Chocolate Hills

2006/02/02 - 2006/02/02

ヒルズにやって来ました！

エリア ボホール島(フィリピン)

LobocからChocolate Hillsへ向かいます。

マホガニーの森

Bilarの教会

Bilarの農業学校

Batuan

Carmenという村にChocolate Hillsがあります。Tagbilaranから約60km離れています。

214段の階段を上って、丘の頂上まで上ります。

About two millon years ago, most of the island of Bohol was below a shallow sea. Coral reefs, similar to those now found offshore of northern Bohol, thrived and extensively covered the sea floor. During stormy days, fragments of corals and shells derived by waves from the reefs were deposited mostly at the landward side of the reefs. The coral and shell fragments formed relatively thin layers (brown) surrounding the live coral reefs (pink).

Slowly, the land rose causing the coral reef formations to emerge out of the sea. The taller arrows shown in the diagram indicate that the southern sections of Bohol island had been uplifted more than the northern sections.

The chocolate hills had been carved out from the relatively thin layers of coral and shell fragments. During the initial stage, the surface may have looked like as shown in this diagram which covers the brown rectangular patch in the previous diagram. Gullies were developed in the low lying areas and lakes occupied pre-existing depressions.

Coral and shell fragments are largely composed of calcium carbonate, a chemical compound which can be dissolved by acidic solution. Rainwater becomes slightly acidic by dissolving some carbon dioxide from the atmosphere. Thus, rainwater can dissolve coral and shell fragments but this happens very slowly. With rainwater acting on the layer of coral and shell fragments to tens to hundreds of thousand of years, gullies were deepened and widened to become streams, lakes were emptied by underground rivers and interconnected conical hills were formed the original flat surface.

When the base of the soluble formation was reached, downcutting ceased and lateral erosion became dominant. Valleys were widened, the remnant of the layers in the highly dissected areas were dissolved away, and the connections between neighboring hills were also dissolved away. Thus, the chocolate hills that you now belold are products of the patient laboring of rainwater on a thin soluble limestome formation.

Based on geological studies conducted by the mines and geosciences bureau of the department of environment and natural resources, there were parts of Bohol that used to be under the sea. These are shown as the blue-colored areas in the map. The parts above sea level, which were confined mostly in the north, northeastern and eastern section, are color-coded green.

The location of the area covered in the first and second block diagrams shown on the left is the rectangle outlined in the map.

トイレの中からもヒルズが見えるよ〜、みたいな・・・。

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