An exceptionally well preserved sand volcano cluster approximately 7 m (23 ft) in diameter lies on top of mass-wasting deposits in the Carboniferous Ross Formation in western Ireland. Sandstone dikes were observed near the volcanoes, emanating from sandstone units beneath the slumped intervals. The volcano cluster was the focus of sedimentary, geophysical (ground-penetrating radar), and surveying (differential global positioning system) methods, with the aim of digitally reconstructing the volcanoes in three dimensions and elucidating their origin and significance.

Data analysis determined that single volcanoes were, in fact, composite, with early small cones being overwhelmed by a later dominant cone during deposition. Volcanoes were sourced through feeder dikes that were correlated through slump horizons to underlying in-situ sandstones. A four-stage origin is inferred: (1) initial overpressured sand escaped up through tension gashes in the slump horizons to deposit multiple, small sand cones on the new sea floor; (2) more widely spaced vents allowed multiphase ejection to envelop initial cones and to produce larger volcanoes with a single vent; (3) composite volcanoes loaded and subsided into the underlying substrate and local sand chamber during continued deposition before final cessation; and (4) deposition of overlying pelagic sediments and lithification. Volcanoes may be sited on local sea-floor, topographic highs.