Cone Karst – Chocolate Hills

This unique karst landscape is composed of smooth, uniformly shaped conical isolated hills that cover a vast area in the central portion of the island. The site was once a platform of thick and widespread buildup of coral reefs that thrived during the Pliocene, approximately 2-5 million years ago and later to form a sedimentary formation.  Soon,   this  limestone formation   was  raised   above   the sea   level    and    fractured.   Rainwater,   streams and groundwater  dissolved  the  limestone,  gradually  forming  the present landscape of cone karst.

Carmen, Bohol

1 hour & 30 minutes travel

HISTORY

Formerly known as Haycock Hills, the Chocolate Hills of Bohol (Figures B5 and B6) is located at the central region of Bohol, and has been declared as a National Geological Monument by the National Committee on Geological Sciences in June 18, 1988. To provide for a stronger basis for protection, Proclamation 1037 was signed by the president declaring the area as a Natural Monument to protect and maintain its natural beauty to provide restraining mechanisms for inappropriate exploitation.

For several decades, the Chocolate Hills has served as the prime tourist spot in Bohol, attracting thousands of tourists each year. The cluster of 1,268 (NCGS Declaration, 1988) conical hills which covers an area of  approximately 139.38 square kilometers are spread out within the towns of Sagbayan, Batuan and Carmen.

The Chocolate Hills Complex in Carmen is located 55 kilometers from Tagbilaran City, where a view deck was installed on top of the Aires Hill peak. Five kilometers from the complex is another view deck at the Sagbayan peak located in the town of the same name. Almost all the hills share similar morphologies with height ranging from 30 to 400 meters and from slight to highly inclined slopes.

The grass species Saccharum spontaneum and Imperata cylindrical covering the hills are responsible for the chocolate-brown color the hills become during the warm, dry months of the year.

This unique karst landscape is composed of smooth, uniformly shaped conical isolated hills that cover a vast area in the central portion of the island. The site was once a platform of thick and widespread buildup of coral reefs that thrived during the Pliocene approximately 2-5 million years ago and later to form a sedimentary formation.

These limestones became the Cortes Limestone Member of the Pliocene Maribojoc Formation. The landscape has been undergoing karstification ever since it started million years ago and
persisted up to the present time. Through the uplift,
fractures and joints were developed, where erosion started and made way for the vertical infiltration of the rainwater.

Underground drainage system consequently developed. Closed depressions or sinkholes continuously developed beside the resistant limestone sections and were continuously filled up with alluvial sediments, and by karst water they became traditional rice fields. During the last several thousands of years, large-scale erosion of the limestone masses by rainwater impregnation and run-offs ensued, forming the present cone-shaped morphology of the famous Bohol Chocolate Hills. These haycock hills are products of continuous reaction of rainwater on a thin soluble limestone formation of the Maribojoc Formation.

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