Chocolate Hills

Bohol, Visayas


The Chocolate Hills is an unusual geological formation in Bohol province, Philippines. There are at least 1,260 hills but there may be as much as 1,776 hills spread over an area of more than 50 square kilometres (20 sq mi). They are covered in green grass that turns brown during the dry season, hence the name.

The Chocolate Hills is a famous tourist attraction of Bohol. They are featured in the provincial flag and seal to symbolize the abundance of natural attractions in the province. They are in the Philippine Tourism Authority's list of tourist destinations in the Philippines; they have been declared the country's third National Geological Monument and proposed for inclusion in the UNESCO World Heritage List.

The Chocolate Hills form a rolling terrain of haycock hills – mounds of a generally conical and almost symmetrical shape. Estimated to be from 1,268 to about 1,776 individual mounds, these cone-shaped or dome-shaped hills are actually made of grass-covered limestone. The domes vary in sizes from 30 to 50 metres (98 to 160 ft) high with the largest being 120 metres (390 ft) in height. Bohol's "main attraction", these unique mound-shaped hills are scattered by the hundreds throughout the towns of Carmen, Batuan and Sagbayan in Bohol.

During the dry season, the grass-covered hills dry up and turn chocolate brown. This transforms the area into seemingly endless rows of "chocolate kisses". The branded confection is the inspiration behind the name, Chocolate Hills.

The Chocolate Hills are conical karst hills similar to those seen in the limestone regions of Slovenia, Croatia, northern Puerto Rico, and Pinar del Río Province, Cuba. These hills consist of Late Pliocene to Early Pleistocene, thin to medium bedded, sandy to rubbly marine limestones. These limestones contain the aboundant fossils of shallow marine foraminifera, coral, mollusks, and algae. These conical karst hills, called mogote, are created by a combination of the dissolution of limestones by rainfall, surface water, and groundwater and their subaerial erosion by rivers and streams after they had been uplifted above sea level and fractured by tectonic processes. These hills are separated by well developed flat plains and contain numerous caves and springs. The Chocolate Hills are considered to be a remarkable example of conical karst topography.

The origin for the conical karst of the Chocolate Hills is described in popular terms on the bronze plaque at the viewing deck in Carmen, Bohol. This plaque states that they are eroded formations of a type of marine limestone that sits on top of hardened clay.The plaque reads:

The unique land form known as the Chocolate Hills of Bohol was formed ages ago by the uplift of coral deposits and the action of rain water and erosion.

The plaque also makes reference to a fanciful explanation of the origin of the Chocolate Hills that is unsupported by any published scientific research, i.e. either Hillmer or Travaglia and others, when it states:
the grassy hills were once coral reefs that erupted from the sea in a massive geologic shift. Wind and water put on the finishing touches over hundreds of thousands of years.

Self-published, popular web pages present a variety of fanciful and less credible explanations about how these hills formed. They include sub-oceanic volcanism; limestone covered blocks created by the destruction of an active volcano in a cataclysmic eruption;coral reefs that were raised from the sea as the result of a massive geologic shift; and tidal movements. The lack of any exposed or associated volcanic rocks anywhere in the Chocolate Hills refutes the popular theories involving volcanic eruptions. These theories involving either a sudden, massive geologic shift, coral reefs being erupted from the sea, or tidal movements lack any collaborating evidence and support among geologists.