Sinuous rilles (like Hadley Rille, near the Apollo 15 landing site) are narrow, long depressions that meander across the lunar surface like a terrestrial river. Lunar geologists think that sinuous rilles formed either as erupting lavas carved their way through the surface, or by roof-collapse of lava tubes. A portion of the rille (named Rima Marius) in today's Featured Image is discontinuous, with a partially-closed depression that possibly marks the source region for this rille. Perhaps the "blockage" in the channel is a intact lava tube roof. While there are no signs of any natural bridge structures or other openings in this region, it is possible that a small section of the lava tube might have simply had its entrance and exit blocked by collapse debris.
Sinuous rilles like Rima Marius are high priority targets for future human lunar exploration in part because they expose deeply buried mare units, meaning that human exploration of locations like Rima Marius will provide important new scientific insights into the duration and evolution of lunar volcanism.
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