Incision of Ma'adim Vallis (Mars) by dry volcanic megafloods effused from multiple highland sources

The Ma'adim Vallis channel system extends ~900 ​km northward across the highlands of Terra Cimmeria into Gusev crater. Formation of this system has previously been attributed to the past operation of aqueous processes variously involving periodic surface runoff from adjacent intercrater plains, releases from one or more highland lakes, sudden and voluminous effusions of groundwater, and/or basal sapping. Some researchers have interpreted Ma'adim Vallis as a product of multiple discrete episodes of highland water flow that collectively occurred over a broad time frame extending from the Noachian to the Amazonian, but others have favored catastrophic development of the system as a result of the partial drainage of a long-lived lake hypothesized to have existed in the Eridania basin in the Late Noachian. Problematically, clear geomorphological and mineralogical evidence is lacking for the past voluminous flow of water along Ma'adim Vallis, and for the existence of one or more long-lived water bodies in adjacent highlands. Instead, the properties of Ma'adim Vallis suggest dry volcanic origins involving effusions of low-viscosity flood lavas from multiple highland sources during the Noachian and Hesperian. The geochemistry of lavas accumulated near the mouth of Ma'adim Vallis suggests viscosities sufficiently low to have allowed for substantial incision into bedrock substrates if lavas were erupted at high effusion rates and with high total volumes. Formation of Ma'adim Vallis is estimated to have required effusion of a minimum lava volume of ~112,000 ​km³. Development of many other highland channel networks on Mars is expected to have involved analogous volcanic processes.