Explosive eruption that ejects lava fragments that do not take on a rounded shape during their flight through the air, because the lava is too viscous or already solidified. These explosive eruptions, which are moderate-sized if compared e.g. to plinian eruptions, commonly eject a large proportion of volcanic ash, breadcrust bombs and blocks. Andesitic and dacitic magmas are most often associated with vulcanian eruptions, because their high viscosity (resistance to flow) makes it difficult for the dissolved volcanic gases to escape except under extreme pressure, which leads to explosive behavior. Vulcanian eruptions are named for Vulcano, one of the Aeolian Islands north of Sicily.
Anak Krakatau in a vulcanian eruption, 23. November 2007. Note bombs or blocks near the ash plume. Photo Marco Fulle. More images from this eruption.