Characteristics
Vulcanian eruptions display several common characteristics. The mass of rock ejected during the eruption is usually between 102 - 106 tonnes and contains a high proportion of non-juvinial material (> 50%). During active periods of volcanic activity, intervals between explosions vary from less than 1 minute (e.g. Anak Krakatoa) to about a day. Pyroclastic flows are also common features of this type of eruption. The gas streaming phase of these eruptions are characterised discrete canon-like explosions, which are a particular features of vulcanian eruptions. These expulsions of gas can reach supersonic velocities resulting in shock waves.
The tephra is dispersed over a wider areas than that from Strombolian eruptions. The pyroclastic rock and the base surge deposits form an ash volcanic cone, while the ash covers a large surrounding area. The eruption ends with a flow of viscous lava. Vulcanian eruptions may throw large metre-size blocks several hundred metres, occasionally up to several kilometres.
Vulcanian eruptions are dangerous to persons within several hundred metres of the vent. One feature of this type of eruption is the "Volcanic bomb." These can be blocks often 2 to 3 m in dimensions. At Galeras a vulcanian eruption ejected bombs which impacted with several volcanologists who were in the crater and many died or suffered terrible injuries.
Read more about this topic: Vulcanian Eruption