Cavern diving is the exploration of permanent, naturally occurring overhead environments while remaining within sight of their entrances. It differs from cave diving in that, while cave divers may penetrate thousands of yards, cavern divers generally go no further than 130 feet from the surface. Additionally, cavern divers keep the entrance clearly in sight at all times, and use a guideline so that, should sight of the entrance be accidentally lost, divers can immediately regain it.
By taking these steps, cavern divers remain able to make emergency swimming ascents and, thus, restore the safety margin they enjoy in open water. Properly trained and equipped wreck and ice divers who wish to remain within recreational diving limits take similar steps to ensure they maintain a comparable safety margin when entering their unique overhead environments.
Because cavern divers remain within the controlled emergency-swimming ascent zone, while cave divers go far beyond it, there are several other significant differences between cavern and cave diving.
Because cavern diving is still a form of recreational scuba, with modest risk factors, it is an activity that a number of experienced recreational divers can learn and enjoy. Cave diving, in contrast, is for a far more select group of individuals. Cave divers should possess near-instructor-quality buoyancy control and general diving skills. They should be utterly committed to diving in a highly disciplined and methodical manner and have an above-average understanding of the technical aspects of diving.