A deposit made of fragments of rock—from so-called ‘bombs’ to dust and ash—shattered by an explosive volcanic eruption. The coarser, heavier particles fall out close to the volcano vent, while the finer dust may be carried hundreds of kilometres. Tephrostratigraphy is the study of sequences of tephra layers and related deposits and their relative ages. It may be used as a tool for correlation in the study of stratigraphic sequences. See Hall and Mauquoy (2005) Holocene 15 on tephra dating, and Xia et al. (2007) Env. Geol. 51, 8 on correlating tephra layers.