Apollinaris Patera

Dwarfed by Olympus Mons and the other immense shield volcanos on Mars, Apollinaris Patera rises only 3 miles or so into the thin martian atmosphere, but bright water-ice clouds can be still be seen hovering around its summit. Mars' volcanic structures known as "paterae" are not only smaller than its shield volcanos but older as well, with ages estimated to be around 3 billion years. Like Apollinaris Patera, narrow furrows typically extend from their central craters or calderas. The large central crater is about 50 miles across.