Crater islands (ring islands) are island chains in the shape of a circular ring. Typically in worldbuilding this arrangements is caused by the edge of a submarine crater having sufficient height to break the surface. This crater may have been created by a volcanic explosion, it may be an impact crater from an asteroid strike, or it may have been generated by some other fantastic means such as magical explosion or superweapon detonation. Crater islands may surround a crater sea.