The Apparent Absence of Kilometer-Sized Pyroclastic Volcanoes on Mercury: Are We Looking Right?

Abstract

Spacecraft data reveal that volcanism was active on Mercury. Evidence of large-volume effusive and smaller-scale explosive eruptions has been detected. However, only large (>~15 km) volcanic features or vents have been found so far, despite abundant high-resolution imagery. On other volcanic planets, the size of volcanoes is anticorrelated with their frequency; small volcanoes are much more numerous than large ones. Here we present results of a numerical model that predicts the shapes of ballistically emplaced volcanic edifices and hence can explain the lack of kilometer-sized constructional explosive volcanoes on the surface of Mercury. We find that due to the absence of the atmosphere, particles are spread on this planet over a larger area than is typical for Earth or Mars. Erupted volumes are likely insufficient to build edifices with slope angles that enable their easy recognition with currently available data or that could survive destruction by subsequent impact bombardment.