Earth

Caves have a shape

Cave morphology is often complex and difficult to describe, however there are few elementary shapes : galleries, shafts, meandering channels,or canyons, rooms. The trend of galleries is prevalently horizontal or slightly inclined, and generally galleries are large (if the size is small they are often called "passages", but this definition is purely speleological and not geologic. From the point of view of the origin, there is no difference between a "passage" and a gallery). The diameters of the galleries can be impressive. The largest gallery in the world is in Deer Cave in Sarawak – its average diameter is over 80 m. Underground meanders, or canyons, are horizontal tracts characterized by a very high and narrow channeling. Meanders is an improper term because these are real underground canyons that are perfectly similar to the entrenched canyons on the surface, eroded by flowing water. Often these are the most difficult passages to explore, because they are frequently very narrow at the base and have water courses flowing on the bottom that can even be quite violent, therefore they must be explored at a mid-height, progressing delicately and painstakingly. Shafts have a vertical trend: they can be perfectly cylindrical tubes, with smooth vertical walls (as in the case of the shafts formed in the phreatic zone, or at high mountain altitudes, due to the presence of snow or ice, or they may develop in ledges, or steps with erosion potholes on the bottom, as in the case of the vertical shafts originated from water courses on the surface, which recede due to the erosion of a water fall. Shafts can be of incredible heights, an example is the Vritiglavica (Slovenia) shaft that is over 643 m deep and has an absolute vertical drop of 500 m. Rooms form due to collapses where shafts and galleries meet. The size of an underground room may at times be immense. The largest chamber in the world is the Sarawak Chamber, in the Lubang Nasib Bagus cave, in the Gunung Mulu karst area in Sarawak. It is 700 x 430 m in size, with a height of 120 m. It is still a mystery how a similar void underground can exist without breaking down.