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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 the lsecond photo 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 the photos below. 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,.. Unike Lechuguilla, this cave can be visited on paid adventure tours. I took the lower photo on one of these in 2016. |
In the image above you can see two raft cones in different stages of genesis:
on the left, a broad cone (similar to the one below) and on the right, a similar
broad-based cone on which an aragonite stalagmite has built up.
Above, a large array of aragonite-coated raft cones in Hoodoo Hall, and below,
the amazing forest of raft cones in Hang Va Cave in Vietnam. Over 300 are found in one chamber.
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Created: June 19, 1995 |