from The American Heritage® Dictionary of the English Language, 4th Edition

  • adj. Composed chiefly of rock fragments of volcanic origin.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • adj. Mostly composed of rock fragments of volcanic origin
  • n. A rock mostly composed of rock fragments of volcanic origin

from The Century Dictionary and Cyclopedia

  • Formed by volcanic agencies, or in the process of being erupted: applied to volcanic breccia or to any angular or comminuted material of igneous origin.
  • n. A pyroclastic rock.


from Wiktionary, Creative Commons Attribution/Share-Alike License

From pyro- +‎ clastic, from Ancient Greek πῦρ (pur, "fire"), and κλαστός (klastos, "broken").


  • The heavier particles stay close to the ground and roll downhill in what we call a pyroclastic flow.

    Asimov's Science Fiction

  • Hundreds of thousands of people live beneath it and could be hit with what are known as pyroclastic flows -- extremely fast-moving, dense clouds of hot ash and rock that flow down the mountain.

    Scientists find it difficult to predict volcano behavior

  • At least 90 people were killed as a superheated clouds of ash, gas and debris known as pyroclastic flows tumbled down the mountain and incinerated villages.

    Some Flights Resume Following Indonesia Volcano

  • Red-hot clouds of gas and fine ash known as pyroclastic density currents flowed down the slopes of Vesuvius, engulfing Pompeii's frescoed villas, as well as its shops, public baths and brothels, where explicit erotic paintings and the customers' graffiti can still be seen. Top Stories

  • Scorching flows of gas and rock - called pyroclastic flows - that spew during each eruption were seen on Merapi's southern slopes just before midnight Friday at speeds of up to 60 mph

    Yahoo! News: Business - Opinion

  • The photo also shows a ground-hugging plume of light gray ash, probably a mix of hot gas and ash in what volcanologists call a pyroclastic flow, descending from the volcano summit.

    Mr. Barlow's Blog

  • An eruption might create something called a pyroclastic flow, or high-speed avalanche of hot rocks and gas.


  • This explanation states that while covering a distance of some three kilometers, the pyroclastic flow picked up volcanic bombs or incandescent blocks of various sizes which began to rotate as they were pushed along, finally acquiring a spherical shape.

    Las Piedras Bola: the great stone balls of Ahualulco

  • These appear to be the biggest manifestations on our planet of a rare pyroclastic-flow crystallization phenomenon.

    The remarkable road to San Marcos, Jalisco

  • Do you think you are far enough away to avoid the pyroclastic flow?

    Tom McIntyre Explains His Picks for our 2009 Hunting and Fishing Heroes and Villians Face-Off


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