Columns are formed by the unions of stalagmites and stalactites. As compound cave formations, they include among their ranks the tallest free-standing speleothems in the world. (Certain flowstone falls–sheets of calcite lining vertical shafts–are undoubtedly taller, but rarely measured). The towering specimens of the first photo, from Ogle Cave in Carlsbad Cavern National Park, New Mexico, USA, are indeed impressive. They are unusually thick for columns but are likely very old. By contrast the next photo shows a thin broomstick column. Often these are so uniform that it is hard to tell where the stalactite and stalagmite met originally, These, however, are only about half as high as the 61-meter tall column in Tham Sao Hin, a cave in Thailand. An image of this can be seen on the Virtual Cave’s page devoted to the world’s largest speleothems.

AUTHOR: Djuna Bewley