An island surrounded by lava flows.
What do you call an island surrounded by lava flows? The Hawaiians call it a Kipuka! Now here’s a Kipuka found on the Moon!
The dark regions of the Moon—the Maria—were once seas filled with lava. And the 2.7 kilometers wide kipuka shown above was originally an impact crater on the ancient lunar surface. Then something interesting happened. The flowing lava during the time of active volcanism breached the western wall of the crater (leftside in the image) and filled it nearly to the rim.
The rim is thus the only remnant of the local lunar surface before the surface was drowned in the lava flows several billion years ago. So while the material inside the crater is relatively new, the rim itself is much older!