ash « Back to Glossary IndexVolcanic tephra that is less than 2 mm in diameter. Related Articles: 16 Energy and Mineral Resources2 Plate Tectonics4 Igneous Processes and Volcanoes5 Weathering, Erosion, and Sedimentary Rocks7 Geologic Time« Back to Glossary Index Author: Chris Associate Professor, Salt Lake Community College, Salt Lake City, Utah View all posts by Chris