1. Sheepeater Cliffs This photo shows columnar basalt at Sheepeater Cliff. The long vertical columns of the cliff are bounded by cooling fractures that formed as the thick lava flow cooled forming a regular set of joints perpendicular to the cooling surfaces

2. Mesa Falls ash-flow tuff and underlying fallout ash exposed in a quarry near Ashton, Idaho. This area was near the depositional margin of the ash flows and consequently the ash-flow tuff is nonwelded and contained abundant large pumice blocks. The tuff was deposited during a large eruption that produced the Henrys Fork caldera southwest of Yellowstone National Park 1.2 million years ago. Photograph by Dan Dzurisin.

3. Yosemite National Park, California. Specimen of metamorphosed tuff, showing faults, collected from the southwest slope of Mount Dana. Circa 1923.

4. During the May 18, 1980 eruption, at least 17 separate pyroclastic flows descended the flanks of Mount St. Helens. Pyroclastic flows typically move at speeds of over 60 miles per hour (100 kilometers

5. Beginning of pyroclastic flow from the August 7, 1980 eruption. USGS Photograph taken on August 7, 1980, by Peter W. Lipman.

6. MSH80_pyroclastic_flows_august7_on_july22_09-30-80.jpg August 7, 1980 pyroclastic flow on top of July 22, 1980 pyroclastic flow. USGS Photograph taken on September 30, 1980, by Lyn Topinka.

7. U.S. Geological Survey scientist examines pumice blocks at the edge of a pyroclastic flow from the May 18, 1980 eruption. USGS Photograph taken on May 30, 1980, by Donald A. Swanson.

8. MSH80_USGS_scientist_examines_pyroclastic_flow_05-30- 80.jpg U.S. Geological Survey scientist examines pumice blocks at the edge of a pyroclastic flow from the May 18, 1980 eruption.

9. Mount Rainier National Park, Washington. Coarse mudflow breccia of the Ohanapecosh Formation at Governors Ridge, near the eastern edge of the Sarvent lava complex. Angular to subrounded blocks of lava form a disrupted framework in a matrix of unstratified and

10. AVO Geologist gets a closer look at the ~4,600 year old pyroclastic flow deposite from Black Peak on the Alaska Peninsula. Picture Date: June, 2003 Image Creator: McGimsey, G.Image courtesy of AVO/USGS.

11. Detailed view of coarse volcanic tuff of post- Miocene age as exposed n shores of Balboa Bay. Moller district, Southwestern Alaska region, Alaska. 1908. Plate 10-B in U.S. Geological Survey. Bulletin 467. 1911.

12. Shore line stack or pillar on east shore of Unga Island. Composed of basaltic lavas and volcanic tuffs. Shumagin district, Southwestern Alaska region, Alaska. 1908. Plate 9-B in U.S. Geological Survey. Bulletin 467. 1911.