December 7, 2012
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. This image shows the Northwestern edge of disconnected depression (14.53°N, 311.43°E) from Rima Marius. Image number M135507533R, incidence angle 58°, image width is 550 meters [NASA/GSFC/Arizona State University].
Topics: Planetary geology, Volcanology, Geology, Hadley–Apennine, Mons Bradley, Marius Hills, Lava tube, Marius, Rille, Volcano, Geology of the Moon