Frozen block of pumice (>50 cm) of White River Ash (WRA) on the rim of Churchill caldera. Surface fines have been winnowed away since the eruption (846-847 CE); however, a few inches below this surface is solid (frozen) WRA.
Image courtesy of AVO/USGS.
Please cite the photographer and the Alaska Volcano Observatory / U.S. Geological Survey when using this image. Full Resolution.