Illustration of pancake domes on Venus. These are volcanic features, unique to the planet Venus, which are remarkably circular with broad, flat tops. They are thought to form from the slow eruption of very viscous, silica-rich lava. They measure around 1 kilometre in height and vary in size up to tens of kilometres across. They are often found in clusters, usually near tesserae regions where the landscape is highly distorted, folded and cracked.