pyroclastic rock

USGS scientist examines pumice blocks at the edge of a pyroclastic flow from Mount St. Helens Rocks from the Bishop Tuff, uncompressed with pumice on left; compressed with fiamme on right. Flight through a μCT-image stack of a lapillus of the volcano Katla in Iceland. Find spot: Beach near Vik at the end of road 215. Acquisition done using "CT Alpha" by "Procon X-Ray GmbH", Garbsen, Germany. Resolution 11,2μm/Voxel, width approx. 24 mm. 3D-Rendering of the above image stack, in parts transparent. Heavy particles in red.

Pyroclastic rocks are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroclasts. Pyroclastic rocks are a type of volcaniclastic deposit, which are deposits made predominantly of volcanic particles. Phreatic pyroclastic deposits are a variety of pyroclastic rock formed from volcanic steam explosions and are entirely composed of accidental clasts. Phreatomagmatic pyroclastic deposits are formed from explosive interaction of magma with groundwater. Pyroclastic material has been produced during some of history's most powerful volcanic eruptions, including the 79 AD eruption of Mount Vesuvius, the 1980 eruption of Mount St. Helens, the large eruptions from the Yellowstone Caldera, and the 1991 eruption of Mount Pinatubo. The word pyroclastic comes from the Ancient Greek words pyr, meaning "fire", and klastos, meaning "broken in pieces".