Paleoflood-Generating Mechanisms on Earth, Mars, and Titan

Channelized, liquid flood flow occurs on Earth and has been inferred for Mars on the basis of morphology. (In this context, such flow is constrained to involve volatiles that can undergo phase transitions under surface conditions and can be stable as liquids over geologically significant periods of time.) On Titan, flood flow has also been inferred to occur or have occurred based on observed atmospheric phenomena and surface morphology. The mechanisms for generating flood flow vary for each of these three bodies. On Earth, the mechanism that generated the largest flooding is wide-spread glaciation, which requires an atmospheric cycle of a volatile that can assume the solid phase. Volcanism is also a prevalent cause for terrestrial megaflooding, with other mechanisms producing smaller, though more frequent, floods. On Mars, the mechanism for flood generation has changed over the history of the planet. Surface storage of floodwater early in the history of that planet gave way to subsurface storage as the climate cooled. As on Earth, flooding on Mars is an effect of the ability of the operative volatile to assume the solid phase, although on Mars, this has occurred in the subsurface. According to this paradigm, Titan conditions preclude extensive megaflooding because the operative volatile, which is methane, cannot easily assume the solid phase under present conditions. However, hypothesized glacial features on Titan may indicate that glaciation could have contributed to flooding, either under special conditions or under a different, past climate regime. By analogy with Earth, cryovolcanism may have contributed to flooding on Titan but has not been adduced from available data. The mechanisms that produce smaller but more frequent floods on Earth, namely extreme precipitation events, appear to be the most important flood generators on Titan under current conditions.