Volcanism on the Moon

By Robert Wickman

Sinuous Rilles

Hadley Rille (from Orbit)		Hadley Rille (from Surface)
Lava Tubes		Posidonius Rille
Schroter's Valley 1		Schroter's Valley 2

Sinuous rilles are probably the most recognizable of small volcanic features on the Moon. Many partially resemble river valleys on the Earth. However, the lunar rilles usually flow away from small pit structures. Also, the lunar samples indicate that the Moon has always been bone dry. Thus, the sinuous rilles probably mark lava channels or collapsed lava tubes that formed during mare volcanism. Still, in some cases, the lunar flows may have melted their way down into older rocks, much like rivers cut into their flood plains on Earth. Similar lava channels and tubes are found in Hawaii, but these are all much, much smaller than those found on the Moon.