Modeling the Dynamics of Dense Pyroclastic Flows on Venus: Insights Into Pyroclastic Eruptions

摘要

On Venus, relatively young deposits near volcanic and coronal summits with unique radar characteristics have been proposed to be emplaced by pyroclastic density currents (PDCs). The proposed units are laterally extensive, long-runout deposits showing moderate to high radar backscatter and circular polarization ratio in 12.6 cm wavelength synthetic aperture radar data. Previous studies have hypothesized that a recent resumption of volcanic activity in the form of PDC-forming eruptions could have emplaced these deposits. We model the dynamics of dense PDCs using a 2D, depth-averaged framework focusing on regions where stereo-derived topography coverage is available; this includes the flanks of Irnini Mons, Anala Mons, Didilia Corona, and Pavlova Corona. Two different mechanisms of initiation which includes impulsive collapse of an eruption column and sustained pyroclastic fountaining are considered. The results emphasize the importance of pyroclastic flow fluidization via high pore pressure in emplacing long-runout deposits along gently sloping (1.2-1.4 km tall as well as pyroclastic fountains lasting >400 s with fountain heights of 50 m are capable of generating pyroclastic flows that could emplace some of the smaller deposits studied. For the large deposits at Irnini Mons, more energetic flows resulting from taller column heights would be necessary; the dynamics of such flows under Venus's conditions are not well understood. Distinguishing between the two initiation styles, that is, column collapse and sustained fountaining is not feasible with currently available datasets and would require higher resolution imagery and topography data.