Viscous (or sticky), non-explosive flows produce distinctive landforms known as lava domes. These circular mounds form as lava slowly oozes from a vent and piles up on itself over time. Lava domes tend to have steep, cliff-like fronts at their leading edge and wrinkle-like pressure ridges on their surfaces. The Chao dacite is a type of lava dome known as a coulée. These elongated flow structures form when highly-viscous lavas flow onto steep surfaces.