The craters pepper the surface of Arabia Terra, a geologically ancient region of northern Mars. They appear as several huge circular pits that resemble Earth's calderas, in which magma beneath a volcano drains after a volcanic eruption, causing the ground above the magma chamber to collapse. Using data from several satellites orbiting Mars, researchers mapped Eden patera in detail. In a report in Nature today (abstract), they describe three separate calderas within the depression, along with possible signs of a lake of solidified lava and a volcanic vent where lava could have oozed out."
Link to Original Source