HiRISE: Enigmatic feature in Athabasca lava flows

What is this enigmatic landform? The circular feature is nearly 2 kilometers (1.2 miles) wide. It looks like a circular island surrounded by a “sea” of smooth-looking lava flows. The Athabasca region contains some of the youngest lava flows on Mars. Therefore, it is highly possible that volcanism played a role in creating this feature… [More at link]