A pyroclastic flow deposit on Venus
Explosive volcanism on Venus is severely inhibited by its high atmospheric pressure and lack of water. This paper shows that a deposit located near 16°S, 145°E, here referred to as Scathach Fluctus, displays a number of morphological characteristics consistent with a pyroclastic flow deposit. These characteristics, particularly the lack of channelization and evidence for momentum- rather than cooling-limited flow length, contrast with fissure-fed lava flow deposits. The total erupted volume is estimated to have been between 225 and 875 km3 but this may have been emplaced in more than one event. Interaction between Scathach Fluctus and a small volcanic cone constrains the flow velocity to 48 m s−1, and plausible volatile concentrations to at least 1.8 wt% H2O, 4.3 wt% CO2 or 6.1 wt% SO2, the latter two values implying that magma was sourced directly from the mantle. The deposit has radar characteristics, particularly an exponential backscatter function, that are similar to those of nearly half the planetary surface, implying that pyroclastic deposits may be much more common on Venus than has been recognized to date, and suggesting both a relatively volatile-rich mantle and a volcanic source for atmospheric SO2.