcano
The most dazzling but destructive natural force on earth. Massive volcanic eruption can turn day into night, releasing the power of an atomic blast.

Volcano Glossary


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Source:
U.S. Department of the Interior