The entrance of pyroclastic flows into the sea, II. theoretical considerations on subaqueous emplacement and welding

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Theoretical models of debris flow emplacement suggest that some types of pyroclastic flow can move into and maintain their integrity underwater. These subaqueous flows can be emplaced at high temperature, cooling only tens of degrees centigrade. Due to the high solubility of steam in rhyolitic glass at pressures of tens of bars, there can be a substantial reduction in glass viscosity after emplacement at moderate water depths. We propose that a subaqueous environment can be more favorable to welding than many subaerial environments. Only flows denser than water are capable of a smooth transition into water. At shallow water depths the interaction of water with hot ash at the flow boundary is potentially explosive which could lead to the destruction of some dense flows. Conditions favorable to the passage of a pyroclastic flow into deep water include steep slopes and large flow rates. © 1980.

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Journal of Volcanology and Geothermal Research