Partly-welded pyroclast flow deposits in Dominica,Lesser Antilles

A Pleistocene pyroclast flow of dacitic andesite composition is described from the island of Dominica, Lesser Antilles. Lateral zonation, from welded tuff to a tuffaceous zone of no welding and pumiceous distal facies is observed with distance from the vent. Comparable but less distinct zonation occurs in vertical sections. Variations in physical properties of the pyroclast flow, such as specific gravity, flattening ratio and grain size are described, and related to the degree of welding. Source of the pyroclast flow is located in the former crater of Micotrin volcano, now plugged by a dome. Eleven chemical analyses reveal small, but significant variations in composition, which, together with systematic variations in phenocryst content, are related to crystal sinking in the magma column prior to eruption.