It is proposed that transient volcanic explosions of the vulcanian type may provide a mechanism for the generation and dispersal of pyroclastic material on Venus. The influence of the Venusian high atmospheric pressure environment implies that continuous discharge plinian eruptive activity is relatively uncommon: the tendency for suppression of exsolution and expansion of magmatic gases favors effusive eruptions. However, it may be possible for explosive activity to occur, in a fashion analogous to vulcanian eruptions on Earth, as a result of the accumulation of hot, pressurized gas under a coherent rock ''lid''. The explosion may be initiated by the failure of this retaining caprock, causing the catastrophic release of the high-pressure gas, which expands out of the vent driving the fragmented caprock material ahead of it and displacing the surrounding atmosphere. On Earth the driving gas may originate either from vaporization of groundwater or from degassing of a stalled magma body in the near-surface crust, whereas on Venus, where the presence of crustal stores of volatile compounds is uncertain, the latter option only is favored: prolonged degassing may lead to an accumulation of gas sufficient to initiate an explosion. This paper presents the results of a numerical model describing the explosion process under boundary conditions representing the Venusian physical environment.

This involves treatments of the acceleration of the driving gas, caprock and displaced atmospheric gas out of the vent and the subsequent motions and aerodynamic interactions between the atmosphere and the ejected blocks of fragmented caprock. In this way, predictions of the eruption velocities and of the resulting distribution of (large) solid ejecta can be obtained for likely conditions on Venus. Deposits of large blocky debris are predicted to range up to a maximum distance of the order of 1 km from the vent on Venus, compared with distances of several kilometers commonly attained by ejecta from transient explosions on Earth. More typical blocky deposits may extend for only a few hundred meters, which implies that they would not be detected in the Magellan radar data. However, the possible presence of associated pyroclastic flow and fine-grained ashfall deposits may constitute aids to the identification of sites of vulcanian eruptions on Venus. ¿ American Geophysical Union 1995