With an image of such magnitude it is difficult to stick to comment on something specific, yet I chose to talk about Vallis Alps.

In the south of Mare Frigoris, not far from the Cassini crater and East Great Plain walled Plato, there is one of the most spectacular lunar valleys: Alpine Valley, which draws a cut through the Alps moon.

Seen in this image, Vallis Alpes (Alpine Valley) is a spectacular feature that extends for 166 km from the Mare Imbrium, trending north-east to the edge of Mare Frigoris. This valley was discovered in 1727 by Francesco Bianchini. The valley is narrow at both ends and in the center extends about 10 kilometers across.

The valley floor has a flat surface, flooded with lava with a narrow 'rille' winding running down the middle. It is generally considered as a "graben", an area between two parallel faults which fell below the surrounding area. It is believed that formed after the formation of the Imbrium basin, but before the lava flows who completed the rille Mar. probably corresponds to a 'lava tube' which collapsed formed in a geological episode later due to the high speed and low viscosity of the magma.

Very interesting indeed to know that Rilles are common on the moon and considered one of the most fascinating volcanic features due to its wide range of scales (from 100 meters to more than 100 km long) and morphologies that feature (linear, curved or sinuous).

Rilles typically form when lava flows erode existing surface, by melting the substrate, mechanical stripping material, or a combination of both thermal and mechanical processes. However, some may have been rilles lava tubes that have suffered roof collapse from their formation.

Attempting to detect this relatively narrow and sinuous rille that runs along the bottom Vallis Alpes is a favorite challenges of amateur observers of the Moon, its exact dimensions are not exactly determined but his view is a very satisfying test as well as in small cratereletas Plato floor that can be seen in this image.

By the way, how can you tell?

Sources:

ESA - European Space Agency

LROC - NASA

Wikispaces - LPOD - Jim Mosher

Computer Physics Lab

Research and Adaptation: Avani Soares