Raft Cones


Raft cones are heaps of sunken “cave rafts” . Cave rafts are delicate, doily-like sheets of calcite or aragonite that occasionally grace the surface of still, supersaturated cave pools. Rafts seem to nucleate on dust grains that settle on pool surfaces. Young rafts may then “raft” together as they grow laterally. In rare instances, rafts attain dinner plate size before their thickness exceeds the capacity of surface tension to support them. They then sink to the pool bottom, where they and their predecessors pile up like so many Corn Flakes. More commonly, however, rafts meet their end much earlier, falling prey to some surface disturbance, such as a ceiling drip. Where drips fall repeatedly, countless drifting rafts will meet their end at one site, and so pile upward forming a cone-shaped cave raft graveyard–a raft cone!

      Dried-up pool basins may be hosts to dozens of raft cones. Occasionally the cones dwarf even cavers, making these especially bizarre but beautiful cavescapes.

      Often ceiling drips remain active following the emergence of a raft cone from a dwindling pool. These continued drips crown many raft cones with unusual stalagmites, made not of massive calcite, but of needly, frost-like aragonite. The columnar projection atop the cone in photo #4 is a rather extraordinary example. If you could hover above this stal, you would likely find that it features a hollow drip canal along its central axis. It seems that drips penetrate raft cones, dissolve raft material, and are then wicked to the outer growing tips of stalagmites where they evaporate and deposit more aragonite.

Raft cones are rather rare as cave formations go. The author knows of only two sites where they are found in the United States, a small cave in Nevada and in Lechuguilla Cave, in New Mexico, where they occur in spectacular size and number. Indeed, Lechuguilla was thought to have the most numerous and tallest raft cones known, as shown in photos 2 to 5. But in 2014 a team of British explorers found a large and spectacular group of such cones in a high chamber in Hang Va, a cave in Phong Nha-Ke Bang National Park in Vietnam, which I visited to obtain photo #1. Unlike Lechuguilla, this cave can be visited on paid adventure tours.

AUTHOR: Djuna Bewley & Dave Bunnell