Studies of Klyuchevskoy Volcano eruptions have revealed a new type of explosive activity classified as pulsating spouting of incandescent bombs. These are series of abrupt impulses of increased rate of bomb ejection which occur at fixed intervals of first few seconds and accompany the weaker spouting. Analyses of published data and video records has shown that the same type of eruptive activity is typical for Tolbachinsky, Kilauea and Etna volcanoes which produce liquid andesite-basaltic magmas. In order to investigate the mechanism of pulsating spouting, authors upgraded the Complex Apparatus for Modeling Basaltic Eruptions (KAMBE) that had been designed earlier. A series of laboratory experiments in a transparent column (h = 16.6 м, Ø = 50 mm) allowed us to reveal a new gas-hydrodynamic regime of foamy bubble clusters. Analysis of natural volcanic and laboratory processes allows assuming that pulsating spouting of incandescent bombs is preceded by the regime of foamy bubble clusters occurring in the gas-liquid magmatic flow ascending along a volcano conduit.