Rille

Rille /ˈrɪl/[1] (German for 'groove') is typically used to describe any of the long, narrow depressions in the surface of the Moon that resemble channels.

Rima Hyginus in Sinus Medii is an example, initially formed through a fault and subsequently subject to volcanic activity.

Leading theories include lava channels, collapsed lava tubes, near-surface dike intrusion, nuée ardente (pyroclastic cloud), subsidence of lava-covered basin and crater floors, and tectonic extension.

It is thought to be a giant conduit that carried lava from an eruptive vent far to the south.

Topographic information obtained from the Apollo 15 photographs supports this possibility; however, many puzzles about the rille remain.