Formation
Precise formation mechanisms of rilles have yet to be determined. It is likely that different types formed by different processes. Common features shared by lunar rilles and similar structures on other bodies suggest that common causative mechanisms operate widely in the solar system. Leading theories include lava channels, collapsed lava tubes, near-surface dike intrusion, nuee ardente (pyroclastic cloud), subsidence of lava-covered basin and crater floors, and tectonic extension. On-site examination would be necessary to clarify exact methods.
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