Sinkholes and Blue Holes

Sinkholes, blue holes and collapse pits where the ground has fallen into a void below, or where a surface layer has slowly settled as soluble rock dissolves beneath it. Some are dry pits, some hold lakes, and the marine ones, called blue holes, drop in dark circles from shallow sea floors. A landform belongs here when its cited article calls it a sinkhole, blue hole or collapse depression. Each member is placed by what its own article says it is, never by its name alone.