Interbedded with the clastic fluvial sediments of the Munster Basin, the Lough Guitane Volcanic Complex represents a rare volcanic episode in the Upper Devonian of SW Ireland. From three distinctly separate volcanic centres, an exclusively rhyolitic suite of thick lava flows and tuffs were erupted. The largest of the centres possessed a system of contemporaneous faults producing a subcircular depressed area, itself enclosed within a graben 1.5 km across. These faults lead to rapid thickness variations in many volcanic units, and a pooled lava flow reaches a thickness of 300 m. The site of a major elongate vent lies along one such fault, and rapid erosion of its poorly lithified walls generated coarse sandstone boulder agglomerates and is related to the absence throughout the complex of normal air-fall tuffs unmixed with terrigenous sand.
The containment of the bulk of the volcanics by contemporaneous faults, and subsequent rapid burial by terrigenous sediments has led to preservation of the volcanic succession virtually intact.