Venus has shield volcanoes, widespread lava flows and some unusual volcanoes called pancake domes and "tick-like" structures which are not present on Earth. Pancake dome volcanoes are up to in diameter and less than in height and are 100 times larger than those formed on Earth. They are usually associated with coronae and "tesserae" (large regions of highly deformed terrain, folded and fractured in two or three dimensions, which are unique to Venus). The pancakes are thought to be formed by highly viscous, silica-rich lava erupting under Venus's high atmospheric pressure.