A cave, by definition, is a large underground chamber. We typically picture a dark opening in the side of a hill or mountain, but caves can occur in many locations and form in many different ways. Caves can be small enough for just one person to fit inside, they can be huge openings, or they can be long tunnels. Something most caves have in common is rocks and/or water - usually erosion of rocky landscapes by wind or water create caves. But many geological processes can form caves. Solutional caves are the most common and occur in karst topography like we have here in Missouri. Solutional caves form when slightly acidic groundwater dissolves or erodes limestone in the ground. Over thousands of years, a large cavern or entire cave system forms. Formations like stalactites and stalagmites can be found in these types of caves. Fracture caves also form in soluble rocks like solutional caves, but these are found between layers of less soluble rock. Fractures occur when the soluble rock dissolves between these layers and causes them to collapse.