A rare geologic phenomenon: One of only six documented double barier reefs in the world, with high floral and faunal diversity, high degree of endemism but degraded and under threat of further destruction.
Danajon Bank's most remarkable feature is the Philippine Double Barrier Reff (PDBR), the only double barrier reef documented in the Philippines and one of only a few listed worldwide.
The PDBR is a unique geologic structure 6,000 years of coral growth. Larger and better defined than most double barrier reefs in the world, the PDBR is spread almost 80 nautical miles (148 km). The outer reef lies 11 km offshore and is composed of several units up to 23 km long each: three big reefs (Cabul-an, Caubyan and Dawajon) and five smaller fragments in the northern outer region. The inner barrier is 2km wide and separated from the coast by an inshore channel 28m deep at most. There is one reef (Calituban) in the inner region. The total reef area is about 46,308 hectares; Caubyan, the largest covers about 14,300 hectares.
The origin of the double barrier can be explained by a restart of subsidence (Downward shift of the Earth's surface relative to sea level) after an initial reef building phase or by the favorable influence of tidal currents on coral growth on a submarine ridge pre-existing in the original lagoon.
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