Morphometric studies of bell hole development on Cayman Brac

Bell holes are cylindrical cavities that extend vertically upwards into ceilings of caves. They have been reported only in the humid tropics. The processes responsible for their formation are not fully identified; different hypotheses have suggested mechanical, chemical or biological action but none of these appears to explain the holes satisfactorily. On the Caribbean island of Cayman Brac bell holes appear to be distributed at random in the entrance zones of certain caves. The environment in which these holes formed and developed is subaerial rather than subaqueous. Fifty-five bell holes from five sample caves were measured in detail with a graduated gauge; profiles were drawn and volumes calculated for each. Bell holes in four of the caves displayed similar morphometry, whereas the holes in the fifth cave were significantly different in size but not shape. All appear to be dissolutional rather than erosional features. Dissolution, enhanced or not by microbiological activity, is thought to take place in a thin film of condensation water.