Just What Exactly Is 40 Fathom Grotto?

Geologically, the Grotto is what is known as an in-line sinkhole. Sinkholes form when the earth and rock above an underground river become weakened by the flow of water underneath. Eventually, this earth and rock collapses. Much of this material is carried away by the current; that which remains forms what is known as a debris cone, which the river now flows up and over.

Sinkholes seldom have perfectly straight walls (the Grotto is no exception). The Grotto’s sides slope outward — often at a substantial angle — resulting in a diameter at the base which is several times greater than it is at the surface. Divers need to bear in mind that, even though they may appear to be in open water, ascents must be made cautiously — lest you clobber yourself on an overhanging ledge.

Conditions at the Grotto »