Image by Clementine via Map-A-Planet
The Moon has few - or perhaps no - conical volcanoes except for low hemispherical domes. And the volcanic features that do exist - domes, sinuous rilles, pyroclastic deposits - are all near maria. So what are rilles and a possible steep-sided volcano doing near the north lunar pole? This Clementine image shows that the floor of the 64 km wide crater De Sitter is cut by two or three rilles. These are not secondary crater chains, and they are not straight, tectonic rilles; they look most like irregular cracks and rilles found in floor-fractured craters (ffc). De Sitter itself doesn’t look like a ffc, but the rilles are similar. I am willing to guess that the rilles are volcanic. And I am also intrigued with the very round, crater-topped hill on De Sitter’s west (left) wall. On this image it looks very unlike most lunar peaks and rim bumps - it looks like a steep-sided dome. I don’t believe very strongly that it is a dome, but the close association with the undoubted rilles makes me suspicious. Unfortunately, because of the always low Sun illumination, it is impossible to see if pyroclastic material is associated with De Sitter. Why is there volcanism (the rilles at least) at 80°N, hundreds of kilometers from the nearest mare deposits at Frigoris? De Sitter is visible from Earth - it would be fascinating to see an image with the crater nearly in profile to look for the possible conical volcano bump…
Clementine spacecraft image.
Rükl plate 5
Yesterday's LPOD: Cut by a Fault
Tomorrow's LPOD: Streaks Across a Mauve Moon